Armature controlled servo motors:
The connections of such type motors are shown below:
In this constant current source is applied to the field winding hence Ifremains constant. However the servo amplifier output is connected to the armature so that the armature current is dependant on the error produced in the system in which the servo motor is being used. The response of the armature controlled DC servo motor to any change in the servo amplifier output is explained as:
1) As current changes, The VoltageVa from servo amplifier also change
2) This will change the armature current
3) So torque produced by the motor changes
4) The motor will respond to change in torque in such a way that the error is minimized.
Advantages of armature controlled DC motor:
1) The time constable La/ Ra is small hence motor responds quickly as compared to the field controlled DC servo motor.
2) Hence this type of motors are practically preferred to the controlled field type motors.
Torque speed characteristics of DC servo motor:
The Torque speed characteristics of DC servo motors are shown below:
1) Its shows that these are linear in nature and shows the effect of the armature voltage Va.
2) Higher torques for the same speed and higher speed for same torque are obtained as the armature voltage is increased.
Applications of DC Servomotors:
1) Position control system
2) Process Controllers
3) Military applications
4) Air craft control systems
5) Servo stabilizers