Dead-zone Effect Research Articles

Observer-based adaptive neural optimal control for discrete-time systems in nonstrict-feedback form

This paper considers the problem of observer-based adaptive near-optimal control for a class of nonstrict-feedback discrete-time nonlinear systems with non-symmetric dead zone. In order to compensate the effect of dead-zone on the control performance, an adaptive auxiliary signal is constructed to estimate the unknown dead-zone parameters. For the unknown nonlinear functions, neural networks (NNs) are introduced to identify them and to estimate the unknown parameters. To resolve the difficulty resulting from the unavailable state variables, an NN-based observer is designed. Moreover, according to the framework of adaptive control, a novel reinforcement learning algorithm is developed to guarantee that the near-optimal control performance is achieved. Finally, some simulation results are provided to illustrate the effectiveness of the proposed control algorithm.

Adaptive Finite-Time Control of Nonlinear Quantized Systems With Actuator Dead-Zone

This paper investigates a finite-time control problem of nonlinear quantized systems with actuator dead-zone in a non-strict feedback form. By combining a simplified dead-zone model and the sector-bound characteristic of a hysteretic quantizer, the control difficulties caused by the coexistence of unknown actuator dead-zone and control signal quantization effect are overcome. By applying the approximation ability of neural network systems, an novel neural adaptive controller is constructed, which can compensate the unknown control gain. The designed neural controller can ensure the transient performance of nonlinear quantized systems with actuator dead-zone in finite-time. Based on the Bhat and Bernstein theorem, the finite-time stability of system is proved. Finally, a numerical example is given to verify the validity of the proposed approach.

Modeling and Two-Input Sliding Mode Control of Rotary Traveling Wave Ultrasonic Motors

Traveling wave ultrasonic motors are actuators relying on piezoelectric ceramics that combine many advantageous features, such as high stalling torque, fast response, compactness, and magnetic resonance compatibility. However, they suffer from nonlinear dynamics, load-dependent dead zones, and the difficulty to control low speeds. In this paper, we present a novel second-order model for traveling wave ultrasonic motors. It is based on a dry friction driving principle and features dead zone effects. Based on the model, a two-input sliding mode controller is designed. It controls both phase difference and frequency of the traveling wave, without the necessity of implementing a signum function. With this controller, the state-of-the-art is extended to the position control case, while at the same time using fine-grained phase difference control for low velocities. Moreover, we show global uniform asymptotic stability for bounded disturbances and that velocity jumps do not appear when the control domains of phase difference and frequency are switched. Finally, both the model and the controller are evaluated via simulations and experiments that include the response to a position step input under various opposing torques.

Equal channel angular extrusion of semicircular AA 5083 covered with copper casing

The microstructural evolution and mechanical behaviour of semicircular AA 5083 billets subjected to equal channel angular extrusion (ECAE), without and with copper casing (CC), are investigated in this work. The semicircular billets, circumferentially covered with and without CC, are extruded up to three passes in route A at room temperature. Even the coarse grain structure of the initial material is significantly refined, the microcracks and the structural defects were observed in the billets extruded without CC due to non-uniform strain distribution. The use of CC on the circumference of the semicircular billets reduces the dead zone effect on the structural homogeneity and minimises the formation of microcracks on the outer periphery of the extruded material. The uniform distribution of the effective strain imposed on the billets ECAE’d with CC enhances the development of equi-axed ultrafine grains at low pressing loads. The newly formed ultrafine grains with a size of few hundreds of nanometres significantly increase the mechanical properties of the ECAE’d AA 5083 with the CC. The obtained results were in good agreement with the earlier reports in which ECAE was carried with back pressure arrangement.

Design and Analysis for Uncertain Repetitive Control Systems With Unknown Disturbances

In this paper, the periodic tracking problem is considered for a class of continuous system with uncertainty, time-varying delay, and unknown bounded external disturbances. To be precise, in order to attenuate the unknown disturbance effectively, the equivalent-input-disturbance (EID) approach is incorporated into the developed algorithm. Then, the sufficient conditions that guarantee the asymptotic tracking performance of the system understudy are established based on the Lyapunov stability theorem. More precisely, Schur complement and free-weighting matrix approach are utilized to derive the main results. Moreover, the proposed EID-based modified repetitive controller (MRC) not only rejects the unknown external disturbance but also deals with the dead zone effect. Finally, two simulation examples are presented to verify the superiority of the proposed EID-based repetitive controller over the conventional repetitive controller.

Equal Channel Angular Extrusion of AA 5083

Equal Channel Angular Extrusion (ECAE) is used as a top down process to produce bulk nano/ultrafine grain structured materials by inducing high amount of strain with less experimental set up. In the present study AA 5083 alloy with circular and square cross sections are extruded at room temperature using two dies having cannels with circular and square cross sections respectively. Both the dies used in this study are having same channel angle (Φ)1200and outer corner angle (Ψ) 200. The circular and square billets are extruded for four times in route BC. The objective of this work is to study the effect of cross section of the billet, number of passes on grain refinement, mechanical properties and wear behaviour of AA 5083. Significant reduction in grain size is observed in extruded material using Field Emission Scanning Electron Microscope (FE-SEM) in the range of 80nm to 600nm after four passes. The microhardness in extruded materials is improved with no. of passes in both cross sectioned billets and it is more predominant for square billets even after two passes. The effect of dead zone is less in case of square billets and hence they have shown more structural homogeneity. The dry sliding wear tests are conducted to study the wear behaviour of the ECAEd materials. It is observed that the wear rate and coefficient of friction are reduced with number of passes in both the cases and rate of decrease is more in case of square billets.

Adaptive backstepping control for air-breathing hypersonic vehicles with input nonlinearities

This paper addresses the control problem of air-breathing hypersonic vehicles subject to input nonlinearities, aerodynamic uncertainties and flexible modes. An adaptive backstepping controller and a dynamic inverse controller are developed for the altitude subsystem and the velocity subsystem, respectively, where the former eliminates the problem of “explosion of terms” inherent in backstepping control. Moreover, a modified smooth inverse of the dead-zone is proposed to compensate for the dead-zone effects and reduce the computational burden. Based on this smooth inverse, an input nonlinear pre-compensator is designed to handle input saturation and dead-zone nonlinearities, which leads to a simpler control design for the altitude subsystem subject to these two input nonlinearities. It is proved that the proposed controllers can guarantee that all closed-loop signals are bounded and the tracking errors converge to an arbitrarily small residual set. Simulation results are carried out to demonstrate the effectiveness of the proposed control scheme.

Adaptive Neural Network Control for Robotic Manipulators With Unknown Deadzone.

This paper addresses the problem of robotic manipulators with unknown deadzone. In order to tackle the uncertainty and the unknown deadzone effect, we introduce adaptive neural network (NN) control for robotic manipulators. State-feedback control is introduced first and a high-gain observer is then designed to make the proposed control scheme more practical. One radial basis function NN (RBFNN) is used to tackle the deadzone effect, and the other RBFNN is also proposed to estimate the unknown dynamics of robot. The proposed control is then verified on a two-joint rigid manipulator via numerical simulations and experiments.

Adaptive neural network control of a flexible string system with non-symmetric dead-zone and output constraint

Abstract This study is concerned with adaptive neural network control for a vibrating flexible string system under the influence of non-symmetric input dead-zone, output constraint and system uncertainties. First, the backstepping method is incorporated into the context of boundary control scheme and the barrier Lyapunov function is exploited to ensure the output constraints are never transgressed. Subsequently, an adaptive neural network control is developed to globally stabilize the string system and compensate for the effect of the input dead-zone. Besides, the online updating laws are introduced to compensate for the uncertainties of the system and the σ-modification is adopted to adjust the robustness of the system. Under the proposed control, the bounded stability of the closed-loop system is proven based on Lyapunov functions without simplifying or discretizing the infinite-dimensional dynamics. Finally, simulation results are presented for control performance verification.

Effect of Optical Microcavity on Absorption Behavior of Homo-Tandem Organic Solar Cells**Supported by the National Natural Science Foundation of China under Grant No 61565015, and the Western Light Talent Training Program of Chinese Academy of Sciences.

The optical microcavity effect of the homo-tandem solar cells is explored utilizing the transfer matrix method. Ultrathin silver can reduce the deadzone effect compared with graphene and PH1000, and leads to a factor of 1.07 enhancement for an electrical field in a metal microcavity. The enhancement is considered to be the fact that strong exciton-photon coupling occurs in the microcavity due to ultrathin Ag. On the basis of the optical enhancement effect, optical behaviors are manipulated by varying the microcavity length. It is confirmed that ultrathin silver can serve as an ideal interconnection layer as the active layer is ∼150 nm thick and the thickness ratio between front and rear active layers lies between 1:1 and 1:2.

Neural network based boundary control of a vibrating string system with input deadzone

Abstract In this paper, a boundary control scheme is developed for a vibrating flexible string system subject to input deadzone and external disturbance. First, a basic boundary control scheme is proposed to suppress the string’s vibration based on the backstepping method. Subsequently, a radial basis function neural network (RBFNN) is utilized to handle the effect of the input deadzone and a disturbance observer is exploited to track the external disturbance. Under the proposed control, the uniformly ultimately bounded stability of the closed loop system is achieved through rigorous Lyapunov analysis without any discretization or simplification of the dynamics in the time and space. Finally, simulation results are demonstrated for control performance verification.

Late Cretaceous climate simulations with different CO2 levels and subarctic gateway configurations: A model‐data comparison

AbstractWe investigate the impact of different CO2 levels and different subarctic gateway configurations on the surface temperatures during the latest Cretaceous using the Earth System Model COSMOS. The simulated temperatures are compared with the surface temperature reconstructions based on a recent compilation of the latest Cretaceous proxies. In our numerical experiments, the CO2 level ranges from 1 to 6 times the preindustrial (PI) CO2 level of 280 ppm. On a global scale, the most reasonable match between modeling and proxy data is obtained for the experiments with 3 to 5 × PI CO2 concentrations. However, the simulated low‐ (high‐) latitude temperatures are too high (low) as compared to the proxy data. The moderate CO2 levels scenarios might be more realistic, if we take into account proxy data and the dead zone effect criterion. Furthermore, we test if the model‐data discrepancies can be caused by too simplistic proxy‐data interpretations. This is distinctly seen at high latitudes, where most proxies are biased toward summer temperatures. Additional sensitivity experiments with different ocean gateway configurations and constant CO2 level indicate only minor surface temperatures changes (<~1°C) on a global scale, with higher values (up to ~8°C) on a regional scale. These findings imply that modeled and reconstructed temperature gradients are to a large degree only qualitatively comparable, providing challenges for the interpretation of proxy data and/or model sensitivity. With respect to the latter, our results suggest that an assessment of greenhouse worlds is best constrained by temperatures in the midlatitudes.

Robust adaptive precision motion control of hydraulic actuators with valve dead-zone compensation

This paper addresses the high performance motion control of hydraulic actuators with parametric uncertainties, unmodeled disturbances and unknown valve dead-zone. By constructing a smooth dead-zone inverse, a robust adaptive controller is proposed via backstepping method, in which adaptive law is synthesized to deal with parametric uncertainties and a continuous nonlinear robust control law to suppress unmodeled disturbances. Since the unknown dead-zone parameters can be estimated by adaptive law and then the effect of dead-zone can be compensated effectively via inverse operation, improved tracking performance can be expected. In addition, the disturbance upper bounds can also be updated online by adaptive laws, which increases the controller operability in practice. The Lyapunov based stability analysis shows that excellent asymptotic output tracking with zero steady-state error can be achieved by the developed controller even in the presence of unmodeled disturbance and unknown valve dead-zone. Finally, the proposed control strategy is experimentally tested on a servovalve controlled hydraulic actuation system subjected to an artificial valve dead-zone. Comparative experimental results are obtained to illustrate the effectiveness of the proposed control scheme.

Deadzone compensation based boundary control of a flexible aerial refueling hose with output constraint

In this paper, boundary control schemes are designed for a flexible aerial refueling hose subject to input deadzone, output constraint and external disturbances, based on partial differential equations (PDEs). Firstly, a basic boundary control scheme, based on the backstepping method, is proposed to regulate the hose’s vibration. A radial basis function (RBF) neural network is used to handle the effect of the input deadzone. Then we propose a new controller based on a barrier Lyapunov function to prevent constraint violation. It is shown that the states of the system are proven to converge to a small neighborhood of zero, and the output constraint is not violated in the presence of the input deadzone and external distrubances. Finally, simulation results are demonstrated for control performance verification.

Adaptive Impedance Control for an Upper Limb Robotic Exoskeleton Using Biological Signals

This paper presents adaptive impedance control of an upper limb robotic exoskeleton using biological signals. First, we develop a reference musculoskeletal model of the human upper limb and experimentally calibrate the model to match the operator’s motion behavior. Then, the proposed novel impedance algorithm transfers stiffness from human operator through the surface electromyography (sEMG) signals, being utilized to design the optimal reference impedance model. Considering the unknown deadzone effects in the robot joints and the absence of the precise knowledge of the robot’s dynamics, an adaptive neural network control incorporating with a high-gain observer is developed to approximate the deadzone effect and robot’s dynamics and drive the robot tracking desired trajectories without velocity measurements. In order to verify the robustness of the proposed approach, the actual implementation has been performed using a real robotic exoskeleton and a human operator.

Vibration Control of a Flexible Robotic Manipulator in the Presence of Input Deadzone

In this paper, a neural network (NN) controller is designed to suppress the vibration of a flexible robotic manipulator system with input deadzone. The NN aims to approximate the unknown robotic manipulator dynamics and eliminate the effects of input deadzone in the actuators. In order to describe the system more accurately, the model of the flexible manipulator is constructed based on the lumping spring-mass method. Full state feedback NN control is proposed first and output feedback NN control with a high-gain observer is then devised to make the proposed control scheme more practical. The effect of input deadzone is approximated by a radial basis function neural network (RBFNN) and the unknown dynamics of the manipulator is approximated by another RBFNN. The proposed NN control is able to compensate for the estimated deadzone effect and track the desired trajectory. For the stability analysis, the Lyapunov's direct method is used to ensure uniform ultimate boundedness (UUB) of the closed-loop system. Simulations are given to verify the control performance of the NN controllers comparing with the proportional derivative (PD) controller. At last, the experiments are conducted on the Quanser platform to further prove the feasibility and control performance of the NN controllers.

Detection of Intermittent Fault for Discrete-Time Systems with Output Dead-Zone: A Variant Tobit Kalman Filtering Approach

This paper is concerned with the intermittent fault detection problem for a class of discrete-time linear systems with output dead-zone. Dead-zone phenomenon exists in many real practical systems due to the employment of low-cost commercial off-the-shelf sensors. Two Bernoulli random variables are utilized to model the dead-zone effect and a variant formation of Tobit Kalman filter is brought forward to generate a residual that can indicate the occurrence of an intermittent fault. A numerical example is presented to demonstrate the effectiveness and applicability of the proposed technique. The statistical performance of the technique is illustrated as well.

Dead-zone effect on the performance of state estimators for hydraulic actuators

State estimation in hydraulic actuators is a fundamental technique for fault detection and it is also a valid tool useful to reduce the installation of sensors. The performance of the linear/linearization based techniques for the state estimation is strongly limited due to hard nonlinearities that characterize hydraulic actuator. One of the most common hard nonlinearities in hydraulic actuator is the dead-zone. This paper focuses on an alternative nonlinear estimation method that is able to fully take into account dead-zone hard nonlinearity and measurement noise. The estimator is based on the state-dependent-Riccati-equation (SDRE). A fifth order nonlinear model is derived and employed for the synthesis of the estimator. Several simulations have been conducted in order to analyse the effect of the dead-zone characteristic on the novel estimator performance, showing comparisons with the largely used extended Kalman filter (EKF). Numerical results demonstrate the effectiveness of SDRE based technique in applications characterized by extended dead-zone for which the EKF method provides poor results.

Adaptive robust disturbance compensating control for a servo system in the presence of both friction and deadzone

An adaptive robust control that does not need sophisticated plant modeling work is proposed for precise output positioning of a servo system in the presence of both friction and deadzone nonlinearities. It is difficult to achieve effective motion control by traditional linear control methodology for these types of nonlinearities, without the aid of a proper compensation scheme for nonlinearity. In this study, dynamic friction is modeled by a Tustin friction model, and inverse deadzone method is adopted to compensate deadzone effect. The adaptive laws of the unknown system dynamic parameters, friction and deadzone, are derived. Furthermore, a robust control method with funnel control is proposed to compensate for unmodeled and estimation errors. The boundedness and convergence of the closed-loop system are ensured by a Lyapunov stability analysis. The performance of the proposed control scheme is verified through experiments on the XY table servo system and the robotic manipulator.

Numerical modeling of simultaneous tracer release and piscicide treatment for invasive species control in the Chicago Sanitary and Ship Canal, Chicago, Illinois

In December 2009, during a piscicide treatment targeting the invasive Asian carp in the Chicago Sanitary and Ship Canal, Rhodamine WT dye was released to track and document the transport and dispersion of the piscicide. In this study, two modeling approaches are presented to reproduce the advection and dispersion of the dye tracer (and piscicide), a one-dimensional analytical solution and a three-dimensional numerical model. The two approaches were compared with field measurements of concentration and their applicability is discussed. Acoustic Doppler current profiler measurements were used to estimate the longitudinal dispersion coefficients at ten cross sections, which were taken as reference for calibrating the longitudinal dispersion coefficient in the one-dimensional analytical solution. While the analytical solution is fast, relatively simple, and can fairly accurately predict the core of the observed concentration time series at points downstream, it does not capture the tail of the breakthrough curves. These tails are well reproduced by the three-dimensional model, because it accounts for the effects of dead zones and a power plant which withdraws nearly 80 % of the water from the canal for cooling purposes before returning it back to the canal.