Papers by Mohammad Farrokhi
Journal of Control
In this manuscript, the laboratory inverted pendulum mounted on a cart has been controlled using ... more In this manuscript, the laboratory inverted pendulum mounted on a cart has been controlled using 2-DOF self-tuning fuzzy PID controller. The robustness of the proposed method is investigated against the uncertainties in the system's parameters and external disturbances. Moreover, the proposed method is tested against measurement noises. Stability of the proposed method is investigated using Bode diagrams in frequency domain. Performance of the 2Dof-fuzzy-PID controller is compared with the 2-DoF PID controller. The practical results indicates better performance of the proposed method.
Soft Computing
In this paper, a strategy involving the combination of optimal discrete-time sliding-mode control... more In this paper, a strategy involving the combination of optimal discrete-time sliding-mode control and recurrent neural networks is proposed for a class of uncertain discrete-time linear systems. First, a performance index based on the reaching law and the control signal is defined. Then, the constrained quadratic programming problem is formulated considering the limitations on the control signal as the static constraint. The dynamic and algebraic model of the neural network is derived based on the optimization conditions of the quadratic problem and their relationship with the projection theory. The proposed method prevents the chattering by selecting proper parameters of the twisting reaching law. The convergence of the neural network is analysed using the Lyapunov stability theory. A singular-value-based analysis is employed for robustness of the proposed method. The stability conditions of the discrete-time closedloop system is analysed by studying eigenvalues of the closed-loop matrix using the singular value approach. The performance of the proposed algorithm is assessed in simulated example in terms of chattering elimination, solution feasibility, and encountering uncertainties and is compared with the recently proposed DSMC methods in the literature.
Journal of Control, 2021
The ever-increasing expansion of automation has led to increasing the use of electric motors that... more The ever-increasing expansion of automation has led to increasing the use of electric motors that makes the main horse power of many instruments. The Switched Reluctance Motor (SRM), as a kind of synchronous motors, has many advantages and can be used instead of other motors to eliminate their problems. However, speed control of this motor is very difficult due to nonlinearities, time variant, and uncertainties. In this article, the speed control of SRM is considered by using an optimal sliding-mode controller. Using the cascade structure, the biggest defect in the SRM (i.e., the torque ripple) is reduced. By converting the first-order sliding-mode control problem to an optimization problem, and solving it in real time using projection recurrent neural network, the proposed controller produces an optimal control signal that does not have chattering, but satisfies the sliding condition. Evaluation of The proposed controller with other controller is carried out by simulation and its e...
Acquiring appropriate tools adaptable to various tasks is the most fundamental feature of the rob... more Acquiring appropriate tools adaptable to various tasks is the most fundamental feature of the robots dealing with environment. Therefore, it would be more beneficial to plan a mechanism amenable to control the robotic fingers. Since robotic fingers have completely nonlinear behavior and their modeling is associated with the difficulties arising from the factors such as friction, physical features of transmission mechanisms, and changes in hand’s orientation, adopting a model-independent method of control will be useful. In this paper, a Takagi-Sugeno-Kang (TSK) fuzzy controller, which adaptively updates its consequence parameters, is employed for position/force control of the fingertips grasping a light and soft ball. Designing in Cartesian space and being modelindependent are some of the most important advantages of this method. In the first step, force and position reference values are calculated using a predetermined stationary grasping strategy. Afterward, the performance of the...
International Journal of Adaptive Control and Signal Processing, 2018
In this article, a real-time block-oriented identification method for nonlinear multiple-input-mu... more In this article, a real-time block-oriented identification method for nonlinear multiple-input-multiple-output systems with input time delay is proposed. The proposed method uses the Wiener structure, which consists of a linear dynamic block (LDB) followed by a nonlinear static block (NSB). The LDB is described by the Laguerre filter lattice, whereas the NSB is characterized using the neural networks. Due to the online adaptation of the parameters, the proposed method can cope with the changes in the system parameters. Moreover, the convergence and bounded modeling error are shown using the Lyapunov direct method. Four practical case studies show the effectiveness of the proposed algorithm in the open-loop and closed-loop identification scenarios. The proposed method is compared with the recently published methods in the literature in terms of the modeling accuracy, parameter initialization, and required information from the system.
IFAC Proceedings Volumes, 2002
A fuzzy control design method for four-wheel-steering vehicles, using fuzzy models, is presented.... more A fuzzy control design method for four-wheel-steering vehicles, using fuzzy models, is presented. The design model is obtained from a vehicle model using fuzzy modeling approach. In the first step of the controller design, an optimal steering controller is proposed for each local model using LQR method. Then, the local controllers are combined using fuzzy rules to form a fuzzy controller. In the next step, an adaptive fuzzy controller is obtained using adaptive control law. Simulation results show the good performance of the proposed controller as compared to the nonadaptive fuzzy controllers.
This paper is concerned with the design of a hybrid state-feedback sliding-mode controller using ... more This paper is concerned with the design of a hybrid state-feedback sliding-mode controller using fuzzy logic for a multivariable laboratory process of quadruple tank system. This apparatus is set to operate in its non-minimum phase mode which is more challenging to control as compared to the minimum phase mode. In the proposed control strategy, the consequent part of the fuzzy rules consists of either a sliding-mode controller (SMC) or a state-feedback controller (SFC). The proposed method takes advantages of the fast transient response of the SMC and the zero steady-state errors in SFC. Experimental results confirm the effectiveness of the proposed method as compared to the standalone SMC and SFC methods, especially when there are uncertainties in the model of the system.
Sixth IFAC Workshop on Time Delay Systems (2006), 2006
In this paper, a new structure for teleoperated systems with time-varying delay in communication ... more In this paper, a new structure for teleoperated systems with time-varying delay in communication channel will be proposed, which provides transparency for the system. The key features of this structure are its simple design as well as the ability to analyse the stability of the closed-loop system using the property of the stable scalar functions and the small gain theorem. In the proposed structure, two local controllers will be designed, such that the transparency of the teleoperated system as well as the local stabilities is guaranteed. One local controller will be designated for position tracking of the slave system and the other one, whilst ensuring the stability of the closed-loop system in presence of time-varying delay in communication channel, performs the force tracking.
Proceedings of the 45th IEEE Conference on Decision and Control, 2006
20th Iranian Conference on Electrical Engineering (ICEE2012), 2012
This paper presents a vision-based navigation strategy for a pan and tilt platform and a mounted ... more This paper presents a vision-based navigation strategy for a pan and tilt platform and a mounted video camera as a visual sensor. For detection of objects, a suitable image processing algorithm is used. Moreover, estimation of the object position is performed using the Kalman filter as an estimator. The proposed method is implemented experimentally to a laboratory-size pan and tilt platform. Experimental results show good target tracking by the proposed method in real-time.
2006 IEEE International Conference on Engineering of Intelligent Systems
This paper presents a neuro-predictive controller for temperature control of automotive air condi... more This paper presents a neuro-predictive controller for temperature control of automotive air conditioning system. A numerical model for the automotive refrigeration cycle, which includes transient operating conditions, has been employed in simulations. In this model, which has been created from numerous laboratory tests on a typical passenger car, the vehicle is divided into two linked modules representing the air conditioning (A/C) system as well as the passenger compartment climate. Moreover, the thermal loads have been considered. This system demonstrates variable and large time delays, which is the case in reality. The simulation results show good performance of the proposed controller.
Journal of Intelligent and Robotic Systems, 2008
In this paper, a simple structure design with arbitrary motion/force scaling to control teleopera... more In this paper, a simple structure design with arbitrary motion/force scaling to control teleoperation systems, with model mismatches is presented. The goal of this paper is to achieve transparency in presence of uncertainties. The masterslave systems are approximated by linear dynamic models with perturbed parameters, which is called the model mismatch. Moreover, the time delay in communication channel with uncertainties is considered. The stability analysis will be considered for two cases: 1) stability under time delay uncertainties and 2) stability under model mismatches. For the first case, two local controllers are designed. The first controller is responsible for tracking the master commands, while the second controller is in charge of force tracking as well as guaranteeing stability of the overall closed-loop system. In the second case, an additional term will be added to the control law to provide robustness to the closed-loop system. Moreover, in this case, the local slave controller guarantees the position tracking and the local master controller guarantees stability of the inner closed-loop system. The advantages of the proposed method are two folds: 1) robust stability of the system against model mismatches is guaranteed and 2) structured system uncertainties are well compensated by applying independent controllers to the master and the slave sites. Simulation results show good performance of the proposed method in motion tracking as well force tracking in presence of model mismatches and time delay uncertainties.
Journal of Dynamic Systems, Measurement, and Control, 2008
This paper presents a simple structure design for bilateral teleoperation systems with uncertaint... more This paper presents a simple structure design for bilateral teleoperation systems with uncertainties in time delay in communication channel. The goal is to achieve complete transparency and robust stability for the closed-loop system. For transparency, two local controllers are designed for the bilateral teleoperation systems. One local controller is responsible for tracking the master commands, and the other one is in charge of force tracking as well as guaranteeing the stability of the closed-loop system in the presence of uncertainties in time delay. The stability analysis will be shown analytically for two cases: (I) the possibly stability and (II) the intrinsically stability. Moreover, in Case II, in order to generate the proper inputs for the master controller in the presence of uncertainties in time delay, an adaptive finite impulse response (FIR) filter is designed to estimate the time delay. The advantages of the proposed method are threefold: (1) stability of the closed-lo...
International Journal of Mathematical Modelling and Numerical Optimisation, 2011
This paper utilizes a class of Mesh Adaptive Direct Search method to design an optimal path for U... more This paper utilizes a class of Mesh Adaptive Direct Search method to design an optimal path for Unmanned Aerial Vehicles (UAVs). To this end, a multi-objective optimization problem is considered for simultaneous optimization of some conflicting objective functions under different kinds of vehicle and mission constraints. Since the path planning for UAVs in a large geographical area is a typical large-scale optimization problem, to avoid memory and computational intensive issues, different techniques such as constructing an adaptive mesh, polling, and barrier approach are incorporated in the proposed algorithm. The proposed method is tested under different scenarios and various realistic terrain environments. The results show effectiveness of the proposed method in guiding UAVs to the final destination by providing near-optimal feasible paths quickly and effectively. The results will also be compared with the Genetic Algorithm approach, which has been recently used for path planning.
The PID controller has been extensively used in control applications. This is mainly due to the f... more The PID controller has been extensively used in control applications. This is mainly due to the fact that despite the simple structure and ease of design of this controller, it still has some degree of robustness. In PID control method, three parameters, namely proportional, integral, and derivative, are being determined in such a way that the response of the system is satisfactory. The proportional part of the PID controller has an important role in determining the overshoot and the rise time, while the integral part reduces the steady-state error, and the derivative portion of the controller is mainly responsible for the stability of the closed-loop system and the smoothness of the response. But the major limitation of PID controller is that its response is only acceptable if the system is working around the operating point, especially when the nonlinearity of the system is complicated. Hence, there is need for more sophisticated control method [1]. Several methods have been proposed in the literature to overcome the weaknesses of the PID controller. Among these methods, there are Zeigler-Nichols PID [10], fuzzy
This paper presents identification of laboratory Twin Rotor MIMO System (TRMS) using fuzzy logic.... more This paper presents identification of laboratory Twin Rotor MIMO System (TRMS) using fuzzy logic. The TRMS is a challenging system to control since it is a non-minimum phase system and is a laboratory bench mark system for air vehicles like helicopters. This system has two degrees of freedom with strong cross-coupling between the vertical and horizontal axes. For optimal tuning of the fuzzy system parameters, the gradient descent algorithm is employed in this paper. In order to reduce the computation complexity and at the same time to increase robustness of the fuzzy model, the online learning method is used here. Experimental results show effectiveness of the proposed approach.
This paper presents a direct adaptive output feedback control design method for uncertain non-aff... more This paper presents a direct adaptive output feedback control design method for uncertain non-affine nonlinear systems, which does not rely on state estimation. The approach is applicable to systems with unknown, but bounded dimensions and with known relative degree. A neural network is employed to approximate and adaptively make ineffective unknown plant nonlinearities. An adaptive control law for the weights in the hidden layer and the output layer of the neural network are also established so that the entire closed-loop system is stable in the sense of Lyapunov. Moreover, the tracking error is guaranteed to be uniformly and asymptotically stable, rather than uniformly ultimately bounded with the aid of an additional adaptive robustifying control part. The proposed control algorithm is relatively strightforward and no restrictive conditions on the design parameters for achieving the systems stability are required. The efficiency of the proposed scheme is shown through the simulation of a non-affine nonlinear system with unmodelled dynamics.
In this paper, the dynamic equations and error reduction of 2DOF gimbal gyros are investigated. O... more In this paper, the dynamic equations and error reduction of 2DOF gimbal gyros are investigated. One of the major error sources in such gyros is the gimbal lock, which causes major errors and losing one degree of freedom. This error source is eliminated in this paper using a permanent magnet motor as the torquer. Moreover, using an LQG/LTR controller will guarantee the closed-loop system stability. In addition, effects of other error sources such as the drift, the measurement noise and the nutation are eliminated or reduced. Using the proposed method, one can easily measure the output angular rates using multiplication of the measured input voltage of the torquer and the system scale factor.
In this paper, an intelligent adaptive controller is designed to position the yaw and pitch angle... more In this paper, an intelligent adaptive controller is designed to position the yaw and pitch angles of a twin rotor MIMO system (TRMS) in two degrees of freedom, based on fuzzy logic. The control objective is to make the TRMS move quickly and accurately to the desired attitudes. Gradient descent algorithm has been used for updating parameters of fuzzy controller in order to increase its robustness against external disturbances and changes of system parameters. Experimental results is compared with the PID controller to show the effectiveness of the proposed method, especially when it encounters system uncertainties and external disturbances.
Sliding Mode Control (SMC) is a powerful approach to solve the tracking problem for dynamic syste... more Sliding Mode Control (SMC) is a powerful approach to solve the tracking problem for dynamic systems with uncertainties. However, the traditional SMCs introduce actuator chattering phenomenon which performs a desirable behavior in many physical systems such as servo control and robotic systems, particularly, when the zero steady state error is required. Many methods have been proposed to eliminate chattering from SMCs which use a finite DC gain controller. Although these methods provide a free chattering control but they only deal with the steady state error and are not able to reject input disturbances. This paper presents a fuzzy combined control (FCC) using appropriate PID and SMCs which presents infinite DC gain. The proposed FCC is a free chattering control which guarantees a zero steady state error and rejects the disturbances. The stability of the closed loop system with the proposed FCC is also proved using Lyapunov stability theorem. The proposed FCC is applied to a two degree of freedom robot manipulator to illustrate effectiveness of the proposed scheme.
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Papers by Mohammad Farrokhi