Abstract: Error motion inspection, diagnosis and compensation methods of NC machines are commented in detail in the domestic and overseas on the recent 20 years, especially the current years. These NC machines are based on the circular interpolation. First, it analyzes the difference in hardware among the seven different kinds of methods. Next, it analyzes the difference in software among the methods done by Y. Kakino, Chinese Taiwan J. M.’ Lai, Korea S. W. Hong and H Pahk K.’, Chinese Zhejiang University and Tianjin University’s motion errors modeling, identification and multi-body system (MBS) errors compensation. Finally, it is pointed out that in order to improve NC machines’ running efficiency and performance quality, such actions as detect-diagnose-compensate method should be taken. This method includes first detecting motion errors then tracing to the organic fault (accuracy abnormal recourse) according to the detected errors, next adjusting machines’ electromechanical system or replacing machines components in order to reduce motion trace errors, finally compensating the decreased errors to improve machines accuracy greatly. It is more significant to compensate motion errors after adjusting machines to the optimal status to reduce condition errors as much as possible. So, a new measurement method known as ‘three-circle method’ (‘Order circle’, ‘NC circle’ and ‘actual circle’) is put forward to resolve these problems effectively.

Key words: Equipment diagnosis, NC machine, Three-circle method