Friction compensation as a fault-tolerant control problem.
ABSTRACT The control of systems that involve friction presents interesting challenges. Recent research has focused on detailed modelling of friction phenomena in order to use robust on-line friction compensation procedures, attempting to cancel out the friction force effect in the feedback control of a mechanical or mechatronic system. However, the friction modelling problem remains a very difficult challenge and this article proposes a new approach to friction compensation which is based on the theory of robust fault estimation. The friction forces acting in a dynamic system can be viewed as actuator faults with time-varying characteristics to be estimated and compensated within an output feedback fault-tolerant control (FTC) scheme, so that the limitations arising from the use of a friction model are obviated. The friction (fault) estimation problem is hence embedded inside a control system with required stability, and performance robustness. This can be a significant advantage over well-known model-based friction compensation methods in which detailed modelling of friction phenomena is essential and for which robustness with respect to friction characteristics is difficult to achieve using non-linear models.
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ABSTRACT: The goal of this paper is to describe a novel fault tolerant tracking control (FTTC) strategy based on robust fault estimation and compensation of simultaneous actuator and sensor faults. Within the framework of fault tolerant control (FTC) the challenge is to develop an FTTC design strategy for nonlinear systems to tolerate simultaneous actuator and sensor faults that have bounded first time derivatives. The main contribution of this paper is the proposal of a new architecture based on a combination of actuator and sensor Takagi-Sugeno (T-S) proportional state estimators augmented with proportional and integral feedback (PPI) fault estimators together with a T-S dynamic output feedback control (TSDOFC) capable of time-varying reference tracking. Within this architecture the design freedom for each of the T-S estimators and the control system are available separately with an important consequence on robust L2 norm fault estimation and robust L2 norm closed-loop tracking performance. The FTTC strategy is illustrated using a nonlinear inverted pendulum example with time-varying tracking of a moving linear position referenceInternational Journal of Control Automation and Systems 12/2013; 11(6):1149-1161. · 0.95 Impact Factor
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ABSTRACT: We propose an estimator for nonlinear systems with unmatched unknown inputs and under measurement noise. The estimator design is based on the combination of observer design for descriptor systems, sliding-modes theory and adaptive control. The estimation of the measurement noise is achieved thanks to the transformation of the original system into a singular form where the measurement noise makes part of the augmented state. Two adaptive parameters are updated online, one to compensate for the unknown bounds on the states, the unknown inputs and the measurement noise and a second one to compensate for the effect of the nonlinearities. To join robust state estimation and unknown-inputs reconstruction, our approach borrows inspiration from sliding-mode theory however, all signals are continuously implemented. We demonstrate that both state and unknown-inputs estimation are achieved up to arbitrarily small tolerance. The utility of our theoretical results is illustrated through simulation case-studies.Systems & Control Letters 12/2012; 61(12):1194–1202. · 1.67 Impact Factor
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ABSTRACT: Starting with the baseline controller design, this paper proposes an integrated approach of active fault tolerant control based on proportional derivative extended state observer (PDESO) for linear parameter varying descriptor systems. The PDESO can simultaneously provide the estimates of the system states, sensor faults, and actuator faults. The L2 robust performance of the closed-loop system to bounded exogenous disturbance and bounded uncertainty is achieved by a two-step design procedure adapted from the traditional observer-based controller design. Furthermore, an LMI pole-placement region and the L2 robustness performance are combined into a multiobjective formulation by suitably combing the appropriate LMI descriptions. A parameter-varying system example is given to illustrate the design procedure and the validity of the proposed integrated design approach. Copyright © 2014 John Wiley & Sons, Ltd.International Journal of Robust and Nonlinear Control 11/2014; · 1.90 Impact Factor