This study deals with dynamic modeling and tracking control of a remotely underwater vehicle (ROV) with six degrees of freedom (DOF). The sliding mode scheme for tracking control of an ROV is a powerful approach to compensate structured and unstructured uncertainties. In this study, performance of sliding mode approach modified by robust adaptive fuzzy control algorithm for an ROV is presented. Fuzzy algorithm is used for on-line estimation of external disturbances as well as unknown nonlinear terms of dynamic model of the ROV. A robust control rule is employed to compensate for estimation errors. The boundedness and asymptotic convergence properties of the control algorithm and its semi-global stability are analytically proven using Lyapunov stability theory and Barbalat's lemma. Moreover, adaptation laws and robust control terms are derived from Lyapunov stability synthises. The adopted control scheme is implemented in numerical simulations, based on the dynamic parameters of Shiraz University Remotely Operated Vehicle (Ariana I ROV). Simulations show the effectiveness of the adopted controller for trajectory tracking.I.
This is report of design, construction and control of “Ariana-I”, an Underwater Remotely Operated Vehicle (ROV), built in Shiraz University Robotic Lab. This ROV is equipped with roll, pitch, heading, and depth sensors which provide sufficient feedback signals to give the system six degrees-of-freedom actuation. Although its center of gravity and center of buoyancy are positioned in such a way that Ariana-I ROV is self-stabilized, but the combinations of sensors and speed controlled drivers provide more stability of the system without the operator involvement. Video vision is provided for the system with Ethernet link to the operation unit. Control commands and sensor feedbacks are transferred on RS485 bus; video signal, water leakage alarm, and battery charging wires are provided on the same multi-core cable. While simple PI controllers would improve the pitch and roll stability of the system, various control schemes can be applied for heading to track different paths. The net weight of ROV out of water is about 130kg with frame dimensions of 130×100×65cm. Ariana-I ROV is designed such that it is possible to be equipped with different tools such as mechanical arms, thanks to microprocessor based control system provided with two directional high speed communication cables for on line vision and operation unit.
This paper introduces an improved version of a sliding-mode slip controller for pneumatic brake system of heavy good vehicles, HGVs. Anti-lock braking function, ABS, has become mandatory for HGVs all over the world to minimize the risk of accidents. The aim of ABS brake function is to reduce the braking distance and maintain maneuverability during steering and braking actuation. Traditional HGV ABS uses a "bang-bang" actuation control approach when it applies and releases the brake pressure to make the ABS periodic actuation. It is a heuristic way of preventing wheel lock using only wheel speed measurement. In order to enhance the ABS performance wheel-slip controller approaches have been represented to maximize the vehicle deceleration by controlling the slip close to the maximum force of the tyre-road interaction. Dynamics in existing pneumatic actuators limited the performance of wheel-slip controllers. It has been shown that the Fast Actuating Brake pneumatic Valve, FABV, can reduce the order of actuator dynamics up to 10 times compared to conventional actuators. This makes it possible to adopt advance control approaches for wheel-slip controllers which provide features such as fast dynamic response, stability and robustness. Sliding-mode control is well-known to be a powerful approach for tracking problems while being robust with respect to unknown perturbations and guarantees the convergence to desired reference in a finite time. The sliding-mode controls robustness and quick convergence properties together with fast and accurate torque actuation of FABV, provide the possibility of an improved ABS functionality for HGVs. Recently, sliding-mode controller was developed for wheel-slip control utilizing the FABV hardware. The results are very promising and shows great potential. In tests it was realized that the controller's performance depends on the vehicle speed. For low vehicle speeds, the sliding-mode wheel slip controller shows slow convergence and a high frequency chattering before standstill. Hence, it was suggested to use different gains during the brake operation to cope with the changes of the dynamics of the system. With the improved sliding-mode controller presented in this paper, the problem has been addressed and convergence to sliding surface is not speed independent. The asymptotic convergence properties of the control algorithm are proven using Lyapunov stability theory and the robustness of the method is studied. Simulation results of the slip control software in the loop (SIL) environment consisting of a quarter and half car models, FABV plant model, force observer and a pressure controller show improvement of the previous wheel-slip controller.
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