Adaptive control of magnetic levitation system subject to external disturbances

In this paper, an adaptive controller is designed for a magnetic levitation system to cope with internal time-varying uncertainties and external disturbances. Since, in experimental studies, in experiments involving the traditional magnetic levitation design it is not easy to realize external disturbances to the system, a horizontal configuration is constructed in this paper. To facilitate the analysis and controller design, the equation of motion is derived in detail. Due to the asymmetric nature of the magnetic loop, there is a big challenge in the controller design process. In addition, since some of the uncertainties enter the system in a mismatched manner, few control strategies are feasible. A multiple-surface sliding control law is proposed with the function approximation technique to stabilize the closed loop system under various uncertainties and disturbances. A rigorous mathematical proof is given to verify the feasibility of the design. Experimental studies are conducted including comparisons with conventional PID design to clarify the performance of the proposed controller.     

Steerable Microinvasive Probes for Localized Drug Delivery to Deep Tissue

Enhanced understanding of neuropathologies has created a need for more advanced tools. Current neural implants result in extensive glial scarring and are not able to highly localize drug delivery due to their size. Smaller implants reduce surgical trauma and improve spatial resolution, but such a reduction requires improvements in device design to enable accurate and chronic implantation in subcortical structures. Flexible needle steering techniques offer improved control over implant placement, but often require complex closed‐loop control for accurate implantation. This study reports the development of steerable microinvasive neural implants (S‐MINIs) constructed from borosilicate capillaries (OD = 60 µm, ID = 20 µm) that do not require closed‐loop guidance or guide tubes. S‐MINIs reduce glial scarring 3.5‐fold compared to prior implants. Bevel steered needles are utilized for open‐loop targeting of deep‐brain structures. This study demonstrates a sinusoidal relationship between implant bevel angle and the trajectory radius of curvature both in vitro and ex vivo. This relationship allows for bevel‐tipped capillaries to be steered to a target with an average error of 0.23 mm ± 0.19 without closed‐loop control. Polished microcapillaries present a new microinvasive tool for chronic, predictable targeting of pathophysiological structures without the need for closed‐loop feedback and complex imaging.     

A new numerical algorithm for sub‐optimal control of earthquake excited linear structures

Exact optimal classical closed–open‐loop control is not achievable for the buildings under seismic excitations since it requires the whole knowledge of earthquake in the control interval. In this study, a new numerical algorithm for the sub‐optimal solution of the optimal closed–open‐loop control is proposed based on the prediction of near‐future earthquake excitation using the Taylor series method and the Kalman filtering technique. It is shown numerically that how the solution is related to the predicted earthquake acceleration values. Simulation results show that the proposed numerical algorithm are better than the closed‐loop control and the instantaneous optimal control and proposed numerical solution will approach the exact optimal solution if the more distant future values of the earthquake excitation can be predicted more precisely. Effectiveness of the Kalman filtering technique is also confirmed by comparing the predicted and the observed time history of NS component of the 1940 El Centro earthquake. Copyright © 2001 John Wiley & Sons, Ltd.     

Multi‐rate digital control for a cascaded system consisting of two subsystems with different input time delays

Abstract

This paper presents a multi‐rate state‐space control scheme for digital control of a cascaded continuous‐time system with fractional time delays. First, a discrete‐time state‐space representation of a continuous‐time system with a fractional input delay is established. Based on the time‐delay digital modelling, an ideal state reconstructor is also presented such that system states are exactly reconstructed via the measurement histories of inputs and outputs without a state observer. Next, a time‐delay subsystem (designated subsystem 1) with a fast sampling rate is designed to form the inner loop of the overall system, then the designed closed‐loop subsystem 1 is cascaded with a time‐delay open‐loop subsystem 2 with a slow sampling rate. A digital modelling of the time‐delay open‐loop subsystem 2, based on a fast‐rate sampling, is also formed for obtaining the digital modelling of the overall cascaded continuous‐time system by using the block‐pulse function approximation. Then, the fast‐rate overall system is converted into a slow‐rate model via the newly developed model conversion technique. Furthermore, subsystem 2 is separated from the slow‐rate overall system via a linear transformation for achieving a reduced‐order subsystem design. As a consequence, a digital control law is determined on some specific goals for the overall system. The proposed method is suitable for digital control of a multivariable, multi‐rate, time‐delay system in which state variables are not accessible.     

含反馈时滞的非线性动力系统参数辨识

以方程残差作为目标函数,运用基因遗传算法同时辨识受控系统的反馈时滞和物理参数。由于遗传算法具备良好的全局特性,且不要求目标函数光滑,该方法既适于线性系统的辨识也适于非线性系统的时滞辨识,方法中引入几种交叉和变异算子同时操作,大大提高了辨识效率和辨识精度,当需辨识参数过多时,可先用开环实验辨识部分系统参数,再用闭环实验辨识时滞和剩余的系统参数。     

Design and Application of Quality Control Strategies at the Operational Level of a Production Process Chain

This paper presents strategies for an automated control of distortion at the operational level of a production process chain, as well as first steps towards a combined implementation in heat‐treatment processes. In order to minimise the loss of production due to quality defects, the first quality control loop will be implemented on an in‐process level. The second control loop within the reach of operational control includes the feedback of post‐process measurements of quality features. As such, the post‐process control loop optimises the set‐values of the in‐process control loop.     

Partition experimental designs for sequential processes: Part I—First‐order models

The output quality or performance characteristics of a product often depend not only on the effect of the factors in the current process but on the effect of factors from preceding processes. Statistically‐designed experiments provide a systematic approach to study the effects of multiple factors on process performance by offering a structured set of analyses of data collected through a design matrix. One important limitation of experimental design methods is that they have not often been applied to multiple sequential processes. The objective is to create a first‐order experimental design for multiple sequential processes that possess several factors and multiple responses. The first‐order design expands the current experimental designs to incorporate two processes into one partitioned design. The designs are evaluated on the complexity of the alias structure and their orthogonality characteristics. The advantages include a decrease in the number of experimental design runs, a reduction in experiment execution time, and a better understanding of the overall process variables and their influence on each of the responses. Copyright © 2001 John Wiley & Sons, Ltd.     

Identification and fine tuning of closed‐loop processes under discrete EWMA and PI adjustments

Conventional process identification techniques of a open‐loop process use the cross‐correlation function between historical values of the process input and of the process output. If the process is operated under a linear feedback controller, however, the cross‐correlation function has no information on the process transfer function because of the linear dependency of the process input on the output. In this paper, several circumstances where a closed‐loop system can be identified by the autocorrelation function of the output are discussed. It is assumed that a proportional integral controller with known parameters is acting on the process while the output data were collected. The disturbance is assumed to be a member of a simple yet useful family of stochastic models, which is able to represent drift. It is shown that, with these general assumptions, it is possible to identify some dynamic process models commonly encountered in manufacturing. After identification, our approach suggests to tune the controller to a near‐optimal setting according to a well‐known performance criterion. Copyright © 2001 John Wiley & Sons, Ltd.     

Feature correlation for weld image-processing applications

Template matching or correlation is an image-processing technique that searches for specific features or characteristics within an image. This paper describes the use of a configurable feature correlation method for the reliable processing of high quality digitized welding images in order to supply measurements for use with a closed loop control system. A generic approach has been adopted to produce a versatile and robust image-processing technique capable of analysing and providing measurements from images with different properties or characteristics. Low cost, commercially available image acquisition hardware was used, and the image-processing software development was undertaken using a commonly available PC-based visual programming environment. The general application of this work has been concerned with the demonstration of vision-based closed loop process control strategies for a series of different welding processes. Closing the process control loop in this manner is believed to represent a significant advancement of the vision-based remote viewing or ‘monitoring’ systems that are presently available.     

Blood glucose concentration control for type 1 diabetic patients: a multiple‐model strategy

In this study, a multiple‐model strategy is evaluated as an alternative closed‐loop method for subcutaneous insulin delivery in type 1 diabetes. Non‐linearities of the glucose–insulin regulatory system are considered by modelling the system around five different operating points. After conducting some identification experiments in the UVA/Padova metabolic simulator (accepted simulator by the US Food and Drug Administration (FDA)), five transfer functions are obtained for these operating points. Paying attention to some physiological facts, the control objectives such as the required settling time and permissible bounds of overshoots and undershoots are determined for any transfer functions. Then, five PID controllers are tuned to achieve these objectives and a bank of controllers is constructed. To cope with difficulties of the presence of delays in subcutaneous blood glucose (BG) measuring and in administration of insulin, a glucose‐dependent setpoint is considered as the desired trajectory for the BG concentration. The performance of the obtained closed‐loop glucose–insulin regulatory system is investigated on the in silico adult cohort of the UVA/Padova metabolic simulator. The obtained results show that the proposed multiple‐model strategy leads to a closed‐loop mechanism with limited hyperglycemia and no severe hypoglycemia.Inspec keywords: blood, patient diagnosis, medical control systems, biochemistry, three‐term control, closed loop systems, diseases, patient treatment, drugs, sugarOther keywords: blood glucose concentration control, type 1 diabetic patients, multiple‐model strategy, alternative closed‐loop method, subcutaneous insulin delivery, type 1 diabetes, transfer functions, control objectives, PID controllers, subcutaneous blood glucose measuring, glucose‐dependent setpoint, closed‐loop glucose–insulin regulatory system, closed‐loop mechanism     

Identification of linear systems captured in a feedback loop

The identification of model parameters using measured input-output data from linear systems operating in a closed loop is discussed. A frequency-domain maximum likelihood estimator which takes into account the correlation between the input and output disturbances is presented. Its properties are analyzed and illustrated by simulation examples and real measurements     

Statistical process monitoring with principal components

Most industrial processes are characterized by a system of several variables, all of which are subject to drifts, disturbances, and assignable causes of variation. In the chemical and process industries, there are often inertial forces arising from raw material streams, reactors and tanks that introduce serial correlation over time into these variables. This autocorrelation can have a profound impact on the effectiveness of the statistical monitoring methods used for such processes. This paper reviews some of the available methodology for multivariate process monitoring and shows the effectiveness of principal components in this context. An application of the principal components approach with correlated observation vectors is presented. The effectiveness of this procedure to indicate process upsets is discussed.     

On designing an efficient control chart to monitor fraction nonconforming

Process control measures are mostly applied in production and manufacturing industries. The most important tool used in these disciplines is control chart. In manufacturing and production processes, when the quality characteristic of interest cannot be directly measured, it becomes essential to apply attribute control charts. To monitor fraction nonconforming of the output, quality practitioners mostly prefer p-chart. In this article, a new progressive mean (PM) control chart is being proposed for monitoring drift in proportion of nonconforming products. The design evaluations of the proposed chart are made and compared through different properties of run length distribution, such as average run length (ARL), standard deviation of run length (SDRL), and some percentile points. The performance of the proposed chart is assessed under zero-state and steady-state scenarios. The proposed PM chart is compared with p-chart, moving average (MA) chart, optimal CUSUM chart, modified exponentially weighted moving average (EWMA) chart, and runs rules p-charts for monitoring fraction nonconforming. The proposed chart spots efficiently sustained disturbances in the process as compared with their existing counterparts. Two illustrative examples are also provided; one from real-life application of nonconforming bearing and seal assemblies data and the other from simulated data for the implementation of PM chart.     

Adaptive neuro-fuzzy approach for predicting hardness of deposited TiN/ZrN multilayer coatings

This paper presents an adaptive neuro-fuzzy approach based on first order function of fuzzy model for establishing the relationship between control factors and thin films properties of TiN/ZrN coatings on Si(100) wafer substrates. A statistical model was designed to explore the space of the processes by an orthogonal array scheme. Eight control factors of closed unbalance magnetron sputtering system were selected for modeling the process, such as interlayer material, argon and nitrogen flow rate, titanium and zirconium target current, rotation speed, work distance, and bias voltage. Analysis of variance (ANOVA) was carried out for determining the influence of control factors. In this study, with the application of ANOVA, the smallest effect of control factors was eliminated. The adaptive neuro-fuzzy inference system (ANFIS) was applied as a tool to model the deposited process with five significant control factors. The experimental results show that ANFIS demonstrates better accuracy than additive model for the film hardness. The root mean square error between prediction values and experimental values were archived to 0.04.     

A self‐tuning run‐by‐run process controller for processes subject to random disturbances

Abstract

In this paper a self‐tuning run‐by‐run process controller is presented. The controller has the capability of choosing a control parameter dynamically in response to the underlying process disturbances. There are two modules in this controller: a self‐tuning loop trigger module and a run‐by‐run feedback control module. In the self‐tuning loop trigger module, two EWMA control charts are used sequentially to determine if there is a large or medium shift in the process output and to trigger a new self‐tuning loop accordingly. In the run‐by‐run feedback control module, the control parameter and control model are re‐tuned sequentially and a new process recipe is generated, on a run‐by‐run basis, to compensate for the process output's deviation from the target. Monte Carlo simulation results show that the self‐tuning run‐by‐run process controller is superior to the current run‐by‐run process controller with a fixed control parameter.     

Assembly sequence planning for processes with heterogeneous reliabilities

Stochasticity in assembly processes is often associated with the processing time and availability of machinery, tools and manpower, however in this paper it is determined by probability of an assembly task successful completion which here is referred to as task reliability. We present a mathematical model for optimising the expected assembly cost, and consider two scenarios: the first a situation where a failure of one assembly task requires rework of that task alone; second a situation in which a failure in the midst of the process requires resumption of previously completed tasks. In the worst case scenario the assembly process must restart from the beginning. We show that the first scenario is insensitive to sequencing unless there are set-up costs. In the second scenario the process is sensitive to tasks’ sequence. We present a heuristic that argues for accomplishing more uncertain tasks (with less reliability) earlier in the process to decrease the expected cost of assembly, and show that in a mutually dependent assembly process, when tasks’ reliabilities are similar, the cheaper tasks should be executed earlier in the process.     

闭链双臂空间机器人动力学建模及力矩受限情况下载荷运动自适应控制

讨论了在输入受限的情况下,漂浮基双臂空间机器人抓持负载后转移目标过程中的建模与自适应控制问题。利用拉格朗日第二类方程建立了开链空间机器人系统动力学模型,之后结合闭链系统的闭环约束条件,获得了闭链双臂空间机器人系统的动力学方程。在这个基础上,考虑到双臂空间机器人及负载存在参数不确定,系统存在外部扰动及输入力矩有限的情况,设计了自适应控制方案,以完成对载荷位置和姿态运动的精确控制。由带饱和函数的控制律限制输入力矩,采用自适应控制器逼近系统的不确定度。方案中利用高精度滤波器估计系统速度及角速度,从而仅需测量其位置信息。通过Lyapunov方法证明了系统的稳定性。最后通过数值仿真实验模拟了平面双臂空间机器人转移目标过程,并证实了上述控制方案的有效性。     

磁势自平衡回馈补偿式直流传感器

研究了一种新型磁势自平衡回馈补偿式直流传感器，介绍了这种传感器的工作原理与设计方案，给出了该系统的稳定性分析、误差分析、暂态性能指标。该传感器将开环原理与闭环原理的优点有机地结合起来，使其既具有准确度高(从传统直流传感器0．5％的测量准确度提高到0．1％)、线性度好、抗干扰能力强的优点，也不存在系统振荡及大功率驱动问题的弱点，且电路结构简单、稳定性好、可靠性高、自动跟踪补偿和响应速度快。     

A simple practical analytic design method for multiloop‐controlled PWM switching regulators

Abstract

In this paper, a simple practical analytic method is proposed for designing multiloop‐controlled pulse width modulation (PWM) switching regulators. First, an equivalent single loop gain is presented and an approximate optimal set of closed‐loop poles is suggested according to the given specification such that the familiar design concept of a single‐loop second order system can be applied directly. In particular, closed form expressions of the feedback gains and the unknown parameters of the standard implemented circuit are derived. This renders the implementation problem surprisingly simple. Finally, some experimental results are also presented to demonstrate the effectiveness of the proposed method.     

Damping characteristics of magneto‐rheological fluid absorber based on closed‐loop proportion integration differentiation control

Aiming at investigating the working of magneto‐rheological fluid absorber, a test system used for detecting the damping characteristics of the magneto‐rheological fluid absorber was designed. The test system included sensors, data acquisition card, and so on. The vibration signals were detected by the sensors, put into LabVIEW data acquisition system, and then collected through the processing of closed‐loop Proportion Integration Differentiation control algorithm. Considering that the feedback current could be output to the magneto‐rheological fluid absorber by the data acquisition card, thus the damping force could be changed. The test results showed that the amplitude of the structure vibration response was obviously reduced through the closed‐loop Proportion Integration Differentiation control algorithm, and the control damping characteristics of the magneto‐rheological fluid absorber was improved.