Worn tool detector utilizing normalized vibration signals

DETAILED DESCRIPTION Pursuant to the present invention the signal waveform from a vibration sensor is connected to a variable gain amplification network including at least one digitally controlled component for effecting a change in gain in the network.
Comparator means are provided for supplying a signal to a microprocessor indicative of the relative difference between the output of the variable gain network and a fixed reference voltage.
The microprocessor is operative to respond to the comparator output and normalize the sensor waveform by varying the gain network until the average amplitude of the waveform is substantially equal to the reference.
During the operational cycle of the machine, an indication of tool wear is provided by sensing the occurrence of impulses in the sensor waveform having amplitudes exceeding the normalized level.
When a given number of successive impulses are detected within a time period associated with the period of rotation of the tool, a warning signal is generated which may be used to retract the tool from the workpiece.
According to another aspect of this invention an adaptive mode is provided whereby the sensor signal is repetitively normalized during machine operation.
The repetitive normalization automatically adjusts for variations in the amplitude of the sensor signal which may be due, for example, to the change in relative distance between the sensor and the tool during the machining operation.
A feature of this invention includes the provision for disregarding potentially erroneous impulses detected by the system circuitry when the tool is not in the position to provide valid data to the sensor.