Mistake Proofing (Poka-Yoke)
Poka-yoke is a low-cost and highly effective way to reduce mistakes and boost quality. It is applicable for virtually all companies, all industries and all technologies. PokaYoke is yet another Japanese word which has come into regular use within the lean manufacturing vocabulary. In essence it is an extremely simple concept that has been applied through common sense for years. Simply put it is the use of simple mechanisms that stop mistakes being made by manufacturing operators without requiring concentration by the operators. Either the operator is alerted that a mistake is about to be made, or the device actually prevents the mistake from being made.

The term "PokaYoke" was popularised by Shigeo Shingo through his book "Zero Quality Control: Source Inspection and the PokaYoke System". Shingo points out that mistakes will always be made (we're only human after all!), but if PokaYokes are implemented then mistakes can be prevented from becoming defects (mistakes that reach the customer).

By eliminating the defect at source, the cost of mistakes within a company is reduced. Often quality inspection will be carried out at the end of a series of processes. If the mistake was made at the start of the process then money has been invested in that part all the way along the process up to the point it is inspected therefore increasing the cost of the mistake. It is also possible (if parts are less than 100% inspected) that the defect may carry on down the production process further increasing the cost of the defect and probably leading to the need for rework.

In order to eliminate mistakes, we need to modify processes so that it is impossible to make them in the first place. With mistake-proofing solutions, many repetitive tasks that depend upon the memory of the worker are built into the process itself. Mistake-proofing frees the time and minds of the workforce to pursue more creative and value-adding activities.

Mistake-proofing also involves a change in the mindset of the organization. Organizations must establish a mistake-proofing mindset that promotes the belief that it is unacceptable to allow for even a small number of product or service defects. In companies that have a six-sigma initiative, the six-sigma objective translates into a goal of less than 3.4 defects per million opportunities or 3.4 DPMO.
A longer-term aim might be to eliminate the source of problem not just prevent it from occurring, this might be best achieved in the design stage.

The best poka-yoke in the world is a robust design. Many of the needs for poka-yokes are attributable to poor designs and/or unrepeatable processes. The second-best poka-yoke in the world is education -the knowledge. The automotive industry is a leader in this area, with the use of its Advanced Product Quality Planning (APQP) guidelines and supplier development programmes. Companies such as Motorola, Allied Signal and General Electric are leaders in this area, because they invested in their Six Sigma and have taken them upstream into the new product development process.