Third stage (the 1980 s in the era background of mechatronics development. Because of the bar uniform motor and permanent magnet materials and control technology of breakthrough in brushless dc servo motor (square wave current drive >, ac servo motor (sine wave current drive) and so on many kinds of new type motor, at the same time, the rapid development of power electronic technology, the microprocessor trigger a servo drive device has experienced the analog and digital simulation the development of hybrid and all words,