Добірка наукової літератури з теми "Modified feedback linearization"

Among the tilt-rotors (quadrotors) developed in recent decades, Ryll’s model with eight inputs (four magnitudes of thrusts and four tilting angles) attracted great attention. Typical feedback linearization maneuvers all of the eight inputs with a united control rule to stabilize this tilt-rotor. Instead of assigning the tilting angles by the control rule, the recent research predetermines the tilting angles and leaves the magnitudes of thrusts with the only control signals. These tilting angles are designed to mimic the cat-trot gait while avoiding the singular decoupling matrix in feedback linearization. To complete the discussions of the cat-gait inspired tilt-rotor gaits, this research addresses the analyses on the rest of the common cat gaits, walk, run, transverse gallop, and rotary gallop. It is found that the singular decoupling matrix exists in walk gait, transverse gallop gait, and rotary gallop gait; the decoupling matrix can hardly be guaranteed to be invertible analytically. Further modifications (scaling) are conducted to these three gaits to accommodate the application of feedback linearization; the acceptable attitudes, leading to invertible decoupling matrix, for each scaled gait are evaluated in the roll-pitch diagram. The modified gaits with different periods are then applied to the tilt-rotor in tracking experiments, in which the references are uniform rectilinear motion and uniform circular motion with or without the equipment of the modified attitude-position decoupler. All the experiments are simulated in Simulink, MATLAB. The result shows that these gaits, after modifications, are feasible in tracking references, especially for the cases equipped with the modified attitude-position decoupler.

In this paper, a robust and constraint feedback linearization controller (FLC) with a modified incremental conductance (Inc.Cond) is proposed for maximum power point tracking (MPPT) in the photovoltaic (PV) systems and overall closed-loop internal stability is guaranteed. The proposed technique is independent with respect to load and is robust against disturbances in the load voltage. A boost chopper converter is utilized as an interface between the PV panel and load to control the system at the best operating point. A modified Inc.Cond method based on current orientation and without division equations is presented. The Inc.Cond method is utilized to generate the desired current for the FLC. The FLC navigates the PV panel to the maximum power point with high speed, whereas the control signal (duty cycle) constraints are monitored. Finally, the MPPT technique is validated through simulation and experimental results and two scenarios are defined to confirm controller robustness and modified Inc.Cond performance.

The underlying circuit control is a key problem of the hybrid energy-storage system (HESS) in electric vehicles (EV). In this paper, a composite non-linear control strategy (CNC) is proposed for the accurate tracking current/voltage of the fully-active HESS by combining the exact feedback linearization method and the sliding mode variable structure control technology. Firstly, by analyzing the circuit characteristics of HESS, the affine non-linear model of fully-active HESS is derived. Then, a rule-based energy management strategy (EMS) is designed to generate the reference current value. Finally, the HESS is linearized by the exact feedback linearization method, and the proposed CNC strategy is developed combined with sliding mode variable structure control technology to ensure fast response, high performance, and robustness. At the same time, the stability proof based on the Lyapunov method is given. Moreover, the performance of the CNC strategy is thoroughly investigated and compared with simulation studies with the traditional PI control and a modified sliding mode control, and its effectiveness under different driving conditions is fully verified.

SUMMARYIn this paper, an optimal fuzzy sliding mode controller has been designed for controlling the end-effector position in the task space. In the proposed control, feedback linearization method, sliding mode control, first-order fuzzy TSK system and optimization algorithm are utilized. In the proposed controller, a novel heuristic algorithm namely self-adaptive modified bat algorithm (SAMBA) is employed. To achieve an optimal performance, the parameters of the proposed controller as well as the input membership functions are optimized by SAMBA simultaneously. In this method, the bounds of structural and non-structural uncertainties are reduced by using feedback linearization method, and to overcome the remaining uncertainties, sliding mode control is employed. Mathematical proof demonstrates that the closed loop system with the proposed control has global asymptotic stability. The presence of sliding mode control gives rise to the adverse phenomenon of chattering in the end-effector position tracking in the task space. Subsequently, to prevent the occurrence of chattering in control input, a first-order TSK fuzzy approximator is utilized. Finally, to determine the fuzzy sliding mode controller coefficients, the optimization algorithm of Self-Adaptive Modified Bat is employed. To investigate the performance of the proposed control, a two-degree-of-freedom manipulator is used as a case study. The simulation results indicate the favorable performance of the proposed method.

In the current paper, a macroscopic differential model for the hysteretic dynamics in shape memory alloy actuators is constructed by using the modified Landau theory of the first order phase transformation. An intrinsic thermo-mechanical coupling is achieved by constructing the free energy as a function depends on both mechanical deformation and the material temperature. Both shape memory and pseudoelastic effects are modeled. The hysteretic dynamics is linearized by introducing another hysteresis loop via nonlinear feedback strategy, which cancels the original one.

The research presents a novel controller designed for robotic systems subject to nonlinear uncertain dynamics and external disturbances. The control scheme is based on the modified super-twisting method, input/output feedback linearization, and time delay approach. In addition, to minimize the chattering phenomenon and ensure fast convergence to the selected sliding surface, a new reaching law has been integrated with the control law. The control scheme aims to provide high performance and enhanced accuracy via limiting the effects brought by the presence of uncertain dynamics. Stability analysis of the closed-loop system was conducted using a powerful Lyapunov function, showing finite time convergence of the system’s errors. Lastly, experiments shaping rehabilitation tasks, as performed by healthy subjects, demonstrated the controller’s efficiency given its uncertain nonlinear dynamics and the external disturbances involved.

In this paper, bifurcations of limit cycles close to certain singularities of the vector fields are explored using an algorithm based on the harmonic balance method, the theory of nonlinear feedback systems and the monodromy matrix. Period-doubling, pitchfork and Neimark–Sacker bifurcations of cycles are detected close to a Gavrilov–Guckenheimer singularity in two modified Rössler systems. This special singularity has a zero eigenvalue and a pair of pure imaginary eigenvalues in the linearization of the flow around its equilibrium. The presented results suggest that the proposed technique can be promising in analyzing limit cycle bifurcations arising in the unfoldings of other complex singularities.

With the introduction of the laterally bounded forces, the tilt-rotor gains more flexibility in the controller design. Typical feedback linearization methods utilize all the inputs in controlling this vehicle; the magnitudes as well as the directions of the thrusts are maneuvered simultaneously based on a unified control rule. Although several promising results indicate that these controllers may track the desired complicated trajectories, the tilting angles are required to change relatively fast or in large scale during the flight, which turns to be a challenge in application. The recent gait plan for a tilt-rotor may solve this problem; the tilting angles are fixed or vary in a predetermined pattern without being maneuvered by the control algorithm. Carefully avoiding the singular decoupling matrix, several attitudes can be tracked without changing the tilting angles frequently. While the position was not directly regulated in that research, which left the position-tracking still an open question. In this research, we elucidate the coupling relationship between the position and the attitude. Based on this, we design the position-tracking controller, adopting feedback linearization. A cat-trot gait is further designed for a tilt-rotor to track the reference; three types of references are designed for our tracking experiments: set point, uniform rectilinear motion, and uniform circular motion. The significant improvement with less steady state error is witnessed after equipping with our modified attitude–position decoupler. It is also found that the frequency of the cat-trot gait highly influenced the steady state error.

L’objectif de cette thèse est de concevoir et de contrôler un système de Robot Parallèle à Câbles (RPC) à quatre câbles pour la manipulation dextre de pièces sur des chaînes de production. Pour une ligne de fabrication déjà installée, l’espace de travail est souvent limité et l’ajout d’un nouveau robot-sériel sur le sol de l’atelier est parfois difficile. L’utilisation du plafond pour fixer une machine lourde n’est pas toujours possible car il pourrait être nécessaire de renforcer la structure. Le RPC est un moyen de réaliser la tâche avec une faible modification de l’atelier existant. La nouveauté du travail réside dans le fait que la majorité des conceptions existantes placent les moteurs d’actionnement et les treuils de la plate-forme de base, alors que dans ce travail, les moteurs d’actionnement sont embarqués sur la plate-forme mobile, ce qui permet de fixer facilement le RPC dans la chaîne de fabrication avec des points d’ancrage simples. Tout d’abord, l’espace de travail du RPC pour l’environnement souhaité est étudié. La nature sous-actionnée du robot et la contrainte d’une force de tension positive du câble imposés en raison de la flexibilité des câbles limitent sont la base d’une étude sur l’espace de travail respectant les conditions d’équilibre statique. Les équations d’équilibre statique classiques ont été utilisés pour calculer l’espace de travail du robot et le comportement correspondant de la plateforme mobile. Les angles d’orientation de la plate-forme ont été présentés. Plusieurs études de cas ont été montres avec différentes charges utiles attachées à la plate-forme mobile. Les dimensions de la plate-forme mobile et la structure de base ont également été modifiées afin de calculer le domaine de l’espace de travail où les performances du robot peuvent être satisfaisantes. Les dimensions du prototype ont été fixées en tenant compte de l’espace de travail. Par la suite, le modèle dynamique classique du RPC a été utilisé pour mettre en œuvre la loi de contrôle. La deuxième partie de la thèse présente la conception et la mise en œuvre des lois de contrôle pour la RPC. La linéarisation classique de la rétroaction entrée- sortie (IOFL) est développée et des résultats de simulation ont été présentés. Le rôle de la dynamique interne présente dans le système en raison de la sous-performance a été démontré en utilisant leur diagramme de phase. Deux solutions possibles ont été envisagées afin de réduire l’effet des dynamiques internes sur le système. La première solution consiste à utiliser des proportions appropriées pour la plate-forme et la structure de base. Des résultats de simulation ont été présentés pour montrer le comportement de la plate-forme lorsque les dimensions sont modifiées. Une linéarisation modifiée de la rétroaction (MFL) a été proposé comme une solution ad-hoc pour éliminer les effets de la dynamique interne. Les résultats de la simulation obtenus montrent que la solution ad-hoc proposée fonctionne efficacement et nettement mieux que la technique classique de l’IOFL pour certaines dimensions du RPC. L’utilisation de cette approche pour différents cas de RPC doit faire l’objet d’une étude enquête. Les résultats expérimentaux validant la technique de l’IOFL sont présentés pour démontrer le comportement satisfaisant de le RPC avec le contrôle. L’objectif global du projet est de développer un robot parallèle à câble qui peut travailler avec un opérateur dans une chaîne de fabrication pleinement fonctionnelle et aider le travailleur à soulever les objets lourds ou chauds. Cette thèse réalise la première étape pour rendre un prototype de RPC qui sera par la suite amélioré pour le rendre collaboratif
This thesis aims to design and control an underactuated Cable-Driven Parallel Robot (CDPR) with four cables for the agile handling of parts in a manufacturing line. For already installed manufacturing lines, most of the available working space is often used, and adding a new serial robot on the workshop ground is sometimes difficult. Using the ceiling to fix heavy machines is not always possible, and it could be necessary to reinforce the structure. CDPR is a way to achieve the work with a light structure, with low modification of the existing workshop. The novelty of the work lies in the fact that the majority of the existing designs place the actuating motors and the winches on the base platform, whereas in this work, the actuating motors are placed on the moving platform, making it convenient for the CDPR to be fixed in the manufacturing line with simple anchor points. First, the workspace of the CDPR for the desired environment is investigated. The underactuated nature of the robot and the positive cable tension constraint imposed due to the flexibility of the cable limit the workspace investigation to static equilibrium conditions. The classical static equilibrium equations have been used to calculate the robot workspace and the corresponding behavior of the plat- form orientation angles have been presented. Several case studies have been shown with different payloads attached to the moving platform. The dimensions of the moving platform and the base structure have also been changed to understand the possible region of the workspace where the robot performance can be satisfactory. The prototype dimensions have been fixed taking into account the workspace performance. Following this, the classical dynamic model developed in the field of CDPR has been used to implement the control law on the CDPR. The second part of the thesis presents the design and implementation of the control laws for the CDPR. The classical Input-Output Feedback Linearization (IOFL) technique is developed and simulation results have been presented. The role of internal dynamics present in the system because of the underactuation is demonstrated using their phase-plane plots. Two possible solutions have been suggested to reduce the effect of internal dynamics on the system. The first solution is to use appropriate dimensions for the platform and the base structure. Simulation results have been presented to show the behavior of the platform when the dimensions are changed. A Modified Feedback Linearization (MFL) has been proposed as an ad-hoc solution for eliminating the effects of the internal dynamics. The simulation results obtained show that the proposed ad-hoc solution performs efficiently and significantly better than the classical IOFL technique for certain dimensions of the CDPR. The use of this approach for different cases of CDPR needs to be investigated. Experimental results validating the IOFL technique are presented to demonstrate the satisfactory behavior of the CDPR with the control law developed during the thesis. The overall objective of the project is to develop a CDPR that can work with an operator in a fully functional manufacturing line and aid the worker in lifting heavy or hot objects. This thesis achieves the first step in making a functional prototype of a CDPR which will be improved further to make it collaborative

This paper presents a new algorithm for the design of linear controllers with special constraints imposed on the control gain matrix. This so called SLC (Structured Linear Control) problem can be formulated with linear matrix inequalities (LMI’s) with a nonconvex equality constraint. This class of prolems includes fixed order output feedback control, multi-objective controller design, decentralized controller design, joint plant and controller design, and other interesting control problems. Our approach includes two main contributions. One is that many design specifications such as H∞ performance, generalized H2 performance including H2 performance, l∞ performance, and upper covariance bounding controllers are described by a similar matrix inequality. A new matrix variable is introduced to give more freedom to design the controller. Indeed this new variable helps to find the optimal fixed-order output feedback controller. The second contribution uses a linearization algorithm to search for a solution to the nonconvex SLC problems. This has the effect of adding a certain potential function to the nonconvex constraints to make them convex. Although the constraints are added to make functions convex, those modified matrix inequalities will not bring significant conservatism because they will ultimately go to zero, guaranteeing the feasibility of the original nonconvex problem. Numerical examples demonstrate the performance of the proposed algorithms and provide a comparison with some of the existing methods.

In this paper, the active-disturbance-rejection control (ADRC) is applied to realize the high-precision tracking control of CNC machine tool feed drives. First, according to the number of the feedback channel, the feed systems are divided into two types: signal-feedback system, e.g., linear motor and rotary table, and double-feedback system, e.g., ball screw feed drive with a load/table position feedback. Then, the appropriate controller is designed to ensure the closed-loop control performance of each type of system based on the idea of ADRC. In these control frameworks, the extended state observers (ESO) estimate and compensate for unmodeled dynamics, parameter perturbations, variable cutting load, and other uncertainties. For the signal-feedback system, the modified ADRC with an acceleration feedforward term is used directly to regulate the load/table position response. However, for the double-feedback system, the ADRC is applied only to the motor position control, and a simple PI controller is used to achieve the accurate position control of the load. In addition, based on ADRC feedback linearization, a novel equivalent-error-model based feedforward controller is designed to further improve the command following performance of the double-feedback system. The experimental results demonstrate that the proposed controllers of both systems have better tracking performance and robustness against the external disturbance compared with the conventional P-PI controller.

This paper presents a modified integral sliding surface, sliding mode control law for pneumatic artificial muscles. The cutoff frequency tuning parameter λ is squared to increase the gradient from absement (integral of position) to position and higher derivatives to reflect the more dominant terms in the actuator dynamics. The sliding mode controller is coupled with proportional and integral action compensation. The control system is sufficiently robust so that use of an observer and input-output feedback linearization are not required. Closed-loop control experiments are compared with traditional sliding mode controller designs presented in the literature for pneumatic artificial muscles. Experiments include the tracking of sinusoidal waves at 0.5 and 1 Hz, tracking of square-like waves with seventh-order trajectory transitions at a rate of 0.2 Hz without and with a steady-state period of 10 seconds, as well as a step input response. These experiments indicate that the control law provides similar bandwidth, tracking, and steady-state performance as approaches requiring nonlinear feedback and model observation for pneumatic artificial muscles. Experiments demonstrate an accuracy of 50 μm at steady-state with no overshoot and maximum tracking errors less than 0.4 mm for smooth square-like trajectories.

Abstract This paper investigates the modeling and control of a physical therapy dynamometer with a flexible shaft and a non-linear damping function. Because of the disparate sizes of patients, the system loading varies. Computer models of the system were created by entering bond graphs into the Computer Aided Modeling Program - Graphical (CAMPG). These models were modified to include the non-linear element and were simulated numerically using the Advanced Continuous Simulation Language (ACSL). Two families of controllers using the feedback linearization technique were formulated, one that treats the system as completely rigid, and a second that accounts for, and attempts to control the system flexibility. It was found that the second family of controllers had a performance advantage, because they can be made less sensitive to parametric variation by increasing the flexibility of the system. Increasing the system flexibility also has a cost advantage, because less sophisticated components can be used.

Due to the nonlinear dynamics of hydraulic systems, applying high performance closed-loop controllers is complicated. In this paper, a single-rod hydraulic actuator is considered in which load displacement (for positioning purposes) is controlled via manipulation of the input voltage to the servo-valve. Dynamics of the servo-valve is described by first and second order transfer functions (named as Models 1 and 2). Through linearization of the system around its operating points, dynamics of the hydraulic actuator is represented in the state space. A full-order observer is designed for on-line states estimation. Then, feedback control system is designed for both regulation and tracking objectives through pole-placement approach based on general canonical control form (GCCF). For tracking of the desired commands, a modified integral control is required (since the plant has not integrator). Results show that the regulation, states estimation, desired tracking and final tracking accuracy are achieved after applying the controller. Required input voltage and load positioning are compared for the two distinct dynamics of the servo-valve (Model 1 and 2).