Structure and theoretical model of novel low frequency tactile sensor based on resonance frequency

In this paper, a resonant tactile sensor at low frequencies which can be used to measure the stiffness of soft objects was presented. And the corresponding theoretical model was deduced. In this work, in order to reduce the resonant frequency of the tactile sensor, soft materials were added to the sensor. Two of the PZTs (Φ6mm x 2mm) act as oscillator and pickup respectively. A soft silicone disc (Φ3mm
^x
3mm) was placed between the PZTs and a hemispherical plastic contact tip (Φ3mm). This structure reduces the resonant frequency to within KHz. Using MATLAB, the theoretical model can be used to calculate the intrinsic frequency of the sensor and the resonant frequency shift of sensor when adding the contact conditions. The frequencies obtained by comparing theoretical calculations and finite element simulations before and after contact between the sensor and the testing object. As the hardness of the tested substance changes, their results very similar and the change the trend was consistent. Despite in the case of contact, because the theoretical model ignored the impedance of the measured objects, they have more errors, which can be compensated in subsequent work. And the importance of frequency reduction was also verified by theoretical calculation. We can obtain that the proposed theoretical model can well describe the sensor behavior, and the proposed sensor structure can well distinguish soft tissues with different hardness, which could potentially be integrated into robotic handles or medical devices to measure hardness.