Zoran Vukić

Adaptive fuzzy ship autopilot for track-keeping

An adaptive fuzzy gain autopilot for ship track-keeping is developed. This autopilot is composed of Sugeno fuzzy type autopilot in an ordinary feedback loop and adjustable scaling factors mechanism in an additional feedback loop. The adjustment mechanism represents a fuzzy controller that changes scaling factors of the base fuzzy autopilot. The control system for the track-keeping is completely described. For the track-keeping problem, the maneuver of way-point turning and ship guiding through a complex path (trajectory) are presented. The influence of sea current and wave disturbances on track-keeping performance was also considered. Simulation results obtained by the Sugeno fuzzy type autopilot are first presented. Then, those results are compared with ones obtained by an adaptive fuzzy autopilot.

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.

Speed and active power control of hydro turbine unit

In the paper, the procedure is given for designing speed and active power controller of hydro turbine units. The procedure is based on mathematical models of the controlled system. The controller parameters are obtained from closed-loop poles and hydro turbine parameters by derived analytical formulas over a wide range of the hydro turbine operating points. The described procedure allows the fast and direct determination of the controller parameters. There is no need for heuristic controller parameters tuning. Results from two hydro turbine units with the controllers designed using the described procedure are given as an illustration.

Methodology of Concept Control Synthesis to Avoid Unmoving and Moving Obstacles (II)

Dynamic path generation problem of robot in environment with other unmoving and moving objects is considered. Generally, the problem is known in literature as find path or robot motion planning. In this paper we apply the behavioral cloning approach to design the robot controller. In behavioral cloning, the system learns from control traces of a human operator. The task for the given problem is to find a controller not only in the form of the explicit mathematical expression. So RBF neural network is used also. The goal is to apply controller for the mobile robot motion planning in situation with infinite number of obstacles. The advantage of this approach lies in the fact that a complete path can be defined off-line, without using sophisticated symbolical models of obstacles.

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.

Underwater Vehicle Localization with Complementary Filter: Performance Analysis in the Shallow Water Environment

Rapid development of underwater technology during the last two decades yielded more affordable sensors and underwater vehicles, and, as a result, expanded their use from exclusively offshore industry towards smaller interdisciplinary research groups. Regardless of application, knowing the location of the vehicle operating underwater is crucial. Relatively inexpensive solution is sensor fusion based on a dynamic model of the vehicle aided by a Doppler Velocity Log and a Ultra-Short Base Line position system. Raw data from the sensors are highly asynchronous and susceptible to outliers, especially in shallow water environment. This paper presents detailed sensor analysis based on experimental data gathered in shallow waters, identifies outliers, presents an intuitive and simple sensor fusion algorithm and finally, discusses outlier rejection. The approach has been experimentally verified on medium size remotely operated vehicle.

Improved Fuzzy Autopilot for Track-Keeping

Abstract Improved 2-input fuzzy autopilot for ship course control and 3-input fuzzy autopilot for track-keeping are proposed. Nonlinear model of a ship and a steering subsystem is used. The 3-input fuzzy autopilot uses heading signal, yaw rate signal and lateral offset from the nominal track to produce a command rudder angle. Input variable fuzzyfication, fuzzy associative memory rules and output set defuzzyfication are described. Obtaining of FAM rules for 3-input fuzzy is described. Dynamical behavior of 2 and 3-input fuzzy autopilot is compared. The influence of wave disturbance, sea current and external disturbance from a passing ship on track-keeping performance was analyzed.

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.