Event-Triggered Control of Robotic Fish With Reduced Communication Rate

Underwater robots often need to communicate with external localization sensors. The low bandwidth in such communications is one of the bottlenecks in achieving accurate tracking control. Toward this end, we adopt a novel periodic event-triggered control (PETC) which allows a robotic fish to reduce its communication load in tracking a desired heading angle with position feedback from an external sensor. To design the PETC, a linear state-space model is derived from a nonlinear dynamic model of the robotic fish with a small perturbation assumption. The PETC consists of an observer, state-feedback controller, integrator, event-trigger rule, and predictor. The observer and state-feedback controller are designed to drive the tracking error to zero. The integrator reduces the steady-state error. The event-trigger rule determines when communication is needed while ensuring the efficacy of the state-feedback controller, and the predictor predicts the state vector for the state-feedback controller when communication is not available. For comparison, an observer-based state feedback control (OSFC) and a proportional-integral-derivative (PID) control are implemented in real-time experiments. Simulations and experimental results show that the PETC can dramatically reduce the number of communication instances without significantly degrading tracking performance, thereby saving communication energy and reducing the need for high bandwidth underwater communication.