Inspection with the aim of finding the bad ones and throwing them out is too late, ineffective, and costly. In the first place, you can't find the bad ones, not all of them. Second, it costs too much. Quality comes not from inspection but from improvement of the process.
[W. Edwards Deming, the American statistician who drove Japan's post-war quality revolution]
Yokeru means to avoid
Poka Yoke is one of the main components of Shingo's Zero Quality Control (ZQC) system -- the idea being to produce zero defective products. One way this was achieved is through the use of poka yoke; a bunch of small devices that are used to either detect or prevent defects from occurring in the first place. These poka yoke methods are simple ways to help achieve zero defects.
A more powerful approach is to design your processes to automatically prevent defects from happening. The Japanese name for such techniques is Poka Yoke, meaning mistake proofing. Poka Yoke has two aspects: prevention and detection. For instance, having different shaped plugs for each type of connection in a PC prevents novices and experts from making mistakes when installing a new PC, and the electric fuses and circuit breakers in your home detect when electrical circuits are overloaded which prevents electrical fires.
Likewise, one of the most common causes of defects – ambiguous requirements - can be prevented by writing comprehensive acceptance tests when each requirement is captured. Furthermore, automating these tests and running them as part of frequent integration-builds help detect defects when they happen.
Ref:
http://www.isixsigma.com/tt/poka_yoke/
http://www.school-for-champions.com/tqm/poka-yoke.htm
John Grout's Poka-Yoke - http://facultyweb.berry.edu/jgrout/
Zero Quality Control By Shigeo Shingo, Andrew P. Dillon - http://books.google.com/books?hl=en&id=gkE8K7axQbYC&dq=poka+yoke&printsec=frontcover&source=web&ots=AiVC2NOBaI&sig=DrrGyvuyGwVe6d4FLkUXcFtzRws&ei=amOUSfCAHIKUsQOR_JiuBw&sa=X&oi=book_result&resnum=12&ct=result#PPA68,M1
