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How does the Servo Motor Work?

By Emma | Published on Sep 15,2015

Before learning how the servo motor works, we should have a little knowing about servo motor.

Servo motor, which is also called the implementation, in the automatic control system, is used as actuators. It can convert the received electrical signal into angular displacement or velocity of motor shaft to output. The servo motor’s main characteristic is that, when the signal voltage is zero, with no rotation, speed can uniformly decrease with the increase of torque.

Servo motor is a typical closed loop feedback system, its gear group driven by the motor. Its terminal (outputs) drives a linear potentiometer as position detection. This potentiometer transform Angle coordinate into a proportional voltage and feedback to control circuit boards, which compares it with input pulse signal to a correct impulse and drive the motor forward or reverse rotary, marking the position of the output of the gear set consistent with expectations to lead correct pulse tends to 0, so as to achieve the purpose of accurate positioning servo motor.

So how does the servo motor work? The principle is very simple.

The inside of the servo motor rotor is a permanent magnets. U/V/W three-phase electric controlled by the drive can form the electromagnetic field. In this field, the rotor rotates and encoder in the motor can feedback signal to drive, which compared with the target to adjust the Angle of the rotor rotation. The precision of the servo motor is determined by the precision of the encoder (line number).

With ac servo motor as an example, this article will detailedly talk about how the servo motor works.

The structure of the ac servo motor stator is basically similar to capacitance split-phase single-phase asynchronous motor. Its stator is equipped with two winding with position difference of 90 °. One is RF excitation winding, which always picks at the ac voltage UF; another is the control winding connecting control signal voltage UC. So ac servo motor is also called the two servo motors.

Ac servo motor rotor is usually made to squirrel-cage type, but in order to make the servo motor has a wide speed range, linear mechanical properties, no "rotation" phenomenon and the properties of fast response, compared with the ordinary motor, it should have the characteristics of big rotor resistance and small moment of inertia.

The structure of the rotor widely applied has two forms: one is cage rotor with high resistivity conducting bar made by conductive materials. In order to reduce the rotational inertia of the rotor, the rotor is always long and thin. Another kind is hollow cup rotor made of aluminum alloy.

Its glass is very thin, only 0.2 0.3 mm. to reduce the magnetic resistance of magnetic circuit, Fixed inside stator should be placed in the hollow cup rotor. The hollow cup rotor’s moment of inertia is small. And this rotor is responsive, and stable running, so is widely used.

Without the control voltage, there is only pulsating magnetic field produced by excitation winding in the stator of ac servo motor and the rotor keeps motionless. With a control voltage,

The Stator then produces a rotating magnetic field, and the rotor rotates along the direction of the rotating magnetic field.

In the case of constant load, the speed of the motor changes with the size of the control voltage. When the control voltage be opposite in phase, servo motor will be reversed.

The working principle of ac servo motor is similar with split-phase single-phase asynchronous motor, but the rotor resistance of the former is much larger than the latter, so compared with the single asynchronous motor, servo motor has three distinctive features:

1, large starting torque

2, a wide operating range

3, No rotation

After reading this article, we believe you can have a basic understanding of how the servo motor work. Hope it can help you.



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