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AmphiBot II: An Amphibious Snake Robot that Crawls and Swims using a Central Pattern Generator
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This article presents AmphiBot II, an am- phibious snake robot designed for both serpentine loco- motion (crawling) and swimming. It is controlled by an on-board central pattern generator (CPG) inspired by those found in vertebrates. The CPG is modelled as a chain of coupled nonlinear oscillators, and is designed to produce travelling waves. Its parameters can be modi- fled on the ∞y. We present the hardware of the robot and the structure of the CPG, then the systematic parameter tests done in simulation and with the real robot to char- acterize how the speed of locomotion depends on the parameters determining the frequency, amplitude and wavelength of the body undulation.
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... Their efficiency was augmented with the inclusion of additional wheels or supports. For instance, Hirose's ACM III showcased 20 wheeled modules, while ACM-R3 and Crespi's AmphiBot I and II had wheels centrally positioned on each joint [4][5][6][15][16][17]. However, the utility of passive wheels was confined to relatively even terrains. ...
... However, the advent of elastic joints and multi-propulsion actuators signals a transformative shift in the compliance control of underwater snake-like robots. For example, while AmphiBot I and II are equipped with wheels for land-based movement, they also incorporate caudal fins to generate thrust underwater [16,17,24]. ...
... Similarly, J i [0 0 L i 1] T , where i belongs to [1,3,5,7]. Subsequently, the tool-coordinate system's position in the zero-coordinate system is depicted in Eq. (17). This allows for the extraction of the robot's head model motion characteristics within an absolute coordinate system. ...
This paper presents the design and analysis of a biomimetic underwater snake-like robot, addressing the main limitations of current underwater robotic systems in terms of maneuverability and adaptability in complex environments. The innovative design incorporates flexible joint modules that significantly enhance the robot’s ability to navigate through narrow and irregular terrains, which is a notable limitation in traditional rigidly connected underwater robots. These flexible joints provide increased degrees of freedom and enable the robot to absorb and release energy, ensuring stability even under external impacts, thus extending the operational lifespan of the robot. Finite element analysis demonstrates the flexible joints’ superior performance in various underwater conditions, offering a greater range of motion and workspace compared to rigid connections. The results indicate that the robot’s modular design, combined with the flexible joint module, leads to improved agility and maneuverability, allowing for precise and intentional operation. The control module, equipped with advanced sensors and a CPU, manages the complex dynamics introduced by the flexible joints, ensuring effective navigation and operation. The specific advantages of this design include the robot’s enhanced structural integrity, its ability to conform to irregular surfaces, and its adaptability to environmental variations. The paper concludes with a discussion on the implications of these findings for the future design and operation of underwater serpentine robots, emphasizing the need for a balance between the effects of elastic modulus and workspace to maximize the benefits of flexible joints.
... It is composed of four rigid links connected by joints actuated by servomotors [16]. Similarly, Amphibot and its improved versions, Amphibot II and Amphibot III, are composed of several identical modules connected by cylindrical joints actuated by servomotors; these robots are amphibious since they can both swim in the water and crawl on the ground, and their control strategy is also inspired by snakes [11,[17][18][19]. The same concept was applied in the development of the Salamandra Robotica II, which uses the same spine elements as the Amphibot for swimming; in addition, it has a passive flexible tail and four limbs [20]. ...
This article presents the design, simulation, and experimental validation of a novel modular aquatic snake robot capable of surface locomotion. The modular structure allows each unit to function independently, facilitating ease of maintenance and adaptability to diverse aquatic environments. Employing the material point method with the moving least squares (MPM-MLS) simulation technique, the robot’s dynamic behavior was analyzed, yielding reliable results. The control algorithm, integral to the robot’s autonomous navigation, was implemented to enable forward propulsion at high speed, steering, and obstacle detection and avoidance. Extensive testing of the aquatic snake robot was conducted, demonstrating its practical viability. The robot showcased promising swimming capabilities, achieving high speeds and maneuverability. Furthermore, the obstacle detection and avoidance mechanisms were proven effective, showing the robot’s ability to navigate through dynamic environments. The presented aquatic snake robot represents an advancement in the field of underwater robotics, offering a modular and versatile solution for tasks ranging from environmental monitoring to search and rescue operations.
... Anguilliform biomimetic robot fish, mainly inspired by the soft eel, have flexible joints and fluctuate their flexible bodies and tail fins to produce motion [60]. The AmphiBot II, which was designed by Alessandro Crespi, featured a maximum torque that was 3.5 times higher than that of the earlier AmphiBot I, which greatly enhanced its propulsion efficiency [61]. Salamandra Robotica II can crawl and swim both on land and in water. ...
The traditional propeller-based propulsion of underwater robots is inefficient and poorly adapted to practice. By contrast, underwater biomimetic robots show better stability and maneuverability in harsh marine environments. This is particularly true of undulating propulsion biomimetic robots. This paper classifies the existing underwater biomimetic robots and outlines their main contributions to the field. The propulsion mechanisms of underwater biomimetic undulating robots are summarized based on theoretical, numerical and experimental studies. Future perspectives on underwater biomimetic undulating robots are also presented, filling the gaps in the existing literature.
... Central pattern generators (CPGs) are neural circuits in the spinal cord that produce rhythmic patterns for gait control [1,2]. CPGs have been mostly modeled by coupled nonlinear oscillators utilizing their synchronization and stability properties, for example, spiking neurons [3][4][5], Van der Pol oscillators [6][7][8], Hopf oscillators [9][10][11], and Kuramoto oscillators [12][13][14]. These models have been applied to gait generation for various types of bio-inspired robots and clinical prosthetic devices [15][16][17][18][19][20][21]. ...
Unidirectionally coupled phase oscillators in a ring are simple structures but unsuitable for application in central pattern generators (CPGs) for six-legged walking due to coexisting stable synchronization patterns. This paper shows that the coupled oscillators can be applied to a CPG by utilizing a non-periodic signal generator as a clock. The non-periodic clock-driven coupled oscillators are implemented by a sequential logic circuit using a field programmable gate array (FPGA) and a nonlinear analog circuit. A laboratory experiment confirms that a hexapod robot mounting the implemented circuits can realize six-legged walking.
... Like their biological counterparts, they can push against obstacles in their environment for locomotion [11,12]. Snake robots also exhibit amphibious multi-modal functionality [13,14] as well as the ability to climb cracks, ladders, and poles. Still, they are not yet designed for climbing shear walls with performance comparable to their legged counterparts. ...
Snakes and their bio-inspired robot counterparts have demonstrated locomotion on a wide range of terrains. However, dynamic vertical climbing is one locomotion strategy that has received little attention in the existing snake robotics literature. We demonstrate a new scansorial gait and robot inspired by the locomotion of the Pacific Lamprey. This new gait allows a robot to steer while climbing on flat, near-vertical surfaces. A reduced-order model is developed and used to explore the relationship between body actuation and the vertical and lateral motions of the robot. Trident, the new wall climbing lamprey-inspired robot, demonstrates dynamic climbing on a flat near vertical carpeted wall with a peak net vertical stride displacement of 4.1 cm per step. Actuating at 1.3 Hz, Trident attains a vertical climbing speed of 4.8 cm/s (0.09 Bl/s) at specific resistance of 8.3. Trident can also traverse laterally at 9 cm/s (0.17 Bl/s). Moreover, Trident is able to make 14\% longer strides than the Pacific Lamprey when climbing vertically. The computational and experimental results demonstrate that a lamprey-inspired climbing gait coupled with appropriate attachment is a useful climbing strategy for snake robots climbing near vertical surfaces with limited push points.
The control of movement in living organisms represents a fundamental task that the brain has evolved to solve. One crucial aspect is how the nervous system organizes the transformation of sensory information into motor commands. These commands lead to muscle activation and subsequent animal movement, which can exhibit complex patterns. One example of such movement is locomotion, which involves the translation of the entire body through space. Central Pattern Generators (CPGs) are neuronal circuits that provide control signals for these movements. Compared to the intricate circuits found in the brain, CPGs can be simplified into networks of neurons that generate rhythmic activation, coordinating muscle movements. Since the 1990s, researchers have developed numerous models of locomotive circuits to simulate different types of animal movement, including walking, flying, and swimming. Initially, the primary goal of these studies was to construct biomimetic robots. However, it became apparent that simplified CPGs alone were not sufficient to replicate the diverse range of adaptive locomotive movements observed in living organisms. Factors such as sensory modulation, higher-level control, and cognitive components related to learning and memory needed to be considered. This necessitated the use of more complex, high-dimensional circuits, as well as novel materials and hardware, in both modeling and robotics. With advancements in high-power computing, artificial intelligence, big data processing, smart materials, and electronics, the possibility of designing a new generation of true bio-mimetic robots has emerged. These robots have the capability to imitate not only simple locomotion but also exhibit adaptive motor behavior and decision-making. This motivation serves as the foundation for the current review, which aims to analyze existing concepts and models of movement control systems. As an illustrative example, we focus on underwater movement and explore the fundamental biological concepts, as well as the mathematical and physical models that underlie locomotion and its various modulations.
Conceiving robots with a variable stiffness continuum structure is a rapidly developing field of research. Swimming snakes provide an excellent bioinspiration source to design such type of robots characterized by variable compliant structures. Appropriate distribution of stiffness should permit to generate desired body shape deformations during swimming and displacements in a cramped space. We modelled the vertebrae anatomy of biological snakes and derived a simplified design. Via the control of the mechanical properties of universal joints, the bioinspired vertebrae compliance effectively mimicked the mechanical properties of biological vertebrae. We describe the method based on orthogonal compliant twist rods we used to build a whole snake robot skeleton. The flexible continuum robot, inspired from swimming snakes, was made of a series of optimized vertebrae. Each one has unique design parameters in order to obtain the stiffness distribution observed in swimming snakes. The resulting structure is a 3D printed monolithic nylon based variable stiffness optimized continuum snake robot. Experimental tests were performed to compare optimized and 3D printed vertebrae deflection angles. We successfully reproduced the variable stiffness observed in biological snakes and obtained the desired motions.
Although locomotion of biological snakes is neither fast nor efficient, it is very flexible in a sense that it allows to move on rough surfaces, creep into tubes or cross obstacles. So an artificial snake may be used for inspection and manipulation in areas where motion is restricted. It is not easy to construct a snake-like robot which can move very similar to real snakes, because a lot of equipment has to be put into the snake’s body and the body must have a small diameter and the proportion of force to weight must be high.
The paper shows the construction of an artificial snake, called GMD-Snake. After discussing the features which such a robot should have we describe mechanics and electronics of our realization. Some technical data of this robot are given and one possible type of locomotion is explained. Finally problems for further research are discussed.
This article presents a project that aims at understanding the neural circuitry controlling salamander locomotion, and developing an amphibious salamander-like robot capable of replicating its bimodal locomotion, namely swimming and terrestrial walking. The controllers of the robot are central pattern generator models inspired by the salamander's locomotion control network. The goal of the project is twofold: (1) to use robots as tools for gaining a better understanding of locomotion control in vertebrates and (2) to develop new robot and control technologies for developing agile and adaptive outdoor robots. The article has four parts. We first describe the motivations behind the project. We then present neuromechanical simulation studies of locomotion control in salamanders. This is followed by a description of the current stage of the robotic developments. We conclude the article with a discussion on the usefulness of robots in neuroscience research with a special focus on locomotion control.
We present AmphiBot I, an amphibious snake robot capable of crawling and swimming. Experiments have been carried out to characterize how the speed of locomotion depends on the frequencies, amplitudes, and phase lags of undulatory gaits, both in water and on ground. Using this characterization, we can identify the fastest gaits for a given medium. Results show that the fastest gaits are different from one medium to the other, with larger optimal regions in parameter space for the crawling gaits. Swimming gaits are faster than crawling gaits for the same frequencies. For both media, the fastest locomotion is obtained with total phase lags that are smaller than one. These results are compared with data from fishes and from amphibian snakes.
Cyberbotics Ltd. develops WebotsTM, a mobile robotics simulation software that provides you with a rapid prototyping environment for modelling, programming and simulating mobile robots. The provided robot libraries enable you to transfer your control programs to several commercially available real mobile robots. WebotsTM lets you define and modify a complete mobile robotics setup, even several different robots sharing the same environment. For each object, you can define a number of properties, such as shape, color, texture, mass, friction, etc. You can equip each robot with a large number of available sensors and actuators. You can program these robots using your favorite development environment, simulate them and optionally transfer the resulting programs onto your real robots. WebotsTM has been developed in collaboration with the Swiss Federal Institute of Technology in Lausanne, thoroughly tested, well documented and continuously maintained for over 7 years. It is now the main commercial product available from Cyberbotics Ltd.
Abstract We have built a biologically and neurally inspired autonomous mobile robotic worm. The main aim of the project is to demonstrate elegant motion on a robot with a large number of degrees of freedom (DOFs) under the control of a simple distributed neural system as found in many animals ' spinal cord. Our robot consists of individually controlled segments that exhibit Central-Pattern-Generator (CPG)-driven biomorphic motion. An important aspect of the project is to achieve a level of modularity while closely mimicking the neural control of e.g., the lamprey. This paper presents our robotic platform and the distributed CPG control algorithms. We will mainly focus on the architecture of the initial system and on future developments, and also report some preliminary experimental results.
A biomechanical study of active cord-mechanism (ACM) is made. ACM is defined as a ″machine having a slender configuration and making active and flexible winding motions with actuators attached along the body″ . It is shown that ACM has the intrinsic ability to be a unique type of locomotor and manipulator. The controlling problem of ACM is then dealt with. Finally, the controlling principle of lateral inhibition is experimentally demonstrated, and twining movement around objects and active insertion into a labyrinth is successfully accomplished.
This article presents a project that aims at constructing a biologically inspired amphibious snake-like robot. The robot is designed to be capable of anguilliform swimming like sea-snakes and lampreys in water and lateral undulatory locomotion like a snake on ground. Both the structure and the controller of the robot are inspired by elongate vertebrates. In particular, the locomotion of the robot is controlled by a central pattern generator (a system of coupled oscillators) that produces travelling waves of oscillations as limit cycle behavior. We present the design considerations behind the robot and its controller. Experiments are carried out to identify the types of travelling waves that optimize speed during lateral undulatory locomotion on ground. In particular, the optimal frequency, amplitude and wavelength are thus identified when the robot is crawling on a particular surface.
In this paper, we present a robotic system for inpipe inspection of underground urban gas pipelines. This robot is developed on the purpose of being utilized as a mobile platform for visual and Non-Destructive Testing (NDT) of the pipeline networks. The robot is configured as an articulated structure-like a snake with a tether cable. Two active driving vehicles are located in front and rear of the system, respectively. Passive modules such as a control module and other optional modules are linked between the active vehicles. It has several characteristic features superior to the others such as flexible wheeled leg mechanisms, a steering mechanism with compliance control. Especially the steering mechanism called Double Active Universal Joint (DAUJ) intrinsically prevents rolling of the robot along the driving direction and enables to control its compliance. Those features provide the robot with excellent mobility inside the highly constrained space while negotiating the complicated configurations of the pipeline networks. We outline the construction of the robot and describe its characteristic features.
Timing of the repetitive movements that constitute any rhythmic behavior is regulated by intrinsic properties of the central
nervous system rather than by sensory feedback from moving parts of the body. Evidence of this permits resolution of the long-standing
controversy over the neural basis of rhythmic behavior and aids in the identification of this mechanism as a general principle
of neural organization applicable to all animals with central nervous systems.