Piezoelectric Dual-Axis Cantilever Force Measurement Probe

A piezoelectric cantilever force sensor consisting of a mechanical cantilever probe, an analog amplifier and an embedded digital signal processing unit is presented. The sensor is constructed from a lead zirconate titanate (PZT) piezo disc, which was cut into four segments and a 33-mm-long metal probe attached to it perpendicularly to the piezo disc plane. The signal of the piezoelectric elements was amplified with a four channel operational amplifier circuit having voltage gain of 10 (20 dB) in each channel and input resistance of 50 M Omega. The digital signal processing was implemented on an Arduino Due -based hardware. Signal pre-processing block consists of three cascaded digital infinite impulse response (IIR) filters were composed: A DC-blocking filter, a notch filter and a low pass filter. Additionally, a moving average filter was implemented to further enhance the system tolerance to power line interference and to reduce the sampling rate to 50 Hz. Finally, a LabVIEW software is used to provide an interface for the Arduino Due. The calibration of the system was carried out with a texture analyzer and it was capable of sensing biaxial forces in the range of 2 millinewton with a RMS error of less than 60 micro Newton and hysteresis in the order of 0.25 millinewton or 12.5% of the full scale reading. Cross talk ratio between axes was 25.3 or 28.0 in dB. The applicable force measurement frequency range was 0.5 - 10 Hz.