Nikola Mišković

Fast in-field identification of unmanned marine vehicles

To design high-level control structures efficiently, reasonable mathematical model parameters of the vessel have to be known. Because sensors and equipment mounted onboard marine vessels can change during a mission, it is important to have an identification procedure that will be easily implementable and time preserving and result in model parameters accurate enough to perform controller design. This paper introduces one such method, which is based on self-oscillations (IS-O). The described methodology can be used to identify single-degree-of-freedom nonlinear model parameters of underwater and surface marine vessels. Extensive experiments have been carried out on the VideoRay remotely operated vehicle and Charlie unmanned surface vehicle to prove that the method gives consistent results. A comparison with the least-squares identification and thorough validation tests have been performed, proving the quality of the obtained parameters. The proposed method can also be used to make conclusions on the model that describes the dynamics of the vessel. The paper also includes results of autopilot design in which the controllers are tuned according to the proposed method based on self-oscillations, proving the applicability of the proposed method.

Marine vehicles' line following controller tuning through self-oscillation experiments

This paper demonstrates the use of self-oscillation identification experiments for tuning line following controllers for marine vehicles. Two approaches are described: first, when the controller output is yaw rate and second when controller output is reference heading. In the first case, low level controller is yaw rate while in the second it is heading controller. The identification by use of self-oscillations (IS-O) has been applied to identify the steering equation (for the case of the first controller) and it was used to identify the heading closed loop (for the case of the second controller). The second controller has been tested on different inner loop structures in order to prove the functionality of the method. The IS-O method has been chosen because of its simplicity and applicability in the field (effects of external disturbances are minimized). The methodology was applied to autonomous catamaran Charlie. The results are presented in the paper and demonstrate that the proposed method for identification as well as the developed algorithms give satisfactory performance. All algorithms and results presented here are a result of a joint work of researchers at the Consiglio Nazionale delle Ricerche, Genova and the University of Zagreb.

AUV identification by use of self-oscillations

Abstract Given the fact that AUV dynamics change depending on the payload, finding a mathematical model in a rather small period of time is quite important. Classical openloop identification methods give accurate parameter identification, but are also time consuming. In the paper we present an identification method based on induced self-oscillations, which has proved to be applicable to underwater vehicles. In addition to that, an error analysis for the proposed method is presented. Experimental results obtained on an underwater vehicle are given and compared to the results obtained using open-loop identification algorithms.

Autotuning Autopilots for Micro-ROVs

Underwater vehicles are highly nonlinear and complex systems, that makes designing autopilots extremely difficult. This paper presents autotuning as a method for tuning parameters of a micro-ROV autopilot. The main benefit of this procedure is that the model of the process does not have to be known. Autotuning is often used for industrial processes but not on marine vessels. This procedure, which is performed in closed-loop, is completely automated and enables the operator to retune an autopilot whenever ROV performance is degraded (due to different operating points, tether influence, currents, etc.). In this article we use already known different autotuning recommendations (primarily designed for type 0 processes) with some modifications which we recommend for micro-ROVs. We also give results of using different types of PID controllers, whose parameters are being tuned. A real life demonstration on a VideoRay Pro II micro-ROV is provided

Guidance and control of an overactuated autonomous surface platform for diver tracking

The high-risk nature of SCUBA diving activities is usually dealt with by pairing up divers and adopting well defined rules for diving operations to reduce the chance of accidents. However, during more challenging dives (such as technical dives) these procedures may not be sufficient to ensure almost accident-free operations, for the divers must manoeuvre in complex 3D environments, carry cumbersome equipment, and focus attention on operational details. Technological advancement and research related to diver safety, navigation and monitoring has been identified as crucial for advancing diving activities. This paper reports current state of research performed at UNIZG-FER related to an autonomous overactuated surface platform used for following divers and transmitting GPS signal to the underwater. The implemented guidance and control algorithms are described and simulations obtained on realistic models developed in the ROS environment are provided. Special attention is given to algorithms for diver tracking by using measurements from a USBL. Diver motion estimators are used to improve the performance of the sparse and noisy USBL measurements. The results presented in this paper are a starting point for in-the-field experiments expected to take place in the real-world environment.

ROV AUTONOMIZATION - YAW IDENTIFICATION AND AUTOMARINE MODULE ARCHITECTURE

The Automarine Module is a simple cost effective method for transforming underwater remotely operated vehicles (ROVs) into autonomous underwater vehicles (AUVs), with minimum development time, and with no ROV circuit alteration. This paper presents architecture of autonomization of the VideoRay Pro II ROV together with its technical specifications. The paper also presents a procedure for open-loop identification of the nonlinear yaw model. Analytical expressions that are used for model identification are also provided.

Identification of Coupled Mathematical Models for Underwater Vehicles

The paper presents the procedure for identification of coupled mathematical models for underwater vehicles. The procedure is performed with the use of a simple laboratory apparatus that consists of a Webcam placed above the experimental pool. The video recording of the underwater vehicle in motion is then analyzed in order to obtain relative speeds within the camera frame. The experiment uses a simple maneuver which excites the vehicle in all controllable directions (in the horizontal plane). The results have shown that even though the system under observation is nonholonomic, the sway motion occurs due to coupling. This allows for determination of dynamic model in uncontrollable directions. The experimental data also show which terms in a general dynamic model can be omitted when dealing with micro underwater vehicles, in order to preserve the simplicity.

Navigation, guidance and control of an overactuated marine surface vehicle

Abstract This article presents navigation, guidance and control (NGC) experimental results obtained on an innovative overactuated unmanned surface marine vessel (USV) capable of omnidirectional motion. The results were obtained during sea trials in real environmental conditions where external disturbances and sensor characteristics have significant influence on the vehicle behavior. While performing the NGC experiments, the following set of behaviors is demonstrated: (1) successful heading control even in cases when the USV is performing simultaneous omnidirectional motion; (2) dynamic positioning algorithm performance with the navigation filter that uses only GPS measurement and a simple uncoupled dynamic model of an overactuated USV; (3) two line following algorithms (one using full actuation capabilities, and the other emulating underactuated line following) and comparing them by using quality metrics; and (4) online modification of mission parameters within the mission control architecture that is based on three layers (primitives, high-level and low-level control). Finally, we use results from multiple days of experiments to show how GPS update frequency influences (i) the quality of DP performance and (ii) the quality of the commanded control signal.

Tracking Divers: An Autonomous Marine Surface Vehicle to Increase Diver Safety

Diving is a high-risk activity due to the hazardous environment, dependence on technical equipment for life support, complexity of underwater navigation, and limited monitoring from the surface. This article describes a new concept of using an autonomous surface vehicle (ASV) as a private satellite that tracks divers, thus significantly increasing diving safety. Since the vehicle is above the diver at all times, acoustic communication with the diver interface in the form of an underwater tablet is more efficient and robust, which enhances diver navigation and enables reliable monitoring from the surface. This article focuses on a diver-tracking control structure that uses a diver motion estimator to determine diver position, even in cases when acoustic position measurements are not available.

Transfer function identification by using self-oscillations

The work presented in this paper deals with the process of transfer function identification by using self-oscillation method (autotuning identification method). The algorithm is given in a general matrix form and some modifications are introduced. The modifications of the algorithm include augmentation of the initial algorithm for Type k systems, systems with delays and discrete-time systems. The paper also includes simulation examples which describe the introduced modifications. Apart from being rather simple, this method is applicable to real systems. Its greatest advantage is quick identification of a transfer function (depends on the system).