Phase control of oscillators for moving body in narrow passage

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. This proposed method is suited for generating oscillation with keeping temperature in SMA constant by using self-sensing, and needs to adjust only one parameter. We confirmed the effectiveness of the proposed driving method against overheating based on 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 are needed to realize higher degree of freedom behavior, and the phases of these actuator outputs also are 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 coupled inputs for oscillators composed by actuators to synchronize the oscillator outputs. To achieve this, a phase model was obtained from an actuator model, which consists of a thermal conductivity model and hysteresis model using a phase reduction analysis. Coupled inputs for proposed connecting method 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.