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Parameter uncertainties in the electromechanical actuator system and the obvious friction nonlinearity in the low speed stage will greatly deteriorate the control performance and even lead to system instability. In this paper, an adaptive super-twisting sliding mode controller with neural network (ASTSMNNC) is proposed for the electromechanical actuator system. The LuGre model is used to describe the nonlinear friction, a nonlinear dual-observer is designed to observe the LuGre model internal friction state, a parameter adaptive law is designed to estimate the unknown parameters existing in the system, the time-varying disturbance in the system is estimated by using the universal approximation property of neural network. The feedforward compensation technology is used to compensate the estimated errors of parameters and the observed error of disturbance, the second-order nonlinear sliding mode is designed to compensate the residual estimated errors of parameters and neural network, and the chattering phenomenon caused by the sliding mode control can be reduced at the same time. What's more, the controller theoretically guarantees a prescribed tracking performance in the presence of various uncertainties, which is very important for high-accuracy control of motion systems. Lyapunov stability theorem is used to prove that the proposed controller can achieve the bounded stability of the system. Extensive comparative experimental results are obtained to verify the high-performance nature of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This article focuses on the asymptotic tracking control problem for uncertain nonlinear systems subject to both multiple disturbances and parametric uncertainties. To address this issue, a parameter adaptation law is synthesized to deal with the parametric uncertainties, and an adaptive-gain disturbance estimator (ADE) is constructed to estimate the mismatched and matched disturbances, and compensate them in feedforward channels, which eliminates the impact of disturbances on tracking performance. Meanwhile, an updated law for estimator gain driven by the estimation errors is utilized in the ADE when facing unknown upper bounds of disturbances, which reduces the conservatism of estimator gain selection and is beneficial to practical implementation. Based on the parameter adaption technique and the presented ADE approach, a composite controller is proposed to ensure an excellent asymptotic output tracking performance. The stability analysis shows the proposed controller can attain asymptotic tracking performance in the presence of both time-variant disturbances and parametric uncertainties. Comparative simulation results of the application to a robot manipulator reveal the validity of the developed approach. [ABSTRACT FROM AUTHOR]

Traditional control methods for precise motion control of electro-hydraulic servo systems are primarily based on rigid-body dynamics of the system. Considering that structural flexibility of the mechanical components have a certain impact on all drive systems, the neglected high-frequency dynamics caused by structural flexibility have become one of the major obstacles when developing better control performance. In this paper, a high-accuracy tracking control is concerned for hydraulic actuators with unmodeled flexible dynamics. Firstly, a damping term is utilized to counterweigh the unmodeled nonlinear flexible function and a dynamic signal is designed to control the dynamic flexible disturbance. Then, in order to process parametric uncertainties along with unmodeled flexible dynamics, an adaptive backstepping controller is proposed. The controller theoretically guarantees global bounded tracking performance via Lyapunov analysis. The experimental and simulation results illustrate the high-performance nature of the proposed controller. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive robust controller with uniform robust exact differentiator has been proposed for a class of nonlinear systems with structured and unstructured uncertainties. The adaptive robust controller is integrated with an uniform robust differentiator to handle the problem of the incalculable part of the derivative of virtual controls and the differential explosion happened in backstepping techniques. The stability of the closed loop system is demonstrated via Lyapunov method ensuring a prescribed transient and tracking performance. Simulation and experimental results are carried out to verify the advantages of the proposed method. [ABSTRACT FROM AUTHOR]

Internal leakage is a typical fault in the hydraulic systems, which may be caused by seal damage, and result in deteriorated performance of the system. To study this issue, this article carries out an experimental investigation of artificial neural network–based detection method for internal leakage fault. A period of pressure signal at one chamber of the actuator was taken in response to sinusoidal-like inputs for the closed-loop controlled system as a basic signal unit, and totally, 1000 periodic signal units are obtained from the experiments. The above experimental measurements are repetitively implemented with 11 different active exerted internal leakage levels, that is, totally 11,000 basic signal units are obtained. For signal processing, the pressure signal in the operation condition without active exerted leakage is chosen to generate a baseline with suitable pre-proceed, and the relative values of the other basic signal units (D-value between the baseline and other original signals) act as the global samples of the following artificial neural networks, traditional back propagation neural network, deep neural network, convolution neural network and auto-encoder neural network, separately; 8800 samples by random extraction as train samples to train the above neural networks and the other samples different from the train samples act as test samples to examine the detection accuracy of the proposed method. It is shown that the deep neural network with five layers can obtain a best detection accuracy (92.23%) of the above-mentioned neural networks. In addition, the methods based on wavelet transform and Hilbert–Huang transform are also applied, and a comparison of these methods is provided at last. From the comparison, it is shown that the proposed detection method obtains a good result without a need to model the internal leakage or a complicated signal processing. [ABSTRACT FROM AUTHOR]

In this paper, adaptive compensation with a robust integral of the sign of the extended error (RISEE) feedback is developed for high precise tracking control of systems in the presence of simultaneous structured and unstructured uncertainties. To handle various uncertainties existing in the system in one controller, we propose an adaptive RISEE controller (ARISEE), in which an adaptive law based on the improved discontinuous projection method is synthesized to handle parametric uncertainties and the RISEE robust term to attenuate unmodelled disturbances. Moreover, the present controller does not need a priori knowledge on the bounds of the lumped disturbances and the gain of the designed robust control law can itself be tuned. The major feature of the proposed controller is that it can theoretically guarantee global asymptotic tracking performance with a continuous control input, in the presence of parametric uncertainties and unmodelled disturbances via Lyapunov analysis. Comparative numerical results verify the effectiveness of the proposed non-linear controller. [ABSTRACT FROM AUTHOR]

This paper focuses on the problem of tracking control of a chain of integrator nonlinear systems with input constraint and hysteresis nonlinearity. Input constraint, always existing in physical systems, has been proved a source of performance degradation. To handle this issue, an effective hyperbolic saturation function is employed, which is bounded no matter how the disturbances and error signals change. Furthermore, hysteresis nonlinearity, which may also limit the system performance, is modelled as a combination of a linear term with constant slope and a bounded disturbance term, which makes it possible to be integrated in the model based controller design. The robust integral of the sign of error (RISE) control is synthesized to guarantee the asymptotic tracking performance in the presence of parametric uncertainties and unmodelled nonlinearities such as external disturbances and unmodelled hysteresis nonlinearity. The closed-loop stability is proved via Lyapunov analysis. Some simulations are carried out to verify the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

In this article, a practical method named feedback nonlinear robust control with disturbance compensation is proposed for a hydraulic system with matched and mismatched generalized uncertainties (e.g. parameter derivations, external disturbances, modeled errors and/or unmodeled dynamics), in which a finite-time disturbance observer and a nonlinear robust controller are integrated together by backstepping method. The finite-time disturbance observer is used to estimate matched and mismatched generalized uncertainties. The design of the nonlinear robust controller is to make the closed-loop system stable. Not only the nonlinearities (e.g. nonlinear flow features of servo-valve) but also matched and mismatched generalized uncertainties are considered by the proposed controller. Furthermore, asymptotic output tracking performance after a time T0 is theoretically ensured by the proposed controller. The high-performance nature of the proposed control strategy is verified by extensive comparative experimental results. [ABSTRACT FROM AUTHOR]

This article concerns the high dynamic tracking control of hydraulic servo systems. Unlike previous works usually dealing with high-accuracy tracking control, the proposed feedback linearization controller in this article guarantees excellent tracking performance even with high-frequency tracking demand. To handle unmatched disturbances in hydraulic systems, backstepping method is synthesized in the proposed controller. Typically, in the hydraulic systems, there also exist direct-current unmodeled disturbances which may lead to steady-state errors. An integral-like feedback term is added in the controller to cancel this unexpected effect. The stability of the closed-loop system is guaranteed via frequency-domain analysis. Three controllers, that is, the proportional–integral controller, the proportional–integral controller with velocity feed-forward scheme and the proposed feedback linearization controller, are compared. Extensive comparative experimental results demonstrate the high dynamic tracking performance of the proposed control strategy. [ABSTRACT FROM AUTHOR]