Planar Path Following of Underwater Snake Robots in the Presence of Ocean Currents

Abstract

Abstract-This paper presents a control system that enables an underwater snake robot to converge towards and follow a straight path in the presence of constant irrotational ocean currents. The robot is assumed to be neutrally buoyant, fully submerged and moving in a virtual plane with a sinusoidal gait and limited link angles. The proposed control approach uses a heading controller that exponentially stabilises the heading of the robot towards the desired heading, which is obtained by an integral line-of-sight guidance law. Uniform semi-global exponential stability of the control system is formally proved using cascaded systems and Lyapunov theory. Simulations are presented that illustrate and validate the theoretical results.

Waypoint guidance control for underwater snake robots exposed to ocean currents

“…In this section, a simplified modelling approach for USRs is introduced briefly and a transformation to make it suitable for path-following is presented. A detailed derivation of the model can be found in [20], [21], an analysis and comparison with the complex model from the previous section in [8], and the model transformation in [17].…”

“…In order to make the model (11) more suitable for controldesign, the point that defines the position of the robot was moved to the pivot point, about which the USR turns in [17]: In the dynamical equations (11f) and (11h) it can be seen that the joint coordinates φ enter the dynamics of both v n and v θ . This can be avoided by moving the point that defines the position of the snake robot by a distance ε in the tangential direction, as can be seen in Fig.…”

“…Hence, this paper extends the waypoint guidance presented in [15] by considering the current effects and thus the control approach presented in [15] falls out as a special case where the current effects are neglected. In addition, the proposed guidance strategy in this paper can be combined with two different straight line path following control approaches previously proposed by the authors in [17], [18] and [19]. An integral line-of-sight (ILOS) path following controller derived based on the model proposed in [4] for USRs for which the stability analysis was studied using a Poincaré map was presented and experimentally validated in [18] and [19].…”

“…An integral line-of-sight (ILOS) path following controller derived based on the model proposed in [4] for USRs for which the stability analysis was studied using a Poincaré map was presented and experimentally validated in [18] and [19]. In [17], a path following controller was proposed based on a control-oriented, simplified model, and a general formal stability proof was presented for the closed-loop system. This paper extends the previous work by the authors on ILOS path following along straight lines presented in [17], [18] and [19], proposing an operator-friendly framework for waypoint guidance control of USRs under the influence of ocean current effects.…”

“…In [17], a path following controller was proposed based on a control-oriented, simplified model, and a general formal stability proof was presented for the closed-loop system. This paper extends the previous work by the authors on ILOS path following along straight lines presented in [17], [18] and [19], proposing an operator-friendly framework for waypoint guidance control of USRs under the influence of ocean current effects. Simulation results are presented for both lateral undulation and eel-like motion patterns illustrating the performance of the proposed waypoint guidance strategy.…”