| 摘要 |
A numerical control unit having a load monitoring function for monitoring a load on a tool drive source during a machining operation. The numerical control unit includes a load monitoring section for monitoring the load on an electric motor; a wear recognizing section for recognizing the current extent of tool wear; a storing section for storing a plurality of preset limit load values corresponding individually to predetermined various extents of tool wear; a calculating section for calculating the current limit load value corresponding to the current extent of tool wear recognized in the wear recognizing section, based on the plurality of preset limit load values stored in the storing section; and a comparing section for comparing the load on the electric motor, monitored in the load monitoring section, to the current limit load value calculated in the calculating section, and for judging on the abnormality of the load. The wear recognizing section recognizes the current extent of tool wear by using one parameter selected from a group consisting of the number of times of use of a tool, the duration of cutting by a tool, the distance of cutting by a tool and the number of times of execution of machining program. The load monitoring section monitors at least one of maximum value, average value and minimum value of the load in a certain procedure of a machining program.
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