Acoustic detection of tool break events in machine tool operations

DETAILED DESCRIPTION An object of the invention is to provide a cutting tool break detection system that improves on state-of-the-art devices in cost, response time, sensitivity, ease of installation and reliability.
Another object is the provision of such a system and method that can discriminate between minor tool breaks and breaks major enough to cause significant marring of the workpiece.
Another object is to extract tool break detection clues from both the acoustic emission energy produced by the break event itself, and from changes in the background cutting noise caused by changed cutting conditions after the break event.
This permits matching the tool break signature detection criteria to the needs of high productivity machining, where high cutting noise sometimes masks the acoustic emission energy, and where it is important to avoid stopping the machining process on false alarms associated with minor tool break events and spurious noise sources.
Another object is to avoid the need for elaborate teaching cycles and measurements before the tool break detection system can be set up to operate on a new workpiece.
Systems based on absolute horsepower or force limits must use test cuts to determine normal deviations of the sensed parameter levels throughout all cuts to be made in machining the part.
Their utility is generally limited to applications in which large numbers of identical parts are to be machined, as opposed to those in which many different parts are to be machined.
This invention relies primarily upon detection and interpretation of transients and level shifts of the vibration signal, rather than crossings of absolute limits, and thus is able to provide good tool break detection performance without the use of any prior information on the specific cuts to be made.
Another object of the invention is to minimize the problems of installing and operating the tool break detection system.
The sensor is small and rugged, and a single sensor mounted a reasonable distance from the tool-workpiece interface is usually sufficient