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This article proposes a new control chart (called the ABS SPRT chart) for Statistical Process Control (SPC) based on Sequential Probability Ratio Test (SPRT). This chart is able to monitor the mean and variance of a variable x simultaneously by inspecting the absolute sample shift |xμ0| (where μ0 is the in-control mean or target value of x). The ABS SPRT chart is designed by an optimization algorithm, aiming at minimizing the Average Extra Quadratic Loss (AEQL) over the process shift domain. The results of intensive performance studies show that the ABS SPRT chart not only uniformly outperforms the CUSUM chart with a Variable Sample Size (VSS) feature, but is also more effective than a 2-SPRT scheme which incorporates a lower-sided SPRT chart and an upper-sided one. From a holistic viewpoint, the ABS SPRT chart detects process shifts in mean and variance faster than the VSS CUSUM chart and 2-SPRT scheme by more than 30% and 13%, respectively. Noteworthily, the design of an ABS SPRT chart is relatively easier than that of a VSS CUSUM chart, and much simpler than the design of a 2-SPRT scheme.  相似文献   

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The double sampling (DS) chart can reduce the sample size when monitoring the process mean. In this study, Duncan's cost model was modified by adding the statistical constraints to develop the design model of DS chart for the optimization of design parameters—sample size, control limit coefficient, warning limit coefficient and sampling interval. A numerical example was provided to illustrate the use of this model. A sensitivity analysis of the effects of model parameters and statistical constraints on the optimal design of DS chart was also performed.  相似文献   

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An economic model including the labor resource and the process stage configuration is proposed to design charts allowing for all the design parameters to be varied in an adaptive way. A random shift size is considered during the economic design selection. The results obtained for a benchmark of 64 process stage scenarios show that the activities configuration and some process operating parameters influence the selection of the best control chart strategy; to model the random shift size, its exact distribution can be approximately fitted by a discrete distribution obtained from a relatively small sample of historical data. However, an accurate estimation of the inspection costs associated to the SPC activities is far from being achieved. An illustrative example shows the implementation of the proposed economic model in a real industrial case.  相似文献   

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Problem-solving processes in technology education: A pilot study   总被引:1,自引:0,他引:1  
This paper reports the preliminary results of a pilot study investigating the nature of problem-solving activity in technology classrooms. The research focuses on the relationship and potential mismatch between teachers' and children's agendas, aims, perceptions and beliefs concerning design and technology activities. A case study of an 11-week project was undertaken with four pupils aged 13. In-depth classroom observation and interviews allowed us to investigate the problem solving used in designing and making a kite, and the pupils' application of the knowledge required. Our analysis charts the influence of the teacher's task structuring and interventions on the children's problem-solving behaviour. The results indicate that the design process is highly complex and not always communicated successfully by teachers. What children typically encounter in design and technology projects are different problems requiring different approaches according to the kind of task and the stage reached in its solution. The popular idea that problem solving in technology denotes a holistic design-and-make process is hence under challenge. Moreover, the assumed access and application of relevant bodies of knowledge from other contexts is highly problematic.  相似文献   

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This paper describes the development of a new version of Witkin's Group Embedded Figures Test (GEFT) and two further tests of a similar type using words and letters. The new form of the Group Embedded Figures Test Consists of a number of original two dimensional figures (complex and simple). Variations of the basic two dimensional figures were obtained by establishing a geometrical progression (from following a set of simple rules) to produce increasing degrees of complexity of the complex figures. This in turn generated more simple figures within them which were used in the test items.By using words and lettersas a means of generating embedded complex/simple shapes, not only are very different types of (overall) shape possible, but also the notion of field dependence/independence can (possibly) be applied to non-spatial (in the usual sense) modes of operating within the curriculum, i.e. the humanities as opposed to design and technology subject areas.  相似文献   

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