Abstract
A flexible biomimetic fish-like robot for use in a flow in narrow passage was developed. Downsizing of the moving body was achieved using shape memory alloy (SMA) actuators. However, overheating an SMA actuator causes phase-transition saturation, and may cause a decrease in the fin vibration amplitude. In order to avoid this problem, a new driving method that utilized a self-excited oscillator was introduced. We confirmed the effectiveness of the proposed driving method against overheating using an experiments and numerical simulations. Simulation proved that this method can keep thrust force of the moving body constant. For the fish-like moving body, multiple actuators were needed to realize higher freedom of behavior, and the phases of these actuator outputs needed to be synchronized to generate fish-like behavior, i.e., traveling wave. On the other hand, in the proposed driving method, the actuator system simulates a self-excited vibration system. Therefore it was necessary to design the connecting inputs of oscillators composed by actuators to synchronize the oscillator outputs. To achieve this, a phase model was obtained from an actuator model, which consisted of a thermal conductivity model and hysteresis model using a phase reduction analysis. Connecting inputs of oscillators were designed based on this phase model, and the relationship between the phase difference of the coupled actuators and the connection gains was examined. Finally, we realized phase control using this designed connection.
