Snake-like Robot Research Articles

Optimization of PID Control of a Snake Robot’s Winding Crawling Motion

This paper explores the application of PID control to the winding crawling motion of a snack robot. Snack robots, mimicking the movement of real life limbless reptile, are designed with ultiple connected segments equipped with actuators and sensors, enabling them to navigate complex environments. The study aims to optimize the ground crawling behavior and obstacle avoidance f the snake-like robot using MATLAB simulation software. Initially, the robot’s joints were modeled in SolidWorks, and their degrees of freedom were programmed in MATLAB’s Simulink to enable controlled rotation. The PID control system was added to manage the robot’s motion, ensuring smooth and accurate crawling.

The Dynamical Model and the Slithering Controller of Continuous Snakelike Robot on Smooth Surface

The Dynamical Model and the Slithering Controller of Continuous Snakelike Robot on Smooth Surface

An active SLAM with multi-sensor fusion for snake robots based on deep reinforcement learning

Snake-like robots can imitate the movement patterns of animals in nature and enter the space that traditional robots cannot enter, which adapt to environments that humans cannot reach, and expand the field of human exploration. However, it is often challenging to realize autonomous navigation and simultaneously avoid obstacles under an unknown environment, that is, active SLAM (Simultaneous Localization and Mapping). This paper proposes an autonomous obstacle avoidance method combined with SLAM based on deep reinforcement learning for a wheeled snake robot by using a multi-sensor. Firstly, we design a modular wheeled snake robot structure with lightweight materials based on orthogonal joints and build a three-dimensional model of a snake robot in Gazebo. Secondly, the SLAM based on two-dimensional LiDAR and IMU is used to realize autonomous navigation under an unknown environment and detect obstacles. At the same time, a Deep Q-Learning-based path planning method of the snake robot is proposed to realize obstacles avoidance during navigation. Finally, simulation studies and experiments show that the designed snake-like robot can realize effective path planning and environmental mapping in environments with obstacles. The proposed active SLAM algorithm improves the success rate of snake-like robot path planning, has better obstacle avoidance ability for obstacles, and reduces the number of collisions compared with the traditional A* and the sampling-based RRT* algorithms.

Novel design and motion analysis of an omni-tread snake-like robot for narrow space inspection

Snake-like robots have a slender body and strong environmental adaptability. This paper aims to propose an omni-tread snake-like robot that can adapt to the needs of specific narrow space exploration missions and provide a basis for design work through necessary motion analysis. The robot adopts the form of three modules in series, and the modules are connected through differential driving joints, which increases the joint torque of the robot. The nested omni-tread structure improves the robot's motion efficiency and environmental adaptability. This paper conducts configuration and motion analysis of the robot. The simulation is performed using the optimization solution method to obtain the joint torque and walking torque of the robot, which guides the design of the robot. The experiment is also conducted with the developed prototype to verify the robot's performance. From the simulation results, the joint torque and walking torque are obtained, and the motors are selected. The motion performance and field applicability of the robot are verified through experiment tests. The experiment results further verify the robot design and analysis work. The structural design of robots and optimization solution method in this paper has certain reference values for other researchers.

A Data-Driven Model with Hysteresis Compensation for I2RIS Robot.

Retinal microsurgery is a high-precision surgery performed on a delicate tissue requiring the skill of highly trained surgeons. Given the restricted range of instrument motion in the confined intraocular space, snake-like robots may prove to be a promising technology to provide surgeons with greater flexibility, dexterity, and positioning accuracy during retinal procedures such as retinal vein cannulation and epiretinal membrane peeling. Kinematics modeling of these robots is an essential step toward accurate position control. Unlike conventional manipulators, modeling these robots does not follow a straightforward method due to their complex mechanical structure and actuation mechanisms. The hysteresis problem can especially impact the positioning accuracy significantly in wire-driven snake-like robots. In this paper, we propose a data-driven kinematics model using a probabilistic Gaussian mixture model (GMM) and Gaussian mixture regression (GMR) approach with a hysteresis compensation algorithm. Experimental results on the two-degree-of-freedom (DOF) integrated robotic intraocular snake (I2RIS) show that the proposed model with the hysteresis compensation can predict the snake tip bending angle for pitch and yaw with 0.45° and 0.39° root mean square error (RMSE), respectively. This results in overall 60% and 70% improvements of accuracy for yaw and pitch over the same model without the hysteresis compensation.

Online Bilateral Predictive Control for Time-Delayed Teleoperation of Snake-like Robots

Controlling the teleoperation of snake-like robots is challenging due to complex nonlinear dynamics and communication delays. This research proposes an online bilateral predictive control architecture to address these issues. This control structure is established by predicting environment force and the user’s future motion. The former uses a model-mediated approach by creating a virtual environment on the master side and the latter adopts an artificial neural network (ANN) for online operator’s motion prediction. The slave controller utilizes transmitted data from ANN to generate required backbone lengths, which are then transformed into the slave's local bending and torsional degrees of freedom through the inverse kinematics of the robot. Motion prediction is examined in two scenarios: when the ANN predicts the trained motions, and when it predicts a different motion. Simulation studies demonstrate that the proposed online bilateral predictive teleoperation structure successfully achieves real-time position synchronization and force feedback, by effectively bypassing communication delays.

Design and architecture of a slender and flexible underwater robot

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.

Enhancing undulation of soft robots in granular media: A numerical and experimental study on the effect of anisotropic scales

Generating efficient locomotion in granular media is important, although it is difficult for robots. Inspired by the fact that sand vipers usually have saw-like scales, in this study, we design a soft undulation robot with tangential anisotropic friction to enhance the undulation performance of soft robots in granular media. A mathematical model was derived and numerical simulations were conducted accordingly to investigate the effectiveness of tangential friction anisotropy for undulation gait generation in granular media. In particular, we introduce a pseudo-rigid-body dynamics model consisting of links and joints while simulating the pneumatic actuation method to more closely approximate the response of soft robots. Moreover, a soft snake-like robot was fabricated, and its forward and reverse undulations were compared in two sets of controlled experiments. The consistency between the experimental results and the numerical simulations confirms that tangential anisotropic friction induces a propulsive effect in undulation, thereby increasing the robot’s locomotion speed. This discovery provides new insights into the design of undulation robots in granular environments.

Snake Robot with Motion Based on Shape Memory Alloy Spring-Shaped Actuators.

This study presents the design and evaluation of a prototype snake-like robot that possesses an actuation system based on shape memory alloys (SMAs). The device is constructed based on a modular structure of links connected by two degrees of freedom links utilizing Cardan joints, where each degree of freedom is actuated by an agonist-antagonist mechanism using the SMA spring-shaped actuators to generate motion, which can be easily replaced once they reach a degradation point. The methodology for programming the spring shape into the SMA material is described in this work, as well as the instrumentation required for the monitoring and control of the actuators. A simplified design is presented to describe the way in which the motion is performed and the technical difficulties faced in manufacturing. Based on this information, the way in which the design is adapted to generate a feasible robotic system is described, and a mathematical model for the robot is developed to implement an independent joint controller. The feasibility of the implementation of the SMA actuators regarding the motion of the links is verified for the case of a joint, and the change in the shape of the snake robot is verified through the implementation of a set of tracking references based on a central pattern generator. The generated tracking results confirm the feasibility of the proposed mechanism in terms of performing snake gaits, as well as highlighting some of the drawbacks that should be considered in further studies.

EELS: Autonomous snake-like robot with task and motion planning capabilities for ice world exploration.

Ice worlds are at the forefront of astrobiological interest because of the evidence of subsurface oceans. Enceladus in particular is unique among the icy moons because there are known vent systems that are likely connected to a subsurface ocean, through which the ocean water is ejected to space. An existing study has shown that sending small robots into the vents and directly sampling the ocean water is likely possible. To enable such a mission, NASA's Jet Propulsion Laboratory is developing a snake-like robot called Exobiology Extant Life Surveyor (EELS) that can navigate Enceladus' extreme surface and descend an erupting vent to capture unaltered liquid samples and potentially reach the ocean. However, navigating to and through Enceladus' environment is challenging: Because of the limitations of existing orbital reconnaissance, there is substantial uncertainty with respect to its geometry and the physical properties of the surface/vents; communication is limited, which requires highly autonomous robots to execute the mission with limited human supervision. Here, we provide an overview of the EELS project and its development effort to create a risk-aware autonomous robot to navigate these extreme ice terrains/environments. We describe the robot's architecture and the technical challenges to navigate and sense the icy environment safely and effectively. We focus on the challenges related to surface mobility, task and motion planning under uncertainty, and risk quantification. We provide initial results on mobility and risk-aware task and motion planning from field tests and simulated scenarios.

Locomotion control of a rigid-soft coupled snake robot in multiple environments

The versatile motion capability of snake robots offers themselves robust adaptability in varieties of challenging environments where traditional robots may be incapacitated. This study reports a novel flexible snake robot featuring a rigid–flexible coupling structure and multiple motion gaits. To better understand the robot’s behavior, a bending model for the soft actuator is established. Furthermore, a dynamic model is developed to map the relationship between the input air pressure and joint torque, which is the model base for controlling the robot effectively. Based on the wave motion generated by the joint coupling direction function in different planes, multiple motion gait planning methods of the snake-like robot are proposed. In order to evaluate the adaptability and maneuverability of the developed snake robot, extensive experiments were conducted in complex environments. The results demonstrate the robot’s effectiveness in navigating through intricate settings, underscoring its potential for applications in various fields.

Robustness Analysis on Joint Path-following Control of a Snake-like Robot Using Port-Hamiltonian Model

Robustness Analysis on Joint Path-following Control of a Snake-like Robot Using Port-Hamiltonian Model

Elastostatic analysis of a module-based shape morphing snake-like robot

This paper describes the stiffness analysis of a module-based shape morphing snake-like robot. Snake-like robots have the characteristic of adapting to unstructured environments by exploiting their ability to reconfigure their body’s shape. However, the excellent mobility contrasts with the ability to transmit high loads, precluding its application in manufacturing operations. This article presents a hybrid structure based on reconfigurable modules equipped with lockable joints. The use of multiple modules in series allows for a large workspace. Furthermore, the parallel structure of the single modules provides for transferring or sustaining high loads. First, the reliability and precision of the theoretical model has been verified using finite element analysis (FEA). The relative errors are less than 5%. Then, a morphing module has been constructed as a physical demonstrator for the kinematic parameters and stiffness parameters used in elastostatic analysis. Finally, a five-segment prototype has been manufactured and tested. There is a deviation between the experimental results and the theoretical results due to manufacturing errors of the prototype but the trend of displacement change shown in the experimental results is basically consistent with the theoretical results.

Snake-like Robots Climbing Various Terrains and their Industrial Applications

Snake-like Robots Climbing Various Terrains and their Industrial Applications

Optimal swimming locomotion of snake-like robot in viscous fluids

Snake-like robots have several joints that enable them to swim in various types of viscous fluids such as water, mud, and clay by varying the undulation. Because the optimal swimming motion is assumed to be different in fluids with different viscosities, we constructed an equation of motion for a snake-like robot swimming in viscous fluids and attempted to find the optimal swimming motion via numerical analysis. We constructed a snake-like robot comprising eight links in this study that could swim in four fluids with different kinematic viscosities, and measured their joint positions and relative angles during swimming. Accordingly, we proposed a method for identifying multiple unknown parameters of fluid forces acting on a body using the unscented Kalman filter, which could determine the unknown added mass and drag coefficient. Subsequently, we clarified that the inertial drag model is effective in water (small viscosity, μ∼1mPas), while the friction drag model is effective in oil (large viscosity, μ>100mPas). By considering the increase in frictional drag due to boundary layer thinning in the proposed model, we identified the constant drag coefficient regardless of the swimming frequency. Next, we employed the constructed numerical model to explore the trade-off relationship between consumed power and velocity during swimming using exhaustive search. Consequently, we confirmed that the swimming frequency decreased as the fluid viscosity increased under the same swimming power consumption. Moreover, the wavelength of undulation was confirmed to be between half and one wavelength, regardless of the viscosity.

Dual-Loop Control of Cable-Driven Snake-like Robots

Snake-like robots, which have high degrees of freedom and flexibility, can effectively perform an obstacle avoidance motion in a narrow and unstructured space to complete assignments efficiently. However, accurate closed-loop control is difficult to achieve. On the one hand, this is because adding too many sensors to the robot will significantly increase its mass, size, and cost. On the other hand, the more complex structure of the hyper-redundant robot also challenges the more elaborate closed-loop control strategy. For these reasons, a cable-driven snake-like robot, which is compact and low cost, with force transducers and angle sensors, is designed in this article. The simpler and more direct kinematic model is studied, which applies to a widely used kinematics algorithm. Based on the kinematic model, the inverse dynamics are resolved. Finally, this article analyzes the sources of the motion errors and achieves dual-loop control through force-feedback and pose-feedback. The experiment results show that the robot’s structure and dual-loop control strategy function with high accuracy and reliability, meeting the requirements of engineering applications and high-precision control.

A Continuum Robot for Remote Applications: From Industrial to Medical Surgery With Slender Continuum Robots

The maintenance of critical industrial components is often hindered by limited access, tortuous passages, and complex geometries. In highly constrained environments, inspection tasks are currently performed with borescopes, but even skilled operators struggle with hard-to-reach targets, and the limited mobility prevents in situ repair when defects are identified. Thanks to an active shape control, snakelike and continuum robots can outperform borescopes for short-range inspection as well as enable intervention. However, their actuation technology limits their scalability in length, as longer bodies pose control challenges due to their intrinsically low stiffness and space constraints. To overcome the limitations of both borescopes and continuum robots, here, we propose a modular design at their intersection, with both active tendon-driven and passively flexible segments. The main elements of the novel design, including the actuation and control interface, are described, and the system is demonstrated in scenarios for aerospace assets, nuclear installations, and robotassisted surgery.

Controlling the Crawling Speed of the Snake Robot along a Cable Based on the Hopf Oscillator

To make the snake robot crawl quickly along the high-voltage cable, this paper employs the Simulated Annealing Algorithm (SAA) to find the optimal step size for the spiral-winding gait of the snake robot and improve its crawling speed along the high-voltage cable. First, a spiral-winding gait for the robot is designed based on the configuration of the snake robot and the crawling environment along the cable. Next, the double-chain Hopf oscillator is used to generate the spiral-winding gait for the snake-like robot. After that, based on the snake robot’s position, the SAA is employed to improve the crawling speed of the snake robot by finding the optimal step size of the spiral-winding gait. Finally, CoppeliaSim 4.0.0 software is used to analyze the optimization effect of the speed of the snake robot crawling along the cable. The results highlight that the maximum crawling speeds of the snake robot are 0.8868 cm/s, 0.8843 cm/s, 0.8598 cm/s, and 0.7971 cm/s, which are 18.01%, 8.16%, 11.01%, and 12.16% lower than the maximum speed obtained using the sampling fit method when the cable friction coefficients are 0.3, 0.4, 0.5, and 0.6. These simulation results verify the effectiveness of the optimized control algorithm.

A Study of Energy-Efficient and Optimal Locomotion in a Pneumatic Artificial Muscle-Driven Snake Robot

This paper presents a study of energy efficiency and kinematic-based optimal design locomotion of a pneumatic artificial muscle (PAM)-driven snake-like robot. Although snake-like robots have several advantages over wheeled and track-wheeled mobile robots, their low energy-locomotion has limited their applications in long-range and outdoor fields. This work continues our previous efforts in designing and prototyping a muscle-driven snake-like robot to address their low energy efficiency limitation. An electro-pneumatic control hardware was developed to control the robot’s locomotion and a control algorithm for generating the lateral undulation gait. The energy efficiency of a single muscle (i.e., PAM), a single 2-link module of the robot, and a 6-link snake robot were also studied. Moreover, the power consumption was derived for the snake locomotion to determine the cost of transportation as the index for measuring the performance of the robot. Finally, the performance of the robot was analyzed and compared to similar models. Our analysis showed that the power consumption efficiency for our robot is 0.21, which is comparable to the reported range of 0.016–0.32 from other robots. In addition, the cost of transportation for our robot was determined to be 0.19 compared to the range of 0.01–0.75 reported for the other mobile robots. Finally, the range of motion for the joints of the robot is ±30∘, which is comparable to the reported range of motion of other snake-like robots, i.e., 25∘–45∘.

Path Following of an Underwater Snake-like Robot Exposed to Ocean Currents and Locomotion Efficiency Optimization Based on Multi-Strategy Improved Sparrow Search Algorithm

In this paper, we propose a cubic spline interpolation method to generate a desired curve path and present an integral line of sight (ILOS) method and a control strategy for course tracking control based on nonsingular terminal sliding mode to enable an underwater snake-like robot (USR) to move towards and follow the path generated by the parametric cubic-spline interpolation (PCSI) path-planning method, while considering the disturbances caused by ocean currents. The efficiency of robot locomotion is an important evaluation criterion for robot design. Thus, we introduce a multi-strategy improved sparrow search algorithm (MISSA) to dynamically choose gait parameters that significantly enhance the efficiency of robot movement. We conduct simulations to demonstrate that the proposed controller enables the USR, subjected to ocean currents, to accurately converge towards and follow the target path. Our results also reveal that MISSA effectively enhances the locomotion efficiency of the robot.