Showing papers presented at "Mediterranean Conference on Control and Automation in 2002"

Experimental comparison of different friction models for accurate low-velocity tracking

Abstract: Low velocity friction causes positioning and contouring errors such as the quadrant glitch in machine tool table systems. Numerous comprehensive friction models are described in literature. A comparison of these models with respect to feedforward friction compensation is not yet available: only comparisons with the Coulomb friction model are available. This paper compares four friction models, one static model and three comprehensive dynamic models, with respect to their friction compensation ability.

Static output feedback for takagi-sugeno systems: an lmi approach

Abstract: This paper studies the design of a static output feedback controller for nonlinear systems described by continuous-time Takagi-Sugeno (T-S) models Motivated by stability results developed for parallel distributed compensation (PDC) controller, an Output PDC (OPDC) controller that corresponds to a nonlinear static output feedback control law is proposed Both stabilisation and poles placement are addressed An example is given to illustrate the approach

Obstacle avoidance in local navigation

Abstract: A reactive navigation system for an autonomous non-holonomic mobile robot in dynamic environments is presented. A new object detection algorithm and a new reactive collision avoidance method are presented. The sensory perception is based in a laser range finder (LRF) system. Simulation results are presented to verify the effectiveness of the proposed local navigational system in unknown environments with multiple moving objects.

Optimal Pursuit under Partial Information

Abstract: In this paper we address the control of a group of agents in the pursuit of one or several evaders that are moving in a non-accurately mapped terrain. We use the framework of partial information controlled Markov processes to describe this type of games. This allows us to combine map building and pursuit into a single stochastic optimization problem, where the cost function to minimize is the time to capture. We show that an optimal policy exists and suggest a value iteration algorithm to compute it. Since in general this algorithm is computationally very intensive, we also consider a “greedy” solution that scales well with the dimension of the problem. Under this policy, at each time step the pursuers move towards the locations that maximize the probability of finding an evader at the next time. We determine conditions under which this is actually optimal.

Visual-based planning and control for nonholonomic mobile robots

Abstract: An integrated visual-based approach to motion planning and control of a nonholonomic wheeled mobile robot is presented. Vision is used to localize the obstacles and the robot and for real-time feedback control of the vehicle motion. An A ∗ based motion planner is used to search the discretized robot configuration space for collisionfree paths. Nonholonomic constraints are taken into account by properly defining cell adjacency in the discretized configuration space and in the choice of the heuristic functions. Path planning results for unicycle and car-like kinematics are presented and compared in simulated environments. The whole system is tested with the mobile robot SuperMARIO in an unknown indoor environment. In the experiments, tracking of the planned trajectories is achieved via visual feedback from a fixed camera and using a dynamic linearizing control law.

Design of Fuzzy Regulator for Power System Secondary Load Frequency Control

Abstract: The stability analysis of nonlinear system that is harmonically linearised is given[10, 3, 11]. With the introduction of fuzzy regulator the nonlinear system consists of linear part and two nonlinear parts. The stability analysis is conducted by use of describing function method and Hurwitz stability criterion. Proportional and derivative parameters of Mamdani type fuzzy regulator gains were preliminary tuned (pre-tuned) by Cohen-Coon and Ziegler-Nichols methods [1, 13]. Stability analysis was conducted for the power system secondary load-frequency control model. The proposed stability analysis presents a good starting point for the design of fuzzy regulator for nonlinear systems.

Modelling and simulation of power electronic systems using a bond graph formalism

Abstract: This paper deals with the modelling of power electronic systems using the bond graph formalism. The switching components are modelled using an ideal representation so that a constant topology system is obtained. The purpose of the present contribution is to discuss a technique that combines bond graph energy-flow modelling and signal-flow modelling schemes for simulation and prototyping of signal processing algorithms in power electronics systems. In this paper, we will discuss models of the use of fully-controlled, semicontrolled and non-controlled switches in the field of power static converters. By concept, a simulation environment can be examined at different abstraction or hierarchy levels. The approach in this paper is, accordingly, the formulation of a simulation task at different levels: component level, topology level, functional description and implementation description. The paper concludes with two practical examples of simulation of power electronics systems.

Think continuous, act discrete: des techniques for continuous systems

Abstract: This contribution addresses the synthesis of discrete supervisors for continuous plants, with a particular emphasis on modular and decentralised control architecture. We follow a well known style of reasoning that has been originally developed in the context of DESs and demonstrate its applicability to the design of hybrid systems.

Fuzzy controller for elimination of the nonlinear resonance phenomenon

Abstract: The paper deals with the ca pability of the fuzzy controller to eliminate the frequency resonance jump o f the nonlinear system. The simulation method is used for the a nalysis purposes. The nonlinear system operates in the forced o scillation mode, and the fuzzy regulator of the Mamdani type is used for elimination of the resonance jump. The proposed method of r esonance jump elimination proved to be reliable and useful.

Design of the ISePorto robocup Middle-Size League Robotic Soccer Team: Control, Localisation and Coordination

Abstract: This paper describes the design and implementation status of the ISePorto robotic football team for participation in Robocup Middle Size League (F2000). The objectives guiding the project were the applications and research in hybrid control and coordination systems. The system has also an educational support role. A special attention is made to the custom design to allow the execution of complex manoeuvres and team coordinated behaviours. The robot has different pass, shot, and manoeuvre capabilities providing high level tactical and strategic planing and coordination. The current team status is also covered.

Ultrasonic and video data fusion for mobile robot navigation

Abstract: A multisensor fusion approach for improving the map-building capability of a mobile robot is presented in this paper. Ultrasonic and video data are used. A modelling technique for indoor environments based on line features extraction from video data and from range data is proposed. The Hough transform is considered for extracting lines from the occupancy grid and from video images.

Distributed parameter modeling of a fixed-bed biofilter with experimental validation

Abstract: This paper is concerned with a pilot-scale fixed-bed biofilter used for nitrogen removal from m unicipal wastewater. Process dynamics is described by a set of mass balance partial differential equations, which allow the evolution of the several component concentrations along the biofilter axis to be reproduced. Based on sets of experimental data collected over a period of several months, alternative model formulations, corresponding to different macroscopic reaction schemes and kinetics, are c onsidered. Based on logarithmic transformations of the output signals and parameters, unknown model parameters are estimated b y minimizing an ou tput error criterion. The good model agreement demonstrates the validity of the modeling assumptions. Particularly, very long transient phases observed after changes in the feed flow rate ca n b e e xplained through the