Analysis of Heading Stability due to Interactions between Pectoral and Caudal Fins in Robotic Boxfish Locomotion

Abstract

Investigating the interaction between fins can guide the design and enhance the performance of robotic fish. In this paper, we take boxfish as the bionic object and discuss the effect of coupling motion gaits among the two primary propulsors, pectoral and caudal fins, on the heading stability of the body. First, we propose the structure and control system of the bionic boxfish prototype. Second, using a one/two-way fluid–structure interaction numerical method, we analyse the key parameters of the prototype and discuss the influence of pectoral and caudal motion gaits on the hydrodynamic performance. Finally, effect of the pectoral and caudal interactions on heading stability of the prototype is systematically analyzed and verified in experiments. Results show that the course-deviating degree, oscillation amplitudes of yawing, rolling, and pitching exhibited by the prototype are smaller than that caused by single propulsor when the motion gaits of both pectoral and caudal fins are coordinated in a specific range. This paper reveals for the first time the effect of interactions between pectoral and caudal fins, on the stability of body's course by means of Computational Fluid Dynamics and prototype experiments, which provides an essential guidance for the design of robotic fish propelled by multi-fins.

Central Pattern Generator (CPG)-Based Locomotion Control and Hydrodynamic Experiments of Synergistical Interaction between Pectoral Fins and Caudal Fin for Boxfish-like Robot

“…In the early work of our lab [ 28 , 51 ], we used the one/two-way FSI numerical analysis method to analyze the key parameters of the prototype. Based on the above simulation analysis, we built a hydrodynamic experiment environment for the robotic fish.…”

“…In order to achieve the best state of swimming for the prototype, it is necessary to analyze the effects of parameters such as amplitude, frequency, offset angle, desired phase lag, and time asymmetric coefficient in the CPG controller based on the phase oscillator model on the swimming performance of the robotic fish. Based on the numerical simulation analysis of our work [ 28 , 51 ], we designed and built the swimming performance testing platform of the robotic fish, and further explored the inner relationship between these parameters by experimental device method, so as to select the best parameters to guide the movement of the robotic fish. Obviously, thrust and lift are the main factors affecting the propulsion capability of the robotic fish prototype, while the turning of the robotic fish is mainly realized by the lateral force generated by the coordinated swing of the pectoral fins and caudal fin.…”

“…The physical object and overall three-dimensional (3D) size of the designed robotic fish are shown in Figure 2 . Based on our previous work [ 28 ], the pectoral and caudal fins of the prototype are made of carbon fiber plates (CFP) and silicone. Meanwhile, part of the carbon fiber plate skeleton of the fin is hollowed out along the radial direction and filled with silicone glue, which endows the fin surface with flexibility and improves the bionic performance of the fin surface flapping.…”

“…Due to the fact that the pectoral and caudal fins are the primary propulsion components of biological fish, many scholars have studied the effects of different forms of pectoral and caudal fins on swimming, including rigid, multibody and soft fins [ 25 , 26 , 27 ]. Oiu et al [ 28 ] reveals for the effect of synergistic interactions between pectoral and caudal fins on the stability of body’s course by means of Computational Fluid Dynamics and prototype experiments. They analyzed the influence of the pectoral and caudal fin synergistically interactions on the heading stability of the prototype and proposed that proper coordination parameters of pectoral and caudal fins can improve the heading stability of robotic fish.…”

“…Motivated by previous research and the work of our team in the field of boxfish-like robots [ 28 ], this paper improves the structure, hardware, and control strategy of robotic fish. Based on the designed six degrees of freedom (DOF) fins (double two-DOF pectoral fins and single two-DOF caudal fin), a CPG-based controller is designed.…”