Showing papers presented at "Mediterranean Conference on Control and Automation in 2011"

A Survey on applications of Pneumatic Artificial Muscles

Abstract: The aim of this article is to present a survey on applications of Pneumatic Artificial Muscles (PAMs). PAMs are highly non-linear pneumatic actuators where their elongation is proportional to the interval pressure. During the last decade, there has been a significant increase in the industrial and scientific utilization of PAMs due to their advantages such as high strength and small weight, while various types of PAMs with different technical characteristics have been appeared in the relative scientific literature. This article will summarize the key enabling applications in PAMs that are focusing in the following areas: a) Biorobotic, b) Medical, c) Industrial, and d) Aerospace applications.

Event-based output-feedback control

Abstract: Event-based control aims at reducing the information exchange over the communication network in control systems. This paper extends an event-based state-feedback approach published recently towards event-based output feedback. The measurable output is affected by measurement noise. The analysis shows that by incorporating a state observer in the event generator, a stable behavior of the event-based control loop can be guaranteed. Moreover, it will be shown that the maximum communication frequency within the control loop is bounded.

Design and control of a lightweight magnetic climbing robot for vessel inspection

Abstract: The inspection of marine vessels is currently performed manually Inspectors use sensors (eg cameras, devices for non-destructive testing) to detect damaged areas, cracks, and corrosion in large cargo holds, tanks, and other parts of a ship Due to the size and complex geometry of most ships, ship inspection is time-consuming and expensive The EU-funded project MINOAS develops concepts for a Marine Inspection Robotic Assistant System to improve and to automate ship inspections As one example of a physical system implementation, we introduce our magnetic wall-climbing robot This remotely operated lightweight system is able to climb a vessels steel frame and is able to deliver visual inspection data on-line For any type of surveying process, the raw and meta data are mandatory in order to compare inspection data over time In this paper, we describe our approach of how the magnetic climbing robot is localized and controlled Additionally, we describe the design of the robot as well as the localization device which is able to provide a real-time 3D pose of the inspection robot

Model predictive quadrotor indoor position control

Abstract: This article addresses the control problem of quadrotors in environments where absolute-localization data (GPS, positioning from external cameras) is inadequate. Based on an attached IMU and an optical flow sensor the quadrotor's translational velocity is estimated using an Extended Kalman Filter. Subject to the velocity measurements, the roll, pitch and yaw (RPY) angles, the angular rates and the translational accelerations a switching Model Predictive Controller is designed. The quadrotor dynamics is linearized at various operating points according to the angular rates and the RP-angles. The switching is inferred according to the various linearized models of the quadrotor. The controller is applied on a quadrotor prototype in low-altitude position hold maneuvers at very constrained environments. The experimental results indicate the overall system's efficiency in position/altitude set-point maneuvers.

An event driven Smart Home Controller enabling cost effective use of electric energy and automated Demand Side Management

Abstract: This paper proposes the design of a Smart Home Controller strategy providing efficient management of electric energy in a domestic environment. The problem is formalized as a binary linear programming problem, the output of which specifies the best time to run of Smart Household Appliances, under a Virtual Power Threshold constraint, taking into account the real power threshold and the forecast of consumption from not plannable loads. This problem formulation allows to analyze relevant scenarios from consumer and energy retailer point of view: here optimization of economic saving in case of multi-tariff contract and Demand Side Management have been discussed and simulated. Simulations have been performed on relevant test cases, based on real load profiles provided by the smart appliance manifacturer Electrolux S.p.A. and on energy tariffs suggested by the energy retailer Edison. Results provide a proof of concept about the consumers benefits coming from the use of local energy management systems and the relevance of automated Demand Side Management for the general target of efficient and cost effective operation of electric networks.

Parameters estimation of a noisy sinusoidal signal with time-varying amplitude

Abstract: In this paper, we give estimators of the frequency, amplitude and phase of a noisy sinusoidal signal with time-varying amplitude by using the algebraic parametric techniques introduced by Fliess and Sira-Ramirez. We apply a similar strategy to estimate these parameters by using modulating functions method. The convergence of the noise error part due to a large class of noises is studied to show the robustness and the stability of these methods. We also show that the estimators obtained by modulating functions method are robust to “large” sampling period and to non zero-mean noises.

Observer design for two-wheeled vehicle: A Takagi-Sugeno approach with unmeasurable premise variables

Abstract: This paper is dedicated to the problem of observer design for Takagi-Sugeno (T-S) nonlinear systems with unmeasurable premise variables (TSUPV) and application to autonomous bicycle system. The main idea is based on the use of differential mean value theorem combined to the sector nonlinearity transformation. The objective of this approach is to make the state estimation error dynamic on a T-S form which allows to apply the classical Lyapunov analysis to derive convergence conditions. The design algorithm is proposed in terms of linear matrix inequalities (LMI). To illustrate the proposed methodology, a nonlinear bicycle model is considered.

On the use of delay timers and latches for efficient alarm design

Abstract: Alarm systems are an important complement to good control systems design. However alarm systems have not received the attention that they deserve and as a result they do not necessarily operate in the most reliable and efficient manner. Delay timers and latches are often used in the process industry to reduce alarm chatter and to minimize nuisance alarms. Effect of varying the size of on-delay, off-delay timers and latches on the accuracy of detection is discussed from a theoretical view point by modeling them using Markov chains. The performance of delay timers is compared to that of the latches. A design procedure for selecting the length of on-delay and off-delay timers based on historical alarm event data and the corresponding 'Return To Normal' (RTN) information is introduced and illustrated using a real industrial case study.

Interdependency modeling and analysis of critical infrastructures based on Dynamic Bayesian Networks

Abstract: This paper presents a novel approach to the critical infrastructure (CI) interdependencies analysis, based on the Dynamic Bayesian Network (DBN) formalism. Our original modeling procedure divides the DBN in three levels: an atomic events level, which models the adverse events impacting on the analyzed CIs, a propagation level, which captures CI interdependencies, and a services level, which allows to monitor the state of provided services. Three types of analyses can be performed: a reliability study, an adverse events propagation study, and a failure identification analysis. A case study provided by Israel Electric Corporation is considered, and explicative simulations are presented and discussed in detail.

Design and experimental evaluation of an innovative SMA-based tendon-driven redundant endoscopic robotic surgical tool

Abstract: The development and experimental evaluation of a prototype endoscopic robotic surgical tool is presented in this article. Smart memory alloys (SMA) are used as wires in a tendon-driven actuation mechanism. The 2N-DOF redundant manipulator is a cascade configuration of N-universal joint modules. The kinematics of the tool is analyzed and simple yet effective controllers relying on a constrained non-linear optimization problem are offered. The surgical tool's shape can be deformed according to a predefined profile leading to more versatile configurations than the existing designs. The efficiency of the overall system is investigated in experimental studies where its performance is evaluated by a customized 3D-video system.

Morse theory and formation control

Abstract: Formation shape control for a collection of point agents is concerned with devising decentralized control laws which will ensure that the formation will move so that certain inter-agent distances assume prescribed values. A number of algorithms based on steepest descent of an error function have been suggested for various problems, and all display the existence of incorrect equilibria, though often the equilibria are saddle points or unstable. This paper introduces Morse theory as a tool for analyzing the number of such equilibria. A key conclusion is that for two-dimensional rigid formations of point agents, there will always be incorrect equilibria associated with any steepest descent law.

Compensation of time-varying input delay for nonlinear systems

Abstract: We consider general nonlinear systems with time-varying input delay for which we design a predictor-based feedback controller. Under the assumptions of forward completeness of the open-loop system and the existence of a (possibly time-varying) stabilizing controller, in the absence of the input delay, our controller achieves global asymptotic stability in the presence of a time-varying input delay. We prove asymptotic stability based on a backstepping transformation which enables us to construct a Lyapunov functional. Our design is illustrated by a numerical example of a second order system.

Fault detection and isolation using Kalman filter bank for a wind turbine generator

Abstract: In this paper, we will tackle the problem of current sensor Fault Detection and Isolation (FDI) of a doubly feed induction generator in wind turbine. First of all, the use of a Kalman filter to detect sensor fault will be illustrated. Then, the detection and the isolation of multiple and simultaneous sensor faults will be treated using a Kalman filter bank in a Generalized Observer Scheme and a Dedicated Observer Scheme respectively. The fault assessment will be performed by the Page-Hinkley's test. The processus of the FDI will be validated on a real-time test bench.

Coverage-oriented coordination of mobile heterogeneous networks

Abstract: The article examines the distributed optimization problem in mobile heterogeneous sensor networks. Most coordination algorithms are designed based on geometric characteristics of the corresponding Voronoi cells of the nodes. However, these works consider networks where the sensing patterns of the nodes are identical. This article considers coordination of heterogeneous networks, where the sensing radii of the nodes differ, while the proposed deployment algorithm for area-coverage optimization is based on a modified Voronoi-like space partitioning scheme. The proposed control scheme is developed in a distributed manner, while the advantages of the proposed technique are validated via simulation studies.

Review on single track vehicle and motorcycle simulators

Abstract: In this paper, we present a review of the existent two-wheeled vehicle simulators. A description of a motorcycle simulator, designed at INRETS-IBISC laboratory is given. Mechatronics aspects and the various consideration to built such a simulation tool will be discussed.

A necessary condition for disturbance decoupling with quadratic stability in switched linear systems

Abstract: This paper deals with the problem of decoupling by feedback a disturbance input from the output of a switched linear system, while achieving, by a suitable choice of the switching rule, quadratic stability. Using geometric methods, a structural obstruction to the solvability of the problem is found and a necessary condition is stated.

Optimal control of variable speed wind turbines

Abstract: This paper proposes a MIMO linear quadratic regulator (LQR) controller designed for a horizontal variable speed wind turbine with focus on the operating range referring to the above rated wind speeds. The operating conditions of wind turbines make them subject to fluctuating loads that create fatigue and lead to damage. Alleviating these loads would reduce the needed materials, and increase the lifespan and the quality of the produced energy. The optimality of the entire system is defined in relation with the trade-off between the wind energy conversion maximization and the minimization of the fatigue in the mechanical structure. The solution of a control using an LQR regulator is presented. The performances of the optimal control are assessed and discussed by means of a set of simulations.

Anthropomimetic robot with passive compliance - Contact dynamics and control

Abstract: This paper develops a dynamic model and designs a controller for a fully anthropomorphic, compliantly driven robot. To imitate muscles, the robot's joints are actuated by DC motors antagonistically coupled through tendons. To facilitate safe interaction with humans, the robot exploits passive mechanical compliance, in the form of elastic springs in the tendons. To enable simulation, the paper first derives a mathematical model of the robot's dynamics, starting from the “Flier” approach. The control of the antagonistic drives uses a biologically inspired puller-and-follower concept where at any instant the puller is responsible for the joint motion while the follower keeps the inactive tendon from slackening. In designing the controller, it was first necessary to use the advanced theory of nonlinear control for dealing with individual joints, and then to apply robust control theory in order to extend control to the multi-joint robot body.

Optimization and control of a distributed Battery Energy Storage System for wind power smoothing

Abstract: This paper presents a methodology to minimize the capacity of a Battery Energy Storage System (BESS) in a distributed configuration of wind power sources. A new semi-distributed BESS scheme is proposed to improve the suppression of the fluctuations in the wind farm power output. The proposed control system is tested for two dissimilar power profiles of the turbines where the turbines are located far from each other geographically. The scheme is analyzed under a variety of hard system constraints. It was observed that the performance of the proposed semi-distributed BESS scheme is better than that of conventional approaches.

LPV modelling and control of a Twin Rotor MIMO System

Abstract: This paper describes the linear parameter varying (LPV) modelling and control of the Twin Rotor MIMO System (TRMS) developed by Feedback Instruments Limited. The nonlinear model of the TRMS is transformed into a quasi-LPV system and then approximated in a polytopic way. Using the LPV LMI pole placement approach, a LPV observer/controller for the TRMS is designed. The proposed modelling and control approach is demonstrated in simulation to prove its effectiveness and performance.

The Navigation Transformation: Point worlds, time abstractions and towards tuning-free navigation

Abstract: This paper proposes a novel solution to the navigation problem by mapping an obstacle cluttered environment to a trivial domain called the point world, where the navigation task is reduced to connecting the images of the initial and destination configurations by a straight line. Due to this effect the underlying transformation is termed the “Navigation Transformation”. The properties of this transformation are studied in this paper as well as its capability to provide a solution to the path and motion planning problems. A construction for such a transformation is proposed. A feedback controller based on the Navigation Transformation is designed that guarantees almost global exponential stability. It is shown that by utilizing the Navigation Transformation, the time for a motion task can be abstracted by means of an appropriately designed time abstracting controller. In addition to the theoretical guarantees, a set of simulation case studies on a star shaped world are provided to demonstrate the effectiveness of the methodology.

Wireless event-triggered controller for a 3D tower crane lab process

Abstract: This paper studies the design and real-time implementation of an event-triggered controller for a nonlinear 3D tower crane where the communication between the controller and the actuators is performed over a low-power wireless network. A flexible Event-Generation Circuit (EGC) is proposed in order to implement event-driven controllers for Networked Control Systems. Furthermore, a detailed experimental analysis on the performance of the event-triggered controller and the influence of packet losses on the transmitted actuation messages are presented. The results show that the event-triggered controllers in networked control systems are able to maintain the same level of performance as compared to periodic controllers, while increasing the sensors/actuators lifetime by reducing network bandwidth utilization.

Input-output finite-time stability of switching systems with uncertainties on the resetting times

Abstract: The concept of Input-Output Finite Time Stability (IO-FTS) is extended to time-dependent switching linear systems, which are systems with different continuous dynamics and that can exhibit state jumps driven by time. Sufficient conditions are given for the analysis of IO-FTS in the case of certain and uncertain resetting times. The presented results require to solve feasibility problems involving Difference/Differential Linear Matrix Inequalities, which can be solved numerically in an efficient way by using off-the-shelf optimization tools, as illustrated by the proposed example.

Combined control of combustion load and combustion position in a moving grate biomass furnace

Abstract: This work presents a combined combustion load and combustion position control for a moving grate biomass furnace. The control design is based on a linearized reduced order model of the process and comprises model predictive control (MPC) with an additional proportional-integral (PI) feedback loop. An analysis for closed-loop stability as well as simulation results are presented. The results demonstrate the effectiveness of the proposed concept.

Funnel control for speed & position control of electrical drives: A survey

Abstract: In this survey we introduce a simple high-gain based adaptive controller — the funnel controller — which neither identifies nor estimates the system under control. The proportional funnel controller is applicable for all (nonlinear) systems with relative degree one or two, stable zero-dynamics (e.g. minimum-phase in the linear case) and known sign of the high-frequency gain; hence only structural knowledge is required for controller implementation. The control performance is inherently robust to parameter uncertainties or variations not affecting the system structure. Furthermore, the funnel controller is capable of reference tracking of time-varying command signals with prescribed transient accuracy: the control error is forced to evolve within a prescribed “funnel”. Its boundary can be fixed by e.g. a decreasing function of time giving an upper bound on the error transient behavior. Finally, we apply the funnel controller for speed and position control of an (unknown) electrical drive with friction and load disturbances. Measurement results are presented and compared with classical PI/PID control. funnel control, non-identifier (high-gain) based adaptive control, prescribed tracking, prescribed accuracy, robustness.

Output control for time-delay nonlinear system providing exponential stability

Abstract: This paper deals with the output stabilization of time-delay systems with sector-bounded nonlinearity. In this paper we will consider the problem of absolute stability for a class of time-delay systems which can be represented as a feedback connection of a linear dynamical system with unknown parameters and a uncertain nonlinearity satisfying a sector constraint. For a class of output control algorithms a controller providing output exponential stability of equilibrium position is proposed.

Passivity indices for symmetrically interconnected distributed systems

Abstract: In this paper, the passivity indices for both linear and nonlinear multi-agent systems with feedforward and feedback interconnections are derived. For linear systems, the passivity indices are explicitly characterized, while the passivity indices in the nonlinear case are characterized by a set of matrix inequalities. We also focus on symmetric interconnections and specialize the passivity indices results to this case. An illustrative example is also given.

A three term controller for ride comfort improvement

Abstract: For a quarter car model, a PID controller that provides ride comfort is developed. The PID controller parameters are derived using a metaheuristic algorithm. The performance of the proposed control scheme and its robustness with respect to uncertainties of the model parameters are examined through computational experiments. The proposed control scheme has satisfactory performance and feeds back only one measurable variable thus providing a simple and cheap solution.

On consensus with a general discrete time convex combination based algorithm for multi-agent systems

Abstract: A general convex combination based model in discrete time for the evolution of multi-agent systems is considered. Sufficient conditions under which an individual limit for each agent's state exists are subsequently derived. Moreover, it is shown that under stronger conditions, those individual limits are equal, i.e., consensus occurs. The relationship of these results to those of other well known consensus models is explained.

Mainstream Traffic Flow Control of merging motorways using Variable Speed Limits

Abstract: Mainstream Traffic Flow Control (MTFC), enabled via Variable Speed Limits (VSL), is a novel proposed motorway traffic management tool. An existing simple local cascade feedback MTFC controller for a single motorway is extended in this paper for application to two merging motorways. A split-range-like scheme is derived that employs VSL at both motorways simultaneously, so as to balance the experienced delay in both of them while keeping capacity-flow conditions in the merge area. The new MTFC controller remains simple yet efficient and suitable for ready field implementation. The controller is evaluated in simulation and compared to the optimal control results. The controller's performance is shown to meet the specifications of delay balancing and to approach the optimal control results for a number of investigated scenarios.