• Title/Summary/Keyword: EWMA controller

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Modifications of single and double EWMA feedback controllers for balancing the mean squared deviation and the adjustment variance (편차제곱평균과 수정량분산의 균형을 위한 단일 및 이중 지수가중이동평균 피드백 수정기의 수정)

  • Park, Chang-Soon;Kwon, Sung-Gu
    • Journal of the Korean Data and Information Science Society
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    • v.20 no.1
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    • pp.11-24
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    • 2009
  • The process controller in the adjustment procedure is often used effectively to control the process level close to target when noise is present and unremovable. Examples of the robust controller are single EWMA controller and double EWMA controller. Double EWMA controller is designed to reduce the offset of the process deviation, which single EWMA can not eliminate. In this paper, the two controllers are modified by taking EWMA of the original controller to reduce the adjustment variance, which may become excessively large when the two given controllers are implemented. It is shown that the EWMA modification of the given controllers is successful in reducing the adjustment variance, while the mean squared deviation increases slightly.

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A Simulation study of EWMA control using dynamic control parameter (동적 모수를 사용한 EWMA 제어의 시뮬레이션 연구)

  • Kang, Seok-Chan;Hwang, Ji-Bin;Kim, Sung-Shick;Kim, Ji-Hyun
    • Journal of the Korea Society for Simulation
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    • v.16 no.2
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    • pp.37-44
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    • 2007
  • EWMA is one of the most popular controller method used in Run-to-Run control system for semiconductor manufacturing. The value of the control parameter in EWMA has major effect on the result. Therefore, it is important to use control parameter value fitting for the process state. When the process is unstable, it is more efficient to change EWMA control parameter dynamically to compensate for the changing process state than using fixed control parameter. In this paper, we review previous studies using dynamic EWMA control parameter and propose a new algorithm complementing the weaknesses of the previous studies. The performance of the proposed algorithm is validated using simulation.

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Recursive Least Squares Run-to-Run Control with Time-Varying Metrology Delays

  • Fan, Shu-Kai;Chang, Yuan-Jung
    • Industrial Engineering and Management Systems
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    • v.9 no.3
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    • pp.262-274
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    • 2010
  • This article investigates how to adaptively predict the time-varying metrology delay that could realistically occur in the semiconductor manufacturing practice. Metrology delays pose a great challenge for the existing run-to-run (R2R) controllers, driving the process output significantly away from target if not adequately predicted. First, the expected asymptotic double exponentially weighted moving average (DEWMA) control output, by using the EWMA and recursive least squares (RLS) prediction methods, is derived. It has been found that the relationships between the expected control output and target in both estimation methods are parallel, and six cases are addressed. Within the context of time-varying metrology delay, this paper presents a modified recursive least squares-linear trend (RLS-LT) controller, in combination with runs test. Simulated single input-single output (SISO) R2R processes subject to various time-varying metrology delay scenarios are used as a testbed to evaluate the proposed algorithms. The simulation results indicate that the modified RLS-LT controller can yield the process output more accurately on target with smaller mean squared error (MSE) than the original RLSLT controller that only deals with constant metrology delays.

A Study on the Relation between Multivariate Process Control Techniques and Trend Algorithm (다변량 공정관리 기술과 추세알고리즘의 연계에 관한 조사연구)

  • Jung, Hae-Woon
    • Journal of the Korea Safety Management & Science
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    • v.13 no.4
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    • pp.225-235
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    • 2011
  • Autoregressed Controller, which have trend algorithm, seeks to minimize variability by transferring the output variable to the related process input variable, while multivariate process control techniques seek to reduce variability by detecting and eliminating assignable causes of variation. In the case of process control, a very reasonable objective is to try to minimize the variance of the output deviations from the target or set point. We also investigate algorithm with relevant Shewhart chart, Theoretical control charts, precontrol and process capability. To help the people who want to make the theoretical system, we compare the main techniques in "a study on the relation between multivariate process control techniques and trend algorithms".

Optimization of Magnetic Abrasive Polishing Process using Run to Run Control (Run to Run 제어 기법을 이용한 자기연마 공정 관리)

  • Ahn, Byoung-Woon;Park, Sung-Jun
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.18 no.1
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    • pp.22-28
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    • 2009
  • In order to optimize the polishing process, Run to Run control scheme has been applied to the micro mold polishing in this study. Also, to fully understand the effect of parameters on the surface roughness a design of experiment is performed. By linear approximation of main factors such as gap and rotational speed of micro quill, EWMA (Exponential Weighted Moving Average) gradual mode controller is adopted as a optimizing tool. Consequently, the process converged quickly at a target value of surface roughness Ra 10nm and Rmax 50nm, and was hardly affected by unwanted process noises like initial surface quality and wear of magnetic abrasives.

Procedure for monitoring special causes and readjustment in ARMA(1,1) noise model (자기회귀이동평균(1,1) 잡음모형에서 이상원인 탐지 및 재수정 절차)

  • Lee, Jae-Heon;Kim, Mi-Jung
    • Journal of the Korean Data and Information Science Society
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    • v.21 no.5
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    • pp.841-852
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    • 2010
  • An integrated process control (IPC) procedure is a scheme which simultaneously applies the engineering control procedure (EPC) and statistical control procedure (SPC) techniques to reduce the variation of a process. In the IPC procedure, the observed deviations are monitored during the process where adjustments are repeatedly done by its controller. Because the effects of the noise, the special cause, and the adjustment are mixed, the use and properties of the SPC procedure for the out-of-control process are complicated. This paper considers efficiency of EWMA charts for detecting special causes in an ARMA(1,1) noise model with a minimum mean squared error adjustment policy. And we propose the readjustment procedure after having a true signal. This procedure can be considered when the elimination of the special cause is not practically possible.