Design of a 3-D Tactile Sensing Array for Incipient Slip Detection in Robotic Dexterous Manipulation

Fully reconfigurable tactile information sensing is indispensable of intelligent robotics intended for varieties of human-machine interactive applications. Current focus of the existing tactile sensors is still mostly on determining contact forces with high sensitivity or large measuring range, yet other tactile information especially the occurrence of incipient slip is equally noteworthy for stable grasping. Herein this article, a tactile sensing array consisted of four separate sensing units of similar pattern is proposed, which allows different areas of the gripper-object interface to change individually. A seesaw-like prototype based on floating electrode structure is introduced into the design of each sensing unit, drastically reducing unexpected coupling induced by the coupled response between in-plane stretch and out-of-plane pressure. The fabricated prototype of the tactile sensing array is of great flexibility and has displayed excellent multidimensional force sensing capability in terms of high sensitivity (2.38 kPa−1 for normal direction and 0.199 kPa−1 for tangential directions) and large measuring range (265 kPa for normal direction and 90 kPa for tangential directions). A feasible scheme based on empirical mode decomposition (EMD) was applied for validation of incipient slippage. Detected vibration component of first intrinsic mode function (IMF1) signals as well as real-time variation of stationary tangential force-to-normal force ratio were both taken into consideration to further divide actual incipient slip from possible regrasping. During extensive in-hand experiments, distinguished features were all successfully confirmed of incipient slippage than possible regrasping circumstances, implying full capability of detecting multidimensional contact forces and dividing incipient slippage simultaneously of this presented sensing array.