A bionic soft tongue driven by shape memory alloy and pneumatics

Soft grippers have exhibited considerable advantages owing to their flexible deformation, compliant operation, and safe interaction with objects. The ability to grip solid and liquid objects can greatly expand the application range of the soft grippers. Dogs stick out their tongues and then curl them backward to form a ladle shape for eating food and drinking water. The large extension ratio and the ladling motion of the tongues endow dogs with flexible operations for both solids and liquids. In this work, inspired by both the extending and ladling motions of dog tongues, a bionic soft tongue with the capability of handling solid and liquid objects was designed. The bionic soft tongue was composed of a tongue base and a tongue tip, which were driven by pneumatics and shape memory alloy wires, respectively. The tongue base was capable of linearly elongating and contracting with a considerable scale, while the tongue tip could be curled into a ladle shape to grasp objects. The dynamic model of the tongue base was developed and then extended to build the model-based feedback controller for the motion control. A phase dynamic model of the tongue tip was simulated for structural optimization. With the model-based feedback controller, the bionic soft tongue could achieve a fast step response and precise position control. Experimental results showed that the bionic soft tongue could grasp different kinds of objects, including of water, rice, and gel balls. This work is expected to expand the application scope of soft grippers.