Open-loop control CNC machine tools This type of control CNC machine tools has no position detection components in the control system, and the servo drive components are usually reactive stepper motors or hybrid servo stepper motors.Every time the CNC system sends a feed command, after the power amplification of the drive circuit, it drives the stepper motor to rotate by an angle, and then drives the screw to rotate through the gear reduction device, which is converted into linear displacement of the moving part through the screw nut mechanism.The moving speed and displacement of the moving part are determined by the frequency and number of input pulses.The information flow of this type of CNC machine tool is one-way, that is, after the feed pulse is sent out, the actual movement value is no longer fed back, so it is called an open-loop control CNC machine tool.CNC machine tools with open-loop control systems have simple structures and low costs.However, the system does not monitor the actual displacement

Closed-loop control of CNC machine tools. Closed-loop control of CNC machine tools is to install a linear displacement detection device directly on the moving parts of the machine tool to directly detect the actual displacement of the workbench. The measured actual displacement value is fed back to the CNC device and compared with the input command displacement value. Compare and use the difference to control the machine tool so that the moving parts move according to the actual required displacement, and ultimately achieve precise movement and positioning of the moving parts.Theoretically, the motion accuracy of the closed-loop system mainly depends on the detection accuracy of the detection device and has nothing to do with the error of the transmission chain, so its control accuracy is high.Figure 1-3 shows the system block diagram of closed-loop control CNC machine tools.In the figure, A is the speed sensor and C is the linear displacement sensor.When the displacement command value is sent to the posi