Smiley W. Cheng

A New Measure of Process Capability: Cpm

A new measure of the process capability (Cpm) is proposed that takes into account the proximity to the target value as well as the process variation when assessing process performance. The sampling distribution for an estimate of Cpm (Ĉpm) and some of i..

Monitoring Process Mean and Variability With One EWMA Chart

Two EWMA charts are usually required to monitor both process mean and variability. In this paper, we propose a new EWMA chart which effectively combines the usual two EWMA charts into one chart. In particular, the new EWMA chart has the property that it is effective in detecting both increases and decreases in mean and/or variability.

A mulvariate measure of process Capability

AbstractA measure of process capability for the multivariate normal case is proposed. This measure takes into account both proximity to the target and the variation observed in the process. The result is analogous to the univariate measure of process capability referred to as Cpm. Some statistical properties associated with the measure are examined. Multivariate specification limits and their creation are also discussed.

Single Variables Control Charts: an Overview

Control charts are widely used in industries to monitor a process for quality improvement. When dealing with variables data, we usually employ two control charts to monitor the process location and spread. We give an overview of the control charts proposed in the last decade or so in an effort to use only one chart to simultaneously monitor both process location and spread. Two approaches have been advocated for using one control chart for process monitoring. One approach plots two quality characteristics in the same chart while the other uses one plotting variable to represent the process location and spread. Copyright

A New Multivariate Control Chart for Monitoring Both Location and Dispersion

ABSTRACT A multivariate exponentially weighted moving average single control chart is developed in this article. This chart is capable of monitoring simultaneously the process mean vector and the process covariance matrix. Our average run length comparison shows that this new chart performs better than the combination of the χ2 chart and the |S| chart when small changes in the process parameters are of interest.

Semicircle Control Chart for Variables Data

To monitor a process for variables data, X and R charts have been used commonly in the last seven decades. Based on an original proposal by Repco and Van Nuland, we propose an improved single chart called the semicircle (SC) chart. This chart is exact a..

A new nonparametric EWMA Sign Control Chart

Research highlights? A new EWMA Sign Chart is proposed for detecting deviation from the process target. ? It is suitable for data came from a process with a non-normal distribution. ? The properties of the EWMA statistics are examined. Example shows that the EWMA chart had better performance compared to Shewhart chart. Many data in practice came from a population/process with a non-normal or often unknown distribution, hence the commonly-used Shewhart control chart, which requires normality of the monitoring statistics, is not suitable. In this paper, a new nonparametric EWMA Sign Control Chart is proposed for monitoring and detecting possible deviation from the process target. The sampling properties of the new monitoring statistics are examined and the average run lengths of the proposed chart are derived for evaluating its performance. An example is used to illustrate the proposed chart and compare with other existing charts, assuming normality. Furthermore, an arcsine transformed EWMA Sign Chart is examined and proposed. The average run lengths of the Arcsine EWMA Chart are more reasonable than those of the EWMA Sign Chart. The Arcsine EWMA Sign Chart is recommended if we were concerned with the proper values of the average run length.

A New EWMA Control Chart for Monitoring Both Location and Dispersion

Abstract A new control chart, which employs the exponentially weighted moving average (EWMA) technique, is proposed. The statistic for the chart defines the area below a straight line as the control region, which makes the charting procedure easier than the usual approach. This chart can effectively monitor the process mean and the increased process variability simultaneously, and can detect the source and the direction of a change easily.

Assessing Process Capability: A Bayesian Approach

Abstract Quality Control Practitioners often base inferences regarding the capability of a process on a point estimate without examining the distributional qualities of the estimator used. A Bayes solution is proposed that provides good statistical analysis that can be easily used and interpreted on the manufacturing floor.

IS THE PROCESS CAPABLE? TABLES AND GRAPHS IN ASSESSING Cpm

A simple decision-making approach was used to assess the capability of a process. Tables and Graphs are generated from this procedure to help the practitioner to use process capability index Cpm to assess the process...