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2012, International Journal of Advanced Robotic Systems
This paper deals with experimental comparison between stable adaptive controllers of robotic manipulators based on Model Based Adaptive, Neural Network and Wavelet -Based control. The above control methods were compared with each other in terms of computational efficiency, need for accurate mathematical model of the manipulator and tracking performances. An original management algorithm of the Wavelet Network control scheme has been designed, with the aim of constructing the net automatically during the trajectory tracking, without the need to tune it to the trajectory itself. Experimental tests, carried out on a planar two link manipulator, show that the Wavelet-Based control scheme, with the new management algorithm, outperforms the conventional Model-Based schemes in the presence of structural uncertainties in the mathematical model of the robot, without pre-training and more efficiently than the Neural Network approach.
Proceedings of the Fourth International Conference on Informatics in Control, Automation and Robotics, 2007
This paper deals with the synthesis of a Wavelet Neural Network adaptive controller for a class of second order systems. Due to its fast convergence, the wavelet neural network is used to approximate the unknown system dynamics. The proposed approximator will be on-line adjusted according to the adaptation laws deduced from the stability analysis. To ensure the robustness of the closed loop system, a modified sliding mode control signal is used. In this work, variable sliding surface is considered to reduce the starting energy without deteriorating the tracking performances. Furthermore, the knowledge of the upper bounds of both the external disturbances and the approximation errors is not needed. The global stability of the closed loop system is guaranteed in the sense of Lyapunov. Finally, a simulation example is presented to illustrate the efficiency of the developed approach.
IEEE Transactions on Magnetics, 2005
We propose an adaptive wavelet neural network (AWNN) control system to control the position of the mover of a permanent-magnet linear synchronous motor (PMLSM) servo drive system to track periodic reference trajectories. The AWNN control system, uses a wavelet neural network (WNN) with accurate approximation capability to represent the unknown dynamics of the PMLSM. It also uses a robust term to confront the inevitable approximation errors due to the finite number of wavelet basis functions and to disturbances, including the friction force. An adaptive learning algorithm that learns the parameters of weight, dilation, and translation of the WNN on line is based on the Lyapunov stability theorem. To relax the requirement for the bound of uncertainty in the robust term, which comprises a minimum approximation error, optimal parameter vectors, higher order terms in Taylor series, and friction force, an adaptive bound estimation law is used; in the estimation, a simple adaptive algorithm estimates the bound of uncertainty. Our simulated and experimental results for periodic reference trajectories show that the dynamic behavior of the proposed control system is robust with regard to uncertainties.
Journal of Intelligent and Robotic Systems, 1996
Neural network based adaptive controllers have been shown to achieve much improved accuracy compared with traditional adaptive controllers when applied to trajectory tracking in robot manipulators. This paper describes a new Recursive Prediction Error technique for estimating network parameters which is more computationally efficient. Results show that this neural controller suppresses disturbances accurately and achieves very small errors between commanded and actual trajectories.
International Journal of Modelling, Identification and Control, 2011
This paper deals with the synthesis of an adaptive fuzzy wavelet network (FWN) controller for an nth order multi input multi output (MIMO) non-linear system suffering from parameters uncertainties and subjected to external perturbation. The proposed approach allows combining the advantages of the fuzzy logic system and those of wavelet networks to approximate quickly the unknown system dynamics with neither a prior knowledge about such dynamics nor offline learning phase. The FWN is adjusted online using some adaptation laws deduced from the stability analysis which guarantees a non-singular control action. Furthermore, the robustness of the proposed method is improved such that the knowledge of the upper bounds of both the external disturbances and the approximation errors is not required. Moreover, a variable sliding mode control (VSMC) technique is proposed to reduce the starting energy, caused by the presence of approximations errors and external disturbances, without deteriorating the tracking performances. To ensure the robustness of the overall closed loop system, analytical demonstration using Lyapunov theorem is considered. Finally, a numerical example is presented to validate our approach and to show the fast convergence, good tracking and the robustness of the closed loop system.
This Paper investigates the mean to design the reduced order observer and observer based controllers for a class of uncertain nonlinear system using reinforcement learning. A new design approach of wavelet based adaptive reduced order observer is proposed. The proposed wavelet adaptive reduced order observer performs the task of identification of unknown system dynamics in addition to the reconstruction of states of the system. Reinforcement learning is used via two wavelet neural networks (WNN), critic WNN and action WNN, which are combined to form an adaptive WNN controller. The “strategic” utility function is approximated by the critic WNN and is minimized by the action WNN. Owing to their superior learning capabilities, wavelet networks are employed in this work for the purpose of identification of unknown system dynamics. Using the feedback control, based on reconstructed states, the behavior of closed loop system is investigated. By Lyapunov approach, the uniformly ultimate boundedness of the closed-loop tracking error is verified. A numerical example is provided to verify the effectiveness of theoretical development.
IEEE Conference on Decision and Control and European Control Conference, 2011
In this paper, a wavelet-based neural network is proposed for the control of nonlinear systems. Activation functions of neural network nodes are determined based on the wavelet transform. The controller can efficiently compensate for the undesired effects of hard nonlinearities such as saturation and/or dead zone of control input. Compared with standard neuro-controllers, the structure of the controller is definite and simple. The proposed controller is localizable and has a systematically chosen structure, which improves the closeloop performance. An off-line algorithm determines the number of nodes. In addition, an on-line algorithm adjusts the parameters of wavelet bases and network weights. Back propagation algorithm with a momentum term is used for updating the weights and parameters of activation functions. This controller reduces the quantity of network parameters, calculation cost and convergence time of online algorithms with respect to the conventional neural network. Also, the controller is able to control unstable and MIMO systems. To illustrate the capability and performance superiority of the proposed controller, two nonlinear systems are controlled and the corresponding results are compared.
—Robot manipulators have become major component of manufacturing industries due to he advantages associated with them like high speed, accuracy and repeata-bility.Two link robot manipulator is a very basic classical and simple example of robot followed in understanding of basic fundamentals of robotic manipulator. Due to uncertainties and non-linearities involved in its behavior, it is a challenging task to control their motion. This paper focuses mainly on the control of robot manipulator by employing design of various controllers like the PD controller, computed torque controller, adaptive controller and a robust adaptive controller. Their design and their performances are compared in extensive simulations carried out in MATLAB/Simulink.
IEEE Transactions on Robotics and Automation, 1990
This paper presents algorithms for continuous-time direct adaptive control of robot manipulatord. Lyapunov theory ig used for controller design and stability investigaüion. Algorithms for rapid continuous-time adaptive control are presented. Key wotdls Adaptive control, Lyapunov stabilit¡ Zz-stabilit¡ Robot control, Rapid parameter estimation. Classifrcatíon systcrn and/or índcx t*ms (if urry) Supplcmentary b íblío gaphícal ínforznat íon ISSN and kcy titlc ISBN Languagc English Numbc¡ of pageø 19 Rccipient'c noúcs Sccurity c lassifrcat io n The rcpofi mzy bc o¡dcrcd frorlrt thc Department of Automatìc Cont¡ol ot bo¡towed through the tJnivcrsity Líbrary 2, Box 107A, 5-227 Og Lund, Swedcn, Telex: 33248 lubbìs lund.
A desired compensation adaptive law-based neural network (DCAL-NN) controller is proposed for the robust position control of rigid-link robots. The NN is used to approximate a highly nonlinear function. The controller can guarantee the global asymptotic stability of tracking errors and boundedness of NN weights. In addition, the NN weights here are tuned on-line, with no off-line learning phase required. When compared with standard adaptive robot controllers, we do not require linearity in the parameters, or lengthy and tedious preliminary analysis to determine a regression matrix. The controller can be regarded as a universal reusable controller because the same controller can be applied to any type of rigid robots without any modifications. A comparative simulation study with different robust and adaptive controllers is included.
Industrial Robot: the international journal of robotics research and application, 2020
Purpose This paper aims to propose an innovative adaptive control method for lower-limb rehabilitation robots. Design/methodology/approach Despite carrying out various studies on the subject of rehabilitation robots, the flexibility and stability of the closed-loop control system is still a challenging problem. In the proposed method, surface electromyography (sEMG) and human force-based dual closed-loop control strategy is designed to adaptively control the rehabilitation robots. A motion analysis of human lower limbs is performed by using a wavelet neural network (WNN) to obtain the desired trajectory of patients. In the outer loop, the reference trajectory of the robot is modified by a variable impedance controller (VIC) on the basis of the sEMG and human force. Thenceforward, in the inner loop, a model reference adaptive controller with parameter updating laws based on the Lyapunov stability theory forces the rehabilitation robot to track the reference trajectory. Findings The e...
International Journal of Adaptive Control and Signal Processing, 2018
In this paper, the problem of simultaneous identification and predictive control of nonlinear dynamical systems using self-recurrent wavelet neural network (SRWNN) is addressed. The structure of the SRWNN is a modification of the wavelet neural network (WNN). Unlike WNN, the neurons present in the hidden layer of SRWNN contain the weighted self-feedback loops. Dynamic back-propagation algorithm is employed to derive the necessary parameter update equations. To further improve the convergence speed of the parameters, a time-varying (adaptive) learning rate is used. Four simulation examples are considered for testing the effectiveness of the proposed method. Furthermore, some disturbance rejection tests are also performed on the proposed method. The results obtained through the simulation study confirm the effectiveness of the proposed method.
This paper proposes an observer based adaptive tracking control strategy for a class of uncertain nonlinear systems with delay in state as well as in input. Self recurrent wavelet neural network (SRWNN) is used to approximate the uncertainties present in the system as well as to identify and compensate the dynamic nonlinearities. The architecture of the SRWNN is a modified model of the wavelet neural network (WNN). However, unlike WNN, since a mother wavelet layer of the SRWNN is composed of self feedback neurons, the SRWNN can store the past information of wavelets. In addition robust control terms are also designed to attenuate the approximation error due to SRWNN. Adaptation laws are developed for the online tuning of the wavelet parameters and the stability of the overall system is assured by using the Lyapunov- Krasovskii functional. Finally some simulations are performed to verify the effectiveness and performance of the proposed control scheme.
A. desired compensation adaptive law-- neural network (DCAL-NN) controller is proposed for the robust position control of rigid-link robots. The NN is used to approximate a highly nonlinear function. The controller can guarantee the &&& asymptotic stability of tracking emrs and boundedness of NN weights. In w. addition, the NN weights here are tuned on-line, with When compared with standard adaptive robot controllers, we do not require persistent excitation conditions, linearity in the parameters, or lengthy and tedious preliminary analysis to determine a regression matrix. The controller can be same controller can be applied to any type of rigid robots wirhout any msififications.
This Paper investigates the mean to design the reduced-order observer and observer-based controllers for a class of uncertain nonlinear systems. A new design approach of wavelet-based adaptive reduced-order observer is proposed. The proposed wavelet adaptive reduced-order observer performs the task of identification of unknown system dynamics in addition to the reconstruction of states of the system. Owing to their superior learning capabilities, wavelet networks are employed in this work for the purpose of identification of unknown system dynamics. Using the feedback control, based on reconstructed states, the behavior of closed-loop system is investigated. A numerical example is provided to verify the effectiveness of theoretical development.
2009 IEEE International Conference on Systems, Man and Cybernetics, 2009
Wavelet neural network based on sampling theory has been found to have a good performance in function approximation. In this paper, this type of wavelet neural network is applied to modeling and control of a nonlinear dynamic system and some methods are employed to optimize the structure of wavelet neural network to prevent a large number of nodes. The direct inverse control technique is employed for investigating the ability of this network in control application. A variety of simulations are conducted for demonstrating the performance of the direct inverse control using wavelet neural network. The performance of this approach is compared with direct inverse control using multilayer perceptron neural network (MLP). Simulation results show that our proposed method reveals better stability and performance in reference tracking and control action. Keywords-wavelet, wavelet neural network, sampling theory, direct inverse control, nonlinear dynamic control I.
This paper introduces an adaptive fuzzy-neural control (AFNC) utilizing sliding mode-based learning algorithm (SMBLA) for robot manipulator to track the desired trajectory. A traditional sliding mode controller is applied to ensure the asymptotic stability of the system, and the fuzzy rule-based wavelet neural networks (FWNNs) are employed as the feedback controllers. Additionally, a novel adaptation of the FWNNs parameters is derived from the SMBLA in the Lyapunov stability theorem. Hence, the AFNC approximates parameter variation, unmodeled dynamics, and unknown disturbances without the detailed knowledge of robot manipulator, while resulting in an improved tracking performance. Lastly, in order to validate the effectiveness of the proposed approach, the comparative simulation results of two-degrees of freedom robot manipulator are presented. Keywords – traditional sliding mode control (TSMC), adaptive fuzzy neural control (AFNC), fuzzy rule-based wavelet neural network (FWNN), sliding mode-based learning algorithm (SMBLA), degrees of freedom robot manipulator (DOFRM)
1995
In this paper, an adaptive controller for robot manipulators which uses neural networks is presented. The proposed control scheme is based on PD feedback plus a feedforward compensation of full robot dynamics. The feedforward signal is obtained by summing up the weighted outputs of a set of fixed multilayer neural nets. The controller is adaptive to robot dynamics and payload uncertainties. A stability analysis which takes into account neural network learning errors is included. Simulation results showing the feasibility and performance of the approach are given.
Control Theory and …, 1996
Abstract: The paper is concerned with the design of a hybrid controller structure, consisting of the adaptive contrul law and a neural-network-based learning scheme for adaptation of time-varying controller parameters. The target error vector for weight adaptation of the ...
IFAC Proceedings Volumes, 1995
This paper presents an approach to feedback adaptive motion control of robot manipulators based on neural networks. The controller includes a set of trained neural networks and an update law to adjust robot dynamics and payload uncertain parameters. The controller is robust to neural networks learning errors using a sign or saturation switching function in the control law. A global stability analysis is given, as well as simulation results to show the practical feasibility and perfonnance for the robust adaptive controller are given.
Mathematical Problems in Engineering, 2015
A decentralized recurrent wavelet first-order neural network (RWFONN) structure is presented. The use of a wavelet Morlet activation function allows proposing a neural structure in continuous time of a single layer and a single neuron in order to identify online in a series-parallel configuration, using the filtered error (FE) training algorithm, the dynamics behavior of each joint for a two-degree-of-freedom (DOF) vertical robot manipulator, whose parameters such as friction and inertia are unknown. Based on the RWFONN subsystem, a decentralized neural controller is designed via backstepping approach. The performance of the decentralized wavelet neural controller is validated via real-time results.
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