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AC Servo principle


What is a Servo?

A servo is a device which controls the angle of a piece of machinery. A motor attached to the servo controls a rotating shaft which changes the angle of the shaft. Servo originates from Latin Servus. (English as Slave)
The function of a Slave is to work with loyalty under his lord?s orders.



Servo system can be briefly classified into following parts:

1.Order part?Movement instruction signal output device.

2.Drive part?A device that receives the output signal from the Order part and drives the execution machinery. ( e.g. servo motor)

3.Feedback part?A device that inspects execution machinery or load status.

4.Execution machinery: A device that receives the output signal from Drive part and generates rotation torque, position status etc.,



AC servo system control structure






Servo driver Internal structure






Servo motor could be classified as follows:

Synchronized type: Applied with PM servo motor. Because of power generation effect when stops, it is easier to brake. (Rotator:
PM Stator: Windings)

Inductive type: The structure is like synchronized type servo motor. It has good torque performance at high speed. However, it is easier to generate heat. (Rotator & stator: windings)

DC type: DC servo motor. As carbon brush will generate powder while rotation, it is not suitable for locations with dust-free
requirement. It is mainly used for small capacity. (Rotator: windings; Stator: PM)



Synchronized AC servo motor



Characteristics:
1.Maintenance free
2.Good environment adaptability
3.Good torque performance
4.Easier to brake
5.Smaller dimension, lighter weight
6.High efficiency

Shortcomings:
1.AMP is more complicated than DC?s
2.Motor could only be driven with relevant power AMP.
3. PM is possible to demagnetize



Inductive servo motor



Characteristics:
1.Maintenance free
2.Good environment adaptability
3.Good torque performance

Shortcomings:
1.Low efficiency
2.AMP is more complicated than DC?s
3.No DB brake
4.Performance will be effected by temperature
5.Motor could only be driven with relevant power AMP.



DC servo motor



Characteristics:
1.Driver structure is simple.
2.DB brake
3.Smaller in volume, low price.
4.High efficiency

Shortcomings:
1.Carbon brush will generate powder.The refore, it cannot be used in locations with dust-free requirement.
2.Poor torque performance at high speed.
3. PM is possible to demagnetize




Motor feedback parts



-incremental encoder
-absolute encoder
-resolver

[markcomp]

AC Servomotor

Generally, modern servo motor refers to AC permanent magnet synchronous servo motor.

Consisted by:
1.Stator windings + rotor
2.Feedback units: Photoelectrical Encoder /Resolver

Characteristics:
1.Maintenance free
2.Good environment adaptability
3.Good torque performance
4.Easier to brake
5.Smaller dimension, lighter weight
6.High efficiency

Structure types

Stator: distribution winding /concentration winding



Strengths?Smaller cogging torque
Shortcomings: Complicated technique, low production for slope slot



Strengths?High power consistency, simple technique, high production
Shortcomings?Without slope slot, cogging torque control needed

Rotor: Inner PM(IPM)/Surface PM(SPM)



Strengths: high reliability, simple technic
Shortcomings: rotor leakage flux and inductance control needed.




Strengths: low leakage flux and inductance
Shortcomings: PM protector needed.


AC 750W servo motor structure characteristics: Concentration winding stator + IPM