CNC machine tools are classified according to the control mode of servo drive

       1. Open-loop control of CNC machine tools. Open-loop control machine tool refers to a control system without a position feedback device, using a stepper motor as a servo drive actuator, and is generally used in economical CNC machine tools with low precision requirements.

       2. Closed-loop control of CNC machine tools. Closed-loop control is to directly install a linear displacement detection device on the moving parts of the machine tool, and feed the directly measured displacement to the comparator of the numerical control device, compare it with the input command, and use the difference to control the moving parts, so that the moving parts Strictly move according to the actual displacement required. Generally used for CNC machine tools that require high speed and high precision, such as boring and milling machines, ultra-precision lathes, ultra-precision grinders and large CNC machine tools.

       3. Semi-closed loop control of CNC machine tools. Most CNC machine tools use a semi-closed loop control system, and its position feedback adopts an angular displacement detection device (such as a photoelectric pulse encoder, etc.), which is installed at the end of the motor or ball screw, and indirectly by detecting the rotation angle of the servo motor or the screw. The displacement of the moving part is detected, and fed back to the comparator of the numerical control displacement device, compared with the input command, and the difference is used to control the moving part; because this control method only performs closed-loop control on the angular displacement of the servo motor or ball screw , and does not realize the closed-loop control of the linear displacement of the moving parts, so it is called semi-closed-loop control. Under normal circumstances, there are many control methods to choose semi-closed-loop control of CNC machine tools.