The characteristics of the half closed loop control of CNC machine tools:

Mounted on the machine tool servo motor drive screw or angular displacement detection device, through which can detect motor or Angle of a ball screw, so as to indirectly detect the displacement of moving parts. Angle of leap shift signal is feedback to the CNC device or servo drive, to achieve the position from a given Angle between the closed-loop automatic adjustment to the motor output. Also, because the servo motor and ball screw is linked together, through the screw can convert rotary motion to linear displacement of the moving parts so indirectly control the movement speed and displacement of moving parts. This structure only for motor closed-loop control or angular displacement of a ball screw, no implementation of the final output of linear displacement closed loop control, so called "half closed loop control system.

Use half closed loop control system of nc machine tools, electrical control and mechanical drive has obvious dividing line, so it's convenient to make debugging, maintenance and fault diagnosis; And clearance, friction of mechanical part of dead zone, the nonlinear stiffness etc.) are outside the closed loop, so the stability of the system is good. Servo motor and photoelectric encoder is usually made into an organic whole, can be directly between motor and screw connection or through the reduction gear connector; Position detection unit and the actual minimum matching between the mobile unit, can be set by the parameters of the numerical control system. It has a drive system is simple and compact structure, low manufacture cost, high cost performance, etc, which has been widely applied in nc machine tools.