Team 7: Hydraulic Integrated Test Stand Project Proposal and Feasibility Study Patrick Anderson, ME Jonathan Crow, ME Jake DeRooy, ME John Sherwood, ME ENGR 339 Senior Design Project December 8, 2014 ENGR 339 Team 7 © 2014 Team 7 and Calvin College ENGR 339 Team 7 Executive Summary The Calvin College Engineering Program’s senior capstone project is composed of two courses, ENGR 339 and ENGR 340. ENGR 339, the first half of the capstone, focuses on the feasibility study of a design project, which is this report. Both courses integrate Christian design norms into the design process, which have also been included within the design project. The engineering team designing this project (HITS) consists of four mechanical engineering students. The design created by HITS will meet the need for a general purpose hydraulic test stand capable of loaded cylinder testing for Best Metal Products (BMP), a local hydraulic cylinder manufacturer. Several testing capabilities are required and have been deemed feasible for a test stand. The component design for the stand is comprised of: a hydraulic circuit, a force generation system, a control system, and a power unit. Each of these components has been researched and all major components have been deemed feasible for implementation within the project. Therefore, HITS will continue with the design work necessary to turn this feasible project into an end product for BMP. 1 Calvin College Engineering Table of Contents Executive Summary ....................................................................................................................................... 1 Table of Contents .......................................................................................................................................... 2 Table of Figures ............................................................................................................................................. 5 Table of Tables .............................................................................................................................................. 6 1 Introduction .......................................................................................................................................... 7 1.1 Course ........................................................................................................................................... 7 1.2 Team ............................................................................................................................................. 7 1.2.1 Patrick Anderson ................................................................................................................... 7 1.2.2 Jonathan Crow ...................................................................................................................... 7 1.2.3 Jake DeRooy .......................................................................................................................... 8 1.2.4 John Sherwood ...................................................................................................................... 8 1.3 2 Problem Definition .............................................................................................................................. 10 2.1 Need ............................................................................................................................................ 10 2.2 Customer ..................................................................................................................................... 10 2.3 Reason for Selection ................................................................................................................... 10 2.4 Requirements .............................................................................................................................. 11 2.4.1 BMP Requirements ............................................................................................................. 11 2.4.2 Team Requirements ............................................................................................................ 11 2.4.3 Team Goals .......................................................................................................................... 12 2.5 3 Chapter Overview ......................................................................................................................... 9 Design Norms .............................................................................................................................. 12 2.5.1 Stewardship ........................................................................................................................ 12 2.5.2 Integrity ............................................................................................................................... 12 2.5.3 Trust .................................................................................................................................... 12 2.6 Project Scope .............................................................................................................................. 12 2.7 Project Breakdown ...................................................................................................................... 13 Project Management .......................................................................................................................... 14 3.1 Team Member Responsibilities................................................................................................... 14 3.1.1 Design Assignments ............................................................................................................ 14 3.1.2 Administrative Assignments ............................................................................................... 14 3.2 Project Status .............................................................................................................................. 15 3.2.1 2 Key Milestones .................................................................................................................... 15 ENGR 339 Team 7 3.2.2 4 Time Tracking ...................................................................................................................... 16 3.3 Course Deliverables .................................................................................................................... 16 3.4 Project Deliverables .................................................................................................................... 17 3.5 Team Meetings ........................................................................................................................... 17 3.6 Data Management and Validation .............................................................................................. 17 Design Process .................................................................................................................................... 18 4.1 Variable Loading Testing ............................................................................................................. 18 4.1.1 Test Scenarios ..................................................................................................................... 18 4.1.2 Test Transitions ................................................................................................................... 18 4.2 Force Generation System ............................................................................................................ 19 4.2.1 Cylinder Bank ...................................................................................................................... 19 4.2.2 Rod Analysis ........................................................................................................................ 21 4.2.3 Sliding Wall .......................................................................................................................... 22 4.2.4 Cylinder Bank Arrangement ................................................................................................ 22 4.3 Cylinder Synchronization Method .............................................................................................. 23 4.3.1 Need for Synchronization ................................................................................................... 23 4.3.2 Hydraulic System Synchronization ...................................................................................... 25 4.3.3 Rail System Synchronization ............................................................................................... 26 4.3.4 Other Design Approaches ................................................................................................... 28 4.3.5 Design Decision ................................................................................................................... 29 4.4 Hydraulic Circuit .......................................................................................................................... 29 4.4.1 Valves .................................................................................................................................. 29 4.4.2 Hoses ................................................................................................................................... 29 4.4.3 Filters ................................................................................................................................... 30 4.4.4 Simulink ............................................................................................................................... 30 4.5 Power Unit .................................................................................................................................. 32 4.5.1 Pump ................................................................................................................................... 32 4.5.2 Motor .................................................................................................................................. 33 4.5.3 Reservoir ............................................................................................................................. 33 4.5.4 Thermal Control .................................................................................................................. 34 4.6 Control System ............................................................................................................................ 35 4.6.1 Sensors ................................................................................................................................ 35 4.6.2 LabVIEW Interface ............................................................................................................... 38 3 Calvin College Engineering 4.6.3 Software to Hardware Interface ......................................................................................... 38 4.6.4 Safety .................................................................................................................................. 38 4.7 User Interface.............................................................................................................................. 39 4.7.1 4.8 6 Test Stand Layout ........................................................................................................................ 39 4.8.1 Component Storage Space .................................................................................................. 39 4.8.2 Component Geometry ........................................................................................................ 40 4.9 5 Graphical User Interface ..................................................................................................... 39 Calvin Prototype .......................................................................................................................... 40 Costs .................................................................................................................................................... 42 5.1 BMP Design ................................................................................................................................. 42 5.2 Calvin Prototype .......................................................................................................................... 42 Conclusion ........................................................................................................................................... 43 6.1 Design Decisions ......................................................................................................................... 43 6.2 Risks ............................................................................................................................................ 43 6.3 Current Status ............................................................................................................................. 43 7 Acknowledgements ............................................................................................................................. 44 8 Works Cited ......................................................................................................................................... 45 9 Appendices .......................................................................................................................................... 48 4 ENGR 339 Team 7 Table of Figures Figure 1: Breakdown of project focus areas. .............................................................................................. 13 Figure 2: Team member responsibilities. ................................................................................................... 14 Figure 3: Cylinder bank requirements. ....................................................................................................... 20 Figure 4: Test cylinder maximum parameters. ........................................................................................... 21 Figure 5: Allowable buckling stress over range of extended lengths. ........................................................ 22 Figure 6: Cylinder arrangement. ................................................................................................................. 23 Figure 7: A perfectly balanced wall. ............................................................................................................ 24 Figure 8: An imbalanced wall. ..................................................................................................................... 25 Figure 9: Initial cam follower rail sketch. .................................................................................................... 27 Figure 10: Roller coaster roller layout [5]. .................................................................................................. 27 Figure 11: Radial and axial load definitions [7]. .......................................................................................... 28 Figure 12: PBC Hevi‐Rail® System [6]. ......................................................................................................... 28 Figure 13: Initial MATLAB Simulink model. ................................................................................................. 31 Figure 14: Initial Simulink simulation for scenario 1. .................................................................................. 32 Figure 15: Types of positive displacement pumps [14]. ............................................................................. 33 Figure 16: Hydraulic reservoir design [15]. ................................................................................................. 34 Figure 17: Aluminum beam force gauge calibration curve with uncertainty [19]. ..................................... 36 Figure 18. Ashcroft pressure transmitters [21]. .......................................................................................... 37 Figure 19: Graphical user interface screens................................................................................................ 39 5 Calvin College Engineering Table of Tables Table 1. Required test parameters. ............................................................................................................ 11 Table 2: Key milestones of ENGR 339/340. ................................................................................................ 15 Table 3: Project time summary. .................................................................................................................. 16 Table 4: Estimated time for future work. ................................................................................................... 16 Table 5: Completed deliverables. ............................................................................................................... 16 Table 6: Future deliverables. ....................................................................................................................... 17 Table 7: Test scenario summary for test cylinder and driving cylinder bank. ............................................ 18 Table 8: Effect of key test transitions on test cylinder. .............................................................................. 19 Table 9: Geometric requirements of components. .................................................................................... 40 Table 10: Required test parameters for Calvin prototype. ......................................................................... 41 Table 11: Total cost of hydraulic integrated test stand, BMP design. ........................................................ 42 Table 12: Total cost of hydraulic integrated test stand, Calvin Prototype. ................................................ 42 6 ENGR 339 Team 7 1 Introduction 1.1 Course The Calvin College Engineering Program’s senior capstone project is composed of two courses: ENGR 339 and ENGR 340. Both courses combine to create a six credit hour, year‐long engineering project that all graduating seniors complete. ENGR 339, the first half of the capstone, focuses on team formation, project identification, and a feasibility study. The second half, ENGR 340, focuses on the in‐depth analysis needed to create a finished product or final design. The final deliverables include this final design, along with a presentation to the engineering department faculty, staff, friends, and family at the senior design open house in early May 2015. Both courses integrate Christian design norms into the design process, in part through holistic engineering lectures outlining and advising on the transition towards full‐time careers. 1.2 Team The engineering team responsible for completing this project consists of four senior mechanical engineering students, hereafter referred to as HITS. Their broad range of skills includes undergraduate research, manufacturing, product design, and economic analysis. The team is well suited for the design project. 1.2.1 Patrick Anderson Patrick Anderson is a mechanical concentration engineering student from Ann Arbor, Michigan who expects to graduate in May 2015. He has gained research experience through internships at the University of Florida and Carnegie Mellon University. He plans to pursue graduate school to study medical applications of mechanical engineering, such as prosthetics and surgical robotics. Patrick’s research experience and interest in control systems will be valuable for hydraulic and control system design. In his free time, he enjoys rock climbing, playing soccer, backpacking, and going to concerts. 1.2.2 Jonathan Crow Jonathan was born and raised in San Diego, California. He will graduate in May 2015 with a BS in international mechanical engineering and a BA in French. Jonathan has industry experience in network systems for DoD applications (SAIC) and product development for chairs (Steelcase). While interning for Steelcase, Jonathan has developed a unique set of research interests including product design, anthropometry, digital human modeling, human factors, and efficient use of space. In his free time, he enjoys playing ultimate frisbee and badminton, cooking, backpacking, traveling, and optimizing every aspect of his life. 7 Calvin College Engineering 1.2.3 Jake DeRooy Jake is an international mechanical concentration engineering student from Grand Rapids, MI, who expects to graduate in May, 2015. Jake hopes to pursue graduate studies in robotics where he can further expand his knowledge of actuation and controls. Jake’s interests in actuation and controls and experience in programming will be valuable to the design of this product. As an intern at Best Metals Products, Jake provides experience with hydraulics as well as strong customer relations. In his free time, Jake enjoys cooking and photography. 1.2.4 John Sherwood John Sherwood is an international mechanical concentration engineering student, and expects to graduate with honors in May, 2015. John grew up in Hoffman Estates, Illinois. He is most passionate about analyzing thermodynamic systems, and intends to pursue graduate school to research the interactions between energy, economics, and public policy. John has gained significant data collection and analysis experience working at Calvin, which will be valuable in designing the control system interface. In his free time, John enjoys photography, rock climbing, and reading philosophy. 8 ENGR 339 Team 7 1.3 Chapter Overview This report contains a proposal and feasibility study for the hydraulic integrated test stand project. A brief description of each chapter of the report is given below. Chapter 1: Introduction Chapter 1 gives a general overview of the Calvin Engineering senior design course. It also introduces Team 7 and provides a brief background of each team member. Chapter 2: Problem Definition Chapter 2 introduces the hydraulic integrated test stand project, including the customer, Best Metal Products. This chapter also lists the requirements and goals for the project as well as a breakdown of its different technical components. Chapter 3: Project Management Chapter 3 assigns technical and managerial tasks to each team member. It also provides a year‐
long schedule for the project and a list of deliverables for the fall and spring semesters. Chapter 4: Design Process Chapter 4 discusses the design alternatives for each component of the hydraulic integrated test stand. In this chapter, alternatives are described and evaluated, initial calculation results are presented, and plans for future design work are given. Chapter 5: Costs Chapter 5 discusses the necessary costs for each component of the hydraulic integrated test stand. This includes costs for both the small demonstration prototype and the full‐sized design that will be delivered to the customer. Chapter 6: Conclusion Chapter 6 evaluates the overall feasibility of the project. This includes a summary of the design decisions, the risks involved, and the current status. Chapter 7: Acknowledgments Chapter 7 thanks the many individuals and groups who contributed time, ideas, and funds to this project. Chapter 8: Works Cited Chapter 8 lists the many sources used throughout the PPFS. Chapter 9: Appendices Chapter 9 provides further background for several chapters, including calculations, computer models, and bills of materials. 9 Calvin College Engineering 2 Problem Definition 2.1 Need The design created by HITS will meet the need for more extensive testing of hydraulic cylinders at Best Metal Products (BMP), a local hydraulic cylinder manufacturer. The chief engineer at BMP, Kurt Skov, expressed a desire to expand the current testing equipment at BMP to include a machine capable of loaded testing. This test stand will be a valuable asset to BMP as they continue to design complex cylinders with unique applications. 2.2 Customer This design is being created to meet the specific need of Best Metal Products. BMP specializes in producing custom welded hydraulic cylinders, including cylinders with multiple rods and valves. BMP has designed several complex cylinders with valves integrated into the cylinders. These designs can require large amounts of testing to perfect the valve selection process. BMP already has numerous test stands, including several testing rigs designed to allow for specific loaded testing of select cylinders. However, the company would like to obtain a universal test stand capable of simulating a variety of loading situations. Best Metal Products currently produces around 700 hydraulic cylinders per day for a wide range of applications. BMP’s cylinders can be found on snowplows, concrete screeds, stump grinders, pizza crust cutters, recreational vehicles, and minesweeping tanks. Each application requires a different testing simulation, underscoring the need for a hydraulic integrated test stand for simulation testing. 2.3 Reason for Selection There are two primary reasons for selecting the hydraulic integrated test stand as the HITS senior design project. First, it provides an opportunity to solve an actual design problem for a local engineering firm. All aspects of the project, such as defining project parameters, managing a budget, and working with a customer, will develop the abilities of each team member. This experience will prove invaluable for future long‐term projects in both industry and graduate school. Second, the hydraulic integrated test stand project serves as the culmination of four years of engineering classes and internships. Almost every engineering class required for mechanical engineering majors at Calvin College is utilized in some way, including: Engineering Graphical Communication, Statics and Dynamics, Circuits Analysis and Electronics, Mechanics of Materials, Machine Design, Dynamics of Machinery, Control Systems, and Thermal/Fluid Sciences. The hydraulic integrated test stand project integrates multiple engineering fields, creating a uniquely interdisciplinary work environment. Not only does the project utilize skills that have been developed throughout our engineering classes at Calvin, but it also requires exploration of previously unknown topics. For instance, HITS has the opportunity to learn a great deal about hydrostatic fluid circuits, an area that is not normally discussed in undergraduate classes. This project is comprehensive in its scope of mechanical engineering subjects yet requires detailed, in‐depth analysis in each area. 10 ENGR 339 Team 7 2.4 Requirements 2.4.1 BMP Requirements BMP requested that the test stand perform the following functions for a variety of cylinder sizes:





Test cylinder under loads Test for seal leakage Control the temperature of the hydraulic fluid Measure cylinder stroke Collect and store testing data Several test parameters have also been specified by Kurt Skov, BMP’s chief engineer. These parameters are typical ranges for BMP cylinders. Table 1. Required test parameters. Given Product Range Cylinder Bore [in] Static Pressure [psi] Min Max 1.0 6.0 500 5000 Dynamic Pressure [psi] 500 3000 Retracted Length [ft] 0.5 6.0 Flow rate [gpm] 2 20 Rod Velocity [ft/s] 0 1.4 2.4.2 Team Requirements HITS used these customer specifications to select the list of project requirements listed below. Req 1.
Device shall perform compression and tension loaded testing with a force accuracy of 2%. Req 2.
Device shall function when the test cylinder is both extending and retracting. Req 3.
Device shall accept test cylinders from 1.0 inches to 6.0 inches in diameter. Req 4.
Device shall accept test cylinders with a retracted length of 6 inches to 6 feet. Req 5.
Device shall provide static pressures ranging from 500 to 5000 psi. Req 6.
Device shall provide dynamic pressures ranging from 500 to 3000 psi. Req 7.
Device shall provide up to 20 gpm of hydraulic fluid. Req 8.
Device shall allow for rod speeds up to 1.4 ft/s. Req 9.
Device shall maintain a hydraulic fluid temperature of 140°F ± 10°F. Req 10.
Device shall preheat hydraulic fluid temperature in reservoir to 140°F within 30 minutes. 11 Calvin College Engineering Req 11.
Device shall measure the stroke of the test cylinder to an accuracy of less than 1/16 inches. Req 12.
Device shall record and locally store displacement and force information for each test. Req 13.
Device shall use LabVIEW software as a primary system controller. Req 14.
Device shall operate in a safe manner under normal conditions. Req 15.
Device shall safely deactivate the hydraulic system in case of an emergency stop. 2.4.3 Team Goals HITS has also identified a number of project goals which will be considered when analyzing design alternatives. Goal 1.
Device should minimize floor space requirements. Goal 2.
Device should be intuitive and easy to use. Goal 3.
Device should minimize cost while maintaining safety and performance. Goal 4.
Device should minimize changeover time necessary between tests. 2.5 Design Norms As a team of Christian engineers, HITS is guided by design norms which ensure the flourishing of God’s people and God’s creation. 2.5.1 Stewardship First, HITS will practice responsible stewardship of resources, both material and human. Where possible, BMP components will be used and recycled. HITS will also respect the physical needs of test stand operators. 2.5.2 Integrity Second, HITS will design a product with integrity in which form complements function. 2.5.3 Trust Lastly, HITS will work diligently to establish a bond of trust with BMP and the general public. Because of the high pressure nature of any project with hydraulic cylinders, trust will be necessary to ensure the safety of all involved. 2.6 Project Scope When BMP originally approached HITS with the project concept, the problem definition included a full physical design that included safety shielding analysis and crane loading design. These components have since been removed at the request of BMP in order to focus on the hydraulic design and force generation components of the stand. Therefore, HITS will focus on the design of the hydraulic circuit, the power unit, the force generation system, the moving wall and rails, and the control system of the test stand. The smaller scope will allow for a more in‐depth 12 ENGR 339 Team 7 analysis of the difficult components of the system to better meet the client’s needs. In addition, focusing on the design of a complex hydraulic and control system will be of more educational benefit to the team members. 2.7 Project Breakdown Before undertaking the challenge of design work, the project must be segmented into manageable focus areas. Figure 1 provides a visual representation of the six major focus areas. At a high level, the project consists of two major design domains: component design and system design. Component design can be further broken down into four focus areas: hydraulic circuit, force generation system, control system, and power unit. System design can be broken down into two focus areas which apply to the system as whole: geometric layout and testing capabilities. While this schema does not reflect time spent in each domain or demonstrate the integral nature of the project, it will provide direction to the research and development process. Figure 1: Breakdown of project focus areas. 13 Calvin College Engineering 3 Project Management 3.1 Team Member Responsibilities Each member of HITS brings a unique skill set to the team. These skill sets were considered in the project definition phase to ensure maximum work satisfaction and productivity. Using the project breakdown in Section 2.7, functional areas were assigned to each member. Administrative tasks were also divided among the members of HITS to assure equilibrium and peace. Figure 2 provides a visual representation of the division of labor. Figure 2: Team member responsibilities. 3.1.1 Design Assignments Co‐leaders were assigned for the four lesser focus areas. John and Jonathan will oversee the development of the force generation system and the overall test stand layout. Patrick and Jake will oversee the definition of test stand capabilities and the development of the control system. For the larger focus areas, hydraulic circuit and power unit, all members were tasked with development as these areas are central to the project and require direct involvement from all team members. 3.1.2 Administrative Assignments Industry Liaison This team member is responsible for communicating regularly with the customer (BMP) and the industrial consultant (Professor Ren Tubergen). The liaison will discuss all design decisions with the customer and solicit feedback. Additionally, the liaison will coordinate meetings with Professor Ned Nielsen and take meeting minutes all team meetings. Jake is well‐suited for this position. As an intern for BMP, Jake will have frequent contact with the customer. Jake is diligent in his note taking and well‐versed in sharing documents using Microsoft One Drive. 14 ENGR 339 Team 7 Team Manager This team member is responsible for coordinating the project schedule, tracking progress, and facilitating team meetings. The team manager will track task completion and perform time tracking analysis. Additionally, the team manager will moderate conflicts among teammates and look for ways for team members to collaborate. Jonathan is well‐suited for this position due to his affinity for Microsoft Excel and his interest in the project management. Budget Manager This team member is responsible for managing the budget for design and prototyping. The budget manager will create the bill of materials and assure that all team accounts are in good standing, both with Calvin College and BMP. Patrick is a well‐suited for this position due to his role as treasurer for the American Society of Mechanical Engineers, Calvin Chapter. Media Coordinator This team member is responsible for team communications to the general public in print and online. The media coordinator will manage the team website and generate all posters and pamphlets. This person will create all graphics for the team and assure consistent visual style throughout all publications, including reports. John is well‐suited for this position due to his interest in photography and his affinity for graphic design. 3.2 Project Status 3.2.1 Key Milestones A list of the key milestones for the class portion is presented in Table 2. While not specific to the project objectives of HITS, this defined the overall timeline of project deadlines. Table 2: Key milestones of ENGR 339/340. Milestone Date Project Proposal 10 Sept 2014
Project Objectives and Requirements 17 Sept 2014
PPFS Outline 24 Sept 2014
Work Breakdown Schedule 8 Oct 2014
First Oral Presentation 17 Oct 2014
Project Poster 31 Oct 2014
PPFS Draft 10 Nov 2014
Website Live 21 Nov 2014
Second Oral Presentation 3 Dec 2014
PPFS Final Draft 8 Dec 2014
15 Calvin College Engineering 3.2.2 Time Tracking At weekly meetings, HITS tracks the time contributed by each team member. To date, Table 3 shows that 39% of proposed project time has been completed. Future work is estimated in Table 4. For a detailed breakdown of future work, see Appendix F. Table 3: Project time summary. Hours Completed Hours Remaining Total Projected Actual 250 300 400 TBD 650 TBD Table 4: Estimated time for future work. Components Estimated Time Wall & Coupling Design Hydraulic Schematic Hydraulic component selection Hydraulic Thermal Design LabVIEW controls User Interface Design Prototype design Prototype build Report Writing Sensor and DAC selection Subtotal Contingency: Total Hours 30 20 30 20 30 10 48 32 22 15 257 50% 386 3.3 Course Deliverables To date, HITS has provided all deliverables on time. Table 5 shows the list of important deliverables which have been completed. Table 5: Completed deliverables. Deliverable 16 Date First Oral Presentation 17 Oct 2014
Project Poster 31 Oct 2014
Second Oral Presentation 3 Dec 2014
PPFS Final Draft 8 Dec 2014
ENGR 339 Team 7 HITS expects to generate a considerable amount of deliverables in the spring, which are detailed in Table 6. Table 6: Future deliverables. Deliverable Date Third Oral Presentation Feb 2015
Final Report Draft Mar 2015
Fourth Oral Presentation Apr 2015
Final Poster Apr 2015
Final Report 1 May 2015
Final Presentation 9 May 2015
3.4 Project Deliverables HITS will generate a full test stand design with drawings and calculations for delivery to BMP. Additionally, a proof of concept prototype will be created for Calvin. Specifications for the Calvin prototype can be found in Section 4.9. 3.5 Team Meetings HITS will meet for a minimum of two hours every Saturday morning. The Team Manager will track and analyze time spent on the project each week. Key topics will be discussed and action items will be assigned to each member. Informal meetings between two or more group members will take place throughout the week to discuss focus areas. 3.6 Data Management and Validation HITS will store all documents, spreadsheets, and presentations in Microsoft One Drive for ease of collaboration and reliable formatting. CAD data and any calculations performed on Calvin College program licenses will be stored on the Calvin server. Backup copies of key documents will be stored on the Calvin server and on flash drives. 17 Calvin College Engineering 4 Design Process 4.1 Variable Loading Testing 4.1.1 Test Scenarios The hydraulic integrated test stand’s primary function is to simulate physical loading situations that occur in real‐world applications. Tensile force can be applied to a hydraulic cylinder’s rod in either direction. At the same time, the rod can move in, out, or stay static while under load. Considering these factors, HITS developed six primary loading scenarios that will be the focus of the hydraulic circuit and control system design. Each scenario involves specific types of fluid flow in the test cylinder and the driving cylinder bank, where hydraulic fluid can be pumped into or metered out of either side of the cylinders. As a result, the driving cylinder bank can provide a driving force against the test cylinder or a resistive force against the movement of the test cylinder. The rods of the test and driving cylinders must move in the same direction in each case. Table 2 shows the details of the six primary loading scenarios. It is most important to notice that pumping and metering capabilities are required for both chambers of the test cylinder as well as for both chambers of the driving cylinder bank. Without these capabilities, the six test scenarios are not possible and it would not be feasible for HITS to design a robust variable loading test stand. Table 7: Test scenario summary for test cylinder and driving cylinder bank. Test Cylinder Force Generation Cylinder(s) Test Scenario Force Direction Velocity Flow Type Force Type Velocity Flow Type 1 ← → Pump In Resistive → Meter Out
2 ← ← Meter Out
Driving ← Pump In 3 ← 0 No Flow 0 No Flow 4 → → Meter Out
Driving → Pump In 5 → ← Pump In Resistive ← Meter Out
6 → 0 No Flow 0 No Flow Details on each testing scenario can be found in Appendix A. This appendix outlines the movement of cylinders, which flow types are present, and the dynamics of the forces in the system. The design process and decisions for the test scenarios was an important first step for HITS. These decisions impact the requirements and decisions of almost every other component of the test stand, including the force generation system, frame design, hydraulic circuit, and control system. 4.1.2 Test Transitions In order for the hydraulic circuit and control system to be designed properly, it is important to consider the transitions between the six primary test scenarios. BMP desires a robust device 18 ENGR 339 Team 7 that will be able to handle a wide variety of tests; such a test could incorporate multiple test scenarios in succession. HITS must have a clear understanding of what is happening inside the cylinders at all points of a test, especially during test transitions, to design a safe, comprehensive test stand. These transitions represent real‐world applications for hydraulic cylinders. For example, a change in velocity direction could represent a transition from extending an excavator bucket to retracting it. A change in force direction could represent a load that pulls on a cylinder but begins to push on the cylinder after a certain point in the stroke. Therefore, it is important for HITS to consider changes in velocity direction and changes in force direction. The key transitions between test scenarios 1 – 6 are summarized in Table 8. The transitions from 1 – 2 and 4 – 5 involve changes in velocity direction. The transitions from 1 – 4 and 2 – 5 involve changes in force directions. The transitions from 1 – 5 and 2 – 4 involve changes in both velocity and force direction. Table 8: Effect of key test transitions on test cylinder. Test Transition Force Direction Change Velocity Direction Change 1 – 2 X 4 – 5 X 1 – 4 X 2 – 5 X 1 – 5 X X 2 – 4 X X Details on each testing scenario transition can be found in Appendix A. This appendix outlines the movement of cylinders, which flow types are present, and the dynamics of the force in the system. 4.2 Force Generation System 4.2.1 Cylinder Bank The cylinder bank is the primary component required to complete loaded testing. It will house several cylinders that will apply loads to the test cylinder. Because hydraulic cylinders are being tested with other cylinders, it is paramount that adequate safety factors are applied to the driving cylinder bank to ensure a long operating lifetime. In this initial feasibility study, a factor of safety for pressure of 1.65 has been applied to determine how feasible a cylinder bank system is for testing cylinders to failure. Driving Cylinder Diameter Figure 3 shows the number of cylinders required within the bank in order to test against the maximum design requirements of a 6‐inch cylinder with a static load of 5,000 psi. The factor of safety for pressure applied is 1.65, which is near 3,000 psi. The graph shows that for a 6‐inch test cylinder, four 4‐inch cylinders are required on the driving cylinder bank. Additionally, it 19 Calvin College Engineering confirms that smaller test cylinders require fewer cylinders within the bank to maintain the same safety factor. 16
Number of Cylinders Required
14
6" bore
12
4" bore
10
2" Bore
8
6
4
2
0
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
Bottom Cylinder Diameter [in]
Figure 3: Cylinder bank requirements. In order to test smaller cylinders, such as a 1‐inch diameter, the cylinder bank will also require smaller bore diameters in order to maintain a minimum pressure for valves to function correctly. Because of this, the cylinder bank will have two 2‐inch diameter cylinders, and four 4‐
inch diameter cylinders. These two sets can be actuated independently of each other in order to maintain an adequate safety factor and the appropriate pressures for the hydraulic circuit. Test Cylinder Maximum Parameters In addition to the cylinder bank analysis, HITS developed a preliminary understanding of the test cylinder parameters. Particularly, HITS focused on the relationship between rod velocity and pump flow rate, shown in Figure 4. The maximum of each parameter has been specified within the problem definition as 1.4 ft/s or 20 gpm, depending on which is achieved first. The small test cylinders require much less hydraulic flow to generate the maximum velocity, while large cylinders will meet the 20 gpm limit at very low velocities. 20 ENGR 339 Team 7 1.4
18
1.2
16
14
12
10
Top Volumetric Flow
Rate
1
Velocity
0.8
8
0.6
6
0.4
4
Rod Velocity
Test Cylinder Flow Rate [gpm]
20
0.2
2
0
0
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
Test Cylinder Bore Size
Figure 4: Test cylinder maximum parameters. 4.2.2 Rod Analysis A buckling analysis was performed on the cylinder rods for the worst case scenario using standard buckling equations for steel [1]. The worst case scenario was determined to be a 6 inch, 6 ft extended length test cylinder while testing the static pressure limit of 5,000 psi. HITS assumed that the ends of the rod were pinned, creating an effective length, L, of half the total length of the rod [1]. Additionally, the reacting forces were assumed to be evenly distributed over four active cylinders. The factor of safety according to the handbook method of determining allowable stress was found to be 1.85 for a 2‐inch diameter rod on the driving cylinder bank [1]. This diameter was determined to be the minimum safe diameter for the driving cylinders, given standard cylinder sizes produced by BMP. The stress acting on one rod was found to be 11.25 ksi, while the allowable stress when fully extended was 16.22 ksi. The allowable stress varied with the rod extension, which is shown visually below. Therefore, the normal rod size for cylinders is deemed feasible for the project, as long as the moment occurring throughout the wall is minimal. 21 Calvin College Engineering 22000
 allow ed
 allowed [psi]
21000
20000
19000
18000
17000
0
2
Lfoot [ft]
4
6
Figure 5: Allowable buckling stress over range of extended lengths. 4.2.3 Sliding Wall In order to apply forces to the test cylinder, it must be physically connected to the cylinder bank. This will be accomplished through a movable steel wall. The wall will be mounted on a sliding rail system, allowing it to move along with the extension and retraction of the cylinder rods. More details on the wall design can be found in Section 4.3.3. 4.2.4 Cylinder Bank Arrangement The driving cylinders will be oriented evenly around the moving wall as shown in Figure 6. The green cylinders in the figure represent the driving cylinders while the purple cylinder represents the testing cylinder. This distribution is pertinent to reduce moments on the moving wall, a topic which is discussed in Section 4.3. 22 ENGR 339 Team 7 Figure 6: Cylinder arrangement. 4.3 Cylinder Synchronization Method 4.3.1 Need for Synchronization A 6‐inch bore cylinder operating at 5000 psi can generate over 70 tons of force. These large forces can become dangerous when small errors in manufacturing or hydraulic synchronization create excessive moments on the moving wall introduced in Section 4.2.3. Figure 7 shows a perfectly balanced wall. Such a wall has no manufactured dimension errors and has a perfectly synced flow and pressure. This figure shows the force generating cylinders in green, opposing the test cylinder in purple. The force generating cylinders are shown on the opposite side of the wall than they would be in reality to help visualize the opposing forces. The calculations performed in Appendix C3 show that such a system has perfectly balanced forces and moments. Therefore, the rollers shown in the image would only support the weight of the wall assembly, an effect which was neglected in the calculations. Neglecting the weight of the wall assembly is justified for initial calculations because it is dwarfed by the large possible moments. 23 Calvin College Engineering Figure 7: A perfectly balanced wall. The perfectly balanced situation shown in Figure 7 is not realistic. Errors in the system can arise from two primary sources: physical errors and hydraulic errors. Physical errors include friction between the rollers and the track, friction within cylinders, and geometrical tolerances. Hydraulic errors arise because of pressure and flow differentials. When attempting to distribute hydraulic fluid to four driving cylinders, it is difficult to divide the flow—and resulting pressure—
perfectly equally. This causes the rods of each driving cylinder to not be perfectly aligned and the rods may not extend at the same rate. This error creates a moment on the sliding wall because the total load is not equally distributed. Together, these two main sources of error cause a stack‐up of complications. Figure 8 shows a wall which includes geometrical tolerances. These errors have been exaggerated to account for friction and hydraulic errors. The force and moment calculations in Appendix C4 show that these stack‐ups can cause moments up to 29,450 ft‐lbf. Due to the high forces at play in this system and the difficulty in maintaining a perfectly balanced system, the cylinder bank must be synchronized in a way that prevents damage to the whole test stand. There are three main ways to synchronize multiple cylinder positions: servovalves, hydraulic circuits, and mechanical linkages [2] [3]. These design alternatives presented below. 24 ENGR 339 Team 7 Figure 8: An imbalanced wall. 4.3.2 Hydraulic System Synchronization Servovalve Synchronization As discussed in Appendix B, servovalves offer the fastest, most precise control of hydraulic systems. HITS could use servovalves to control the force generating cylinders as well as the test cylinder. The lack of a deadband in these valves gives them a very fast response time, ranging between 3 and 10 milliseconds [4]. This incredibly fast response time, along with integrated controls, makes servovalves an ideal choice for control. However, servovalves do have limitations and other concerns. First of all, they are very expensive. Our customer estimated that servovalves for our flow rates would cost up to $2,000. Since the test stand would require a high‐caliber servovalve for all seven cylinders in the test stand, the servovalve costs alone present a barrier for feasibility. In addition, due to their complexity, servovalves are much more likely to break easily and have short lifetimes. Replacing servovalves when they wear out would increase the total cost of the test stand over its lifetime. While servovalves are an excellent choice for controlling the variable loading test requirements, HITS deemed them unfeasible for the test stand due to BMP’s cost and durability requirements. In addition, there would be no way for HITS to prove the validity of their system with a prototype using servovalves; one such part would consume the team’s entire budget. Therefore, HITS deemed servovalves unfeasible due to this inability to provide a proof‐of‐concept for its test stand. Hydraulic Circuit Synchronization The position of multiple hydraulic cylinders can be controlled with several types of fluid power circuits. The simplest way to do this is flow control [2]. However, there are several issues with 25 Calvin College Engineering only using flow control which arise from high levels of uncertainty. HITS cannot guarantee that a flow divider circuit would suffice for cylinder synchronization, and therefore will not pursue that option. There are also more complex hydraulic circuits, such as a master‐slave arrangement, that can control the position of multiple hydraulic cylinders. However, these systems require extensive knowledge about hydraulic circuits, and require high levels of complex design to synchronize up to 4 cylinders. HITS is not confident enough in its hydraulic knowledge to ensure proper implementation of these systems, which makes them not feasible for the purpose of this course. 4.3.3 Rail System Synchronization A high strength guide rail system can be used in place of hydraulic controls to equalize the forces. This system uses some form of rail and rollers to absorb force and moment imbalances and bring the system into equilibrium. This method fundamentally differs from hydraulic synchronization. Hydraulic synchronization works to prevent force imbalances from happening in the first place. A rail system deals with existing force imbalances by adding extra forces into the system. A rail system and hydraulic synchronization system are not independent and can coexist. However, the sizing of the rail system depends on how well a hydraulic circuit can synchronize the cylinders. HITS initially examined high strength linear roller bearings for a rail system. However, the linear roller bearings have a maximum reliable force rating of 3,000 lbf. HITS decided to instead analyze the forces using cam followers riding on a steel bar, as cam rollers have larger load ratings than roller bearings. A sketch of this situation is shown in the circle in Figure 9. Cam followers are readily available with dynamic load ratings exceeding 10,000 lbf. The cam followers were added into the force and moment equations found in Appendix C4. HITS calculated the necessary distance between the cam followers and the wall, shown as a blue arrow, to prevent excessive loads on the cam follower. HITS determined that a distance of 13.25 inches between the roller and wall on each side of the wall will be sufficient to maintain acceptable forces on the cam follower. This distance is not excessively large, making the cam follower on a rail design feasible. 26 ENGR 339 Team 7 Figure 9: Initial cam follower rail sketch. The possible 29,450 ft‐lbf moments calculated in Section 4.3.1 can be applied in the XZ‐plane and the XY‐plane as defined in Figure 6. This requires the roller rail system to be designed to handle two directions of moment resistance. HITS considered using multiple orientations of rollers, similar to the rollers found on a roller coaster. This roller layout is demonstrated in Figure 10. While HITS estimates this design would be feasible, it would require space‐consuming round rails. Figure 10: Roller coaster roller layout [5]. HITS instead decided to look into using cam rollers capable of withstanding both large radial loads and large axial loads. Figure 11 shows the load directions for radial and axial loads. Cam rollers, such as PBC’s Hevi‐Rail® cam rollers can be purchased which can withstand the 10,000 lbf 27 Calvin College Engineering assumed in the moment calculations in both radial and axial directions [6]. Therefore, using these types of cam rollers is feasible. Figure 11: Radial and axial load definitions [7]. Figure 12: PBC Hevi‐Rail® System [6]. 4.3.4 Other Design Approaches The problem of hydraulic desynchronization can be prevented through the hydraulic circuit design, absorbed through a rail system, or incorporated into the design. A potential alternative would be to design the system so that it is not negatively affected from generating moments. This could be done by to installing a free‐floating force plate between the driving cylinders and the testing cylinder, connected to each cylinder by a drive‐shaft coupling. This type of system would allow the force plate to rotate if the driving cylinders were desynchronized. Additionally, all force would still be axially transmitted to the test cylinder. If the cylinders became too desynchronized, compromising the safe operation of the test stand due to an extreme force plate angle, a sensor would alert the system to stop the test. This type of system cannot be accurately analyzed for feasibility until the hydraulic circuit is designed. This is because this design would only function safely under stable or oscillatory desynchronization patterns. Under unstable desynchronization patterns, which happens when the cylinders become sufficiently out of phase, the output of the hydraulic circuit is unknown and the proper operation of the free‐floating force plate is unknown. Therefore, the stability of this type of system will only be known later in the design process. 28 ENGR 339 Team 7 4.3.5 Design Decision HITS has decided to pursue using rails to maintain synchronization in the system. The initial calculations show that this system is feasible given the constraints. This solution gives a robust, long lasting system which is easy to control. HITS will still attempt to synchronize the system using basic hydraulic methods; however, HITS will not use servo valves to perform this function. Additionally, HITS will incorporate safety shutoff measures into the control system which will deactivate the hydraulic system if cylinder pressures or wall position deviate from an acceptable state. 4.4 Hydraulic Circuit The hydraulic circuit in the hydraulic integrated test stand is much more complex than what is found in many hydraulic circuits. This complexity stems from the precision and speed needed to control the magnitude of the force created by the force generation system (see Section 4.2). In addition, the circuit involves up to seven hydraulic cylinders. 4.4.1 Valves Valves work as the backbone of the hydraulic system. The valve selection process can determine the success of the entire hydraulic design. HITS performed extensive research into many different forms of valves. A discussion of this research can be found in Appendix B. HITS has determined that the hydraulic circuit will need a number of different types of valves. First, the hydraulic circuit will need to use pilot‐controlled pressure relief valves. These valves will work as a mechanical fail‐safe for the hydraulic system. If the pressure within the hydraulic circuit exceeds the maximum preset value, the pilot‐controlled pressure relief valve will direct all pressurized hydraulic fluid directly into the reservoir. These valves are readily available on the market and have been specially designed for safety considerations. HITS expects to integrate several other valve types into the hydraulic circuit, including simple “bang‐bang” directional control valves. The details and applications of these valves will be explored using Simulink software. For additional details, see Section 4.4.4. Based on the synchronization design decision in Section 4.3.5, the test stand will not require the use of servovalves. 4.4.2 Hoses Fittings BMP uses two standard hose connections. The first system, known as National Pipe Thread (NPT), originates from the thread form found in plumbing applications. The second method, known as SAE O‐Ring fittings, was specifically designed for the hydraulic power industry. HITS would like to use these fittings to develop unity between this test stand and BMP’s existing equipment. HITS plans to use SAE O‐Ring fittings when possible, only using NPT fittings when connecting to a component that is manufactured with NPT fittings. 29 Calvin College Engineering Sizing The hoses in the hydraulic system need to be designed to handle the high pressures and flow found in the hydraulic circuit. The hoses will be sized based on Parker’s Hydraulic Hose, Fittings, and Equipment Technical Handbook [8]. 4.4.3 Filters Hydraulic fluid filters are an important aspect of all hydraulic systems. Hydraulic fluid contamination from metal particles produced by mechanical components causes 75% of hydraulic system failures [9] [10]. Proper filtration results in longer machine life and better operation. Additionally, servo‐valves, which HITS has explored, require individual filters to protect their spool. The zero‐lap design of servo‐valves means that any damage to the valve spool will cause hydraulic leaking. The filtration system could be provided with a kidney‐loop filtration system [11]. A kidney‐loop filtration is an external low pressure, low flow system attached to the reservoir which continuously filters the hydraulic fluid. A HITS team member has previously designed a kidney loop filtration system using inexpensive parts, such as pumps for lawn sprinkler systems and bag style filters. HITS plans to use a similar design to maintain hydraulic fluid cleanliness. 4.4.4 Simulink HITS used MATLAB Simulink in order to effectively design a hydraulic circuit, anticipate issues, and evaluate stability of the hydraulic circuit. This instability comes from valve delays or controls having unintended conflicts with each other. Simulink allows HITS to design the hydraulic circuit in graphical form. The visual representation of the circuit in Simulink contains the formulas to model the physical relationships between components in the system. Simulink allows HITS to incorporate many types of valves, including delays between the controller input and valve reaction, in the model to predict and circumvent system instability. Figure 13 shows the initial Simulink model used to evaluate the stability of the system. This model is still very simplified since it does not incorporate any feedback controls. It also uses a fixed orifice for flow metering rather than a variable orifice or proportional valve. The model in Figure 13 was run in Simulink to mimic test scenario 1 (see Appendix A). The results of this test are shown in Figure 14. 30 ENGR 339 Team 7 Figure 13: Initial MATLAB Simulink model. The effects of the model’s simple valves can be seen in the middle graph in Figure 14. The model shows a large spike in fluid flow of the test cylinder. Closed loop controls should be able to minimize these unintended effects in pressure and flow. This initial simulation shows that the metering force feedback can be used to provide resistive force. It also shows the feasibility of simulating the hydraulic circuit before investing in circuit components. 31 Calvin College Engineering Figure 14: Initial Simulink simulation for scenario 1. 4.5 Power Unit 4.5.1 Pump The pump makes up the driving force behind a hydraulic circuit. A pump’s sole purpose is to displace fluid. Despite the common belief, pumps do not create pressure. Pumps create “the flow necessary to develop pressure” [12]. Pumps are divided into two major categories: positive displacement and non‐positive displacement. Non‐positive displacement pumps are commonly used in civil engineering applications. Non‐positive displacement pumps cannot generate high pressures because they lack internal seals. Large pressure differentials across the pump causes the fluid to push backwards through the pump [12]. Conversely, positive displacement pumps have internal seals which essentially eliminate the back flow of fluid in high pressure situations. 32 ENGR 339 Team 7 If fluid flow is obstructed, positive displacement pumps will continue to displace fluid, allowing pressure to build up until they explode. All positive displacement pumps must be used with pressure relief valves (see Appendix B) to prevent damage to machinery and operators. Hydraulic circuits use positive displacement pumps to maintain the high pressures needed for driving forces. Positive displacement pumps, which will be referred to as hydraulic pumps in this report, come in fixed displacement or variable displacement types. Fixed displacement pumps are the simplest pumps, designed to displace the same volume of fluid for each revolution. Variable displacement pumps change the geometry of the pumping chamber to change the volume of fluid displaced with each revolution [12]. HITS will use a variable displacement hydraulic pump to power the hydraulic circuit. The variable displacement pump is needed to account for the large range of fluid flow needs in the hydraulic integrated test stand. Hydraulic Supply Company offers a 1,518 page catalogue which includes hundreds of pumps offered by EATON Corp [13]. A variety of different positive displacement pump types are shown below in Figure 15. HITS has verified that pumps are available in the estimated size range and plans to use this catalogue to select a pump that meets the performance requirements. Figure 15: Types of positive displacement pumps [14]. 4.5.2 Motor Hydraulic pumps are usually sold apart from a motor. A motor must be selected to drive the hydraulic pump. The motor sizing will be performed after a pump has been sized and selected. Purchased pumps provide sizing information to be used with motor sizing. 4.5.3 Reservoir A well‐designed hydraulic reservoir performs more functions than simply storing the hydraulic fluid when not in use by the hydraulic circuit. A hydraulic reservoir should be designed to allow the hydraulic fluid to decontaminate, de‐aerate, and fully mix before being returned to the circuit [15]. Figure 16 shows a typical schematic for a hydraulic reservoir that allows for all of these functions to be performed. 33 Calvin College Engineering Figure 16: Hydraulic reservoir design [15]. Hydraulic reservoirs can be purchased predesigned based on the storage capacity. HITS plans on purchasing a predesigned hydraulic reservoir which is properly sized for this hydraulic system. A tank should be sized to hold “two to four times the pump flow in gpm” [15]. 4.5.4 Thermal Control Thermal control of the hydraulic fluid is vitally important in order to maintain a constant viscosity, along with other intrinsic physical properties. Constant viscosity, which is a constant resistance to flow, is necessary to help prevent hydraulic leakage throughout the system. The amount of leakage through a spool and sleeve interface is found by: ∆ Where Equation 1
is the leakage flow rate, is the spool diameter, is the radial clearance, is the viscosity, is the length of leakage path, ∆ is the pressure difference across the clearance [16]. A lower viscosity, caused by a temperature increase, will cause more fluid to leak throughout the system. A 20°C rise in temperature can halve the viscosity of the fluid, which would in turn double the leakage rate [17]. Additionally, the internal leakage increases the power losses within the system. This further exasperates the problem, because the pump will have to input more energy into the fluid stream. Higher oil temperatures also significantly affect the wear of various hydraulic seals. As oil temperature increases, the frictional coefficient increases causing more damage to the material 34 ENGR 339 Team 7 surface [18]. This means that over time, the clearance in seal interfaces will increase, further increasing the leakage flow rate. Therefore, temperature control is vitally important to the function of a hydraulic system. Because the fluid will be pressurized to 5,000 psi, significant heat buildup is expected through pump inefficiencies and frictional losses throughout the hydraulic circuit. While the design of the hydraulic circuit must be known before calculating the heat transfer to the fluid, an industry standard is to use the hydraulic reservoir as a heat sink, and to size it to between two and a half and three times the maximum volumetric flow rate, per minute, of the fluid [17]. The volumetric flow rate parameter of the HITS system is 20 gallons per minute, making an initial estimate of the reservoir size 60 gallons for adequate temperature control and filtration. HITS will analyze the use of cooling fins or a cooling fan if calculations show that the reservoir size is not large enough to adequately control the system temperature. Additionally, HITS will include resistive heating elements to preheat the oil to the proper temperature. These elements will be sized to meet the requirements of Req 10. The calculation of this sizing can be done using ∆
Equation 2
Where is the heater element size, is the mass of hydraulic fluid in the reservoir, is the specific heat of the hydraulic fluid, ∆ is largest temperature difference required, is the time to heat oil specified in Req 10. 4.6 Control System 4.6.1 Sensors The precision of testing equipment heavily depends on the precision offered by the sensors being used. The test stand under consideration will use sensors as part of the feedback control system to accurately control the force being exerted on the cylinder in testing. BMP requested that the variations of the force exerted on the cylinder in testing be limited to 40 lbf. HITS has found that this range of forces is not feasible. Force Gauges Force gauges consist of strain gauges mounted to deflection beams. A force exerted on the deflection beam causes strain, which is measured by the strain gauge. HITS requires a system capable of measuring over a range of several hundred pounds force to 70 tons of force. This force range is dictated by the pressure range and cylinder diameter requirements. HITS considered designing a custom force gauge to meet the application needs. HITS decided not to pursue this option since the uncertainty of a deflection beam force gauge would far surpass the minimum force variation requirements. To justify this fact, HITS referred to a report written for ENGR 382 by a HITS team member [19]. Figure 17 shows a calibration curve with uncertainty which was calculated in the ENGR 382 project. The calibration curve in Figure 17 was for an aluminum beam force gauge. The maximum force in Figure 17 is less than 25% of the maximum force needed by HITS. The error at this maximum force is over ±700 lbf. This implies that any error on a custom designed force gauge would be unacceptable. 35 Calvin College Engineering Figure 17: Aluminum beam force gauge calibration curve with uncertainty [19]. HITS has instead decided to purchase a load cell. Load cells sized for the required force range can be purchased with less than 0.1% error [20]. These load cells will be used in tandem with pressure gauges to allow for two methods for force checking. Pressure Gauges A force measurement can also be achieved by measuring the pressures of the hydraulic fluid entering and exiting the force generation cylinders. The accuracy of the final force measurement is controlled by the accuracy of the force‐generating cylinders’ bores, the frictional effects of the wall, and the accuracy of the pressure gauges’ measurements. HITS identified Ashcroft A2 Heavy Industrial Pressure Transmitters, shown in Figure 18, as a representative pressure gauge of the market’s measurement standards. Ashcroft claims an accuracy of ±0.25% measurement accuracy for the high precision line of pressure transmitters [21]. 36 ENGR 339 Team 7 Figure 18. Ashcroft pressure transmitters [21]. HITS decided to round the uncertainty of the sensor up to ±0.4% to account for variations in cylinder bore dimensions. The uncertainty gives a worst‐case force uncertainty of 1200 lbf, assuming the use of four 4‐inch bore cylinders in the force generation unit. This force fluctuation does not include frictional losses in the movement of the wall. The frictional losses in the movement of the wall can be estimated based on the weight of the wall and bearing selection through a calibration process. Frictional losses to the hydraulic cylinders can be established by measuring friction forces in hydraulic cylinders provided by BMP. Additionally, the test stand can be calibrated to account for these losses and variants. Neither the pressure gauge nor the load cell is capable of measuring the worst case load within ±40 lbf, the force tolerance originally requested by BMP. HITS has determined that the original 40 lbf error is not a feasible error due to this fact. However, it should be noted that the errors of both measuring systems are still less 1% of the total force being measured. Therefore, HITS decided that a feasible force fluctuation would be ±2.0% of the total force, as seen in Req 1. Displacement Sensors HITS has identified a cable extension transducer as a cost effective method for displacement measuring. This sensor consists of a string wound around a drum. Displacement causes the string to pull out of the spool. The rotational motion of the spool is recorded with a potentiometer. Cable extension transducers can be found which allow for errors of just over 1/16 inches [22]. This error is acceptable for the purpose of syncing the position of the hydraulic cylinders. However, this error is higher than is desired for recording the stroke displacement data for a cylinder, because it would not meet Req 11. 37 Calvin College Engineering HITS plans to use a magnetic tape linear encoder for the more accurate stroke displacement measurements. A well‐implemented magnetic tape linear encoder is capable of measuring distances with less than 1/32 inches error over the entire stroke [23]. A third option for displacement sensing would be an optical encoder. This option allows for errors as small as 0.0001 inches [24]. However, it is expected that this product will be much more expensive than a magnetic tape linear encoder, and therefore will likely only be used if BMP expresses a desire for this extra precision. 4.6.2 LabVIEW Interface LabVIEW is an excellent visual programming tool for managing control systems. Its applications include data acquisition and analysis, instrument control, embedded control systems, and automated test systems [25]. Per Req 13, the LabVIEW environment will be used for the test stand. This will serve several functions. First, HITS will be able to create a visual program for the control system and include the many useful functions of LabVIEW in one program. Also, LabVIEW will allow BMP manufacturing employees to easily operate the test stand and visually monitor various system parameters. Finally, HITS will develop a LabVIEW environment that can automatically test the six test scenarios described in Section 4.1.1. In addition, BMP engineers will be able to create new tests within the established LabVIEW program. Ease of modification ensures that the test stand will be a useful tool for BMP well into the future, even for more complex tests that have not been addressed or anticipated in this report. The LabVIEW environment will be developed during the spring semester (ENGR 340). Given the wide range of LabVIEW capabilities, HITS is confident in feasibility of this aspect of the project. 4.6.3 Software to Hardware Interface The interface between the LabVIEW environment and the sensors and valves requires Analog‐
to‐Digital Converters (ADCs) and Digital‐to‐Analog Converters (DACs). Each sensor and valve requires a different style of DAC and ADC. They may also require amplifiers or filters. The pin diagrams on both the sensors and valves specifies the information on which signals are given and required. HITS will use this information along with helpful guides provided by National Instruments, the makers of LabVIEW, to select the ADCs and DACs after the valves and sensors have been selected. 4.6.4 Safety Safety is a key part of the control system. The control system must have a robust design, making it almost impossible for the end user to run the test stand in a dangerous way. This involves restricting the end user’s editing abilities of parts of the LabVIEW system. It also involves incorporating errors and safety switches within LabVIEW. External safety switches must also be incorporated into the control system to allow for emergency stopping. Safety within the control system will be addressed during the spring semester (ENGR 340). It is dependent on the LabVIEW environment, which will also be developed during the spring semester. HITS believes that this aspect of the project is feasible as safety features are a common aspect of LabVIEW control systems. 38 ENGR 339 Team 7 Safety control extends beyond the LabVIEW environment into the valve and sensor selection process. HITS has explained these fail‐safe measures in the valve and sensor sections (Sections 4.4.1 and 4.6.1). 4.7 User Interface The user interface will be intuitive, robust, and easy to learn for any BMP employee, ensuring the test stand’s versatility. The LabVIEW environment mentioned in Section 4.6.2 will be accessed from a PC computer in an enclosure to protect the PC from the harsh industrial environment. Inputs to the LabVIEW environment will be performed with a panel mount industrial keyboard with a touchpad. These keyboards are similar to the input devices used on the heavy machinery currently used at BMP. The display will be a standard computer monitor under a protective plastic shield. 4.7.1 Graphical User Interface The graphical user interface (GUI) will be incorporated into the LabVIEW environment. A set of 5 screens will guide the user through the testing process as shown in Figure 19. This list of inputs may be modified as the control system is further developed. Figure 19: Graphical user interface screens. 4.8 Test Stand Layout 4.8.1 Component Storage Space The test stand must be roughly equivalent in size to a lab bench. In order to fit all of the components into this space, the size of each component must be considered. An ergonomic rule of thumb is that counter height should be 3 inches below elbow height in a standing position, 39 Calvin College Engineering which is about 1 meter for the average worker. Assuming a component storage area with depth of 1.5 m, length of 2 m, and height of 1 m gives a total of 3 m3 of storage space. 4.8.2 Component Geometry To meet space requirements, the volume and geometry of each component must be considered. Table 9 lists major components and relevant sizing requirements. Hoses, valves, and sensors provide some flexibility in component placement, but careful attention must be shown as to not kink hoses or tangle sensor wires. Table 9: Geometric requirements of components. Component Oil Reservoir 4 in. Drive Cylinder 2 in. Drive Cylinder Hoses Sensors Valves Oil Recovery Pan Human Interface Cooling Fan Pump Pump Motor Qty. 1 4 2 10 20 10 1 1 1 1 1 Geometric Requirements Box, must assure that hoses can fit around it. Must have ability to actuate freely Must have ability to actuate freely Cannot handle sharp corners; no kinks. N/A N/A Access for servicing is key. Eye level, no interference with test cylinder. Adequate air flow needed for heat transfer N/A Adequate air flow needed for heat transfer 4.9 Calvin Prototype HITS will design and construct a prototype hydraulic integrated test stand. HITS anticipates that the whole system, including cylinders, rail system, pump, and other components, will no larger than an Engineering Building table. This prototype will serve as a primary deliverable for the Calvin Engineering Senior Design night in May 2015. The small size of the Calvin prototype will make both the design and construction more feasible for HITS to accomplish. In addition, it will be much cheaper due to the reduced number of parts and materials (see Sections 5 and Appendix E). The reduced cost makes the Calvin prototype much more feasible for the scope and budget of a typical Calvin Engineering Senior Design Project. However, HITS must address the tradeoff between meeting budget requirements and designing a prototype that proves that the BMP design will perform well. For example, a more complex hydraulic circuit better reflects the potential issues and complexities of the BMP design, but it will cost much more due to the additional valves and other components. The Calvin prototype will require much lower flow rates and operating pressures than the full BMP design. Because of this, the test stand will be inherently safer to operate at the Calvin Engineering Building. HITS anticipates that the Calvin prototype will use four driving cylinders 40 ENGR 339 Team 7 placed in the corners of the sliding wall (see Sections 4.2.3 and 4.2.4) rather than the six driving cylinders of the BMP design. This design will provide a proof‐of‐concept of the hydraulic circuit without the added complexity of two different sets of driving cylinders. HITS will conduct a complete engineering analysis of the prototype frame, rail system, hydraulic system, and control system in the spring semester. In addition, the prototype user interface will reflect the industrial‐grade quality and ease of use expected by BMP, with a built‐in computer and industrial keyboard as described in Section 4.6.2. Table 10: Required test parameters for Calvin prototype. Given Product Range Cylinder Bore [in] Static Pressure [psi] Min Max 1.0 3.0 500 2500 Dynamic Pressure [psi] 500 1500 Retracted Length [ft] 0.5 3.0 Flow rate [gpm] 2 10 Rod Velocity [ft/s] 0 0.7 41 Calvin College Engineering 5 Costs HITS estimated costs for each component area of the hydraulic integrated test stand. Since there are two primary deliverables—the full test stand design for BMP and the small physical prototype for the Calvin Engineering Senior Design Night—two different cost estimates were developed. While some components have not been officially selected at this point in the project, approximations were made based on typical online quotes. See Appendix E for a full bill of materials for the BMP Design and the Calvin Prototype. 5.1 BMP Design Table 11 summarizes the approximate costs for each component area of the BMP hydraulic integrated test stand. Table 11: Total cost of hydraulic integrated test stand, BMP design. Component Category Force Generation System Hydraulic Circuit Power Unit Control System Miscellaneous Total Cost [$] 63400 17100 14000 10000 5000 Hydraulic Integrated Test Stand $109500 5.2 Calvin Prototype Table 12 summarizes the approximate costs for each component area of the BMP hydraulic integrated test stand. BMP has agreed to purchase or provide components that will be reusable for their own uses. In addition, several past senior design projects have parts (such as a motor) that can be reused by HITS. The remaining component costs will be covered by the team budget. Table 12: Total cost of hydraulic integrated test stand, Calvin Prototype. 42 Component Category Force Generation System Hydraulic Circuit Power Unit Control System Miscellaneous Total Cost [$] TBD 400 TBD TBD 260 Hydraulic Integrated Test Stand $660 ENGR 339 Team 7 6 Conclusion The senior design project outlined within this study has been deemed feasible. The hydraulic circuit, including the valves and hoses, can be successfully modeled using Simulink software. A force generation system comprised of a bank of hydraulic cylinders is a feasible method to complete loaded testing on a test cylinder. LabVIEW, along with several sensors and valves, can be implemented to control the system. Finally, a pump and motor can be found to meet the required specifications. Therefore, HITS will continue with the design work necessary to turn this feasible project into an end product design for Best Metals Products. 6.1 Design Decisions HITS has decided to pursue using rails to maintain synchronization in the system. The initial calculations show that a rail system is feasible given the constraints. HITS will still attempt to synchronize the system using basic hydraulic methods; however, HITS will not use servo valves to perform this function. HITS also decided on the number of cylinders required for the force generating system based on requiring a safety factor of 1.65. The cylinders that will comprise the force generating system will be four 4‐inch diameter cylinders and two 2‐inch diameter cylinders. In order to adequately measure data points for the test stand, HITS will use a purchased load cell in combination with pressure gauges to gather accurate data on the forces in the system. The two types of sensors will create a redundant system to fact‐check the results. Because pump and motor design are outside the scope of this project, HITS will spec purchasable power unit and reservoir from outside suppliers to power the system and cool hydraulic fluid. Additionally, HITS will design a kidney loop filtration system to remove particulate from the hydraulic fluid, because a team member has prior experience with designing this type of filtration. The prototyping requirements for the Calvin College Senior Design night were also determined, along with an initial idea for the design. To reduce the complexity of the full design while maintaining the ability to prove the concept, the Calvin prototype will consist of a smaller desk sized machine with only four 2‐inch diameter hydraulic cylinders for force generation. 6.2 Risks There are two primary risks involved with this project: complexity of design and cost required. HITS must keep the costs close to $100,000 in order to meet customer requests and Goal 3. Additionally, the prototype cost must remain at a feasible budget for the Calvin engineering department. The complexity of the design could drastically increase costs, or become too complicated to adequately design or build. 6.3 Current Status Table 3 shows that 39% of proposed project time has been completed. HITS expects an additional 400 hours of work before the final design is completed. The team is on track to finish by the end of next semester. 43 Calvin College Engineering 7 Acknowledgements Calvin College has provided significant opportunities and learning experiences that have gone above and beyond a normal undergraduate degree. We are incredibly thankful for all of the faculty and staff of the college who have been instrumental in our education by intentionally building into us within and outside of the classroom. Particularly, we would like to thank Professors Nielsen and Tubergen for their direct support on our senior design project. Best Metal Products has also largely contributed to this senior design project by providing a problem to solve, along with many resources for support. We would like to thank Kurt Skov in particular for advising on the project and offering his wisdom in designing various hydraulic components. In addition, we would like to thank our families and friends for their support and encouragement in undertaking this project. 44 ENGR 339 Team 7 8 Works Cited [1] W. Riley, L. Sturges and D. Morris, Mechanics of Materials, Wiley, 2006. [2] Hydraulics & Pneumatics, "Synchronizing cylinder movement," 6 December 2010. [Online]. Available: http://hydraulicspneumatics.com/other‐technologies/book‐2‐chapter‐22‐
synchronizing‐cylinder‐movement?page=1. [Accessed 6 December 2014]. [3] G. T.‐C. C. Hong Sun, "Motion Synchronization for Multi‐Cylinder Electro‐Hydraulic System," IEEE/ASME Transactions on Mechatronics, vol. 7, no. 2, pp. 171‐181, 2002. [4] Moog Inc, "Moog‐Valves‐D791_D792‐Catalog‐en," Moog Inc, [Online]. Available: http://www.moog.com/literature/ICD/Moog‐Valves‐D791_D792‐Catalog‐en.pdf. [Accessed 01 12 2014]. [5] Coaster‐lab, "Coaster‐Lab Amusement Ride Inventions," Coaster‐Lab, [Online]. Available: http://coaster‐lab.com/. [Accessed 06 12 2014]. [6] PBC Linear, "PBC Linear Cam Roller Technology," PBC Linear, 2014. [Online]. Available: http://www.pbclinear.com/Download/Catalog/Cam‐Roller‐Technology‐Catalog.pdf. [Accessed 06 12 2014]. [7] BWC, "Technical Data," Bishop‐Wisecarver Group, 2012. [Online]. Available: http://bwc.staging.mo.autoupdate.com/faq_dualvee.vp.html. [Accessed 06 12 2014]. [8] Parker, "Hydraulic Hose, Fittings, and Equipment Technical Handbook," 09 2007. [Online]. Available: www.parker.com/literature. [Accessed 03 11 2014]. [9] Parker Hannifan Corporation, "Hydraulic Cartridge Systems Division ‐ Technical Data," [Online]. Available: http://www.parker.com/portal/site/PARKER/menuitem.223a4a3cce02eb6315731910237ad
1ca/?vgnextoid=f616af5c6f65e210VgnVCM10000048021dacRCRD&vgnextfmt=EN. [Accessed 2 December 2014]. [10] Wikipedia, "Hydraulic machinery," 15 October 2014. [Online]. Available: http://en.wikipedia.org/wiki/Hydraulic_machinery. [Accessed 2 December 2014]. [11] Moog Inc., "Moog Industrail Controls," Moog Inc., [Online]. Available: http://www.moog.com/literature/ICD/760_CDS6541_G.pdf. [Accessed 02 12 2014]. [12] Hydraulics Pneumatics, "Fundamentals of Hydraulic Pumps," 01 01 2012. [Online]. Available: http://hydraulicspneumatics.com/200/TechZone/HydraulicPumpsM/Article/False/6401/Te
chZone‐HydraulicPumpsM. [Accessed 03 11 2014]. [13] Hydraulic Supply Company, 2012 Stock Products Catalogue, 2012. [14] H. M. M. R. J. B. J. Richard K. Tessmann, "Basic Hydraulic Pump and Circuit," in Handbook of Hydraulic Fluid Technology, New York, NY, Marcel Dekker, Inc., 2000, p. 1258. [15] B. Trinkel, Fluid Power eBook ‐ Fluid Power Basics, Hydraulics & Pneumatics, 2007. [16] M. G. Rabie, Fluid Power Engineering, Egypt: McGraw‐Hill, 2009. 45 Calvin College Engineering [17] J. Trott, "Provide added cooling for compact hydraulic systems," Hydraulics & Pneumatics, 31 August 2013. [18] N. Al‐Araji and H. Sarhan, "Effect of Temperature on Sliding Wear Mechanism under," International Journal of Engineering, vol. 5, no. 2, pp. 176‐184, 2011. [19] J. J. DeRooy, "Force Gauge Design Problem," Calvin College, Grand Rapids, 2014. [20] Sentran, "Precision Low Profile Load Cell," Sentran, [Online]. Available: http://www.sentranllc.com/pdfs/PHB&W.pdf. [Accessed 02 12 2014]. [21] Aschcroft Inc., "Model A2 Heavy Industrial Pressure Transmitter," Stratford, CT, 2012. [22] Celesco, "PT101 Instrument Grade Absolute Linear Position," Celesco, 02 2013. [Online]. Available: http://www.celesco.com/_datasheets/pt101.pdf. [Accessed 02 12 2014]. [23] Baumer, "Linear encoders without Bearings incremental," Baumer, 24 06 2014. [Online]. Available: http://pfinder.baumer.com/pfinder_motion/downloads/Produkte/PDF/Datenblatt/Drehge
ber_lagerlos/Baumer_MIL10_DS_EN.pdf. [Accessed 02 12 2014]. [24] Renishaw, "RESOLUTE absolute optical encoder," Renishaw, 2013. [Online]. Available: http://resources.renishaw.com/en/details/data‐sheet‐resolute‐absolute‐optical‐encoder‐
with‐biss‐serial‐communications‐‐53925. [Accessed 02 12 2014]. [25] National Instruments, "LabVIEW System Design Software," 2014. [Online]. Available: http://www.ni.com/labview/. [Accessed 5 November 2014]. [26] Sun Hydraulics Corporation, "Sun Hydraulics Technical Tips ‐ Solenoid Operated Directional Valves," 16 06 2014. [Online]. Available: www.sunhydraulics.com. [Accessed 03 11 2014]. [27] "Wikipedia," 12 April 2014. [Online]. Available: http://en.wikipedia.org/wiki/Electrohydraulic_servo_valve. [Accessed October 2014]. [28] Moog Inc., "Servo Valves: 3‐Stage Flow Control, 79 Series," December 2011. [Online]. Available: http://www.moog.com/literature/ICD/Moog‐Valves‐79‐Series‐Catalog‐en.pdf. [Accessed October 2014]. [29] Moog Inc., "Electrohydraulic Valves...A Technical Look," [Online]. Available: http://www.moog.com/literature/ICD/Valves‐Introduction.pdf. [Accessed 3 November 2014]. [30] J. L. Johnson, "What is the difference between a servovalve and a proportional valve?," Hydrualics & Pneumatics, 8 August 2012. [Online]. Available: http://hydraulicspneumatics.com/hydraulic‐valves/what‐difference‐between‐servovalve‐
and‐proportional‐valve. [Accessed 3 November 2014]. [31] Sun Hydraulics Corporation, "Electro‐Proportional Terms and Definitions," Sun Hydraulics, 2010. [Online]. Available: http://www.sunhydraulics.com/sites/default/files/media_library/tech_resources/rel‐
Prop_terms‐definitions.pdf. [Accessed 3 November 2014]. [32] Eaton, "Eaton Servo‐Performance Proportional Directional Valve," June 2014. [Online]. Available: http://www.eaton.com/ecm/groups/public/@pub/@eaton/@hyd/documents/content/pll_
2164.pdf. [Accessed 3 November 2014]. 46 ENGR 339 Team 7 [33] Moog Inc., "Servovalves and Proportional Valves," [Online]. Available: http://www.moog.com/products/servovalves‐servo‐proportional‐valves/industrial/flow‐
control/analog‐without‐integrated‐electronics/direct‐operated‐servo‐valves‐for‐analog‐
signals‐79‐100‐79‐200‐series/. [Accessed 3 November 2014]. [34] Hydraulics & Pneumatics, "Directional‐control valves," 1 January 2012. [Online]. Available: http://hydraulicspneumatics.com/200/TechZone/HydraulicValves/Article/False/6408/Tech
Zone‐HydraulicValves. [Accessed October 2014]. [35] Max Machinery, "Testing electro hydraulic servo valves and proportional valves," 2014. [Online]. Available: http://www.maxmachinery.com/industry‐application/electro‐hydraulic‐servo‐
valves‐and‐proportional‐valves. [Accessed 4 November 2014]. [36] Spirax Sarco, "Control Valve Characteristics," 2014. [Online]. Available: http://www.spiraxsarco.com/resources/steam‐engineering‐tutorials/control‐hardware‐el‐
pn‐actuation/control‐valve‐characteristics.asp. [Accessed 4 November 2014]. [37] Hydraulics & Pneumatics, "Pressure‐control valves," 1 January 2012. [Online]. Available: http://hydraulicspneumatics.com/200/TechZone/HydraulicValves/Article/False/6411/Tech
Zone‐HydraulicValves. [Accessed October 2014]. [38] Sun Hydraulics Corporation, "Flow Divider and Flow Divider/Combiner Valves," 16 June 2014. [Online]. Available: http://www.sunhydraulics.com/sites/default/files/media_library/tech_resources/TT_US_Fl
owDivider‐New.pdf. [Accessed 5 November 2014]. [39] Donaldson Filters, "FPK02‐Inline Cartridge Filters," Donaldson Filters, [Online]. Available: http://www.donaldson.com/en/ih/support/datalibrary/001361.pdf. [Accessed 02 12 2014].
47 Calvin College Engineering 9 Appendices 48 ENGR 339 Team 7
Table of Contents
Table of Figures .......................................................................................................................................................50
Table of Tables ........................................................................................................................................................51
A.
Testing Scenarios ............................................................................................................................................52
1.
Test Scenario 1 ...........................................................................................................................................52
2.
Test Scenario 2 ...........................................................................................................................................52
3.
Test Scenario 3 ...........................................................................................................................................53
4.
Test Scenario 4 ...........................................................................................................................................53
5.
Test Scenario 5 ...........................................................................................................................................54
6.
Test Scenario 6 ...........................................................................................................................................54
7.
Test Scenario 1 – Test Scenario 2 ...............................................................................................................55
8.
Test Scenario 4 – Test Scenario 5 ...............................................................................................................55
9.
Test Scenario 1 – Test Scenario 4 ...............................................................................................................55
10.
Test Scenario 2 – Test Scenario 5 ..........................................................................................................56
11.
Test Scenario 1 – Test Scenario 5 ..........................................................................................................56
12.
Test Scenario 2 – Test Scenario 4 ..........................................................................................................56
B.
Valve Research ...............................................................................................................................................57
13.
Valve Function .......................................................................................................................................57
14.
Valve Actuation ......................................................................................................................................60
C.
Calculations ....................................................................................................................................................63
1.
Rod Buckling Analysis .................................................................................................................................63
2.
Number of Driving Cylinders Required ......................................................................................................66
3.
Moment Balance on a Perfectly Balanced Wall .........................................................................................68
4.
Moments Resulting from Geometric Stack-up, Top ...................................................................................70
5.
Moments Resulting from Geometric Stack-up, Side ..................................................................................72
6.
Moments Resulting from Force Generation Pressure Differentials ...........................................................74
D.
CAD Drawings .................................................................................................................................................77
E.
Bill of Materials...............................................................................................................................................78
F.
1.
Force Generation System ...........................................................................................................................78
2.
Hydraulic Circuit .........................................................................................................................................79
3.
Power Unit .................................................................................................................................................80
4.
Control System ...........................................................................................................................................81
Estimate of Future Work ................................................................................................................................82
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Table of Figures
Figure A1: Test scenario 1. .......................................................................................................................... 52
Figure A2: Test scenario 2. .......................................................................................................................... 53
Figure A3: Test scenario 3. .......................................................................................................................... 53
Figure A4: Test scenario 4. .......................................................................................................................... 54
Figure A5: Test scenario 5. .......................................................................................................................... 54
Figure A6: Test scenario 6. .......................................................................................................................... 55
Figure B1: Typical directional control valve application …………………..…………………………………………………… 55
Figure B2: Directional valve flow paths ………………………………………………..…………………………………………..… 56
Figure B3: Flow characteristics of different flow metering valves …………………………………………………..….. 57
Figure B4: Cracking pressure difference for direct-acting and pilot-acting valves …………………………….…. 58
Figure B5: Spool-type flow divider valve …………………………………………………………………………………………..… 58
Figure B6: Solenoid operated cartridge valve ………………………………………………………………………………………. 59
Figure D1: Initial wall geometric layout ……………………………………………………………………………………………..… 75
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Table of Tables
Table E1: Cost of force generation system components for BMP design................................................... 78
Table E2: Cost of force generation system components for Calvin prototype. .......................................... 78
Table E3: Cost of hydraulic circuit components for BMP design. ............................................................... 79
Table E4: Cost of hydraulic circuit components for Calvin prototype. ....................................................... 79
Table E5: Cost of power unit components for BMP design. ....................................................................... 80
Table E6: Cost of power unit components for Calvin prototype. ............................................................... 80
Table E7: Cost of control system components for BMP design. ................................................................. 81
Table E8: Cost of control system components for Calvin prototype. ......................................................... 81
Table F1: Detailed estimate of future work. ............................................................................................... 82
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A. Testing Scenarios
1.
Test Scenario 1
The first test scenario moves the rods of the test cylinder and cylinder bank out of the cylinder
(to the right in Figure A1). This movement is created by driving force in the test cylinder. Fluid is
pumped into the cap end of the cylinder while fluid in the head end is allowed to drain to the
reservoir. The pressure differential that is created across the cylinder drives the rod out. At the
same time, the driving cylinder bank provides a resistive force against this movement. The rods
of the driving cylinders move to the right in the diagram, so fluid must exit from the head end.
The fluid flow is metered out, meaning that the hydraulic system limits the amount of flow that
can exit the cylinder. This means that the driving cylinder bank provides a resistive force against
the driving force of the test cylinder.
Figure A1: Test scenario 1.
2.
Test Scenario 2
Test Scenario 2 is essentially the opposite of Test Scenario 1. The rods of the test and driving
cylinders move into the cylinders, meaning that the wall moves to the left in Figure A2. This
movement is accomplished by pumping fluid into the head end of the driving cylinder bank and
metering fluid out of the cap end of the test cylinder. Therefore, the driving cylinder bank
provides the driving force for the movement of the wall while the test cylinder provides the
resistive force against the movement of the wall.
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Figure A2: Test scenario 2.
3.
Test Scenario 3
The third test scenario is a static test. Fluid is not actively pumped or metered and the wall and
rods do not move. This test is designed to test the seals in the head end of the test cylinder.
High pressure is built up in the cap end of the driving cylinders to provide a driving pressure.
This will create a force to the left in Figure A3 that is applied to the test cylinder. The seals are
tested because the test cylinder must resist the force without leaking fluid or losing pressure in
the head end.
Figure A3: Test scenario 3.
4.
Test Scenario 4
As in Test Scenario 1, Test Scenario 4 moves the rods and wall to the right (Figure A4. However,
this is accomplished with a driving force from the driving cylinder bank rather than the test
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cylinder. Fluid is pumped into the cap end of the driving cylinders, moving the rod out of the
cylinder. This force is resisted by metering fluid out of the test cylinder.
Figure A4: Test scenario 4.
5.
Test Scenario 5
As in Test Scenario 2, Test Scenario 5 moves the rods and wall to the left (Figure A5). The driving
force is provided by pumping fluid into the head end of the test cylinder. The movement of the
rods and wall is resisted by metering fluid out of the cap end of the driving cylinder bank.
Figure A5: Test scenario 5.
6.
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Test Scenario 6
ENGR 339 Team 7
Like Test Scenario 3, Test Scenario 6 is a static test. In order to test the seals in the head end of
the test cylinder, a driving pressure is built up in the cap end of the driving cylinder bank. This
creates a force that attempts to pull the rod of the test cylinder out of the cylinder (to the right
in Figure A6). Since the test is static, no fluid moves in or out of the cylinders and the wall should
not move.
Figure A6: Test scenario 6.
7.
Test Scenario 1 – Test Scenario 2
Test Scenarios 1 and 2 both involve the cap end of the test cylinder and the head end of the
driving cylinder bank. In Test Scenario 1, fluid is pumped into the test cylinder and metered out
of the driving cylinder bank. In Test Scenario 2, fluid is pumped into the driving cylinder bank
and metered out of the test cylinder. This means that the wall moves to the right in Test
Scenario 1 and to the left in Test Scenario 2 (Figure A1 and Figure A2. It is reasonable to assume
that BMP would want to be able to run these tests in succession, allowing them to analyze the
cap end of the test cylinder under pumping-in and metering-out conditions.
8.
Test Scenario 4 – Test Scenario 5
The transition from Test Scenario 4 to 5 is similar to the transition from Test Scenario 1 to 2.
However, Test Scenarios 4 and 5 both involve the head end of the test cylinder and the cap end
of the driving cylinder bank. In Test Scenario 4, fluid is pumped into the driving cylinder bank
and metered out of the test cylinder. In Test Scenario 5, fluid is pumped into the test cylinder
and metered out of the driving cylinder bank. The velocity direction of the rods and wall changes
from out (to the right in Figure A4) to in (to the left in Figure A5). By running these tests in
succession, BMP can analyze the head end of the test cylinder under metering-out and
pumping-in conditions.
9.
Test Scenario 1 – Test Scenario 4
In Test Scenarios 1 and 4, the rods and wall move in the same direction (to the right in Figure A1
and Figure A4), but the direction of the force applied to the test cylinder changes. In other
words, the test cylinder changes from providing a driving force to a resistive force: fluid is
pumped into the cap end and then metered out of the head end. At the same time, the driving
cylinder bank changes from metering fluid out of the head end (resistive force) to pumping fluid
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into the cap end (driving force). This is a complicated transition, but it is applicable to real-world
situations.
10.
Test Scenario 2 – Test Scenario 5
Similar to the transition from Test Scenario 1 to 4, the transition from Test Scenarios 2 to 5
involves a change in force direction with a consistent velocity direction. In both cases, the rods
move into the cylinders and the wall moves to the left (Figure A2 and Figure A5). However, the
direction of the force on the test cylinder changes, so it must change from metering fluid out of
the head end to pumping fluid into the cap end. Simultaneously, the driving cylinder bank
changes from pumping fluid into the head end (driving force) to metering fluid out of the cap
end (resistive force).
11.
Test Scenario 1 – Test Scenario 5
The transition from Test Scenario 1 to 5 involves a change in force direction and a change in
velocity direction. The test cylinder provides the driving force in both cases: in Test Scenario 1,
fluid is pumped into the cap end, but it is pumped into the head end for Test Scenario 5. The
driving cylinder bank provides the resistive force in both cases: in Test Scenario 1, fluid is
metered out of the head end, but it is metered out of the cap end in Test Scenario 5. This
changes the direction of the resistive force that is applied to the test cylinder. The rods move
out of the cylinders in Test Scenario 1 (to the right in Figure A1) and into the cylinders in Test
Scenario 5 (to the left in Figure A5).
12.
Test Scenario 2 – Test Scenario 4
Similar to the transition from Test Scenario 1 to 5, the transition from Test Scenarios 2 to 4
involves a change in force direction and velocity direction. Here, the test cylinder provides the
resistive force: in Test Scenario 2, fluid is metered out of the cap end, but it is metered out of
the head end in Test Scenario 4. The driving cylinder bank provides the driving force in both
cases: in Test Scenario 2, fluid is pumped into the head end, but it is pumped into the cad end in
Test Scenario 4. This changes the direction of the driving force that is applied to the test
cylinder. The rods move into the cylinders in Test Scenario 2 (to the left in Figure A2) and out of
the cylinders in Test Scenario 4 (to the left in Figure A4).
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B. Valve Research
13.
Valve Function
Valves are an essential element for controlling hydraulic fluid in a fluid power circuit. Valves
come in many varieties, allowing them to perform many different tasks in a circuit. The function
of four types of valves is explained here.
Directional Control Valves
Directional control valves are essential for fluid power circuits that involve hydraulic cylinders. In
order for the cylinder rod to be driven both in and out, the circuit must change which side of the
cylinder receives fluid from the power unit. This is accomplished with directional control valves.
These valves have a spool which can be shifted to multiple positions [1]. There are typically
three or four positions, meaning that there are three or four ways that the fluid can be directed
through the circuit. For example, Figure B1 shows a hydraulic cylinder driven by a simple fluid
power circuit. The directional control valve in the middle of the schematic has three positions,
each represented by a side-by-side square. The position on the left directs fluid into the head
end of the cylinder (with the rod) and allows fluid to pass out of the cap end (without the rod)
into the reservoir. This results in the rod moving into the cylinder. The position on the right
accomplishes the opposite motion: by pumping fluid into the cap end and allowing the fluid in
the head end to move into the reservoir, the rod moves out of the cylinder. The center position
blocks off each port, resulting in no flow and no rod movement. Because this directional control
valve has three spool positions and four ports that enter and exit the valve, it is called a “4-port,
3-position spool valve” [1].
Figure B1: Typical directional control valve application [1].
While this basic function is similar across all directional control valves, the spool can be actuated
in a number of different ways (Figure B2, below). Solenoids and pilot circuits are the simplest,
most common method for obtaining discrete spool movements. Valve actuation is explained in
further detail in Section 14.
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Figure B2: Directional valve flow paths [2].
Flow Metering Valves
The ability to control the flow—and, therefore, the pressure—of a fluid power circuit is also very
important. This concept is called flow metering. Flow metering valves work by changing the size
of an orifice within the valve through which the fluid passes. As with directional control valves,
there are many methods for achieving good flow control. For example, flow metering valves can
be differentiated based on the size and shape of the plug that fills the orifice [3]. Figure B3,
below, illustrates many different flow characteristics that can be obtained with different types
of valve plugs. In Figure B3, the x-axis is the percent that the orifice is open, and the y-axis is the
percent of the total potential flow that is going through the valve. In addition, flow metering
valves can also have a fixed orifice for use in simple applications where no adjustment is
necessary [4].
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ENGR 339 Team 7
Figure B3: Flow characteristics of different flow metering valves [3].
Pressure Relief Valves
Pressure relief valves are a safety mechanism that prevents too much pressure from building up
in the circuit. When the pressure acting on the valve reaches a pre-determined threshold (called
the cracking pressure), the valve opens and hydraulic fluid is released to the reservoir [5]. This
ensures that the pressure in a hydraulic circuit is at a safe level at all times. This is important for
the safety of both the expensive circuit components and for the personnel operating the
system.
Pressure relief valves are generally controlled mechanically by a poppet and spring (direct-acting
relief valves) or by a pilot circuit. However, spring-controlled or poppet-controlled pressure
relief valves are usually used in low-flow applications, so HITS will not be using direct-acting
relief valves.
Pilot-controlled pressure relief valves have two stages: the first stage (the pilot stage) has a
small spring-controlled valve that in turn operates the main relief valve [5]. The force supplied
by the pilot stage allows the pilot-controlled pressure relief valves to operate at much higher
pressures than direct-acting relief valves. Additionally, the pilot circuit supply can be connected
to remote parts of the circuit, providing safety pressure relief where it is most needed. Figure
shows how the secondary pilot circuit in a pilot-acting relief valve reduces the cracking pressure
of the valve. This prevents high amounts of fluid to bypass through the valve before the
pressure reaches the maximum setting.
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Figure B4: Cracking pressure difference for direct-acting and pilot-acting valves [5].
Flow Divider-Combiner Valves
Flow divider-combiner valves can either divide flow and send it to two actuators or, by operating
in reverse, combine flows from two sources [Parker - Flow Divider/combiner valves]. Like flow
control valves, divider-combiner valves typically have two orifices that control the amount of
flow that passes through either branch (Figure B5). By using a spool valve, the flow can be
divided equally (same size orifice on each side) or proportionally (one orifice larger than the
other) [4]. More accurate flow divider-combiner valves can synchronize the speed of two
cylinders by precisely controlling the amount of fluid sent to each cylinder. For applications that
require more than two outlets, divider-combiner valves with specified flow splitting ratios can
be used in series [6]. HITS will evaluate the hydraulic circuit and determine the type and number
of flow divider-combiner valves necessary for properly distributing fluid.
Figure B5: Spool-type flow divider valve [4].
14.
Valve Actuation
Hydraulic valves can be manually operated or automated. The rapid response and complexity of
the hydraulic circuit used in this application will eliminate the possibility of using manually
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ENGR 339 Team 7
operated valves. Automated hydraulic valves are actuated in one of three ways: solenoid
operated, pilot operated, and electrohydraulic controlled valves.
Solenoid Operated Valves
Solenoid operated valves have a very fast response for an automated valve. They work by using
an electric solenoid to shift a spool within the valve body. Figure B6 shows a solenoid operated
cartridge valve, which contains the electric solenoid (black) and spool. The valve body is not
present in this figure since this would be incorporated into a machined valve manifold. The
simplicity and speed of the solenoid operated valves makes them a very attractive option,
however solenoid valves cannot perform at higher fluid flow rates. The internal forces caused by
the hydraulic fluid moving through the valve limits the flow rate of a solenoid operated valve to
12 gpm [7]. This limit is below the needs for our hydraulic circuit, removing solenoid operated
valves as an option.
Figure B6: Solenoid operated cartridge valve [7].
Pilot Operated Valves
Pilot operated valves function in the same way as solenoid operated valves except they replace
the solenoid actuator with a pilot actuator. The pilot actuator consists of a low-flow hydraulic
circuit which pushes the valve spool to control the position of the valve. The pressure in the
pilot circuit allows the pilot operated valves to hold the hydraulic circuit open in higher flow
situations since the pilot circuit provides more force than a solenoid can generate.
The addition of the pilot circuit adds complexity to the hydraulic circuit. Each pilot operated
valve requires at least one additional solenoid operated valve to control the pilot circuit. The
pilot circuit also needs to use flow dividers to obtain power from the power unit. This adds time
delays, components, and control challenges into the system. HITS prefers to avoid using pilot
operated valves to circumvent these issues.
Advanced Control Valves
Advanced control valves combine aspects of directional valves and flow-metering valves for
applications that require precise position, velocity, pressure, or force control [8] [9] [10]. This
advantage is obtained by using an electrical signal to accurately dictate the position of the valve
spool. In this way, the size of the orifice changes and the signal controls how much hydraulic
fluid passes through the valve. Rather than only having two positions (open or closed), an
Advanced control valve can be positioned at any setting between open and closed. This allows
the valve to accomplish directional control and flow-metering at the same time.
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There are two main categories of advanced control valves: servovalves and servo-proportional
valves (or, simply “proportional valves”) [8] [11]. This distinction is quite subtle. Moog Inc. states
that their servovalves “are nearly always zero lapped or axis cut (no mechanical deadband),”
whereas their servo-proportional valves “may have a mechanical deadband” [8]. Mechanical
deadband refers to the minimum input necessary to produce flow or pressure output [12].
Physically, mechanical deadband results in a time delay between the control signal and the
valve’s reaction. Hydraulics & Pneumatics confirms Moog Inc. by explaining that a servovalve
has “less than 3% center overlap,” but a proportional valve has “more than 3% center overlap”
[11].
Servovalves and servo-proportional valves come in several varieties. The primary difference
comes from how the valve spool is actuated. Advanced control valves can have two stages or
three stages. Typically, an electrical current is provided to a solenoid or torque motor, which in
turn operates an internal pilot circuit. This pilot stage then causes displacement in the main
spool [10]. Moog Inc. describes several methods for actuating their servovalves and servoproportional valves, including Direct Drive and ServoJet [8].
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C. Calculations
1.
Rod Buckling Analysis
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2.
66
Number of Driving Cylinders Required
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3.
68
Moment Balance on a Perfectly Balanced Wall
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4.
70
Moments Resulting from Geometric Stack-up, Top
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5.
72
Moments Resulting from Geometric Stack-up, Side
ENGR 339 Team 7
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Calvin College Engineering
6.
74
Moments Resulting from Force Generation Pressure Differentials
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D. CAD Drawings
Figure D1: Initial wall geometric layout.
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Calvin College Engineering
E. Bill of Materials
1.
Force Generation System
BMP Design
Table E1: Cost of force generation system components for BMP design.
Component
Company
Quantity
Unit Cost [$]
Total Cost [$]
4 in. Hydraulic
Cylinder
BMP
4
250
1000
2 in. Hydraulic
Cylinder
BMP
2
200
400
Frame
BMP to source
1
30000
30000
Rails
PBO Linear
4
5000
20000
Rollers
PBO Linear
8
1500
12000
Force Generation System
63400
Calvin Prototype
Table E2: Cost of force generation system components for Calvin prototype.
Component
Wall Mechanism
2 in. Hydraulic
Cylinder
Frame
Rails
Rollers
Company
Calvin to build
Quantity
1
Unit Cost [$]
TBD
BMP
3
TBD
TBD
Calvin to build
Calvin to build
Calvin
1
4
8
TBD
TBD
TBD
TBD
TBD
TBD
Force Generation System
78
Total Cost [$]
TBD
TBD
ENGR 339 Team 7
2.
Hydraulic Circuit
BMP Design
Table E3: Cost of hydraulic circuit components for BMP design.
Component
Company
Quantity
Unit Cost [$]
Total Cost [$]
Hoses
McMaster
1
1000
1000
Pressure Relief
Valve
MOOG
5
500
2500
4-way Directional
Control Valve
MOOG
4
400
1600
Flow DividerCombiner Valve
MOOG
4
600
2400
Hydraulic Circuit
7500
Calvin Prototype
Table E4: Cost of hydraulic circuit components for Calvin prototype.
Component
Company
Quantity
Unit Cost [$]
Hose
BMP
15
0
0
Pressure Relief
Valve
Eaton
3
40
120
4-way Directional
Control Valve
MOOG
4
40
160
Flow DividerCombiner Valve
Eaton
3
40
120
Hydraulic Circuit
Total Cost [$]
400
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Calvin College Engineering
3.
Power Unit
BMP Design
Table E5: Cost of power unit components for BMP design.
Component
Company
Quantity
Unit Cost [$]
Pump
Eaton
1
TBD
TBD
Motor
Eaton
1
TBD
TBD
Reservoir
LDI Industries
1
TBD
TBD
Thermal
Components
LDI Industries
1
TBD
TBD
Power Unit
Total Cost [$]
~ 14000
Calvin Prototype
Table E6: Cost of power unit components for Calvin prototype.
Component
Company
Quantity
Unit Cost [$]
Pump
Calvin
1
TBD
TBD
Motor
Calvin
1
TBD
TBD
Reservoir
Calvin to build
1
TBD
TBD
Thermal
Components
Calvin to build
1
TBD
TBD
Power Unit
80
Total Cost [$]
TBD
ENGR 339 Team 7
4.
Control System
BMP Design
Table E7: Cost of control system components for BMP design.
Component
Company
Quantity
Unit Cost [$]
Total Cost [$]
6 ft. Position
Sensor
Honeywell
4
400
1600
Pressure Sensor
Honeywell
6
150
900
80 ton Load Cell
Sentran
1
2000
2000
LabVIEW
National
Instruments
1
3000
3000
DAC System
Honeywell
1
2000
2000
Computer
HP
1
500
500
Control System
10000
Calvin Prototype
Table E8: Cost of control system components for Calvin prototype.
Component
Company
Quantity
Unit Cost [$]
Position sensor
Honeywell
2
TBD
TBD
LabVIEW
Calvin
1
TBD
TBD
DAC System
Calvin
1
TBD
TBD
Strain Gage
Calvin
2
TBD
TBD
Thermocouple
Calvin
2
TBD
TBD
Control System
Total Cost [$]
TBD
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Calvin College Engineering
F. Estimate of Future Work
Table F1: Detailed estimate of future work.
Future Tasks
Wall & Coupling Design
Rail Design
Roller and support design
Wall strength analysis
Cylinder Coupling Design
Hydraulic Schematic
Metering Control
Simulink Development
Simulation Testing
Hydraulic component selection
Valve Selection
Power Unit Selection
Thermal System Selection
Quote management
Filter system design
Hydraulic Thermal Design
Heat flow requirements
Analyze fins & Fans
Select components
LabVIEW controls
Control Design
Control Testing
Control documentation
Research, general
User Interface Design
Input and control
Error messages
Prototype design
Power Unit Selection
Cylinder Sizing
Frame Design
Rail Design
FEA testing
Print Making
Prototype build
Frame Construction
Assembly
Initial Testing
Detailed Testing
Report Writing
Formatting
Writing
Editing
Sensor and DAC selection
Sensor Selection
DAC selection
Subtotal:
Contingency:
Total Hours
82
Estimated Time
Subtotal
30
8
8
8
6
20
8
4
8
30
8
8
7
3
4
20
6
8
6
30
8
8
8
6
10
7
3
48
8
8
8
8
8
8
32
8
8
8
8
22
8
8
6
15
8
7
257
50%
386