Zeroing control system for numerically control apparatus

Claim 1

A numerical control apparatus operated by a signal outputted from a proximal point detecting means, mounted on a movable part of a working machine, which detects said movable part being in close proximity of a zero point of the machine said zero point being defined as reference point for movement of said machine, and a signal outputted from a machine position detecting means for detecting the position of the movable part of said machine when the machine is to return to said zero point comprising: a zeroing means having, (a) a waveform producing means for transforming an output signal from said machine position detecting means into a waveform; (b) a grid signal producing means for producing signals based on the output signal of the waveform from said waveform producing means and which represent a grid formed on said movable part; (c) a data processing means for processing pulses produced during the time period that occurs from the separation of said proximal point detecting means from a ridge to detection of a first grid signal that is produced when the machine is moved in a direction approaching the machine zero point; (d) a pulse number processing means for processing the number of pulses produced between adjacent elements in said grid; (e) an intermediate point processing means for processing an intermediate position between the adjacent elements of said grid on the basis of the output signal of the pulse number processing means; (f) a grid shift quantity processing means for processing a grid shift quantity on the basis of the output signals of said data processing means and said intermediate point processing means; (g) a code determination means for determining the direction of grid shifting in either a negative or positive direction, with said positive and negative directions being artificially selected based upon and in the original plane of movement of said machine and on the basis of grid shift data outputted from said grid shift quantity processing means; and (h) a memory means for storing data outputted from said code determination means.