Dead-zone Phenomenon Research Articles

Optimized dead-zone inverse control using reinforcement learning and sliding-mode mechanism for a class of high-order nonlinear systems

An optimized control method is developed for a class of high-order nonlinear dynamic systems having controller dead-zone phenomenon. Dead-zone refers to the controller with zero behavior within a certain range, so it will inevitably affect system performance. In order to make the optimized control eliminate the effect of dead zone, the adaptive dead-zone inverse and reinforcement learning (RL) techniques are combined. The main idea is to find the desired optimized control using RL as the input of dead-zone inverse function and then to design the adaptive algorithm to estimate the unknown parameters of dead-zone inverse function, so that the competent system control can be yielded from the dead-zone function. However, most existing RL algorithms are difficult to apply in the dead zone inverse methods because of the algorithm complexity. The proposed RL greatly simplifies the algorithm because it derives the training rules from the negative gradient of a simple positive function yielded by the partial derivative of Hamilton–Jacobi-Bellman (HJB) equation. Meanwhile, the proposed dead-zone inverse method also requires fewer adaptive parameters. Finally, the proposed control is attested through theoretical proofs and simulation examples.

Optimised backstepping control for the nonlinear strict-feedback system having unknown control dead-zone

In this article, the optimised backstepping (OB) strategy is extended to deal with the dead-zone control problem for a class of the nonlinear strict feedback systems. Since the dead-zone phenomenon is frequently encountered in the control of nonlinear strict feedback system, it is very necessary to consider the effect of dead-zone in the OB control. However, the published OB control methods are to rarely deal with the dead-zone problem because of the complex algorithm of reinforcement learning (RL). In this OB control, the dead-zone problem is effectively solved by utilising a simplified RL algorithm. For effective eliminating the effect of dead-zone, an adaptive compensation of dead-zone function's remainder is added to this RL. Since the RL under identifier-critic-actor architecture is implemented in every backstepping step, the requirement of complete dynamic acknowledge is released. Ultimately, the validity of this OB method is certified both theory and simulation.

Dynamic Threshold Finite-Time Prescribed Performance Control for Nonlinear Systems With Dead-Zone Output.

This article investigates the tracking control problem for nonlinear systems. An adaptive model is proposed to represent the dead-zone phenomenon and solve its control challenge with a Nussbaum function in conjunction. Drawing inspiration from the existing prescribed performance control schemes, a novel dynamic threshold scheme is developed that fuses a proposed continuous function with a finite-time performance function. A dynamic event-triggered strategy is applied to reduce the redundant transmission. The proposed time-varying threshold control strategy has fewer updates than the traditional fixed threshold and improves the efficiency of resource utilization. A command filter backstepping approach is employed to prevent the complexity explosion faced by the computation. The suggested control strategy ensures that all system signals are bounded. The validity of the simulation results has been verified.

Adaptive fixed-time consensus control of nonlinear multiagent systems with dead-zone output

This paper proposes a fixed-time leader-follower consensus tracking control scheme for uncertain multiagent systems with unknown dead-zone output. First, a novel approximate dead-zone model was introduced to accurately represent the dead-zone phenomenon in the output channel of nonlinear multiagent systems. Furthermore, the model presented is a smooth function, which greatly simplifies the process of fusing it with the backstepping technique. Second, we present a Nussbaum function to compensate for the uncertain gain from the output dead-zone nonlinearity. Third, unlike previous works, we first consider practical fixed-time consensus issues for multiagent systems with output dead-zone. Finally, according to the fixed-time control theory, the tracking error of the multiagent systems converges to the region around zero within a fixed time, which is confirmed by the simulations.

Observer-based self-organizing adaptive fuzzy neural network control for non-linear, non-affine systems with unknown sign of control gain and dead zone: A case study of pneumatic actuators

In this paper, an observer-based self-organizing adaptive fuzzy neural network (OSOAFNN) control for non-linear, non-affine systems with the unknown sign of control gain and dead zone is presented. First, a reverse dead-zone compensator scheme to cope with the impact of dead-zone phenomenon existing in control input is investigated. Then, an observed-based control approach to address immeasurable states of the system is proposed, utilizing this approach all states of the system are not needed to be available. A self-organizing fuzzy neural network (SOFNN) technique is presented to approximate the non-linear and unknown function of the observer error dynamics. The proposed fuzzy neural network (FNN) model benefits from two main advantages: (1) the number of rules is automatically generated or pruned and (2) the parameters of antecedent and consequent part of SOFNN are updated through the hybrid tuning, simultaneously. Furthermore, the control law contains a Nussbaum function which deals with the unknown sign of control gain. As the system states are immeasurable, the strictly positive real (SPR) Lyapunov function to guarantee the closed-loop system stability, and tracking error convergence to zero is employed, as well as the boundedness of control parameters are assured through a projection law merged with adaptive law. Finally, the controller is practically implemented on a non-linear, non-affine pneumatic system with unknown dead zone which exploits just a sensor for output measuring. Experimental results show that the proposed controller has satisfactory performance in tracking different trajectories, and tracking error for desired signal case I and case II is limited to [−1.5, 1.5] and [−1,1]mm, respectively.

Modeling and control of an invasive mechanical ventilation system using the active disturbances rejection control structure

We propose a mandatory invasive mechanical ventilator prototype for severe COVID-19 patients with volume and pressure control operation modes. This system comprises basic pneumatic elements and sensors. Its performance is similar to commercial equipment, and it presents robustness to external disturbances and parametric uncertainties. To develop a control strategy, we propose a mathematical model with a variable structure that incorporates the dead zone phenomenon of the proportional valve, and considers external disturbances and parametric uncertainties. Based on this model, we propose a global control strategy that is based on pressure and flow regulation controllers, which use the active disturbances rejection control structure (ADRC). In this strategy, we propose robust state observers to estimate disturbances and the signals necessary for implementing the controllers. We illustrate the performance of the prototype and the control strategy through numerical simulations and experiments. We also compare its performance with PID controllers. These results corroborate its effectiveness and the possibility of its application in invasive mechanical ventilators with a simple structure, which can significantly help critical care of COVID-19 inpatients.

Hydrodynamic behaviors of a spouted fluidized bed with a conical distributor and auxiliary inlets for the production of polysilicon with wide-size-distribution particles

In order to improve the fluidization quality of wide-size-distribution (WSD) particles in a spouted bed reactor for the production of polysilicon, a conical distributor with one central gas inlet and six auxiliary inlets was designed and applied in a cold-model reactor to form a spouted fluidized bed. The effects of the central and auxiliary gas velocities on the solid holdup were studied in the gas distributor region. The hydrodynamic behaviors inside the conical distributor were analyzed by pressure fluctuation in the time domain (standard deviation) and the frequency domain (power spectral density, PSD). The gas distribution was measured by the gas tracing method. It was found that the auxiliary gas feed significantly re-distributed the solid particles and effectively improved the fluidization quality; the dead zone phenomenon was well suppressed even at a low superficial gas velocity. Based on different flow behaviors, a regime map of fluidization was determined for fixed bed, bubbling bed, spouted bed, and spouted fluidized bed regimes. These results provided guidance for the reactor design because the gas and solid distributions would significantly affect the deposition efficiency of polysilicon.

Finite-Time Synchronization Control for Bilateral Teleoperation Systems With Asymmetric Time-Varying Delay and Input Dead Zone

In this article, the synchronization control problem of bilateral teleoperation systems with time-varying delays and input dead zones is addressed. A novel radial basis function network (RBFN)-based adaptive finite-time synchronization control scheme is proposed, where system uncertainties, asymmetric time-varying delays, and dead-zone phenomena are considered simultaneously. Specifically, an RBFN is designed to approximate system uncertainties and unknown nonlinearities. The approximation error as well as the time-associated uncertainty and the nonlinear margin of the dead zone is compensated by an adaptive compensator. Using a Lyapunov-Krasovskii function and the finite-time stability criteria, the system is proved to be semiglobally practically finite-time stable. The theoretical analysis is given to prove the stability of the closed-loop system. The tracking performance of the designed controller is demonstrated by comparative simulation studies and experiment results.

Design and implementation of flywheel energy storage system control with the ability to withstand measurement error

In this paper, attempts are made to design an offset and dead zone resistant digitalized vector control system for the flywheel energy storage system (FESS) based on the permanent magnet assisted synchronous reluctance motor (PMa-SynRM). Typically, in the motor drive set, current sensors are used. Current sensors in the industrial application consist of offset and dead zone phenomena and disturb the performance of the control system. Therefore, the effects of these phenomena in FESS designed control system are investigated, and a modified control system with using a proper filter to eliminate these phenomena is proposed. The proposed filter can eliminate these phenomena from the measured current without any decreasing in signal magnitude. The proposed control system eliminates speed ripple caused by the dead zone and offset effects. The performance of FESS is improved under the modified control system. Simulation and experimental results of the modified control system for FESS are presented to verify the performance of the energy storage drive and the theories.

A low-speed linear stage based on vibration trajectory control of a bending hybrid piezoelectric ultrasonic motor

The speed control tends to receive the restriction of dead-zone phenomenon when an ultrasonic motor (USM) works at the low speed range. A linear motion stage is designed and fabricated, in which a bending hybrid type USM using two separated bending modes is chosen for the low speed characteristic study. The shape and size of the vibration trajectory of the driving foot can be changed flexibly to realize the control of the output speed by controlling the vibration amplitudes of the driving foot in vertical and horizontal directions independently. The low speed characteristic experiment of the motion stage is accomplished based on a conventional PID controller, the speeds of 5 mm/s, 10 mm/s, 20 mm/s, 50 mm/s are achieved in the step control, respectively. In the sinusoidal speed control experiment, the reference speed varies sinusoidally with an amplitude of 20 mm/s, the maximum phase lag and amplitude error are lower than 3° and 3%, respectively. It is demonstrated that the low speed movement of the proposed linear motion stage can be realized by changing the vibration trajectory of the driving foot.

Backlash estimation for industrial drive-train systems

Backlash in gearing and other transmission components is a common positioning-degrading phenomenon that develops over time in industrial machines. High-performance machine tool controls use backlash compensation algorithms to maintain accurate positioning of the tool to cope with such deadzone phenomena. As such, estimation of the magnitude of deadzones is essential. This paper addresses the generic problem of accurately estimating the width of the deadzone in a single-axis mechanical drive train. The paper suggests a scheme to estimate backlash between motor and load, employing a sliding mode observer and a nonlinear adaptive estimator. The efficacy of the approach is illustrated via simulations.

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.

Adaptive positioning control of an ultrasonic linear motor system

A 3PRR parallel precision positioning system, driven by three ultrasonic linear motors, was designed for use as the object stage of a scanning electron microscope (SEM). To improve the tracking accuracy of the parallel platform, the positioning control algorithms for the drive joints needed to be studied. The dead-zone phenomenon caused by static friction reduces the trajectory tracking accuracy significantly. Linear control algorithms such as PID (Proportion Integration Differentiation) are unable to compensate effectively for the dead-zone nonlinearity. To address this problem, two types of feedforward compensation control algorithms have been investigated. One is constant feedforward with the integral separation PID; the other is adaptive feedback and feedforward based on the model reference adaptive control (MRAC). Simulations and experiments were conducted using these two control algorithms. The results demonstrated that the constant feedforward with integral separation PID algorithm can compensate for the time-invariant system after identifying the dead-zone depth, while the adaptive feedback and feedforward algorithm is more suitable for the time-varying system. The experimental results show good agreement with the simulation results for these two control algorithms. For the dead-zone nonlinearity caused by the static friction, the adaptive feedback and feedforward algorithm can effectively improve the trajectory tracking accuracy. A positioning system has been built for the driven joints of the 3-PRR in SEM.The dead-zone of the system has been identified and applied to compensation.The proposed control algorithm improves the tracking precision significantly.

Adaptive Fuzzy Tracking Control of Nonlinear Time-Delay Systems With Dead-Zone Output Mechanism Based on a Novel Smooth Model

This paper presents a novel fuzzy adaptive controller for controlling a class of dead-zone output nonlinear systems with time delays. A new approximate model is first designed to describe a special dead-zone phenomenon encountered by the output mechanism of nonlinear systems, and the proposed smooth model can be conveniently fused with available adaptive fuzzy control techniques. In addition, the coupling effect that the dead-zone output and the time-delayed states coexist in a common coupling function makes the tracking control design more complicated. To further address this difficulty, a compensation method using mean-value theorem with Lyapunov–Krasovskii function is presented in this paper. By using the proposed output dead-zone model, and based on Lyapunov synthesis, a new optimized algorithm is developed to guarantee the prescribed convergence of tracking error and the boundedness of all the signals in the closed-loop systems. Simulations have been implemented to verify the performance of the proposed fuzzy adaptive controller.

Adaptive control for electromechanical systems considering dead-zone phenomenon

The electromechanical gyrostat is a fourth-order nonautonomous system that exhibits very rich behavior such as chaos. In recent years, synchronization of nonautonomous chaotic systems has found many useful applications in nonlinear science and engineering fields. On the other hand, it is well known that the finite-time control techniques demonstrate good robustness and disturbance rejection properties. This paper studies the potential application of the finite-time control techniques for synchronization of nonautonomous chaotic electromechanical gyrostat systems in finite time. It is assumed that all the parameters of both drive and response systems are unknown parameters in advance. Moreover, the effects of dead-zone nonlinearities in the control inputs are also taken into account. Some adaptive controllers are introduced to synchronize two gyrostat systems in different scenarios within a given finite-time. Two illustrative examples are presented to demonstrate the efficiency and robustness of the proposed finite-time synchronization strategy.

사역대가 포함된 유압 위치 시스템의 LQG/LTR 제어

A LQG/LTR(linear quadratic Gaussian/loop transfer recovery) controller with an integrator is designed to control the electro-hydraulic positioning system. Without considering the nonlinearity in the dead-zone, computer simulations are performed and show good performances and tracking abilities with the feedback controller based on the linear system model. However, the performance of the closed loop hydraulic positioning system shows big steady-state error in real system because of the dead-zone. In this paper, the feedback controller with a nonlinear compensator is introduced to overcome the dead-zone phenomenon in hydraulic systems. The inverse dead-zone as a nonlinear compensator is used to cancel out the dead-zone phenomenon. Experimental tests are performed to verify the performance of the controller.

An adaptive H∞ control for robotic manipulator with compensation of input torque uncertainty

This paper examines the problem of link position tracking control for robot manipulators with input toque uncertainty. It is assumed that the input torque uncertainty can be regarded as dead-zone phenomena at each link of manipulator and all the system parameters for robotic manipulator and dead-zone model are unknown. The proposed method ensures that the unknown parameters are estimated adaptively, besides, an approximated errors of input nonlinearities and external disturbances are attenuated by means of H∞ control performance. In spite of considering the nonlinear adaptive H∞ control problems, based on our proposed method, the compensator can design without solving the Hamilton-Jacobi-Isaacs equation. Numerical simulation results are given to illustrate the effectiveness of our proposed method.

ADAPTIVE FEED-FORWARD COMPENSATOR FOR HARMONIC CANCELLATION IN ELECTRO-HYDRAULIC SERVO SYSTEM

Since the dead zone phenomenon occurs in electro-hydraulic servo system,the output of the system corresponding to a sinusoidal input contains higher harmonic besides the fundamental input,which causes harmonic distortion of the output signal. The method for harmonic cancellation based on adaptive filter is proposed. The task is accomplished by generating reference signals with frequency that should be eliminated from the output. The reference inputs are weighted by the adaptive filter in such a way that it closely matches the harmonic. The output of the adaptive filter is a harmonic replica and is injected to the fundamental signal such that the output harmonic is cancelled leaving the desired signal alone,and the total harmonic distortion (THD) is greatly reduced. The weights of filter are adjusted on-line according to the control error by using least-mean-square (LMS) algorithm. Simulation results performed with a hydraulic system demonstrate the efficiency and validity of the proposed adaptive feed-forward compensator (AFC) control scheme.

Dead zone phenomenon in distance relaying of overhead transmission lines

This paper refers to the distance protection of overhead transmission line. The phenomenon of ‘dead zones’ in distance relay operation is established. This phenomenon consists of a segment of an overhead line, inside the distance relay reach, where the relay can not detect a fault. The nature of the dead zone phenomenon is the most complex when the distance protection of mutually coupled lines is considered. Thus, clarifying the nature and proposing measures for elimination of dead zones from distance protection are main objectives of this paper. A simple example is considered to get a qualitative insight into the dead zone appearance. Presented considerations are illustrated by example belonging to the actual power system of Yugoslavia.

An Integrated System for Supervisory Process Control using ADA

The paper presents an integrated software package for supervisory process control using ADA language. This system performs process control using classical and heuristic controllers, supervision in order to detect abnormal situations and on-line monitoring. Using ADA language, the definition of the different processes (control, supervision and monitoring) can be easily implemented using the concurrent programming techniques inherent to the language. Specifically, a rule-based system which compensates for dead-zone phenomena in a position control servomechanism is developed. The supervisor module is designed to detect and avoid undesirable on-linear control phenomena such as steady state errors, limit cycling or excursions into unwanted zones. It constitutes an intelligent compensator for system input nonlinearities which may be generalized to other non-linearity types.