Bio-inspired flexible joints with passive feathering for robotic fish pectoral fins

Abstract

In this paper a novel flexible joint is proposed for robotic fish pectoral fins, which enables a swimming behavior emulating the fin motions of many aquatic animals. In particular, the pectoral fin operates primarily in the rowing mode, while undergoing passive feathering during the recovery stroke to reduce hydrodynamic drag on the fin. The latter enables effective locomotion even with symmetric base actuation during power and recovery strokes. A dynamic model is developed to facilitate the understanding and design of the joint, where blade element theory is used to calculate the hydrodynamic forces on the pectoral fins, and the joint is modeled as a paired torsion spring and damper. Experimental results on a robotic fish prototype are presented to illustrate the effectiveness of the joint mechanism, validate the proposed model, and indicate the utility of the proposed model for the optimal design of joint depth and stiffness in achieving the trade-off between swimming speed and mechanical efficiency.

Dynamic Analysis of a Robotic Fish Propelled by Flexible Folding Pectoral Fins

“…For example, in ref. [17], the authors had to anchor their robot to be able to measure the feathering angle of fins by using cameras. A demonstration diagram of the experimental system is summarized in Fig.…”

“…For example, while the parameters C D , C L , and C M were obtained through CFD simulation, 24 they could be found through matching data between simulation and experiment under the mode of turning and forward swimming. 17,18,30 For our work, an experimental identification is more priority due to accuracy under practical condition. The coefficient C D is first determined by the underwater movement measurement of the robot body through pulleys and a rope connected to a free falling object, 31 and the resulting value is C D = 0.0175.…”

“…On the other hand, the propulsive mechanism and the factors impacting on motion efficiency of the pectoral fin such as the shape of fins, the flexibility of fins, or joints were explored with empirical investigations for both real fish and robotic fish, 5,12,13 while the numerical simulation such as computational fluid dynamics (CFD) was paid attention by reliability and accuracy despite timeconsuming computation. 14,15 More suitable for designing controllers, the analysis modeling for the pectoral fin has attracted attention in some recent researches [16][17][18] in which the blade element theory was used to establish hydrodynamic interactions. Different from the above approaches, analysis modeling using Morison's model has not mentioned to the robotic fish with the rowing pectoral fin.…”

“…Different from the mechanical designs presented in refs. [17,18], our fin type composes two fin panels connected to a hinge peduncle through the flexible joints. It is noted that the thrust/drag area ratio in fin movement direction between recovery stroke and power stroke is scrutinized to minimize drag force, which is compared with a multi-DOFs fin structure in refs.…”

Model Predictive Control-Based Path-Following for Tail-Actuated Robotic Fish

“…The latter makes optimal control an important problem for robotic fish. Much of the work done for robotic fish has been in robot development [2][3][4][5][6][7][8][9][10][11] and modeling [12][13][14][15][16][17][18]. There has also been extensive work on motion control of robotic fish, which has mainly been focused on the generation of fish-like swimming gaits, and on control to drive the robot to achieve a desired motion.…”