The control mode of CNC machine tool servo drive can be divided into two control methods: open-loop control and closed-loop control (semi-closed-loop) according to its structure. What are the specific control methods of the servo drive?
1. Feedback compensation open-loop control
The accuracy of the open-loop system is very low. This is because the servo actuator step error, start and stop error and mechanical system error directly affect the positioning accuracy. Compensation types are applied for improvement. The system has the advantages of open-loop and closed-loop, namely open-loop stability and closed-loop accuracy. The system will not oscillate due to the resonant frequency of the machine tool, creep and misalignment. The feedback compensated open-loop control does not require gap compensation and pitch compensation.
2. Semi-closed-loop control
For the closed-loop control system, reliable stability and high precision can be obtained by reasonable design. However, the position signal of the table needs to be measured directly by the installation and maintenance of the required position detection device such as grating, magnetic ruler or linear induction synchronizer. The equivalent feedback signal of position output is obtained indirectly by measuring the angular displacement of drive shaft or wire rod. Since the error caused by this part of the transmission cannot be included in the closed-loop system, there is no transmission chain from the rotating shaft to the table, so the error caused by this part of the transmission cannot be automatically compensated by the closed-loop system. Therefore, the closed-loop control system composed of equivalent feedback signals is called semi-closed-loop servo driver, and this control mode is called semi-closed-loop control mode.
3. Closed-loop control
Because of the accuracy of the open loop control, the servo motor controller cannot meet the requirements of the machine tool. In order to improve the control accuracy of servo drive, the most basic method is to adopt closed-loop control. In other words, there is both a front control channel and a feedback channel to detect the output. By comparing the command signal with the feedback signal, the deviation signal is obtained, and the closed-loop control system with deviation control is formed.
4. Feedback compensation semi-closed-loop control
The servo driver control compensation principle is the same as the open-loop compensation system. Two independent measuring systems consisting of a rotary transformer and an induction synchronizer are both operating on the format. The disadvantages of the system are high cost, two sets of detection systems, the advantages of the system is easier to adjust than the full closed-loop system, good stability, suitable for use as a high-precision large CNC machine feed driver.