How does the PLC control the servo motor?

Before answering this question, we should first understand the purpose of the servo motor. Compared with ordinary motors, servo motors are mainly used for accurate positioning. Therefore, controlling the servo is actually controlling the position of the servo motor. In fact, the servo motor also adopts two other working modes, namely speed control and torque control, but the application is less.

The speed control is generally realized by the frequency converter, and the speed control is performed by the servo motor, which is generally used for fast acceleration and deceleration or precise speed control, because compared with the frequency converter, the servo motor can reach thousands of revolutions in a few millimeters, because the servo is closed-loop , the speed is very stable. Torque control mainly controls the output torque of the servo motor, also because the servo motor responds quickly. With the above two kinds of control, the servo drive can be used as a frequency converter, and the analog control is generally used.

The main application of servo motors is positioning control. Position control has two physical quantities that need to be controlled, namely speed and position. Rather, it controls how fast the servo motor gets to where and stops exactly.

The servo drive controls the distance and speed of the servo motor by the frequency and number of pulses it receives. For example, we agree that a servo motor rotates every 10,000 pulses. If the PLC sends 10,000 pulses in one minute, the servo motor will complete one revolution at 1r/min. If 10,000 pulses are sent in one second, the servo motor will complete one revolution at a speed of 60r/min.

Therefore, the PLC controls the servo motor by controlling the sending pulse, and the physical sending of the pulse, that is, the PLC transistor output is a very common method, and a low-end PLC is generally used. The mid-to-high-end PLC transmits the number and frequency of pulses to the servo drive through communication.

For programming, this is very different. Japanese PLCs take the form of instructions, while European PLCs take the form of function blocks. But the essence is the same. For example, in order to control the absolute positioning of the servo, we need to control the output channel of the PLC, the number of pulses, the pulse frequency, the acceleration and deceleration time, and when the servo drive completes the positioning, whether it encounters the limit, etc. No matter what kind of PLC, it is nothing more than the control of these physical quantities and the reading of motion parameters, but the realization methods of different PLCs are different.