Department of Control (1996 - Present)
electrical engineering
, Pittsburgh, U.S.A
electrical engineering
, Pittsburgh, U.S.A
electrical engineering
, University of Tehran, Iran
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Professor Vahid J. Majd received his B.Sc. degree in 1989 from the electrical engineering department of the University of Tehran, Iran. He then received his M.Sc. and Ph.D. degrees in the area of Control Theory from the electrical engineering department of the University of Pittsburgh, PA, U.S.A. in 1991 and 1995, respectively. He is currently an associate professor in the control system department of Tarbiat Modares University, Tehran, Iran, and is the director of intelligent control systems laboratory. His areas of interest include: intelligent identification and control, multi-agent learning, fuzzy control, cooperative control, formation control, robust nonlinear control, fractional order control, and systems biology.
This paper addresses the push recovery of quadruped robots trotting on even terrain. Push recovery is the ability of a legged robot to maintain its balance in the presence of sudden external forces applied to the robot. Due to the nature of this dynamical gait, the quadruped robot can be modeled as a biped robot where each two cross legs of the quadruped are modeled as a virtual leg. Then, the virtual biped model is further reduced to a two-dimensional linear inverted pendulum plus flywheel model (LIPFM). Moreover, using the concept of capture points for the biped model, the desired locations for the center of pressure (COP) of the legs for recovering the robot's balance are calculated by designing a two-dimensional dynamic capture point es
This paper addresses a practical finite-time leader-following formation controller design for the second-order stochastic Lipchitz nonlinear systems under uncertain communication environments and external disturbances. It is desired that the orientation of the formation change according to the variations in the leader’s orientation. The time-varying weighted topology matrix is modelled as a linear combination of a finite number of constant Laplacian matrices with time-varying coefficients. The proposed back-stepping sliding-mode controller guarantees that all the signals in the closed-loop system remain bounded in probability and the norm of sliding trajectories converge almost surely in finite-time to an arbitrary small neighbourhood of
In this paper, the fault-tolerant formation control of nonlinear stochastic multi-agent systems in the presence of actuator faults, disturbances, and time-varying weighted topology is considered. While most traditional fault-tolerant control methods in the literature use fixed weights on the topology edges, in this study these weights are considered time-varying using a pre-designed function, which allows formulating the system more realistically. Moreover, in contrast with previous works on fault-tolerant multi-agent systems, in this study, the model of the agents is considered to be stochastic in general. Furthermore, the actuators of the agents are considered to have a time-varying fault of additive and multiplicative types. A passive an
In this paper, state estimation and adaptive sliding mode control (SMC) of uncertain fractional-order Markovian jump systems (FO-MJSs) with time delay and input nonlinearity are considered. A non-fragile observer is proposed to estimate the system states, and an observer-based adaptive sliding mode controller is synthesized to ensure the reachability of the sliding surfaces in the state-estimation space in finite time. The sufficient condition for stochastic stability of the error system and sliding mode dynamics is derived in the form of linear matrix inequalities (LMIs). Finally, some numerical examples are presented to illustrate the effectiveness of the proposed method.
This paper addresses the design of a non-fragile exponential polynomial observer for a class of fractional-order nonlinear systems. Existence of the observer is proven and a sufficient condition for the stability of the state estimation error dynamics with a predetermined exponential convergence rate is derived employing the Lyapunov stability theorem. The exponential stability criterion is proposed in the form of linear matrix inequalities (LMIs). Moreover, some numerical examples have been provided to illustrate the effectiveness of the proposed approach. The synchronisation of fractional-order Lorenz systems has been investigated using the proposed method. Then, the proposed method has been applied to the chaotic communication problem of
This paper extends the idea of switching T-S fuzzy systems with linear consequent parts to nonlinear ones. Each nonlinear subsystem is exactly represented by a T-S fuzzy system with Lure’ type consequent parts, which allows to model and control wider classes of switching systems and also reduce the computation burden of control synthesis. With the use of a switching fuzzy Lyapunov function, the LMI conditions for asymptotic stability of the system with maximum decay-rate and disturbance attenuation properties under arbitrary switching law are derived. Moreover, several numerical examples are provided to demonstrate the effectiveness of the proposed approaches to reduce the computational burden of control synthesis and improving the closed
This study discusses a robust distributed finite-time formation control of the stochastic Lipchitz multi-agent systems within the actuator fault. Furthermore, the orientation of formation is often adjusted in step with the leader's orientation. The agents are modeled as stochastic nonlinear systems either thanks to their intrinsic behavior or working in a very random vibrating environment. Additionally, biased and effectiveness faults are considered. To cater to these, employing a distributed sliding-mode approach and the infinitesimal operation, a robust finite-time fault-tolerant controller is presented in mean-square sense. Finally, a multi-aircraft model under stochastic wind is used to validate the effectiveness of the offered control
In recent years, three-dimensional measurement techniques have been widely used in medical sciences, and thus, depth detection in an image plays an important role in computer vision applications. In this paper, we discuss the estimation of the distance between the head of an endoscope and the small intestine septum and its problems. The main objective is to detect the depth of the small intestine to estimate distance. Images were collected through video sampling, and then the data are preprocessed. Morphological reconstruction, bounding box, Convex Hull, and Euclidean distance are employed to update the mentioned distance. At the end of this process, the outputs are simulated, and we are given the output distance in centimeters. This method
This paper extends the idea of switching TS fuzzy systems with linear consequent parts to nonlinear ones. Each
In this paper the problem of non-fragile adaptive sliding mode observer design is addressed for a class of nonlinear fractional-order time-delay systems with uncertainties, external disturbance, exogenous noise, and input nonlinearity. An H-infinity observer-based adaptive sliding mode control considering the non-fragility of the observer is proposed for this system. The sufficient asymptotic stability conditions are derived in the form of linear matrix inequalities. It is proven that the sliding surface is reachable in finite time. An illustrative example is provided which corroborates the effectiveness of the theoretical results.
In this paper the problem of non‐fragile adaptive sliding mode observer design is addressed for a class of nonlinear fractional‐order time‐delay systems with uncertainties, external disturbance, exogenous noise, and input nonlinearity. An H∞ observer‐based adaptive sliding mode control considering the non‐fragility of the observer is proposed for this system. The sufficient asymptotic stability conditions are derived in the form of linear matrix inequalities. It is proven that the sliding surface is reachable in finite time. An illustrative example is provided which corroborates the effectiveness of the theoretical results.
In this article, a robust adaptive intelligent fault-tolerant controller with prescribed performance is proposed for an uncertain quadruped robot with actuator fault. The control system comprised of three terms: (1) a full-state feedback controller which includes the prescribed performance function, (2) an adaptive intelligent wavelet-based Takagi-Sugeno fuzzy network (TSFN), and (3) a robust control term. The proposed controller does not utilize the robot dynamic model. A wavelet-based TSFN is utilized to approximate adaptively the lumped nonlinear terms, parameter uncertainties, and defective torque signal. The wavelet block acts as a feature extractor, reduces the number of fuzzy rules, and also acts as a normalization function. The para
This paper offers a new push recovery method to stabilize the quadruped robots walking on even terrains in the presence of external disturbance forces exerted on the body and legs of the robot. To avoid force sensors, a class of nonlinear observers is usually used to estimate all the forces that are applied to the leg joints. However, such estimations involve permanent errors in the case of fast varying external forces. A new sliding-mode control method is designed to enable the robot to track a desired gait with high precision despite the persisting estimation error of the original nonlinear disturbance observer. A new push recovery method that uses the estimations of the disturbance observer is proposed to help the robot maintain its bal
This article discusses a finite-time fault-tolerant consensus control for stochastic Euler-Lagrange multi-agent systems. First, the finite-time consensus controller of Euler-Lagrange multi-agent systems with stochastic disturbances is presented. Then, the proposed controller is extended as a fault-tolerant controller in the presence of faults in the actuators. In these two cases, the sliding-mode distributed consensus controllers are designed. The results guarantee that by using these controllers, the consensus tracking errors converge to a desired area near the origin in finite-time with the mean-square sense and also remain bounded in probability. In the simulation section, a robotic manipulator model with actuator faults and stochastic d
This paper addresses the cooperative stochastic state estimation of a moving target using a switching sensor network that may contain communication delays. The switching in the graph of the sensor network may be due to local communication failures of the neighboring sensors or due to their movements. The network may have heterogeneous sensors with different measurement vectors of various combinations of states. Using a Kalman filter, the states of the target system are estimated at each node having only its local neighboring information. The network nodes cooperate locally with a packet-based communication to improve the estimation. Finally, numerical examples are provided to show the effectiveness of the scheme. The results are compared wi
In this paper, a novel fault accommodation strategy is proposed for the legged robots subject to the actuator faults including actuation bias and effective gain degradation as well as the actuator saturation. First, the combined dynamics of two coupled subsystems consisting of the dynamics of the legs subsystem and the body subsystem are developed. Then, the interaction of the robot with the environment is formulated as the contact force optimization problem with equality and inequality constraints. The desired force is obtained by a dynamic model. A robust super twisting fault estimator is proposed to precisely estimate the defective torque amplitude of the faulty actuator in finite time. Defining a novel fractional sliding surface, a frac
The problem of cooperative optimal control of multiagent systems with linear periodic continuous-time dynamics is considered. The state consensus problem is formulated as an optimal control problem in which the consensus requirement is reflected in the cost. The cost optimization of each subsystem is considered over finite horizon while the states of the agents converge to a common value, with a control signal that depends on the interactions of the neighboring subsystems. The proposed control law consists of a local and regional terms to capture local measurements and measurements due to interactions with the neighboring agents, respectively. These two terms are obtained by solving a Hamilton-Jacobi-Bellman partial differential equation. A
This paper considers the redesign control problem based on integral sliding control theory for a class of uncertain nonlinear switched systems where the primary control law is designed based on the dissipativity of the unperturbed system. Unlike the existing works, the model is considered nonlinear with different input channels and matched and unmatched perturbations. The dissipativity-based redesign strategy includes an integral sliding mode control with a common sliding surface with smooth changes in the switching instances. The sliding surface depends on the initial value of states such that the controlled system operates on the sliding mode from the initial time and the sliding dynamics are stable. Moreover, the reachabilit
In this study, a novel strategy based on the integration of differential algebraic spectral theory (DAST) and spectral Lyapunov function is presented to analyze and design a time-varying extended state observer (TESO) for a class of nonlinear systems with unknown dynamics. The simultaneous estimation of the lumped disturbance and state vectors are achieved by using a TESO based on the time-varying parallel differential (PD) eigenvalues of the observer. The observer bandwidth design is based on the combination of DAST and spectral Lyapunov function. By using this method, a systematic approach is derived to obtain the observer parameters, which improves boundedness of the observer estimation error in terms of transient and persistent performa
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