Electronically controlled thread-cutting machine

Claim 1

An electronically controlled machine for cutting a thread in a workpiece, comprising: a spindle; a thread-cutting tool coupled to said spindle; a multi-phase stepping motor coupled to said spindle for rotationally driving said spindle and tool, said tool engaging the workpiece to effect cutting of the thread thereby causing translational movement of said spindle and tool relative the workpiece; said driving motor having a shaft, a stator with a multi-phase stator winding, a rotor with at least one pair of magnetic poles, and sensor means for producing digital information signals indicative of the angular position of said rotor; a DC source; control means connected to said DC source and said multi-phase driving motor for producing cyclic driving pulses and delivering said cyclic driving pulses to said stator winding; and means connected to said sensor means and said control means for selecting the sequence of said cyclic driving pulses in response to said digital information signals, said selecting means including counter means for counting a sum of said digital information signals indicative of the number of revolutions of said spindle, memory means for storing a value indicative of a preselected number of revolutions of said spindle, and comparing means for comparing said sum contained in said counter means with said value stored in said memory means, said selecting means effecting reversal of the rotating sense of said motor upon coincidence of said sum and said value, thereby determining the dimension of the thread being cut.