Inter - Bayamon Lecture MECN 4110 1 Mechanisms Design MECN 4110 Professor: Dr. Omar E. Meza Castillo omeza@bayamon.inter.edu http://facultad.bayamon.inter.edu/omeza Department of Mechanical Engineering Inter American University of Puerto Rico Bayamon Campus Inter - Bayamon Syllabus Catalog Description: Analysis of mobility and kinematics of mechanisms. Application of the graphical and computerized techniques of position analysis, speed, and acceleration in mechanisms. Design of levies and gears. Introduction to the synthesis of mechanisms. Prerequisites: ENGR 2220 – Computerized Engineering Graphics, MECN 3120 – Vector Mechanics for Engineers: Dynamics. MECN 4110 Course Text: Norton, Robert L., Design of Machinery: An Introduction to the Synthesis and Analysis of Mechanisms and Machines, 3rd. Ed., McGraw-Hill, 2004. 2 Lecture 1 Inter - Bayamon MECN 4110 Syllabus Absences: On those days when you will be absent, find a friend or an acquaintance to take notes for you or visit the web page. Do not call or send an email the instructor and ask what went on in class, and what the homework assignment is. Homework assignments: Homework problems will be assigned on a regular basis. Problems will be solved using the Problem-Solving Technique on any white paper with no more than one problem written on one sheet of paper. Homework will be collected when due, with your name written legibly on the front of the title page. It is graded on a 0 to 100 points scale. Late homework (any reason) will not be accepted. 3 Lecture 1 Inter - Bayamon MECN 4110 Syllabus Problem-Solving Technique: A. Known B. Find C. Assumptions D. Schematic E. Analysis, and F. Results Quiz : There are several partial quizzes during the semester. Partial Exams and Final Exam: There are three partial exams during the semester, and a final exam at the end of the semester. 4 Lecture 1 Inter - Bayamon MECN 4110 Syllabus Laboratory Reports: There seven or eight experimental laboratories throughout the semester. Laboratory reports must be submitted by each group, one week after the experiment is done. The report must be written in English, in a professional format. Final Project: There is a final project, it will consist in the design of a mechanism with application of course knowledge. 5 Lecture 1 Inter - Bayamon MECN 4110 Course Grading The total course grade is comprised of homework assignments, quizzes, partial exams, final exam, and a project as follows: Homework 15% Quiz 15% Laboratory Reports 20% Partial Exams 20% Final Exam 20% Final Project 10% 100% Cheating: You are allowed to cooperate on homework by sharing ideas and methods. Copying will not be tolerated. Submitted work copied from others will be considered academic misconduct and will get no points. 6 Lecture 1 Inter - Bayamon MECN 4110 Course Materials Most Course Material (Course Notes, Handouts, Homework, Final Project, and Communications) on Web Page Power Point Lectures will posted every week or two. Office Hours: Tuesday and Thursday @ 5:50 to 7:20 PM Email: mezacoe@gmail.com 7 Lecture 1 Inter - Bayamon MECN 4110 Tentative Lectures Schedule Topic Lecture Introduction of Mechanism and Kinematics 8 1, 2 and 3 Lecture 1 Inter - Bayamon Reference MECN 4110 Myska, David H. Machines & Mechanisms: applied kinematic analysis, 2nd Ed., Prentice Hall, 2002 Sandor, G. N., and Erdman A. G., Mechanism Design: Analysis and Synthesis, 4th. Ed., Prentice Hall, 2001 Waldron, Kenneth J. and Kinzel, Gary L., Kinematics, Dynamics, and Design of Machinery, John Wiley & Sons, Inc, 2004. 9 Lecture 1 Inter - Bayamon One thing you learn in science is that there is no perfect answer, no perfect measure. A. O. Beckman Topic 1: Mechanism and Kinematics MECN 4110 Introduction and Basic Concepts 10 Lecture 1 Inter - Bayamon MECN 4110 Course Objectives Up on completion of this chapter, the student will be able to Explain the need for kinematic analysis of mechanism. Define the basic components that comprise a mechanism. Draw the kinematic diagram from a view of a complex mechanism. Compute the number of degrees of freedom of a mechanism. Identify a four bar mechanism and classify it according to its possible motion. Identify a slider crank mechanism. 11 Lecture 1 Inter - Bayamon 1.1 ANALYSIS AND SYSTHESIS Analysis: the techniques that allow the designer to critically examine an already existing or proposed design in order to judge its suitability for task. MECN 4110 Synthesis (or Design): the process of prescribing the sizes, shapes, material compositions, and arrangements of parts so that the resulting machine will perform the prescribed task. 12 Lecture 1 Inter - Bayamon MECN 4110 1.2 DESIGN PROCESS 13 Lecture 1 Inter - Bayamon MECN 4110 1.3 THE ENGINEERING REPORT LAB REPORT GUIDE Title Page of Lab Report (2) Table of Contents (3) Abstract (5) Objectives and Introduction (15) Theory (15) Result and Discussion (35) Conclusions (15) References (10) 14 Lecture 1 Inter - Bayamon 1.4 UNITS There are several systems of units used in engineering. The most common in the United States are: MECN 4110 The U.S. foot-pound-second (fps) system, The U.S. inch-pound-second (ips) system, and The System International (SI) 15 Lecture 1 MECN 4110 Inter - Bayamon 1.4 UNITS 16 Lecture 1 Inter - Bayamon MECN 4110 1.5 THE SCIENCE OF MECHANICS Statics: deals with analysis of stationary systems, that is, those in which time is not a factor. Dynamics: deals with systems that change with time. Kinematics: the study of motion, quite apart from the forces which produce that motion. More particularly kinematics is the study of position, displacement rotation, speed, velocity, and acceleration. Kinetics: the study of force on system in motion. 17 Lecture 1 Inter - Bayamon MECN 4110 1.5 THE SCIENCE OF MECHANICS 18 Lecture 1 Inter - Bayamon MECN 4110 1.5 THE SCIENCE OF MECHANICS Reuleaux’ Definition: Machine: a combination of resistant bodies so arranged that their means the mechanical forces of nature can be compelled to do work accompanied by certain determinate motion. Mechanism: an assemblage of resistant bodies, connected by movable joints, to form a closed kinematic chain with one link fixed and having the purpose of transforming motion. Structure: also a combination of resistant bodies connected by joints, but its purpose is not to d work or to transform motion. A structure is intended to be rigid. 19 Lecture 1 Inter - Bayamon MECN 4110 1.5 THE SCIENCE OF MECHANICS 20 Lecture 1 Inter - Bayamon MECN 4110 1.6 DEGREE OF FREEDOM (DOF) OR MOBILITY A mechanical system’s mobility (M) can be classified according to the number of degrees of freedom (DOF) that it possesses. The system’s DOF is equal to the number of independent parameters (measurements) that are needed uniquely define its position in space and at any instant of time. This system of the pencil in the plane has three DOF The pencil in the this example represents a rigid body, or link, which for purposes of kinematics analysis we will assume to be incapable of deformation. 21 Lecture 1 Inter - Bayamon 1.6 DEGREE OF FREEDOM (DOF) OR MOBILITY MECN 4110 DOF of rigid body in Space DOF of Rigid body in Plane 22 Lecture 1 Inter - Bayamon MECN 4110 1.6 DEGREE OF FREEDOM (DOF) OR MOBILITY 23 Lecture 1 Inter - Bayamon 1.7 TYPES OF MOTION Pure rotation Reference line MECN 4110 Reference line 24 Lecture 1 Inter - Bayamon MECN 4110 1.7 TYPES OF MOTION Pure translation 25 Lecture 1 Inter - Bayamon 1.7 TYPES OF MOTION Complex Motion : Rotation + Translation MECN 4110 q 26 Lecture 1 Inter - Bayamon MECN 4110 1.7 LINKS, JONTS AND KINEMATIC CHAINS Linkages are the basic building blocks of all mechanisms. A linkage consist of links (or bars), generally considered rigid, which are connected by joints, such as pins (or revolutes), or prismatic joints to form open or closed chains (or loops). Such kinematic chains, with at least one link fixed, become (1) mechanisms if at least two other links retain mobility, or (2) structures if no mobility remains. 27 Lecture 1 Inter - Bayamon MECN 4110 1.7 LINKS, JONTS AND KINEMATIC CHAINS 28 Lecture 1 Inter - Bayamon MECN 4110 1.7 LINKS, JONTS AND KINEMATIC CHAINS A link is an rigid body that possesses at least two nodes that are points for attachment to other links. 29 Lecture 1 Inter - Bayamon 1.7 LINKS, JONTS AND KINEMATIC CHAINS Link of different order: Binary link : one of 2 nodes Ternary link : one of 3 nodes MECN 4110 Quaternary link : one of 4 nodes 30 Lecture 1 Inter - Bayamon MECN 4110 1.7 LINKS, JONTS AND KINEMATIC CHAINS A joint is an connection between two or more links (at their nodes), which allows some motion, or potential motion, between the connected links. Joints (also called kinematic pairs) can be classified in several ways: 1. By the type of contact between the elements, line, point or surface. 2. By the number of degrees of freedom allowed at the joint. 3. By the type of physical closure of the joint: either force or form closed. 4. By the number of links joined (order of the joint). 31 Lecture 1 Inter - Bayamon 1.7 LINKS, JONTS AND KINEMATIC CHAINS The kinematic pairs can be: Lower pair (surface contact): are the joints with surface contact between the pair elements. MECN 4110 Higher pair (point or line contact): are the joints with point or line contact between the pair elements. 32 Lecture 1 Inter - Bayamon MECN 4110 1.8 JOINT PAIRS: THE SIX LOWER PAIRS Lower Pair: Name (symbol) DOF Contains Revolute (R) 1 R Prismatic (P) 1 P Screw or Helical (H) 1 R+P Cylindric (C) 2 R+P Spherical (S) 3 R+R+R Planar or Flat (F) 3 R+P+P Planar Mechanism 3-D Mechanism DOF: Degree of Freedom 33 Lecture 1 Inter - Bayamon MECN 4110 1.8 JOINT PAIRS: THE SIX LOWER PAIRS Revolute (R): Rotating full pin joint Dq 34 Lecture 1 Inter - Bayamon MECN 4110 1.8 JOINT PAIRS: THE SIX LOWER PAIRS Prismatic (P): Translating full slider joint DX 35 Lecture 1 Inter - Bayamon MECN 4110 1.8 JOINT PAIRS: THE SIX LOWER PAIRS Helical (H): 36 Lecture 1 Inter - Bayamon MECN 4110 1.8 JOINT PAIRS: THE SIX LOWER PAIRS Cylindric (C) : 37 Lecture 1 Inter - Bayamon MECN 4110 1.8 JOINT PAIRS: THE SIX LOWER PAIRS Spherical (S): 38 Lecture 1 Inter - Bayamon MECN 4110 1.8 JOINT PAIRS: THE SIX LOWER PAIRS Flat (F) : 39 Lecture 1 Inter - Bayamon 1.8 JOINT PAIRS: HIGHER PAIRS AND HALF JOINT Roll-slide (Half or RP) joint Dq MECN 4110 DX Linkage against Plane (Force close) 40 Lecture 1 Inter - Bayamon 1.8 JOINT PAIRS: HIGHER PAIRS AND HALF JOINT Higher Pair: 2 DOF DX MECN 4110 Dq Pin in Slot (Form Close) 41 Lecture 1 Inter - Bayamon MECN 4110 1.9 PLANAR MOTION Lower pair or Full joint : 1 DOF joint Higher pair, half joint : > 1 DOF, roll-slider Joint order = number of link joined - 1 First order pin joint First o rder pin join t S econd ordorder er pin jopin int joint Second 42 Lecture 1 Inter - Bayamon MECN 4110 1.9 PLANAR MOTION KINEMATIC CHAIN: An assemblage of links and joints, interconnected in a way to provide a controlled output motion in response to a supplied input motion. CRANK: Link that makes a complete revolution and is pivoted to ground. ROCKET: Link that has oscillatory (back and forth) rotation and is pivoted to ground. COUPLER (or connecting rod): Link that has complex motion and is not pivoted to ground. GROUND: defined as any link or links that are fixed (nonmoving) with respect to the reference frame. 43 Lecture 1 Inter - Bayamon 1.10 DETERMINING DEGREE OF FREEDOM OR MOBILITY Degree of Freedom (DOF): Number or inputs that need to be provided in order o create a predictable output. Also: number of independent coordinates required to define its position. In Planar Mechanisms: MECN 4110 1 link in the plane has 3 DOF 44 Lecture 1 Inter - Bayamon 1.10 DETERMINING DEGREE OF FREEDOM OR MOBILITY 2 links in the plane have 6 DOF Dy1 MECN 4110 Dq1 Dy2 Dx1 45 Dx2 Dq2 Lecture 1 Inter - Bayamon 1.10 DETERMINING DEGREE OF FREEDOM OR MOBILITY 2 links connected by a full joint have 4 DOF Dy Dx MECN 4110 Dq1 46 Dq2 Lecture 1 Inter - Bayamon 1.10 DETERMINING DEGREE OF FREEDOM OR MOBILITY 2 links connected by a roll-slide (half) have 5 DOF Dq2 Dx1 Dy Dq1 MECN 4110 Dx2 47 Lecture 1 Inter - Bayamon 1.10 DETERMINING DEGREE OF FREEDOM OR MOBILITY Gruebler’s equation DOF or M = 3L – 2J – 3G MECN 4110 Where: M=degree of freedom or mobility L= number of links J=number of joints G=number of grounded links (always 1) M = 3(L - 1) – 2J 48 Lecture 1 Inter - Bayamon 1.10 DETERMINING DEGREE OF FREEDOM OR MOBILITY Kutzbatch’s equation modification of Gruebler’s MECN 4110 M = 3(L – 1)– 2J1 – J2 Where: M= degree of freedom or mobility L= number of links J1= number of DOF (full) joints J2= number of DOF (half) joints Full Joint = 1 Half Joint = 0.5 49 Lecture 1 Inter - Bayamon MECN 4110 1.10 DETERMINING DEGREE OF FREEDOM OR MOBILITY 50 Lecture 1 Inter - Bayamon MECN 4110 1.10 DETERMINING DEGREE OF FREEDOM OR MOBILITY 51 Lecture 1 Inter - Bayamon MECN 4110 1.11 MECHANISMS AND STRUCTURES If the DOF is positive, it will be a mechanism, and the links will have relative motion. If the DOF is exactly zero, then it will be a structure, and no motion is possible. If the DOF is negative, then it is a preloaded structure, which means that no motion is possible and some stresses may also be present at the time of assembly. 52 Lecture 1 MECN 4110 53 Lecture 1 Inter - Bayamon Inter - Bayamon MECN 4110 1.12 EXAMPLES 54 Lecture 1 Inter - Bayamon MECN 4110 1.12 EXAMPLES 55 Lecture 1 Inter - Bayamon MECN 4110 1.12 EXAMPLES 56 Lecture 1 Inter - Bayamon MECN 4110 1.12 EXAMPLES 1. Number or links L = 4 2. Number of (full joint) 4 joints J=4 3. Number of ground link G=1 M = 3(4 - 1) – 2x4 M= 1 57 Lecture 1 Inter - Bayamon MECN 4110 1.12 EXAMPLES 1. Number or links L = 9 2. Number of full joints 10 and half joints 2 J=12 3. Number of ground link G=1 M = 3(9 - 1) – 2x12 M= 0 58 Lecture 1 Inter - Bayamon MECN 4110 Homework1 http://facultad. bayamon.inter.edu/omeza/ Omar E. Meza Castillo Ph.D. 59 Lecture 1