Servo Motor

Abstract

The electric motors are built in three basic sizes of power (hp): small, medium and large. Their major types are:- DC motors uses direct electrical current and provides momentary power bursts. They have many types: Brushless DC used to drive CD-ROM, Xerox machine, etc, Limited-angle torque used in direct laser mirrors, PM DC Motor, Coreless DC Motor with no iron core used to drive in magnetic tape drives, Linear DC Motor used in fast trains that has a stator and a slider.- AC motors (alternating current), have many types: Single phase AC induction motors only with one discrete waveform used in fans and washing machine. Three phase AC induction motors used in high power applications. Single phase AC synchronous motors used in audio turntables, telescopes. Three phase AC synchronous motors used in traction motor and TGV locomotives and could be used as alternators.- Universal motors that can operate on either AC or DC current and are used in vacuum cleaners, food mixers, etc.- Special motors: used for special applications, can be customized and cost less than standard motors with the same power rating. Motor starters used to start up large motors with very high starting torque and the Gear Motors attached with a set of gears to drive a secondary drive shaft.- Servo motor: is a motor equipped with a control unit, receives requests for specific movements and follow it. Receives two inputs: an energy source and a command source. The main parts are: the motor, the gearbox and the electronics regulator. They are useful in robotics, are small and extremely powerful, are compact, provide more power and have fine controls. The servo amplifiers are part of a closed loop control system, the ideal servo possesses a constant velocity, the ability to maintain a speed. A tachometer input is used to generate a proportional signal to the motor speed.- Stepping Motors: The stepper motors move in discrete steps; are less expensive and easier to use than a servo motor, most of them have a home switch associated with each motor that will allow the software to determine the starting. They have advantages over servo motors because they are low cost, work on open loop, low maintenance, excellent holding and low speeds, no tuning required and are very rugged on any environment but it also have disadvantages because they are rough performance, limited sizes, noisy and the torque decreases with speed.The theoretical servo must be able to provide the infinite acceleration this can be seen by abruptly starting and stopping the servo motor. The servo amplifier will respond proportionally to changes in the velocity input command, and drive the servo in a way to hold a position; it will trip the solenoid breaker by energizing it and when it is activated low it will be disabled.The servos are constructed from three basic pieces: a motor, a feedback device and a control unit; when the control circuit detects that the position is correct it stops the motor, the amount of power applied to the motor is proportional to the distance it needs to travel.The servo mechanism is an automatic device which uses error sensing feedback to correct the performance of a mechanism, it may or may not use a servomotor; today it is used in automatic machine tools and antennas.The servo applications are:- Floppy Disk: a magnetic disk using magnetic pulses.- Printer: used in a billing or accounting machine having a single servo motor.- Scanner: optical or servo controlled limited rotation motors are behind many innovative products across many industries.- CD-ROM: type of optical disk used to store digital data and is a read-only data storage and suitable for multimedia applications.- Hard Disk Drive: very important within the PCs, has improved reliability, capacity, speed, power usage and weight, its use of a servo motor or many servos to control data entry. It is high technology; the principle of storage is using the controller to change the polarity of the magnetic on the surface to store the data. The surface must be very smooth; any scratch will cause damage to the data. Each track is divided into equal arc or sectors, which are the coordinates of the data.A hard disk contains 1 to 10 identical platters that are stacked in parallel to form a cylinder. The data is stored in microscopic areas called magnetic domains.The read-write head is the key component that performs the reading and writing functions; passing a current through the coil, which is part of the actuator-assembly, derives the sliding motion. To write information to the disk an electromagnetic flux is transmitted through the head. During the read request the data is interpreted when the magnetic fields brings about an electrical change.It uses voice coil actuators to position the heads on the surface, this actuator is one instance of servo system; it also makes them far less sensitive to thermal effects than older hard disks were, it includes a feature called thermal recalibration but it has one side effect which is that if you attempt to access the disk while it is taking effect, there is a slight pause until it completes.When the computer is switched off, the head is usually pulled to a safe parking zone to prevent the head from scratching against the data. It also contains a PCB controller circuit board that regulates data traffic.Today’s storage capacity is measured in terms of GB, we measure the performance in data rate, it is known as data transfer rate and refers to the speed and the seek rate refers to the total span of time between the file request by the CPU to the point when the first byte of the file is sent to the CPU.