Servo drive control mode

　　CNC servo control in the machine according to its structure can be divided into open-loop control and closed-loop (semi-closed loop) control. If the classification, open-loop control can be divided into ordinary type and feedback compensation type, closed-loop (semi-closed loop) control can be divided into ordinary type and feedback compensation type.

　　Feedback compensated open loop control

　　The accuracy of the open-loop system is low, which is due to the servo drive step error, starting and stopping error, the mechanical system error will directly affect the positioning accuracy. Should be compensated to improve, this system has both open-loop and closed-loop advantages, that is, with open-loop stability and closed-loop accuracy. Not because of the resonant frequency of the machine, crawling, malfunctioning caused by system oscillation. Feedback compensation type open loop control does not require gap compensation and pitch compensation.

　　Closed-loop control

　　As the accuracy of open-loop control can not meet the requirements of the machine, in order to improve the servo drive control accuracy, the most fundamental way is to use closed-loop control. That is, not only the predecessor control channel, but also the feedback output of the feedback channel, the command signal and feedback signal after the deviation signal to form a bias control of the closed-loop control system.

　　Semi - closed - loop control

　　For the closed-loop control system, a reasonable design can be reliable stability and high accuracy, but the direct measurement of the table position signal needs to use such as grating, magnetic tape or linear induction synchronizer installation, maintenance requirements higher position Detection device. Through the measurement of the displacement of the drive shaft or the screw angle, the equivalent feedback signal of the position output can be obtained indirectly. Since the error caused by this part of the transmission can not be closed in the closed-loop system does not contain the drive chain from the rotation axis to the table, so this part of the transmission error can not be closed-loop system automatically compensated, so called the equivalent feedback signal Of the closed-loop control system for the semi-closed-loop servo drive, this control is called semi-closed-loop control.

　　Feedback compensated semi - closed - loop control

　　This servo drive control compensation principle and open-loop compensation system is the same, by the rotary transformer and induction synchronizer composed of two sets of independent measurement system are to work in a scale mode. The system has the disadvantage of high cost, use two sets of detection system, the advantage is easier than the whole closed-loop system adjustment, good stability, suitable for high-precision large-scale CNC machine tool feed drive.