In the previous article, we mainly introduced the function of CNC milling machine servo system and open-loop servo system. Today we continue to understand the closed-loop servo system and semi-closed-loop servo system.
Closed-loop servo system is suitable for servo drive feed motion control, through the installation of the moving parts on the scale directly measured linear displacement and feedback to the milling machine CNC system, in the numerical control system for position control.
In the digital closed-loop servo system, the CNC system through the servo bus and servo drives, gratings and encoders for data exchange. Among them, the grating for position detection, and position information through the servo bus feedback to the milling machine CNC system, the location control. The encoder on the servo motor performs speed detection and feeds the speed information to the servo drive for speed control.
In the closed loop servo system, the position loop contains the entire mechanical transmission chain, the transmission chain error can be fully compensated, the position control accuracy is high, but the stability of the servo system is poor.
The semi-closed-loop servo system is suitable for servo-driven feed motion control. The linear displacement is measured indirectly by the encoder on the servo motor and fed back to the numerical control system, and the position control is carried out in the numerical control system.
In the digital semi-closed-loop servo system, the CNC system through the servo bus and servo drives, encoders for data exchange. Among them, the encoder is both angular displacement detection and speed detection. The angular displacement information is fed back to the milling machine via the servo bus for position control. The speed information is fed back to the servo drive for speed control.
In a semi-closed loop servo system, the position loop contains part of the mechanical transmission chain, can not completely compensate for the error of the transmission chain, the position control accuracy is lower than the closed loop servo system, but the milling machine servo system stability is better.