Artificial Fingertip with Embedded Fiber-Shaped Sensing Arrays for High Resolution Tactile Sensing

Replication of the human sense of touch would be highly advantageous for robots or prostheses as it would allow an agile and dexterous interaction with the environment. The article presents an approach for the integration of a micro-electromechanical system sensing skin with 144 tactile sensors on a soft, human-sized artificial fingertip. The sensing technology consists of thin, 1D sensing strips which are wrapped around the soft and curved fingertip. The sensing strips include 0.5 mm diameter capacitive sensors which measure touch, vibrations, and strain at a resolution of 1 sensor/mm2. The method allows to leverage the advantages of sensing skins over other tactile sensing technologies while showing a solution to integrate such skins on a soft three-dimensional body. The adaptable sensing characteristics are dominated by the thickness of a spray coated silicone layer, encapsulating the sensors in a sturdy material. We characterized the static and dynamic sensing capabilities of the encapsulated taxels up to skin thicknesses of 600 mu m. Taxels with 600 mu m skin layers have a sensitivity of 6 fF/mN, corresponding to an similar to 5 times higher sensitivity than a human finger if combined with the developed electronics. They can detect vibrations in the full tested range of 0-600 Hz. The softness of a human finger was measured to build an artificial sensing finger of similar conformity. Miniaturized readout electronics allow the readout of the full finger with 220 Hz, which enables the observation of touch and slipping events on the artificial finger, as well as the estimation of the contact force. Slipping events can be observed as vibrations registered by single sensors, whereas the contact force can be extracted by averaging sensor array readouts. We verified the sturdiness of the sensing technology by testing single coated sensors on a chip, as well as the completely integrated sensing fingertip by applying 15 N for 10,000 times. Qualitative datasets show the response of the fingertip to the touch of various objects. The focus of this article is the development of the sensing hardware and the basic characterization of the sensing performance.