The main parts of the automated motorized object lifting jack are as follows:
- DC motor: an electric motor is a machine which converts electrical energy into mechanical energy. Its action is based on the principle that when a current carrying conductor is placed on a magnetic field, it experiences a magnetic force whose direction is given by Fleming’s left hand rule. When a motor is in operation, it develops torque. This torque can produce mechanical rotation. D.C motors are also like generators classified into shunt wound or series wound or compound wound motors.
- Lead Screw: A lead screw is a portable device consisting of s screw mechanism used to raise or lower the load. The lead screw can be short, tall, fat or thin depending on the amount of pressure they will be under and space that they need to fit into. It is made of various types of metals but the screw itself is made of lead. A large amount of heat is generated in it and long lifts can cause serious overheating. To retain the efficiency, it must be used under ambient temperatures, otherwise lubricants must be applied. These are oil lubricants intended to enhance the equipment’s capabilities. Apart from proper maintenance, to optimize the capability and usefulness of lead screw it is imperative to employ it according to its design and construction.
- Batteries: In isolated systems away from the grid, batteries are used for storage of excess solar energy which can be converted into electrical energy. In fact for small units with output less than one kilowatt, batteries seem to be less the only technically and economically available storage means. Since both the photovoltaic system and batteries are high in capital costs , it is necessary that the overall system be optimized with respect to available energy and local demand pattern.
- Ball bearing: This is a type of rolling element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support and radial and axial loads. It achieves this by using atleast two races to contain the balls and transmit the loads through the balls.
- Spur gears: These are designed to transmit motion and power between parallel shafts which are the most economical gears in the power transmission industry. Two types are used in this model:
- Internal spur gear These spur gears are turned inside out. In other words, the teeth are cut into the inside diameter while the outside diameter is kept smooth. This design allows for the driving pinion to rotate internal to the gear, which, in turn, allows for clean operation. Intended for light duty applications, these are gears always available only in brass. When choosing a mating spur gear always remember that the difference in the number of teeth between the internal gear and pinion should not be less than 12 or 15.
- External spur gear Perhaps the most often used and simplest gear system, external spur gears are cylindrical gears with straight teeth parallel to the axis. They are used to transmit rotary motion between parallel shafts and the shafts that rotate in opposite directions. They tend to be noisy at high speeds as the two gear surfaces come into contact at once.
- Limit Switch It is a switch operated by the motion of a machine part or presence of an object. It is used for control of a machine, as safety interlocks, or to count objects passing a point. It is a electromechanical device that consists of an actuator mechanically linked to a set of contacts. When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection. It is used in a variety of applications and environments because of their ruggedness, ease of installation, and reliability of operation. It can determine the presence or absence, passing, positioning and end of travel of an object. It was first used to define the limit of travel of an object, hence the name ‘limit switch.’
- Control switch It is used in order to start or stop the entire operation of the object lifting jack. The type of switch that is used is known as a toggle switch. The toggle switch is a class of electrical switches that are manually actuated by a mechanical lever, handle, or rocking mechanism. This is designed to provide the simultaneous actuation of multiple sets of electrical contacts, or the control of large amounts of electric current or mains voltages. 1.3.8 Control cables These are used in order to connect the battery to the motor and the switch. 1.3.9 Base and Frame A base for the entire set-up has also been made. The motor is mounted on an inverted U shaped support frame. Ball rollers are attached to four ends of the base for movement and are electrically controlled by switch.
The load on the screw is the load which is to be lifted W, twisting moment M, between the screw threads and force F at the handle to rotate the screw. The load W is compressive in nature and induces the compressive stress in the screw. It may also lead the screw to buckle. The load F produces bending and it is maximum, when the screw is at its maximum lift. The screw also experiences twisting moment due to F, the hear stress is also induced in the screw due to the twisting moment between the threads of screw and nut.
Step I : Problem Specification
It is required to design an object lifting jack for supporting the machine parts during their repair and maintenance. It should be a general purpose jack with a load carrying capacity of 50 KN and a maximum lifting eight of 0.3m. The jack is so operated by means of a D.C motor.
Step II : Selection Of Materials
- The frame of the object lifting jack has complex shape. It is subjected to compressive stress. Grey cast iron is elected as the material for the frame. Cast iron is cheap and it can be given any complex shape without involving costly machining operations. Cast iron has higher compressive strength compared with steel. therefore, it is technically and economically advantageous to use cast iron for the frame.
- The screw is subjected to torsional moment, compressive force and bending moment. From strength consideration, EN8 is selected as material for screw.
- There is a relative motion between the screw and the nut, which results in friction. The friction causes wear at the contacting surfaces. When the same material is used for these two components, the surfaces of both components get worn out, requiring replacement. This is undesirable. The size and shape of the screw make it costly compared with the nut. The material used for the nut is stainless steel.
Step III : Design of object lifting jack
The object lifting jack is an intermittently use device and wear of threads is not an important consideration. Therefore, instead of trapezoidal threads, the screw is provided with square threads. Square threads have higher efficiency and provision can be made for self-locking arrangement. When the condition of self-locking is fulfilled, the load itself will not turn the screw and descend down, unless an effort in the reverse direction is applied.
- It is very fast working
- No manual work-out needed
- Very effective for heavy lift
- Cost effective
- Low cost
- Small in size
- Light weight