Project Report Hydrualic Scissor Lift

1Fabrication of Hydraulic Ladder A Project submitted in partial fulfillment for the award of the Degree of Bachelor of Technology in Department of Mechanical Engineering Guided by: Submitted by: Mr. Dayal Singh Rathore Pradeep Attal (33) Department of Mechanical Engineering Shubham Saxena (52) Sunil Kumar Dhakar (55) Vinod Kumar Sharma (59) Vishal Bajpai (61) Department of Mechanical Engineering Jaipur Engineering College and Research Centre, Shri Ram Ki Nangal via Vatika, Tonk Road ,Jaipur Annexure - 1 2 Candidate Declaration We Pradeep, Shubham, Sunil, Vinod and Vishal hereby declare that the work presented in this Project entitle “Fabrication of Hydraulic Ladder” in partial fulfillment of the requirements for the award of Degree of Bachelor of Technology, submitted in the Department of Mechanical Engineering of JECRC, Jaipur, is an authentic record of my own work under the supervision of Mr. Dayal Singh Rathore. I also declare that the work embodied in the present thesis is my original work/extension of the existing work and has not been copied from any Journal/thesis/book, and has not been submitted by me for any other Degree/Diploma. (Name & Signature of Candidate) Enrolment No.:…………………... Date:……………………………… 3 Annexure - II Certificate of the Supervisor(s) This is to certify that the Project entitled “ Fabrication Of Hydraulic Ladder” submitted by Pradeep, Sunil, Shubham, Vinod and Vishal for the award of Degree of Bachelor of Technology in the Department of Mechanical Engineering of JECRC, Jaipur, is a record of authentic work carried out by him/her under my/our supervision. The matter embodied in this Project is the original work of the candidate and has not been submitted for the award of any other degree or diploma. It is further certified that he/she has worked with me/us for the required period in the Department of Mechanical Engineering at JECRC, Jaipur. (Name and Signature of Supervisor) Date:………………………………….      4 Acknowledgements I would like to express my sincere gratitude to my project guide “Mr. Dayal Singh Rathore” for giving me the opportunity to work on this topic. It would never be possible for us to take this project to this level without his innovative ideas and his relentless support and encouragement. Pradeep (33), Sunil (55), Shubham (52), Vinod (59) and Vishal (61) 5 Abstract The following paper describes the design as well as analysis of a hydraulic scissor lift. Conventionally a scissor lift or jack is used for lifting a vehicle to change a tire, to gain access to go to the underside of the vehicle, to lift the body to appreciable height, and many other applications also such lifts can be used for various purposes like maintenance and many material handling operations. It can be of mechanical, pneumatic or hydraulic type. The design described in the paper is developed keeping in mind that the lift can be operated by mechanical means by using pantograph so that the overall cost of the scissor lift is reduced. The upward motion is achieved by the application of pressure to outside of the lowest set of support elongating the crossing pattern and propelling the work platform vertically. In our case our lift was needed to be designed a portable and also work without consuming any electric power so we decided to use a hydraulic hand pump to power the cylinder also such design can make the lift more compact and much suitable for medium scale work. This paper describes the complete study of components (hydraulic cylinder, scissor arms, spacing shaft and platform), selection of materials and analyzes the dimensions of components. Further fabrication of all the parts and assembly is carried out. Keywords— Hydraulic scissor lift, pantograph, hand pump, vonmisses stresses 2 SCAFFOLD 2.1.3 COMPONENTS OF SCISSOR LIFT 3.5 DESIGN ANALYSIS CHAPTER 3: CONSTRUCTION 3.4 MATERIAL SELECTION 3.4 DESCRIPTION AND FUNCTIONING 4.1 TYPES OF LIFTS 3. SCOPE OF THE STUDY .5 CONSTRUCTION OPERATION AND TOOLS CHAPTER 4: WORKING 4.4 DESIGN THEORY 2.3 MECHANICAL SCISSOR LIFT 2.1 OBJECTIVE 1.2 HISTORY OF HYDRAULIC LIFT CHAPTER 2: LITERATURE REVIEW 2. 6 TABLE OF CONTENT CHAPTER 1: INTRODUCTION 1.1 UPRIGHT’S SCISSORS LIFT 2.2 PRINCIPLE OF OPERATION OF A HYDRAULIC LIFT 4.2 HYDRAULIC SCISSOR LIFT 3.3 CYLINDER SELECTION 4.6 FUTURE IMPROVEMENT CHAPTER 5: NEW DEVELOPMENT (Experiment) 5.5 WORKING PROCESS 4.1 WORKING PRINCIPLE 4. 10 CUSTOM DESIGN CHAPTER 6: CONCLUSION 6.5.1 CONLUSION 6. WHAT CAUSES DEFLECTION 5. 7 5.6 WHAT CAN BE DONE TO LIMIT DEFLECTION 5.2 IMPORTANCE OF THE STUDY 5.8 TYPICAL APPLICATIONS 5.7 SUMMARY ON DEFLECTION 5.2 RECOMMENDATIONS CHAPTER 7: REFERENCES .4 DEFLECTIONS IN SCISSOR LIFT 5.9 COMMON INDUSTRIES SERVED 5.3 ANALYSIS OF MECHANICAL PROPERTY REQUIRMENTS OF MACHINE COMPONENTS 5. 8 List of Tables- Table 4............36 .Standards for single acting cylinder ……………………………………………....1..Input variables and values associated with the design………………….2...35 Table 4. 4..………47 Fig.24 Fig 3. ………………………………………………………50 Fig..1 Upright Scissor Lift…………………………………………………………………..4 Platform roll-outs/extensions………………………………………….48 Fig. 5.3 Scissor jack: Loading applied at the bottom………………………………….3 Mechanical Scissor Lift………………………………………………………………18 Fig 3.9 Overhead Lift System ……………………………………………………………….4 Scissor Jack: Free body diagram……………………………………………………. …………….37 Fig. ……………………………………….27 Fig 4....11 Multi-Axis Extended Reach Lift………………………………………………….13 Lifting car through Scissor Lift.3 Explosion proof lights and switch (TK only)……………………………….2 Accordion skirt/bellows……………………………………………………………..46 Fig.8 Dual Mast Work Platform…………………………………………………. 5.33 Fig 4.…..………. 5..50 Fig. 5.3 Scissor Arms.. ……………………………………………………51 . 5..2 Scaffold Tower ……………………………………………………………………….16 Fig 2.1 Foot control for vertical or horizontal travel. 5.1 Pascal Law…………………………………………………………….37 Fig.32 Fig 4..10 Multi-Axis Paint Booth Lift ……………………………………………………….6 Rubber bumper stops (rail guided lifts only) ………………………………………......... 47 Fig.2 Schematic diagram of hydraulic scissor lift………………………………………….12 Multi-Axis Blast Booth Lift..24 Fig 3.50 Fig. 5.49 Fig.49 Fig. ………………………………………………………………………...49 Fig.. 5..5 Electric/hydraulic power unit………………………………………………………. 5....……………47 Fig. 5. 5. 9 List of Figures- Fig 2.26 Fig 3.1 Hydraulic Scissor Lift……………………………………………………………….46 Fig..2 Hydraulic Multiplication…………………………………………………….17 Fig 2.……….7 Large Work Platform ………………………………………………………………. 5.. 5.4 Hydraulic Scissor Lift Schematic Diagram…………………………………………. A hydraulic pallet lift is a mechanical device used for various applications for lifting of the loads to a height or level. The lift is expected to work with minimal technical challenges and greater comfort due to its wide range of application. These types of lifts are used to achieve high travel with relatively short platform. A scissor lift provides most economic dependable & versatile methods of lifting loads. . The main objective of the devices used for lifting purposes is to make the table adjustable to a desired height. the maximum height) the device can be used in any height within this range and can be descend immediately in case of emergency. warehousing. A multiple height scissor lift is made up of two or more leg sets. The user then stands on the platform and controls their ascent or descent via a control deck situated there. The device can easily be handled to the site to be used with a tow-van and then powered by a generator. They usually consist of the work platform itself – often a small metal base surrounded by a cage or railings and a mechanical arm used to raise the platform. military. as a part of the design. and can result in very large forces required to begin lifting even a moderate amount of weight if the actuator is not in an optimal position. etc. convey and/or transfer material between two or more elevations. schools. Actuator force is not constant. This factor depends on the position of the points chosen to connect an actuator and the number of cross bar stages. A lift table is defined as a scissor lift used to stack. This lift table raises load smoothly to any desired height. The scissor lift can be used in combination with any of applications such as pneumatic. grocery distribution. Elevated work platforms are mechanical devices that are used to give access to areas that would previously be out of reach. 10 CHAPTER 1 INTRODUCTION 1. The frame is very sturdy & strong enough with increase in structural integrity. Industrial scissor lifts & tilters are used for a wide variety of applications in many industries which include manufacturing. The amount of force required from the actuator is also amplified. They are also known as Aerial Work Platforms (AWPs). The scissor lift contains multiple stages of cross bars which can convert a linear displacement between any two points on the series of cross bars into a vertical displacement multiplied by a mechanical advantage factor. Lift tables may incorporate rotating platforms (manual or powered). hydraulic. it has few moving parts which may only require lubrication.e. since the load factor decreases as a function of lift height. tilt platforms etc. mechanical. Between the heights of lift (i.1 OBJECTIVE- The project is aimed at designing and constructing a hydraulically powered scissors lift to lift and lowers worker and his working equipment with ease and in the most economical way. mostly on buildings or building sites. Scissor lift design is used because of its ergonomics as compared to other heavy lifting devices available in the market. hospitals and printing. raise or lower. and can be operated independent of a second party. However generally they are designed to lift fairly light loads and so cannot be used to elevate vehicles. Above all it has a high capacity in terms of load lifting. A pantograph is connected in a manner based on parallelograms so that the movement of one pen. minting. If the first point traces a line drawing. for example allowing them to hold pieces of glass to install window planes.2 HISTORY OF HYDRAULIC LIFT- 1. it allows smooth movement without jerking due to steady increase in fluid pressure.1 Hydraulic Lifting Platform: The hydraulic lift makes use of fluid pressure to produce smooth movement during lifting. hydraulic lifts are heavier because of the amount of fluid in circulation in the system. The most common type is the articulated Elevated Work Platform. Scissor lifts (Aerial work platforms in general) are generally used for temporary. The challenges of this system are. or a pen will draw miniaturized copy fixed to the other. pneumatic or mechanical (via a lead screw or rack and pinion system). or other dangerous heights. enlarged. in extreme cold conditions. . firstly. making them highly flexible as opposed to things such as lifts or elevators. The contraction of the scissor action can be hydraulic. generators or pieces of architecture for which a crane would more likely be used.2. Secondly. engraving and milling. They are designed to lift limited weights. different kinds of pantographs are used for other forms of duplication in areas such as sculpture. They are temporary measures and usually mobile. Depending on the precise task there are various different types of aerial work platform which utilize separate mechanisms and fuel sources. which distinguishes them from permanent access equipment such as elevators. an identical. Other uses include use by fire brigade and emergency services to access people trapped inside buildings. In conclusion. In some cases however elevated work platforms can be designed to allow for heavier loads. exile access purposes such as maintenance and construction work for emergency access. majority of lift platform in market make use of hydraulic. Using the same principle. 1. produces identical movements in a second pen. This then allows workers to work on areas that don’t include public walkways. such as top-story outdoor windows or gutters to provide maintenance. It has some benefits when compared to other lifting device. its dependency on power supply is eliminated. the fluid can falter or get frozen which might leads to leakage in hydraulic lines or pipes. in tracing an image. Most are powered either pneumatically or hydraulically. (EWP) or ‘hydraulic platforms’ (and also known as boom lifts or cherry picker). Some can be fitted with specialist equipment. 11 Some forms of aerial work platform also have separate controls at the bottom to move the actual AWP itself while others are controlled entirely on the platform or towed by other vehicles. There is problem of accumulation of debris in oil tank. h) Hydraulic system requires too many accessories to function efficiently. b) It requires trained personnel to operate it. j) Hydraulic system is not flexible for usage because its component parts are not fully attach as a whole.Hydraulic Lifting Platform . k) There is frequent problem of seal leakage. f) Sometime debris from improperly preserved oil block oil tubes and at times disrupts proper functioning of the system. due to leakage that might emanate from the system. it require a temperature range for it proper storage.1 . g) There is always problem of valve failure. i) There is risk of slipping while working with hydraulic system. d) It is very difficult to move from place to place due to its complex design. c) Since it make use of oil. e) Studies have shown that hydraulic lift that operates on two cylinders at most time experience delay in one of the cylinder to actuate due to poor cross feeding between cylinders. Fig 1. 12 a) It is not economical to the common technician or artesian. l) Aging problem of oil leads to failure in valves and shorter life of pumps. The challenges of this system are.2. c) Electric lift cannot be used where the electric power is fluctuation. h) Over heating in electrical coil could damage the system. f) The electrical control unit must not be exposed to water or higher temperature. a) Due to frequent raising and lowering of the lift. i) Fuses easily blow-out when they are used as safety device.Electric Lifting Platform . The device could be put to stand still during electricity/power outage. there is possibility of snapping in the electric cable which could lead to exposure of the cable and could lead to electrocution.2 ELECTRICLIFTING PLATFORM These lift devices make use of electromagnetic power to raise or lower through the use of electric motor. k) It is expensive to acquire. j) Dirt in electrical system could also lead to malfunctioning of the system. Fig 1. b) It requires other accessories to be operated.. and there is potential of electrocution when electric cables are exposed. 13 1. e) It requires regular maintenance.2 . d) It requires trained personnel to operate it successfully. The device could be very expensive and there is high probability of jerking during startup of the device through the torque created by the electric motor. g) Electrically operated solenoid valve could easily get damage during operation with irregular voltage supply. the ram moves up and the cage is lifted. Testimonies from operators of this device show that the failure rate of the device is very high due to frequent air leakage during operation as a result of failure in valves. It runs between guides of hard wood round steel. A platform or a cage is fitted to the top end of ram on which goods may be placed or the persons may stand. In order to balance the weight of the cage sliding balance weights are provided. As the liquid under pressure is admitted to the cylinder. The cage moves in the downward direction when the liquid from the fixed cylinder is removed. 14 Hydraulic lift is a device for carrying persons and loads from one floor to another.2. 1.Pneumatic System The challenges of this system are. The cage is suspended by ropes. The lift of the cage is equal to the stroke of the ram. . but it acquires its driving force/pressure from the air.. same as in the case of a hydraulic crane. Direct acting hydraulic lift- The direct acting hydraulic lift consist of a ram sliding in a cylinder. in a multi- storey building. It is fitted with a jigger which is exactly. a) There is high risk of air leakage.3 PNEUMATIC SYSTEM/AIRBAG This device also operates like the hydraulic device.3. The hydraulic lifts are of the following types. Suspended hydraulic lift- The suspended hydraulic lift is a modified form of the direct acting hydraulic lift. Fig 1. 15 b) Pneumatic systems are frequent with valve leakage. c) The air bag is not flexible during usage. . 1 UPRIGHT’S SCISSORS LIFT In Selma California. Before now. several scientist and engineers have done a lot of work as regards the scissors lift in general. upright was founded by an engineer. A review of some of that work gives the design and construction of a hydraulic scissors lift a platform. they improved upon their product line by introducing the sigma arm speed level. Walkce Johnson who created and sold the first platform which was called a “scissors lift” due to the steel cross bricking that supported the platform giving it the product name “magic carpet”. there is a manufacturer of aerial platforms by name “UPRIGHT”. According to Wikipedia article. This feature continued to be unique to be upright product and allow self-leveling of the platform on rough terrains. By 1986. they had introduced their first sigma arm lift. The drive towards better and greater scientific and technological outcome has made the world dynamic.Upright Scissor Lift . The magic carpet was able to provide instant revenue for the young company due to its quick popularity among its companies. model SL20. 16 Chapter-2 REVIEW OF RELATED LITERATURE Man’s quest for improvement has never been satisfied.. Fig 2.1. this world – wide company was founded in 1946. Wikipedia further explained that the company constructed innovating and by early 1930s their product included the X – series scissors lift. In 1990. 2. and now it manufactures and distributes its product. The tubes are either steel or aluminum. Boards provide a working surface for users of the scaffold. The tubes come in a variety of length and a standard diameter of 48. In 1995 they produced their first trailer mounted boom. a flat materials usually made of wood is placed on top so that the worker can stand comfortable on top. especially the scissors lift.3mm. they are either “black” or galvanized.2 SCAFFOLD Scaffold allows workers to transport themselves and their materials to elevated heights. If steel. Tubes are generally bought in 6. Scaffolds cannot be adjusted automatically and they only can remain fixed the way it is arranged unless rearranged. irons or woods which are arranged in such a way that workers or operators can climb on the arranged pipes to get to elevated heights. The 8P37 (known as AS38) in 1996. They are seasoned wood and are very strong. scaffold is cross section of pipes. According to Google internet search machine. they are used in building sites and construction sites but used mainly in building sites. After arranging the pipes. usually up and down in an unfinished building. Scaffolds are designed to allow workers get to elevated heights. This truly innovated company has left their mark with the other products including compact scissors design and modular alloy bridging.7kg/m as opposed to 4.Scaffold Tower . 2.4kg/m) and also a greater flexibility and so less resistance to force. as standard equipment for a variety of application it is now a visual application in numerous fields and locations.. although composite scaffolding using filament wound tubes of glass fiber in a nylon or polyester matrix. Fig 2. 17 Upright introduced an equal innovative family of boom lift in 1990s. as well as expanding the versatility of instant span towers with aircraft docking and faced system. Scaffolds for increased height are preferably made of hardened materials like metal pipes. you will find upright products.3m length and can be cut down to certain typical sizes.2. The basic difference between the two types of tubes is the lower weight of aluminum tubes (1. this mechanism has to be driven to bring the platform back down.Mechanical Scissor Lift A general knowledge however. ..3 MECHANICAL SCISSOR LIFT The mechanical scissors lift is used for lifting materials especially on construction sites. This is one of the most recent advancement on scissors lift. the power needed to drive the machine is manual. regarding screws will reveal the loss due to friction in the screw threats. cannot be overemphasized as it can be used in almost every part of the country whether there is availability of electricity or not. the lift utilizes a belt drive system connected to a load screw which constructs the “X” pattern on tightening and expands it on loosening.r. The scissor lift has a unique mechanism which uses worm and worm wheel. Therefore. There. Unlike the hydraulic systems. each rotation of the angle. since the applied force from the wheel is converted to linear motion of the lift by help of the lead screw. Its suitability however. This can be used to lift the working and equipment to a height. Also. We have calibrated the lift w. 18 2. This mechanism provides a self-locking system which makes the scissor lift completely safe for use. and much energy is expanded to achieve a desired result. Fig 2.3. The lead screw actually does the work. This gives us the opportunity to use this lift as a machine part for accurate elevation.t. the efficiency of this device is low due to losses in friction. 150+4+800 = 874. direction and rate of flow are controlled by values. Although these methods are efficient and satisfactory. maintenance and repairs does not allow these lifts to exist in common places. Considerations made during the design and fabrication of a single acting cylinder is as follows: a.5+40+8.65 kg . c. General cost of material and fabrication techniques employed Hydraulic cylinder: The hydraulic cylinder is mounted in inclined position. in which the pressure. Hydraulic systems are used to control and transmit power. pneumatic or mechanical means.5 = 750 kg rounding the mass to 800kg  Mass of top frame= 22. b.4 DESIGN THEORY In this chapter. 19 2. The total load acting on the cylinder consists of:  Mass to be put on lift: 500 kg Taking FOS = 1. An actuator is used to convert the energy of the fluid back into mechanical power. Economic availability. they exist lots of limitations and complexity of design of such lifts as well as high cost of electricity. and a final here modified to further enhance the functionality of the design. The idea of a hydraulically powered scissors lift is based on Pascal’s law employed in car jacks and hydraulic rams which states that “pressure exerted anywhere in a conformed incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio remains the same” In this section all design concepts developed are discussed and based on evaluation criteria and process developed.150kg Total Mass: 22. the pressure drop a cross the actuator and its overall efficiency. Functionality of the design. A pump driven by a prime mover such as an electric motor creates a flow of fluid. Manufacturability.5 kg  Mass of each link: 5 kg (5*8) = 40kg  Mass of links of cylinder mounting = 4kg  Mass of cylinder=8. Most lifting devices are powered by either electricity. The amount of output power developed depends upon the flow rate. mathematical relationships are developed for the various parameters necessary for the implementation of this design and arranged in sections below corresponding to the sequence of their implementation.5 for mass in pallet 500 x 1. Angle of link with horizontal Mounting of cylinder on the links Length of link.24mm2 Pressure = (Force/Area) =(8580. For calculations we will consider α=300 Thus substituting α=300 in eqn (1). Xmi=(2i-1)*Hyo* +(2i2 -2i+1)*by * =Hyo* +(2i2 -2i+1)*by * = (7848 X 0.e when the scissor links are closed. Force at middle of link.52bar 2. the levels are numbered from the top.81 = 8580.708N.1 Design Of Link- Now Let Hy0 =Mass applied on the lift=800kg B=Mass of the lit which the cylinder needs to lift=74. Forces at the end of link: as forces at ends of link are same in magnitude.316N X2=Hyi*i =8580.48N . Formula used- Where W = Load to be lifted S= a2 + L2 -2aL*cos α S = Distance between end points of cylinder.316N  Only two forces are calculated here 1.316/3117.316*1*0.  In our case. 2.112N Resultant of X 2 & HYi/4 R1 = √(11787.65x 9.6 m α = angle of cylinder with horizontal.5 X cot 200 )+(732.5*(cot20/2) =11787.65kg Hyi=Total weight =8580.4.316/4)2 R1 = 11980.25 X cot200 ) =11512.316N Scissors lift calculations: For a scissor lift Force required to lift the load is dependent on. For level 1 X1 = XBi-1 for level 2 X 2= XBi-2 The angle of cylinder with horizontal is θ=200. We get F=8580. Hyi=8580.112)2 +(8580. L= length of link = 0.316N Selecting 63mm diameter cylinder Area of the cylinder= force/pressure Area = (3. Above force will act on all the joints at end of each link. 20 Total load = 874.14*632)/2 =3117.316 X 0.24*10-6 ) =27. Now force acting on the intermediate point of link is given by. Now the maximum force will act on the cylinder when the cylinder is in shut down position i. 970 mm the clearance is given as the piston is used to slide forward and backward. therefore a cylinder of 75 / 50 is used. Where to = stress imparted on the tube. 5. that is general cost of materials and fabrication techniques employed. Based on strength basis F = d × tc × σt 5. L = length of rod. Fcr = π 2 × E I / 4 L2 8. Tensile strength = 42kgf/mm2 = 412. Design of End Cover Material used Mild steel. since the available size is Φ75mm then Thickness t. FOS = 4.794 – 49. Outer Diameter = d + 2 to 2.75.9856 N/mm2 . To check the piston rod for column action when a structure is subjected to compression it undergoes visibly large displacements transverse to the load then it is said to buckle. σy= yield point. t = (D – d) 3. L / K is 73. Where the Slenderness ratio. Base The base structure is built-up of C – channels and hollow bars are usually used in engineering applications due to their high rigidity. The internal resistance of piston is given by. But the piston rod diameter is rounded off to 32 mm in order to sustain buckling load. Force F= Area × Stress 4. Where σw = working stress Piston Head Piston head diameter is 49. The piston head length is chosen based on piston seals to fox and width also no of seals to fix. But the standard size is Φ75. For one end fixed and other end free C = 0. . Hoop stress induced can be found by t = di/2 × {√st + (1– 2μ)p / st-(1+μ)p –1} 1. σt = 541. I = radius of gyration. for small lengths the process is elastic since the buckling displacements disappear when the load is removed. K = Minimum radius of gyration and is given by K = √I/A 6. Cylinder Bore = φ80 Standards for single acting cylinders- Material – structure steel st-42 hollow tube.5 DESIGN ANALYSIS- Design Considerations made during the design and fabrication of a portable work platform being elevated by two hydraulic cylinders is as follows: (a) Functionality of the design (b) Manufacturability Economic availability.25 Let Fcr = Critical buckling load. The thickness is found by industrial formula tc = d√(3 × σw / 16 × P). Design Analysis 1. Design of Piston Rod For piston rod material of mild steel EN – 8. 21 2.02 N/mm2. Critical load using Euler’s Formula Fcr = C × π2 × E / (L / K) 2 7. The total load on the platform and load kept on it is taken by the two cylinders and four supports which are made up of C – Channels. The supports and the two cylinders are flexibly coupled to the base there by not transmitting the full load on to the base. 22 strength as compared to the other bars. the chosen C channel is ISMC (Indian standard medium weight channel). . It was rather found out that. 23 CHAPTER. The name scissors lift originated from the ability of the device to open (expand) and close (contract) just like a scissors. and someone will be beneath controlling it.1 TYPES OF LIFTS- Classification based on the type of energy used- (a) Hydraulic lifts (b) Pneumatic lifts (c) Mechanical lifts Classification based on their usage- (a) Scissor lifts (b) Boom lifts (c) Vehicle lifts 3. to be controlling the device himself. The initial idea of design considered was the design of a single hydraulic ram for heavy duty vehicles and putting it underneath. resulting in an elongation of the cross pattern. factories. it is better to adopt this design concept to the production of the machine. fixing of bill boards. The force applied to extend the scissors mechanism may by hydraulic. workshops. residential/commercial buildings to repair street lights. The extension or displacement motion is achieved by the application of force to one or more supports.3 CONSTRUCTION 3. but this has limitations as to the height and stability. Therefore further research was made to see how to achieve this aim. The term “scissor” comes from the mechanic which has folding supports in criss cross “X” pattern. estimating as well the cost of expanding energy more that result gotten as well the maintenance etc.2 HYDRAULIC SCISSOR LIFT- A scissor lift or mechanism is a device used to extend or position a platform by mechanical means. pneumatic or mechanical (via a lead screw or rack and pinion system). electric bulbs etc. there is a possibility of the individual ascending/descending. The need for the use of lift is very paramount and it runs across labs. . Considering the need for this kind of mechanism. expanded and less-efficient. the engineers may run into one or more problems when in use. risk of having the batteries discharged during an emergency. Also. as well as maintenance cost. Several challenges were encountered in this very design. Fig 3.2.1.e. 24 Fig 3. the individual ascending / descending is still the same person controlling it. Some amongst many include. It is the consideration of these factors that initiated the idea of producing this hydraulically powered scissors lift with independent operator.Schematic diagram of hydraulic scissor lift . low efficiency. the control station will be located on the top frame. I.. dependent operation. The idea is geared towards producing a scissors lift using one hydraulic ram placed across flat. extended time of operation.Hydraulic Scissor Lift Before this time scissors lift existing use mechanical or hydraulic system powered by batteries for its operations. in between two cross frames and powered by a pump connected to a motor wheel may be powered by a pump generator. 2. A scissor lift is a device used for lifting purposes. the lift’s base frame is mounted to the floor and should not experience deflection. that are stacked on top of each other.3 COMPONENTS OF SCISSOR LIFT- 1. a boom lift can be used. which is driven by total weight supported by the legs. control valves and connections and the motor. 3. but also contributes to an increased collapsed height of the lift. Eccentric loads applied to this unsupported end of the platform can greatly impact bending of the platform. of its clearance hole or bushing. Scissors Arms.Platform bending will increase as the load’s center of gravity moves from the center (evenly distributed) to any edge (eccentrically loaded) of the platform. Also.All entrapped air must be removed from the hydraulic circuit through approved “bleeding” procedures – air is very compressible and is . h yd r a u l i c . scissors leg length. e . the rollers roll back towards the platform hinges and create an increasingly unsupported.Normally. p n e u m a t i c o r electrical. as the scissors open during rising of the lift. 4. i . and each pin has a running clearance between the O. Platform Structure. The scissor lift can be used in combination w i t h a n y o f t h e p r e v i o u s l y m e n t i o n e d a p p l i c a t i o n . Increased platform strength via increased support structure material height does improve resistance to deflection. 25 A scissors lift is attached to a piece of equipment having a work station known as scissors lift table that houses the pump. the generator. of the pin and the I. it sacrifices heights for a large work station. Where more height is needed. overhung portion of the platform assembly. For those cases where the scissors lift is mounted to an elevated or portable frame. Hydraulic Circuit – Air Entrapment. a scissors mechanism is proposed. This mechanism is incorporated with a power screw and the top of the scissors is attached a table platform. the more pinned connections there are to accumulate movement. In order to reduce the inadequacies of the devices mentioned above. 3. the reservoir. which may only require lubrication. Pinned Joints. the base frame must be rigidly supported from beneath to support the point loading created by the two scissors leg rollers and the two scissors leg hinges.D. or pantographs. 5. but can create a potentially undesirable increased collapsed height of the lift. it has few moving parts. its objectives is to make the table adjustable to desirable height. or deflection. the more difficult it is to control bending under load. Increased leg strength via increased leg material height does improve resistance to deflection. A scissor lift provide the most economic dependable and versatile methods of lifting loads.Leg deflection due to bending is a result of stress. This lift table raises the load smoothly to any desired height. The more scissors pairs. A scissors lift does not go as high as a boom lift. when compressing these designed clearances.D. and available leg cross section. The longer the scissors legs are.Scissors lifts are pinned at all hinge points. Base Frame. This device will make use of the power generated from a power screw to raise or lower a platform manually. And because there is an approximate 5:1 ratio of lift travel to cylinder stroke for most scissors lift designs (with the cylinders mounted horizontally in the legs). 7. Load Placements. or evenly distributed. and the scissors table compresses under load until the maximum system pressure is reestablished. Hydraulic Circuit – Fluid Compressibility.All high pressure.Resistance Cylinders lay nearly flat inside the scissors legs when the lift is fully lowered and must generate initial horizontal forces up to 10 times the amount of the load on the scissors lift due to the mechanical disadvantage of their lifting geometry. Off- centered loads because the scissors lift to deflect differently than with centered.3. End loads (inline with the scissors) are usually shared well between the two scissors leg pairs. or otherwise bounces (like a spring) during operation. the resulting lift movement is 5 times the change in oil column height in the hose. Cylinder Thrust.Load placement also plays a large part in scissors lift deflection. are not shared well . Fig 3. however. there is a resulting 5:1 ratio of scissors lift compression to cylinder compression. flexible hosing is susceptible to a degree of hose swell when the system pressure is increased.Oil or hydraulic fluid will compress slightly under pressure. 9. 26 often the culprit when a scissors lift over-compresses under load. there are tremendous stresses (and resulting deflection) placed on the scissors inner leg member(s) that are designed to resist these cylinder forces. And. Hydraulic Circuit – Hose Swell. 8. And. As a result.Scissor Arms 6. resulting vertical lift movement is 5 times that amount of change. System pressure drops slightly because of this increased hose volume.. loads. Side loads (perpendicular to the scissors). as already mentioned above with any change in column length of the lifting actuator/cylinder. as with compressibility. 27 between the scissors leg pairs and must be kept within acceptable design limits to prevent leg twist (unequal scissors leg pair deflection) – which often results in poor roller tracking. Wheels Scissors Arms: this component is subjected to buckling load and bending load tending to break or cause bending of the components. Fig 3. unequal axle pin wear. hence strength is required. Hence based on strength. Hardness and stiffness are needed mechanical properties. Top Platform: this component is subjected to the weight of the workman and his equipment. degree of deflection is directly related to change in system pressure and change in component stress as a result of loading and unloading. Base Platform: this component is subjected to the weight of the top plat form and the scissors arms. stiffness. Scissors lifts typically experience their highest system pressure and highest stresses (and therefore the highest potential for deflection) within the first 20% of total available vertical travel (from the fully lowered position). the frame of the plat form is mild steel and the base is wood. toughness and hardness. It is subjected to direct compressive force which imposes a bending stress which may cause buckling of the component. therefore strength. A recommended material is stainless steel. Mild steel is used. Lift Elevations. The recommended material is mild steel.Hydraulic Scissor Lift Schematic Diagram .4. Hydraulic Cylinder: this component is considered as a strut with both ends pinned. It is also responsible for the stability of the whole assembly. and misalignment of cylinder mounts. plasticity and hardness.. Hence necessary material property must include strength. 10.during Transfer As mentioned above. It is also subjected to internal compressive pressure which generates circumferential and longitudinal stresses all around the wall thickness. ductility. Engineering materials are mainly classified as: Metal and their alloys. These properties include: Strength: it is the ability of a material to resist the externally applied force without break down or yielding the internal resistance offered without break down or yielding the internally applied force is called stress. Ductile materials . Also. the cost of materials in any machine is a good determinant of the cost of the machi8ne. A ductile material is both strong and plastic.4. Non-ferrous metals are those which have a metal other than iron as there main constituent. brass. based on the particular working conditions machine component were designed for only the ferrous metals have been considered. plastic etc. Plasticity: it is property of a material which retains the deformation produced under load.1 Material Selection- Material selection plays a very important role in machine design. certain mechanical properties of metals have greatly influenced our decisions. tin. More than the cost is the fact that materials are always a very decisive factor for a good design. copper. permanently. Also. wrought iron and steels. aluminum etc. The choice of the particular material for the machine depends on the particular purpose and the material for the machine depends on the particular purpose and the mode of operation of the machine components. For the purpose of this project. such as cast iron. Non-metals such as glass. such as iron.4 MATERIAL SELECTION 3. Stiffness: it is the ability of a material to resist deformation under stress. such as copper. steel. zinc etc. Ferrous metals are those metals which have iron as their main constituent. rubber. Ductility: a very important property of the material enabling it to be drawn into wire with the application of a tensile force. it depends on the expected mode of failure of the components. metals are further classified as ferrous metals and non-ferrous metals. Elasticity: it is the property of a material to regain its original shape after deformation when the external force are removed. For example. 28 3. aluminum. copper and aluminum in order of diminishing malleability. wielded and down.4. it also measure of the ability of a metal to cut another metal. Hardness it embraces difference properties such as resistance to water.05 to 0. Toughness: it is the property of a material to resist fracture due to high impact loads like hammer blows. This property decreases. But first. nickel. solid and hollow constructional sections. its greater strength giving it under viable advantages. . It can even be cast. They also have high strength and toughness. Among its application are plates for ship building. bicycle frame tubes. Cast iron is a brittle material. it is the property of breaking of a material with little permanent deformation when subjected to tensile load. Examples include. 29 commonly used in engineering practical (in order of diminishing ductility) are mold steel. though not very successfully.3 percent carbons it has for almost all purpose replaced wrought iron. molybdenum etc. scratching. lead soft steel. Brittleness: it is the properties of a material opposite to ductility. nuts. studs etc. wrought iron. a look at the operations and tools involved. A malleable material is plastic but not 80 essentially strong. Mild steel can be rolled. sheet metal parts and steel castings such as flywheels and locomotive wheel centers. aesthetics and how coefficient of friction were considered to meet all requirements and the choice of stainless steel for the scissors members. toughness and strength.2 Choice of Stainless and Mild Steel Mild Steel contains 0. the procedures followed to achieve a positive result are laid down in the preceding text. bolts. Malleability: it is a special case of ductility which permit materials to be rolled or hammered into thin sheets. aluminum. 3. wrought iron. the properties of rust and corrosion resistance. zinc tin and lead. mesh work. 3. when heated. copper. Stainless Steel: these are steel with high rust and corrosion resistance to meet specific application requirements.5 CONSTRUCTION OPERATION AND TOOLS In the design and construction of the hydraulic scissors lift. brittle materials snap off without giving any sensible elongation. deformation and machinability etc. It is an alloy of iron with about 11% chromium and other metals like nickel. The basic dimensions were marked out using on Engr’s rule and scriber and then cut with the use of hack saw after being welded firmly clamped to the vice. Drilling 4. Welding machine 7. Hollow pins of external diameter corresponding to the drilled holes we then fit into holes and welded in order to strengthen the position then joined together to give the “X” pattern using bolts and nuts. After marking out. Hack saw 4. Scissors Arms. Marking out 2. It is usually made up of pipes with rectangular cross-section and have high resistance to bending. this is used because the base frame is responsible for the stability of the platform.1 Construction Procedure- Base Platform. They are then joined together by welding to give the base frame. they were cut to the required sizes holes of appropriate diameter were drilled at both ends and the middle of each member.the material used for this purpose is mild steel angle bar. Pliers 8. The material is stainless steel for corrosion and rust resistance to give high strength. Electric grinder 3. spanner 9. Engineers rule 2. Try square 10. Drilling machine 6. (3×3 inch) thickness 3mm. Hand file 5.5. Joining (welding and bolt and nut) Tools 1. . Cutting 3. Scriber 3.these include the members that are arranged in a cross-cross ‘X’ pattern and whose construction is responsible for lifting the platform and extension and lowering of the platform. 30 Operations 1. The scissors arms were brazed to increase the strength and bending resistance. The scissors arm connected to the platform is also connected with one end hinged and the other fitted with roller to effect extension and contraction of the lit. The timber was equally into the required dimensions. The hydraulic cylinder is connected to the first arm of the scissors lift with both ends hinged. The force is as a result of the pressure of the hydraulic supplied to the cylinder by the pump from the reservoir. The lift is fitted with wheels to aid mobility from one location to another. This cylinder provides the force needed to lift the load on the platform. Painting of the entire unit is done to improve it aesthetics and increase the corrosion and resistance to rust. Assembling of various components of the hydraulic scissors lift- The scissors assemblage was mounted on the base frame with one end hinged and the other fitted with roller (bearing) to produce the needed motion of rolling along the rail to cause lifting and lowering of the scissors lift. . 31 Top Platform- The material used for the construction of this component is mild steel angle bar for the frame and timber for the base of the platform. The angle bar is cut into the required sizes and welded to form a rigid platform. drilled at the edges and fastened using bolt and nut to secure it in position at the base of the platform. Fig 4. The fluid is almost always an oil of some sort. The pump pressure is usually between 300-400 pounds per square inch (PSI) and pushes the liquid to the bottom of the piston to lift it from its seat which relatively lifts the load connected to the head of the piston-cylinder assembly.1 WORKING PRINCIPLE- Hydraulic lift is a system where a liquid. usually crude oil. 32 CHAPTER. This is a very flexible pumping system and can be used to produce low.. This system is capable of producing a higher volume of fluid than the mechanical lift pump. The picture below . The basic idea behind any hydraulic system is very simple: Force that is applied at one point is transmitted to another point using an incompressible fluid. The pump produces oil on both the upstroke and the down stroke. The required power oil or produced water is reclaimed and reused to continue operating the wells.1. is pumped down hole under high pressure to operate a reciprocating pump or a jet pump. The pump stroke speed is not easily adjustable due to varying load. Pascal Law Pascal's law or the principle of transmission of fluid-pressure is a principle in fluid mechanics that states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure variations (initial differences) remain the same.Pascal Law Hydraulic Lift basically works on the principle of Pascal Law. Hydraulic lift uses a pump and pumps oil very high pressure. The force is almost always multiplied in the process.4 WORKING 4.to high-volume wells. Hydraulic Multiplication Because of the shape of the original device. a pantograph also refers to a kind of structure that can compress or extend like an accordion. and provide many years of trouble free operation. The pipe can also fork. dependable. In this drawing. and versatile method of lifting heavy loads. The neat thing about hydraulic systems is that it is very easy to add force multiplication (or division) to the system. A Scissors lifts provide the most economical. Fig 4. so that one master cylinder can drive more than one slave cylinder if desired. then the force is transmitted to the second piston through the oil in the pipe. allowing it to snake through all sorts of things separating the two pistons. If you apply a downward force to one piston (the left one in this drawing). capacity. The great thing about hydraulic systems is that the pipe connecting the two cylinders can be any length and shape. When force is applied to the left piston. These lift tables raise the loads smoothly to any desired height. and can be easily configured to meet the specific speed. the efficiency is very good -. Since oil is incompressible. and foot print requirement of any hydraulic lifting application. it will move nine units for every one unit that the right piston . scissor lifts. all you do is change the size of one piston and cylinder relative to the other. temporary fences. and other scissor mechanisms such as the pantograph used in electric locomotives and trams.almost all of the applied force appears at the second piston. In a hydraulic system. Scissors lifts have few moving parts. two pistons (red) fit into two glass cylinders filled with oil (light blue) and connected to one another with an oil-filled pipe. are well lubricated. 33 shows the simplest possible hydraulic system: A Simple hydraulic system consisting of two pistons and an oil-filled pipe connecting them. forming a characteristic rhomboidal pattern. And is by far the most popular and efficient of all styles of scissors tables used in material handling applications. This can be found in extension arms for wall-mounted mirrors. as shown here: The piston on the right has a surface area nine times greater than the piston on the left..2. The lift does not lifting immediately. because of the inherent limits of vertical – only movement. Four slave pistons. When the required height is reached the circuit is closed. (Actually. in almost all cars on the road today two master cylinders are driving two slave cylinders each. Assume that the piston on the left is 2 inches in diameter (1-inch radius). critical problems are solved. a 900-pound upward force will appear on the right. To determine the multiplication factor.2 PRINCIPLE OF OPERATION OF A HYDRAULIC LIFT (EXTENSION AND CONTRACTION) A scissors lift is a type of platform that can usually only move vertically. one at each wheel. actuate to press the brake pads against the brake rotor to stop the car. 4. The mechanism to achieve this is the use of linked. pneumatic or mechanical (via a lead screw or rack and pinion system). but this time. and power the generator. elongating the crossing pattern and propelling the work platform vertically. the operators climbs on the platform and switches open the hydraulic circuit thereby leading to an upward extension. known as a scissors mechanism. the load screw is replaced by a hydraulic ram powered by a pump and on electric motor and generator. it is hydraulic.26. but in this case. The brakes of a car are a good example of a basic piston-driven hydraulic system. When work is done. the scissors lift is folded by hydraulic means and handled back to the point of collection. while the area of the piston on the right is 28. Is its independent operation and increased efficiency. The piston on the right is 9 times larger than the piston on the left. Depending on the power system employed on the lift. it is pushing on the piston in the brake's master cylinder. Click the red arrow to see the animation. folding supports in a criss-cross “X” pattern. The area of the two pistons is Pi * r . The only catch is that you will have to depress the left piston 9 inches to raise the right piston 1 inch. you can still stop the car. but rather a simple release of hydraulic or pneumatic pressure. start by looking at the size of the pistons. and the force is multiplied by nine on the right-hand piston. it may require no power to enter “desert” mode. The contraction of the scissor action can be hydraulic.) In most other hydraulic systems. This scissors lift can be handled by one person to a place of use. So if you apply a 100-pound downward force to the left piston. That way if one of the master cylinders has a problem or springs a leak.14. 34 moves. What that means is that any force applied to the left-hand piston will appear 9 times greater on the right-hand piston. One outstanding feature about this design however. The platform may also have extending “bridge” to allow closer access to the work area. Scissors lifts has developed overtime. and lifting stops the control panel or station is located on the top frame. The upward motion is achieved by the application of pressure to the outer side of the lowest set of supports. Fluid power is one of the greater form of power where small input results in a very large output. The area of the left piston is therefore 3. The hydraulic type. This is the main reason that these methods of powering the lift . and at each stage of its development. When you depress the brake pedal in your car. while the piston on 2 the right is 6 inches in diameter (3-inch radius). hydraulic cylinders and pistons are connected through valves to a pump supplying high-pressure oil. 3 CYLINDER SELECTION The hydraulic cylinder (or the hydraulic actuator) is a mechanical actuator that is used to give a unidirectional stroke. . 4. some external actin force on the piston rod causes its return. The return stroke is affected by a mechanical in one direction only. Single Acting Cylinders Single acting cylinders use hydraulic oil for a power stroke in one direction only.1. Table 4. as it allows a fail – safe option of returning the platform to the ground by release of a manual valve. The return stroke is affected by a mechanical spring located inside the cylinder. 35 (hydraulic) is preferred. For single acting cylinders with no spring. notably in engineering. It has many applications.Standards for single acting cylinder Double Acting Cylinders Double acting cylinder uses compressed air or hydraulic fluid to pour both the forward and return strokes. This makes them ideal for bushing and pulling and pulling within the same application they are suitable for full stroke working only at slow speed which results in gentle contact at the ends of stroke. 4 DESCRIPTION AND FUNCTIONING- The machine consists of a worm and worm wheel.Input variables and values associated with the design 4. The physics is explained below. the pinion gets driven by the rotating worm wheel. Equations: . 36 Table 4. The worm wheel and pinion are attached to a common shaft and thus.2. shaft in a slot and the lift scissors. rack and pinion. Rotation of handle attached to worm/worm wheel drives the system. The rack moves forward and this drives the main scissor mechanism. 4.4. They are temporary measures and usually mobile.. Other uses include use by fire brigade and emergency services to access people trapped inside buildings.It consist of the work platform itself – often a small metal base surrounded by a cage or railings and a mechanical arm used to raise the platform.4.Scissor Jack: Free body diagram 4. such as top- story outdoor windows or gutters to provide maintenance. 37 Fig.3 Scissor jack: Loading applied at the bottom Fig. This then allows workers to work on areas that don’t include public walkways. making them highly flexible as opposed to things such as lifts or elevators. for example allowing them to hold pieces of glass to install window planes. Some can be fitted with specialist equipment. Depending on the precise task there are various different types of aerial work platform which utilize separate mechanisms and fuel sources. . or other dangerous heights. The user then stands on the platform and controls their ascent or descent via a control deck situated there.5 WORKING PROCESS. 6 FUTURE IMPROVEMENTS: We can increase contact force between shaft and pinion so as to prevent slipping and allow lifting of larger weights. Scissors arms II. Hydraulic cylinder III. . 38 It is necessary to evaluate the particular type of forces imposed on components with a view to determining the exact mechanical properties and necessary material for each equipment. A very brief analysis of each component follows thus: I. Top plat form IV. Base plat form V. Number of plates in the scissors can be increased to improve the height to number of rotations ratio. 4. 1 SCOPE OF THE STUDY The design and construction of the hydraulic scissors lift is to lift up to a height of 3. Changing of street lights. Hence . stiffness.2m and carrying capacity of less than 500kg (500 kilograms) with the available engineering materials. Hence based on strength.2 IMPORTANCE OF THE STUDY 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. A very brief analysis of each component follows thus: Scissors arms Hydraulic cylinder Top plat form Base plat form Wheels Scissors Arms: this component is subjected to buckling load and bending load tending to break or cause bending of the components.3 ANALYSIS OF MECHANICAL PROPERTY REQUIREMENT OF ESSENTIAL MACHINE COMPONENTS. It is necessary to evaluate the particular type of forces imposed on components with a view to determining the exact mechanical properties and necessary material for each equipment. 5. A recommended material is stainless steel. 39 Chapter-5 NEW DEVELOPMENT 5. 5. there is for academic purpose. plasticity an hardness. 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. It is also subjected to internal compressive pressure which generates circumferential and longitudinal stresses all around the wall thickness. Hydraulic Cylinder: this component is considered as a strut with both ends pinned. a similar project for general carrying – capacity with a selection of better engineering materials. painting of high buildings and walls around the school environment. However. It is subjected to direct compressive force which imposes a bending stress which may cause buckling of the component. ductility. at transfer elevations. Load transfer should be made over the hinge or fixed end of the lift platform to avoid placing concentrated load on the less supported. hence strength is required. the frame of the plat form is mild steel and the base is wood. over hung end of the platform. at lower. Two moving roller and two fixed hinge points. The recommended material is mild steel. base frame should be adequately attached to the surface on which they are mounted. Top Platform: this component is subjected to the weight of the workman and his equipment. therefore strength. toughness and hardness. it is critical to design the conveyor or transfer system to ensure that these elevations are above the scissor lift’s “critical zone” of the first 20% of the lift available travel. provided the platform is equipped with “trapped” roller or is otherwise capable of withstanding this edge loading without risk of platform tipping up or losing contact with the rollers. working capacities.1 LIMITING DEFLECTION IN SCISSOR LIFT- Selecting a lift with design capacity greater than required for the application. Mild steel is used. . Base frame that are not bolted. Avoid transfer of load within the first 20% of lift travel: To minimize stress and deflection.4 DEFLECTIONS IN SCISSORS LIFT 5. Bases must also be rigidly supported beneath the entire perimeter of the frame in order to withstand without deflection on the four point loads imposed upon the frame from above by the four scissor-legs. most scissor lift design for duty at higher capacities will experience less stress in all structural components as well as lower system pressures. load should not be transfer over the sides of a raised scissor lift is much more difficult to control deflection when the load is not shared equally between the two scissor legs pairs. 5. welded or otherwise attached to withstand the upward force created by the eccentric loading of the platform will contribute to deflection by bending or moving while resisting such forces.4. Transfer load over fixed end of the lift platform: First if possible. Ensure that the based frame is lagged down and fully supported: First. It is also responsible for the stability of the whole assembly. Reduced stresses and pressure always result in reduced deflection. Hardness and stiffness are needed mechanical properties. 40 necessary material property must include strength. Base Platform: this component is subjected to the weight of the top plat form and the scissors arms. Wheels: the wheels are position at the base part of the scissors lift and enable the lift to move from one place to the other without necessary employment of external equipment like car. The industry standard goes on to outline the maximum allowable deflection based on platform size and number of scissors mechanisms within the lift design. Although.1 accurately points out that “it is the responsibility of the user/purchaser to advise the manufacturer where deflection may be critical to the application”.Safety Requirements for Industrial Scissors Lifts states that. The longer the scissors legs are. Understanding these Top 10 root causes helps to pinpoint and apply effective measures to limit deflection. whenever loads are applied to or removed from the lift. this chapter has highlighted the features and constraints in the design and fabrication of a prototype unit. remove a load and it expands. the more difficult it is to control bending under load. but can create a potentially undesirable increased collapsed height of the lift. 41 5. ANSI MH29. . scissors leg length. scissors lift acts very much like a spring would – apply a load and it compresses. Increased leg strength via increased leg material height does improve resistance to deflection. all industrial scissors lifts will deflect under load”. there are few literatures on the design of scissors lift. typically measured from the floor to the top of platform deck. and available leg cross section. it is important to understand the contributing factors to a lift’s total deflection. ANSI MH29. An open. which is driven by total weight supported by the legs. or raised. There are also application-specific characteristics that may promote deflection. Scissors Legs- Leg deflection due to bending is a result of stress.4.5 What Causes Deflection? Before attempting to discuss how to limit scissors lift deflection. 5. It has been noted that there are industrial best practices which can be applied to reduce the impact or amount of deflection being experienced.2 Deflection Defined- Deflection in scissors lifts can be defined as the resulting change in elevation of all or part of a scissors lift assembly. Each component within the scissors lift has the potential to store or release energy when loaded and unloaded (and therefore deflect).1 . D. Eccentric loads applied to this unsupported end of the platform can greatly impact bending of the platform. there is a resulting 5:1 ratio of scissors lift compression to cylinder compression. Pinned Joints Scissors lifts are pinned at all hinge points. and the scissors table compresses under load until the maximum system pressure is re- . the rollers roll back towards the platform hinges and create an increasingly unsupported. or pantographs. or otherwise bounces (like a spring) during operation. Also. And because there is an approximate 5:1 ratio of lift travel to cylinder stroke for most scissors lift designs (with the cylinders mounted horizontally in the legs). Increased platform strength via increased support structure material height does improve resistance to deflection. For those cases where the scissors lift is mounted to an elevated or portable frame. The more scissors pairs. when compressing these running clearances under load. the lift’s base frame is mounted to the floor and should not experience deflection. Hydraulic Circuit – Hose Swell All high pressure. the base frame must be rigidly supported from beneath to support the point loading created by the two scissors leg rollers and the two scissors leg hinges. as the scissors open during raising of the lift. of its clearance hole or bushing. overhung portion of the platform assembly. For example: 1/16” of fluid compressibility in the cylinder(s) translates into 5/16” of vertical lift movement. but also contributes to an increased collapsed height of the lift. 42 Platform Structure Platform bending will increase as the load’s center of gravity moves from the center (evenly distributed) to any edge (eccentrically loaded) of the platform. To effectively resist deflection. System pressure drops slightly because of this increased hose volume. Hydraulic Circuit – Air Entrapment All entrapped air must be removed from the hydraulic circuit through approved “bleeding” procedures – air is very compressible and is often the culprit when a scissors lift over- compresses under load. the potential for deflection increases. Base Frame Normally. Hydraulic Circuit – Fluid Compressibility Oil or hydraulic fluid will compress slightly under pressure.D. and each pin has a running clearance between the O. that are stacked on top of each other. or deflection. flexible hosing is susceptible to a degree of hose swell when the system pressure is increased. of the pin and the I. the more pinned connections there are to accumulate movement. as with compressibility. Select a Lift with a Design Capacity Greater Than Required for the Application Most scissors lifts designed for duty at higher capacities will experience less stress in all structural components. 5. are not shared as well between the scissors leg pairs and must be kept within acceptable design limits to prevent leg twist (unequal scissors leg pair deflection) – which. Listed below are the most common of these methods. unequal axle pin wear. Lift Elevation During Transfer As mentioned above.6 What Can Be Done To Limit Deflection? There are a variety of proven methods to reduce scissors lift deflection. to provide the reader an understanding of where to begin when attempting to reduce or eliminate deflection during load transfer (i. with varying design and cost impacts to accomplish each. Side loads (perpendicular to the scissors). applying a load. Reduced stresses & pressures always result in reduced deflection. the resulting vertical lift movement is 5 times the amount of deflection or movement of cylinder hinge points mounted to leg cross members. however. degree of deflection is directly related to change in system pressure and change in component stress as a result of loading and unloading. As a result. Off-centered loads cause the scissors lift to deflect differently than with centered or evenly distributed. And. and misalignment of cylinder mounts. loads. And. Cylinder Thrust Resistance Cylinders lay nearly flat inside the scissors legs when the lift is fully lowered and must generate initial horizontal forces up to 10 times the amount of the load on the scissors lift due to the mechanical disadvantage of their lifting geometry. there are tremendous stresses (and resulting deflection) placed on the scissors inner leg member(s) that are designed to resist these cylinder forces. or de-rated. as already mentioned above with any changes in column length along the line of the lifting actuator(s)/cylinder(s). End loads (in- line with the scissors) are usually shared well between the two scissors leg pairs. or removing a load). 43 established. Load Placement Load placement also plays a large part in scissors lift deflection. Scissors lifts typically experience their highest system pressure and highest stresses (and therefore the highest potential for deflection) within the first 20% of total available vertical travel (from the fully lowered position). the resulting lift movement (deflection) is 5 times the change in oil column height in the hosing. often results in poor roller tracking.e. in no particular order. The amount of . as well as lower system pressures. at lower. working capacities. in addition to platform movement due to deflection. loads should not be transferred over the sides of a raised scissors lift. to achieve high vertical lifting forces with mechanical actuators. Second. Use Mechanical Actuators in lieu of Hydraulic Actuators Although it is more difficult. it is critical to design the conveyor or transfer system to ensure that these elevations are above the scissors lift’s “critical zone” of the first 20% of the lift’s available travel. Ensure that the Base Frame is Lagged Down and Fully Supported First. and more expensive. so consult the manufacturer to obtain a more specific estimate of reduction in deflection. Make it rule to only transfer over the ends of the lift – in line with the scissors legs. or is otherwise capable of withstanding this edge loading without risk of the platform tipping up or losing contact with the rollers. welded. Minimize Potential for Air Entrapment Scissors lift manufacturers provide an approved method of “bleeding” entrapped air from a new or repaired hydraulic system which may have had air introduced. Limit or Eliminate Hosing Flexible hose lengths should be limited wherever possible and replaced with pipe or mechanical tubing as practicable to minimize or eliminate swell as the system pressure fluctuates. It is much more difficult to control deflection when the load is not shared equally between the two scissors leg pairs. Next. or fixed. Refer to the O&M manual for this procedure. Base frames that are not bolted. if possible. base frames should be adequately attached to the surface on which they are mounted. Transfer Loads Over Fixed End of the Platform First. bases must be rigidly supported beneath the entire perimeter . and then safely cracking open fittings near high spots in the system where air accumulates. load transfer should be made over the hinged. they do eliminate the issue of fluid compressibility and provide a more accurate and repeatable means of achieving – and holding – a desired transfer elevation. Avoid Transfer of Loads within First 20% of Lift’s Travel To minimize stresses and deflection at transfer elevations. 44 this reduction varies depending on the lift’s design. or otherwise attached to withstand the upward forces created by eccentric loading of the platform will contribute to deflection by bending or moving while resisting such forces. This usually involves operating an empty lift through multiple cycles. overhung end of the platform – provided the platform is equipped with “trapped” rollers. end of the lift platform to avoid placing concentrated loads on the less supported.  Generally they are designed to lift fairly light loads and so cannot be used to elevate vehicles.8 TYPICAL APPLICATIONS:  A hydraulic pallet lift is a mechanical device used for various applications for lifting of the loads to a height or level. there is always a chance that it matters greatly.  Elevated work platforms are mechanical devices that are used to give access to areas that would previously be out of reach. 80% less than the 5:1 ratio experienced normally. and mounted beneath the scissors lift deck or an adjoining fixed landing. Platform Locking Pins When there is no alternative to transferring loads over the sides of a lift. These pins can be manual or powered. Use Vertical Acting Actuators in lieu of Horizontal Mounts Some permanent installations may accommodate actuators which are mounted vertically beneath the lift instead of horizontally inside the lift structure. generators or pieces of architecture for which a crane would more likely be used. Vertical orientation of the actuators provide a 1:1 ratio of lift travel to actuator stroke instead of the 5:1 ratio normal with horizontal mounting of the actuators inside the scissors. consider using platform locking pins.1accurately points out that “It is the responsibility of the user/purchaser to advise the manufacturer where deflection may be critical to the application. and then retracted before the lift can be operated again. 45 of the frame in order to withstand without deflection the four point loads imposed upon the frame from above by the four scissors legs – (2) moving roller points and (2) fixed hinge points. The pins are extended into receivers located in the mating elevated structure during load transfer.7 Summary On Deflection- Deflection is a normal and expected characteristic of industrial scissors lifts. or whenever lift deflection must be held to near zero in any transfer orientation. This means a 1:1 ratio of lift deflection to actuator compression. .” Though deflection is easier to qualify than it is to quantify. Most are powered either pneumatically or hydraulically. The most common type is the articulated Elevated Work Platform. there are industry best practices which can be applied to reduce the impact or amount of deflection being experienced. Vertical mounting and pushing upward against underneath side of the platform to raise the lift also eliminates the high stresses usually exerted at the actuator thrust inner leg member(s). In some cases however elevated work platforms can be designed to allow for heavier loads. (EWP) or ‘hydraulic platforms’ (and also known as boom lifts or cherry picker). 5. And though odds are that most scissors lift users have not had to concern themselves with this issue because their lifting application is fairly immune to the effects of deflection. mostly on buildings or building sites. 5. ANSI MH29. 5.2 Accordion skirt/bellows .8. 5.1 Foot control for vertical or horizontal travel Fig. 46 • Paint/Powder/Coating Application • Blast Booth/Room (Stripping & Surface Prep) • Welding/Fabrication/Assembly • Wash/Rinse (Prep) • Fall Protection/Safety/Ergonomics • Maintenance/Inspection • Material Handling/Loading Bays • Clean Room 5.1 STANDARD LIFT OPTIONS : Fig. 5.4 Platform roll-outs/extensions Fig.5.. 47 Fig.5 Electric/hydraulic power unit .3 Explosion proof lights and switch (TK only) Fig.5... 48 Fig.6 Rubber bumper stops (rail guided lifts only) 5.5.Custom lift systems for specific applications are as shown below- .10 CUSTOM DESIGN.9 COMMON INDUSTRIES SERVED: • Aircraft & Aerospace • Agricultural & Construction Equipment • Electrical Power and Distribution • Light Rail and Bus Manufacturing/Maintenance • Military Equipment • Rail Car and Locomotive Manufacturing/Maintenance • Rail Systems • Transit Authorities • Trucks and Recreational Vehicles 5. 8 Dual Mast Work Platform Fig.7 Large Work Platform Fig.5.9 Overhead Lift System .5. 49 \ Fig... 5. Fig.12 Multi-Axis Blast Booth Lift .11 Multi-Axis Extended Reach Lift Fig.5.10 Multi-Axis Paint Booth Lift Fig..5.Standard and custom multi-axis personnel lifts..5. 50 Multi-Axis Lifts.. Utilized in applications from wash. or to access work along a fixed area of travel (rail guided lift). CASE STUDY AND DESIGN METHODOLOGY- In a typical production plant. where the lift needs to be moved around to perform work (manually positioned lift). more ergonomic and cost effective solution for positioning workers. Those platforms are called skillet and.Lifting car through Scissor Lift The aim of this work is to design a new lifting table with the cheapest actuation commercially available. Fig.. it is possible to observe. the platforms on which the operator can stay and proceed to assembly. A skillet has a tubular structure that supports any elements needed to move the platform and to make the operator able to carry out properly the assembly operations. and assembly. 5. along the line of handling. thanks to their versatility and modularity. 51 Scissor Lifts & Work Platforms: Scissor lifts typically operate in two axis of movement and are designed for applications where people and material need only up and down travel (stationary lift). . welding. scissor lifts offer a safer. to metal blasting. they may be used in different quantities according to the production rate. in order to replace two commercial lifting tables actually in use on the skillets along the handling line. prep and paint. Systems utilize pneumatic/hydraulic power units for hazardous areas such as paint applications or can be configured with electric/hydraulic power units for non- hazardous environments.13. with times established by the product manufacturing. simple and able to respond to the functional requirements. 2. It can also lift heavier loads. The scissor lift can be designed for high load also if a suitable high capacity hydraulic cylinder is used. but has a low operating cost. The main constraint of this device is its high initial cost. The shearing tool should be heat treated to have high strength. the scissor lift can lift a load of 1. Savings resulting from the use of this device will make it pay for itself with in short period of time and it can be a great companion in any engineering industry dealing with rusted and unused metals. The hydraulic scissor lift is simple in use and does not required routine maintenance. 1. 52 CHAPTER. 3. but has a low operating cost. Savings resulting from the use of this device will make it pay for itself with in short period of time and it can be a great companion in any engineering industry dealing with rusted and unused metals. . 5.1 CONCLUSION The design and fabrication of a portable work platform elevated by a hydraulic cylinder was carried out meeting the required design standards. The shearing tool should be heat treated to have high strength. It can also lift heavier loads.5 – 2 tons. It can also lift heavier loads. 4. The hydraulic scissor lift is simple in use and does not required routine maintenance. The design and fabrication of a portable work platform elevated by a two hydraulic cylinders was carried out successfully meeting the required design standards. Savings resulting from the use of this device will make it pay for itself with in short period of time and it can be a great companion in any engineering industry dealing with rusted and unused metals. The scissor lift can be design for high load also if a suitable high capacity hydraulic cylinder is used. but has a low operating cost. For the present dimension we get a lift of 5 ft. The main constraint of this device is its high initial cost. The shearing tool should be heat treated to have high strength. The portable work platform is operated by hydraulic cylinder which is operated by a motor. The portable work platform is operated by hydraulic cylinder which is operated by the hand pump.6 CONCLUSION 6. The scissor lift can be design for high load also if a suitable high capacity hydraulic cylinder is used. The hydraulic scissor lift is simple in use and does not required routine maintenance. The main constraint of this device is its high initial cost. 1 Performance Analysis- Maximum height attained = 46.1. Thus. hydraulic pressure system. It is also suggested that the spindle and 40 nut should not be exposed to moisture so that it would not be susceptible to corrosion thereby reducing its strength and toughness. .20 INR Nut.100 INR Stationary and measurement.8 cm increase) Maximum load successfully tested = 5-6 kgs 6.2 RECOMMENDATIONS- It is recommended that the screw and thread should be lubricated frequently so as to reduce the amount of effort required to operate the system.8 cm (21. which should make it commercially available and attractive. 53 6.200 INR U Clip. its wide application in industries. This also reduces the amount of wear between the screw and the nut.70 INR L coupler. maintenance of huge machines.5000 INR L beam.600 INR Other expenditure. for lifting of vehicle in garages.2 Apparatus Budget- Cylinder. screw washer. and for staking purpose. Hence. bolt. 9000 INR 6.300 INR Traveling expenditure.500 INR Rectangular bar. The device affords plenty of scope for modifications for further improvements and operational efficiency. it is recommended for the engineering industry and for commercial production.300 INR Funner blade.1.1000 INR Total. 6.200 INR Furniture.5000 INR Screwed rod.Approx. K. 21/04/2011 . R.. R. [4]. Barsel. John Wiley & Sons. [6]. 2006.Autoquip. [2]. ‘Aerial Lift Safety: Operating Requirements’ retrieved online: 21/04/2011. ‘Mechanical Engineering Science’. 2nd Edition. WCB Standards: A324 Forklift Mounted Work Platforms Retrieved Online 21/04/2011. K. [8].S. Eurasia Publishing House.K. retrieved online at www. and Gupta. R. 54 CHAPTER-7 REFERENCES [1]. 21/04/2011. Gupta. John Wiley & Sons. [3].. ‘Theory of Machines’. Understanding Scissor Lift Deflection. Chaurasia Publishing House.. 2nd Edition. Wikipedia. R.. R. 1998. Hedge. ‘Fluid Mechanics’.K...com. Elevating Work Platform. Franklin Mill. 4th Edition. 1995 [5]. Retrieved online at www. 3rd Edition. 2006. Ltd. Ltd. ‘Machine Design’. [7]. Khurmi.