The servosystem is one in which the output is some mechanical variable like position, velocity or acceleration. Such systems are generally automatic control system which work on the error signals. The error signals are amplified to drive the motors used in such systems. These motors used in servosystems 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, into the angular velocity or movement of shaft.
1.1 Requirement 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 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.