Unknown Input Disturbance Research Articles

Adaptive control for an uncertain robotic manipulator with input saturations

In this paper, we address the control problem of an uncertain robotic manipulator with input saturations, unknown input scalings and disturbances. For this purpose, a model reference adaptive control like (MRAC-like) is used to handle the input saturations. The model reference is input to state stable (ISS) and driven by the errors between the required control signals and input saturations. The uncertain parameters are dealt with by using linear-in-the-parameters property of robotic dynamics, while unknown input scalings and disturbances are handled by non-regressor based approach. Our design ensures that all the signals in the closed-loop system are bounded, and the tracking error converges to the compact set which depends on the predetermined bounds of the control inputs. Simulation on a planar elbow manipulator with two joints is provided to illustrate the effectiveness of the proposed controller.

Two novel approaches of UIF design for T-S fuzzy system

This paper researches the state estimation problem for a class of T-S fuzzy system which subject to unknown input. For this set of system, two approaches are studied to design the UIF. A converted system is constructed in the first method to solve the insolubility problem of inequalities because of the existence of the unknown input. The second method establishes filter structure and achieves the purpose of estimating the system states through adopting the direct way. By employing unknown input filter, the paper makes a smooth estimation not only to the system states, but also to the estimate signals and unknown disturbance inputs. At last, a simulation example is used to illustrate the effectiveness of the proposed UIF.

Disturbance Observer Design for Utilizing of Time-delayed Vision Measurements in High Dynamical Systems

The utilization of vision information for control in intelligent technical applications with high dynamics has been a central issue. The main obstacles are the low sampling rate of the cameras (about 60Hz of a commercial camera) compared to the required sampling rate of the high dynamic applications (over 1kHz) and the time-delayed measurements due to the image processing. A model-based Event-Triggered Observer (ETO) [12] has been proposed for linear systems to observe and predict the undelayed continuous state variables of the system from the sampled and delayed measurements where the sampling rate and the delay- time can be constant or variable. However, the disturbances like the sensor noise and the perturbations of the environment were not handled within [12]. As is well known, the disturbances decline the performance of the model-based observer. To keep the performance of the state-estimation and prediction, an effective solution is to adopt into account the unknown dynamic effects due to the disturbances by integrating them into the state-estimation. A survey [13] has shown different methods of dealing with the disturbance estimation to improve the accuracy of the estimation of the system internal states. Unlike other mentioned methods in [13], the so-called Unknown Input Observer (UIO), shows significant advantages with the ability to estimate the unknown input disturbances and the system internal states simultaneously by augmenting the state space of a classical state observer like Luenberger-Observer with a disturbance model [14,15]. In this paper, an Extended Event-Triggered Observer (EETO) is proposed, which based on the proposed ETO in [12] and is extended with an UIO. The new proposed EETO can estimate undelayed continuous state variables from the time-delayed measurements under the disturbances. An example system with a second-order delay behavior is simulated, whose output is sampled and delayed. The simulation results show the performance of the proposed Extended Event-Triggered Observer.

Global adaptive stabilisation for nonlinear systems with unknown control directions and input disturbance

ABSTRACTThis paper addresses the global adaptive stabilisation via switching and learning strategies for a class of uncertain nonlinear systems. Remarkably, the systems in question simultaneously have unknown control directions, unknown input disturbance and unknown growth rate, which makes the problem in question challenging to solve and essentially different from those in the existing literature. To solve the problem, an adaptive scheme via switching and learning is proposed by skilfully integrating the techniques of backstepping design, adaptive learning and adaptive switching. One key point in the design scheme is the introduction of the learning mechanism, in order to compensate the unknown input disturbance, and the other one is the design of the switching mechanism, through tuning the design parameters online to deal with the unknown control directions, unknown bound and period of input disturbance and unknown growth rate. The designed controller guarantees that all the signals of the resulting closed-loop systems are bounded, and furthermore, the closed-loop system states globally converge to zero.

Fractional robust control design for fuzzy dynamical systems: An optimal approach

We propose an optimal approach to a new control design for fuzzy dynamical systems in this paper. Consider the system containing uncertainty, which may includes the unknown system parameter and input disturbance. And the uncertainty can be prescribed with a fuzzy set. A new class of factional-type robust controls are proposed, whose structure is deterministic and is not if-then rule-based. Furthermore, the control gain design is formulated as a constrained optimization problem, which minimizes both the average fuzzy performance and control effort. We show that the solution of this optimization problem always exists and is unique. And the closed-form solution and closed-form minimum cost are derived. The resulting control can guarantee the uniform boundedness and uniform ultimate boundedness of the uncertain system, while minimizing both the average fuzzy performance and control effort.

Vibration control of a Timoshenko beam system with input backlash

In this study, a novel boundary control algorithm is designed for a class of Timoshenko beams with unknown external disturbance and uncertain input backlash non-linearity. The Timoshenko beam is described by partial differential equations as governing equations and ordinary differential equations as boundary conditions. The representation of input backlash is modified as a desired control input associated with input non-linear error, which will be transformed into the external disturbance. The unknown ‘disturbance-like’ item is defined based on input error and disturbance, and the boundary of this unknown ‘disturbance-like’ item will be estimated by a disturbance observer. The unknown backlash can be handled and the ultimately uniform stability of the closed-loop system is ensured. Numerical simulations are provided to verify the performance of the author's proposed control.

내부 모델 기반 외란 관측기를 이용한 수직 1축 머니퓰레이터의 속도 제어기 설계

This paper deals with a robust speed control problem of a vertical one-link manipulator in the presence of parameter uncertainties and unknown input disturbance. Uncertain load weight causes an additional sinusoidal disturbance in the rotation of the link. In order to improve the robustness against parameter uncertainties and external input disturbances, this paper employs an internal model-based disturbance observer approach. Comparative computer simulations are performed to test the performance of the proposed controller. The simulation results show the enhanced performance of the proposed method.

Adaptive Control of Multi-Input Aeroelastic System with Constrained Inputs

The development of an adaptive control system for the control of an uncertain aeroelastic system, in the presence of constraints on the leading- and trailing-edge control surface deflections, is the subject of this paper. The model describes the nonlinear plunge and pitch dynamics of a prototypical wing section. The open-loop system exhibits limit-cycle oscillations beyond a critical freestream velocity. It is assumed that all the system parameters, except the signs of principal minors of the high-frequency gain matrix, are unknown, and external disturbance inputs are present. The objective is to design a saturating control system for suppressing the limit-cycle oscillations. An adaptive control system is designed for tracking reference pitch angle and plunge displacement trajectories. For avoiding singularity in the adaptive law, a decomposition of the input matrix is used for the design. For the analysis of the effect of input saturation, an auxiliary dynamic system is introduced. By the Lyapunov stability analysis, it is shown that the trajectories of the closed-loop system are uniformly ultimately bounded. Simulation results are presented that show suppression of oscillatory responses despite symmetric and nonsymmetric input constraints, uncertainties in the system parameters, and wind gust.

Distributed adaptive fuzzy iterative learning control of coordination problems for higher order multi-agent systems

In this paper, the adaptive fuzzy iterative learning control scheme is proposed for coordination problems of Mth order (M ≥ 2) distributed multi-agent systems. Every follower agent has a higher order integrator with unknown nonlinear dynamics and input disturbance. The dynamics of the leader are a higher order nonlinear systems and only available to a portion of the follower agents. With distributed initial state learning, the unified distributed protocols combined time-domain and iteration-domain adaptive laws guarantee that the follower agents track the leader uniformly on [0, T]. Then, the proposed algorithm extends to achieve the formation control. A numerical example and a multiple robotic system are provided to demonstrate the performance of the proposed approach.

Linear active disturbance rejection control of the hovercraft vessel model

A linearizing robust dynamic output feedback control scheme is proposed for earth coordinate position variables trajectory tracking tasks in a hovercraft vessel model. The controller design is carried out using only position and orientation measurements. A highly simplified model obtained from flatness considerations is proposed which vastly simplifies the controller design task. Only the order of integration of the input-to-flat output subsystems, along with the associated input matrix gain, is retained in the simplified model. All the unknown additive nonlinearities and exogenous perturbations are lumped into an absolutely bounded, unstructured, vector of time signals whose components may be locally on-line estimated by means of a high gain Generalized Proportional Integral (GPI) observer. GPI observers are the dual counterpart of GPI controllers providing accurate simultaneous estimation of each flat output associated phase variables and of the exogenous and endogenous perturbation inputs. These observers exhibit remarkably convenient self-updating internal models of the unknown disturbance input vector components. These two key pieces of on-line information are used in the proposed feedback controller to conform an active disturbance rejection, or disturbance accommodation, control scheme. Simulation results validate the effectiveness of the proposed design method.

The Design of Robust Controller for Networked Control System with Time Delay

This paper considers the stability andH∞control problem of networked control systems with time delay. Taking into account the influence of network with delay, unknown input disturbance, and uncertainties of the system modeling, meanwhile we establish a precise, closed-loop model for networked control systems with time delay. By selecting a proper Lyapunov-Krasovskii function and using Lyapunov theorem, a sufficient condition for stability of the system in the form of LMI is demonstrated, corresponding controller parameters are acquired, and the convergence of the control algorithm is proved. The simulation example shows that the construction of the network robust control system with time delay indeed improves the stability performance of the system, which indicates the effectiveness of the design.

Bond-Graph-Based Multivariable non linear UlO-type estimation

This paper studies observers for multivariable systems with nonlinear components and unknown disturbance inputs. In order to apply procedures dedicated to linear systems, the nonlinearity is first modeled as an unknown input variable and an unknown input observer for multivariable linear systems is studied. An integrated approach is proposed from modeling to observer synthesis with the bond graph approach. This result is used to provide a methodology similar to the one applied for the classical input-output decoupling problem in control theory. An application is proposed and simulation results prove the validity of the approach.

Multiple model estimator based detection of abnormal cell overheating in a Li-ion battery string with minimum number of temperature sensors

This paper proposes modeling of abnormal cell overheating caused by internal short circuit in a cell of a Li-ion battery string by augmenting the cell state space model with unknown input disturbance. Furthermore, with minimum number of temperature sensors, in order to identify which of the cells in the string is experiencing the abnormal overheating, a multiple model estimator (MME) is used. Simulation results demonstrate that the proposed MME can detect the abnormally overheating cell as well as quickly detect that an abnormal overheating event occurred in the battery string.

Design of a Robust <i>H</i><sub>∞</sub> Fault-Detection Filter for Uncertain Disturbance System

The problem of robust fault detection filter is investigated for a class of systems with unknown disturbance and fault inputs. Attention is focused on formulating the design the residuals match with reference model. The robustness of the residual system is proved to be stability. The existence condition of the above filters, which can guarantee the robustness against disturbances and sensitivity against fault are solved by LMI. Finally, an example is given to illustrate the feasibility of the proposed method.

A robust composite nonlinear control scheme for servomotor speed regulation

A parameterised design of robust composite nonlinear controller is proposed for typical second-order servo systems subject to unknown constant disturbance and control input saturation. The control law consists of a linear feedback part for achieving fast response, a nonlinear feedback part for suppressing the overshoot, and a disturbance-compensation mechanism for erasing the steady-state error. An extended state observer is adopted to estimate the unknown disturbance. The closed-loop stability is analysed theoretically. The control scheme is applied to the speed regulation of permanent magnet synchronous motor, and numerical simulations are carried out. The results confirm that the proposed control scheme can achieve fast, smooth, and accurate speed regulation, and has a certain degree of robustness with respect to the amplitude of disturbances and the perturbations of system parameters.

H ∞ and Sliding Mode Observers for Linear Time-Invariant Fractional-Order Dynamic Systems With Initial Memory Effect

The H∞ and sliding mode observers are important in integer-order dynamic systems. However, these observers are not well explored in the field of fractional-order dynamic systems. In this paper, the H∞ filter and the fractional-order sliding mode unknown input observer are developed to estimate state of the linear time-invariant fractional-order dynamic systems with consideration of proper initial memory effect. As the first result, the fractional-order H∞ filter is introduced, and it is shown that the gain from the noise to the estimation error is bounded in the sense of the H∞ norm. Based on the extended bounded real lemma, the H∞ filter design is formulated in a linear matrix inequality form, and it will be seen that numerical methods to solve convex optimization problems are feasible in fractional-order systems (FOSs). As the second result of this paper, not only state but also unknown input disturbance are estimated by fractional-order sliding-mode unknown input observer, simultaneously. In this paper, it is shown that the design and stability analysis of the two estimation techniques are not related with the initial history. Through two numerical examples, the performance of the fractional-order H∞ filter and the fractional-order sliding-mode observer is illustrated with consideration of the initialization functions.

Attenuation of disturbances introduced by dynamic links in precision motion systems using model-based observers

This paper presents an extension to the Unknown Input Disturbance Observer (UIDO) and the Disturbance Estimation Filter (DEF). This extension enables the inclusion of the mechanics of dynamic links to the observer model, in order to attenuate the specific disturbances introduced by those dynamic links. A design method of the state space feedback gain based on the dynamics, and an observer gain based on basic Kalman filter theory is given. It is shown how the observer is designed for a practical example; the cable schlepp within the wafer stage of a lithography machine. Using a simple model of the cable schlepp the disturbance observer design has been validated with an experiment on an actual machine.

Russian

In the paper, we discuss a problem of the dynamic reconstruction of unknown input disturbances in nonlinear vector equations with delay in control. A regularizing algorithm is proposed for reconstructing these disturbances simultaneously with the processes. The algorithm is stable with respect to information noises and computational errors.

슬라이딩 모드 제어기법을 이용한 도립진자 시스템 제어

슬라이딩모드 제어의 문제는 제어입력에 포함된 알려지지 않은 외란 등 비선형 입력으로 인한 채터링의 발생이다. 본 연구는 채터링 발생의 문제를 해결하기 위한 제어 알고리듬에 대하여 고찰하고 채터링을 억제하는 슬라이딩모드 제어기를 설계하고자 한다. 슬라이딩모드 제어 시 발생하는 채터링을 억제하기 위해 알려지지 않은 외란을 포함한 비선형 입력에 대하여 평활함수를 적용한다. 이 방법에 의하여 도립진자 시스템의 동적 방정식에 포함된 비선형 요소와 외란에 의한 문제가 해결될 수 있음을 보인다. 또 슬라이딩모드 제어를 위한 제어 입력을 시스템에 적용하였고, 제안한 제어기의 제어성능을 검증하기 위하여 도립진자를 대상으로 컴퓨터 모의실험을 수행하였다. 모의실험 결과 제어입력에 포함된 큰 폭의 채터링이 제거되었음을 확인할 수 있다. A problem of sliding mode control is chattering because of controle input signal included unknown disturbance and nonlinear input parameters. This paper presents a sliding mode controller design to inverted pendulum system. In this paper, a sliding mode control algorithm to reduce a chattering is proposed. The reduction of chattering is accomplished by smoothing function for nonlinear control input. In this method, the dynamic equations of the inverted pendulum is decoupled by considering nonlinear parameters and external disturbances. Therefore, this study is applied to obtain switching control inputs for sliding mode controller. The proposed technique is tested to the control of inverted pendulum through computer simulations. The result shown reduced chattering in control input.

Active Perturbation Rejection in Motion Control of Milling Machine Tools

This article deals with the robust control problem of the motion axes of milling machine tools subjected to perturbation forces induced by the metal machining process. A position output feedback control scheme is proposed for robust rejection of unknown cutting and friction perturbation forces and robust tracking tasks of motion trajectories planned for a three-axis milling machine tool. The Coulomb friction, viscous damping and cutting forces are considered as terms of an unknown time-varying disturbance input signal affecting the dynamics of the motion axes of the milling machine. In the motion control design, the perturbation signal is modeled locally by a fourth degree Taylor time-polynomial family. Then, a state observer is designed to estimate the disturbance and velocity signals required for implementation of the proposed motion controllers. Simulation results are included to show the robust performance of the proposed motion control scheme and the fast and effective estimation of the perturbation and velocity signals.