Accommodation Control Research Articles

Fault Accommodation Control for a Biped Robot Using a Recurrent Wavelet Elman Neural Network

A model-based fault accommodation control scheme that uses a recurrent wavelet Elman neural network (RWENN) is proposed to achieve satisfactory control without performance degradation for biped robot locomotion with unknown uncertainties and faults. In the fault accommodation scheme, a computed torque control is the main control that is used to track the desired trajectory when there is no fault; and a compensation control is used to eliminate the unknown model uncertainties. The proposed RWENN has an input from a context layer with self-feedback and an output recurrent layer to the hidden layer, which increases the precision and convergence time of the network compared with a recurrent neural network, a recurrent fuzzy neural network, and a recurrent wavelet neural network, so that any dynamic change, such as a fault on the system, can be estimated properly. Thus, it enhances the capability of fault accommodation. The adaptive laws of the RWENN-based fault accommodation control are derived from the Lyapunov theorem; hence, the stability of the system can be guaranteed. Finally, a case study of biped robot control with multiple faults and uncertainties is analyzed, and the effectiveness of the proposed fault accommodation scheme is demonstrated by simulation results. Its superiority is also assessed by a numerical comparison with other neural-network-based control schemes.

Improved adaptive fault‐tolerant control design for hypersonic vehicle based on interval type‐2 T‐S model

SummaryThis study proposes an improved adaptive fault estimation and accommodation algorithm for a hypersonic flight vehicle that uses an interval type‐2 Takagi‐Sugeno fuzzy model and a quantum switching module. First, an interval type‐2 Takagi‐Sugeno fuzzy model for the hypersonic flight vehicle system with elevator faults is developed to process the nonlinearity and parameter uncertainties. An improved adaptive fault estimation algorithm is then constructed by adding an adjustable parameter. The quantum switching module is also applied to the estimation part to select an appropriate algorithm in different fault cases. The estimation results from the given fuzzy observer are used to design a type‐2 fuzzy fault accommodation controller to stabilize the fuzzy system. The stability of the proposed scheme is analyzed using the Lyapunov stability theory. Finally, the validity and availability of the method are verified by a series of comparisons on numerical simulation results.

既存の地域冷暖房と連携したスマートヒートグリッド（SHG）に関する研究

In Japan, the need to reduce energy consumption for business use and household use is questioned. Therefore, further promotion of energy conservation is necessary. Community-wide energy utilization is one way to deal with it. Smart Heat Grid (SHG)is a heat accommodation system between buildings with distributed energy systems. Heat router is the core technical element of SHG. Choose the optimal transport power among the buildings that heat interchange, and send and receive heat. The effectiveness of heat router was confirmed by 38 control experiments. That objective is to confirm whether heat accommodation control can be stably performed within the assumed time. As a result, it was confirmed that the target error is within 10% of the design flow rate, and the time to shift to the different heat interchange state is within 10 minutes. This time it was done with the control system from the center, but in future it will be made it a distributed control system. This results was confirmed the possibility of extensibility of SHG. Simulation of existing DHC coordinated type SHG was conducted for existing buildings, in case of 10%, 30%, 50% heat accommodation to annual heat load. It was targeted the existing DHC in the metropolitan area and the four model buildings of hotels, offices, commercial facilities and hospitals. For DHC, it was also examined the latest heat source system using gas engine type CGS. As a result, the following conclusions were obtained. (1) BAU ratio of energy saving , current DHC 0.76 ~ 10.08%, New DHC 1.19% ~ 13.83%. (2) The effective cross-sectional area of the heat accommodated piping was 30% to 60% as compared with the total supply system. (3) The proportion of time that the heat source of the model building supplementarily operates decreases, and the heat accommodation greatly contributed. (4) Waste heat (hot water) of the gas engine greatly contributes to the thermal demands of the model building. This study checked a business-related evaluation. (internal rate of return, net present value, the accumulated deficit cancellation year) Since risk of fluctuation in purchased energy cost can be considered in the future, sensitivity analysis in which the utility fee is reduced by 10% · 30% was made. If SHG can be applied 1/2, 2/3 business subsidy (it is carried out now), this result can be confirmed that it is profitable business.

Optimal tuning of multivariable disturbance‐observer‐based control for flicker mitigation using individual pitch control of wind turbine

Multivariable disturbance accommodated observer based control (DOBC) scheme is presented to mitigate loads generated due to wind shear and tower shadow using individual blade pitch for above-rated wind speed condition of wind turbine. Wind shear and tower shadow add flickers as 1p, 3p, 6p and so on, (p is the rotor rotational frequency) for three-bladed wind turbine. Novel DOBC with individual pitch control (IPC) to mitigate the flickers is presented and linear state-space model of wind turbine with tower dynamics is developed. The proposed controller is tuned using optimal control theory to reduce fatigue of drive-train, tower and to regulate output power. The authors have tested the controller on NREL's 5 MW wind turbine, FAST (fatigue, aerodynamics, structures and turbulence) code is used for load modelling and MATLAB/Simulink is used for the simulation. A comparison of power spectral density of generator speed, drive-train torsion and tower fore-aft moment shows better mitigation to the flickers by proposed controller as compared with proportional–integral (PI) and disturbance accommodation control (DAC) with collective pitch control. Furthermore, it shows less degradation in the performance as moving away from the operating point for above-rated wind speed condition of wind turbine. It is concluded that proposed multivariable controller shows better mitigation to turbulent and cyclic aerodynamic loads, provide better regulation to output power using IPC of wind turbine and increased the lifetime of drive-train torsion and tower as compared with PI and DAC.

Incipient sensor fault estimation and accommodation for inverter devices in electric railway traction systems

SummaryThis paper proposes an incipient sensor fault estimation and accommodation method for three‐phase PWM inverter devices in electric railway traction systems. First, the dynamics of inverters and incipient voltage sensor faults are modeled. Then, for the augmented system formed by original inverter system and incipient sensor faults, an optimal adaptive unknown input observer is proposed to estimate the inverter voltages, currents and the incipient sensor faults. The designed observer guarantees that the estimation errors converge to the minimal invariant ellipsoid. Moreover, based on the output regulator via internal model principle, the fault accommodation controller is proposed to ensure that the vod and voq voltages track the desired reference voltages with the tracking error converging to the minimal invariant ellipsoid. Finally, simulations based on the traction system in CRH2 (China Railway High‐speed) are presented to verify the effectiveness of the proposed method. Copyright © 2016 John Wiley & Sons, Ltd.

Observer-based fault detection and accommodation for nonlinear time-delay systems with a prescribed performance mechanism

In this paper, delay-independent fault detection and accommodation (FDA) control is developed for a class of uncertain nonlinear time-delay systems with multiple time-delay faults and external disturbances. Compared with the existing results, the system states are unmeasurable and the bounds of model uncertainties and the disturbances only exist but are unknown. A novel parameter-varying observer is designed for fault detection and state estimation. The modified prescribed performance bound (PPB) is used as detection threshold. It is shown that the state estimate error is guaranteed within a PPB before the fault occurs. Then, a backstepping-based adaptive fuzzy fault accommodation controller is designed and activated after the detection, which compensates multiple time-delay faults and guarantees the state estimate error which has violated the performance constraint returns into a new PPB. The effectiveness of the proposed FDA method is illustrated through a simulation example on the robot manipulator system.

Mixed carbonate–siliciclastic sedimentation in forebulge grabens: An example from the Ediacaran Bambuí Group, São Francisco Basin, Brazil

Mixed carbonate–siliciclastic successions have been described in multiple Phanerozoic sedimentary settings recording the dynamic interplay of tectonics, eustasy, climate, in situ carbonate production, and variations in siliciclastic sediment supply. The Ediacaran Bambuí 1st-order sequence (i.e., Bambuí Group) covers most of the intracratonic São Francisco basin (southeast Brazil) and encompasses thick packages of carbonate and fine- to coarse-grained siliciclastic strata. Recording a marine foreland basin stage that developed in the São Francisco plate during the Neoproterozoic–early Paleozoic West Gondwana assembly, the Ediacaran deposits unconformably overlie Archean–Paleoproterozoic metamorphic assemblages of the Sete Lagoas basement high and fill a series of kilometer-long grabens in the southern São Francisco basin. Seismic data reveal that these troughs developed through the extensional reactivation of ancient basement structures along with the tectonically driven forebulge uplift of the Sete Lagoas high, in the early evolutionary stages of the Bambuí basin cycle. Based on the detailed description of continuous drill cores of a well recently drilled during hydrocarbon exploration campaigns, we recognized two transgressive–regressive 2nd-order sequences preserved within one of the focused grabens: (i) Sequence 1 includes the glaciogenic deposits of the basal Carrancas Formation that grade upward into the carbonate ramp successions of the Sete Lagoas Formation; (ii) Sequence 2 contains the siliciclastic-dominated and deep water to deltaic strata of the Serra de Santa Helena Formation and passes upward into peritidal carbonates of the Lagoa do Jacaré Formation. These sedimentary successions encompass suites of retrogradational, aggradational, and progradational lower-rank cycles and are bounded by erosional surfaces. Regional seismic interpretation, well data, and the available literature indicate that most of these deposits and their correlatives are continuous over most of the Sete Lagoas basement high, showing remarkable variations within the studied forebulge grabens. Our analysis demonstrates that the depositional architecture of Sequence 1 and Sequence 2 marks the interplay of successive episodes of tectonically driven forebulge uplift and regional eustatic and climatic changes. The latter are mainly recorded by the lower second-order sequence (Sequence 1), which contains typical sedimentary features deposited in the aftermath of an important glaciation affecting lower latitudes during the late Neoproterozoic. An additional local accommodation control is restricted to the forebulge grabens and is associated with episodic and local subsidence pulses. As indicated by lower- to higher-rank cycles, it has been responsible for the deposition of thicker transgressive to early regressive successions, a few gravitational flow deposits, and the development of the deltaic to shallow marine carbonate cycles of Sequence 2. The overall stratigraphic architecture of the studied successions suggests that several basin mechanisms operating during the Phanerozoic were also present in the late Neoproterozoic. The close association between organic-rich post-glacial shales, potential reservoir facies, and rift-related migration paths and hydrocarbon traps indicate that forebulge grabens represent important elements to consider in hydrocarbon exploration campaigns.

Fault detection and accommodation of saturated actuators for underactuated surface vessels in the presence of nonlinear uncertainties

This paper investigates a fault detection and accommodation (FDA) problem of saturated actuators for trajectory tracking of underactuated surface vessels (USVs) in the presence of nonlinear uncertainties. A robust fault detection observer and a time-varying detection criterion are presented to detect the actuator faults distinguished from uncertainties in nonlinear dynamics and external disturbances. Then, we develop an adaptive fault accommodation scheme using the dynamic surface design to compensate the detected faults. For the fault accommodation control, the auxiliary variables and their dynamics are derived to consider the saturation problem of actuators with the nonholonomic property of USVs and to analyze the stability of the sway dynamics clearly. To ensure that tracking errors are globally uniformly ultimately bounded, the projection algorithm is employed for the design of the bounded virtual and actual control laws. The effectiveness of the proposed FDA system is demonstrated by simulation results.

Disturbance-Observer-Based Control and Related Methods—An Overview

Disturbance-observer-based control (DOBC) and related methods have been researched and applied in various industrial sectors in the last four decades. This survey, at first time, gives a systematic and comprehensive tutorial and summary on the existing disturbance/uncertainty estimation and attenuation techniques, most notably, DOBC, active disturbance rejection control, disturbance accommodation control, and composite hierarchical antidisturbance control. In all of these methods, disturbance and uncertainty are, in general, lumped together, and an observation mechanism is employed to estimate the total disturbance. This paper first reviews a number of widely used linear and nonlinear disturbance/uncertainty estimation techniques and then discusses and compares various compensation techniques and the procedures of integrating disturbance/uncertainty compensation with a (predesigned) linear/nonlinear controller. It also provides concise tutorials of the main methods in this area with clear descriptions of their features. The application of this group of methods in various industrial sections is reviewed, with emphasis on the commercialization of some algorithms. The survey is ended with the discussion of future directions.

Dieseline fueled flexible fuel compression ignition engine control based on in-cylinder pressure sensor

This paper conducts research on the fuel accommodation control of a fuel-flexible engine. Blended fuels from gasoline and diesel are tested on a compression ignition engine. Two problems with the fuel-flexible engine are studied. One problem is that the engine brake torque output is different with different fuels, and the other problem is that the thermal efficiency deteriorates without recalibration. One open-loop control method and one closed-loop control method based on cylinder pressure sensor are proposed to deal with the fuel accommodation control problems. The open-loop control method features fuel blend ratio detection, which is a new dimension of input for the conventional MAP based engine management system. Gasoline and diesel blend ratio detection methods are studied, and the result also provides information for the closed loop control method as a feedforward controller. An indicated mean effective pressure based method is proposed for the engine brake torque difference problem, and a feedback controller with indicated mean effective pressure maximum seeking algorithm is used to optimize engine efficiency. The fuel injection amount and timing will be adjusted according to the fuel estimation result and the feedback control algorithms. Results show that the methods proposed could identify fuel blend ratio quite accurately, the engine brake torque output could follow the target value well, and the engine thermal efficiency could be optimized.

Microfluctuations in accommodation: an update on their characteristics and possible role

Following the recognition, some 80 years ago, that the accommodation of the eye is not stable but fluctuates over a range of about ±0.5 D, mainly at frequencies of up to a few Hz, there has been a continuing interest in the characteristics of these microfluctuations (MFs) and their possible role in the control of accommodation. This paper reviews relevant work carried out since 1988, when we previously reviewed the same topic (Charman WN, Heron G. Fluctuations in accommodation: a review. Ophthalmic Physiol Opt 1988; 8: 153-164). Studies relating to the effects on the MFs of stimulus form, luminance and vergence are described, together with those of pupil diameter, age and ametropia. Important advances in the understanding of the links between the characteristics of the MFs and those of the cardiopulmonary system, higher-order aberrations and ocular depth-of-focus are outlined. Only limited progress has been made in understanding the role of MFs in accommodation control. While the dependence of the characteristics of the MFs in relation to observing conditions is now reasonably well understood, their involvement in accommodation control still needs clarification. The current consensus appears to be that any role is more likely to be concerned with maintaining an appropriate response, rather than in initiating responses to abrupt changes in stimulus vergence. Fluctuations at lower temporal frequencies (<0.6 Hz) are probably important to the control process, which may make use of the associated changes in the contrast and spatial frequency spectrum of the retinal image.

Automated Fault Diagnosis and Accommodation Control for Mechanical Systems

In this paper, a fault diagnosis and accommodation control scheme is designed, which is applicable to mechanical systems. First, the fault detection is developed by designing a nonlinear observer. Second, the fault isolation is achieved by using multiple fault observers. Third, when a fault is diagnosed, an adequate fault accommodation control is triggered to compensate the effects of the fault function. Finally, case study is given to illustrate the effects of the proposed method.

Delay‐independent fault detection and accommodation for non‐linear strict‐feedback systems with unknown time‐varying delays

This study presents a time-delay-independent fault detection and adaptive accommodation control scheme for strict-feedback systems with unknown multiple time-delayed non-linear faults. The magnitude and occurrence time of the multiple faults with unknown time-varying delays are unknown. First, a detection threshold is derived to design a time-delay-independent fault detection scheme for the time-delay systems and the fault detectability is analysed. Second, an adaptive approximation design for a time-delay-independent fault accommodation control is addressed. The adaptation technique is applied to learn weights of function approximators and thus the multiple faults can be compensated after the detection of the first fault. It is shown that all signals of the closed-loop system are semi-globally uniformly ultimately bounded and the tracking error converges to an adjustable neighbourhood of the origin.

Effect of correction of aberration dynamics on chaos in human ocular accommodation

We used adaptive optics to determine the effect of monochromatic aberration dynamics on the level of chaos in the accommodation control system. Four participants viewed a stationary target while the dynamics of their aberrations were either left uncorrected, defocus was corrected, or all aberrations except defocus were corrected. Chaos theory analysis was used to discern changes in the accommodative microfluctuations. We found a statistically significant reduction in the chaotic nature of the accommodation microfluctuations during correction of defocus, but not when all aberrations except defocus were corrected. The Lyapunov exponent decreased from 0.71 ± 0.07 D/s (baseline) to 0.55 ± 0.03 D/s (correction of defocus fluctuations). As the reduction of chaos in physiological signals is indicative of stress to the system, the results indicate that for the participants included in this study, fluctuations in defocus have a more profound effect than those of the other aberrations. There were no changes in the power spectrum between experimental conditions. Hence chaos theory analysis is a more subtle marker of changes in the accommodation control system and will be of value in the study of myopia onset and progression.

유연 관절 로봇의 적응 고장 수용 제어

본 논문은 다수의 구동기 고장을 가진 유연 관절 로봇의 적응 고장 수용 제어기를 제안한다. 다수의 구동기 고장의 크기와 일어나는 시간은 알려지지 않는다고 가정한다. 구동기 고장을 수용하기 위해 추종 오차의 수렴율과 오버슈트의 최대치로 특성화된 미리 정의된 성능을 보장하는 유계 조건을 갖는 적응 고장 수용 제어기를 설계한다. 르아프노브 안정도 이론을 이용하여 페루트 시스템의 모든 신호가 준 전역적이고 균일하고 궁극적으로 유계됨을 증명하고 추종 오차가 미리 정의된 성능 유계에서 벗어나지 않음을 보인다. This paper proposes an adaptive fault accommodation control approach for flexible-joint (FJ) robots with multiple actuator faults. It is assumed that the value and occurrence time of multiple actuator faults are unknown. An adaptive fault accommodation control scheme with prescribed performance bounds, which characterize the convergence rate and maximum overshoot of tracking errors, is designed to accommodate the actuator faults. From the Lyapunov stability theorem, it is proved that all signals of the closed-loop system are semi-globally uniformly ultimately bounded and tracking errors are preserved within prescribed performance bounds regardless of actuator faults.

Refraction in Children

The prevalence of refractive errors in children has been extensively researched. Comparisons between studies can, however, be compromised because of differences between accommodation control methods and techniques used for measuring refractive error. The aim of this study was to compare spherical refractive error results obtained at baseline and using two different accommodation control methods-extended optical fogging and cycloplegia-for two measurement techniques-autorefraction and retinoscopy. Participants included 25 school children aged 6 to 13 years (mean age, 9.52 ± 2.06 years). The refractive error of one eye was measured at baseline and again under two different accommodation control conditions: extended optical fogging (+2.00DS for 20 minutes) and cycloplegia (1% cyclopentolate). Autorefraction and retinoscopy were both used to measure the most plus spherical power for each condition. A significant interaction was demonstrated between measurement technique and accommodation control method (p = 0.036), with significant differences in spherical power evident between accommodation control methods for each of the measurement techniques (p < 0.005). For retinoscopy, refractive errors were significantly more positive for cycloplegia compared with optical fogging, which were in turn significantly more positive than baseline; whereas for autorefraction, there were significant differences between cycloplegia and extended optical fogging and between cycloplegia and baseline only. Determination of refractive error under cycloplegia elicits more plus than using extended optical fogging as a method to relax accommodation. These findings support the use of cycloplegic refraction compared with extended optical fogging as a means of controlling accommodation for population-based refractive error studies in children.

Multifractality in steady-state accommodation is robust to dynamic correction of aberrations using adaptive optics

When fixating on a stationary object, the human eye exhibits microfluctuations in accommodation. Changes in the magnitude of these fluctuations reflect changes in the accommodation control system. We used adaptive optics to determine the effect of monochromatic aberration dynamics on the control of steady-state accommodation of four subjects. The subjects viewed a stationary stimulus at 2 D while selective Zernike aberrations were corrected. The fluctuations in accommodation were characterised using a wavelet-based multifractal formalism approach. We found that for all subjects, and all experimental conditions, the accommodative fluctuations were multifractal. For one subject, we found that the width of the multifractal spectrum was statistically significantly larger when even-order aberrations were corrected as compared to no aberrations corrected. Hence, in general, for the subjects tested, the multifractal nature of steady-state accommodation control is unaffected by the manipulation of monochromatic aberration dynamics. Averaging across all subjects and experimental conditions, the mean spectrum was right-skewed with a most frequently occurring Hölder exponent of 0.31 ± 0.08. Future applications of multifractal analysis to accommodation control are discussed.

Actuator fault detection and adaptive accommodation control of flexible-joint robots

This study presents a fault detection and adaptive accommodation control scheme for flexible-joint (FJ) robots with model uncertainties and multiple actuator faults. It is assumed that the value and occurrence time of multiple actuator faults are unknown. A fault detection scheme is designed to detect the first actuator fault of uncertain FJ robots and the fault detectability characterising the class of actuator faults is analysed. Then, we design an adaptive fault accommodation control scheme with prescribed performance bounds, which characterise the convergence rate and maximum overshoot of tracking errors to accommodate the actuator faults and to compensate the effect caused by them. The proposed accommodation controller is developed based on the dynamic surface design and the adaptive technique. From the Lyapunov stability theorem, it is proved that all signals of the closed-loop system are semiglobally uniformly ultimately bounded and tracking errors are preserved within prescribed performance bounds regardless of actuator faults that occur after the first fault detection. A simulation example of a three-link FJ robot is provided to illustrate the effectiveness of the proposed scheme.

LoadFrequency Control Assessment using Restoration Index with Artificial Bee Colony Algorithm for Interconnected Power System with Disturbance Accommodation Controller

Based on the concept of Modern Control theory, an optimal robust power system controller for power restoration problem using Disturbance Accommodation theory has been adopted in this paper. This proposed methodology is applied to a TwoArea Two-Unit thermal Reheat Interconnected Power System (TATURIPS) taking into account of Super Conducting Magnetic Energy Storage (SMES) device and Gas Turbine (GT) unit in either area to meet out the system uncertainties due to various disturbances. For Load-Frequency Control (LFC) a decentralized PI controller for each area and a centralized Disturbance Accommodation Controller (DAC) in TATURIPS co-ordinated with SMES and GT units as back-up energy suppliers have been implemented in this proposed methodology. Feasible Restoration Index (FRI) and Complete Restoration Index (CRI) are computed for various disturbances based on settling time of the output response of the system and the control input deviation. The decentralized controller is tuned using the Artificial Bee Colony (ABC) algorithm. With these two Restoration Indices obtained from the Intelligent Controller (IC) as well as DAC, the conditions required to be satisfied in ensuring the restoration of the power system are listed out and with proper implementation will result in high degree of reliability and stability of power supply reducing the frequency deviations to a greater extent and the settling time is also reduced to a minimum time span.

${\cal L}_{\infty}$-Gain Adaptive Fuzzy Fault Accommodation Control Design for Nonlinear Time-Delay Systems

In this paper, an adaptive fuzzy fault accommodation (FA) control design with a guaranteed L(∞)-gain performance is developed for a class of nonlinear time-delay systems with persistent bounded disturbances. Using the Lyapunov technique and the Razumikhin-type lemma, the existence condition of the L(∞) -gain adaptive fuzzy FA controllers is provided in terms of linear matrix inequalities (LMIs). In the proposed FA scheme, a fuzzy logic system is employed to approximate the unknown term in the derivative of the Lyapunov function due to the unknown fault function; a continuous-state feedback control strategy is adopted for the control design to avoid the undesirable chattering phenomenon. The resulting FA controllers can ensure that every response of the closed-loop system is uniformly ultimately bounded with a guaranteed L(∞)-gain performance in the presence of a fault. Moreover, by the existing LMI optimization technique, a suboptimal controller is obtained in the sense of minimizing an upper bound of the L(∞)-gain. Finally, the achieved simulation results on the FA control of a continuous stirred tank reactor (CSTR) show the effectiveness of the proposed design procedure.