Design and analysis of bio-mimicking tactile sensor for upper limb prosthesis

Tactile sensing is crucial sensory feedback that helps humans and robots to perceive their surroundings in a better way. The performance of a prosthetic hand is severely restricted by the scant tactile information provided by their sensors in contrast to the extensive tactile feedback of the human hand which has mechanoreceptors and capable of detecting both static and dynamic stimulus. Previous studies were mostly limited to detecting static stimulus and low frequency dynamic stimulus. However, some are capable of measuring both static and dynamic stimulus, but they are costly and unable to measure stimulus in frequency range of mechanoreceptors. A novel bio-mimicking tactile sensor with the ability to detect both static and dynamic forces in the frequency range of mechanoreceptors is presented in this paper. Proposed sensor design is inspired by human touch sensing receptors and targeted for use in upper limb prosthetics. A piezoelectric material is used for measuring dynamic stimulus in the sensor, whereas for evaluating static stimulus, principle of differential capacitance is utilized. A mathematical model is developed, and finite element analysis is performed using COMSOL, so that natural frequency of the sensor lies in the range of Ruffini endings (slow adapting receptor) and Pacinian corpuscles (fast adapting receptor). Results show that the first frequency of the beam is 324 Hz, which lies in the sensing range of Ruffini endings and Pacinian corpuscles. Sensor shows more than 99% agreement when results are validated by comparing eigenfrequency analysis and analytical model. The present research offers design of a bio-mimicking tactile sensor for a prosthetic hand, which is expected to incorporate prosthetic hand with touch sensing capabilities closer to that of a human hand.