08-01-2013, 01:02 PM
MOTORISED SCREW JACK
1MOTORISED.doc (Size: 310 KB / Downloads: 39)
INTRODUCTION
A screw jack is a device used to fully or partially lift a vehicle or other object off the ground. Depending on their size, these devices can be used to raise the corner of a vehicle, or to lift it several feet in the air so workers can access the bottom of the vehicle. Screw jacks are often found in machine shops, auto repair facilities and in the automotive racing industry. Many vehicles also have a screw jack included with the spare tire kit, so drivers can repair a flat tire more easily. Very large screw jack systems are even used to lift houses for foundation repair or replacement.
These devices are typically made of steel, lead or lightweight stainless steel. They are available in two basic varieties, scissor jacks and “worm gear” screw jacks. Another type of jack design, based on hydraulic principles, is primarily used in industrial and manufacturing facilities and does not operate like a screw jack.
Scissor screw jacks are the most basic model, and are typically used for flat tire repair. They have a scissor-like design that is operated using a large lead screw. The bottom of the jack rests on the ground while the top fits under the body of a car. A screw is inserted in the center of the scissor system and is turned to the right to raise the jack and lift the car. After the tire is replaced, the screw is turned to the left to lower the car back to the ground.
Worm gear screw jacks have a body shaped like a very large screw. At the top is a lifting platform, which is used to support a vehicle, house or other object. As the jack is operated using a ratcheting motion, the lifting platform is raised up the height of the screw-shaped body. A worm gear screw jack typically offers a greater level of precision and consistency than a scissor jack, and may also be capable of lifting heavier loads. This device is also known as a "machine screw jack."
DESCRIPTION
In this project we are presenting the prototype of motorized screw jack. To design its structure aluminum sheet is used. It is a combination of bed, cover, platform, a large screw jack etc.
Bed, it is actually the base of the screw jack over which whole structure is designed. Two slant plates of aluminum are used to connect the base with the lifting platform. And the width of platform is equal to the distance between these two plates (you can see it in picture also).
Now to make motion in the screw so that lifting can be done high torque motor is used which is connected with it by the help of coupler.
Here to control the DC Motor we have used the remote to control the motion of the jack.
COMPONENTS DETAILS
1. DC MOTOR
2. Motor driver
3. RF TX/RX
4. Encoder/decoder
DC MOTORS:
Basically, the motors can be categorized into two parts, AC and DC. The basic principle of operation is almost same. In any electric motor, the operation is based on simple electromagnetism. A current carrying conductor generates a magnetic field; when this is placed in an external magnetic field, it will experience a force proportional to the current in the conductor, and the strength of the external magnetic field. The internal configuration of a DC motor is designed to harness the magnetic interaction between a current carrying conductor and an external magnetic field to generate rotational motion.
DC Motors can be classified as:
Externally Excited DC Motor:
This type of DC motor is constructed such that the field is not connected to the armature. This type of DC motor is not normally used
Shunt DC Motor:
The motor is called a "shunt" motor because the field is in parallel, or "shunts" the armature. This type of motor runs practically constant speed, regardless of the load. It is the type generally used in commercial practice and is usually recommended where starting conditions are not usually severs. Speed of the shunt-wound motors may be regulated in two ways: first, by inserting resistance in series with the armature, thus decreasing speed: and second, by inserting resistance in the field circuit, the speed will vary with each change in load: in the latter, the speed is practically constant for any setting of the controller. A shunt wound motor has a high-resistance field winding connected in parallel with the armature. It responds to increased load by trying to maintain its speed and this leads to an increase in armature current. This makes it unsuitable for widely-varying loads, which may lead to overheating.
Series DC Motor:
The motor field windings for a series motor are in series with the armature.
This type of motor speed varies automatically with the load, increasing as the load decreases. Use of series motor is generally limited to case where a heavy power demand is necessary to bring the machine up to speed, as in the case of certain elevator and hoist installations, for steel cars, etc. Series-wound motors should never be used where the motor can be started without load, since they will race to a dangerous degree. A series wound motor has a low-resistance field winding connected in series with the armature. It responds to increased load by slowing down and this reduces the armature current and minimizes the risk of overheating.
Compound DC Motor:
A compounded DC motor is constructed so that it contains both a shunt and a series field. This particular schematic shows a cumulatively-compounded" DC motor because the shunt and series fields are aiding one another combination of the shunt wound and series wound types combines the characteristics of both. Characteristics may be varied by varying the combination of the two windings. These motors are generally used where severe starting conditions are met and constant speed is required at the same time.
Speed control:
Generally, the rotational speed of a DC motor is proportional to the voltage applied to it, and the torque is proportional to the current. Speed control can be achieved by variable battery tapings, variable supply voltage, resistors or electronic controls.
In a circuit known as a chopper, the average voltage applied to the motor is varied by switching the supply voltage very rapidly. As the "on" to "off" ratio is varied to alter the average applied voltage, the speed of the motor varies. The percentage "on" time multiplied by the supply voltage gives the average voltage applied to the motor. Therefore, with a 100 V supply and a 25% "on" time, the average voltage at the motor will be 25 V. During the "off" time, the armature's inductance causes the current to continue through a diode called a "fly back diode", in parallel with the motor. At this point in the cycle, the supply current will be zero, and therefore the average motor current will always be higher than the supply current unless the percentage "on" time is 100%. At 100% "on" time, the supply and motor current are equal. The rapid switching wastes less energy than series resistors. This method is also called pulse-width modulation (PWM) and is often controlled by a microprocessor. An output filter is sometimes installed to smooth the average voltage applied to the motor and reduce motor noise.
DC MOTOR DRIVER:
As the most of the PORT of MCU or any other controlling ICs are not powerful enough to drive DC motors directly so we need some kind of drivers. A very easy and safe is to use popular L293D chips. It is a 16 PIN chip. The pin configuration is shown in the diagram.
This chip is designed to control 2 DC motors. There are 2 INPUT and 2 OUTPUT pins for each motor. The diagram with proper connection is shown in the next diagram. The ‘RA3’ and ‘RA2’ pins are used to control the motor one and ‘RA0’ and ‘RA1’ pins are used to control motor B. Pin1 and Pin9 are enable pins. If these pins are not connected to +5V, then both the drivers will remain deactivated until they are enabled. Whatever power supply we provide at pin 8 and pin 16, this supply will go to both motors. Hence we have to be careful about the rating of motors while connecting the power supply to this IC using this IC.