Evaluation of error bound for a DT sliding mode control with disturbance observer

In this paper an estimate of the upper bound of control error for discrete-time implementation of a Sliding Mode Control (DTSMC) combined with disturbance observer is investigated. Having in mind application to PZT high bandwidth actuators and since high accuracy is required the special attention is paid to avoid chattering. Selected structure of proposed SMC controller is proven to offer chattering-free motion. The proposed structure also avoids deadbeat poles that are the cause of large control action which is not desirable in practical applications. The proposed scheme is shown to allow a maximum error bound of O(T) for the system with disturbance. The main disturbances are represented by hysteresis and the time variation of the piezo stack parameters. The evaluation of the upper bound of error in such a system is shown and experimentally verified. Closed-loop experiments are presented using the proposed method to verify the theoretical results

Sliding mode control based piezoelectric actuator control

In this paper a method for piezoelectric stack actuator control is proposed. In addition a brief discussion about the usage of the same methods for estimation of external force acting to the actuator in contact with environment is made. The method uses sliding mode framework to design both the observer and the controller based on an electromechanical lumped model of the piezoelectric actuator. Furthermore, using a nonlinear differential equation the internal hysteresis disturbance is removed from the total disturbance in an attempt to estimate the external force acting on the actuator. It is then possible to use this external force estimate as a means of force control of the actuator. Simulation and experiments are compared for validating the disturbance and external force estimation technique. Some experiments that incorporate disturbance compensation in a closed-loop SMC control algorithm are also presented to prove the effectiveness of this method in producing high precision motion

Discrete sliding mode control of piezo actuator in nano-scale range

In this paper Discrete Sliding Mode Control (SMC) of Piezo actuator is demonstrated in order to achieve a very high accuracy in Nano-scale with the desired dynamics. In spite of the fast dynamics of the Piezo actuator the problem of chattering is eliminated with the SMC control structure. The Piezo actuator suffers from hysteresis loop which is the inherent property and it gives rise to the dominant non-linearity in the system. The proposed SMC control structure has been proved to deliver chattering free motion along with the compensation of the non linearity present due to hysteresis in the system. To further enhance the accuracy of the closed loop system and to be invariant to changes in the plant parameters a robust disturbance observer is designed on SMC framework by taking into consideration the lumped nominal plant parameters. Experimental results for closed loop position are presented in order to verify the Nano-scale accuracy

A study on high accuracy discrete-time sliding mode control

In this paper a Discrete-Time Sliding-Mode based controller design for high accuracy motion control systems is presented. The controller is designed for a general SISO system with nonlinearity and external disturbance. Closed-Loop behavior of the general system with the proposed control and Lyapunov stability is shown and the error of the closed loop system is proven to be within an o(T2). The proposed controller is applied to a stage driven by a piezo drive that is known to suffer from hysteresis nonlinearity in the control gain. Proposed SMC controller is proven to offer chattering-free motion and rejection of the disturbances represented by hysteresis and the time variation of the piezo drive parameters. As a separate idea to enhance the accuracy of the closed loop system a combination of disturbance rejection method and the SMC controller is explored and its effectiveness is experimentally demonstrated. Closed-loop experiments are presented using PID controller with and without disturbance compensation and Sliding-Mode Controller with and without disturbance compensation for the purpose of comparison

Sliding mode based piezoelectric actuator control

In this paper a control of method for a piezoelectric stack actuator control is proposed. In addition briefly the usage of the same methods for estimation of external force acting to the actuator in contact with environment is discussed. The method uses sliding mode framework to design both the observer and the controller based on an electromechanical lumped model of the piezoelectric actuator. Furthermore, using a nonlinear differential equation the internal hysteresis disturbance is removed from the total disturbance in an attempt to estimate the external force acting on the actuator. It is then possible to use this external force estimate as a means of force control of the actuator. Simulation and experiments are compared for validating the disturbance and external force estimation technique. Some experiments that incorporate disturbance compensation in a closed-loop SMC control algorithm are also presented to prove the effectiveness of this method in producing high precision motion

Sliding-Mode control for high-precision motion control systems

In many of today's mechanical systems, high precision motion has become a necessity. As performance requirements become more stringent, classical industrial controllers such as PID can no longer provide satisfactory results. Although many control approaches have been proposed in the literature, control problems related to plant parameter uncertainties, disturbances and high-order dynamics remain as big challenges for control engineers. Theory of Sliding Mode Control provides a systematic approach to controller design while allowing stability in the presence of parametric uncertainties and external disturbances. In this thesis a brief study of the concepts behind Sliding Mode Control will be shown. Description of Sliding Mode Control in discrete-time systems and the continuous Sliding Mode Control will be shown. The description will be supported with the design and robustness analysis of Sliding Mode Control for discrete-time systems. In this thesis a simplified methodology based on discrete-time Sliding Mode Control will be presented. The main issues that this thesis aims to solve are friction and internal nonlinearities. The thesis can be outlined as follows: -Implementation of discrete-time Sliding Mode Control to systems with nonlinearities and friction. Systems include; piezoelectric actuators that are known to suffer from nonlinear hysteresis behavior and ball-screw drives that suffer from high friction. Finally, the controller will be implemented on a 6-dof Stewart platform which is a system of higher complexity. -It will also be shown that performance can be enhanced with the aid of disturbance compensation based on a nominal plant disturbance observer

An H ∞ almost disturbance decoupling robust controller design for a piezoelectric bimorph actuator with hysteresis

10.1109/87.748143IEEE Transactions on Control Systems Technology72160-174IETT

Design, Modeling, Identification and Control of Mechatronic Systems

Les societats modernes plantegen nous reptes que demanden noves maneres de tractar els projectes d'enginyeria. Els enginyers han d'afrontar aquests reptes i desenvolupar solucions òptimes i eficients pels problemes clàssics i nous. Els diferents avenços produïts en la tecnologia hi poden ajudar, però una nova manera de tractar els problemes enginyerils és també necessària, no considerant únicament les diferent especialitats de l'enginyeria aïlladament. En aquest context, podem parlar de la creació d'una nova filosofia de fer enginyeria: la Mecatrònica. La Mecatrònica s'ha definit com l'aplicació de decisions complexes a l'operació de sistemes físics. La Mecatrònica ha estat també definida com la integració o sinergia de diferents disciplines de l'enginyeria. Aquestes disciplines inclouen l'enginyeria mecànica, l'enginyeria elèctrica, l'enginyeria electrònica, l'enginyeria de control, les comunicacions industrials i l'enginyeria de software. No obstant, la importància del concepte no està únicament en la definició sinó a la filosofia que hi ha al fons. És important de veure, que la Mecatrònica no és només la suma dels resultats de diferents disciplines, sinó la filosofia enginyeril per afrontar els problemes com un de sol, fent servir les eines que subministren les diferents disciplines. La present tesi es divideix en dos parts que tracten problemes de diferent natura. La primera part es titula Regles de disseny i modelat d'actuadors per l'optimització de sistemes mecatrònics i es centra en proporcionar un anàlisis detallat de diferents actuadors utilitzant un procediment general, orientat a millorar el disseny de l'actuador. S'introdueix una nova metodologia per analitzar actuadors lineals electromagnètics i hidràulics modelitzant la seves magnituds mecàniques (força, treball i desplaçament) com a funcions de la geometria i les propietats del material, estudiant l'escalabilitat (en el sentit de produir la mateixa distribució de tensions i deformacions per diferents mides). La motivació de realitzar aquest treball neix de la necessitat d'estructures i sistemes lleugers i de volum reduït, que han de ser integrats en el procediment de disseny el més aviat possible. Per tant, s'estudien les relacions geomètriques, les proporcions i les propietats dels materials que maximitzen les magnituds mecàniques de sortida dels actuadors per un volum i pes limitat, així com l'escabilitat per la seva posterior integració en estructures. Els resultats són validats mitjançant anàlisi dimensional de les expressions obtingudes i comparant els resultats numèrics amb dades d'actuadors industrials. Es considera el comportament estàtic de diferents classes d'actuadors, incloent actuadors hidràulics i electromagnètics lineals. La segona part es titula Identificació i Control d'Actuadors Piezoelèctrics. Els actuadors piezoelèctrics estan demostrant ser una solució fiable per moltes aplicacions, des del microposicionament (màquines eina, dispositius òptics o microscopis moderns) al control actiu d'estructures. La principal motivació de la segona part de la tesis és aprofundir en models per representar el comportament histerètic dels actuadors piezoelèctrics per posteriorment aplicar els models al desenvolupament de controladors pels sistemes histerètics. Es desenvolupa inicialment un estudi general dels actuadors piezoelèctrics per després tractar la seva modelització. Degut a l'elevat comportament no-lineal observat es necessita un model d'histèresis. El model de Bouc-Wen ha estat escollit i s'ha treballat en la identificació dels paràmetres del model i la seva validació. Un cop el sistema ha estat modelat, s'olinebreak ha dissenyat un nou controlador lineal i s'ha implementat en una plataforma experimental utilitzant un DSP (Processador digital de senyal). Encara que les dues parts estan clarament diferenciades, la unitat de la tesis pot ser trobada a les arrels de la Mecatrònica. La tesis tracta la resposta a una sola pregunta: Com podem millorar un sistema mecatrònic? No obstant, la resposta és doble: Dissenyant i modelant actuadors òptims considerant el sistema o estructura complet i controlant el sistema adequadament fent servir els models desenvolupats.Fast changing societies come up with new challenges that require new engineering approaches. Engineers have to face such challenges and provide novel and more efficient solutions to classical and new problems. This can be done by using different relevant advances produced in technology. Furthermore, a new way of addressing the engineering problems has to be applied, not considering only isolated engineering specialties. In this frame, we can talk about the creation of a new engineering philosophy: Mechatronics. Mechatronics has been defined as the application of complex decision making to the operation of physical systems. Mechatronics has been also defined as the integration or synergy of different engineering disciplines. Such disciplines may include Mechanical Engineering, Electrical Engineering, Electronics Engineering, Control Engineering, Industrial Communications and Software Engineering. Nevertheless, the importance of the concept does not lie only in the definition but in the philosophy behind it. It is very important to note that Mechatronics is not only the sum of the results of the different disciplines, but the engineering philosophy to face engineering problems as a whole, employing the tools provided by the different disciplines. The present thesis has been divided in two parts that deal with problems of different nature. The first part is titled Design Rules and Actuator Modeling for the Optimization of Mechatronic Systems and focuses on providing the detailed analysis of different actuators using a general procedure and oriented towards improving the actuator design. It introduces a new methodology to analyze linear electromagnetical and hydraulic actuators by modeling their maximum output mechanical quantities (force, work and stroke) as functions of the geometry and material properties and discusses the scalability (in the sense of producing the same stress and strain distribution for different sizes). The motivation to undertake such a work stems from the need for light and volume reduced structures and systems, which are to be integrated in the design procedure as early as possible. Hence, the geometric relationships, aspect ratios and material properties that maximize the actuator output quantities with a certain limited volume or weight, along with their scalability for the integration in structures are studied. A validation of the results is done by performing dimensional analysis of the expressions obtained and comparing numerical results with industrial actuator data. The static behavior of different classes of actuators is considered. Such actuators include linear hydraulic and electromagnetic actuators. The second part is titled Identification and Control of Piezoelectric Actuators}. Piezoelectric actuators are proving to be a reliable solution for many engineering applications, ranging from micro-positioning (machine tools, optic devices or modern microscopes) to active control of structures. The main motivation of this thesis part is to delve into models to represent the hystereticbehavior of piezoelectric actuators in order to apply them to the conception of controllers for such hysteretic systems. A general study of piezoelectric actuators is performed to later deal with the modeling of such actuators. Due to the high non-linear behavior observed, the problem of identifying and modeling the actuator requires a hysteresis model. The Bouc-Wen model has been chosen and investigations to identify its parameters and to validate the model have been undertaken. Once the system has been identified, a linear controller has been designed and implemented in a real platform, employing a DSP (Digital Signal Processor). Although the two parts are clearly differentiated, the thesis unity can be found in the roots of Mechatronics. The thesis deals with the response to one single question: How can we improve a mechatronic system? However, the answer is twofold: By designing and modeling optimum actuators taking into account the whole system or structure and by controlling the system appropriately using developed models.Postprint (published version