It is a feedback control system in which a controlled variable or the output is a mechanical position or its time derivatives like velocity and acceleration.

Servomotors have two main classifications based on servomechanism i.e.

1. DC Servomotors

  1. Armature controlled DC motor
  2. Field Controlled DC motor

2. AC Servomotors

1. DC Servomotors

DC ServoMotor essentially an ordinary DC motor except for some minor difference and constructional features. For servo applications, a DC motor is required to produce Rapid acceleration from standstill. Therefore, a physical requirement of such a motor or low inertia and high starting torque. Low inertia is attained by reducing armature diameter with the corresponding increase in armature length.

a). Armature controlled DC motor




Ra = armature resistance

La = inductance of armature winding

Va = applied armature winding

Ia = armature current

Eb = back emf

J = Moment of inertia acting on motor shaft

B = viscous friction acting on motor shaft

Tm = Torque developed by the motor

θ = Angular displacement i.e. output

b). Field Controlled DC Motor


Servomechanism | Servomotor & Applications

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