Cooperative Collision Avoidance Control of Servo/IPMC Driven Robotic Fish With Back-Relaxation Effect

In this letter, a collision avoidance control strategy is developed for a robotic fish that is propelled by a two-joint fishtail, comprising a servo motor and an ionic polymer-metal composite (IPMC), which are used as solid and soft actuators, respectively. In this dual-actuator system, the forward motion of the fish is controlled by the servo motor, which generates a flapping motion at its first joint, and the turning motion of the fish is controlled by bending the IPMC at its second joint. When a constant voltage is applied to the IPMC, the robotic fish is observed to demonstrate a short-term turning characteristic, and this is attributed to the back-relaxation phenomenon inherent in the IPMC. In order to capture this unique characteristic, a data-driven approach is adopted to model the fish's lateral acceleration response when subjected to an IPMC voltage input. Experimental tests, including bending tests on an individual IPMC slice and turning tests on the robotic fish (with the servo/IPMC tail), are conducted to collect sufficient data to identify a transfer function that relates the voltage applied to the IPMC with the lateral acceleration response of the fish. This transfer function is then integrated with a collision avoidance control law (based on the collision cone concept) to determine the IPMC voltages for a pair of robotic fish to avoid collisions. Experiments are performed to validate the collision avoidance control law.