A Study on Sinus-Lifting Motion of a Snake Robot With Sequential Optimization of a Hybrid System

In this paper, we consider “sinus-lifting motion” of a living snake, in which a snake lifts up some parts of its body from the ground, and switches the lifted parts dynamically. It is not clear whether imitating the sinus-lifting motion is the best locomotion or not for a snake like robot. The aim of this paper is to propose an appropriate motion pattern to a snake like robot considering the optimality of the sinus-lifting motion. We introduce two physical parameters, constraint forces and energy efficiency, as cost functions to optimize and propose switching strategies for generating optimal motion patterns of a snake like robot

Control of snake robots with switching constraints: trajectory tracking with moving obstacle

We propose control of a snake robot that can switch lifting parts dynamically according to kinematics. Snakes lift parts of their body and dynamically switch lifting parts during locomotion: e.g. sinus-lifting and sidewinding motions. These characteristic types of snake locomotion are used for rapid and efficient movement across a sandy surface. However, optimal motion of a robot would not necessarily be the same as that of a real snake as the features of a robot’s body are different from those of a real snake. We derived a mathematical model and designed a controller for the three-dimensional motion of a snake robot on a two-dimensional plane. Our aim was to accomplish effective locomotion by selecting parts of the body to be lifted and parts to remain in contact with the ground. We derived the kinematic model with switching constraints by introducing a discrete mode number. Next, we proposed a control strategy for trajectory tracking with switching constraints to decrease cost function, and to satisfy the conditions of static stability. In this paper, we introduced a cost function related to avoidance of the singularity and the moving obstacle. Simulations and experiments demonstrated the effectiveness of the proposed controller and switching constraints

Singularity Analysis of a Snake Robot and an Articulated Mobile Robot With Unconstrained Links

In this paper, we analyze the conditions related to singular configurations with unconstrained links and present related theorems and lemmas for a snake robot and an articulated mobile robot. A snake robot and an articulated mobile robot have links that have passive or active wheels and the links are serially connected by active joints. The singular configuration should be avoided if the robots are automatically controlled because they cannot execute intended motion when they are in the singular configuration. We derive a novel necessary and sufficient condition for the singular configurations of the snake robot; this removes some limitations of the traditional condition for a snake robot without unconstrained links. We also derive the necessary and sufficient conditions for the singular configurations of the articulated mobile robot, and the structural conditions under which a real articulated mobile robot does not have a singular configuration. These conditions are proved by analyzing the elements of matrices included in the kinematic model and considering the geometrical meaning of the elements. In addition, we propose evaluation indices representing the distance from the singular configurations of a snake robot. We verify the effectiveness of these indices through simulations

Formation Control of Underactuated Bio-inspired Snake Robots

This paper considers formation control of snake robots. In particular, based on a simplified locomotion model, and using the method of virtual holonomic constraints, we control the body shape of the robot to a desired gait pattern defined by some pre-specified constraint functions. These functions are dynamic in that they depend on the state variables of two compensators which are used to control the orientation and planar position of the robot, making this a dynamic maneuvering control strategy. Furthermore, using a formation control strategy we make the multi-agent system converge to and keep a desired geometric formation, and enforce the formation follow a desired straight line path with a given speed profile. Specifically, we use the proposed maneuvering controller to solve the formation control problem for a group of snake robots by synchronizing the commanded velocities of the robots. Simulation results are presented which illustrate the successful performance of the theoretical approach.© ISAROB 2016. This is the authors' accepted and refereed manuscript to the article. Locked until 2017-07-27

Modeling and Control of Head Raising Snake Robots by Using Kinematic Redundancy

In this paper, we consider trajectory tracking control of a head raising snake robot on a flat plane by using kinematic redundancy. We discuss the motion control requirements to accomplish trajectory tracking and other tasks, such as singular configuration avoidance and obstacle avoidance, for the snake robot. The features of the internal motion caused by kinematic redundancy are considered, and a kinematic model and a dynamic model of the snake robot are derived by introducing two types of shape controllable point. The first is the head shape controllable point, and the other is the base shape controllable point. We analyzed the features of the two kinds of shape controllable point and proposed a controller to accomplish the trajectory tracking of the robot’s head as its main task along with several sub-tasks by using redundancy. The proposed method to accomplish several sub-tasks is useful for both the kinematic model and the dynamic model. Experimental results using a head raising snake robot which can control the angular velocity of its joints show the effectiveness of the proposed controller

Modified serpentine motion of the snake robot

The frequent occurrence of earthquake in New Zealand drives the research on snake robot for search and rescue operation because of its elongated body shape and locomotion mimicry of the biological snake. Both features are in favour of moving the snake robot through the earthquake disaster area. To facilitate the robot control and information gathering, it is usually required to install a camera on the snake robot head so that the video images of the disaster area can be send back to the human operator. This thesis presents the simulation of a snake robot performing serpentine motion. A camera is attached on the snake robot head to obtain the video image along the line of sight. A remote controller is incorporated to control the advancement based on the video images. This simulation reveals that the video images from the camera oscillate seriously because the camera on the snake robot head follows serpenoid curve during the locomotion. As a result, both robot control and information gathering are affected. A solution is proposed to stabilize the snake robot head and its camera by introducing a correction at the joint between the robot head and its body. This correction aligns the camera sight direction with the moving direction of the snake robot to yield satisfactory video images. Finally, an actual snake robot is implemented with a wireless camera installed on the head to show the effect of correction. Experiments are conducted to control the advancement of snake robot remotely just based on the video images obtained from the camera. This greatly improves the performance of the snake robot

Bio-Inspired Robotics

Modern robotic technologies have enabled robots to operate in a variety of unstructured and dynamically-changing environments, in addition to traditional structured environments. Robots have, thus, become an important element in our everyday lives. One key approach to develop such intelligent and autonomous robots is to draw inspiration from biological systems. Biological structure, mechanisms, and underlying principles have the potential to provide new ideas to support the improvement of conventional robotic designs and control. Such biological principles usually originate from animal or even plant models, for robots, which can sense, think, walk, swim, crawl, jump or even fly. Thus, it is believed that these bio-inspired methods are becoming increasingly important in the face of complex applications. Bio-inspired robotics is leading to the study of innovative structures and computing with sensory–motor coordination and learning to achieve intelligence, flexibility, stability, and adaptation for emergent robotic applications, such as manipulation, learning, and control. This Special Issue invites original papers of innovative ideas and concepts, new discoveries and improvements, and novel applications and business models relevant to the selected topics of ``Bio-Inspired Robotics''. Bio-Inspired Robotics is a broad topic and an ongoing expanding field. This Special Issue collates 30 papers that address some of the important challenges and opportunities in this broad and expanding field