The term servo or servo-mechanism refers to a feedback control system in which the controlled variable is:
- Mechanical position, or
- Time derivatives e.g. velocity and acceleration.
Following characteristics are usually required for a feedback control system:
i. High accuracy;
ii. Remote operation;
iv. Unattended control.
Following are the essentials of a feedback control system:
- An error detecting device. It determines when the regulated quantity is different from the reference quantity and sends out the error signal to the amplifier.
- An amplifier. The amplifier receives the error signal and then supplies power to the error-correcting device, which in turn changes the regulated quantity so that it matches the reference input.
A servo-motor should entail the following characteristics:
- The output torque of the motor should be proportional to the voltage applied (i.e. the control voltage which is developed by the amplifier in response to an error signal).
- The direction of the torque developed by the servo-motor should depend upon the instantaneous polarity of the control voltage.