System for stopping spindle at commanded position

A system for stopping a spindle at a commanded position operating at a commanded speed, comprising:

• an electric motor;
• a speed detector, operatively connected to said electric motor, for detecting a speed of rotation of said electric motor and for producing an actual speed signal;
• a speed control circuit, operatively connected to said speed detector and to receive the commanded speed, for effecting control to nullify the offset of the actual speed from the commanded speed;
• a spindle operatively connected to and driven by said electric motor;
• and
• a position control circuit, operatively connected to said spindle and said speed control circuit, for generating a position offset signal corresponding to an offset of a position of a predetermined portion of said spindle from the commanded position at which said portion of said spindle is to be stopped, the rotation of said spindle being controlled by said speed control circuit to maintain said commanded speed and by said position commanded to nullify said position offset signal, said position control circuit comprising:
• a resolver, operatively connected to said spindle, having a secondary coil and having two primary coils producing output voltages;
• a resolver exciting signal generator, operatively connected to said resolver, for supplying an exciting signal to the secondary coil of said resolver;
• a synchronous rectifier circuit, operatively connected to one of the primary coils of said resolver, for providing synchronous rectification of the output voltage from said one of said primary coils;
• a quadrant discrimination circuit, operatively connected to the other of said primary coils, for converting the output voltage from said other of said primary coils into rectangular waves;
• a waveform combining circuit, operatively connected to said synchronous rectifier circuit and said quandrant discrimination circuit, for combining the output voltage of said synchronous rectifier circuit and the output voltage from said quadrant discrimination circuit to produce said position offset signal which smoothly crosses a zero level at the commanded position at which said spindle is to be stopped;
• and
• a stopping position adjusting circuit, operatively connected to said waveform combining circuit, for adjusting a position of a lattice point at which said position offset signal crosses the zero level.