What is Servo Motor Control of CNC Machine Tool
Servo motor is an engine that controls the operation of mechanical components in the servo system of a CNC machine tool, and is an indirect speed change device for auxiliary motors. The servo motor can control the speed and position accuracy very accurately, and can convert the voltage signal into torque and speed to drive the control object. Generally, we control the servo motor of the machine tool in three ways: position, speed and torque.
From a control point of view, both speed control and torque control are independent control functions. The target physical quantity of speed control is the rotation speed of the motor, and the target physical quantity of torque control is the torque of the motor. However, the specific control method used for implementation still depends on the needs of customers.
If the user has no requirements for the speed and position of the machine tool motor, as long as a constant torque is output, the torque mode is naturally used.
If there is a certain accuracy requirement for position and speed, but not very concerned about real-time torque, and it is not convenient to use torque mode, it may be better to use speed or position mode. If the host controller has a better closed-loop control function, the speed control effect will be better. As far as the response speed of the servo drive is concerned, the torque mode calculation is small and the drive responds quickly to the control signal; the position mode calculation is large, and the drive response to the control signal is slow.
When there are relatively high requirements for dynamic performance in motion, the motor needs to be adjusted in real time. Then if the calculation speed of the controller itself is very slow (for example, PLC, or low-end motion controller), use position control. If the controller calculation speed is relatively fast, you can use the speed method to move the position loop from the driver to the controller, reducing the workload of the driver and improving efficiency (such as most of the motion controllers); if there is a better upper controller , You can also use the torque control method to remove the speed loop from the drive. This is generally only a special controller to do this, and at this time, there is no need to use a servo motor.
Generally speaking, whether the control of the CNC machine tool drive is good or not, there is now a more intuitive way of comparison, called the response bandwidth. When torque control or speed control, a square wave signal is given to him through the pulse generator, which makes the motor continuously rotate forward and reverse, and constantly increase the frequency. The oscilloscope displays a frequency sweep signal. When the vertex reaches 70.7% of the high value, it means that it has been out of step. The frequency at this time can show whose product is better. The general current loop can reach more than 1000 Hz, but the speed loop can only do it tens of Hz.
