(1) How does PLC control servo motors?
Before answering this question, we must first understand the purpose of servo motors, compared with ordinary motors, servo motors are mainly used for precise positioning, so what we usually call the control servo is actually the position control of the servo motor. In fact, servo motors also use two other working modes, that is, speed control and torque control, but the application is relatively rare.
Speed control is generally realized by frequency converter, and servo motor is used for speed control, which is generally used for rapid acceleration and deceleration or precise speed control, because compared with the frequency converter, the servo motor can reach several thousand revolutions within a few millimeters, and the speed is very stable because the servo is closed-loop. Torque control is mainly to control the output torque of the servo motor, also because of the fast response of the servo motor. With the above two types of control, the servo drive can be used as an inverter, which is generally controlled by analog.
The main application of servo motor is positioning control, position control has two physical quantities to control, that is, speed and position, to be exact, is to control how fast the servo motor arrives at what place, and stop accurately.
The servo drive controls the distance and speed at which the servo motor travels by the frequency and number of pulses it receives. For example, we agree that the servo motor makes one revolution every 10,000 pulses. If the PLC sends 10,000 pulses in one minute, then the servo motor will complete a circle at a speed of 1r/min, and if it sends 10,000 pulses in one second, then the servo motor will complete a circle at a speed of 60r/min.
Therefore, the PLC controls the servo motor by controlling the pulses sent, and sending the pulses in a physical way, that is, using the transistor output of the PLC is the most commonly used way, and generally the low-end PLC adopts this method. The mid-to-high-end PLC transmits the number and frequency of pulses to the servo drive through communication.
These two methods are just different in the implementation channels, but the essence is the same, and it is the same for our programming. This is what I want to tell you, to learn the principles, to touch the bypass, not to learn for the sake of learning.
For programming, this is very different, the Japanese PLC is in the form of instructions, while the European PLC is in the form of function blocks. But the essence is the same, for example, to control the servo to go 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 we need to know when the servo drive positioning is completed, whether it touches the limit and so on. 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 implementation methods of different PLCs are different.
(2) How to design a servo system?
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