Modeling, Control and Energy Efficiency of Underwater Snake Robots

This thesis is mainly motivated by the attribute of the snake robots that they are able to move over land as well as underwater while the physiology of the robot remains the same. This adaptability to different motion demands depending on the environment is one of the main characteristics of the snake robots. In particular, this thesis targets several interesting aspects regarding the modeling, control and energy efficiency of the underwater snake robots. This thesis addresses the problem of modeling the hydrodynamic effects with an analytical perspective and a primary objective to conclude in a closed-form solution for the dynamic model of an underwater snake robot. Two mathematical models of the kinematics and dynamics of underwater snake robots swimming in virtual horizontal and vertical planes aimed at control design are presented. The presented models are derived in a closed-form and can be utilized in modern modelbased control schemes. In addition, these proposed models comprise snake robots moving both on land and in water which makes the model applicable for unified control methods for amphibious snake robots moving both on land and in water. The third model presented in this thesis is based on simplifying assumptions in order to derive a control-oriented model of an underwater snake robot moving in a virtual horizontal plane that is well-suited for control design and stability analysis. The models are analysed using several techniques. An extensive analysis of the model of a fully immersed underwater snake robot moving in a virtual horizontal plane is conducted. Based on this analysis, a set of essential properties that characterize the overall motion of underwater snake robots is derived. An averaging analysis reveals new fundamental properties of underwater snake robot locomotion that are useful from a motion planning perspective. In this thesis, both the motion analysis and control strategies are conducted based on a general sinusoidal motion pattern which can be used for a broad class of motion patterns including lateral undulation and eel-like motion. This thesis proposes and experimentally validates solutions to the path following control problem for biologically inspired swimming snake robots. In particular, line-of-sight (LOS) and integral line-of-sight (I-LOS) guidance laws, which are combined with a sinusoidal gait pattern and a directional controller that steers the robot towards and along the desired path are proposed. An I-LOS path following controller for steering an underwater snake robot along a straight line path in the presence of ocean currents of unknown direction and magnitude is presented and by using a Poincaré map, it is shown that all state variables of an underwater snake robot, except for the position along the desired path, trace out an exponentially stable periodic orbit. Moreover, this thesis presents the combined use of an artificial potential fields-based path planner with a new waypoint guidance strategy for steering an underwater snake robot along a path defined by waypoints interconnected by straight lines. The waypoints are derived by using a path planner based on the artificial potential field method in order to also address the obstacle avoidance problem. Furthermore, this thesis considers the energy efficiency of underwater snake robots. In particular, the relationship between the parameters of the gait patterns, the forward velocity and the energy consumption for the different motion patterns for underwater snake robots is investigated. Based on simulation results, this thesis presents empirical rules to choose the values for the parameters of the motion gait pattern of underwater snake robots. The experimental results support the derived properties regarding the relationship between the gait parameters and the power consumption both for lateral undulation and eel-like motion patterns. Moreover, comparison results are obtained for the total energy consumption and the cost of transportation of underwater snake robots and remotely operated vehicles (ROVs). Furthermore, in this thesis a multi-objective optimization problem is developed with the aim of maximizing the achieved forward velocity of the robot and minimizing the corresponding average power consumption of the system

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

An integrated approach for monitoring structural deformation of aquaculture net cages

The majority of present marine finfish production is conducted in flexible net cages which can deform when they are subjected to water movements generated by currents. The ability to monitor net deformation is important for performing cage operations and evaluation of fish health and welfare under changing environment. This paper presents a new method for real-time monitoring of net cage deformations that is based on an integrated approach where positioning sensor data is incorporated into a numerical model. An underwater positioning system was deployed at a full-scale fish farm site, with three acoustic sensors mounted on a cage measuring positions of the net at different depths. A novel numerical model with an adaptive current field was used to simulate net cage deformations, where the magnitude and direction of the current could be adapted by continuously assessing deviations between the simulated and the measured positions of the net. This method was found to accurately predict the pre-defined current velocity profiles in a set of simulated experiments. In the field experiment, a good agreement was also obtained between the simulated positions of the net and the acoustic sensor data. The integrated approach was shown to be well suited for in-situ real-time monitoring of net cage deformations by using a significantly reduced number of sensors.publishedVersio

Seatonomy applied in an operational analysis and overall system design for an autonomous underwater vehicle

This report presents results obtained by applying the Seatonomy concept for analysing autonomous operations handled in CageReporter project. The analysis results in this document are based on the Autonomous Job Analysis (AJA) concept introduced in the Seatonomy method. This includes analysis to identify autonomous capabilities that the system must possess for the various operations related to A) Fish conditions, B) Cage inspection and C) Production environment. Furthermore, the activity includes system design with focus on architecture, error management and safe mode.publishedVersio

Seatonomy applied in an operational analysis and overall system design for an autonomous underwater vehicle

This report presents results obtained by applying the Seatonomy concept for analysing autonomous operations handled in CageReporter project. The analysis results in this document are based on the Autonomous Job Analysis (AJA) concept introduced in the Seatonomy method. This includes analysis to identify autonomous capabilities that the system must possess for the various operations related to A) Fish conditions, B) Cage inspection and C) Production environment. Furthermore, the activity includes system design with focus on architecture, error management and safe mode

Locomotion Efficiency Optimization of Biologically Inspired Snake Robots

Snake robots constitute bio-inspired solutions that have been studied due to their ability to move in challenging environments where other types of robots, such as wheeled or legged robots, usually fail. In this paper, we consider both land-based and swimming snake robots. One of the principal concerns of the bio-inspired snake robots is to increase the motion efficiency in terms of the forward speed by improving the locomotion methods. Furthermore, energy efficiency becomes a crucial challenge for this type of robots due to the importance of long-term autonomy of these systems. In this paper, we take into account both the minimization of the power consumption and the maximization of the achieved forward velocity in order to investigate the optimal gait parameters for bio-inspired snake robots using lateral undulation and eel-like motion patterns. We furthermore consider possible negative work effects in the calculation of average power consumption of underwater snake robots. To solve the multi-objective optimization problem, we propose transforming the two objective functions into a single one using a weighted-sum method. For different set of weight factors, Particle Swarm Optimization is applied and a set of optimal points is consequently obtained. Pareto fronts or trade-off curves are illustrated for both land-based and swimming snake robots with different numbers of links. Pareto fronts represent trade-offs between the objective functions. For example, how increasing the forward velocity results in increasing power consumption. Therefore, these curves are a very useful tool for the control and design of snake robots. The trade-off curve thus constitutes a very useful tool for both the control and design of bio-inspired snake robots. In particular, the operators or designers of bio-inspired snake robots can choose a Pareto optimal point based on the trade-off curve, given the preferred number of links on the robot. The optimal gait parameters for the robot control system design are then directly given both for land-based and underwater snake robots. Moreover, we are able to obtain some observations about the optimal values of the gait parameters, which provide very important insights for future control design of bio-inspired snake robots

Serpentine motion control of snake robots for curvature and heading based trajectory - parameterization

The control problem for the serpentine motion of a planar snake under the assumption of a trajectory characterized by its curvature and heading is examined in this article. The time varying curvature and heading attributes of the trajectory result in a sinusoidal reference signal for the joint angles. An inner loop PD-controller is used for trajectory tracking by compensating the effects of the snake's dynamics, while an outer loop first-order controller is used for the formation of the reference joint angles by tracking the desired heading and velocity. Simulation studies on spiral curves are included to investigate the efficiency of the controller

Underwater Communication and Position Reference System

This report presents results obtained in the CageReporter project regarding the development of a low cost hydroacoustic subsea communication system adapted for use in fish cages. The report mainly addresses tasks regarding the optimization of sender and receiver technology, as well as algorithms for advanced signal processing to optimize bandwidth while ensuring stable real-time communication during operations in fish cages. The solutions have been tested and validated in full scale field trials in two fish farms. In addition, this activity presents a solution developed to obtain a relative position reference system where the main challenge was to develop a realistic real-time map of the fish cage. The report describes the analytical study that conducted to place the acoustic transmitters. The proposed configuration has been tested in full scale. Afterwards, the obtained experimental data have been used to develop and validate numerical methods that estimate a high-resolution real-time map of the fish cage. The work furthermore includes the development of algorithms for state estimation to increase accuracy and reduce target noise. The accuracy of the position reference system has been validated through multiple filed trials.publishedVersio

Seatonomy applied in operational analysis of an autonomous net cleaning robot - NetClean 24/7 report for work package H1.1: Operational analysis and overall system design

This report presents an analysis of the autonomous cleaning operations handled in the NetClean 24/7 project. The analysis was conducted using the Autonomous Job Analysis (AJA) concept introduced in the Seatonomy method. This includes the identification of the autonomous capabilities that a tetherless cleaning robot needs to conduct simultaneous net cleaning and inspection, as well as system design requirements and specifications related to equipment, sensors, actuators, architecture, error management and safe modes.Seatonomy applied in operational analysis of an autonomous net cleaning robot - NetClean 24/7 report for work package H1.1: Operational analysis and overall system designpublishedVersio

Serpentine motion control of snake robots for curvature and heading based trajectory - parameterization

The control problem for the serpentine motion of a planar snake under the assumption of a trajectory characterized by its curvature and heading is examined in this article. The time varying curvature and heading attributes of the trajectory result in a sinusoidal reference signal for the joint angles. An inner loop PD-controller is used for trajectory tracking by compensating the effects of the snake's dynamics, while an outer loop first-order controller is used for the formation of the reference joint angles by tracking the desired heading and velocity. Simulation studies on spiral curves are included to investigate the efficiency of the controller.This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Control & Automation (MED), 2012 20th Mediterranean Conference on , © IEEE, after peer review. To access the final edited and published work see http://dx.doi.org/10.1109/MED.2012.6265693 © 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