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Book summary · Quality and Six Sigma · Intermediate

Zero Quality Control: summary and review

Source Inspection and the Poka-Yoke System

By Shigeo Shingo. First published 1986.

The short answer

Shigeo Shingo argues that defects come from errors nobody checks at the moment they happen, so sorting finished parts cannot get you to zero. His alternative has four parts: inspect the conditions of an operation before it runs, check every piece, feed results back at once, and install cheap poka-yoke devices that prevent the error or stop the process when it occurs. The publisher counts 112 shop-floor device examples. Despite the name, it does not abolish checking; it moves it to the source. Read it if you design fixtures, assembly stations or checks.

Read it if

  • You are deciding between more inspectors and changing the process, and your defect list is mostly omissions, wrong parts and wrong orientation.
  • You are an engineer or supervisor assigned to error-proof one step and want many worked device examples to adapt.
  • Your plant relies on sampling and charts for problems that are really operator or machine slips.

Skip it if

  • You want a general lean introduction. This book covers one topic, defect prevention, in depth.
  • Your defects are drift in a measured dimension on a fast or continuous process. One reference source lists high-speed production and destructive testing as poor fits, and charts handle drift better.

When it pays off: After you have standard work in place and a defect Pareto showing that the top defects are errors, not drift. Read it before you buy more gauges or hire inspectors.

The core ideas, in plain language

  1. 1

    Errors are not defects

    An error is a slip by a person or machine. It becomes a defect only when it passes to the next step or the customer. So the work is to stop the error at the source, not to sort the defect later.

  2. 2

    Three kinds of inspection

    Judgment inspection sorts good from bad after the fact and does not lower the defect rate. Informative inspection uses results to correct the process, either by the next operation checking (successive checks) or by the operator checking their own work (self-checks). Source inspection checks the conditions before the operation runs. Faster feedback wins.

  3. 3

    Checking every piece becomes affordable

    A sampling plan by design leaves some parts unchecked. Shingo's answer is to check every item, made cheap by devices that do it automatically as part of the cycle.

  4. 4

    Prevent first, detect second

    A control poka-yoke stops the process or makes the error physically impossible. A warning poka-yoke signals and relies on a person to react. Prefer control wherever the error can be fully prevented.

  5. 5

    Three ways a device senses

    Contact methods sense shape, size or presence. Fixed-value methods confirm a set number of parts or motions. Motion-step methods confirm the sequence. The best-known story, as reported by Wikipedia, has an assembler lay out the required springs first, so a leftover spring shows one was omitted.

How to use it on Monday morning

  1. 1

    Sort last month's problems by error type

    Take a month of scrap, rework and complaints. Tag each defect as omitted part, wrong part, wrong orientation, wrong setting, or drift. Only the first four are poka-yoke candidates. Use a defect check sheet to count them.

  2. 2

    Break down one recurring error at one station

    Stand with the operator for a full cycle and list each step and the error possible at it. For each, ask whether the wrong action can be made impossible. If not, can it be detected in the same cycle?

  3. 3

    Prototype the cheapest device and attack it

    Try a pin, a jig cut, a counting tray or a limit switch. Then make the error on purpose and confirm the device stops it. Run it one shift and ask the operator what slowed them.

  4. 4

    Start one successive check and watch for bypass

    Have the next operator check one key characteristic of the previous step and return findings the same shift. Check weekly that no device has been bypassed.

What to be careful about

  • A translated 1986 book

    Reader reviews on Goodreads are mixed on style: one says the writing may not suit Western readers and is harder without an engineering background, while another calls it well translated. Examples come from 1980s assembly and machining.

  • It oversells the case against statistics

    John Grout and Brian Downs, in the mistakeproofing.com tutorial, note research finding ZQC less effective than SPC for variance in measured values, though suited to attribute data such as omissions. Keep control charts for drift.

  • Not every fix counts as poka-yoke

    Michel Baudin argues the spring-in-a-dish example neither prevents an error nor detects it at once, so it is a method, not a device. He says anything that adds labor will be bypassed in an emergency.

Zero Quality Control compared with Understanding Variation

Choose Zero Quality Control when your defects are mistakes you can design out of a step. Choose Understanding Variation when the problem is drift in a measured number and you need to know whether a change is real signal. A plant with both problems needs both books.

Read the summary of Understanding Variation.

Tools and templates on LeanSuite that go with it

Book details

Bibliographic details of Zero Quality Control
TitleZero Quality Control: Source Inspection and the Poka-Yoke System
AuthorShigeo Shingo
First published1986. English edition, Productivity Press, 1986, translated by Andrew P. Dillon with a preface by Norman Bodek. It is a translation of a Japanese book (Furyo zero e no chosen); the original publication year was not verified.
Edition shownHardcover, first English edition (now listed by Routledge), Productivity Press, 1986
ISBN-13978-0915299072

Details checked against public records on 7 October 2026. Other editions have other ISBNs. We carry no affiliate links.

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