Reiji Kobayashi

A novel propulsion mechanism using a fin with a variable-effective-length spring

Since the propulsion mechanism in fluid using an elastic fin, such as the caudal fin or the pectoral fin of fish, is effective. However, the optimum elasticity of the fin is not constant and changes with the movement task and environment. It is very difficult to exchange fins of different stiffness while the robot is swimming. Thus, we attempt to develop a variable-stiffness fin with a variable-effective-length spring. The apparent stiffness of this spring can be changed dynamically. The present paper describes the thrust force, and flow velocity corresponding to the self propelled speed of the fin in a uniform flow. And we compared the thrust efficiency in a uniform flow with the evaluating value of the thrust efficiency in a no flow. Furthermore, we developed a flow visualization system and discussed the flow-field around the fin in a uniform flow.

Thrust Force Characteristics of Propulsion Mechanism in Fluid Using Fin with Dynamic Variable-Effective-Length Spring

We aimed to develop a propulsion mechanism using a variablebending-stiffness fin of which stiffness can be changed dynamically. As the one such variable-stiffness fin, we have developed a fin with a variableeffective-length spring. The apparent bending stiffness of the fin can be changed dynamically. We have measured the thrust force of the propulsion mechanism using a fin with a variable-effective-length spring and visualized flow around the fin. In this paper, we describe the structure of the propulsion mechanism in fluid using a fin with a variable-effective-length spring, and the thrust force characteristics with changing effective length of the spring dynamically. Furthermore, we discuss the relationship between thrust force and flow around the fin.