Variable Stiffness Flapping Robot

Compliance can increase the thrust generated by the fin of a bio-inspired underwater vehicle. To improve the performance of a compliant fin, the compliance should change with the operating conditions; a fin should become stiffer as the oscillating frequency increases. This paper presents a novel variable-stiffness flapping (VaSF) mechanism that can change its stiffness to maximize the thrust of a bio-inspired underwater robot. The mechanism is designed on the basis of an endoskeleton structure, composed of compliant and rigid segments alternately connected in series. To determine the attachment point of tendons, the anatomy of a dolphin’s fluke is considered. Two tendons run through the mechanism to adjust the stiffness. The fluke becomes stiffer when the tendons are pulled to compress the structure. The thrust generated by a prototype mechanism is measured under different conditions to show that the thrust can be maximized by changing the stiffness. The thrust of the VaSF device can approximately triple at a certain frequency just by changing the stiffness. This VaSF mechanism can be used to improve the efficiency of a bio-inspired underwater robot that uses compliance.

Related papers and patents

Yong-Jai Park, Tae Myung Huh, Daegeun Park, and Kyu-Jin Cho, “Design of a variable-stiffness flapping mechanism for maximizing the thrust of a bio-inspired underwater robot,” Bioinspiration & Biomimetics, Vol. 9, No. 3, p. 036002, Mar. 2014.
Yong-Jai Park and Kyu-Jin Cho, “Design and Manufacturing a Bio-inspired Variable Stiffness Mechanism in a Robotic Dolphin”, in The 6th International Conference on Intelligent Robotics and Application (ICIRA), pp. 302–309, Sep. 2013.
Yong-Jai Park and Kyu-Jin Cho, “Stabilizing the head motion of a robotic dolphin with varying the stiffness of a caudal fin,” in 2013 13th International Conference on Control, Automation and Systems (ICCAS), pp. 901–904, Oct. 2013.
Yong-Jai Park, Daegeun Park, and Kyu-Jin Cho, "Design and Manufacturing a Robotic Dolphin to Increase Dynamic Performance," in 2013 10th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI), pp. 76–77, Oct. 2013.
Tae Myung Huh, Yong-Jai Park, and Kyu-Jin Cho, "Design and Analysis of a Stiffness Adjustable Structure Using an Endoskeleton," International Journal of Precision Engineering and Manufacturing, Vol. 13, No. 7, pp. 1255-1258, Jul. 2012.