Servo of dc main shaft by him motive of encourage type dc and speed of dc main shaft control unit composition. Unit of speed of dc main shaft is the career of double closed circuit that makes by speed annulus and voltaic annulus control a system, use at controlling the armature voltage of main shaft electromotor, undertake constant torsion timing. Control a system advocate loop is used turn over circuit of shunt-wound and reversible commutate, because the size of main shaft electromotor is large, so advocate the power switch component of loop uses brilliant brake to provide element mostly. Timing of motive of main shaft dc still includes constant power timing, by excitation control loop is finished. Because give priority to axial electromotor to be electromotor of his encourage type, excitation winding needs to have power supply of another direct current source, with abate excitation means of control loop electric current makes electromotor rises fast. After using speed of dc main shaft to control unit, require 3 level of 2 ～ only mechanical gearshift, can satisfy requirement of timing of main shaft of numerical control machine tool. CNC MillingCNC Machining