A method based on spindle motor current harmonic distortion measurements for tool wear monitoring

This paper deals with an indirect measurement of tool wear from spindle motor current. The main focus of this paper is on harmonic analysis of motor current. In this research, the nonlinear harmonic distortion caused by tool breakage and tool wear in the turning process is scrutinized. Representation of fundamental and harmonic components of the signals indicates that the amplitude of fundamental and odd order harmonic components of the signal for worn tool is higher than sharp tool. As the result of increasing harmonics the waveform of AC current signal becomes more distorted. The total harmonic distortion and crest factor measurements, which indicate the level of distortion in the current signal, are proposed as the measures for detecting tool wear and tool breakage by measuring electric current signal. The results show that the total harmonic distortion and crest factor measures increases as tool wear occurs and abruptly increases when there is tool breakage.