Ubirajara F. Moreno

A dynamic output feedback controller for NCS based on delay estimates

The stabilization of a network controlled system including a global time-varying delay is investigated in this note. This delay is considered to be unknown but it is assumed that a bounded error estimate is available. The exponential uncertainty induced by the time-varying delay is decomposed into the sum of a polytopic term and an uncertain bounded term. Sufficient conditions to design a dynamic output feedback controller depending on an estimate of the time-varying delay are proposed as linear matrix inequalities. An illustration shows how our methodology enlarges the design techniques of the literature.

Absolute stabilization of discrete-time systems with a sector bounded nonlinearity under control saturations

This paper presents some results on absolute stabilization of nonlinear discrete-time systems under control saturations. The studied control law consists of the feedback of both the states and of the nonlinearity present in the dynamics of the controlled system. Saturations are taken into account by modelling the nonlinear saturated system through deadzone nonlinearities satisfying a modified sector condition. Thus, as for continuous-time systems, LMI absolute stabilization conditions are proposed for the design of the feedback gains, both in the local and global stability contexts. Some relations of the proposed results with the dissipativity and passivity theory are included and a numerical example is reported

Trajectory Tracking of a Nonholonomic Mobile Robot with Kinematic Disturbances: A Variable Structure Control Design

In this paper, a trajectory tracking control for a nonholonomic mobile robot subjected to kinematic disturbances is proposed. A variable structure controller based on the sliding mode theory is designed, and applied to compensate these disturbances. To minimize the problems found in practical implementations of the classical variable structure controllers, and eliminate the chattering phenomenon, is used a neural compensator, which is nonlinear and continuous, in lieu of the discontinuous portion of the control signals present in classical forms. This proposed neural compensator is designed by the Gaussian radial basis function neural networks modeling technique and it does not require the time-consuming training process. Stability analysis is guaranteed based on the Lyapunov method. Simulation results are provided to show the effectiveness of the proposed approach.

Friction Compensation in Flexible Joints Robot with GMS Model: Identification, Control and Experimental Results

Abstract In this paper the position control of robot manipulators considering joint flexibilities and friction compensation is presented. For the control purposes a cascade control strategy is presented and the friction compensation is described using the Generalized Maxwell-Slip (GMS) model. The GMS parameters are identified and a friction observer based on this model is proposed and incorporated to the cascade strategy so that the stability and performance can be improved. An experimental setup was constructed to validate the proposed control and friction compensation strategy: a planar two degrees of freedom robot with joint flexibilities prototype. The behavior of the cascade control with GMS model was tested in simulation and it was validated in the experimental setup.

Generation of Trajectories Using Predictive Control for Tracking Consensus with Sensing

Abstract This work presents a cooperation strategy for teams of multiple vehicles to solve the rendezvous problem. The approach is based on consensus algorithms, which are basically characterized by information exchange among the team members. The proposal is based on predictive control, in order to compute decentralized control laws, considering constraints and different response requirements. Our work allows considering together vehicles without and with non-holonomic restrictions while optimizing the sensing range, particularly that of fixed frontal cameras, by managing orientation in the way to the rendezvous point. We show the effectiveness of our strategy with simulation results.

STABILITY AND STABILIZATION OF A CLASS OF UNCERTAIN NONLINEAR DISCRETE-TIME SYSTEMS WITH SATURATING ACTUATORS

Abstract This paper presents some results on stability and stabilization of a class of uncertain nonlinear discrete-time systems under control saturations. The studied control law consists of the feedback of both the states and of the nonlinearity present in the dynamics of the controlled system. Saturations are taken into account by modeling the nonlinear saturated system through a deadzone nonlinearity satisfying a modified sector condition. Thus, as for precisely known systems, LMI stability and stabilization conditions are proposed, which can be cast into convex programming problems. Some relations of the proposed results with the poly-quadratic stability concept are included.

Improving the operational conditions for the sucker-rod pumping system

In this work a new perspective of a sucker-rod pumping system control is presented. The strategy consists in associating the bottom hole pressure measurement and dynamometer cards analysis in a cascaded control. In the proposal, the widely applied control strategies based on dynamometer cards are combined with the strategy based on the measurement of the bottom hole pressure, since the development of low cost downhole sensors turned possible the measurement of downhole variables. The simulation results are analyzed in order to evaluate the operational conditions propitiated by the sucker-rod pumping cascaded control, in a hardware in the loop platform.

Generation of Trajectories Using Predictive Control for Tracking Consensus with Sensing and Connectivity Constraint

This work presents a cooperation strategy for teams of multiple autonomous vehicles to solve the rendezvous problem. The approach is based on consensus algorithms, which are basically characterized by information exchange among the team members. The proposal is based on predictive control in order to compute decentralized control laws, considering constraints and different response requirements according to the application scenario, for example, constraints related to coverage and connectivity of the group. Our work allows considering together vehicles without and with non-holonomic restrictions while optimizing the sensing range, particularly that of fixed frontal cameras, by managing orientation in the way to the rendezvous point. We show the effectiveness of our strategy with simulation results.

Sucker-rod pumping system: Simulator and dynamic level control using bottom hole pressure

In this work a new perspective of the control of a sucker-rod pumping system is presented. In despite of the widely application of control strategies based on dynamometer cards recognition they present several limitations in the control and maintenance aspects. Nowadays, with the development of a new class of low cost downhole sensors, new control strategies could bee applied. In this work, a control framework using the bottom hole pressure combined with a variable speed drive (VSD) structure is proposed. A hardware in the loop simulation platform was developed to evaluate the measure of the bottom hole pressure contribution in a sucker-rod pumping control system.

Kernel-Function-Based Models for Acoustic Localization of Underwater Vehicles

This paper proposes a novel design for the localization system of autonomous underwater vehicles (AUVs) using acoustic signals. The solution presented exploits models based on kernel functions with two main purposes: 1) to reject outliers; and 2) to correct or improve accuracy of measurements. The localization system discussed is based on well-established techniques such as support vector data description (SVDD) and autoassociative kernel regression (AAKR) derived from machine learning theory that utilizes heuristic models for classification and regression tasks, respectively. By coupling the algorithm to the navigation system, we seek to reduce the sensitivity of the localization scheme to the reflected acoustic waves or fluctuations of underwater channel properties without modifying the solution used for data fusion or overloading the algorithm embedded in the vehicle. Data collected in the field with a light underwater vehicle (LAUV) were used to demonstrate the advantages of the proposed approach.