Kiểm tra là một hoạt động bắt buộc nhưng không có giá trị, và mục tiêu của chúng tôi là làm ít nhất có thể, miễn là chúng tôi tiếp tục thực hiện các yêu cầu của khách hàng. Kế hoạch lấy mẫu số chấp nhận (c = 0) bằng 0 yêu cầu kiểm tra ít hơn nhiều so với kế hoạch ANSI / ASQ Z1.4 tương ứng (trước đây là MIL-STD 105) và trở nên khả thi khi nhà cung cấp cực kỳ tin tưởng vào mức chất lượng của nó.1
Một kế hoạch ANSI / ASQ Z1.4 bao gồm cỡ mẫu n và số chấp nhận c. Thanh tra kiểm tra n mục, và chấp nhận lô nếu c hoặc ít lỗi hoặc không phù hợp được tìm thấy. Các kế hoạch này được thiết kế để mang lại (khoảng) cơ hội chấp nhận 95% ở mức chất lượng chấp nhận được (AQL), đây là một trong những thông số cho lựa chọn của kế hoạch.
William A. Levinson, P.E., FASQ, CQE, CMQOE is the principal of Levinson Productivity Systems P.C. and the author of the book The Expanded and Annotated My Life and Work: Henry Ford's Universal Code for World-Class Success.
I was instroduced Squeglia's c=0 plan at March of 2018. I was wanted to know Squeaglia's calculation logic to define sample size.
Tôi đọc cuốn sách của ông, ấn bản thứ 5 nhưng không tìm ra. Vì vậy, tôi rất cảm ơn bạn cho bài viết của bạn. Và tôi có một câu hỏi về bài viết của bạn.
On Squeaglia's book, He told that he used Hypergeometric distirbution for more exact calculation, but you used only Binomial distribution
On the 5th edition, "Zero Acceptance Number Sampling Plans", I couldn't find out how he calculate sample size n.
Thanks to Mr. Levinson for his paper on C=0 sampling plans. The sample size formula presented in his paper is one of the most useful tools available. I would like to add that recently under AS9138 and ARP9013 the definitions have been standardized for Acceptable Quality Level (AQL), Equal Risk Point (ERP), Lot Tolerance Percent Defective (LTPD), and Rejectable Quality Level (RQL). They are in fact simply different points on the same operating characteristic curve having probability of acceptance 0.90-0.95, 0.50, 0.10, and 0.05 respectively. During world war two, the point-of-view of the consumer (LTPD) was abandoned in favor of the producer's point-of-view (AQL) because, as HR Bellinson stated; 20,000,000 identical items were being procured from more than 50 different suppliers, and a c=0 sampling plan was thought to be unfair to small suppliers; rejecting their product more often than large suppliers product having exactly the same quality level (ASA 105th annual meeting, January 27th 1946.). Of course AQL based sampling plans can have larger sample sizes than c=0 plans in order to "bend" the operating characteristic curve at the AQL point providing a high probability of acceptance, while still holding the same consumer's LTPD point. It is improper to say that a c=0 plan has an AQL because by design, its point-of-view is the consumer, not the producer. This is the reason for the 0.542 probability of acceptance in Mr. Levinson's example with n=15, c=0 for a lot is 4% nonconforming (4.0 AQL). We can not design a set of consistent c=0 sampling plans with the producer's risk in mind. This was the main thrust and birth of AQL based sampling plans.
With the consumer in mind - A sampling plan which is finding the nonconformities most of the time, is doing its intended job and therefore does not need to be tightened. It is only when the economics of the situation dictate that the expense of finding a few nonconformities later outweighs the expense of more inspection that we will tighten inspection.
There are many attribute sampling procedures such as MIL-STD-105, MIL-STD-1916, APR9013, and AS9138 to name a few. Most have differing poin-of-view and it all becomes a little confusing, but thankfully the underlying mathematics remains constant and reveals that it is simply a different color "lipstick" on the same OC Curve.
© 2019 Quality Digest. Copyright on content held by Quality Digest or by individual authors. Contact Quality Digest for reprint information. “Quality Digest" is a trademark owned by Quality Circle Institute, Inc.
Thời gian đăng bài: 15-10-2019