Speed control is generally realized by a frequency converter, and a servo motor is used for speed control. It is generally used for fast acceleration or deceleration or precise speed control, because compared to the frequency converter, the servo motor can reach several thousand revolutions within a few millimeters. Since the servos are closed loop, the speed is very stable. Torque control mainly controls the output torque of the servo motor, also because of the fast response of the servo motor. Using the above two kinds of control, the servo drive can be regarded as a frequency converter, and it is generally controlled by analog.
The main application of servo motor is positioning control. Position control has two physical quantities that need to be controlled, namely speed and position. To be precise, it is to control how fast the servo motor reaches and where it stops accurately.
The servo drive controls the distance and speed of the servo motor by the frequency and number of pulses received. For example, we agree that the servo motor will make one revolution every 10,000 pulses. If the PLC sends 10,000 pulses in one minute, the servo motor will complete one revolution at a speed of 1r/min. If it sends 10,000 pulses in one second, the servo motor will complete one revolution at a speed of 60r/min. ring.
Therefore, PLC controls the servo motor by controlling the pulses sent. It is the most common way to send pulses physically, that is, using the transistor output of the PLC. Generally, low-end PLCs use this method. In the high-end PLC, the number and frequency of pulses are transmitted to the servo drive through communication, such as Profibus-DP CANopen, MECHATROLINK-II, EtherCAT and so on. These two methods are just different in the channels of realization, the essence is the same, and it is the same for our programming. This is what I want to say to you, to learn the principles, learn by analogy, rather than learn for the sake of learning.
For program writing, this difference is very big. Japanese PLC adopts instruction method, while European PLC adopts function block form. But the essence is the same. For example, to control the servo to take an absolute positioning, we need to control the output channel of the PLC, the number of pulses, the pulse frequency, the acceleration and deceleration time, and the need to know when the servo drive is positioned, whether it hits the limit, etc. Wait. No matter which kind of PLC, it is nothing more than the control of these physical quantities and the reading of motion parameters, but different PLC implementation methods are different.