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AC Servo Motor Torque Speed Characteristics

By Shaquila | Published on Nov 02,2015

Torque calculation for a sample data:

Ia =0.17A

Speed N= 850 rpm

For speed 850rpm- Eb = 0.96V

Therefore power P = Eb*Ia = 0.96*0.17 = 0.1632 watts.

T= P*1.019 * 10^4*60/2piN

T = 0.1632*1.019*10^4 *60/2*3.142*850

T = 18.68 Gm-cm

Compared with induction motor, a ac servo motor does not conform to the characteristic, namely high inductance to resistance ratio. Instead, it is featured with:

1. Linear torque-speed characteristics.

2. Negative slope of the torque-speed characteristics.

3. Be parallel to one another for various values of the control voltage applies.

It is obvious that the torque-speed is becoming more linear with the increasing of rotors resistance. When in a low inductance to resistance ratio, the torque-speed characteristics are almost linear.

Actually, motor with almost linear torque-speed characteristics is well designed. Only when encountered with a detectable error at a low voltage, can it smoothly rotates. And It rarely works at high speed. Hence for a given value of control voltage, torque-speed characteristics are almost linear. The following fig illustrates the torque-speed characteristics for various control voltages.

All the characteristics are equally spaced for equal increments of control voltage as shown.


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