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• 'Aizat Hafiz'

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Literature Review Introduction A motorized lift table is a device functions to lower and raise goods or/and person which usually are used to raise heavy and large distance relatively for small distance. Typically, a motorized lift table operated by using scissor mechanism which is can contract and retract. Lift table is ergonomics to the user when they can adjust it to the desired height when operated. (Lift table, n.d.).The application for lift table can be found mainly in automotive industry, patient bed, heavy industry and many more. History Starting 1950s, hydraulic scissor lifting tables became the most used design by the manufacturer of automotive industries. By starting with simple design, the lift table has undergo invention from time to time until now. Table 1 retrieved from (heckert-engineering) company can briefly describe how the invention evolved. Year

Description

1950

Picture

Advantages

Disadvantages

hydraulic scissor

Simple

- needs oil

lifting tables

design

-piston sealing needs

became the

maintenance

most used design

- no constant level

"hydraulic system has won the race" 1980

1st ball screw

constant

- complicated design

tables appear to

level

- high forces in the

fulfill the

- no oil

lifting system

new skillet systems

reduced

- speed is “not

as conveyor lines

forces in

constant”

appear :

lifting system

- large amount of

new requirements "keep the level" "no oil" 1985

bearings

"development of ball screw tables" 1990

1st “push chain”

- constant

- chain with much

appears, in France

speed

wear and tear

only

- a high torque geared

“search for a

motor is necessary

better solution than ball screw” “constant speed” 1994

1st ball screw table

- constant

ball screw needs

with cam

speed

maintenance

"constant speed”"

- less power

- high inner forces

required

because of cantilever

- small

situation

geared motor 1999

1st timing belt table

- constant

-high inner load because

"low

speed

of cantilever situation

maintenance"

- low maintenance - less power required

2001

1st flat belt table

- constant

-high inner load because

speed

of cantilever

- low

situation

maintenance - less power required

2002

1st spiral lifter

constant

- at least 2 cylinders

"mechanical

speed

necessary to stabilize

driven cylinder"

- direct

the platform

carried load 2002

different solutions

none

in flat belt design

-no constant speed - more power required - safety against breakage < 6

2003

advanced flat belt

constant

table

speed

additional

- low

deflection pulley

maintenance

None

“at scissor

- less power

leg”

required - low inner forces - safety against breakage > 8

2003

different solutions

none

in flat belt design

no constant speed - more power required - safety against breakage < 6

2004

advanced push

advanced

- at least 2 chains

chain table

chain

necessary to stabilize

with reduced

the platform

wear out Table 1

Principle of Operation Scissor Mechanism According to (Germany Patent No. 5,694,864, 1997), a scissor mechanism is device used to extend or retracted position a platform by mechanical means. In scissor mechanism having two scissor arm which pivotally linked each other. The term scissor come from the mechanism used which is with construct linked, folding in a cross „X‟ pattern. The displacement achieves by applying force to one of the support arm. The support arm mounted on slider joint is then roll horizontally resulting an elongation of the crossing pattern. Usually the arm is attached with its coupler with the shaft and bearings. The shaft is attached along with driving member like motor and hydraulic. The shaft functions to transmit power and move the two members of scissor in parallel so that the platform can be elevated or lower evenly. (Patent No. 6679479, 2004)

Base Chassis Most small lifting device are not attached to the ground and therefore they are portable. This means that chassis or base are needed to support the lifting mechanism. The chassis can be as simple as a base or foot mounted to one end of the lifting device as seen. Common mounting base is designed

larger footprint to make lifting device more stable and reduce its ground pressure. To allow for movement simple wheels are commonly engaged along with chassis. (Alex Gibbs) Caster wheels are commonly used in situations where manoeuvrability and durability are priorities. A caster wheel is a wheel that pivots around an axis that is off set to the wheels contact point with the ground, this allows the wheel to track straight when pushed in a straight line however it can still pivot freely when a lateral force is applied . (Patent No. 383787, 1994) Belt and Pulley System A pulley is a wheel work usually with belt to support belt movement along the circumference. Pulleys are used in a variety of ways to lift loads, apply forces, and to transmit power. Meanwhile, belt and pulley system is characterised by two or more pulleys in common to a belt. This allows for mechanical power, torque, and speed to be transmitted across axles. A belt drive is analogous to that of a chain drive, however a belt sheave may be smooth (devoid of discrete interlocking members as would be found on a chain sprocket, spur gear, or timing belt) so that the mechanical advantage is approximately given by the ratio of the pitch diameter of the sheaves only, not fixed exactly by the ratio of teeth as with gears and The example of uses of belt pulley is in agricultural tractors in the early 1950s .It had limited use as the tractor and equipment being powered needed to be stationary. It has thus been replaced by other mechanisms, such as power take-off and hydraulics. (Pulley, n.d.) References Alex Gibbs, R. H. (n.d.). Belly Pan Jack. Saluki Engineering Company. heckert-engineering. (n.d.). A Brief History of Scissors Lifting Tables Used In Automotive Industries. etrieved ecember 1 , 1 , from www.heckertengineering.com fileadmin rief istory T.pdf Langewellpott, E. (1997, December 9). Germany Patent No. 5,694,864. Lift table. (n.d.). Retrieved December 12, 2013, from http://en.wikipedia.org/wiki/Lift_table Pulley. (n.d.). Retrieved December 14, 2013, from http://en.wikipedia.org/wiki/Pulley U., F. (1994, Feb 1). Patent No. 383787. Watkins, D. (2004, January 20). Patent No. 6679479.