Control apparatus for drilling machine

Abstract

A drilling machine comprises an electric drill having a drill motor for rotating an annular drilling tool and a feed control motor for moving the annular drilling tool forward and backward with respect to a workpiece, both connected to an AC power source, and an electromagnetic base for fixing the electric drill on an object to be drilled. A control apparatus for the drilling machine comprises a switching element for controlling a power supply timing of an AC power to the feed control motor, a detector for detecting a load current of the drill motor, a sawtooth signal generator synchronized with each of positive and negative half cycles of the AC power source, a first pulse generator synchronized with the negative half cycle of the AC power source, a second pulse generator synchronized with the sawtooth wave signal, a duty ratio of the second pulse increasing as the load of the drill motor decreases, a third pulse generator synchronized with the sawtooth wave signal, a duty ratio of the third pulse increasing as the time passes from activation of the drill motor, an OR gate for obtaining a logical sum of the first and third pulses, an AND gate for obtaining a logical product of the first and second pulses, the output of the AND gate controlling the switching timing of the switching element.