仿生机器鱼S形起动的控制与实现

给出一种仿生机器鱼S形起动的控制方法.结合北美狗鱼S形起动的形态特征及水动力学知识, 建立了多关节链式结构仿生机器鱼的S形起动模型.整个过程设计为两个阶段: 1)弯曲阶段:以转向速度最大化为目标.在鱼体S形变保证重心稳定平移的前提下, 增大较长转向力臂处的转向力矩,提高转向速度,使鱼体迅速转向目标方向. 2)伸展阶段:以增大前推力为目标.始终保持部分将要伸展的鱼体垂直前进方向,以L形滑动方式打开鱼体. 同时,为保证转向精度,采用模糊控制调节已展开鱼体关节的小角度转动,实时纠正鱼体展开所引起的游动方向偏离. 在S形起动末期,采用变幅值——频率的中枢模式发生器(Central pattern generator, CPG)实现向稳态游动方式的过渡:前期为保证游动方向及获取较大推进力,采用小幅值——高频率的CPG信号, 后期则进入大幅值——低频率的稳态游动.最终,采用四关节仿生机器鱼验证了该方法的有效性, 实现了峰值转速为318.08±9.20°/s、转向误差为1.03±0.48°的较好结果, 对提升水下游动机器人的机动性能具有指导意义.

Control and Implementation of S-start for a Multijoint Biomimetic Robotic Fish

This paper is devoted to the S-start maneuvers for a biomimetic robotic fish using the body and/or caudal fin (BCF) mode. Considering the morphological characteristics of Esox masquinongy in S-start and basic principles on fluid dynamics, an S-start control method for a multijoint robotic fish is developed. Specifically, two stages of S-start are further identified: 1) Bending stage: To ensure the maximum turning speed, fish increases the effective area in the posterior which is far from the rotation center to gain the maximum moment. At this point, fish bends its body into S-sharp. The other benefit from the S-sharp is to reduce the movement of center of gravity, thus helping keep body balance and strengthen the body stability in turning. Under the action of turning moment, the fish turns to the goal direction quickly. 2) Unbending stage: An L-shift method is designed to obtain the main propulsive force. In this method, there are always some bending joints perpendicular to the swimming direction to provide the force. At the same time, fuzzy logic method is adopted to control the turning action of unbending joints in a relative small angle to guarantee the turning accuracy. At the end of S-start, central pattern generator (CPG) is employed to smoothly switch to the steady swimming. In order to ensure the swimming direction and obtain the major propulsive force, small amplitudes and high frequency for CPG are adopted at the beginning. Then, relatively large amplitudes and low frequency are chosen in steady swimming. At last, the experimental results on a four-joint robotic fish demonstrate the validity of this method, in which the robot attained a maximum turning speed of 318.08±9.20°/s and a turning accuracy of 1.03±0.48°. The results obtained will shed light on the maneuverability of swimming robots.