Servomotor Part 5
1.1 Comparison Between A.C. and D.C. servomotors
A.C
Servomotor
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D.C.
Servomotor
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1) Low power output of about 0.5 W to 100 W.
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1) Deliver high power output
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2) Efficiency
is less about 5 to 20 %.
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2) High
Efficiency.
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3) Due to absence of commutator maintenance is
less.
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3) Frequent maintenance required due to
commutator.
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4) Stability problems are less.
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4) More problems of stability.
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5) No radio frequency noise.
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5) Brushes produce radio frequency noise.
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6) Relatively stable and smooth operation.
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6) Noisy operation.
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7) A.C. amplifier used have no drift.
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7) Amplifiers used have a drift.
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1.2 Comparison Between armature Controlled and Field Controlled D.C. Servomotors
Field
Controlled
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Armature
Controlled
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1) Due to low power requirement amplifiers are
simple to design.
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1) High power amplifiers are required to design
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2) Control
voltage is applied to the field.
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2) Control
voltage is applied to the armature.
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3) Time constant is large.
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3) Time constant is small.
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4) This is open loop system.
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4) This is closed loop system.
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5) Armature current is kept constant.
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5) Field current is kept constant.
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6) Poor efficiency.
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6) Better efficiency.
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7) Suitable for small rated motors.
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7) Suitable for large rated motors.
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8) Costly as field coils are must.
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8) Permanent
magnet can be used instead of field coils which makes the motor less
expensive.
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