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| articles:pdca-the_origin [2022/02/18 09:44] – [The Shewhart Cycle (1939)] rrandall | articles:pdca-the_origin [2022/03/15 08:27] – [The "Deming Cycle" revised... (1951)] rrandall |
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| The whole picture, however, is radically different just as soon as we admit that we have only a probable science. Even when we limit ourselves to trying to stay within tolerance limits, it is necessary for economic reasons will give valid predictions only in a state of statistical control and for attaining maximum quality assurance in all kinds of work, including that where tests are destructive, to introduce the concept of action limits A and B and the aimed-at value C, fig. 6. | //The whole picture, however, is radically different just as soon as we admit that we have only a probable science. Even when we limit ourselves to trying to stay within tolerance limits, it is necessary for economic reasons will give valid predictions only in a state of statistical control and for attaining maximum quality assurance in all kinds of work, including that where tests are destructive, to introduce the concept of action limits A and B and the aimed-at value C, fig. 6.// |
| {{ :articles:shewhart_fig_6.png?direct&600 |}} | {{ :articles:shewhart_fig_6.png?direct&600 |}} |
| But in order to specify C we must first apply the operation of statistical control. In fact the C must really come from Step III and after suitable action limits A and B have been established in Step II. But these action limits can not be set without some knowledge of the tolerance limits that are specified in Step I. I think it is particularly important to note that the third step can not be taken by simply inspecting the quality of the objects as objects, but instead must be taken by inspecting the objects in a sequence ordered in relation to the production process. In fact these three steps must go in a circle instead of in a straight line, as shown schematically in fig. 10. It may be helpful to think of the three steps in the mass production process as steps in the scientific method. | //But in order to specify C we must first apply the operation of statistical control. In fact the C must really come from Step III and after suitable action limits A and B have been established in Step II. But these action limits can not be set without some knowledge of the tolerance limits that are specified in Step I. I think it is particularly important to note that the third step can not be taken by simply inspecting the quality of the objects as objects, but instead must be taken by inspecting the objects in a sequence ordered in relation to the production process. In fact these three steps must go in a circle instead of in a straight line, as shown schematically in fig. 10. It may be helpful to think of the three steps in the mass production process as steps in the scientific method.// |
| <blockquote column 30%>The three steps in fig. 10 correspond to the three steps in a dynamic scientific process of acquiring knowledge.</blockquote> | <blockquote column 30%>The three steps in fig. 10 correspond to the three steps in a dynamic scientific process of acquiring knowledge.</blockquote> |
| In this sense, specification, production, and inspection correspond respectively to making a hypothesis, carrying out an experiment, and testing the hypothesis. The three steps constitute a dynamic scientific process of acquiring knowledge. From this viewpoint, it might be better to show them as forming a sort of spiral gradually approaching a circular path which would represent the idealized case where no evidence is found in Step III to indicate a need for changing the specification (or scientific hypothesis) no matter how many times we repeat the three steps. Mass production viewed in this way constitutes a continuing and self-corrective method for making the most efficient use of raw and fabricated materials. | //In this sense, specification, production, and inspection correspond respectively to making a hypothesis, carrying out an experiment, and testing the hypothesis. The three steps constitute a dynamic scientific process of acquiring knowledge. From this viewpoint, it might be better to show them as forming a sort of spiral gradually approaching a circular path which would represent the idealized case where no evidence is found in Step III to indicate a need for changing the specification (or scientific hypothesis) no matter how many times we repeat the three steps. Mass production viewed in this way constitutes a continuing and self-corrective method for making the most efficient use of raw and fabricated materials.// |
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| {{ :articles:shewhart_fig_10.png?direct&600 |}} | {{ :articles:shewhart_fig_10.png?direct&600 |}} |
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| From the viewpoint of specification, it is of interest to note that for the meaning of control to be operationally definite, not only certain criteria of control, but also the operation of selecting the objects whose qualities are to be tested must be specified. The choice of criteria to be used as a method without a knowledge of the results of prior attempts to control quality, one can not specify in a perfectly definite way just how many data are required and in what sequence these data shall be used in applying control criteria to give the quality assurance intended by the design specification. For these reasons it seems that operationally verifiable control requirements, and requirements as to how many data shall be obtained to provide adequate quality assurance, can only be set down in Step III, and then only by one having his eye both on the intent of design requirements and upon the accumulated inspection results to date, indicating the degree to which a state of statistical control has been approached. Hencethedesignspecification must be supplemented in Step III by inspection practices providing adequate data and satisfactory criteria of control for each type of product. | //From the viewpoint of specification, it is of interest to note that for the meaning of control to be operationally definite, not only certain criteria of control, but also the operation of selecting the objects whose qualities are to be tested must be specified. The choice of criteria to be used as a method without a knowledge of the results of prior attempts to control quality, one can not specify in a perfectly definite way just how many data are required and in what sequence these data shall be used in applying control criteria to give the quality assurance intended by the design specification. For these reasons it seems that operationally verifiable control requirements, and requirements as to how many data shall be obtained to provide adequate quality assurance, can only be set down in Step III, and then only by one having his eye both on the intent of design requirements and upon the accumulated inspection results to date, indicating the degree to which a state of statistical control has been approached. Hencethedesignspecification must be supplemented in Step III by inspection practices providing adequate data and satisfactory criteria of control for each type of product. |
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| Furthermore, since the running record of past results must play such an important part in judging the degree to which control has been attained, it is necessary that Step III provide such a continuing record or quality report. The graphical control chart (Criterion I) is admirably adapted to this end. The mathematical theory of distribution characterizing the formal and mathematical concept of a state of statistical control constitutes an un-limited storehouse of helpful suggestions from which practical criteria of control must be chosen, and the general theory of testing statistical hypotheses must serve as a background to guide the choice of methods of making a running quality report that will give the maximum service as time goes on. | Furthermore, since the running record of past results must play such an important part in judging the degree to which control has been attained, it is necessary that Step III provide such a continuing record or quality report. The graphical control chart (Criterion I) is admirably adapted to this end. The mathematical theory of distribution characterizing the formal and mathematical concept of a state of statistical control constitutes an un-limited storehouse of helpful suggestions from which practical criteria of control must be chosen, and the general theory of testing statistical hypotheses must serve as a background to guide the choice of methods of making a running quality report that will give the maximum service as time goes on.// |
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| Upon reading the source materials, we recognize that it is quite a //stretch// to cite the PDCA as the same as the "Shewhart Cycle". Rather than a basis for continual/continuous improvement, Shewhart's "cycle" would be better described as a "closed-loop" self-correcting system intended to achieve "optimization" of a process | Upon reading the source materials, we recognize that it is quite a //stretch// to cite the PDCA as the same as the "Shewhart Cycle". Rather than a basis for continual/continuous improvement, Shewhart's "cycle" would be better described as a "closed-loop" self-correcting system intended to achieve "optimization" of a process |
| ===== The Deming Cycle (1950) ===== | ===== The Deming Cycle (1950) ===== |
| {{ :articles:1950_deming_cycle_transparent.png?direct&400|Deming Cycle introduced in 1950}} | {{ :articles:1950_deming_cycle_transparent.png?direct&350|Deming Cycle introduced in 1950}} |
| Inspired by the "Shewhart Cycle", W. Edwards Deming created his own "Deming Cycle", which he introduced in 1950 at a "Japanese Union of Scientists and Engineers" (JUSE) sponsored eight-day seminar on statistical quality control for managers and engineers. His straight-line: Step 1- "Design", Step 2 – "Produce", Step 3 - "Sell" was converted to a circle with a fourth step added: Step 4 - "Redesign through marketing research". | Inspired by the "Shewhart Cycle", W. Edwards Deming created his own "Deming Cycle", which he introduced in 1950 at a [[http://juse.or.jp/english/|"Japanese Union of Scientists and Engineers" (JUSE)]] sponsored eight-day seminar on statistical quality control for managers and engineers. His straight-line: Step 1- "Design", Step 2 – "Produce", Step 3 - "Sell" was converted to a circle with a fourth step added: Step 4 - "Redesign through marketing research". |
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| Deming stressed the importance of constant interaction among design, production, sales, and research and that the four steps should be rotated constantly, with quality of product and service as the aim. | Deming stressed the importance of constant interaction among design, production, sales, and research and that the four steps should be rotated constantly, with quality of product and service as the aim. |
| For a more detailed article on the history of PDCA / PDSA, read: {{ :articles:evolution_of_the_pdca_cycle.pdf |"Evolution of the PDCA Sysle"}}. | For a more detailed article on the history of PDCA / PDSA, read: {{ :articles:evolution_of_the_pdca_cycle.pdf |"Evolution of the PDCA Sysle"}}. |
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| ===== ISO Promotes PDCA ===== | ===== ISO Promotes PDCA ===== |
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| Contrary to the wishes of Deming, ISO began promoting "//the corruption PDCA//" in ISO 9001:2000 and continued it in ISO 9001:2008. While this may have seemed like a good idea, in theory, its application was confusing to many uses... and auditors. | Beginning with ISO 9001:2000, ISO began promoting what Deming called "//the corruption PDCA//". This continued in ISO 9001:2008. While this may have seemed like a good idea, in theory, its application was confusing to many users... and auditors. |
| {{ :articles:pdca_from_iso_9001_2008_transparent.png?direct&600 |}} | {{ :articles:pdca_from_iso_9001_2008_transparent.png?direct&600 |}} |
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| {{ :articles:pdca_from_iso_9001_2015_transparent.png?direct&600 |}} | {{ :articles:pdca_from_iso_9001_2015_transparent.png?direct&600 |}} |
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| | Worse, in an effort to address ISO 9001:2015 / AS9100:2016, sec. 4.4.1, some companies have used the above PDCA diagram (or variations/modifications of it) in an effort to describe the sequence and interaction of their processes. |
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| | While ISO itself has not provided direct guidance as to whether this approach is acceptable, AS9100 uses ISO 9001 as a "base/foundation" by simply adding requirements to the ISO 9001 standard. An AS9100 user asked "//Is using the process diagram in Figure 2 from clause |
| | 0.3.2, in your quality manual for interaction between the processes sufficient?//". |
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| | The official [[https://iaqg.org/|IAQG]] response was "//No//." Further explanation was provided stating: "//This diagram is not intended to define an organization’s processes and their interaction.//" And "//In addition, Annex A.1 of the standard provides this statement: “The structure of clauses is intended to provide a coherent |
| | presentation of requirements, rather than a model for documenting an organization".//" |
| ===== Major PDCA / PDSA Cycle Obstacles ===== | ===== Major PDCA / PDSA Cycle Obstacles ===== |
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| ===== A Better Alternative ===== | ===== A Better Alternative ===== |
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| Clearly, "continuous improvement" of any individual process has its limits. However, few companies reach that point where they're struggling to improve further. Ultimately, improvements take place in spurts. | Clearly, the "continuous improvement" of any individual process has its limits. However, while recognizing that improvements take place in spurts, I rarely see //significant// improvements taking place in ISO 9001 or AS9100 registered companies. |
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| Rather than use the PDCA model, a much better approach is to follow the DMAIC model (Define, Measure, Analyze, Improve and Control). As improvements are made, the PDCA cycle fails to address "Control" (sustainment) of the improvement... to ensure that the process doesn't revert to its previous condition. | Rather than use the PDCA model, a much better approach is to follow the DMAIC model (Define, Measure, Analyze, Improve, and Control). As improvements are made, the PDCA cycle fails to address "Control" (sustainment) of the improvement... to ensure that the process doesn't revert to its previous condition. |
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| As you move from one process to another, utilizing DMAIC, you can re-visit any of the processes previously improved to determine whether another DMAIC would be appropriate (for greater improvements). | As you move from one process to another, utilizing DMAIC, you can re-visit any of the processes previously improved to determine whether another DMAIC would be appropriate for further improvements. |
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| {{ :articles:dmaic-aug-2019-01.png?direct&800 |}} | {{ :articles:dmaic-aug-2019-01.png?direct&800 |}} |
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| To further enhance the effectiveness of DMAIC, many users incorporate TRIZ into the Analyze & Improve portions of the DMAIC process. | To enhance the effectiveness of DMAIC, many users incorporate TRIZ into the Analyze & Improve portions of the DMAIC process. |
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| [{{ :articles:2048px-40_principles_of_triz_method_720dpi.jpeg?direct&800 |40 principles of TRIZ. Copyright By FotoSceptyk – Own work, CC BY-SA 4.0, \\ https://commons.wikimedia.org/w/index.php?curid=45719323 }}] | [{{ :articles:2048px-40_principles_of_triz_method_720dpi.jpeg?direct&800 |40 principles of TRIZ. Copyright By FotoSceptyk – Own work, CC BY-SA 4.0, \\ https://commons.wikimedia.org/w/index.php?curid=45719323 }}] |
