Mechatronic extension of a tap holder for process monitoring

Sensor systems based on passive radio-requestable surface acoustic wave (SAW) devices are capable of wirelessly monitoring physical or chemical quantities from distances up to 3 m. For tests under realistic conditions in machining operations, the authors have implemented a SAW device connected to a patch antenna into the length compensation of a tap holder. In a first step, the SAW device was a 2-bit identification (ID) tag operating at 2.4 GHz and interrogated by an FM CW signal. Normally, only one bit is visible and serves as an OK signal for the whole setup whereas the second bit is switched off. The latter plays the role of an alarm bit to be turned on if an error occurs during tapping: the error-e.g., a missing core hole-results in a compression of the length compensation and thus activates a Reed contact which in turn switches the alarm bit from low to high. The present contribution discusses the parts of the mechatronic system, viz., the SAW element, the other RF components and the request unit, as well as their interaction and problems involving the system design