Obstacle-aided Locomotion Research Articles

Form Closure for Fully Actuated and Robust Obstacle-Aided Locomotion in Snake Robots

Form Closure for Fully Actuated and Robust Obstacle-Aided Locomotion in Snake Robots

Improved Jacobian matrix estimation applied to snake robots.

Two manipulator Jacobian matrix estimators for constrained planar snake robots are developed and tested, which enables the implementation of Jacobian-based obstacle-aided locomotion (OAL) control schemes. These schemes use obstacles in the robot's vicinity to obtain propulsion. The devised estimators infer manipulator Jacobians for constrained planar snake robots in situations where the positions and number of surrounding obstacle constraints might change or are not precisely known. The first proposed estimator is an adaptation of contemporary research in soft robots and builds on convex optimization. The second estimator builds on the unscented Kalman filter. By simulations, we evaluate and compare the two devised algorithms in terms of their statistical performance, execution times, and robustness to measurement noise. We find that both algorithms lead to Jacobian matrix estimates that are similarly useful to predict end-effector movements. However, the unscented filter approach requires significantly lower computing resources and is not poised by convergence issues displayed by the convex optimization-based method. We foresee that the estimators may have use in other fields of research, such as soft robotics and visual servoing. The estimators may also be adapted for use in general non-planar snake robots.

Reaction Force Analysis for Obstacle-Aided Locomotion of Snake Robot Using Piecewise Helixes

Snake robots can use numerous joints to move in various manners. One of them is the obstacle-aided locomotion, a method in which a robot moves by pushing obstacles. In our previous study, we proposed a three-dimensional obstacle-aided locomotion using piecewise helixes, which is composed of an obstacle-contacting part and a grounding part. However, this method is imperfect. This is because when depending on the contact condition with obstacles, the reaction force may make it difficult for the robot to maintain contact with the obstacles or to propel itself. In this study, we analyze the reaction force received from obstacles during the obstacle-aided locomotion to improve the performance of the method. Using these analysis results, we evaluate the contact points of the obstacle-contacting part from two perspectives. The first considers the maintenance of contact with the obstacle, and the second considers the factors that interfere with propulsion. The reaction force was confirmed experimentally using a force sensor. Additionally, the theory of the factors that interfere with the propulsion and maintenance of contact with the obstacle was verified using experiments of the obstacle-aided locomotion in several environments.

Obstacle-Aided Locomotion of a Snake Robot Using Piecewise Helixes

A non-wheeled snake robot can propel itself by pushing against obstacles. This is called obstacle-aided locomotion. To expand the exploration range of a snake robot using this method, it is preferable to utilize obstacles that are both on the ground and by the side or above. To achieve these goals, we propose an obstacle-aided locomotion using piecewise helixes. This target shape comprises grounding and obstacle-contacting parts. The length and shape of the grounding part can be changed from a straight line to a circular arc. The height of the obstacle-contacting part can be changed or its direction can be reversed. The robot can adapt to various obstacles by appropriately changing its body shape. In addition, we propose a snake robot locomotion in a flat ground using the same shape as that used for obstacle-aided locomotion. This involves a combination of shift control and rolling motion. The robot can move in a straight line in the forward or lateral direction or can turn in a circular arc using the proposed method. Finally, experiments that confirm the effectiveness of the proposed method are presented.

The Redesigned Serpens, a Low-Cost, Highly Compliant Snake Robot

The term perception-driven obstacle-aided locomotion (POAL) was proposed to describe locomotion in which a snake robot leverages a sensory-perceptual system to exploit the surrounding operational environment and to identify walls, obstacles, or other structures as a means of propulsion. To attain POAL from a control standpoint, the accurate identification of push-points and reliable determination of feasible contact reaction forces are required. This is difficult to achieve with rigidly actuated robots because of the lack of compliance. As a possible solution to this challenge, our research group recently presented Serpens, a low-cost, open-source, and highly compliant multi-purpose modular snake robot with a series elastic actuator (SEA). In this paper, we propose a new prototyping iteration for our snake robot to achieve a more dependable design. The following three contributions are outlined in this work as a whole: the remodelling of the elastic joint with the addition of a damper element; a refreshed design for the screw-less assembly mechanism that can now withstand higher transverse forces; the re-design of the joint module with an improved reorganisation of the internal hardware components to facilitate heat dissipation and to accommodate a larger battery with easier access. The Robot Operating System (ROS) serves as the foundation for the software architecture. The possibility of applying machine learning approaches is considered. The results of preliminary simulations are provided.

Modeling for Hybrid Obstacle-Aided Locomotion (HOAL) of Snake Robots

Snake robots able to operate in cluttered environments will be fit for a multitude of applications pertinent for society such as search-and-rescue operations, fire fighting and traversing otherwise unavailable tight spaces. Obstacle-aided locomotion is a propulsion strategy suitable for such applications, where obstacles in the workspace of the robot are used as assets for forward propulsion instead of avoided as hindrances in the path of the snake. To enable this, this paper extends and adapts the notion of classical hybrid position/force control and related concepts to obstacle-aided locomotion of snake robots. The resulting framework is denoted Hybrid Obstacle-Aided Locomotion (HOAL). The resulting library of concepts and notations and a suitable model of the snake robot and its environment enable us to partition the available degrees of freedom into orthogonal subspaces where control schemes for force and motion can be implemented independently. Furthermore, part of the mathematical model that makes up HOAL is presented to motivate its functionality.

Economic model predictive control for obstacle-aided snake robot locomotion

Abstract This paper studies the application of economic model predictive control (MPC) to snake robot locomotion. The proposed MPC algorithm integrates the gait pattern creation into the closed loop by maximizing the forward snake velocity. We consider both purely planar locomotion as well as obstacle-aided locomotion. A compliant obstacle-snake contact model is introduced, rendering the interaction dynamics considered in the optimal control problem smooth. We illustrate the efficacy of the scheme by numerical simulations. The emerging gait patterns are undulatory and can make simultaneous use of anisotropic ground friction and obstacles.

Serpens: A Highly Compliant Low-Cost ROS-Based Snake Robot with Series Elastic Actuators, Stereoscopic Vision and a Screw-Less Assembly Mechanism

Snake robot locomotion in a cluttered environment where the snake robot utilises a sensory-perceptual system to perceive the surrounding operational environment for means of propulsion is defined as perception-driven obstacle-aided locomotion (POAL). From a control point of view, achieving POAL with traditional rigidly-actuated robots is challenging because of the complex interaction between the snake robot and the immediate environment. To simplify the control complexity, compliant motion and fine torque control on each joint is essential. Accordingly, intrinsically elastic joints have become progressively prominent over the last years for a variety robotic applications. Commonly, elastic joints are considered to outperform rigid actuation in terms of peak dynamics, robustness, and energy efficiency. Even though a few examples of elastic snake robots exist, they are generally expensive to manufacture and tailored to custom-made hardware/software components that are not openly available off-the-shelf. In this work, Serpens, a newly-designed low-cost, open-source and highly-compliant multi-purpose modular snake robot with series elastic actuator (SEA) is presented. Serpens features precision torque control and stereoscopic vision. Only low-cost commercial-off-the-shelf (COTS) components are adopted. The robot modules can be 3D-printed by using Fused Deposition Modelling (FDM) manufacturing technology, thus making the rapid-prototyping process very economical and fast. A screw-less assembly mechanism allows for connecting the modules and reconfigure the robot in a very reliable and robust manner. The concept of modularity is also applied to the system architecture on both the software and hardware sides. Each module is independent, being controlled by a self-reliant controller board. The software architecture is based on the Robot Operating System (ROS). This paper describes the design of Serpens and presents preliminary simulation and experimental results, which illustrate its performance.

SnakeSIM: a ROS-based control and simulation framework for perception-driven obstacle-aided locomotion of snake robots

Biological snakes are capable of exploiting roughness in the terrain for locomotion. This feature allows them to adapt to different types of environments. Snake robots that can mimic this behaviour could be fitted with sensors and used for transporting tools to hazardous or confined areas that other robots and humans are unable to access. Snake robot locomotion in a cluttered environment where the snake robot utilises a sensory–perceptual system to perceive the surrounding operational environment for means of propulsion can be defined as perception-driven obstacle-aided locomotion (POAL). The initial testing of new control methods for POAL in a physical environment using a real snake robot imposes challenging requirements on both the robot and the test environment in terms of robustness and predictability. This paper introduces SnakeSIM, a virtual rapid-prototyping framework that allows researchers for the design and simulation of POAL more safely, rapidly and efficiently. SnakeSIM is based on the robot operating system (ROS) and it allows for simulating the snake robot model in a virtual environment cluttered with obstacles. The simulated robot can be equipped with different sensors. Tactile perception can be achieved using contact sensors to retrieve forces, torques, contact positions and contact normals. A depth camera can be attached to the snake robot head for visual perception purposes. Furthermore, SnakeSIM allows for exploiting the large variety of robotics sensors that are supported by ROS. The framework can be transparently integrated with a real robot. To demonstrate the potential of SnakeSIM, a possible control approach for POAL is considered as a case study.

Snake-Like Robot with Fusion Gait for High Environmental Adaptability: Design, Modeling, and Experiment

A snake changes its gait to adapt to different environments. A snake-like robot that is able to perform as many or more gaits than a real-life snake has the potential to successfully adapt to a range of environments, similar to a real-life snake. However, only a few mechanisms in the current snake-like framework can perform common gaits. In this paper, a novel snake-like robot is developed to resolve this problem. A multi-gait is established and used as a reference for the articulation design. A non-snake-like mechanism with linear articulation is combined with the classical swing joint. A prototype is designed and constructed for verification and analysis. Two basic main gaits, namely, serpentine and rectilinear locomotion, are fused, and a novel obstacle-aided locomotion based on rectilinear motion is developed. The experiment demonstrates that the robot can generate all of the expected gaits with high movement efficiency.

Perception-Driven Obstacle-Aided Locomotion for Snake Robots: The State of the Art, Challenges and Possibilities †

In nature, snakes can gracefully traverse a wide range of different and complex environments. Snake robots that can mimic this behaviour could be fitted with sensors and transport tools to hazardous or confined areas that other robots and humans are unable to access. In order to carry out such tasks, snake robots must have a high degree of awareness of their surroundings (i.e., perception-driven locomotion) and be capable of efficient obstacle exploitation (i.e., obstacle-aided locomotion) to gain propulsion. These aspects are pivotal in order to realise the large variety of possible snake robot applications in real-life operations such as fire-fighting, industrial inspection, search-and-rescue, and more. In this paper, we survey and discuss the state of the art, challenges, and possibilities of perception-driven obstacle-aided locomotion for snake robots. To this end, different levels of autonomy are identified for snake robots and categorised into environmental complexity, mission complexity, and external system independence. From this perspective, we present a step-wise approach on how to increment snake robot abilities within guidance, navigation, and control in order to target the different levels of autonomy. Pertinent to snake robots, we focus on current strategies for snake robot locomotion in the presence of obstacles. Moreover, we put obstacle-aided locomotion into the context of perception and mapping. Finally, we present an overview of relevant key technologies and methods within environment perception, mapping, and representation that constitute important aspects of perception-driven obstacle-aided locomotion.

Experimental Investigation of Obstacle-Aided Locomotion With a Snake Robot

In a recent paper, the authors have proposed a control strategy for a snake robot during obstacle-aided locomotion. In this paper, experimental results are presented where the controller is shown to successfully maintain the forward propulsion of a physical snake robot in a course with different obstacle configurations.

Hybrid Modelling and Control of Obstacle-Aided Snake Robot Locomotion

A snake can traverse cluttered and irregular environments by using irregularities around its body as push points to aid the propulsion. This characteristic feature of biological snake locomotion, which is denoted as obstacle-aided locomotion, is investigated for snake robot locomotion purposes in this paper. The paper presents a hybrid model of the dynamics of a planar snake robot interacting with obstacles in its environment. Obstacle contact forces are calculated by formulating and solving a linear complementarity problem (LCP). The existence and uniqueness properties of the state evolution of the hybrid model are investigated. The paper also presents a hybrid control strategy employing measured contact forces to maintain propulsion while simultaneously preventing the snake robot from being jammed between obstacles in its path. The simulation results validate the hybrid modelling approach and the effectiveness of the proposed control strategy.

Snake Robot Obstacle-Aided Locomotion: Modeling, Simulations, and Experiments

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Snakes utilize irregularities in the terrain, such as rocks and vegetation, for faster and more efficient locomotion. This motivates the development of snake robots that actively use the terrain for locomotion, i.e., obstacle-aided locomotion. In order to accurately model and understand this phenomenon, this paper presents a novel nonsmooth (hybrid) mathematical model for wheel-less snake robots, which allows the snake robot to push against external obstacles apart from a flat ground. The framework of nonsmooth dynamics and convex analysis allows us to systematically and accurately incorporate both unilateral contact forces (from the obstacles) and isotropic friction forces based on Coulomb's law using set-valued force laws. The mathematical model is verified through experiments. In particular, a back-to-back comparison between numerical simulations and experimental results is presented. It is, furthermore, shown that the snake robot is able to move forward faster and more robustly by exploiting obstacles. </para>