Sharif Digital Repository

The performance of hapticdevicesisevaluatedbasedontheconceptoftransparency, whiletheirstabilityhasprevalentlybeenevaluatedbasedonthepassivitycriterion. Duetotheconservativenessofpassivity, itappearsasanobstacletoimprovingtransparency.Inthepresentpaper, passivityissuggestedtobereplacedbythecomplementarystabilitycriterionwhichaccoun tsfortherobuststabilityoftheinteractioninthepresnceofuncertainuserhanddynamics. Inthisrespect, analgorithmisproposedwhichguaranteestransparencyofthehapticdeviceinastablemanne r.Assumingthatthedynamicsofthedeviceisknown, acertaincompensatorystructureisassigned. Thisspecialstructureguaranteestransparencyofthedevicebycompensatingforthedynami... 

This paper is concerned with tracking state trajectory at remote controller, stability and performance of linear time-invariant noiseless dynamic systems with multiple observations over the packet erasure network subject to random packet dropout and transmission delay that does not necessarily use feedback channel full time. Three cases are considered in this paper: (1) without feedback channel, (2) with feedback channel intermittently and (3) with full time availability of feedback channel. For all three cases, coding strategies that result in reliable tracking of state trajectory at remote controller with asymptotically zero mean absolute estimation error are presented. Asymptotic mean... 

This paper proposes a scheme for computing the stable regions from which the parameters of fractional-order proportional-integral (PI) and proportional-derivative (PD) controllers can be selected. In particular, a previously investigated method for plotting the stability regions of PI λ and PDμ controllers is extended to their integer-order approximations. Next, the two stability regions are compared and their overlapping sections, referred to as the implementable stability region, are derived. In order for the final closed-loop system to be stable, the designer must choose the controller parameters from the overlapping section of the two stability regions. Simulation results for two example... 

In this paper, modeling and vibration control of a strain-gradient clamped-free Euler-Bernoulli micro-beam exposed to varying disturbance is studied. A strain-gradient model of the Euler-Bernoulli micro-beam is represented in this paper and consisted of one partial differential equation and six ordinary equations as governing motion equation and boundary conditions, respectively. A boundary controller is proposed to suppress the system's vibration. The controller is derived based on the direct Lyapunov method. An adaptation law is devised to assure system's stability under parametric uncertainties. With the proposed adaptive robust boundary control, uniform boundedness under environmental... 

This study investigates the asymptotic swarm stabilisation of fractional-order swarm systems in the presence of two different kinds of model uncertainties and external disturbances while the upper bound of the uncertainties is a linear function of pseudo-states norms with unknown coefficients. To this end, first a fractional-integral sliding manifold is constructed and then an adaptive-robust sliding mode controller is designed to guarantee the asymptotic swarm stability in a fractional-order linear time-invariant swarm system. The stability analysis of the proposed control system is done based on the Lyapunov stability theorem. Using the proposed controller, the coefficients of the upper... 

Animal walking is one of the most robust and adaptive locomotion mechanisms in the nature, involves sophisticated interactions between neural and biomechanical levels. It has been suggested that the coordination of this process is done in a hierarchy of levels. The lower layer contains autonomous interactions between muscles and spinal cord and the higher layer (e.g. the brain cortex) interferes when needed. Inspiringly, in this study we present a hierarchical control architecture with a state of the art intrinsic online learning mechanism for a dynamically walking 5-link biped robot with compliant knee joints. As the biological counterpart, the system is controlled by independent control... 

A simple fractional differentiator-based controller is proposed to suppress chaos in a 3D single input chaotic system by stabilizing some of the fixed points. The tuning procedure for the proposed controller is based on the stability concepts in the incommensurate fractional order systems. To show the efficiency of the controller, some numerical simulations are given. Also, to evaluate the practical capability of the proposed controller, we experimentally apply it to control chaos in a chaotic circuit. Moreover, some mathematical analyses are presented to show the applicability of the proposed controller, when its structure is not exactly implementable. © Birkhäuser Boston 2009  

Resonant converters are hard nonlinear systems which are comprised of both continuous and discontinuous nonlinearities. Many nonlinear modeling approaches lead to a very awkward, unsystematic stability analysis and controller design. Hence, stability analysis and stabilizing controller design of the popular LLC resonant converter still remain challenging as direct consequences of the absence of a "systematic modeling". In this paper, the LLC resonant converter is modeled in the form of Piece-Wise Affine (PWA) systems and a Direct Piece-Wise Affine (DPWA) model of the DC-DC LLC resonant converter is proposed. No dynamic is omitted in the modeling approach, and accordingly, the proposed... 

In the field of mobile robotics, legged locomotion plays an essential role in transporting robots over various terrain types. A significant portion of research on legged robots has been focused on one-legged robots. In contrast with different types of locomotion of multi-legged robots, one-legged robots have only one type of motion, called hopping. Hopping motion, as a type of hybrid behavior, is generally comprised of flight and stance phases. Dynamic stabilizing of hopping motion provides a challenging control problem because of its nonlinear and hybrid behavior. The majority of one-legged hopping robots investigated so far are only capable of hopping with one side of their leg. In this... 

To deal with strong nonlinearity in nonlinear systems, a new method called cascade multiple-model predictive controller based on gap metric and stability margin, is proposed. The gap metric is utilized to describe the nonlinear system by a linear model bank. It is possible to select nominal local models from the linear model bank by an algorithm based on the gap metric and stability margin to avoid the redundancy of the local controllers. By scheduling proportional controller for each nominal local model, the robust stability is guaranteed whereas there will be no guarantee for the desired performance. Then, by designing a model predictive controller in the cascade structure, the closed loop... 

This work deals with the robust D-stability test of linear time-invariant ( LTI ) general fractional order control systems in a closed loop where the system and - or the controller may be of fractional order. The concept of general implies that the characteristic equation of the LTI closed loop control system may be of both commensurate and non-commensurate orders, both the coefficients and the orders of the characteristic equation may be nonlinear functions of uncertain parameters, and the coefficients may be complex numbers. Some new specific areas for the roots of the characteristic equation are found so that they reduce the computational burden of testing the robust D-stability. Based on... 

Dynamic instabilities are quite common in planing crafts. This study deals with the elimination of one type of dynamic instabilities known as porpoising. The controller device is a pneumatically driven trim tab that applied to the transom of the boat. The governing dynamic equations of the planing craft and the pneumatically driven system are derived. The stability analysis of the system is carried out and porpoising instability is shown under some conditions. A dual control scheme consisting of the actuator control subsystem (inner control subsystem) and the planing craft (outer control subsystem) is proposed in order to control the planing craft from porpoising instability. Since the... 

In this study, an impulsive state feedback controller has been proposed for the treatment of hepatitis-C-infected patients under Pegylated-Interferon (PEG-IFN-α2b) therapy. The Neumann model has been utilized as the representative of the hepatitis C virus (HCV) dynamics. In order to consider the drug efficacy variation between injections, the pharmacokinetics/pharmacodynamics (PK/PD) equations have been included in the model. The impulsive nature of the drug injection also has been considered in the disease dynamics. In the proposed treatment method, the drug dose limitation has been addressed as an input nonlinearity. The asymptotical stability of the control method under the impulsive... 

In this paper, we propose a decentralized control scheme for combined motion/force control of nonredundant multi-manipulator robotic systems, cooperatively grasping a rigid body in a prespecifled position/force trajectory. The proposed control scheme uses the impedance method for modeling the internal force exerted by the end effectors to the object. The precise mathematical analysis of the overall dynamical system and the proposed controller are presented and the stability of the overall system is studied. The proposed controller, then, is applied to a cooperative system composed of two PUMA560 manipulators and the simulation results are presented to verify the proposed control scheme  

This paper presents a new optimization-based approach to determine the class of stabilizing control structures with the necessary set of feedback links for interconnected systems. The proposed approach relies on a graph theoretic interpretation and its equivalence in terms of binary linear programs (BLP). To carry out the primary goal, first, the stabilizability of an LTI system under the decentralized control structure is presented in terms of a BLP. Next, two graph-based criteria are proposed to characterize stabilizing control structures with the required feedback links. Finally, all possible stabilizing control structures with the necessary feedback links are derived via solving a set of... 

This paper investigates the influence of residual bow on the stability of a rotating system consisting of an unbalanced Jeffcott rotor with anisotropy and two nonlinear journal bearing supports. The motion equations of the rotor system are formulated and analyzed considering most common faults and features including coupling effects of unbalance, anisotropy and residual shaft bow, by applying Lagrangian dynamics and Floquet theory. Time varying system properties of stiffness and damping are introduced into the equations of motion affecting the rotor behavior, and the influence is studied with respect to the extent of the bearing nonlinearity and the rotor anisotropy. Increasing area of... 

The stability and integrity of structures under indeterminant external loadings, particularly earthquakes, is a vital issue for the design and safe operation of marine and offshore structures. Over the past decades, many structural control systems, such as viscous-based systems, have been developed and embedded in marine and offshore structures, particularly oil platforms to maintain the stability and mitigate the seismic hazards. Rapid improvement in intelligent materials, including shape memory alloys (SMAs) and Magnetorheological fluid (MRF), have led to the design and development of efficient structural control elements. The present work aims to establish a framework for the structural... 

A dc-dc resonant converter has the advantage of overcoming switching losses and electromagnetic interference which are the main limitations of high frequency power converters. Nevertheless, the modeling and stability analysis of dc-dc resonant converters are considerably more complex than pulsewidth modulation counterparts. The conventional averaged linearized model of the resonant converter has limitations due to averaging and linearization. First of all, the linearized model has large modeling error in presence of large variations of reference voltage and input voltage. Furthermore, Converging area for stabilizing controllers is smaller in the averaged model. In order to overcome these... 

This paper is concerned with the disturbance attenuation problem of fuzzy large-scale systems which consist of N interconnected subsystems which are represented by Takagi-Sugeno fuzzy models. Using Lyapunov function and linear matrix inequalities (LMIs), a criterion is proposed to have a prescribed level of disturbance attenuation. A numerical example is given to illustrate the control design procedure and its effectiveness  

This study presents an online motion planning algorithm for generating reference trajectories during flight phases of a planar monopedal robot to transfer the configuration of the mechanical system from a specified initial pose to a specified final one. The algorithm developed in this research is based on the reachability and optimal control formulations of a time-varying linear system with input and state constraints. A two-level control scheme is developed for asymptotic stabilisation of a desired period-one orbit during running of the robot. Within-stride controllers, including stance and flight phase controllers, are employed at the first level. The flight phase controller is a feedback...