A differential strategy for measurement of a static force in a single-point diamond cutting by a force-controlled fast tool servo

This paper presents a new strategy for applying a piezoelectric (PZT) force sensor to the measurement of static force in a force sensor-integrated fast tool servo (FS-FTS) system for single-point diamond cutting on planar brittle material substrates. A conventional PZT force sensor unit composed of a PZT force sensor and a charge amplifier cannot be employed for measurement of static force due to the discharging characteristics of PZT materials. In this paper, to realize the long-term stable measurement of static cutting force, the time constant of the PZT force sensor unit is set to be infinitely large by removing the feedback resistor from the charge amplifier. The influence of bias current leakage, which arises as a result of removing the feedback resistor, is compensated through obtaining the differential output of the two PZT force sensor units having identical charge amplifiers and identical thermal characteristics. After microgroove-cutting experiments to verify the stability of the PZT force sensor unit in the conventional FS-FTS unit, a theoretical model for the PZT force sensor unit is established. Some basic experiments are then carried out to verify the feasibility of the proposed differential measurement strategy. Furthermore, a modified FS-FTS unit with a pair of PZT force sensor units based on the proposed strategy is developed, and its effectiveness is demonstrated through experiments.