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fabrication of double scissor car jack pdf

INTRODUCTION
Screw type mechanical jacks were very common for jeeps and trucks since World War II vintage. These jacks were activated by using the lug wrench as a handle for the ratchet action to the jack. Screw type jacks continued in use for small capacity requirements due to low cost of production to raise or lower the load. A control tab is marked up/down and its position determines the direction of movement and with no maintenance. The virtues of using a screw as a machine element was first demonstrated by Archimedes in 200BC with his device used for pumping water.
There is evidence of the use of screws in the Ancient Roman world but it was the great Leonardo da Vinci, in the late 1400s, who first demonstrated the use of a screw jack for lifting loads. Leonardo’s design used a threaded worm gear, supported on bearings, rotated by the turning of a worm shaft to drive a lifting screw to move the load.
With the industrial revolution of the late 18th and 19th centuries, came the first use of screws in machine tools, via English inventors such as John Wilkinson and Henry Maudsley. The most notable inventor in mechanical engineering from the early 1800s was undoubtedly the mechanical genius Joseph Whitworth, who recognized the need for precision as important in industry.
Over the next 30 years the Duff Manufacturing Company became the largest manufacturer of lifting jacks in the world, developing many new types of jack for various applications including its own version of the ball bearing screw jack.
There was a clear potential for using this technology for other applications and only 10 years later, in 1940, the first worm gear screw jack, that is instantly recognizable today, was offered by DuffNorton, for adjusting the heights of truck loading platforms and mill tables. With the ability to be used individually or linked mechanically and driven by either air or electric motors or even manually, the first model had a lifting capacity of 10 tons with a raise of 2inch or 4inch.
Various Developments in Lifting Devices are lever, screw threads, gear, hydraulics, wheels and axles.

2. DRAWBACKS OF EXISTING JACK
In the repair and maintenance of automobiles, it is often necessary to raise an automobile to change a tire or access the underside of the automobile. Accordingly, a variety of car jacks have been developed for lifting an automobile from a ground surface. Available car jacks, however, are typically manually operated and therefore require substantial laborious physical effort on the part of the user. Such jacks present difficulties for the elderly and handicapped and are especially disadvantageous under adverse weather conditions.
Furthermore, available jacks are typically large, heavy and also difficult to store, transport, carry or move into the proper position under an automobile. In addition, to the difficulties in assembling and setting up jacks, such jacks are generally not adapted to be readily disassembled and stored after automobile repairs have been completed. Car jacks must be easy to be used even by women or whoever had problem with the tire in the middle of nowhere.
In the light of such inherent disadvantages, commercial automobile repair and service stations are commonly equipped with large and hi-tech car lift, wherein such lifts are raised and lowered via electrically-powered systems. However, due to their size and high costs of purchasing and maintaining electrically-powered car lifts, such lifts are not available to the average car owner. Engineering is about making things simpler or improving and effective. Such electrical-powered portable jacks not only remove the arduous task of lifting an automobile via manually-operated jacks, but further decrease the time needed to repair the automobile. Such a feature can be especially advantageous when it is necessary to repair an automobile on the side of a roadway or under other hazardous conditions. There are also reports on car jacks which lead to a serious failures.

3. POWER SCISSOR JACK
Scissor jacks are mechanical devices and have been in use since 1930s. A scissor jack is a device constructed with a cross-hatch mechanism, much like a scissor, to lift up a vehicle for repair. It typically works in a vertical manner. The jack opens and folds closed, applying pressure to the bottom supports along the crossed pattern to move the lift. When closed, they have a diamond shape. Scissor jacks are simple mechanisms used to handle large loads over short distances. The power screw design of a common scissor jack reduces the amount of force required by the user to drive the mechanism. Most scissor jacks are similar in design, consisting of four main members driven by a power screw.
To overcome aforesaid draw backs, a power scissor jack which has a frame type design utilizing the power from the battery of the automobile has been developed and fabricated. The power screw of the jack will be driven by the power gun connected to the battery parallely and at the same time the developed jack can be safely used during night time with an attachment of low wattage LED bulbs. The jack is embedding 2 trunions to ensure smooth and uniform lifting and lowering of jack.

4. FABRICATION
The fabrication process started with identification of suitable materials for various parts.
(a) Top Arms and Bottom Arms
As per design calculations the cross section of arms is selected as Channel Section

5. CONCLUSIONS
In this work a power scissor jack which can be operated by a power gun has been designed and fabricated. The jack has been designed to a pay load of 4.5kN. The salient features of the present fabrication are elimination of human effort to operate the jack, through a simple electrical device which can be actuated by a 12 V battery and provision of a light source to facilitate convenient operation during night time. The assembly of the component can be achieved in 100 minutes. Another feature of the unit is provision of two trunions on both the sides of the jack to ensure jerk free operation. The elements which are useful are readily available commercially for easy replacement of failed components, if required.