DEPARTMENT OF INDUSTRIAL AND MANUFACTURING
ENGINEERING
DESIGN OPTIMIZATION OF A HYDRAULIC MOBILE WORK
PLATFORM ELEVATOR
STUDENT NAME: MKHULULI SANTUNGWANA (H140517E)
SUPERVISED BY
: ENGINEER E MAPUTI
A HIT 300 Project submitted in partial fulfillment of the
requirements of the requirements of a Bachelor of Technology
(Honors) in Industrial and Manufacturing Engineering
November 2017
COPYRIGHT
All rights reserved. No part of this research may be reproduced, stored in any retrieval system, or
transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or
otherwise for purpose, without the prior written permission of the author or of Harare Institute of
Technology on or behalf of the author.
i
DECLARATION
I MKHULULI SANTUNGWANA, registration number H140517E do hereby declare that this
research project is my original work except where sources have been acknowledged, under the
esteem guidance of my lecturers and my supervisor Engineer Maputi of Harare Institute of
Technology. The work has never been submitted, nor will it ever be, to another University in the
awarding of a degree.
Harare institute of Technology
Department Of Industrial and Manufacturing Engineering
P.O. Box Be277 Belvedere
Harare
Zimbabwe
STUDENT ………………………………………………... DATE………………………….
SUPERVISOR SIGNATURE ……………………………...DATE………………………….
ii
ACKNOWLEDGEMENTS
Firstly, I thank God for the gift of life and guidance in this project and my studies as a whole. I
want to express my sincere gratitude to Engineer Maputi and other lecturers for their assistance
and support rendered throughout the project. Finally, special thanks go to my family for financial
and moral support in the course of this project.
iii
ABSTRACT
The conventional use of ropes, ladders, scaffolds and mechanical scissors lifts in accessing
elevated heights poses a lot of limitations (time and energy consumption, comfortability and
amount of load applied on the plat form), which a hydraulic mobile work platform elevator will
achieve. However the position of the actuator has a direct effect on the mechanical and velocity
ratio of the system, therefore prudent placement of the cylinder can influence the magnitude of
the force applied and the stress levels in adjacent arms. In this project the maximum weight to
strength ratio and the optimum hydraulic cylinder orientation is determined to achieve a height of
4m with a maximum work platform load of 200kg. In carrying out the research the designer use
the information obtained from internet, experts and textbooks.
iv
Table of Contents
COPYRIGHT ................................................................................................................................... i
DECLARATION ............................................................................................................................ ii
ACKNOWLEDGEMENTS ........................................................................................................... iii
ABSTRACT ................................................................................................................................... iv
Table of Contents ............................................................................................................................ v
List of Tables ................................................................................................................................. ix
List of Figures ................................................................................................................................. x
CHAPTER 1 ................................................................................................................................... 1
1.1
Introduction ...................................................................................................................... 1
1.2
Background ...................................................................................................................... 1
1.3
Problem statement ............................................................................................................ 1
1.4
Aim ................................................................................................................................... 3
1.5
Objectives ......................................................................................................................... 3
1.6
Scope ................................................................................................................................ 3
1.7
Justification ...................................................................................................................... 4
1.8
Expected results................................................................................................................ 4
1.9
Research Questions .......................................................................................................... 4
1.10
Research Methods......................................................................................................... 4
1.11
Conclusion .................................................................................................................... 5
CHAPTER 2 - LITERATURE REVIEW ....................................................................................... 6
2.0
Introduction .......................................................................................................................... 6
2.1
The types of work platform elevator designs ................................................................... 7
2.1.1
Scaffolds: .................................................................................................................. 7
v
2.1.2
Straight Boom lift ................................................................................................... 10
2.1.3
Upright’s Scissors ................................................................................................... 11
2.1.4
Articulated Boom lifts............................................................................................. 13
2.1.5
Mechanical Scissors lifts......................................................................................... 15
2.1.6
Direct acting hydraulic Lift ..................................................................................... 16
2.1.7
Suspended hydraulic lifts ........................................................................................ 18
2.2
CONCLUSION .............................................................................................................. 19
CHAPTER 3- RESEARCH METHODOLOGY .......................................................................... 20
3.0
INTRODUCTION ............................................................................................................. 20
3.1
RESEARCH STRATEGIES .......................................................................................... 20
3.2
RESEARCH METHODS............................................................................................... 20
3.3
DATA COLLECTION METHODS AND TOOLS ....................................................... 20
3.3.1
Informal Interviews ................................................................................................. 20
3.3.2
Observations ........................................................................................................... 21
3.3.3
Questionnaires......................................................................................................... 21
3.3.4
Electronic means ..................................................................................................... 21
3.3.5
Library Research ..................................................................................................... 21
3.3.6
Engineering tools used ............................................................................................ 22
3.4
ETHICAL CONSIDERATIONS ................................................................................... 22
3.5
CONCLUSION .............................................................................................................. 22
CHAPTER 4 – DESIGN ............................................................................................................... 23
4.0
INTRODUCTION ............................................................................................................. 23
4.1
CONCEPTUAL DESIGN .............................................................................................. 23
4.1.1
Concept One............................................................................................................ 23
vi
4.1.2
Concept two ............................................................................................................ 24
4.1.3
Concept three .......................................................................................................... 26
4.2
CONCEPT SELECTION ............................................................................................... 27
4.2.1
CONCEPT SELECTION METHODOLOGY ....................................................... 29
4.2.2
Concept Screening .................................................................................................. 29
4.3
DESIGN AND DEVELOPMENT ................................................................................. 33
4.3.1
4.4
Selection of Materials ............................................................................................. 33
DESIGN CALCULATIONS.......................................................................................... 37
4.4.1
Payload Calculation ................................................................................................ 37
4.4.2
Cylinder Force Calculation ..................................................................................... 38
4.4.3
Pressure Calculation................................................................................................ 38
4.4.4
Electric Motor Calculations .................................................................................... 39
4.5
CONCLUSION .............................................................................................................. 39
CHAPTER 5 - ECONOMIC ANALYSIS .................................................................................... 40
5.0
INTRODUCTION ............................................................................................................. 40
5.1
BILL OF MATERIALS ................................................................................................. 40
5.2
LABOUR COSTS .......................................................................................................... 41
5.3
CAPITAL INVESTMENT ............................................................................................ 42
5.4
MAKE OR BUY ANAYSIS .......................................................................................... 42
5.4.1
5.5
Estimated pay back ................................................................................................. 43
CONCLUSION .............................................................................................................. 44
CHAPTER 6 – CONCLUSIONS AND RECOMMENDATIONS .............................................. 45
6.0
6.1
INTRODUCTION ............................................................................................................. 45
LIMITATIONS .............................................................................................................. 45
vii
6.2
RECOMMENDATIONS AND CONCLUSIONS ........................................................ 45
REFERENCES ............................................................................................................................. 47
APPENDIX A: WORKING DRAWINGS ................................................................................... 49
viii
List of Tables
Table 1: Concept Screening Matrix .............................................................................................. 30
Table 2: Concept scoring matrix ................................................................................................... 32
Table 3 Bill of Materials ............................................................................................................... 41
Table 4 Labor Costs ...................................................................................................................... 42
Table 5 Cost of Present Machines (* Figures indicate analysis used) ......................................... 43
Table 6 Undiscounted payback estimate....................................................................................... 44
ix
List of Figures
Figure 1.3.1 Typical warehouse ...................................................................................................... 2
Figure 1.3.2 : Automation workstation ........................................................................................... 3
Figure 2.1.1 A mobile scaffold (http//gopa@theconstructor.org/2017/9) ...................................... 8
Figure 2.1.2 A Scaffold (http://www.horizonplatforms.co.uk/2016/9) .......................................... 9
Figure 2.1.3 A straight boom lift .................................................................................................. 10
Figure 2.1.4 Typical Upwright scissors lifts designs (http://www.scissorslifttable.com, 2016) .. 12
Figure 2.1.5 Articulated Boom lifts (http://www.horizonplatforms.co.uk/2016/10) .................... 14
Figure 2.1.6 Articulated boom lift in a warehouse (http://www.horizonplatforms.co.uk/2016/9) 14
Figure 2.1.7 Mechanical Scissors lift (http:// www.made-in-china.com/2016/9)......................... 15
Figure 2.1.8 Direct acting lifts schematic (http://www.lifteye.co.nz/2016/09) ............................ 17
Figure 2.1.9 Suspended hydraulic lift schematic (http://www.lifteye.co.nz/2016/9) ................... 19
Figure 4.1.1 Horizontal cylinder orientation................................................................................. 24
Figure 4.1.2 Cylinder Orientation at an angle to the horizontal ................................................... 25
Figure 4.1.3 Cylinder orientation positioned vertically ................................................................ 26
Figure 4.3.1 Work platform top frame .......................................................................................... 33
Figure 4.3.2 Scissors Arm............................................................................................................. 34
Figure 4.3.3 Hydraulic Cylinder ................................................................................................... 34
Figure 4.3.4 Cylinder Shaft 1 ........................................................................................................ 35
Figure 4.3.5 Cylinder Shaft 2 ........................................................................................................ 36
Figure 4.3.6 Elevator Wheel ......................................................................................................... 37
x
CHAPTER 1
1.1
Introduction
The project of a mobile work platform elevator exploits the scissors lift mechanism and entails
the design and manufacture of a hydraulically operated machine that will enable an efficient, safe
and durable lifting and lowering of the platform.
1.2
Background
In most organisations in Zimbabwe that are into manufacturing, warehousing, pallet handling,
vehicle loading, work positioning there is an inevitable need to raise and lower large, heavy
loads through relatively small distances. In addition most large factory workshops, commercial
buildings there is little space to use the conventional lifting mechanisms like fork lifters and
overhead cranes, there is need therefore to design simple to operate, ergonomic mobile
workstations that reduce fatigue in the operators and thus increasing production levels.
(Kissinger, 2016). Companies that are into bill board advertising also employ workstation
elevation mechanisms and in most cases use primitive although reliable mechanisms such as
scaffolds and ladders.
The proposed design uses the scissors mechanism actuated by a hydraulic cylinder. The first
scissors platforms have been around since the mid-20th century although improvements have
been made in the materials used and safety, since then, the basic scissors mechanism design is
still in use (Momin et al, 2015). Although different actuation mechanisms have been exploited,
the use of hydraulics has proven to be to a larger extent the most efficient, reliable, safe and
economic means of actuation.
1.3
Problem statement
The reach of heights and areas otherwise inaccessible by workers in commercial buildings,
warehouses and workshops with optimized work flow layout arrangements like the one shown in
fig 1.3.1 and fig 1.3.2, has resulted to a larger effect to repetitive strain injury (RSI) on the
workers due to repeated bending and stretching as they stock their goods and some of the goods
gets damaged in the process (i.e non optimum working postures). In addition this has also
resulted in primitive technical means of creating an optimum height quickly and
easily.(Delleman,2017).
Figure 1.3.1 Typical warehouse
2
Figure 1.3.2 : Automation workstation
1.4
Aim
To design and manufacture a hydraulic mobile work platform elevator
1.5
Objectives
 To develop maximize weight to strength ratio
 To optimize the hydraulic cylinder orientation
 To design the work platform unit with 200kg load carrying capacity
1.6
Scope
The proposed design will maximise the rate of work platform ascent and descent in safe and
ergonomic manner with particular focus to increasing manufacturing production and thus
ultimately creating an opportunity of growth for the local industry in Zimbabwe.
3
1.7
Justification
The design will bring about a lot of employee satisfaction due to the safer, ergonomic and faster
ease of access of elevated heights at an unprecedented rate. There will be a reduction in height
related accidents in any organisation that implements this design and this is in line with the
Factories and Works Act (Chapter 14:01). An increased productivity and customer satisfaction as
a result of this design is definite, thereby conforming to ISO 9001:2008 series and OSHAS. In
addition the use of this design subscribes to the Value Addition and Beneficiation cluster of the
country economic blueprint, the ZimAsset with particular attention to the SME sector.
1.8
Expected results
A fully functional work platform elevator assembled from locally available materials
1.9
Research Questions
i.
What is the current work platform elevators used in Zimbabwe?
ii.
What are the ranges of heights of commercial buildings and warehouses in
Zimbabwe?
iii.
What are the benefits of using hydraulics in platform elevators?
iv.
Which market does the proposed design intend to serve?
v.
How long will it take to complete the proposed design? How much will the complete
proposed design cost and will it be afforded by the intended market?
1.10 Research Methods
The designer will gather all the information relating to all the platform elevation processes used
by in Zimbabwe through:
 Industrial visits
 Library
 The use of the internet
 Consulting lecturers
4
1.11 Conclusion
The use of hydraulics in work platform elevation is an engineering opportunity that SMEs should
invest in because it will empower them for smooth transition from small to large scale
production. In addition storage costs for warehouses will reduce significantly since storage will
done vertically and commercial buildings maintenance costs will also reduce due to the ease of
access of elevated heights.
5
CHAPTER 2 - LITERATURE REVIEW
2.0 Introduction
In most organizations and industries in Zimbabwe and throughout the highly industrialized
economies, heightened customer preferences and demands has resulted in an increase in the costs
of storage of raw materials, part products or sub-assemblies or finished products. As previously
outlined in the preceding chapter most of the industries are storing vertically upwards and hence
various work platforms have been developed in an attempt to maximize the available space in an
economic matter.
Detailed overviews of the various work platform elevation mechanisms will be the focus of this
chapter with particular attention to the most important factors that affect the existing designs
performance such work platform deflections and anti-fall mechanisms employed. In addition as
outlined by Kissinger (2016):“There are hundreds of different lifts on the market and picking the right lift optimizes
productivity and operator safety on job site and there are four major features to consider when
selecting the right work platform elevator which include working height, plat form size, worksite
impact and lifting capacity”( page 1)
The work platform deflection is the resulting change in elevation of all or part of the elevation
mechanism measured from the floor to the top of the work platform whenever loads are applied
or removed from the elevator (Hatti et al, 2015). The anti-fall mechanism is that feature or device
in the work platform elevator that ensures that the whole design remains at the intended height
even if the source of the lifting power encounters a fault .This is a protection device that ensures
safety of the loads and thus eliminating the occurrence of fatal incidents and accidents (Hicks
and Kaminski, 2012).
A number of work platform elevators have been developed ranging from the traditional
scaffolding to ordinary scissors lifts, vehicle boom lifts and the hydraulic scissors lifts. In all the
6
designs, a lot of safety has to be taken into consideration, hence the need for expending a great
deal engineering effort to translate customer specifications to order release all the way to the
design, manufacturing and to the customer feedback and thereby completing the product quality
cycle. In this chapter therefore considerations from various information sources such as the
current SME industry in Zimbabwe, the information will be gathered by conducting industrial
visits at Mbare Magaba and Gazaland industries. Other sources include the use of manuals,
journals, books, patents, published internet sources and market surveys in Zimbabwe and
globally.
2.1
The types of work platform elevator designs
2.1.1 Scaffolds:
This is a work platform lifting assembly that is composed of cross sections of pipes, iron or
wood. Equipment and personnel are elevated heights by negotiating the cross section of the
pipes, iron or wood manually. The work platform is normally made of boards of seasoned wood
and is very light and strong for ease of carrying up the cross sections (Mishra, 2017). A typical
example is shown below in Fig.2.1.1
Therefore the whole structure has to be pushed when moved over small distances but for larger
distances disassemble of the whole structure has to be done otherwise the whole structure
generally is bulky. With respect to deflections scaffolds are very rigid due to the nature of their
design provided that they have been properly mounted and the cross structures are tightly
securely to each other. In addition from an anti-fall consideration perspective if appropriate
structural joining processes are used such as the mechanical joints (i.e. bolts, nuts and clamps)
the probability for scaffold collapse is greatly minimised.
Normally weights of the tubes of steel or aluminium are used which should be of light weight
for ease of mounting and the weights range from around 4.4 kg/m and 1.7kg/m respectively.
(Manoharrao and Jamgekar (2016)).
7
Figure 2.1.1 A mobile scaffold (http//gopa@theconstructor.org/2017/9)
8
Figure 2.1.2 A Scaffold (http://www.horizonplatforms.co.uk/2016/9)
2.1.1.1 Advantages of scaffolds
i.
Scaffolds are cheaper relative to other work platform elevators
ii.
They can support larger weights over longer heights.
iii.
They are stable and reliable
2.1.1.2 Disadvantages
i.
It is labour intensive i.e. energy consumption during installation and comfortability as
outlined by Ubale, et al 2015.
9
ii.
It has to be re-arranged every time it is mounted
iii.
It cannot be easily adjusted
iv.
A lot of time and effort has to be invested to cater for the great deal of safety
consideration.
2.1.2 Straight Boom lift
These are hydraulic operated lifting mechanisms usually connected to vehicles allowing for
mobility from place to place although custom made design depending on the preferences of the
customer as shown in Fig 2.1.3
Figure 2.1.3 A straight boom lift
10
Straight boom lifts have the capability to lift heavy equipment and loads due to the fact that they
only elevate work plat forms in a particular direction and thus they are incapable to lift to
elevations with obstructions. As in the case above they can elevate vertically although designs
are available that can move horizontally while some can even rotate. (Rubenstone, 2014)
Common applications of these types of elevators are in electrical companies like ZESA and
municipality engineering staff (Harare City Council when they are carrying out maintenance
particularly in street lighting maintenance.
2.1.2.1 Advantages
i.
They can lift and hold heavy equipment over long periods of time.
ii.
They can elevate equipment and personnel up to heights or distances otherwise
considered impossible.
iii.
They are foldable and hence can be used in confined warehouses.
2.1.2.2 Disadvantages
i.
Straight boom lifts are complex and intricate in design and therefore call for high level of
maintenance especially the joints in the boom
ii.
They are very expensive and purely mechanical.
iii.
Due to the nature of their design their management from an operator’s perspective can
prove to be difficult since the higher or further they go the more they move away from
their centre of gravity.
In the dimension of capability of the straight boom lifts to accommodate deflection, they are
fairly good in that respect since the work platform design is in such a way that it can be safely
secured on boom design.
2.1.3 Upright’s Scissors
These were made as early as the 1940s by an American Manufacturer of aerial platforms called
UpWright hence the name of this type of design is after the company name. It’s called a scissors
due to arrangement of the steel crossing assembly which is metaphorically derived from the
scissors. An illustration of the commonly available design is shown in figure below in fig 2.4
11
Figure 2.1.4 Typical Upwright scissors lifts designs (http://www.scissorslifttable.com, 2016)
2.1.3.1 Advantages
i.
They operate in a smooth manner due to the nature of their power source which is
normally hydraulics.
ii.
Relatively less costly maintenance costs
12
iii.
Easier to operate in working areas outside operator’s normal ergonomic power zone
(Abhinay and Sampath, 2014)
iv.
These designs are unique and can allow self-levelling of platform on rough terrain
v.
They have high load bearing capacity as described by Dabhi, et al. 2015.
2.1.3.2 Disadvantages
i.
UpWright scissors due to the fact that they use mostly hydraulics, therefore requires a
high level of skill to maintain.
ii.
Incapable to operate at heights or distances where there are obstructions or impediments.
iii.
These designs are susceptible to fatigue failure due to repetitive loading and unloading
particularly the cross members ultimately affecting the useful life of the machine.
(Manoharrao and Jaingekar, 2016)
2.1.4 Articulated Boom lifts
These designs are mostly effective when working on heights or distances with obstacles or cases
which are otherwise considered inaccessible. These designs are very similar to straight boom lifts
from a principle of operation dimension but the only difference is their ability to articulate.
13
Figure 2.1.5 Articulated Boom lifts (http://www.horizonplatforms.co.uk/2016/10)
Figure 2.1.6 Articulated boom lift in a warehouse
(http://www.horizonplatforms.co.uk/2016/9)
14
2.1.4.1 Advantages of articulated boom lifts
i.
They enable ease of access to otherwise heights and distances considered inaccessible.
ii.
They can be used without the presence of riggers.
2.1.4.2 Disadvantages of articulated boom lifts
i.
They require high level of experience to operate
ii.
A high level of investment is required particularly from a maintenance perspective
iii.
A smaller work platform is used in these design limits the number and size of material
carried on the platform.
2.1.5 Mechanical Scissors lifts
In these designs the principle of operation is very much similar to Upwright Scissors lift in the
sense that they exploit the scissors mechanism to elevate the work platform. The only difference
in this instance is the source of power in which in this case is mechanical.
Figure 2.1.7 Mechanical Scissors lift (http:// www.made-in-china.com/2016/9)
15
In most designs the screw mechanism is used in which the drive is manual similar to that of a car
scissors jack where a lever is used and the screw converts the lever motion to the elevation of the
work platform. In that respect a lot of input energy has to be expended to enable the screw to
enable the elevation of the platform.
2.1.5.1 Advantages
i.
Considering the fact that the power source is manual, this therefore means that these
designs can be used in work stations that do not have access to electricity.
2.1.5.2 Disadvantages
i)
A lot of effort has to be expended to overcome the frictional forces associated with
the screw.
ii)
The designs have very low efficiency
2.1.6 Direct acting hydraulic Lift
These are smooth elevation lifts whose principle of operation consists of motion of a ram in a
pressurized cylinder as shown in Fig 2.1.8
16
Figure 2.1.8 Direct acting lifts schematic (http://www.lifteye.co.nz/2016/09)
A work platform is fitted on the end of the ram and therefore this implies that the height of
elevation or distance of travel is dependent on the stroke of the ram. The rate of ascent or descent
of the work platform is dependent on the rate at which the fluid fills the cylinder cavity in which
the ram is sliding.
2.1.6.1 Advantages of direct acting lifts
i.
They have higher stability during loading and unloading
ii.
They are simple to install and have reduced service requirements
iii.
They have increased capability to minimize deflection of the platform.
iv.
Most advanced designs are safe due to the presence of the rupture valve connected in
the hydraulic lines.
2.1.6.2 Disadvantages
i.
They require regular and consistent maintenance
ii.
They are inefficient due to the fact that more energy is used in the hydraulic systems.
iii.
The length of the cylinder in most cases is proportional to the length of elevation; this
therefore has limitations concerning flexibility with respect to elevation at different
heights.
17
Direct acting lifts have been used in domestic elevators in tall buildings even though as
mentioned earlier on the fact that the height of elevation is proportional to length of the cylinder
means that consideration for cylinder has to be done. This could prove to be challenge in
applications where space is not available.
2.1.7 Suspended hydraulic lifts
The principle of operation similar to that of cranes in that work platform is suspended on ropes
and at the other end close to the drum that houses the cable are weights to counter balance the
effect of the weight of the work platform.
2.1.7.1
Advantages of suspended hydraulic lifts
i.
They have increased operating time
ii.
They ensure comfortable and less noisy work platform elevation
iii.
They only operate in three phase when ascending and single phase when in descent
thereby conserving energy.
iv.
In addition they provide low unit costs with minimal inventory
v.
They also have high velocity ratio
2.1.7.2
Disadvantages of suspended hydraulic lifts
i)
High level of investment from a cost of installation and maintenance dimension
ii)
Suspended hydraulic lifts have the same implications compared to direct acting
except the fact that this type of elevation can be used in areas with very limited space.
18
Figure 2.1.9 Suspended hydraulic lift schematic (http://www.lifteye.co.nz/2016/9)
2.2
CONCLUSION
The various work platform designs were covered in this chapter and it should be highlighted that
their application is a function of the operating parameters (height of elevation intended), cost of
the design, and ease of maintenance, speed of ascent or descent and the weight to be elevated. In
addition some of these designs had a great influence towards selection of the proposed design.
19
CHAPTER 3- RESEARCH METHODOLOGY
3.0 INTRODUCTION
The gathering, collection and analysis of all the information related to this project had to be done
in a procedural way so as to ensure that industry requirements have a great influence on the
proposed design . Research methodology of a mobile work platform elevator includes research
strategies, primary and secondary data collection methods, sample selection, analysis, and ethical
consideration and research limitations.
3.1
RESEARCH STRATEGIES
These are the research techniques that were employed in the gathering of information that has
been instrumental in developing mobile work platform elevator design. They also focused on
demand for such designs by SMEs in Zimbabwe who are facing challenges being unable to pay
for storage costs as their production increases.
3.2
RESEARCH METHODS
Although these methods were qualitative in nature attempts were made to get more objective and
deductive ways of conducting the research. The selection of the work stations to conduct the
research initially catered for all industries large to small but because of subdued industrial
activity in Zimbabwe, most research was conducted in small scale sectors located in Mbare and
Gazaland Industrials located close to Glenview in Harare.
3.3
DATA COLLECTION METHODS AND TOOLS
Research instruments such as informal interviews, questionnaires and surveys on site were used
in collecting relevant data as discussed below. Desk research was also conducted on the internet
as well as the library.
3.3.1 Informal Interviews
In depth verbal interviews with a number of randomly selected individuals and organizations to
ascertain the magnitude of the need of a mobile work platform elevator was carried out. Informal
20
in the sense that there was no prior arrangement made with the interviewees and most of the
people interviewed were informal business entrepreneurs located in various industrial sites in
Harare.
3.3.2 Observations
Industrial visits in most cases were carried out in the businesses that required advancement in
their material handling processes to observe the effects of the increase in demand for space, since
most of these SMEs are now realising the need to invest in equipment that ensure effective space
utilization. Although the selection of these industries was carried out in a purposive manner, it
provided the designer in-depth knowledge, experience, and acceptance that improve on the state
of current work platform elevation equipment.
3.3.3 Questionnaires
Structured closed and open ended questionnaires were prepared for well-established
organisations like Machinery Exchange in Masasa in Harare. This was done so as to ensure that
these questions satisfy the objectives of the research which were premised on gathering as much
information although biased towards the qualitative dimension. Semi structured and unstructured
questionnaires were carried out in Mbare and other upcoming SMEs in and around Harare.
3.3.4 Electronic means
The internet provided most of the information particularly the state of the global state of mobile
work platform elevation equipment in use today. Research on user manuals for the equipment in
question were also obtained on the internet, these provide the vital information of the safety
features that are in place in most work platform elevation machinery.
3.3.5 Library Research
Library research was conducted for the purposes secondary data through the use of journal,
patents and books from recognized research sites such as EBSCO HOST, SAGE, and
SPRINGER. More so, it also gave the researchers access to engineering handbooks and journals
for some of the design aspects and calculations.
21
3.3.6 Engineering tools used
i.
Microsoft Excel tool was also used to analyze data and to draw statistics charts.
ii.
Microsoft Word tool was used to type the whole document for the project.
iii.
Autodesk Inventor 2016 was used to come up with design drawings and working
drawings.
iv.
In addition various work shop inferences on the practicality of the proposed designs and
their applicability was conducted.
3.4
ETHICAL CONSIDERATIONS
The participants of the research were fully participative because some considered it as an
opportunity to grow their businesses. The aim was to reassure participants that their involvement
was purely voluntary and they were free to withdraw from it at any point for any reason and
there were no immediate rewards associated with their participation. This therefore means that
participants were not made to commit to consent and briefing letters or debriefing and
withdrawal letters.
3.5
CONCLUSION
All the information that was gathered through the mentioned instruments and the tools stated
were of great help to the researcher in compiling this document. The researcher also learnt that
there were some sources which were not reliable in the information which they were giving.
22
CHAPTER 4 – DESIGN
4.0 INTRODUCTION
In this chapter various conceptual designs of hydraulic work platform elevators suggested will be
generated and criteria to determine the most suitable or best design concept will be made. The
process involves comparing the relative strengths and weakness of the concepts and selecting
one or more concepts for further investigation or development. The concepts will be represented
in a 3 dimensional configuration depending on the orientation of the cylinder. Calculations of the
most suitable design concept will be made so as to obtain a robust design that meets safe and
ergonomic ease of access of elevated heights.
4.1
CONCEPTUAL DESIGN
Three concepts of the hydraulic work platforms will be generated and their relative advantages
and disadvantages will also be outlined.
4.1.1 Concept One
The hydraulic mobile work platform concept shown above has the cylinder orientation
positioned horizontally relative to the base. This concept when the cylinder is fully extended the
work platform will be at the least height. In that position the work load can be placed safely on
the platform. When the cylinder if fully retracted the work platform will be at its highest position
and according to this design the maximum height attainable is 4m. The wheels are designed in
such a way that they are locked during ascent of work platform for safety purposes of the crew
on the platform. In addition this design has limit switches that cut the power to the motor
whenever the work platform has reached its minimum or maximum heights.
4.1.1.1 Advantages
i.
Easy to assemble and manufacture
ii.
Minimum cylinder force is required to raise or lower the platform.
iii.
Easy to maintain due to minimum cylinder movement and the only movement is the
extension or retraction of the piston.
23
Figure 4.1.1 Horizontal cylinder orientation
4.1.1.2 Disadvantages
i.
Cylinder orientation limits the minimum and maximum height to be reached.
ii.
The shafts that hold the cylinder in position is susceptible to fatigue failure and they bend
eventually therefore reducing the efficiency of the whole machine.
iii.
Requires constant lubrication of the joints for smooth operation.
4.1.2 Concept two
In this concept the cylinder orientation changes relative to the position of the work platform, so
as the cylinder extends the work platform raises to the height intended. As the cylinder retracts
the work platform reaches the lower height level intended. In addition the system is designed in
such a way the when the maximum of minimum height is reached power is cut to the motor thus
24
preventing oil from being pumped to the actuator (cylinder). This design concept is the most
available in the market although it has its pros and cons.
Figure 4.1.2 Cylinder Orientation at an angle to the horizontal
4.1.2.1 Advantages
i.
They can achieve minimum height possible during retraction of the cylinder.
ii.
This concept is more reliable and is smooth during operation.
4.1.2.2 Disadvantages
i.
They are more vulnerable to deflection due to cylinder orientation
ii.
The useful life of the design concept is greatly reduced due to movement of the cylinder
during ascent or descent of the work platform.
25
iii.
A lot of cylinder force is had to be applied to raise the platform since the component of
force does the actual work.
iv.
Also requires consistent lubrication to operate reliably.
4.1.3 Concept three
In this concept the cylinder is vertically positioned relative to the base of the machine and as the
cylinder retracts the work platform is lowered towards the base. If the cylinder extends, the work
platform rises to the height required until it reaches the maximum height possible as per design
specifications
Figure 4.1.3 Cylinder orientation positioned vertically
26
In this design concept like all the other concepts, cylinder force is maximum during ascent and
minimum during descent due to the factor of gravity.
4.1.3.1 Advantages
i.
It can achieve maximum height relative to other designs since the cylinder is positioned
vertically.
ii.
There is also minimum movement of the cylinder that has positive effect on the useful
life of the design.
iii.
Easy to assemble.
4.1.3.2 Disadvantages
i.
Cannot lower the plat form to the minimum height possible and hence for most designs
there has to be provision for a small ladder to access the work platform when in its lowest
position
ii.
The cylinder mounting bolts have to be secured frequently because as a result of the
repetitive actuation of the cylinder, these movements have an effect of loosening the
bolts.
iii.
It also requires constant lubrication for smooth operation
iv.
The cylinder mounting bolts only are not adequate enough to support the cylinder
therefore stiffeners have to be secured either by welding or mechanical joining processes.
4.2
CONCEPT SELECTION
The following selection criterion was used to come up with the best design from the concepts
explained above:
a) Functionality
The design of the components, their arrangement, orientation and individual transformations
have to contribute to the overall performance of the machine and ensure successful completion of
the objectives of the elevator. In this case to raise a payload of 200kg up a height of 2metres.
These components undergo a variety of machining processes and appropriate selection of the
materials used is very imperative for safe operation of the entire design. Basic machining
27
operations such turning, milling and fabrication processes are used to come up with the
dimensional relationships amongst these components. This therefore implies that selection of the
appropriate materials, tools and sequence of machining and fabrication processes was an
important consideration as this translated to the cost of assembly of the entire project
b) Ease of Assembleability
The bringing up of the individual components and parts that make up the complete design has to
be done in a cost effective manner in the least possible time. Ease of grasping, handling,
manipulation and insertion were factored in the concept development and selection process. In
addition a rigorous process of minimizing the number of parts or individual components that
constitute the entire assembly was also carried out.
c) Maintainability and Serviceability
All the components in the design were made from locally available materials and the designs are
simple and straight forward. This implies that ease of ensuring that selected design is kept in an
operable state is made possible by carrying out the necessary maintenance activities. In that
respect particular concern in keeping the hydraulic circuit as clean as possible and protected from
foreign matter entry has to be prioritized. Emphasis is made that most maintenance effort has to
be expended in ensuring continual operation of the hydraulic circuit as this is one of the most
important component of the mobile work platform elevator.
d) Product safety and reliability
In the context of the hydraulic mobile work platform elevator, safe ascend or descend of the
work platform was also an important factor and this is where the gap of the design is premised.
Apart from the safe ascend or descend consideration, the anti-fall mechanism in case of
hydraulic failure enabled success of the design selected. Deflection of the work platform was
also kept to an accepted level in terms of the requirements of the Factories and Works Act. The
selection of the appropriate materials for all the constituents of the selected design also
contributed to the safety of the elevator as each component was designed in a manner that
ensured they are capable to resist any loads acting on them. This was made possible by the
calculations that will follow in this chapter.
28
e) Mechanical Strength
The design has to be able to reach the design stipulated height and carry the recommended
weight capacity without mechanical failure as a result of the individual components failure to
withstand the forces concerned during ascent or descent.
4.2.1 CONCEPT SELECTION METHODOLOGY
A two-stage concept selection methodology is to be used by the researcher. The first stage is
called concept screening and the second is called concept scoring. Each is supported by a
decision matrix which is used by the team to rate, rank and select the best concept(s). The
methodology of concept selection helps to manage the complexity of evaluating a number
of product concepts. In addition a concept that is already in the market is used to benchmark the
generated concepts in an attempt to come up with a better concept. Screening is a quick,
qualitative and approximate evaluation aimed at producing a few viable alternatives, while
scoring is a careful quantitative analysis of these relatively few concepts in order to choose the
single concept most likely to lead to product success. (Ulrich and Epinger).
4.2.2 Concept Screening
Relative score
rating from reference concept
Better than
(+)
Same as
(0)
Worse than
(-)
29
CRITERIA
CONCEPT
1: CONCEPT
2: CONCEPT
3: The
Horizontal
Angular
Vertical cylinder Reference
cylinder
cylinder
orientation
orientation
orientation
concept
+
0
+
0
of
+
_
+
0
Maintainability&
_
0
-
0
Cost
0
-
0
0
Ease of Assembly
+
-
+
0
SUM ( + )
3
0
3
0
SUM ( - )
1
3
1
7
SUM ( 0 )
1
2
2
0
NET SCORE
2
-3
2
0
RANK
1
3
1
4
YES
NO
REVISE
NO
Safety
Ease
Manufacture
Serviceability
CONTINUE?
Table 1: Concept Screening Matrix
30
4.2.2.1 Concept Scoring
In this stage, the designer weigh the relative importance of the selection criteria and focuses on
more refined comparisons with respect to each criterion. The concept scores are determined by
the weighted sum of the ratings Table 4.2.2 illustrates the scoring matrix used. In this stage the
concepts are rated as below:
Relative Performance
Rating
Much worse than reference concept
1
Worse than reference concept
2
Same as reference concept
3
Better than reference concept
4
Much better than the reference point
5
31
Criteria
Weight %
CONCEPT ONE
CONCEPT THREE
Rating
Rating
Weighted
Weighted
Score
Score
Safety
30
4
1.2
2
0.6
Ease of Manufacture
15
3
0.45
3
0.45
Maintenance
10
5
0.5
4
0.4
Cost
25
3
0.75
3
0.75
Ease of Assembly
20
3
0.6
3
0.6
Total Score
100
and
Serviceability
3.5
2.8
1
2
DEVELOP
NO
Rank
Continue?
Table 2: Concept scoring matrix
After the scoring matrix it is discovered that development of concept one with the cylinder
orientation in the horizontal position is to be done. The design development and calculations of
the chosen concept will then be concentrated on to ensure that the design will fully satisfy its
intended objectives.
32
4.3
DESIGN AND DEVELOPMENT
4.3.1 Selection of Materials
4.3.1.1 Top frame
This is the platform on which the work force will be standing whilst carrying out various work at
elevated areas. It therefore means that it has to be light and robust; the base has to be made of
wood while the base frames and hand rails are designed from mild steel.
Figure 4.3.1 Work platform top frame
These are the most important components of the design of work platform elevator since they are
susceptible to fatigue failure and they have to be designed from material that will resist this type
of failure. In as much as they have to be failure resistant, low weight to strength ratio has to be
achieved while minimizing the cost.
33
Figure 4.3.2 Scissors Arm
4.3.1.2 Hydraulic Cylinder
This is the source of the power for most of the work of ascent or descent of the work platform.
Figure 4.3.3 Hydraulic Cylinder
34
For the purpose of this design, to safely raise a work payload of 200kg up a height of 4m,
cylinder has to provide a pressure of close to 50 bars.
4.3.1.3 Cylinder Shaft 1
Figure 4.3.4 Cylinder Shaft 1
35
4.3.1.4 Cylinder Shaft 2
Figure 4.3.5 Cylinder Shaft 2
4.3.1.5 The Wheels
These will ensure the mobility aspect of the design and safety considerations have to be factored
in because the elevator has to be stationary when the work platform is raised. Movement has to
be in such a way that the work platform is in its lowest position possible. The wheels are made of
rubber as shown in the fig 4.3.2 below: -
36
Figure 4.3.6 Elevator Wheel
4.4
DESIGN CALCULATIONS
4.4.1 Payload Calculation
Mass to be put on the platform
=
200kg
Taking Factor of Safety
=
4
Mass on platform
=
800kg
Mass of each arm
=
0.2kg * 8 = 1.6kg
Mass of the cylinder
=
4.150kg
Total mass of system
=
805.75kg
Total payload on work platform
=
7904N
37
4.4.2 Cylinder Force Calculation
From Principle of virtual work formulation
= ( WP / Tan Ѳ) + (3* WF / 4 TanѲ)………. (1)
FC
Where WP = Weight of platform
WF = Weight of arms
Ѳ = Angle between arms to the horizontal
FC = 7859.77 / Tan Ѳ ………………………… (2)
This implies that as Ѳ increases FC decreases hence
4.4.3 Pressure Calculation
Maximum force will act on the cylinder when in shut position i.e. when the scissors links are
closed. For calculations Ѳ = 30 , then substitute Ѳ in equation (1)
FC = (7904/ Tan30 ) + (3*1.6) / (4* Tan30 )
= 13692 N
Selecting 60mm as the cylinder diameter,
Area of the cylinder
=(
(
))
= (900 )mm2
Pressure of cylinder
= Force / Area
= (13692 / 900
38
)
= 48.42 bars
4.4.4 Electric Motor Calculations
The speed (N)
Power
= 2480 revs per minute
=2hp =1492 W
= 1.492 kW
( )
(1)
T
4.5
CONCLUSION
The above calculations are very imperative for the safe performance of the mobile work platform
elevator and therefore they should be factored in to enable reliability of the design.
39
CHAPTER 5 - ECONOMIC ANALYSIS
5.0 INTRODUCTION
The analysis and evaluations of the selected design is to be completed in this chapter. The bill of
materials and labor costs and make or buy analysis is determined.
5.1
BILL OF MATERIALS
The materials that are needed to construct the machine are all listed by the researcher as shown
on the table below. Table 5.1 below shows the bill of materials for the manufacture of the
prototype.
PART
MATERIALS
SIZE
Electric Motor
COST
2 Horse Power
$40
Hydraulic Pump
Cast Iron Gear Pump
$50
Coupling
Plastic
$5
Tank
Mild Steel
Hydraulic hoses
Flexible rubber
D.C.V Supports
Hand Operated
Power Pack Base
Mild Steel
500*800*4mm plate
$10
Scissors Arms
Mild Steel tube(*8)
Rectangular(40*20mm)
$10
30 litres
$10
3/8 “
$20
$20
40
Work Platform
Mild Steel
500*800*4mm plate
$10
Rails
Mild steel
1/2” Round Bars
$5
Double acting
$20
Cylinder
Cylinder Shafts
Mild steel
$15
Transportation Costs
$10
Direct on line circuit
$10
Bolts and Nuts
Mild Steel
M12*50mm
TOTAL COSTS
$3
$238
Table 3 Bill of Materials
5.2
LABOUR COSTS
For the construction of the machine the manufacturing operations such as welding, turning
drilling and electrical wiring with the operator’s labor costs are listed by the researcher on the
table below. Table 4 below shows the operations, tasks, operator and operator labor cost.
41
Operation
Task
Operator
Cost
Welding
To weld:
-the frame
-to weld the base stand
To turn :
-Cylinder shafts
-Feed rollers
-To drill base and
Nuts holes
-To wire the D.O.L
Components
Welder
$ 30
Turner machinist
$ 25
Turner machinist
$5
Electrician
$ 15
Turning
Drilling
Electrical wiring
Total cost
$ 75
Table 4 Labor Costs
5.3
CAPITAL INVESTMENT
Startup capital investment = Bill of materials + Total cost of labor
5.4
MAKE OR BUY ANAYSIS
The cost of buying the similar machines from South Africa, India and Kenya are presented by
the researcher below. Table 5 below shows the present least costs of purchasing chaff cutter
machines with respect to the country.
42
COUNTRY
BUY (excl. vat & shipping)
MAKE
South Africa
$ 425
-
India
$ 400*
-
Kenya
$ 500
-
Zimbabwe
-
$313*
DIFFERENTIAL AMOUNT*
400
Cost benefit
(313)
87
Table 5 Cost of Present Machines (* Figures indicate analysis used)
The work platform elevator can be bought in India at $400 which is the least cost, comparing the
least cost with the make cost.
Since the cost of making the machine is $313
7
Thus making the machine is cheaper than purchasing the currently least cost machine by 21.75%
5.4.1 Estimated pay back
Startup investment = $313
% markup = 25% (the designer has made an assumption on the makeup of 25%, assuming this
makeup is not going to be affected by any economic fluctuation)
Estimated investment = $391.25
Estimated selling price = $391.25 * 15% = $391.25 * 1.15 = $449.94 excl. vat
43
The table 6 below shows the estimated undiscounted pay back.
Investment ($)
Cash flow
(391.25)
449.94
Payback
(391.25/449.94) *12
= 10.4 months
Table 6 Undiscounted payback estimate
5.5
CONCLUSION
All the costs associated with making this design have been identified and. The bill of materials
and the make buy analysis has been presented.
44
CHAPTER 6 – CONCLUSIONS AND RECOMMENDATIONS
6.0 INTRODUCTION
This chapter is the end point of this project it contains the results of the whole project.
Recommendation are made based on the researcher’s opinion and final conclusions drawn from
the project after prototype testing and also included as a seal to the project work
When the machine was tested it exhibited good functionality, reliability, durability and safety
features. The results were in line with the set of objectives. The machine is capable of delivering
the intended functions in the desired manner. The machine is safe to operate, it has less
vibrations. The machine is user, environmental friendly and aesthetically pleasing. All the
stakeholders and other interested parties were satisfied by the results of the machine.
6.1
LIMITATIONS
The time constraint that was available for completion of the project and that limited the
researcher from collecting as much information as possible about the applicability of the design.
The finance of the researcher also limited him to use primitive components to demonstrate the
mechanism. For example the motor should have been fitted with limit switches that cut off power
to the motor once the optimum minimum cylinder orientation is attained.
6.2
RECOMMENDATIONS AND CONCLUSIONS
On view of the prototype, the machine is very robust and all aspects were considered right from
the conceptual design. To thoroughly exhaust all the possible optimization techniques, the
researcher recommends the use of algorithms that do not have algorithm specific parameters
other than population size, number of iterations and elite size such as Teaching- Learning Based
Algorithm (TLBO) in conjunction with other software like Mat lab. Ergonomic and safety
consideration was of great importance in designing this machine which resulted in the machine
being declared ergonomically fit. The machine is very safe and can be used in all work place or
even at home. Parts that constitute the function of the design were kept to a minimum to avoid
component redesign.
45
From the results obtained after testing the prototype although not exhaustive this project is a real
success. The machine has the potential to solve the problem at hand. All the set of objectives has
fully achieved with some difficulties. The design is worth investing in and there is a potential for
further improvements without any major changes to the original design. From the data collected
on prototype analysis and evaluation the researcher can safely conclude that the project is a
successful one.
46
REFERENCES
1. R.SKhurmi and G.K Gupta. Textbook of Machine Design,. 14. s.l. : Eurasia Publishing
House (Pvt) Ltd, 2005.
2. KAMINSKI, CHRIS HICKS AND JACEK. ANTI-FALL DEVICE. US6854715B2 U.S.A,
OCTOBER 10, 2012. GRANT.
3. DESIGN AND ANALYSIS OF HYDRAULIC PALLET SYSTEM IN CHAIN CONVEYOR.
SETU DABHI, et al. 2, NEW DEHLI : INTERNATIONAL JOURNAL FOR RESEARCH IN
ENGINEERING AND TECHNOLOGY, 2015, Vol. 3. 1SSN.
4. Design, analysis and development of multi-utility home equipment using scissors lift
mechanism. DIVYESH PRAFULLA UBALE. 3, NEW YORK : INTERNATIONAL
JOURNAL OF SCIENTIFIC RESEARCH AND MANAGEMENT, 2015, Vol. 3. ISSN.
5. Design, Manufacturing and analysis of hydraulic scissors lift. Gaffar G. Momin, Rohan
Hatti and Karan Dalvi. 2, New Dehli : International Journal of Egineering Research and
General Science, 2015, Vol. 3.
6. JUSTIN KISSINGER. ehstoday.com/mobile_platforms. www.ehstoday.com. [Online]
JANUARY 01, 2016. [Cited: SEPTEMBER 26, 2017.] www.ehstoday.com.
7. Maintenance Operations: Workstation Adjustment, Working Posture, and Workers’
Perceptions. DELLEMAN, NICO J. 1, 2016, Vol. 6.
8. GOPAL MISHRA. THE CONSTRUCTOR- CIVIL ENGINEERING HOME. [DOCUMENT]
s.l. : THE CONSTRUCTOR, 2017.
9. SPARKMAN, DAVID. Scissors Lift Accidents Spur OSHA to issue Hazard Warning.
MATERIAL HANDLING AND LOGISTICS. NEW YORK : NEWSBEAT, APRIL 2106. 1.
PAGE 3-7.
47
10. RUBENSTONE, JEFF. With boom lifts reaching new heights, JLG Expands Training.
ENGINEERING NEWS RECORDS. s.l. : ENR, MARCH 2014. Vol. 273, 12. ISSN.
11. DESIGN AND ANALYSIS OF AN AERIAL SCISSORS LIFT. SAMPATH, M.ABHINAY
AND
P.
5,
NEW
YORK :
INTERNATIONAL
ENGINEERING, SEPTEMBER 2014, Vol. 1. ISSN.
48
JOURNAL
OF
MECHANICAL
APPENDIX A: WORKING DRAWINGS
49
50
51
52
53
54
55
56
57
58
APPENDIX B: GANTT CHART
TASK
AUGUST
SEPTEMBER
1 TOPIC
SELECTION
2 PRESENTATION
OF PROPOSALS
3 LITERATURE
REVIEW
4 RESEARCH
METHODOLOGY
5 DESIGN
DRAWINGS
6 B.O.M
7
PROGRESS
EVALUATION
8 PROTOTYPE
FABRICATION
9 FINAL PROJECT
PRESENTATION
59
OCTOBER
NOVEMBER