ABSTRACT
The tip-over of scissors ladders in operation has frequently resulted in the death and/or severe injuries of workers. The objective of this study is to solve the problem of instability and enhance the understanding of its major mechanisms, factors influencing the scissors lift stability. A ladder as we know is used for gaining height in carrying out various tasks and activities. It is a conventional means for such activities. Various types of ladders are in existence which serves under different and more demanding conditions. For engineering related tasks including repairs and maintenance at heights well above human reach, there arises a need for an improved means to carry out such tasks with the vision of incorporating ease of operation using engineering principles. A problem resembling the aforementioned one within the Faculty of Engineering, University of Benin, has been identified and as such channels this project with the aim of designing a lifting system to gain access to the height of high-rise buildings in the faculty of Engineering. A rated load of 100kg is one of the key specifications.
In achieving such a lifting system, studies were carried out and three concepts on how this lift would become a reality were considered, with only one selected as the desired concept. The first concept is a hydraulic powered scissors ladder. The second is a power screw, and the third is similar to the first but differs with respect to the power source; a motorized power screw scissors ladder. It incorporates rollers, bearings, links, angle bar, connecting rods and a carriage. A decision matrix using functional weighting was used to draw the conclusion on the selected concept, the detailed design and necessary calculations were done for several parts of the system and a Solid Works CAD was done to observe the system better.
At certain stages of fabrication of the lift system, issues relating to rigidity of the lift at certain heights were revealed. In a bid to tackle this wobbling effect, slight modifications to the number of links, and the geometry of the base link and frame were made and consequently better rigidity was achieved. The fabricated work is quite large in size and heavy as materials used were chosen to ensure rigidity which is important if maintenance personnel are to use it and be assured of safety.
Upon series of successive tests and modifications done on the equipment, the hydraulic system was able to lift the scissors ladder and it worked and performed optimally. The force
required to lift the scissors ladder from an initial height of 0.931m was designed to be 4KN as opposed to the previously designed force of 7.5KN with a power requirement of 689.67watts.
The lift with its limitations opens a door for an improvement in rigidity and mobility where better materials should be a focal issue, but it assuredly does its tasks, meeting specifications in ratings and areas of operation. In a few ways, this work establishes a foundation for more work to be done in making the system a better one with a wider scope.
Table of Contents
CERTIFICATION……………………………………………………………………………………………………………..I DEDICATION………………………………………………………………………………………………………………..II ACKNOWLEDGEMENTS………………………………………………………………………………………………. III ABSTRACT…………………………………………………………………………………………………………………. IV TABLE OF CONTENTS………………………………………………………………………………………………….. VI LIST OF FIGURES………………………………………………………………………………………………………. VIII LIST OF TABLES………………………………………………………………………………………………………….. IX LIST OF GRAPHS…………………………………………………………………………………………………………. IX CHAPTER 1…………………………………………………………………………………………………………………..1
INTRODUCTION……………………………………………………………………………………………………………1
1.1 BACKGROUND TO THE STUDY…………………………………………………………………………………..1
1.2 STATEMENT OF THE PROBLEM………………………………………………………………………………… 2
1.3 AIM AND OBJECTIVES………………………………………………………………………………………………2
1.4 SCOPE OF THE WORK……………………………………………………………………………………………… 2
1.5 JUSTIFICATION FOR THE WORK…………………………………………………………………………………2
CHAPTER 2…………………………………………………………………………………………………………………..3
LITERATURE REVIEW…………………………………………………………………………………………………….3
2.1 HISTORY…………………………………………………………………………………………………………………3
2.2 RELATED LITERATURE………………………………………………………………………………………………4
2.3 CONCEPT OF LIFTING……………………………………………………………………………………………….5
2.3.1 What is a lift?……………………………………………………………………………………………………… 5
2.3.2 Types of lifts…………………………………………………………………………………………………………5
2.4 COMPARISON OF CURRENT DESIGN OF LIFT SYSTEMS…………………………………………………6
2.4.1 HYDRAULIC POWERED LIFT…………………………………………………………………………………… 6
2.4.2 PULLEY……………………………………………………………………………………………………………….. 7
2.4.3 LADDER……………………………………………………………………………………………………………..10
2.4.4 CRANE……………………………………………………………………………………………………………….10
2.4.5 SCAFFOLD…………………………………………………………………………………………………………. 12
2.4.6 HOIST……………………………………………………………………………………………………………….. 14
CHAPTER 3…………………………………………………………………………………………………………………17
MATERIALS AND METHOD…………………………………………………………………………………………. 17
3.1. CONCEPTUAL DESIGN……………………………………………………………………………………………17
3.1.1. Design concepts…………………………………………………………………………………………………17
3.1.2. Design consideration and factors…………………………………………………………………………19
3.1.3 Design matrix……………………………………………………………………………………………………. 20
3.1.4 Decision Matrix Analysis………………………………………………………………………………………22
3.2. DETAILED DESIGN…………………………………………………………………………………………………22
3.2.1 Design of Hydraulic Cylinder……………………………………………………………………………….. 25
3.3. MATERIAL SELECTION………………………………………………………………………………………….. 35
3.4. BILL OF ENGINEERING MATERIALS AND EVALUATION……………………………………………… 36
3.5. MACHINING COST……………………………………………………………………………………………….. 36
3.6. TOTAL COST…………………………………………………………………………………………………………37
CHAPTER 4…………………………………………………………………………………………………………………38
TESTING, RESULT AND DISCUSSION……………………………………………………………………………..38
4.1 PROCEDURE………………………………………………………………………………………………………….38
4.2 TEST……………………………………………………………………………………………………………………. 38
4.3 OBSERVATION……………………………………………………………………………………………………… 39
4.4 MODIFICATION OF DESIGN……………………………………………………………………………………. 39
4.5 RESULTS………………………………………………………………………………………………………………. 39
4.6 DISCUSSION…………………………………………………………………………………………………………. 40
4.7 MAINTENANCE AND PRECAUTION OF THE SCISSORS LIFT…………………………………………. 40
CHAPTER 5…………………………………………………………………………………………………………………41
5.1 CONCLUSION……………………………………………………………………………………………………….. 41
5.2 RECOMMENDATIONS…………………………………………………………………………………………….41
REFERENCES……………………………………………………………………………………………………………… 43
List of Figures
Fig 2.1: Hydraulic Powered Lift…………………………………………………………………………….. 7
Fig 2.2 Fixed Pulleys……………………………………………………………………………………………..8
Fig 2.3 Movable Pulley…………………………………………………………………………………………. 8
Fig. 2.4 Compound Pulley………………………………………………………………………………………9
Fig. 2.5 Hydraulic Crane……………………………………………………………………………………… 11
Fig 2.6 Tubular Scaffolds……………………………………………………………………………………..14
Fig 2.7 Different types of Hoist mechanism…………………………………………………………… 15
Fig.3.1. Scissors Ladder under consideration…………………………………………………………. 17
Fig.3.2. Manually operated Screw Jack…………………………………………………………………. 18
Fig.3.3. Hydraulic arm in operation………………………………………………………………………. 19
Fig.3.4 Free body diagram…………………………………………………………………………………… 23
Fig.3.5. Notations……………………………………………………………………………………………….. 26
Fig.3.6 Possible position for Hydraulic Cylinder……………………………………………………. 27
Fig.3.7. Scissors ladder……………………………………………………………………………………….. 28
Fig.3.8. Characteristic triangle for calculating input length vector……………………………..28
Fig.3.9 free body diagram with hydraulic positioned………………………………………………. 29
Fig.3.10. Forces acting on the ladder…………………………………………………………………….. 30
Fig.3.11. Free body diagram for scissors arm…………………………………………………………. 31
Fig.3.12. Scissors ladder at minimum height………………………………………………………….. 34
Fig.3.13, scissors ladder at maximum height………………………………………………………….. 35
List of Tables
Table 3.1: Functional Weighting by Row-Column Method……………………………………… 20
Table 3.3: Table Showing the Relationship between Alpha (α) and Height………………… 24
Table3.4: Table showing the lift angle and the maximum force in the system…………….. 25
Table3.5. Table showing the relation between lift and angle and force in cylinder……… 33
Table 3.3 Bill of Engineering Materials and Evaluation………………………………………….. 36
Table 3.4: Machining Cost……………………………………………………………………………………36
Table 3.5: Total Cost……………………………………………………………………………………………37
List of Graphs
Graph 3.1 Graph showing the relationship between height raised and lift angle…………..25
Graph 3.2 Graph showing the relationship between Force required and lift angle………..34
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND TO THE STUDY
There is a need at one point or the other in workshops, industries, firms and other forms of establishments to perform one or more operations at certain heights, whether it is maintenance or repair work. This has resulted in the design, production and manufacture of various lifting equipment to help achieve these heights. Tasks such as repairs, replacements and other maintenance activities are inevitable for all establishments, particularly large companies
/industries, and in situations where they have to be carried out above ground level, a safe, reliable, easy and efficient means must be made available.
The Faculty of Engineering and the University of Benin at large is not an exemption to this fact as problems ranging from installation and replacement of lighting systems, installation of projectors and replacement of damaged ceiling boards come up from time to time. To this effect, a lifting system, a Scissors Ladder, with which these lingering problems can be tackled, has been designed.(Edegbe, 2015.)
A Scissor Ladder or mechanism is a tool that uses mechanical means to extend a platform. The word “scissor” comes from the mechanics of criss-cross “X” pattern which have folding supports. Through applying force to one or more supports, the extension or displacement movement is accomplished, resulting in an elongation of the cross pattern. Use hydraulic, pneumatic or mechanical (via a lead screw or rack and pinion system) the pressure applied to extend the function of the scissors.(Izui et al, 2009; Okolie, 2012)
The scissors ladder previously designed came down with a number of problems like inability to lift load, high frictional resistance which sum up to an inadequate drive system.
A drive is a part of mechanical device which brings about the dynamic movement of a system. Types of drives are namely: conveyor belts, power screws, pulley and belts, hydraulic drives, rack and pinion, gear box etc.
This project is focused on the design and construction for the drive system of a scissors ladder to convey a maintenance crew member and his equipment to elevated heights of high rise
buildings in the faculty of engineering such as the faculty workshop and lecture theaters, ensuring a safe and efficient working environment.
1.2 STATEMENT OF THE PROBLEM
This project focuses on improving the drive system of the earlier manufactured scissors ladder to transport a worker and his tools to a height of 3 meters above ground level, safely at ease.
Specifications such as safety and ease of use, etc., are required to perform any function at certain heights in a particular environment. This project therefore takes into account the bulk of these criteria.
1.3 AIM AND OBJECTIVES Aim:
To design for the improvement of the drive system of a scissors ladder.
The objectives of the project are:
- Redesign for the power that could effectively carry the load.
- Determine the height at which the power will be effective.
- Reduction of frictional resistance.
- Construction and testing of the machine.
1.4 SCOPE OF THE WORK
The design and construction for the drive system of a scissors ladder is to lift to a height to about 3m and a carrying capacity of not more than 100kg (1000N).
1.5 JUSTIFICATION FOR THE WORK
The design and construction of a hydraulic scissors lift is to lift a worker together with the working equipment comfortably and safely to a required working height not easily accessible. It may be used without a necessary external assistance or assistance from a second party due to the concept of the design. This project will be an important engineering tool or device used in maintenance jobs like changing of street lights, painting of high buildings and walls around the Faculty of Engineering and the University environment at large.
DESIGN AND CONSTRUCTION FOR THE IMPROVEMENT OF THE DRIVE SYSTEM OF SCISSORS LADDER
