Monitoring of drill fracture from the current measurement of a three-phase induction motor

The use of three-phase induction motor current to detect tool fracture in drilling operations is presented in this paper. The basic principles of three-phase induction motors are briefly described and then an equivalent circuit diagram of induction motors is given. Based on the equivalent circuit diagram, the square stator current of induction motors is approximately proportional to the electromagnetic torque developed by the motor. Since the occurrence of tool fracture will cause the variations in the motor torque, measurement of the stator current appears to be an indirect technique for sensing tool fracture. Experimental results have shown that drill fracture can be clearly recognized from the stator current of a three-phase induction spindle motor system. Copyright (C) 1996 Elsevier Science Ltd