Set-based path following and obstacle avoidance for underwater snake robots

Abstract

This article presents a set-based guidance strategy for path following with obstacle avoidance for underwater snake robots conducting planar sinusoidal motion. The guidance scheme is designed such that the robot follows a straight path and avoids obstacles on the way by following a circle around them. In order to enable a switching between these two tasks, we generalize a strategy that was introduced for surface vessels, by making the switching condition independent of the dynamics and thus applicable for a larger class of systems. The guidance system is shown to fulfil the control objectives at a kinematic level. We present new test results that validate the set-based guidance scheme for the first time experimentally.

Path Following, Obstacle Detection and Obstacle Avoidance for Thrusted Underwater Snake Robots

“…i.e., to make each joint have the same value, providing an even curvature along the whole robot. This is different from Kohl et al (2017) where undulations are used for propulsion, and the joint references include an additional sinusoidal term with a phase shift between the joints. Instead (2) ensures that the joints are used only for directional control, while the thrusters are used to propel the robot forward.…”

“…(D) Use the pinhole camera model, camera focal length f and the actual area of the shape A r to calculate the 3D-position of the detected shape relative to the camera coordinate frame. Algorithm 1, which is based on set-based theory described in , , and Kohl et al (2017).…”

“…For more details, see section 2.3 and Moe and Pettersen ( 2016 ). To achieve a guidance system with a path following and an obstacle avoidance mode, we employ a guidance law from Kohl et al ( 2017 ) which is suitable both for straight line and circular path following. The latter is applied for obstacle avoidance to encircle obstacles on the way.…”

“…This paper presents a path following control strategy that is able to make the thrusted USR follow the desired reference path. Furthermore, the developed obstacle detection scheme was successfully applied and combined with a set-based collision avoidance method (Moe and Pettersen, 2016 ; Kohl et al, 2017 ). This approach ensures obstacle avoidance when necessary and path following otherwise.…”

“…The path following control concept and obstacle avoidance for USRs without thrusters has been investigated in Kohl et al ( 2017 ). Here, both the direction and propulsion are achieved through the undulatory motion of the joints.…”