Showing papers in "Quality Technology and Quantitative Management in 2019"
TL;DR: In this paper, the Adaptive Exponentially Weighted Moving Average (AEWMA) chart is optimized for a wide range of mean shifts using zero and steady state modes, and the suggested AEWMA chart offers a more balanced protection for detecting both small and large shifts in the process mean than the classical EWMA chart.
Abstract: The Adaptive Exponentially Weighted Moving Average (AEWMA) chart, which combines the Shewhart and classical EWMA schemes, is usually designed using the Average Run Length () as the criterion to be optimized. The shape of the run length distribution is known to change according to the magnitude of the shift in the process mean, ranging from highly skewed when the process is in-control or nearly to approximately symmetric when the shift is large. Therefore, the Median Run Length () provides a more meaningful interpretation than the . In this paper, the is used as an alternative performance criterion, and the AEWMA chart is optimized for a wide range of mean shifts using zero and steady state modes. Comparative results show that the suggested AEWMA chart offers a more balanced protection for detecting both small and large shifts in the process mean than the classical EWMA chart, in terms of the performance. The construction of the -based AEWMA chart is also illustrated using an example, and it is com...
41 citations
TL;DR: The proposed VSSI AI chart shows a better performance than the EWMA, EWMA AI and Syn AI charts, in terms of the ATS and EATS criteria.
Abstract: A variable sample size and sampling interval (VSSI) control chart using the auxiliary information (VSSI AI) is proposed for efficiently monitoring the process mean. The control chart’s statistics, ...
30 citations
TL;DR: In this article, a quasi-birth-and-death process is used to analyze an M/M/c balking retrial queue with vacation policies and derive the useful formulae for computing the rate matrix and stationary probabilities.
Abstract: This paper deals with an M/M/c balking retrial queue with vacation. Both single and multiple vacation policies are analysed. This system is investigated as a quasi-birth-and-death process. Using the matrix-geometric method, we derive the useful formulae for computing the rate matrix and stationary probabilities. Various system performance measures are further developed in the matrix-form expressions. We construct a cost function to determine the optimum value of servers and the optimum mean service rate subject to the stability condition at minimum cost. Quasi-Newton method, Nelder–Mead simplex method and simulated annealing method are employed to perform the optimization tasks. Under optimum operating conditions, we provide the numerical results for a comparison of vacation policies. An application example is given to illustrate the system’s potential applicability.
27 citations
TL;DR: The effect of measurement errors on the performance of adaptive control charts has rarely been investigated in the univariate case and, as far as we know, it has not been investigated at all in the multivariate case as mentioned in this paper.
Abstract: The effect of measurement errors on the performance of adaptive control charts has rarely been investigated in the univariate case and, as far as we know, it has not been investigated at all in the...
26 citations
TL;DR: This paper presents an exact approach based on integral equations for studying the run length performance of the EWMA control chart with runs rules using either simulation or Markov chains.
Abstract: The EWMA chart is a control chart that is able to quickly detect small to moderate shifts in the process mean. Runs rules is a popular technique in the area of control charts that are used to improve the performance of the standard Shewhart control chart for the mean. Recently, several researchers investigated the performance of EWMA type control charts incorporating runs rules using either simulation or Markov chains. As these methods only yield approximate results, in this paper, we present an exact approach based on integral equations for studying the run length performance of the EWMA control chart with runs rules.
25 citations
TL;DR: This work studies customer equilibrium balking strategies in single-server Markovian queueing systems with a single working vacation and vacation interruption, where the server undertakes workload with a lower service rate rather than completely stops working during the vacation period.
Abstract: In this work, we study customer equilibrium balking strategies in single-server Markovian queueing systems with a single working vacation and vacation interruption. That is, the server undertakes w...
24 citations
TL;DR: A general overview of research conducted in the field of process capability using bibliometric indicators reveals that W.L. Pearn and C.W. Wu are the two most influential authors in process capability research and Journal of Quality Technology, and Quality and Reliability Engineering International are theTwo most influential journals for publishing process capability researches.
Abstract: Bibliometric research focuses on the analysis of the bibliographic indicators quantitatively. It is a useful way for classifying information according to different variables, including journals, in...
23 citations
TL;DR: This model has a potential applications in various fields, such as in the cognitive radio network and the manufacturing systems, and some important performance measures, stochastic decomposition property of the system size distribution and the reliability indices are obtained.
Abstract: This paper deals with a batch arrivals queue with general retrial time, breakdowns, repairs and reserved time Here we assume that customers arrive according to compound Poisson processes Any arri
21 citations
TL;DR: In this paper, a two-phase partially accelerated degradation test (PADT) is proposed, which is designed to efficiently obtain product lifetime information in the development stage for new products, when reliability-related information is generally limited and there is limited sample availability.
Abstract: Securing reliability information on newly developed products is difficult, as only a few samples are available in the development stage. In practice, life tests for new products are conducted under both the normal use condition and accelerated stress conditions. In this study, a two-phase partially accelerated degradation test (PADT) is proposed, which is designed to efficiently obtain product lifetime information in the development stage for new products, when reliability-related information is generally limited and there is limited sample availability. In the first phase, a two-stress-level PADT plan is developed to estimate the parameters of an accelerated degradation model based on the D-optimality criterion. In the second phase, a three-stress-level compromise plan is developed such that the asymptotic variance of maximum likelihood estimate of q-th quantile of the lifetime distribution under the use condition is minimized. Finally, the two-phase systematic test plan is illustrated with a num...
20 citations
TL;DR: An extension study on the optimal periodic replacement policy for repairable products under the free-repair warranty with a new and more general type of repair, called the GPP repair, which is defined based on the Generalized Polya Process and which is more close to practical situations than the ‘minimal repair’.
Abstract: This article provides an extension study on the optimal periodic replacement policy for repairable products under the free-repair warranty. A new and more general type of repair, called the ‘GPP re...
17 citations
TL;DR: An autoregressive moving average model-filtered hidden Markov model is proposed to fit the multi-phase degradation data with unknown number of jump points, together with an iterative algorithm for parameter estimation that converges fast with satisfactory parameter estimates accuracy, regardless of the jump point number.
Abstract: The performance of certain critical complex systems, such as the power output of ground photovoltaic (PV) modules or spacecraft solar arrays, exhibits a multi-phase degradation pattern due to the redundant structure. This pattern shows a degradation trend with multiple jump points, which are mixed effects of two failure modes: a soft mode of continuous smooth degradation and a hard mode of abrupt failure. Both modes need to be modeled jointly to predict the system residual life. In this paper, an autoregressive moving average model-filtered hidden Markov model is proposed to fit the multi-phase degradation data with unknown number of jump points, together with an iterative algorithm for parameter estimation. The comprehensive algorithm is composed of non-linear least-square method, recursive extended least-square method, and expectation–maximization algorithm to handle different parts of the model. The proposed methodology is applied to a specific PV module system with simulated performance measur...
TL;DR: The results show that the proposed model has the best comparative performance, and the sensitivity analyses can help supply chain managers make decisions regarding adjustments in quality management and production rates.
Abstract: Traditional view of quality has proved to underestimate quality-related cost, and the concept of quadratic quality loss proposed by Dr Taguchi is a more realistic function for measuring quality. To...
TL;DR: By applying the supplementary variable technique, the steady state joint distribution of the server and the number of customers in the orbit is obtained and various interesting performance measures are derived.
Abstract: In this paper, an M/G/1 retrial queue with general retrial times and Bernoulli working vacation interruption is considered. If the server is busy, an arriving customer either enters an orbit with p...
TL;DR: In this paper, the covariance matrix of multiple variables was monitored using a control chart restricted to multivariate normal distribution and when the process distribution was non-normal, the performance was improved.
Abstract: Most existing control charts monitoring the covariance matrix of multiple variables were restricted to multivariate normal distribution. When the process distribution is non-normal, the performance...
TL;DR: In this paper, two attribute control charts under multiple dependent state sampling (MDS) and its modification are proposed to monitor the multivariate Poisson count data and the sensitivity of the sensitivity is evaluated.
Abstract: In this paper, two attribute control charts under multiple dependent state sampling (MDS) and its modification are proposed to monitor the multivariate Poisson count data. The sensitivity o...
TL;DR: The optimal replacement age is investigated when a component failure is not detected immediately until a k-out-of-n: G system fails, to minimize the expected total system cost when a generalized block replacement model is developed using downtime period.
Abstract: In this study, an optimal maintenance policy is developed for a k-out-of-n: G system subject to two types of maintenance services, preventive maintenance and corrective maintenance. We investigate ...
TL;DR: A generalized linear model for beta-distributed data in multistage processes is proposed in order to estimate the distribution parameters and two approaches for process monitoring and control are developed: they are model-based SPC charts and a beta regression model.
Abstract: Multistage statistical process control (SPC) is an effective procedure for ensuring quality of products in multistage manufacturing processes. Effective SPC approaches for monitoring and controlling quality in multistage processes are limited. Beta distributed data explained by process input variables are generally prevalent in multistage process industries. In this paper, we propose a generalized linear model for beta-distributed data in multistage processes in order to estimate the distribution parameters and develop two approaches for process monitoring and control: they are model-based SPC charts and a beta regression model. The proposed control charts outperform the existing control charts in terms of the out-of-control average run length for the detection of process mean shifts.
TL;DR: The short-term (also known as zero-state mode) run-length theoretical properties of the four different types of synthetic and runs-rules monitoring schemes that were empirically analyzed in another paper are discussed.
Abstract: Part of this work was supported by the SARChI Chair at the University of Pretoria. Sandile Shongwe’s
research was supported in part by the National Research Foundation (NRF) and Department of Science and
Technology’s Innovation Doctoral scholarship (SFH14081591713; Grant number: 95208) as well as
Department of Statistics’ STATOMET and Marien Graham’s research was supported in part by NRF’s
Thuthuka program (TTK14061168807, Grant number: 94102).
TL;DR: This paper investigates the availability and optimal maintenance policy for inspected Markov systems with down time threshold, and a maintenance model is formulated to find the optimal inspection interval, T*, which minimizes the long-run average cost rate.
Abstract: Practically, many repairable systems are subject to neglected failures, i.e. if some failures can be repaired promptly they will not affect system availability. This paper investigates the ...
TL;DR: Due to the non-substitutability of the product, the monopoly manufacturer designs warranty to reduce maximally warranty cost as discussed by the authors.Although the monopoly manufacturers maintains responsibly produc....
Abstract: Due to the non-substitutability of the product, the monopoly manufacturer designs warranty to reduce maximally warranty cost. Although the monopoly manufacturer maintains responsibly produc...
TL;DR: The results show that the Run Rules chart requires a much larger amount of Phase I data to sufficiently reduce the between-practitioners variability, and the properties of Run rules chart with estimated parameters under the non-normal distributed data are investigated.
Abstract: Run Rules Xˉ chart are often implemented for process monitoring. The process observations are usually assumed normally distributed, and the process parameters are assumed known. In fact, a ...
TL;DR: In this paper, a two-stage approach was proposed to deal with lifetime data from experiments with subsampling, which can deal with life-span data with a two stage approach.
Abstract: Accelerated life tests usually contain subsampling, which represents a restriction on randomization. The two-stage approach can deal with lifetime data from experiments with subsampling. However, t...
TL;DR: The dual response surface optimization (DRSO) approach as discussed by the authors attempts to simultaneously optimize the mean and standard deviation of a response variable, which can be used to optimize both the response variable and the response surface.
Abstract: The dual response surface optimization (DRSO) approach attempts to simultaneously optimize the mean and standard deviation of a response variable. In DRSO, the mean and standard deviation o...
TL;DR: A new exponentially weighted moving average (EWMA) interquartile range control chart with single sampling and double sampling schemes, respectively, for detecting the out-of-control variance/standard deviation of a critical quality characteristic that exhibits a non-normal or unknown distribution.
Abstract: Control charts are effective tools for signal detection for both manufacturing and service processes. Much of the data in service industries come from processes exhibiting non-normal or unknown dis...
TL;DR: The results show that the proposed method is able to make a trade-off between the quality-control cost and the customer waiting time, and indicate how the resulting design is sensitive to the misspecification of the input parameters.
Abstract: The main purpose of this paper is to design a control chart for monitoring the service processes in congested immobile single-stage service systems where customer arrivals are time dependent. It is...
TL;DR: Overlapping coefficient is a direct measure of similarity between two distributions which is recently becoming very useful in many fields of applications including microarray analysis for t... as discussed by the authors, and is used in many microarray applications.
Abstract: Overlapping coefficient is a direct measure of similarity between two distributions which is recently becoming very useful in many fields of applications including microarray analysis for t...
TL;DR: A procedure for determining LOD appropriately to control the actual POD in detecting the contamination by genetically modified grains (GM grains) from heterogeneous grain lots is proposed and it is shown that the optimal value of LOD can be determined that minimizes the total cost of inspection.
Abstract: A limit of detection (LOD) of analytical instruments is usually arbitrarily defined, for example, as the level of contamination at which the probability of detection (POD) is 50 or 95%. However, these definitions are ignoring the sampling uncertainty that emerges in the process of preparing test portions. Consequently, the actual POD becomes considerably smaller than the nominal POD. In this paper, we propose a procedure for determining LOD appropriately to control the actual POD in detecting the contamination by genetically modified grains (GM grains) from heterogeneous grain lots. We consider an actual procedure used in the sampling inspection. (1) The sample grains are drawn as increments from a lot. (2) The collected grains are combined to yield a composite to transport to the laboratory. (3) The test portions are created by sub-sampling from the composite in the laboratory. We first show that we can construct an optimal sampling plan for controlling POD under a given value of LOD: optimal num...
TL;DR: This research addresses a way of overcoming the disadvantage of the control chart by giving visual information on the time progress by locating areas indicating a caution and a warning of an out-of-control condition on the controlchart using AIC.
Abstract: The (x¯,s) control chart is one of simultaneous control charts to monitor process mean and variance on x¯-s coordinate. The primary purpose of the (x¯,s) control chart has been the judgement of the...
TL;DR: A self-starting monitoring scheme is proposed in this paper for the simultaneous detection of variance and coefficients in linear profiles with unknown error distributions and a recursive algorithm is provided to quickly calculate statistics sequentially.
Abstract: A self-starting monitoring scheme is proposed in this paper for the simultaneous detection of variance and coefficients in linear profiles with unknown error distributions. Based on the glo...
TL;DR: A two-stage method composing of quality verification and selection decision for multiple-line supplier selection problems for semiconductor manufacturing, which test whether the new supplier has a significantly better capability than the existing supplier based on the multiple- line yield index in the stage ofquality verification.
Abstract: Supplier selection is an essential issue, particularly, for semiconductor manufacturing. Nowadays, since high demands in the globally competitive semiconductor manufacturing environment, multiple-l...