Maintaining desired speed of cutting tool in numerically controlled machine tool

Claim 1

In the art relating to numerically controlled machine tools of the type comprising an element that is movable to effect relative motion between a cutting tool and a workpiece, program means for effecting predetermined motions of said element relative to a system of coordinate axes, a pulse generator which generates pulses at a fundamental frequency controlled by the program means, each pulse corresponding to a predetermined increment of motion of said element along an axis, and function generator means to which pulses are fed and which is operatively associated with the program means to distribute pulses to the several axes in such a manner that the frequency of pulses assigned to each axis corresponds to the component along that axis of the programmed vector of motion of said element, the method of maintaining the speed of motion of said element at substantially the value which the fundamental frequency assigns to movement of the element along an axis, even at times when the element is programmed to move obliquely to axes, which method is characterized by: A. counting successive pulses into successive equal groups, the number of pulses in each group being an integral multiple of the number of axes so that the pulses of a group can have only a limited number of possible distributions among the several axes; B. for each such possible pulse distribution predetermining a number of supplemental pulses which is a function of a relationship between the total distance that the cutting tool would traverse in movement along the axes in the pattern signified by the pulse distribution and the direct distance traversed in such movement; C. as each group of pulses in counted, recording the number of pulses of the group that are distributed to each of the different axes, for determination of the number of supplemental pulses that is appropriate to the pulse distribution of the group; D. generating the number of supplemental pulses determined to be appropriate to the pulse distribution of each counted group and injecting such number of supplemental pulses between pulses of the fundamental frequency that are generated immediately after the group has been counted, to produce pulses at an augmented frequency; and E. feeding pulses of the augmented frequency to the function generator means.