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线驱动柔性仿生推进器尾部刚度优化机理与运动控制研究
廖晓村
Source Publication中国科学院自动化研究所
2024-05-14
Pages186
Subtype博士
Abstract

自然界的鱼类经过长期的自然选择,进化出许多独特的生理结构与行为方式,展现出非凡的水下运动性能和环境适应能力。然而,目前的仿生机器鱼的各方面运动性能均无法与生物鱼类相媲美,还需更为深入的探究。受自然界鱼类的启发,本文围绕线驱动机器鱼以及变刚度机器鱼的结构设计、运动建模、性能优化以及游动控制等方面开展研究,旨在实现性能更优的仿生机器鱼,主要内容如下:

一、为了模拟自然界鱼类的复杂而连续的尾部波动,设计了一种双线驱动柔性仿鱼尾推进机构,其采用双拉线模拟鱼类肌腱以实现仿鱼尾摆动,采用弹簧钢片模拟鱼类脊柱,不仅可以实现仿鱼类的能量存储与释放机制,而且规避了离散关节式仿生脊柱所存在的关节摩擦损耗问题。进一步,分析了鱼尾的机构耦合性及其运动学模型,提出了一种基于数据驱动的运动解耦控制算法和仿鱼波动控制算法,以实现仿鱼尾波动。为了评估游动性能,提出了适用于稳态分析的速度估计模型和适用于动态分析的动力学模型,通过不同频率和振幅下的仿真和实验速度对比验证了模型的准确性。最后,探究了线驱动和弹性元件相结合在机器鱼中的新优势,结果表明,相比于多关节机器鱼,基于双线驱动柔性仿鱼尾推进机构的机器鱼能够实现更平滑的舵机输出功率、更小的舵机负载、更高的摆动频率、更快的游速、更低的运输成本(Cost of Transport, COT)。

二、为了充分利用柔性鱼尾的储能机制以提升机器鱼的游动性能,需探索柔性鱼尾的刚度在宽频段内对游速、推力等游动性能的影响。为此,在双线驱动柔性机器鱼的基础上,引入了一个高效的传动机构,其能够将电机的连续旋转运动转化为仿鱼尾的往复摆动,并设计了一款能够实现高频游动的线驱动柔性机器鱼,以满足在宽频段内鱼尾刚度优化的需求。基于机器鱼的动力学模型,依次分析了鱼尾的主动段柔性和被动段柔性的储能情况以及对游动性能的影响,进一步对主动段柔性和被动段柔性的刚度进行优化,以提升机器鱼的游动性能。所设计的线驱动柔性机器鱼的最快游速达0.92 m/s (1.87 BL/s, Body Length Per Second),最低COT为12.17 J/m/kg。

三、为了模拟鱼类的在线刚度调节机制以提升机器鱼的游动性能,提出了一种快速在线变刚度机构,其通过调节基于弹簧钢片的弹性脊柱的有效长度,实现鱼尾刚度在大范围内快速在线调节。为了探究鱼尾刚度调节对游动性能的影响,分析了鱼尾刚度模型以及刚度调节的响应时间,提出了基于凯恩法的动力学模型,利用莫里森方程和升阻力模型并结合计算流体动力学分析了水动力,并通过游速、推力等性能分析验证了所设计的变刚度机器鱼的快速且大范围的刚度调节能力以及所提模型的准确性。在此基础上,通过充分利用可调刚度的优势改善机器鱼在多阶段直游运动和快速定向运动的游动性能。对于多阶段直游运动,通过构建的动力学模型,对多阶段内的实时速度与期望速度的误差以及功率损耗同时进行优化,得到机器鱼各阶段内的最优刚度、最优频率与最优振幅。对于快速定向运动,通过结合鱼类的C转策略以及可调刚度的优势,构建闭环控制策略,并以最小化定向时间为优化目标,对策略参数进行优化。仿真和实验结果验证了多阶段直游运动策略以及快速定向运动策略的有效性。

Other Abstract

After long-term natural selection, fish in nature have evolved many unique physiological structures and behaviors, demonstrating extraordinary underwater motion performance and environmental adaptability. However, the current bionic robotic fish cannot compete with biological fish in all aspects of motion performance, and more in-depth research is needed. Inspired by fish in nature, this dissertation focuses on the structural design, motion modeling, performance optimization and swimming control of wire-driven robotic fish and variable stiffness robotic fish, aiming to achieve the bionic robotic fish with better performance. The main contents are summarized as follows.

Firstly, in order to emulate the complex and continuous tail fluctuations of fish in nature, a dual-wires driven flexible fishtail-like propulsion mechanism is designed. It adopts dual wires to emulate fish tendons for achieving fishtail-like swing, and utilizes spring steel to emulate fish spine, which not only realizes the fish-like mechanism of energy storage and release, but also avoids the friction loss of joint existing in the discrete-joint-based bionic spine. Further, the mechanism coupling and kinematic model of the fishtail are analyzed, and a data-driven motion decoupling control algorithm and fish-like fluctuation control algorithm are proposed to realize the fishtail-like fluctuation. In order to evaluate swimming performance, a speed estimation model suitable for steady-state analysis and a dynamic model suitable for dynamic analysis are proposed. The accuracies of the two model are verified by the comparison between simulation and experimental speeds at different frequencies and amplitudes. Finally, the new advantage of combining wire-driven mechanism with elastic component in robotic fish is explored. The results show that compared with multi-joints robotic fish, the robotic fish based on dual-wires driven flexible fishtail-like propulsion mechanism can achieve smoother output power of servomotor, smaller load  of servomotor, higher swing frequency, faster swimming speed, and lower cost of transport (COT).

Secondly, in order to make full use of the energy storage mechanism of the flexible fishtail so as to improve the swimming performance of robotic fish, it is necessary to explore the effect of the stiffness of the flexible fishtail on swimming performance (e.g., swimming speed and thrust) in a wide frequency band. To this end, based on the dual-wires driven flexible robotic fish, an efficient transmission mechanism is introduced, which can convert the continuous rotational motion of the motor into the fishtail-like back-and-forth swing. A wire-driven flexible robotic fish capable of achieving high-frequency swimming is developed, which meets the need of fishtail stiffness optimization in a wide frequency band. Based on the dynamic model of robotic fish, the energy storages of the active segment flexibility and the passive segment flexibility for the fishtail as well as their impacts on swimming performance are analyzed in turn. The stiffness of the active segment flexibility and passive segment flexibility is further optimized to improve the swimming performance of robotic fish. The designed wire-driven flexible robotic fish obtains a maximum swimming speed of 0.92 m/s (1.87 BL/s, body length per second) and a minimum COT of 12.17 J/m/kg.

Thirdly, in order to emulate the online stiffness adjustment mechanism of the fish in nature to improve the swimming performance of robotic fish, a fast online variable stiffness mechanism is proposed. The fast and online stiffness adjustment over a large-scale range is achieved by adjusting the effective length of the spring-steel-based elastic spine. In order to explore the effect of fishtail stiffness adjustment on swimming performance, the fishtail stiffness model and the response time of stiffness adjustment are analyzed, and a dynamic model based on Kane method is proposed. Combining the Morrison equation, Lift-drag model and Computational Fluid Dynamics, the hydrodynamic force is analyzed. The ability to adjust stiffness fleetly over a large-scale range for the designed variable stiffness robotic fish and the accuracy of the proposed model are verified by the analyses of swimming performances, such as swimming speed and thrust. On this basis, the swimming performances of robotic fish in multi-stages straight swimming motion and fast directional motion are improved by taking full advantage of the adjustable stiffness. For the multi-stages straight swimming motion, based on the developed dynamic model, the error between the real-time speed and the expected speed as well as the power consumption in the multi-stages swimming are simultaneously optimized, and the optimal stiffness, frequency and amplitude of the robotic fish in each stage are further obtained. For fast directional motion, a closed-loop control strategy is established by combining the fish-like C-turn strategy with the advantage of adjustable stiffness, and the strategy parameters are optimized by minimizing the time of the directional motion as the optimization goal. Simulation and experimental results verify the effectivenesses of the two strategies for the multi-stages straight swimming motion and the fast directional motion.

Keyword线驱动柔性机构 快速在线变刚度机构 柔性鱼尾刚度优化 游动控制
Subject Area自动控制技术
MOST Discipline Catalogue工学::控制科学与工程
Language中文
IS Representative Paper
Sub direction classification智能机器人
planning direction of the national heavy laboratory水下仿生机器人
Paper associated data
Document Type学位论文
Identifierhttp://ir.ia.ac.cn/handle/173211/57156
Collection毕业生_博士学位论文
毕业生
Recommended Citation
GB/T 7714
廖晓村. 线驱动柔性仿生推进器尾部刚度优化机理与运动控制研究[D],2024.
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