A gecko-inspired adhesive robotic end effector for critical-contact manipulation

It is an emerging challenge for robots to achieve non-destructive pick-and-place manipulation for delicate objects under low normal preload, i.e., critical-contact manipulation. The prominent on-off controllable property of the gecko-inspired microwedge adhesive makes critical-contact manipulation possible for robotic end effectors. However, it is difficult for end effectors to actuate the micron-scale microwedge adhesive and detect the adhesion state. In this paper, a gecko-inspired adhesive robotic end effector for critical-contact manipulation is proposed, which consists of a half-scissor variable-scale actuator, a 3-axis high-sensitivity isotropic flexible capacitive tactile sensor, and the microwedge adhesive. The half-scissor variable-scale actuator is designed to provide pure large shear loading for the microwedge adhesive at micron-scale displacement by merely controlling the normal macro-scale displacement of the actuator. Besides, the 3-axis high-sensitivity isotropic flexible capacitive tactile sensor is designed for accurate detection of multi-axis contact forces and the adhesion state between the adhesive and objects to ensure the success of the critical-contact manipulation. The sensor can sense the shear and normal forces by detecting variations of the overlap and distance between electrodes, while the design of the finger-like electrodes improves the sensitivity. In addition, a set of experiments on manipulating objects are implemented and the results show that the proposed robotic end effector can provide pure large shear loading for the microwedge adhesive at micron-scale displacement and can detect the adhesion state between the microwedge adhesive and objects accurately to stably grasp delicate objects in critical-contact condition.