Optimization on driving method of moving body in narrow passage considering nonlinearity of shape memory alloy actuator

Abstract

Authors developed the flexible biomimetic fish-like robot for usage in narrow passage flow. The robot mainly consists of three sections: a control section, actuator section and flexible fin section. By using the shape memory alloy (SMA) actuators, downsizing and lightening has been achieved. At first, we constructed the fluid-body coupled model of robot fish for consideration of undulatory swimming and nonlinearity of SMA characteristics. We also constructed experimental model to confirm the validity of analytical model. It is known that dynamics of SMA actuator depends on ambient temperature. Therefore over-heating of SMA actuator may cause accumulation of heat in actuator section of the moving body, and decrease of the amplitude of the caudal fin and the thrust force. Thus, in this study, to improve the driving characteristics of actuator, we identified the relation between temperature and moment of SMA actuator. Next, we constructed the fluid-moving body interaction model which is considering the dynamics of actuator. We searched the local optimal input for SMA actuator based on optimization theory. As a result, it was found that for maintaining high thrust force SMA actuator needs to be driven keeping the temperature around 340[K].