Expert system of machine tool equipped with NC unit

An expert system of a machine tool equipped with an NC unit, characterized by provision of a knowledge base storing expert knowledge regarding investigation of causes of various failures, a reasoning mechanism for deducing the cause of a failure based on the expert knowledge stored in the knowledge base, and conversational means for inputting the expert knowledge to the knowledge base, deleting and modifying the expert knowledge, and for conversing with the reasoning mechanism when failure diagnosis is performed;

• wherein the knowledge base stores knowledge for extracting digital input/output information, which is exchanged by the NC unit and the machine tool, as well as information internally of the NC unit;
• the reasoning mechanism discriminating the causes of failures in the NC unit and machine tool based on said information automatically extracted by said expert knowledge when a failure occurs.