Speed Control Principle of DC Servo Motor

With the development of science and technology, servo motor products are widely used in many applications and machinery productions including some special applications. We know that servo motor device can be divided into AC servo motor and DC servo motor.  Servo has three control methods: speed control mode, torque control mode and position control mode. As one of the control modes, do you know the speed control principle of DC servo motor device? In this article, we will talk about this issue.

Servo mainly relies on pulses for positioning. Basically, it can be understood that when the servo motor receives 1 pulse, it will rotate the angle corresponding to 1 pulse to achieve displacement. The servo motor itself can send pulses, so each time the servo motor rotates one angle, a corresponding number of pulses will be sent out. In this way, it corresponds to the pulse received by the servo motor, and it is also called a closed loop. So, the system will know the quantities of pulses sent to the servo motor and the quantities received at the same time. This way can control the rotation of the motor very accurately to get precise positioning, which can reach 0.001mm.

We know that DC servo motor components are divided into brush and brushless motors. Brushed electric motors have the characteristics of low cost, simple structure, large starting torque, wide speed range and easy control. They need maintenance, but they are easy to maintain, and you just change carbon brushes. And they generate electromagnetic interference, and have requirements for the environment. Therefore, it can be used in common industrial and civilian occasions that are sensitive to cost.

The brushless electric motor is small in size, light in weight, large in output, fast in response, high in speed, small in inertia, smooth in rotation, and stable in torque. The control is complicated and it is easy to realize intelligence. Its electronic commutation method is flexible, and it can be square wave commutation or sine wave commutation. The motor is maintenance-free, highly efficient and has low operating temperature, low electromagnetic radiation and long life. So, it can be used in various environments.

AC servo motor devices are also brushless motors, which are divided into synchronous and asynchronous motors. At present, synchronous motors are generally used in motion control. They have a large power range and can achieve great power, large inertia, low maximum rotation speed, and rapid decrease as the power increases. Therefore, it is suitable for low-speed and smooth running applications.

Since the rotor inside the servo motor is a permanent magnet, the U/V/W three-phase electricity controlled by the driver forms an electromagnetic field. The rotor rotates under the action of this magnetic field. At the same time, the encoder of the motor feedback signal to the driver, and the driver compares the target with the feedback value. The values are compared, and the angle of rotation of the rotor is adjusted. The servo motor accuracy is determined by the accuracy of the encoder.