Papers by Keyword: Control Chart

Abstract: Traditional control charts often struggle to simultaneously detect both small and large shifts in process parameters. This study proposes the AEWMA-Max method, an improved variant of the Adaptive Exponentially Weighted Moving Average Max (AEWMAM) chart, to address this challenge in the context of monitoring temperature fluctuations in vannamei shrimp ponds. The research employs a data set containing 26 out-of-control and 64 in-control temperature measurements. AEWMA-Max utilizes a dynamically adjusted smoothing parameter (L) to achieve optimum sensitivity for both subtle and significant deviations from the desired temperature range. Through extensive simulations and comparisons with existing control charts, L = 2.642 was identified as the most effective value for this specific application. The amount of out-of-control data on the control chart is the better metric for determining the best charts used in monitoring the process. Based on the monitoring results, the proposed AEWMA-Max method demonstrably outperforms traditional charts in detecting both small and large temperature shifts, offering enhanced process control and potentially improved shrimp survival rates.

Abstract: The monitoring of processes is a vital mechanism for ensuring that such processes remain safe and under control. The present research aims to solve problems associated with correlated data by applying the Box-Jenkins method integrated with statistical process control (SPC) tools, namely the Shewhart chart, the moving average chart, the cumulative sum (CUSUM) chart, and the exponentially weighted moving-average (EWMA) chart. The efficiency of the four SPC tools was also compared in terms of the false alarm rate (FAR) and the missed detection rate (MDR). The findings indicated that the EWMA chart was the most effective in detecting anomaly, the Shewhart chart and the moving average chart produced high MDR, and the CUSUM chart suffered the highest FAR.

Abstract: Process quality control utilizes inspection of a product while it is being produced through testing periodic samples of products. After this, if product quality characteristics have been changed, the process is stopped, and a search is made for an assignable cause. The objective of a process-capability study is to assess the ability of a process to meet product specifications. During a quality improvement initiative, capability-estimates are obtained at start and at end of study to reflect the occurred improvement. Several capability-estimates show how a process is capable of meeting its specification limits. Essentially, capability-estimates reflect the non conformance rate of a process in a single number form. This involves calculating some ratio of process specification limits. In this study, the production of a fluorescent lamp consisting of a glass tube is considered. Tube quality is affected by the production line conditions. So, the maintenance of the production line is an important stage to increase tube quality. In this paper glass tube quality is studied. Minitab is a statistical software was used to analyze obtained data. The results showed an obvious improvement of part quality after maintenance stage. All measurements were done in Toshiba factory for fluorescent lamp manufacturing.

Abstract: In order to control a process that has short production cycle and where the product type and specifications change often with conventional shewhart control charts such as and control charts, a new control chart must be applied every time the parameters change . As this is a very inefficient method in terms of the cost and time, CV control chart using coefficient of variation statistics was developed. As CV control chart reflects only the current sample data on control chart, it can be useful when there is a significant change in process. However, it does not respond sensitively to a process that has subtle change or requires a high control level. CV-EWMA control chart was researched to monitor small shifts in CV. This study proposes a way to improve accuracy and precision of population parameter estimation of conventional CV-EWMA control chart and applied it to a control chart before analyzing its performance. As a result, the accuracy and precision of conventional CV-EWMA control chart has been improved and it was verified that the proposed control chart is a proper control chart to control small shifts of CV.

Abstract: This paper is based on a company that manufactured the nuclear power components. This paper Studies the quality management that aimed at characteristics of multi specification and small batch production. The components which are produced at this company have been used in new energy field. Quality of nuclear power components can meet the technical requirements or not is very important to the operation and safeguard of nuclear power station in future. Group technology combined with statistical process control technology and applied in the quality management system to analyze the testing data of each working procedure in multi-kind and small-quantity production to achieve the goal of improve and control the quality of the product.

Abstract: For the quality control of developed small batch manufacturing mode, a method based on stochastic weighted theory is proposed to optimize control parameters of control charts. The small sample data is sampled again by stochastic weighted method to obtain more information. Then, the sample data’s distribution parameters are estimated. After the estimated distribution parameter are tested, control parameters of control charts could be optimized dynamically. The method improves deficiencies of traditional control charts under low-volume production and realizes the quality control of small batch manufacturing. Experiments show that the optimized control parameters approach theory true values and are better than the traditional control charts’ control parameters. Therefore, the proposed method is fit for the quality control of small batch manufacturing.

Abstract: A single chart, instead of and R charts or and S charts, to simultaneously monitor the process mean and variability would reduce the required time and effort. A number of studies have attempted to find such charts. Moreover, a number of studies demonstrated that the adaptive control charts may detect process shifts faster than the fixed control charts. This paper proposes the EWMA loss chart with variable sample sizes and sampling intervals (VSSI) to effectively monitor the difference of process measurements and target. An example is used to illustrate the application and performance of the proposed control chart in detecting the changes in the difference of the process measurements and target. Numerical analyses demonstrated that the VSSI EWMA loss chart outperforms the fixed sampling interval EWMA average loss chart and the Shewhart joint and S charts. Therefore, the VSSI EWMA loss chart is recommended.

Abstract: Aiming at the problem of less quality characteristics data in multi-specification and small-batch production, matter-element theory was applied to adjust similarity of factors affecting the quality during the processing, thus similar processes was divided and data shortage problem was resolved. In addition, the relative range method was applied to translate characteristics data, thus drawing the control chart to judge process control state.Through the analysis of a case,the validity of quality control method was verified in the multi-specification and small-batch production.

Abstract: According to the characteristics of quality management and control in mold manufacturing process, this paper adopts SPC technology to solve the problem of mold production quality control. First of all, it expounded the mechanism of SPC to control the quality and take the machining process of the stamping die mold as an example, using statistical techniques to control the production process quality effectively; Secondly, by using control chart, whether the production process in a state of statistical control could be quickly determined, and the fixture loosening caused by abnormal production would be found and eliminated timely; Finally, through the process capability analysis, the level of process ability could be timely understood, and then two effective measures of improving production processes were put forward in order to reduce the feed rate and improve the process ability of workers.

Abstract: Combined with the actual working condition and related standards, the galvanized layer uniformity detection of transmission tower materials is studied and the sampling scheme of galvanized layer uniformity detecting is formulated. With the help of the diagonal test point arrangement form which is used in flatness error detection, a double cross shaped test point arrangement form was established for the galvanized layer uniformity detecting of angle steel tower materials. In order to quantitatively evaluate the thickness uniformity of the galvanized layer and realize information management, the X-Rs control chart was applied in the galvanized layer uniformity detecting.