System for controlling numerically controlled machine tool used for cutting threads

摘要

A system for controlling the operation of a numerically controlled machine tool used for cutting threads on workpieces, in which means are provided so that the quality of the products may not be adversely affected even when the thread cutting operation is interrupted for some reasons incidental to the thread cutting. The control system comprises a thread cutting interruption control circuit consisting of an adder-subtractor automatically carrying out addition or subtraction of the output of a thread pitch memory to and from a pair of outputs of a function generator variable depending on the position of the tool along a predetermined path, a temporary memory storing the information of a thread cutting command position read by a tape reader and stored in a first memory, and a thread cutting command position changing circuit applying the output of the adder-subtractor to the first memory in response to the application of an interruption instruction signal during the thread cutting operation thereby replacing the information of the thread cutting command position previously stored in the first memory by the output of the adder-subtractor, and, on the other hand, applying the output of the temporary memory to the first memory in response to the application of a restarting instruction signal thereby restarting the thread cutting cycle again after elimination of the cause requiring the interruption.