The control mode of the CNC machine tool servo driver can be divided into two control methods: open-loop control and closed-loop (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 step error of the servo drive, the start and stop error, and the error of the mechanical system directly affect the positioning accuracy. The compensation type should be used for improvement. The system has the advantages of open-loop and closed-loop, namely open-loop stability and closed-loop accuracy. The system does not oscillate due to the machine's resonant frequency, creep and misalignment. Feedback compensation type open-loop control does not require backlash compensation and pitch compensation.
2. Semi-closed loop control
For the closed-loop control system, through reasonable design, reliable stability and high precision can be obtained. However, the position signal of the table needs to be directly measured by position detection devices such as gratings, magnetic scales or linear induction synchronizers required for installation and maintenance. By measuring the angular displacement of the transmission shaft or the wire rod, the equivalent feedback signal of the position output is obtained indirectly. 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, a closed-loop control system composed of equivalent feedback signals is called a semi-closed-loop servo drive, and this control mode is called a semi-closed-loop control mode.
3. Closed-loop control
Due to the accuracy of open-loop control, servo motor controllers cannot meet the requirements of machine tools. In order to improve the control accuracy of the servo drive, the most basic method is to use the closed-loop control method. That is to say, there are both pre-stage control channels and feedback channels to detect the output. The command signal is compared with the feedback signal to obtain the deviation signal, forming a closed-loop control system with deviation control.
4. Feedback compensation semi-closed loop control
The control compensation principle of the servo drive is the same as that of the open-loop compensation system. Two separate measurement systems consisting of a resolver and an inductive synchronizer work on the format. The disadvantage of this system is high cost and two sets of detection systems. The advantage is that it is easier to adjust than the full closed-loop system and has better stability. It is suitable for use as a feed driver for large-scale CNC machine tools with high precision.