Tactile piezoresistive sensors for robotic application: design and metrological characterization

Microfabricated tactile sensors gain importance for their application in bio-robotics. They are useful for the measurement of contact properties, in particular force and pressure, in three main fields, i.e., prosthetics and artificial skin, minimal access surgery and collaborative robotics. Among the different technological solutions, piezoresistive materials proved to be suitable for such an application. These materials show a change of electrical resistivity as a function of the applied strain. This work describes the design of a 2x2 array of piezoresistive elements and the experimental setup arranged for the array characterization, intended to be embedded within an artificial fingertip. The size of the bare array is 1.5x1.5x0.65 mm(3). The finger has been designed to bio-mimic the behaviour of a human finger tip, thanks to the external layer of dragon skin. The static calibration of the sensors has been carried out by applying quasi-static normal loads on the mesa of each sensor of the array in two configurations (i.e., bare array and the array embedded in a fingertip). The sensors showed a linear response; the sensitivity ranges from 34 mV/N to 65 mV/N for the bare array, and from 16 mV/N to 39 mV/N for the array in the fingertip. No significant cross-talk (similar to 2%) has been observed during the test on the bare array. Further tests will be designed to characterize the response to tangential loads and assess the dynamic response of the sensors, as well as additional features which can be crucial for bio-robotic applications.