Comparison of servomotors

Servomotor Part 5
1.1 Comparison Between A.C. and D.C. servomotors

A.C Servomotor
D.C. Servomotor
1)  Low power output of about 0.5 W to 100 W.
1)  Deliver high power output
 2)  Efficiency is less about 5  to 20 %.
2)   High Efficiency.
3)  Due to absence of commutator maintenance is less.
3)  Frequent maintenance required due to commutator.
4)  Stability problems are less.
4)  More problems of stability.
5)  No radio frequency noise.
5)  Brushes produce radio frequency noise.
6)  Relatively stable and smooth operation.
6)  Noisy operation.
7)  A.C. amplifier used have no drift.
7)  Amplifiers used have a drift.

1.2 Comparison Between armature Controlled and Field Controlled D.C. Servomotors

Field Controlled
Armature Controlled
1)  Due to low power requirement amplifiers are simple to design.
1)  High power amplifiers are required to design
 2)  Control voltage is applied to the field.
2)   Control voltage is applied to the armature.
3)  Time constant is large.
3)  Time constant is small.
4)  This is open loop system.
4)  This is closed loop system.
5)  Armature current is kept constant.
5)  Field current is kept constant.
6)  Poor efficiency.
6)  Better efficiency.
7)  Suitable for small rated motors.
7)  Suitable for large rated motors.
8)  Costly as field coils are must.
8) Permanent magnet can be used instead of field coils which makes the motor less expensive.


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