24-07-2014, 10:26 AM
Portable Powered Screw Jack Unit
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ABSTRACT
This report analyses the modification of the existing motor screw jack by incorporating an electric motor in the screw in order to make load lifting easier. In this modified design, the power screw is rotated through its connecting gear with the pinion gear when electrical power flows through the cigarette lighter receptacle connected to the motor, plugged to the automobile 12 V battery source to generate power for the prime mover (motor), which transmits its rotating speed to the pinion gear meshing with the bigger gear connected to thepower screw to be rotated with required speed reduction and increased torque to drive the power screw. The significance and purpose of this work is to modify the existing car jack in order to make the operation easier, safer and more reliable in order to reduce health risks especially back ache problems associated with doing work in a bent or squatting position for a long period of time. The modified car jack is easy to use by pregnant women or whoever had problem with the vehicle tyres along the road. The designed motorised jack will also save time and requires less human energy to operate. The design when adopted will effectively curb the problems associated with Ergonomics - which is a fundamental concept of design proces.
INTRODUCTION
Doing work in a bent or squatting positionfor a period of time is not ergonomic to human body. It gives back ache problem in due of time. Amechanical jack is a device which lifts heavy equipment and vehicles so that maintenance can be carried out underneath. [Budynas, andNisbett, 2008].Car jacks usually use mechanical advantage to allow human being to lift a vehicle. There are two types of automotive car jacks: Hydraulic and Screw types. Most car jacks that are included with cars are screw types. These two categories also have many subcategories of jacks. Hydraulic jacks have theshape of a bottle, or are built into a trolley (the "floor jack") or the like. By operating the handle, which is a lever (a simple machine), fluid is compressed and routed to an actuating cylinder. This results in lift.
Other examples of hydraulic types are hydraulic jack,bottle jack, floor jack, friction jack, and racketing jack. A jackscrew is a type of jack which is operated by turning a lead screw. It is also known as a screw jack, and is commonly used as car-jacks. In the case of a screw jack, a small force applied in the horizontal plane is used to raise or lower large load. [Khurmi and Gupta, 2005]. Of the screw-type mechanisms, there are scissor jacks, common in newer cars, and bumper jacks, common in older cars. A jackscrew's compressive force is obtained through the tension force applied by its lead screw. An Acme thread is most often used, as this thread is very strong and can resist the large loads imposed on most jackscrewswhile not being dramatically weakened by wear over many rotations.
An inherent advantage is that, if the tapered sidesof the screw wear, the mating nut automatically comes into closer engagement, instead of allowing backlash to develop [Rajput, 2007].These types are self-locking, which makes them intrinsically safer than other jack technologies like hydraulic actuators which require continual pressureto remain in a locked position. The correct projection of a screw thread is tedious and takes a considerable time, so threads are shown conventionally onengineering drawings. [Parker and Pickup, 1976]. Most jackscrews are lubricated with grease. Ball screws are a more advanced screw mechanisms thatuses a recirculation-ball nut to minimize friction and prolong the life of the screw threads. The thread profile of such screws is semi-circular to properlymate with the bearing balls.