A GIM-Based Biomimetic Learning Approach for Motion Generation of a Multi-Joint Robotic Fish

In this paper, we propose a biomimetic learning approach for motion generation of a multi-joint robotic fish. Based on a multi-joint robotic fish model, two basic Carangiform swimming patterns, namely ＂cruise＂ and ＂C sharp turning＂, are extracted as training samples from the observations of real fish swimming. A General Internal Model （GIM）, which is an imitation of Central Pattern Generator （CPG） in nerve systems, is adopted to learn and to regenerate coordinated fish behaviors. By virtue of the universal function approximation ability and the temporal/spatial scalabilities of GIM, the proposed learning approach is able to generate the same or similar fish swimming patterns by tuning two parameters. The learned swimming patterns are implemented on a multi-joint robotic fish in experiments. The experiment results verify the effectiveness of the biomimetic learning approach in generating and modifying locomotion patterns for the robotic fish.     

Design and Experiments of a Robotic Fish Imitating Cow-Nosed Ray

<正> The cow-nosed ray is studied as natural sample of a flapping-foil robotic fish.Body structure, motion discipline, and dynamicfoil deformation of cow-nosed ray are analyzed.Based on the analysis results, a robotic fish imitating cow-nosed ray,named Robo-ray Ⅱ, mainly composed of soft body, flexible ribs and pneumatic artificial muscles, is developed.Structure andswimming morphology of the robotic prototype are as that of a normal cow-nosed ray in nature.Key propulsion parameters ofRobo-ray Ⅱ at normal conditions, including the St Number at linear swimming, thrust coefficient at towing are studied throughexperiments.The suitable driving parameters are confirmed considering the efficiency and swimming velocity.Swimmingvelocity of 0.16 m·s~(-1)'and thrust coefficient of 0.56 in maximum are achieved in experiments.     

Kinematic Comparison of Forward and Backward Swimming and Maneuvering in a Self-Propelled Sub-Carangiform Robotic Fish

We make a thorough kinematic comparison of forward and backward swimming and maneuvering on a self-propelled robot platform that uses sub-carangifbrm swimming as the primary propulsor. An improved Central Pattern Generator （CPG） model allowing free adjustment of phase relationship and directional bias is employed to achieve flexible swimming and smooth transition. Considering the characteristics of forward swimming in carangiform fish and backward swimming in anguilliform fish, various backward swimming patterns for the sub-carangiform robotic fish are suitably created by reversing the direction of propagating propulsive waves. Through a combined use of the CPG control and closed-loop swimming direction control strategy, flexible and precise turning maneuvers in both forward and backward swimming are implemented and compared. By contrast with forward swimming, backward swimming requires a higher frequency or an increased lateral displacement to reach the same relative swimming speed. Noticeably, the phase difference shows a greater impact on forward swimming than on backward swimming. Our observations also indicate that the robotic fish achieves a larger turning rate in forward maneuvering than in backward maneuvering, yet these two maneuvers display comparable turning precision.     

Biological Inspiration: From Carangiform Fish to Multi-Joint Robotic Fish

This paper presents a novel approach to modelling carangiform fish-like swimming motion for multi-joint robotic fish so that they can obtain fish-like behaviours and mimic the body motion of carangiform fish. A given body motion function of fish swimming is firstly converted to a tail motion function which describes the tail motion relative to the head. Then, the tail motion function is discretized into a series of tail postures over time. Thirdly, a digital approximation method calculates the taming angles of joints in the tail to approximate each tail posture; and finally, these angles are grouped into a look-up table, or re-gressed to a time-dependent function, for practically controlling the tail motors in a multi-joint robotic fish. The paper made three contributions: tail motion relative to the head, an error function for digital approximation and regressing a look-up table for online optimization. To prove the feasibility of the proposed methodology, two basic swimming motion patterns, cruise straight and C-shape sharp turning, are modelled and implemented in our robotic fish. The experimental results show that the relative tail motion and the approximation error function are good choices and the proposed method is feasible.     

Optimal Control of a Mackerel-Mimicking Robot for Energy Efficient Trajectory Tracking

A robotic fish, BASEMACK1, is designed and fabricated by mimicking the shape of a live mackerel. Three DC servo-motors are serially linked together and actuated to mimic the mackerel＇s Carangiform motion. Hydrodynamic characteristics of a fish-mimetic test model are experimentally identified and utilized in order to numerically simulate fish swimming. The discrete set of kinematic and dynamic parameters are obtained by considering required horizontal and lateral forces and minimum energy consumption. Using the optimized parameter set, optimal control of the robot is studied.     

Fuzzy Vorticity Control of a Biomimetic Robotic Fish Using a Flapping Lunate Tail

Vorticity control mechanisms for flapping foils play a guiding role in both biomimetic thrust research and modeling the forward locomotion of animals with wings, fins, or tails. In this paper, a thrust-producing flapping lunate tail is studied through force and power measurements in a water channel. Proper vorticity control methods for flapping tails are discussed based on the vorticity control parameters: the dimensionless transverse amplitude, Strouhal number, angle of attack, and phase angle. Field tests are conducted on a free-swimming biomimetic robotic fish that uses a flapping tail. The results show that active control of Strouhal number using fuzzy logic control methods can efficiently reduce power consumption of the robotic fish and high swimming speeds can be obtained. A maximum speed of 1.17 length specific speed is obtained experimentally under conditions of optimal vorticity control. The St of the flapping tail is controlled within the range of 0.4～0.5.     

Fish and Robots Swimming Together in a Water Tunnel: Robot Color and Tail-Beat Frequency Influence Fish Behavior

The possibility of integrating bioinspired robots in groups of live social animals may constitute a valuable tool to study the basis of social behavior and uncover the fundamental determinants of animal functions and dysfunctions. In this study, we investigate the interactions between individual golden shiners (Notemigonus crysoleucas) and robotic fish swimming together in a water tunnel at constant flow velocity. The robotic fish is designed to mimic its live counterpart in the aspect ratio, body shape, dimension, and locomotory pattern. Fish positional preference with respect to the robot is experimentally analyzed as the robot''s color pattern and tail-beat frequency are varied. Behavioral observations are corroborated by particle image velocimetry studies aimed at investigating the flow structure behind the robotic fish. Experimental results show that the time spent by golden shiners in the vicinity of the bioinspired robotic fish is the highest when the robot mimics their natural color pattern and beats its tail at the same frequency. In these conditions, fish tend to swim at the same depth of the robotic fish, where the wake from the robotic fish is stronger and hydrodynamic return is most likely to be effective.     

Use of a self-propelled,fish-shaped,computer model to study the effects of shape and tail-beat frequency on torque and velocity in salmon-shaped fish

The relationship between fish shape, swimming ability and energy consumption during swimming in fish is complex and not well understood. In this paper, we show how a self-propelled 3-D fish model can be used to examine the effect of controlled changes in some shape parameters. Parameters of the model fish are modified and the resulting fish activated for short swimming episodes during which swimming velocity, torque and energy expenditure are calculated in the computer environment. The effect of shape was determined for two different fish shapes swimming at three different tail-beat frequencies (1.43, 0.94 and 0.64?Hz). The simulation results indicate that fish model one (based on a salmon) has stronger swimming ability than fish model two (a modified salmon fish shape) even though energy expenditure of fish shape two is greater than that of fish shape one. In the same fish types, the fish-swimming velocity and energy expenditure are proportional to tail-beat frequency. This model has the potential to be useful, particularly for predicting fish behavior in fish swim ways and the tail-water of energy turbines.     

Using Echo Ultrasound from Schooling Fish to Detect and Classify Fish Types

Fish finders have already been widely available in the fishing market for a number of years.However,the sizes of these fishfinders are too big and their prices are expensive to suit for the research of robotic fish or mini-submarine.The goal of thisresearch is to propose a low-cost fish detector and classifier which suits for underwater robot or submarine as a proximity sensor.With some pre-condition in hardware and algorithms,the experimental results show that the proposed design has good per-formance,with a detection rate of 100 % and a classification rate of 94 %.Both the existing type of fish and the group behaviorcan be revealed by statistical interpretations such as hovering passion and sparse swimming mode.     

Kinematics Modeling and Experiments of Pectoral Oscillation Propulsion Robotic Fish

A robotic fish driven by oscillating fins, "Cownose Ray-I", is developed, which is in dorsoventrally flattened shape withouta tail. The robotic fish is composed of a body and two lateral fins. A three-factor kinematic model is established and used in thedesign of a mechanism. By controlling the three kinematic parameters, the robotic fish can accelerate and maneuver. Forwardvelocity is dependent on the largest amplitude and the number of waves in the fins, while the relative contribution of fin beatfrequency to the forward velocity of the robotic fish is different from the usual result. On the other hand, experimental results onmaneuvering show that phase difference has a stronger effect on swerving than the largest amplitude to some extent. In addition,as propulsion waves pass from the trailing edge to the leading edge, the robotic fish attains a backward velocity of 0. 15 m·s^-1.     

Mechanical properties of a bio-inspired robotic knifefish with an undulatory propulsor

South American electric knifefish are a leading model system within neurobiology. Recent efforts have focused on understanding their biomechanics and relating this to their neural processing strategies. Knifefish swim by means of an undulatory fin that runs most of the length of their body, affixed to the belly. Propelling themselves with this fin enables them to keep their body relatively straight while swimming, enabling straightforward robotic implementation with a rigid hull. In this study, we examined the basic properties of undulatory swimming through use of a robot that was similar in some key respects to the knifefish. As we varied critical fin kinematic variables such as frequency, amplitude, and wavelength of sinusoidal traveling waves, we measured the force generated by the robot when it swam against a stationary sensor, and its velocity while swimming freely within a flow tunnel system. Our results show that there is an optimal operational region in the fin's kinematic parameter space. The optimal actuation parameters found for the robotic knifefish are similar to previously observed parameters for the black ghost knifefish, Apteronotus albifrons. Finally, we used our experimental results to show how the force generated by the robotic fin can be decomposed into thrust and drag terms. Our findings are useful for future bio-inspired underwater vehicles as well as for understanding the mechanics of knifefish swimming.     

The systematics of fish metabolic response to changes in hydrogen ion concentrations in the pH gradient field

It has been revealed that a change in water pH during free swimming of fish in the pH gradient field optimizes fish growth and their physiological state. Fish locomotor activity rises. However, despite additional activity, the fish energy budget improves, energy consumption decreases weight gain, and the efficiency of food utilization for growth increases. The changes in growth parameters and in energy caused by swimming in the pH gradient field are closely correlated. This is evidence of the systemic character of fish response to changes in the pH of water. The changes in one metabolic parameter can be used to assess other parameters. The results of this study should be considered for the improvement of juvenile fish farming techniques.     

Go reconfigure: how fish change shape as they swim and evolve

The bodies of fish change shape over propulsive, behavioral, developmental, and evolutionary time scales, a general phenomenon that we call "reconfiguration". Undulatory, postural, and form-reconfiguration can be distinguished, studied independently, and examined in terms of mechanical interactions and evolutionary importance. Using a combination of live, swimming fishes and digital robotic fish that are autonomous and self-propelled, we examined the functional relation between undulatory and postural reconfiguration in forward swimming, backward swimming, and yaw turning. To probe how postural and form reconfiguration interact, the yaw turning of leopard sharks was examined using morphometric and kinematic analyses. To test how undulatory reconfiguration might evolve, the digital robotic fish were subjected to selection for enhanced performance in a simulated ecology in which each individual had to detect and move towards a food source. In addition to the general issue of reconfiguration, these investigations are united by the fact that the dynamics of undulatory and postural reconfigurations are predicted to be determined, in part, by the structural stiffness of the fish's body. Our method defines undulatory reconfiguration as the combined, point-by-point periodic motion of the body, leaving postural reconfiguration as the combined deviations from undulatory reconfiguration. While undulatory reconfiguration appears to be the sole or primary propulsive driver, postural reconfiguration may contribute to propulsion in hagfish and it is correlated with differences in forward, and backward, swimming in lamprey. Form reconfigures over developmental time in leopard sharks in a manner that is consistent with an allometric scaling theory in which structural stiffness of the body is held constant. However, correlation of a form proxy for structural stiffness of the body suggests that body stiffness may scale in order to limit maximum postural reconfiguration during routine yaw turns. When structural stiffness and undulatory frequency are modeled as determining the tail's undulatory wave speed, both factors evolve under selection for enhanced foraging behavior in the digital fish-like robots. The methods used in making these distinctions between kinds of reconfiguration have broad applicability in fish biology, especially for quantifying complex motor behaviors in the wild and for simulating selection on behavior that leads to directional evolution of functional phenotypes.     

Evaluation of Adult White Sturgeon Swimming Capabilities and Applications to Fishway Design

Concern over passage of sturgeon barriers, has focused attention on fishway design that accommodates its swimming performance. In order to evaluate swimming performance, regarding fish ladder type partial barriers, wild adult sturgeons, Acipenser transmontanus; 121–76m fork length, were captured in the San Francisco Bay Estuary and Yolo Bypass toe drain. Hydrodynamic forces and kinematic parameters for swimming performance data were collected in a laboratory flume under three flow conditions through barriers and ramp. The experiments were conducted in a 24.4 m long, 2.1 m wide, and 1.62 m deep aluminum channel. Two geometric configurations of the laboratory model were designed based on channel characteristics that have been identified in natural river systems. At a given swimming speed and fish size, the highest guidance efficiencies of successful white sturgeon passage as a function of flow depth, flow velocity, turbulence intensity, Reynolds number, Froude number and shear velocity observed in the steady flow condition, tested with the horizontal ramp structure, occurred at an approach velocity of 0.33 ms^-1. The guidance efficiency of successful sturgeon passage increased both with increasing flow velocity and Froude number, and decreased both with the flow depth and the turbulence intensity. This study also provides evidence that tail beat frequency increases significantly with swimming speed, but tail beat frequency decreases with fish total length. Stride length increases both with swimming speed and fish total length. The importance of unsteady forces is expressed by the reduced frequency both with swimming speed and fish total length. Regression analysis indicates that swimming kinematic variables are explained by the swimming speed, the reduced frequency and the fish total length. The results emphasize the importance of fish ladder type patchiness when a fishway is designed for the passage of sturgeon.     

锦鲫的摄食代谢与运动代谢及其相互影响

为了探讨锦鲫(Carassius auratus)幼鱼摄食后特殊动力作用(SDA)的变化特征及运动代谢与摄食代谢之间的相互影响,实验首先灌喂锦鲫4%体重的饲料和等体积的纤维素(湿重),测定灌喂前后的耗氧率;另设灌喂饲料、灌喂纤维素、空腹组(对照组)3个组,测定3组的临界游泳速度(Ucrit)和运动耗氧率(MO2);然后在70%、0%临界游泳速度下,分别测定饱足摄食组和空腹组的耗氧率。结果显示:1灌喂饲料后代谢率快速上升,达到峰值后又迅速下降,代谢时间较短,没有一个相对稳定的平台期,灌喂纤维素后代谢率没有显著性变化(P0.05)。提示锦鲫幼鱼的特殊动力作用功率曲线为一个典型的"三角型"模型,且在特殊动力作用总耗能中,生化特殊动力作用占特殊动力作用总耗能的绝大部分,而机械特殊动力作用只占特殊动力作用的极少部分。2锦鲫幼鱼在摄食后临界游泳速度显著下降(P0.05),代谢率显著升高(P0.05)。摄食后的运动过程中,代谢率从摄食开始到代谢率回落至空腹组代谢的标准误范围内的首个数据所对应的时间长度均为6.5 h,且摄食代谢无显著性差异。提示,对锦鲫幼鱼来说,摄食代谢降低了其运动能力,而运动代谢并没有影响摄食代谢。     

Automated Reconstruction of Three-Dimensional Fish Motion,Forces, and Torques

Fish can move freely through the water column and make complex three-dimensional motions to explore their environment, escape or feed. Nevertheless, the majority of swimming studies is currently limited to two-dimensional analyses. Accurate experimental quantification of changes in body shape, position and orientation (swimming kinematics) in three dimensions is therefore essential to advance biomechanical research of fish swimming. Here, we present a validated method that automatically tracks a swimming fish in three dimensions from multi-camera high-speed video. We use an optimisation procedure to fit a parameterised, morphology-based fish model to each set of video images. This results in a time sequence of position, orientation and body curvature. We post-process this data to derive additional kinematic parameters (e.g. velocities, accelerations) and propose an inverse-dynamics method to compute the resultant forces and torques during swimming. The presented method for quantifying 3D fish motion paves the way for future analyses of swimming biomechanics.     

鱼类通过鱼道内水流速度障碍能力的评估方法

鱼类通过鱼道内水流速度障碍能力的量化对鱼道设计有重要理论和实际价值,其基础是鱼类游泳能力的测定.首先对鱼类游泳能力的研究方法进行了概述总结,指出了鱼类游泳能力经典测试方法存在测定流场与自然情况相差较大的不足;分析了关键要素如鱼类行为特征、生理耗能规律及水力特性对鱼类通过水流速度障碍能力的影响;提出了分析鱼类游泳行为和能力与特征流场的关系,探讨鱼类通过水流障碍行为规律和生理疲劳恢复特征,通过研究仿自然流态下的鱼类自由游泳行为、水力计算及生理耗能的关系,构建多因素鱼类游泳能力关系式,定量评价鱼类通过鱼道内水流速度障碍的发展方向.     

Parametric study of the swimming performance of a fish robot propelled by a flexible caudal fin

In this paper, we aim to study the swimming performance of fish robots by using a statistical approach. A fish robot employing a carangiform swimming mode had been used as an experimental platform for the performance study. The experiments conducted aim to investigate the effect of various design parameters on the thrust capability of the fish robot with a flexible caudal fin. The controllable parameters associated with the fin include frequency, amplitude of oscillation, aspect ratio and the rigidity of the caudal fin. The significance of these parameters was determined in the first set of experiments by using a statistical approach. A more detailed parametric experimental study was then conducted with only those significant parameters. As a result, the parametric study could be completed with a reduced number of experiments and time spent. With the obtained experimental result, we were able to understand the relationship between various parameters and a possible adjustment of parameters to obtain a higher thrust. The proposed statistical method for experimentation provides an objective and thorough analysis of the effects of individual or combinations of parameters on the swimming performance. Such an efficient experimental design helps to optimize the process and determine factors that influence variability.     

Group swimming behaviour and energetics in bluegill Lepomis macrochirus and rainbow trout Oncorhynchus mykiss

Group swimming size influences metabolic energy consumption and swimming behaviour in fishes. Hydrodynamic flows and vortices of other fish are thought to be beneficial in terms of the energetic costs of swimming. Similarly, abiotic obstructions have been shown to have similar benefits with respect to metabolic consumption in swimming fish such as rainbow trout Oncorhynchus mykiss. The current study works to examine metabolic rates and swimming behaviours as a function of group swimming with bluegill sunfish Lepomis macrochirus and O. mykiss. Fishes were subjected to individual and group swimming in a respiratory swim tunnel to determine oxygen consumption as a proxy for the metabolic rate of swimming fish. In addition, fish movements within the swim tunnel test chamber were tracked to examine group swimming behaviour. We hypothesized that fish would benefit metabolically from group swimming. In the case of O. mykiss, we also hypothesized that groups would benefit from the presence of an abiotic structure, as has been previously observed in fish swimming individually. Our results suggest that the influence of group size on swimming metabolism is species specific. While L. macrochirus show decreased metabolic rate when swimming in a group compared to individually, O. mykiss did not show such a metabolic benefit from group swimming.     

鲢幼鱼通过水流速度障碍的模拟

鱼类能否通过水流速度障碍直接影响过鱼设施的过鱼效果。利用计算机技术,综合水力因素、鱼类行为、地理特征及环境因子,展开鱼类通过水流速度障碍的模拟,有助于过鱼设施的优化设计。以国外涵洞式鱼道模拟软件Fish Xing为切入点,结合主要模块和关键因子,对我国特有鱼类鲢幼鱼进行模拟,得到鲢通过不同水流速度障碍的成功率;对比鲢在物理模型中的游泳表现,从模型主要模块和影响鱼类游泳表现的关键因子角度,分析影响鱼类通过水流速度障碍模拟的因素。结果表明,Fish Xing软件不能精确模拟鲢通过水流速度障碍的表现。分析表明,该软件在地理要素、管道特征和水力信息等参数方面具备独特的优势,但对我国鱼类有一定局限性,主要体现在鱼类的生物学信息如鱼类游泳特征等方面存在不足;进行鱼过障碍的模拟需要深入研究目标鱼类的生理特征、游泳能力及其与水力环境因子的响应关系。