Abstract: An operation history display device of a numerical control apparatus by which a fault causing factor can be easily specified. Key input means outputs the key signal of an operation key depressed by an operator to input a command to the numerical control apparatus. Change detection means detects a change of an output signal and outputs the signal to which the change is caused. Operation history control means stores the signal name and the like of the signal to which the change is caused to a history buffer together with a present time output from a timer as history data. Thereafter, display control means displays the history data stored in the history buffer on a display unit in response to a predetermined operation performed by the operator.

Abstract: There is provided a numerical control unit having a processor (102a), a control program memory (102b), a memory (102c) for storing files, and input means (102d) for accessing the files. The processor (102a), in accordance with the control program, processes externally entered control data to numerically control a machine connected thereto. The arrangement is such that the name of a file to be protected is stored in the memory (102c) of the numerical control unit and, the name of an object file is compared with the protected file name in the memory (102c), when a modification command and the name of the object file are entered from the input means (102d). Processing for modifying the file is executed, on the condition that there is a processing confirmation input from the input means (102d), when the object is a file protected file.

Abstract: In an apparatus wherein a memory is subdivided into plural storage areas, and predetermined data are adapted to be written into respective ones of the storage areas, a method of reconfiguring the storage areas of the memory. The leading addresses of the respective storage areas and the sizes of blank portions of the respective storage areas are stored while it is discriminated whether a blank portion exists in a predetermined one of the storage areas. When there is no blank portion or substantially no blank portion in the predetermined storage area, the blank portions of the remaining storage areas are reduced in size on the basis of the leading addresses and the sizes of the blank portions. The predetermined storage area is enlarged by an amount equal to the amount of blank portion reduction effected in the remaining areas.

Abstract: An electrode retraction control system of an electric discharge machine for rapidly retracting an electrode from a workpiece, in which the retraction velocity and readvance velocity of an electrode (EP) moving relative to a workpiece (WK) are set to a velocity obtained by multiplying, by a fixed multiplication factor (a, k), a velocity decided on the basis of a gap sensing voltage (Vd) corresponding to the magnitude of a gap between the workpiece (WK) and the electrode (EP), the velocity being held constant during retraction and readvance. Machining efficiency is advanced by raising the retraction velocity and readvance velocity of the electrode (EP).