FPGA based on-line tool breakage detection system for CNC milling machines

On-line tool breakage detection is one of the most important mechatronics problems in automated CNC machines. In this paper an on-line tool breakage detector for milling machines is described. The detector employs the cutting forces on the movement axis to compute the discrete wavelet transform of the resultant force. The novelty of this work is to apply the discrete wavelet transform of the resultant cutting force an autocorrelation algorithm to detect tool breakage in the form of an asymmetry weighting function and to implement the algorithm by using hardware signal processing techniques. The cutting force signals are taken from the current at the axis motor drivers for a sensorless instrumentation approach. The system has three parts: the signal conditioners, the data acquisition system and the hardware signal processing unit. The hardware signal processing unit was designed by following the system on-a-chip approach and it includes three application specific digital signal processing units, general synchronization, interface and control, implemented in a single field programmable gate array and a coefficient read-only memory. On-line detection and low-cost are guaranteed by following this approach. The detector system is a stand-alone unit and does not require microprocessors or computers to perform its task. Experimental results that show the overall system performance are presented. (C) 2003 Elsevier Ltd. All rights reserved.