Abstract-Increasing efficiency by improving locomotion methods is a key issue for underwater robots. Moreover, a number of different control design challenges must be solved in order to realize operational swimming robots for underwater tasks. This paper proposes and experimentally validates a straight line path following controller for biologically inspired swimming snake robots. In particular, a line-of-sight (LOS) guidance law is presented, which is combined with a sinusoidal gait pattern and a directional controller that steers the robot towards and along the desired path. The performance of the path following controller is investigated through experiments with a physical underwater snake robot for both lateral undulation and eel-like motion. In addition, fluid parameter identification is performed and simulation results based on the identified fluid coefficients are presented to obtain back-to-back comparison with the motion of the physical robot during the experiments. The experimental results show that the proposed control strategy successfully steers the robot towards and along the desired path for both lateral undulation and eel-like motion patterns.Index Terms-Underwater snake robots, modeling of swimming robots, model identification, LOS path following controller.

Abstract-This paper proposes and experimentally validates a straight line path following controller for underwater snake robots in the presence of constant irrotational currents of unknown direction and magnitude. An integral line-of-sight (LOS) guidance law is presented, which is combined with a sinusoidal gait pattern and a directional controller that steers the robot towards and along the desired path. The stability of the proposed control scheme in the presence of ocean currents is investigated by using Poincaré map analysis. Simulation results are presented to illustrate the performance of the proposed path following controller for both lateral undulation and eellike motion. In addition, the performance of the path following controller is investigated through experiments with a physical underwater snake robot. The experimental results show that the proposed control strategy successfully steers the robot towards and along the desired path in the presence of an unknown constant irrotational current in the inertial frame.Index Terms-Underwater snake robots, modeling of swimming robots, path following controller, integral LOS.

Abstract-Increasing efficiency by improving the locomotion methods is a key issue for underwater robots. Hence, an accurate dynamic model is important for both controller design and efficient locomotion methods. This paper presents a model of the kinematics and dynamics of a planar, underwater snake robot aimed at control design. Fluid contact forces and torques are modeled using analytical fluid dynamics. The model is derived in a closed form and can be utilized in modern model-based control schemes. The proposed model is easily implemented and simulated, regardless of the number of robot links. Simulation results with a ten link robotic system are presented.

Abstract-This paper considers straight line path following control of underwater snake robots in the presence of constant irrotational currents. An integral line-of-sight (LOS) guidance law is proposed, which is combined with a sinusoidal gait pattern and a directional controller that steers the robot towards and along the desired path. Integral action is introduced in the guidance law to compensate for the ocean current effect. The stability of the proposed control scheme in the presence of ocean currents is investigated. In particular, using Poincaré map analysis, we prove that the state variables of an underwater snake robot trace out an exponentially stable periodic orbit when the integral LOS path following controller is applied. Simulation results are presented to illustrate the performance of the proposed path following controller for both lateral undulation and eel-like motion.

The aim of this article is to provide a survey on the most popular modeling approaches for PMAs (pneumatic muscle actuators). PMAs are highly non-linear pneumatic actuators where their elongation is proportional to the interval pressure. During the last decade, there has been an increase in the industrial and scientific utilization of PMAs, due to their advantages such as high strength and small weight, while various types of PMAs with different technical characteristics have appeared in the literature. This article will: (a) analyse the PMA's operation from a mathematical modeling perspective; (b) present their merits and drawbacks of the most common PMAs; and (c) establish the fundamental basis for developing industrial applications and conducting research in this field.