A study on a multivariate EWMA controller

Many manufacturing processes have, by nature, Multiple Input and Multiple Output (MIMO) variables. However, despite its frequent use in practice, MIMO process feedback control has not been fully investigated in the literature. Under a linear MIMO model, this paper proposes a Multivariate Exponentially Weighted Moving Average (MEWMA) controller. The stability conditions of this controller and the feasible region of its associated discount factor are derived. A discount factor which minimizes the total Mean Square Error (MSE) of the process output is obtained under the assumption that the process disturbance is either a white noise series or an IMA(1,1) series. An example is given to demonstrate the applicability of the proposed method. Some related issues are also discussed.     

On-line tuning of a single EWMA controller based on the neural technique

The exponentially weighted moving average (EWMA) controller has been proven to be an effective algorithm in the control the modern manufacturing system. The performance of the EWMA controlled process is based on choosing the correct EWMA gain. Most related research has focused on analysing the optimal EWMA gain in the static condition. The objective was to propose an approach based on the neural technique for on-line tuning of the single EWMA gain. The underlying approach indicated that the network learns very quickly when taking autocorrelation function and sample partial autocorrelation function patterns as the input features. It is shown that the sequence of the EWMA gains, generated by the proposed adaptive approach, converges close to the optimal controller value under several disturbance models, including IMA(1,1), and step and small ramp disturbances. In addition, the approach possesses a superior controlled output performance compared with the previous adaptive system.     

Stability and performance of a double MEWMA controller for drifted MIMO systems

Many semiconductor manufacturing processes have, by nature, Multiple-Input and Multiple-Output (MIMO) variables. For a drifted MIMO process, the double Multivariate Exponentially Weighted Moving Average (dMEWMA) controller is a popular run-to-run controller for adjusting the process mean to a desired target. The stability conditions of a dMEWMA controller have received considerable attention in the literature. There are two limitations in the existed literature. First, these approaches only demonstrate that the asymptotic mean will meet a desired target; however, they do not show that mean square error matrix for a process is bounded. Second, they do not have an explicit expression of the process output of the dMEWMA controller for any production run t. Hence, by using a conventional state space formulation, it is impossible to address the process performance (such as process fallout rate of the dMEWMA controller) analytically. Using a different approach, this paper derives an analytical expression for the process output of a dMEWMA controller. The problems of the stability conditions and the performance of the dMEWMA controller can then be addressed successfully.     

Modeling and analysis of EWMA control schemes with variance-adjusted control limits

A stochastic model of the EWMA control chart employing the variance-adjusted control limits is presented. The average run length for various shifts in the process mean is approximated by using a Markov chain approach. Following this, an alternative basis for the design of EWMA schemes is proposed. Computational results are presented and the impact of employing the variance-adjusted control limits on the average run length is investigated. Finally, conditions that permit the use of the asymptotic control limits in place of the variance-adjusted control limits are also identified.     

Economic design of a variable sampling rate EWMA chart

A Variable Sampling Rate (VSR) control chart is a control chart whose sampling scheme is to vary the sampling interval and the sample size for the next sample depending on the current chart statistic. A VSR EWMA chart is an EWMA chart with the VSR sampling scheme. An economic model, which was developed for a VSR chart, is also applied here to evaluate the efficiency of the VSR EWMA chart. The properties of the VSR EWMA chart are obtained by using a Markov chain approach. The model contains cost parameters which allow the specification of the costs associated with sampling, false alarms and operating off target as well as search and repair. This economic model can be used to quantify the cost saving that can be obtained by using a VSR chart instead of a Fixed Sampling Rate (FSR) chart and can also be used to gain insight into the way that a VSR chart should be designed to achieve optimal economic performance. It is shown that with some design parameter combinations the economically optimal VSR chart has a lower false alarm rate than the FSR chart.     

Design and stability analysis of a CMOS feedback laser driver

A feedback laser driver circuit has been developed to control the average optical output power of a double heterostructure CW laser diode and also to operate with a wideband amplitude modulation. The average light power monitoring is realized by measuring the photoelectric current of a photodiode integrated inside the package of the laser diode. Safety features, including transient signal suppression, protect the laser against excessive light power. To obtain responses that are not out of the absolute maximum ratings of the laser diode light power, a study of the feedback loop stability is necessary. Two transconductance structures, using inverting and noninverting circuits are compared using the dominant pole compensation method. Then, the more stable driver circuit is analyzed and integrated using CMOS technology.     

Performance analysis of an integral controller

Manufacturing processes need to be controlled during operation to provide quality products that satisfy the needs of the customer. A performance analysis of an integral controller is described in this paper. The controller can be used to control the quality of products manufactured at the output of a production process. The controller design procedure is based on an integral controller algorithm. The algorithm is developed by the application of modelling and process control techniques. The controller algorithm is simulated to find input adjustments that compensate exactly for the forecast disturbance (noise) inflicting a dynamic process, in which the adjustments minimize the output variance. The product variability (control error sigma) is minimized by maintaining the output quality variable at or near the controller set point. The integral controller can be useful in the control of sheet and film forming processes.     

Dynamic transient analysis by a mixed,iterative method

Mixed methods solved by an iterative process have been shown to provide an inexpensive procedure for improving the results of standard displacement analysis. This paper shows the possibilities present in their application to dynamic problems, where again accuracy improvement is achieved at small additional expense. The advantages of the formulation presented are particularly noteworthy in explicit forms where the difficulties of ‘hour-glass’ modes associated with minimal integration rules ae avoided without cost increase.     

Output feedback SSR damping controller design based on modular discrete-time dynamic model of TCSC

This paper presents the use of a modular, sample invariant, six samples per cycle, discrete-time model of a thyristor controlled series capacitor (TCSC) for output feedback-based subsynchronous resonance (SSR) damping controller (SSDC) design. An SSDC is used to alleviate the instability of torsional modes caused by external fixed capacitors used in conjunction with a TCSC. It is found that damping torque analysis-based design of an SSDC using a non-local signal like generator slip is straightforward and the resulting SSDC has a simple compensator structure. On the other hand, the residues and pole-zero configuration with the line current magnitude as a feedback signal are such that it is relatively more difficult to obtain a robust design, especially if several subsynchronous torsional modes are present. Eigenvalue analysis and digital simulation studies indicate that the TCSC model can accurately predict the behaviour of a TCSC with and without a damping controller.     

Extension of distance measurement range in a sinusoidal wavelength-scanning interferometer using a liquid-crystal wavelength filter with double feedback control

The optical path difference (OPD) and amplitude of a sinusoidal wavelength scanning (SWS) are controlled with a double feedback control system in an interferometer, so that a ruler marking every wavelength and a ruler with scales smaller than a wavelength are generated. These two rulers enable us to measure an OPD longer than a wavelength. A liquid-crystal Fabry-Perot interferometer (LC-FPI) is adopted as a wavelength-scanning device, and double sinusoidal phase modulation is incorporated in the SWS interferometer. Because of a high resolution of the LC-FPI, the upper limit of the measurement range can be extended to 280 microm by the use of the phase lock where the amplitude of the SWS is doubled in the feedback control. The ruler marking every wavelength is generated between 80 microm and 280 microm, and distances are measured with a high accuracy of the order of a nanometer in real time.     

Finite Element Stress and strain analysis of a double shear creep specimen

This paper reports on creep stress and strain results obtained by the finite element method (FEM) for a double shear specimen which was recently developed [1]. It considers stress redistribution during creep, small changes in specimen geometry during testing and high local stress states at the positions where the specimen is loaded. The results of the present study show that the unconstrained double shear test technique proposed in [1] yields viable results for shear strains of at least up to 0.10. ([1]: C. Mayr et al., Materials Science and Engineering, A 199 (1995) p. 121)     

Pressure transient analysis of deformable reservoirs

A new integrated methodology of evaluating the change in the permeability of a fractured or pressure-sensitive porous reservoir based on analytical or numerical simulation of a fluid inflow to a well has been proposed. The analysis draws on results of well tests. Analytical solutions of direct and inverse problems allow an evaluation of the permeability variation with decreasing pressure. Numerical simulation of an unsteadystate fluid inflow to a well (a direct problem) allows determining the diagnostic signs of variation in the reservoir permeability from the dynamics of the bottom hole pressure and an assessment of the evaluations obtained from solving an inverse problem. The methodology has been approved using results of some well tests.     

Dual-wavelength distributed feedback fiber laser based on double exposure and equivalent phase shift method

A special sampling structure based on double exposure technology is proposed to achieve dual-wavelength lasing in the distributed feedback fiber laser. This structure is composed of two grating pitches in one sampling period, which could be realized by changing the fiber's length in the fabrication. Through employing an equivalent phase shift, only a submicrometer-level precision is required for precise phase control. Then a stable dual-wavelength laser with the spacing of 400?pm is obtained in the experiment successfully. The output power is 30.46?μW and the sidemode suppression ratio is 46?dB under a pumped power of 146?mW.     

Stability analysis and controller synthesis for hybrid dynamical systems

Wherever continuous and discrete dynamics interact, hybrid systems arise. This is especially the case in many technological systems in which logic decision-making and embedded control actions are combined with continuous physical processes. Also for many mechanical, biological, electrical and economical systems the use of hybrid models is essential to adequately describe their behaviour. To capture the evolution of these systems, mathematical models are needed that combine in one way or another the dynamics of the continuous parts of the system with the dynamics of the logic and discrete parts. These mathematical models come in all kinds of variations, but basically consist of some form of differential or difference equations on the one hand and automata or other discrete-event models on the other hand. The collection of analysis and synthesis techniques based on these models forms the research area of hybrid systems theory, which plays an important role in the multi-disciplinary design of many technological systems that surround us. This paper presents an overview from the perspective of the control community on modelling, analysis and control design for hybrid dynamical systems and surveys the major research lines in this appealing and lively research area.     

Early effects of temperature-dependent yield stress in a transient analysis of fracture

Summary A semi-infinite crack grows due to stress wave diffraction in a thermoelastic solid. A rudimentary inelastic zone at the crack edge acts both as a heat flux site and as a crack-blunting mechanism. The first-step transient analysis treats constant crack/zone extension speeds and elastic properties. The yield stress, however, is allowed to vary with temperature.A relation involving the a priori unknown heat flux in the zone and an expression for the temperature response at the zone edge are found in the period right after fracture/zone initiation.These indicate that the applied (incident wave) stress must exceed the value necessary for zone formation predicted by a non-thermal analysis. The zone edge temperature increases rapidly at first, but then begins to level off in the same range of values noted in steady-state analyses at the time limit of the model validity. This temperature rise varies inversely with zone growth rate. A temperature-dependent yield stress definitely enhances the temperature rise, although the rise histories for this and a constant yield stress do not differ markedly in form.     

Accuracy of a class of concurrent algorithms for transient finite element analysis

The accuracy of a new class of concurrent, procedures for transient finite element analysis is examined. A phase error analysis is carried out which shows that wave retardation leading to unacceptable loss of accuracy may occur if a Courant condition based on the dimensions of the subdomains is violated. Numerical tests suggest that this Courant condition is conservative for typical structural applications and may lead to a marked increase in accuracy as the number of subdomains is increased. Theoretical speed-up ratios are derived which suggest that the algorithms under consideration can be expected to exhibit a performance superior to that of globally implicit methods when implemented on parallel machines.     

低温液体泵变频器运行异常的技术分析及改造

宝钢7#60000 m3/h空分设备配套10台低温液体泵所使用的T05系列变频器经常发生异常,导致空分设备工况波动,产品纯度降低。从变频器的安装位置和本体两方面分析了异常发生的原因,对变频器实施移位、改型改造和开发变频器的制动功能后,运转平稳。简介T05系列变频器及电机的技术参数,介绍运行异常现象和改造效果。     

An analysis of the transient stresses in a heavy duty switching unit

An analysis has been made of the transient bending and shear stresses set up in the drive shaft of an 11 W ring main switch unit manufactured by South Wales Switchgear Ltd. The analysis compares theoretical bending and shear stress plots along the main shaft with experimental values obtained from electrical resistance strain gauges.