CONTENTSContents Sr. No. 1 2 3 4 5 INTRODUCTION 1.1 Necessity / Application of scissor lift 1.2 Literature survey PROPOSED WORK 2.1 Proposed project 2.2 List of components and function 2.3 Working principle 5 6 7 8 8 9 10 2.4 Technical Parameter 12 2.5 Main components and design 2.5.1 Worm and worm Gear 13 13 2.5.2 Rack and Pinion 14 2.5.3 Scissor linkages 2.6 Drafting and 3D model 2.7 Calculations 2.8 Estimated time required 15 16 22 26 2.9 Cost 26 Risk management Advantages and disadvantages Feasibility study 29 5.1 Economic feasibility 5.2 Technical / operational feasibility 6 7 Page No. Conclusion Future Scope 30 31 31 31 32 33 1 LIST OF TABLES Title Table No. Page No. 1. System Components 10 2. Technical Parameters 13 3. Time Required 26 4. Cost of material 27 5. Cost of standard parts 27 6. Miscellaneous Cost 28 LIST OF FIGURES Figure No. Title Page No. 1. Prototype of scissor lift 10 2. Worm & Worm Wheel 13 3. Rack & Pinion 14 4. Scissor Linkages 15 5. 3D model 6. Link Design 23 7. F.B.D 24 16-22 Abstract Scissor lifts (Aerial work platforms in general) are generally used for temporary, flexible access purposes such as maintenance and construction work or by firefighters for emergency access, which distinguishes them from permanent access equipment such as elevators. They are designed to lift limited weights. The contraction of the scissor action can be hydraulic, pneumatic or mechanical (via a lead screw or rack and pinion system). 2 The main objective of scissor lift is to save time required in building platforms or temporary lifts. Once the lift is constructed according to requirement, much time is saved .Its portability can enable the workers to use it at various working areas whenever needed . Considering the cost of lift it is suitable and more productive than making temporary platforms at construction sites with help of bamboo sticks or other materials. Maintenance cost is almost negligible as only lubrication is required for components. 1. Introduction A scissor lift is a type of platform that can usually only move vertically. The mechanism to achieve this is the use of linked, folding supports in a criss-cross”X” pattern, known as a pantograph (or scissor mechanism). The upward motion is achieved by the application of pressure to the outside of the lowest set of supports, elongating the crossing pattern, and propelling the work platform vertically .Scissor lifts (Aerial work platforms in general) can generally used for temporary, flexible access purposes such as maintenance and construction work, which distinguishes them from permanent access equipment such as elevators. 3 Platform used for painting a wall at a certain height. In emergency cases while extinguishing fire or by firefighter As a vertical lift for supplying material or things on a certain height or upper storey. o Eg.1Necessity / Application of scissor lift It can be used at construction sites for temporary or portable platform. To elevate workers and their tools to a desired height for a job. 4 . 1. 2.1. and mechanical lifts. They can be operated with hydraulics. Grove Manufacturing. or mechanically via screws or a rack-and-pinion system. he formed a partnership with two friends. During a stop at the Hoover Dam. compressed air connectors. 2.1. in 1967 he and his wife headed out on a road trip. Aerial work platforms eventually began being designed with a variety of additional features. bought a small metal fabrication business. scissor lifts. and various other adaptations for tools. As for John L. The aerial work platform invention is widely credited to John L. Many are now equipped with electrical outlets. a company called Selma Man lift introduced a model in 1966. The company was named JLG Industries Inc. Grove witnessed two workers electrocuted while working on scaffolding.. requiring an external force to move them. or mounted to a vehicle for movement. who was an American inventor and industrialist. Proposed Work 5 . There are three main types of aerial work platforms: boom lifts. Grove.2 Literature Survey. However. self-propelled with controls at the platform. pneumatics. When Grove returned home from his trip. They are either unpowered units. Through this “tragic event” John Grove saw a large untapped market for a product that could put workers in the air more safely to perform construction and maintenance tasks. even before JLG's first model. and with the aid of 20 employees it released its first aerial work platform in 1970. and began designing concepts for the aerial work platform. after selling his previous business. Grove. 2. shaft in a slot and the lift scissors (X linkages) . The rack moves forward and this drives the main scissor mechanism at its bottom linkage. 2. The worm wheel and pinion are attached to a common shaft and thus. the pinion gets driven by the rotating worm wheel. Rotation of handle attached to worm/worm wheel drives the system. rack and pinion. Thus the rotary motion to worm is converted into reciprocating / linear motion by using a pinion which moves the rack.1 Proposed Prototype The machine consists of a worm and worm wheel.2 List of components and its function Name Function Scissor lift platform Scissor linkages Rack and pinion arrangement Platform to be elevated To provide elevation to platform To transfer power from worm wheel to scissor linkages Worm and worm wheel To transfer power from hand lever to rack with self-locking mechanism Hand lever To provide Mechanical power 6 . 3 Working Principle of prototype 7 .2. As shown in image the handle is provided to provide clockwise rotational motion to the worm gear. The forward linear motion of rack results in forcing the scissor lift in upward direction. but in an axis which is perpendicular to the axis of a worm. The rotational motion of the worm is transmitted to the worm wheel as rotational motion. The worm rotates the shaft attached with it. The rotational motion of the handle is transmitted to the rotational motion in the same axis of worm as they are attached along the same axis. 8 . which in turn rotates the pinion in the same sense as the worm. The pinion rotates in a clockwise direction which moves the rack in forward linear motion. This upward motion is desired to raise the height of a load for any application. 2.4 Technical parameter (Prototype) Lifting height 1.8 ft Minimum height 100 mm Length 1000mm Breadth 300mm 9 . The anticlockwise rotation of handle leads to the downward motion of scissor mechanism. This downward motion is required when a load is to be lowered.The opposite happens when the handle is rotated in anti-clockwise direction. As the load increases the effort required to raise the load is also increasing. 4Main Components and their design 2.1 Worm and worm gear 10 .5.25Kgs 2.Net weight 20. Like other gear arrangements. The image shows a section of a gear box with a worm gear driven by a worm. one of the six simple machines.a) Worm & Worm Wheel A worm drive is a gear arrangement in which a worm (which is a gear in the form of a screw) meshes with a worm gear (which is similar in appearance to a spur gear).5. 2. A worm is an example of a screw. The two elements are also called the worm screw and worm wheel.2Rack and pinion 11 . or the worm drive as a unit. a worm drive can reduce rotational speed or transmit higher torque. the worm gear. The terminology is often confused by imprecise use of the term worm gear to refer to the worm. rotational motion applied to the pinion causes the rack to move relative to the pinion.5. thereby translating the rotational motion of the pinion into linear motion.3 Cross / Scissor linkages 12 .a) Rack & Pinion A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack". 2. elongating the crossing pattern. Extension is achieved by applying pressure to the outside of a set of supports located at one end of the mechanism. mechanical or simply muscular means. This can be achieved through hydraulic. pneumatic.6 Drafting and 3D model 13 . folding supports in a criss-cross 'X' pattern. 3.a) Scissor Linkages A scissors mechanism uses linked. 14 . 15 . 16 . 17 . 18 . 19 . Angle (θ) = 110o Min.5 mm Total length of material required (l' )=2× AB=1465 mm For Double Stage:- 20 .2.7 Calculations Link Design: Assumptions Max. Height (AC) = 600 mm 10o< θ < 110o Max.0o We’ve to find Length of Link (AB) =? If we design the scissor for single stage:- In OO’A θ O' A sin = 2 OA O' A= OA= AC 600 = =300 mm 2 2 AB 2 AB=732. Angle (θ) = 10. FBD of Link: 21 .4 mm l )=4 × AB=1425.6 mm Total length of material required ¿ < 1465 mm In case of double stage we can save material so we’ve chosen to go for double stage scissor mechanism.O' A= AC =150 mm 4 ∴ AB=356. F y × 2 cos θ+ F x × 2 sin θ− 2 l l ×l cos θ=0 W ∑ M E=0 . −W + R y 1 + F y =0 2 ∑ F x=0.−R x1 +F x=0 l l W ∑ M B =0 . R y 1 × 2 cos θ−R x 1 × 2 sinθ + 2 ×l cos θ=0 When W = 50 N Θ Fx Fy Rx1 Ry1 By assuming θ we get these values: 10o 20o 30o 1131 550 346 200 200 200 1131 550 346 0 0 0 40o 238 200 238 0 50o 168 200 168 0 60o 115 200 115 0 22 . Solution: ∑ F y =0. Mechanism study 15 3. Design study 2. Manufacturing 20 5.No Task 1. Testing 5 6.*Values approximated to near values. Eliminations of errors and faults 10 Cost Approximately 11000-12000 Rs 23 . All the forces are expressed in Newtons (N).8 Estimate Time required Sr. 2.9 No.of days 15 2. Design 30 4. Cost Estimation Cost of Material: Sr no 1 Name of Material Qty Material Cost of material manufacturing Scissor lift Arms 6 MS 3000 2 Lifting platform 1 MS 1200 3 Base Plate 1 MS 1200 4 Bars 6 MS 900 Laser cut & Drilling Laser cut & Bending Laser cut & Bending Machining 5 Handle 1 MS 150 6 Shaft 1 MS 230 Total 6680 Machining Cost of Standard parts: Sr no 1 2 3 4 Part Rack and pinion Worm and wormwheel Rack support Pinion support blocks Quantity Cost 1 1 1 2 Total 1500 1150 150 450 3250 Miscellaneous Costs: Sr no 1 2 3 Details Fasteners Accessories Painting Cost 300 1100 150 24 . 25 .4 Transport Total 250 1800 3. Risk management While operating scissor lift there are chances of sudden collapse of platform due to overload. It doesn’t rotates reversely unless it is operated by handle. To eliminate this risk a locking system should be provided which can stop motion of linkages when in locked position In prototype as worm and worm wheel is used. Periodically lubrication is to be done for smooth working.This mechanism provides a self-locking system which makes the scissor lift completely safe for use. Effort required to lift material increases with increase in weight. Disadvantages: Scissor lift occupies substantial floor space which makes it unsuitable for smaller applications. 26 . Advantages and Disadvantages Advantages: • The scissor lift has a unique mechanism which uses worm and worm wheel . Height of the elevation is limited. this mechanism has to be driven to bring the platform back down. • Unlike the hydraulic systems.4. This gives us the opportunity to use this lift as a machine part for accurate elevation. Maintenance cost is almost negligible as only lubrication is required for components. Conclusion As a whole. it has been concluded that this System if very beneficial according to economic as well as technical point of view. Hence the system is feasible. Only single worker is required to operate the lift and thus it saves man power as compared to temporary platforms which need labors while being construct. 27 .1 Economic feasibility Considering the cost of lift it is suitable and more productive than making temporary platforms at construction sites with help of bamboo sticks or other materials.5. Once the lift is made there is no wastage of time as compared to time required for temporary platforms in assembly and disassembly while shifting them at other work stations.Feasibility study 5.2 Technical / operational feasibility There is no need of external support for the platform as the linkages itself work as supporters. 6. 5. 28 . • • Hydraulic actuators can be used for heavy applications. • Number of plates in the scissors can be increased to improve the height to number of rotations ratio.Future Scope • We can increase contact force between shaft and pinion so as to prevent slipping and allow lifting of larger weights.7. 29 . \ 30 . 31 . 32 .