Design of a swimming snake robot

This paper presents the design and realization of a bioinspired snake robot that can move on the water surface. This robot mimics the locomotion strategies of anguilliform fishes such as eels and lampreys, which have a thin, long, cylindrical body and whose movement resembles the crawling of a snake. An autonomous underwater vehicle with such a shape can pass through narrow crevices and reach places inaccessible to other swimming robots. Moreover, this locomotion entails a high energy efficiency and outstanding agility in maneuvers. The body of the bioinspired robot consists of a modular structure in which each module contains a battery, the electronic board, and a servo motor that drives the following module. The head of the robot has a different shape as it contains a camera and an ultrasonic sensor used to detect obstacles. In addition to the design of the robot, this paper also describes the implementation of the kinematic model

Алгоритм определения внутренней геометрии манипулятора змеевидного типа при движении лидирующего звена по наращиваемой траектории

In the paper, we have formulated the invariant description form for geometry of a spatial, kinematically redundant manipulator with the orthogonal non-coplanar axes of rotation of the joints. We have obtained the explicit equations for determining the angular coordinates from the condition that points of joints belong to the smooth parametrically given curve. Inequality constraints on the relative position of neighboring parts of the manipulator have been formulated. We have proposed an algorithm for solving equations and the method of planning changes for hinge coordinates for the movement of joints points along the spatial curve that is formed by incremental addition of target points for the head link positions of the manipulator. The method has been applied for planning movements of a hyper-redundant manipulator with a fixed root link and a snakelike robot when moving along the path built on the basis of current and forecasted positions of joints in the Cartesian space.Сформулированы инвариантная к системе внешних координат форма задания геометрии пространственного кинематически избыточного манипулятора с последовательно ортогональными некомпланарными осями шарниров вращения. Получены аналитические выражения для определения угловых шарнирных координат из условий принадлежности точек шарниров параметрически заданной гладкой кривой, уравнение для координат положения точек на кривой и неравенства-ограничения на взаимное положение смежных звеньев манипулятора. Предложен алгоритм решения уравнения и метод планирования законов изменения шарнирных координат, обеспечивающий перемещения точек шарниров по пространственной траектории, наращиваемой добавлением целевых точек для головного звена манипулятора. Метод применен для планирования движения гиперизбыточного манипулятора с неподвижным основанием и змеевидного робота при перемещении по траектории, выстраиваемой на основе текущих и прогнозируемых положений шарниров в декартовом пространств

SUAS: A Novel Soft Underwater Artificial Skin with Capacitive Transducers and Hyperelastic Membrane

The paper presents physical modeling, design, simulations, and experimentation on a novel Soft Underwater Artificial Skin (SUAS) used as tactile sensor. The SUAS functions as an electrostatic capacitive sensor, and it is composed of a hyperelastic membrane used as external cover and oil inside it used to compensate the marine pressure. Simulation has been performed studying and modeling the behavior of the external interface of the SUAS in contact with external concentrated loads in marine environment. Experiments on the external and internal components of the SUAS have been done using two different conductive layers in oil. A first prototype has been realized using a 3D printer. The results of the paper underline how the soft materials permit better adhesion of the conductive layer to the transducers of the SUAS obtaining higher capacitance. The results here presented confirmed the first hypotheses presented in a last work and opened new ways in the large-scale underwater tactile sensor design and development. The investigations are performed in collaboration with a national Italian project named MARIS, regarding the possible extension to the underwater field of the technologies developed within the European project ROBOSKIN

Anisotropic body compliance facilitates robotic sidewinding in complex environments

Sidewinding, a locomotion strategy characterized by the coordination of lateral and vertical body undulations, is frequently observed in rattlesnakes and has been successfully reconstructed by limbless robotic systems for effective movement across diverse terrestrial terrains. However, the integration of compliant mechanisms into sidewinding limbless robots remains less explored, posing challenges for navigation in complex, rheologically diverse environments. Inspired by a notable control simplification via mechanical intelligence in lateral undulation, which offloads feedback control to passive body mechanics and interactions with the environment, we present an innovative design of a mechanically intelligent limbless robot for sidewinding. This robot features a decentralized bilateral cable actuation system that resembles organismal muscle actuation mechanisms. We develop a feedforward controller that incorporates programmable body compliance into the sidewinding gait template. Our experimental results highlight the emergence of mechanical intelligence when the robot is equipped with an appropriate level of body compliance. This allows the robot to 1) locomote more energetically efficiently, as evidenced by a reduced cost of transport, and 2) navigate through terrain heterogeneities, all achieved in an open-loop manner, without the need for environmental awareness

Envirobot: A Bio-Inspired Environmental Monitoring Platform

Autonomous marine vehicles are becoming essential tools in aquatic environmental monitoring systems, and can be used for instance for data acquisition, remote sensing, and mapping of the spatial extent of pollutant spills. In this work, we present an unconventional bio-inspired autonomous robot aimed for execution of such tasks. The Envirobot platform is based on our existing segmented anguilliform swimming robots, but with important adaptations in terms of energy use and efficiency, control, navigation, and communication possibilities. To this end, Envirobot has been designed to have more endurance, flexible computational power, long range communication link, and versatile flexible environmental sensor integration. Its low level control is powered by an ARM processor in the head unit and micro processors in each active module. On top of this, integration of a computer-on-module enables versatile high level control methods. We present some preliminary results and experiments done with Envirobot to test the added navigation and control strategies

Analysis of underwater snake robot locomotion based on a control-oriented model

This paper presents an analysis of planar underwater snake robot locomotion in the presence of ocean currents. The robot is assumed to be neutrally buoyant and move fully submerged with a planar sinusoidal gait and limited link angles. As a basis for the analysis, an existing, controloriented model is further simplified and extended to general sinusoidal gaits. Averaging theory is then employed to derive the averaged velocity dynamics of the underwater snake robot from that model. It is proven that the averaged velocity converges exponentially to an equilibrium, and an analytical expression for calculating the forward velocity of the robot in steady state is derived. A simulation study that validates both the proposed modelling approach and the theoretical results is presented.Prepint - (c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Shape Control of a Snake Robot With Joint Limit and Self-Collision Avoidance

This paper proposes a shape control method for a snake robot, which maintains head position and orientation, and avoids joint limits and self-collision. We used a passive wheeled snake robot that can switch the grounded/lifted status of its wheels. We derived a kinematic model of the robot that represents its redundancy as both joint angles [the shape controllable points (SCPs)] and the null space of the control input. In the control method, the shape is changed by sequential control of the SCPs, and the null space of the control input is used for joint limit and self-collision avoidance. Jumps in control input do not occur, although the controlled variable and the model are switched. Simulations and an experiment were used to demonstrate the effectiveness of the proposed method

Motion control of a snake robot moving between two non-parallel planes

A control method that makes the head of a snake robot follow an arbitrary trajectory on two non-parallel planes, including coexisting sloped and flat planes, is presented. We clarify an appropriate condition of contact between the robot and planes and design a controller for the part of the robot connecting the two planes that satisfies the contact condition. Assuming that the contact condition is satisfied, we derive a simplified model of the robot and design a controller for trajectory tracking of the robot’s head. The controller uses kinematic redundancy to avoid violating the limit of the joint angle and a collision between the robot and the edge of a plane. The effectiveness of the proposed method is demonstrated in experiments using an actual robot

Where to place cameras on a snake robot: Focus on camera trajectory and motion blur

Visual information is heavily used in robotics, in particular for SLAM applications. Visual SLAM algorithms depend on robust feature extraction and reliable state estimation. Quality of the visual information highly depends on how that information is captured. The nature of snake robots' locomotion presents considerable challenges on the quality of images captured by an onboard mobile camera. Although placing the camera on the "head" of the snake robot has advantages when the robot is stationary since the body can be used as a manipulator observing for the environment, how to place the camera in order to capture more useful images for navigation during locomotion is not clear. In this paper, we present a comparative study to discuss implications of the camera location on field coverage and types of image quality for three snake gaits: Rolling, sidewinding and linear progression. Camera pose during locomotion is examined in detail and quality of images are quantified using a motion blur metric which relates camera egomotion to blur. Linear progression is found to be very promising in terms of supplying sharper images. But, there are also other merits that can be exploited in different locomotion types and camera locations