Servomotors

Servomotors

The servo system is one in which the output is some mechanical variable like position, velocity or acceleration. Such systems are generally automatic control systems which work on the error signals. The error signals are amplified to drive the motors used in such systems. These motors used in servo systems are called servomotors. These motors are usually coupled to the output shaft i.e. load through gear train for power matching.

These motors are used to convert electrical signal applied, into the angular velocity or movement of shaft.

1. Requirements of Good Servomotor

The servomotors which are designed for use in feedback control systems must have following requirements :

i) Linear relationship between electrical control signal and the rotor speed over a wide range. 

ii) Inertia of rotor should be as low as possible. A servomotor must stop running without any time delay, if control signal to it is removed. For low inertia, it is designed with large length to diameter ratio, for rotors. Compared to its frame size, the rotor of a servomotor has very small diameter.

iii) Its response should be as fast as possible. For quickly changing error signals, it must react with good response. This is achieved by keeping torque to weight ratio high.

iv) It should be easily reversible.

v) It should have linear torque - speed characteristics.

vi) Its operation should be stable without any oscillations or overshoots.

2. Types of Servomotors

The servomotors are basically classified depending upon the nature of the electric supply to be used for its operation.

The types of servomotors are as shown in the following chart :