Robust Adaptive Dynamic Surface Control for a Class of Nonlinear Dynamical Systems with Unknown Hysteresis

The output tracking problem for a class of uncertain strict-feedback nonlinear systems with unknown Duhem hysteresis input is investigated. In order to handle the undesirable effects caused by unknown hysteresis, the properties in respect to Duhem model are used to decompose it as a nonlinear smooth term and a nonlinear bounded “disturbance-like” term, which makes it possible to deal with the unknown hysteresis without constructing inverse in the controller design. By combining robust control and dynamic surface control technique, an adaptive controller is proposed in this paper to avoid “the explosion complexity” in the standard backstepping design procedure. The negative effects caused by the unknown hysteresis can be mitigated effectively, and the semiglobal uniform ultimate boundedness of all the signals in the closed-loop system is obtained. The effectiveness of the proposed scheme is validated through a simulation example

Teaching data-driven control: from linear design to adaptive control with throttle valves

Electric throttle valves represent a challenge for control design, as their dynamics involve strong nonlinearities, characterized by an asymmetric hysteresis. Carrying experiments on multiple valves, a large variability in the characteristics of each valve and erratic steady-state behaviors can also be noticed, impairing classical model-based control strategies. Nevertheless, local data-driven linear models can be obtained and simple proportional-integral (PI) controllers, tuned individually for each valve with the appropriate data set, provide good tracking performance. As these controllers cannot be transposed from one valve to another, a robust strategy and an adaptive controller (using identification in closed-loop and controller re-design) may be necessary to propose a general method. This work aims at promoting control education on a simple yet challenging process, going from frequency analysis and linear design to an adaptive control method implemented with an online recursive algorithm.Comment: 12 page

Force Controlled Piezoelectric Fiber Press

The study of the properties of paper in in the micro scale requires the use of devices on the same dimensional order. Paper fiber bonds, the construction unit of paper sheets, can be manufactured, manipulated and tested thanks to a variety of micro actuators. In the manufacturing process of paper fiber bonds, a tool able to press the fibers together is paramount, along with a force control scheme that can guarantee an acceptable performance from the actuator in question. This thesis proposes an open-loop force control technique for a piezoelectric stack actuator, consisting of the compensation of the hysteresis and creep nonlinearities and vibrations. The hysteresis compensation is based on model inversion, resorting to the Prandtl-Ishlinskii method for modeling static hysteresis. Creep compensation, on the other hand, consists of an inverse multiplicative structure, meaning that no model inversion is required and therefore simplifying the process. Last, vibration is dealt with by means of an input shaping technique. The thesis starts with a literature study, followed by the discussion of the method to be implemented and the selection of the required software and hardware for the experiments, as well as the design of a custom-built test platform. The second half of the thesis begins with the characterization of the actuator and tackles the design and implementation of the control. The experimental results show that an open-loop control scheme is possible for force control of a piezoelectric actuator and proves its efficiency and convenience for micromanipulation tasks: hysteresis is reduced to less than 3 %, creep is kept under 1 % and overshoot is decreased to less than 10 % at low inputs and apparently eliminated at higher inputs. Also, the results suggest that this method can easily be extended to other types of actuators and applications, albeit certain additional issues might have to be taken into consideration

Control of an IPMC soft actuator using adaptive full-order recursive terminal sliding mode

The ionic polymer metal composite (IPMC) actuator is a kind of soft actuator that can work for underwater applications. However, IPMC actuator control suffers from high nonlinearity due to the existence of inherent creep and hysteresis phenomena. Furthermore, for underwater applications, they are highly exposed to parametric uncertainties and external disturbances due to the inherent characteristics and working environment. Those factors significantly affect the positioning accuracy and reliability of IPMC actuators. Hence, feedback control techniques are vital in the control of IPMC actuators for suppressing the system uncertainty and external disturbance. In this paper, for the first time an adaptive full-order recursive terminal sliding-mode (AFORTSM) controller is proposed for the IPMC actuator to enhance the positioning accuracy and robustness against parametric uncertainties and external disturbances. The proposed controller incorporates an adaptive algorithm with terminal sliding mode method to release the need for any prerequisite bound of the disturbance. In addition, stability analysis proves that it can guarantee the tracking error to converge to zero in finite time in the presence of uncertainty and disturbance. Experiments are carried out on the IPMC actuator to verify the practical effectiveness of the AFORTSM controller in comparison with a conventional nonsingular terminal sliding mode (NTSM) controller in terms of smaller tracking error and faster disturbance rejection

A shape memory alloy-based biomimetic robotic hand : design, modelling and experimental evaluation

Every year more the 400,000 people are subject to an upper limb amputation. Projections foresee that this number may double by the 2050. Infections, trauma, cancer, or complications that arise in blood vessels represent the main causes for amputations. The access to prosthetic care is worldwide extremely limited. This is mainly due to the high cost both of commercially available prostheses and of the rehabilitation procedure which every prostheses user has to endure. Aside from high costs, commercially available hand prostheses have faced high rejection rates, mainly due to the their heavy weight, noisy operation and also to the unnatural feel of the fingers. To overcome these limitations, new materials, such as Shape Memory Alloys (SMAs), have been considered as potential candidate actuators for these kind of devices. In order to provide a contribution in the development of performant and easily affordable hand prostheses, the development of a novel and cost-effective five-fingered hand prototype actuated by Shape Memory Alloy (SMA) wires is presented in this work. The dissertation starts with the description of a first generation of a SMA actuated finger. Structure assemblage and performances in term of force, motion and reactiveness are investigated to highlight advantages and disadvantages of the prototype. In order to improve the achievable performances, a second generation of SMA actuated finger having soft features is introduced. Its structure, a five-fingered hand prosthesis having intrinsically elastic fingers, capable to grasp several types of objects with a considerable force, and an entirely 3D printed structure is then presented. Comparing this prototype with the most important prostheses developed so far, relevant advantages especially in term of noiseless actuation, cost, weight, responsiveness and force can be highlighted. A finite element based framework is then developed, to enable additional structure optimization and further improve the SMA finger performances. On the same time, a concentrated parameters physics-based model is formulated to allow, in the future, an easier control of the device, characterized by strong nonlinearities mainly due to the Shape Memory alloy hysteretic behavior.Jedes Jahr werden weltweit bei mehr als 400.000 Menschen Amputationen der oberen Gliedmaßen durchgeführt. Prognosen gehen davon aus, dass sich diese Zahl bis zum Jahr 2050 verdoppeln wird. Hauptursachen der Amputationen sind Infektionen, Unfälle, Krebs oder Durchblutungsstörungen. Der Zugang zu prothetischer Versorgung ist besonders in den Entwicklungsländern stark eingeschränkt. Dies liegt vor allem an den hohen Kosten sowohl der im Handel erhältlichen Prothesen als auch des Rehabilitationsprozesses, den jeder Prothesenträger durchlaufen muss. Neben den hohen Kosten haben kommerziell erhältliche Handprothesen aufgrund ihres hohen Gewichts, des lauten Betriebes und auch des unnatürlichen Gefühls hohe Ablehnungsraten. Um diese Einschränkungen zu überwinden, wurden neue Materialien, wie z.B. Formgedächtnislegierungen (SMAs), als potenzielle Materialien für den Antrieb von Prothesen untersucht . Um einen Beitrag zur Entwicklung von leistungsfähigen und erschwinglichen Handprothesen zu leisten, wird in dieser Arbeit die Entwicklung eines neuartigen und kostengünstigen Fünf-Finger-Handprototyps vorgestellt, der durch Drähte aus Formgedächtnislegierungen aktiviert wird. Die Doktorarbeit beginnt mit der Beschreibung der ersten Generation eines SMA-aktivierten Fingers. Zuerst wird der Aufbau und das Wirkungsprinzip des SMA Fingers erläutert und die Leistungs- und Bewegungsfähigkeit des Systems untersucht sowie Vor- und Nachteile des Prototyps dargestellt. Anschließend, um die erreichbare Leistungsfähigkeit zu verbessern, wird eine zweite Generation von SMA-gesteuerten Fingern vorgestellt, die eine vollständig in 3D gedruckte Struktur aufweisen. Diese Fünffinger-Handprothese mit inhärent elastischen Fingern ermöglicht nicht nur das Greifen unterschiedlich geformter Objekte sondern auch das Heben und Halten schwerer Gegenstände. Dieser neuartige Prototyp wird mit den wichtigsten bisher entwickelten Prothesen verglichen und die relevanten Vorteile insbesondere in Bezug auf geräuschlose Ansteuerung, Kosten, Gewicht, Reaktionszeit und Kraft hervorgehoben. Abschließend wird ein Finite-Elemente-Modell entwickelt, mit Hilfe dessen die Fingerstruktur weiter optimiert und die Leistungsfähigkeit des SMA-Fingers noch verbessert werden kann. Zusätzlich wird ein Konzentriertes-Parameter-Modell formuliert, um, in der Zukunft, eine leichtere Regelung des Systems zu ermöglichen. Dieses ist notwendig, da der SMA-Finger starke Nichtlinearitäten aufweist, die auf das hysteretische Verhalten der Formgedächtnislegierung zurückzuführen sind

The Separation Principle in Stochastic Control, Redux

Over the last 50 years a steady stream of accounts have been written on the separation principle of stochastic control. Even in the context of the linear-quadratic regulator in continuous time with Gaussian white noise, subtle difficulties arise, unexpected by many, that are often overlooked. In this paper we propose a new framework for establishing the separation principle. This approach takes the viewpoint that stochastic systems are well-defined maps between sample paths rather than stochastic processes per se and allows us to extend the separation principle to systems driven by martingales with possible jumps. While the approach is more in line with "real-life" engineering thinking where signals travel around the feedback loop, it is unconventional from a probabilistic point of view in that control laws for which the feedback equations are satisfied almost surely, and not deterministically for every sample path, are excluded.Comment: 23 pages, 6 figures, 2nd revision: added references, correction

Analysis of collocated feedback controllers for four-bar planar mechanisms with joint clearances

International audienceThis article presents an analysis of two-dimensional four-bar mechanisms with joint clearance, when one joint is actuated by collocated open-loop or state feedback controllers (proportional-derivative, state feedback linearization, passivity-based control). The study is led with numerical simulations obtained with a projected Moreau-Jean's event-capturing algorithm. The contact/impact model uses kinematic coefficients of restitution, and Coulomb's friction. The focus is put on how much the performance deteriorates when clearances are added in the joints. It is shown that collocated feedback controllers behave in a very robust way

Polarization Dynamics in Nonlinear Photonic Resonators

The global market demand for higher-bandwidth communication is increasing exponentially. Although optical networks provide high transmission speed using light to transmit signals, a bottleneck-inducing conversion is often needed to perform the processing of optical signals in the electrical domain. Such processing imposes a major barrier that would limit the high transmission speed of fiber-optic communications. This bottleneck conversion may be mitigated by extending signal-processing capabilities directly into the optical domain itself. Thus, I have studied the dynamics of optical polarization in a nonlinear photonic resonator to understand a new optical physical behavior to enhance the capabilities of optical signal processing. I present a theoretical model and experimental investigation to study the simultaneous occurrence of two optical nonlinear processes---nonlinear polarization rotation (NPR) and dispersive optical bistability. These two optical nonlinear processes within a nonlinear photonic resonator produce an optical signal exhibiting hysteresis curves in its state of polarization (SOP). Bistable action accompanied with simultaneous NPR is a significant departure from traditional optical memory, where the optical signal only exhibits hysteresis curves in the output power. Bistable polarization rotation (BPR) term is used to refer to the new physical process of bistable action accompanied by simultaneous NPR. I have leveraged this new physical process of the bistable polarization rotation to realize a hysteresis-shape transformation and optimization. A diversity of hysteresis shapes are demonstrated in optical power including the canonical counter-clockwise (CCW) shape (S-shape), the clockwise (CW) shape (inverted S-shape), and butterfly shapes. The control of the shape is performed downstream of the nonlinear photonic resonator within which the bistable signal is generated. I have derived a mathematical model to study this transformation process. Critical to our model, a generalized Malus\u27 law of a non-ideal linear polarizer and an elliptical input polarization. Since all hysteresis shapes originate from the same bistable signal, all shapes exhibit the same switching input powers. Moreover, the shape-control process is used to enhance the bistable switching contrast to surpass 20 dB for the CCW and CW shapes. Additionally, the new technique of hysteresis shape control enables the ability of simultaneous distribution of the bistable signal into multiple paths. In each path, the optical signal can be independently controlled to produce a hysteresis shape. For example, CCW and CW shapes can be configured in two locations using the same BPR signal. The theoretical and experimental work reported here is carried out for the case of a Fabry-Perot semiconductor optical amplifier as the nonlinear photonic resonator. Both the new physical process and the new control capability presented here are extendable to other nonlinear media (such as Kerr media) and other photonic resonators (such as ring and distributed feedback resonators). The dissertation outcomes detail processes and techniques to enhance the performance of all-optical combinational gates, such as photonic AND and XOR gates, as well as all-optical sequential devices, such as photonic flip-flops

Adaptive backstepping control of some uncertain nonlinear oscillators

A backstepping-based adaptive controller is designed for a class of uncertain second orded nonlinear systems under the strict-feedback form. It is shown that the closed loop is globally uniformly ultimately bounded and we give explicit bounds on both the asymptotic and transient performance. The control strategy is applied to a system typically found in base isolation schemes for seismic active protection of building structures. This system exhibits a hysteretic nonlinear behavior which is described analytically by the so-called Bouc–Wen model. Unlike other control schemes, the developed backstepping control does not require an exact knowledge of the model parameters. They are only defined within known intervals. The practical effectiveness of the controller is illustrated by numerical simulations.Postprint (published version

Inverse Compensation of Hysteresis using Modified Generalized Prandtl-Ishlinskii Hysteresis Model

Smart material based actuators, due to their properties of high precision, fast response, high power density, and small sizes, have become ideal actuators in many industrial applications, i.e. micro positioning, atomic force microscopy, and so forth. However, these smart actuators exhibit hysteresis nonlinear effects, which may worsen tracking performances, lead oscillations or even instabilities. Therefore, the existence of the hysteresis nonlinearities limits the utilization of smart material based actuators, and became the bottleneck of the control strategies development for systems with the smart actuators. In order to overcome the effects of the hysteresis, a number of hysteresis models have been proposed in the literatures. Among them, the Prandtl-Ishlinskii (PI) model, thanks to its significant analytical invertible property, has become one of the most popular hysteresis models. Nevertheless, the PI model can only describe a kind of symmetric, rate-independent, and non-saturated hysteresis, which restricts the use of PI model. Therefore, it requires to generalize the PI model, making it able to represent more complicated hysteresis phenomena, while keeping analytically invertible property. In this thesis, based on the PI model and the Generalized Prandtl-Ishlinskii (GPI) model available in the literature, a modified Generalized Prandtl-Ishlinskii (mGPI) model is proposed, which aims to redefine the play operator in the GPI so as to describe a kind of asymmetric and saturated hysteresis nonlinearities. According to the proposed mGPI model, an analytical inverse model is also derived, which can be used as an inverse compensator of the hysteresis nonlinearities. To validated the proposed inverse model, simulation results are provided confirming the proposed analytical inverse of the mGPI model