Bruce I read the article on the Pinto. Very sobering. To me it is obvious that Ford’s decision was unethical and shows how pragmatism can lead us into treacherous waters. But do you have an example of a less ethically problematic or more nuanced situation where the cost of the mistake proofing process could exceed the benefit?

Also, Sid, what would Shingoe say when you can’t create a device to mistake-proof? What if you want to mistake proof a process, or a situation where a human being has to make a judgment call? Is that even possible, or does that just create Muri?

For context, I’m a Grower at a nursery. We have some mechanized processes, but much of what we do involves looking at a living thing in front of us and deciding if it should get planted or thrown out. Things often get planted when they shouldn’t be. We try to establish standards and training, but mistakes still get through due to human nature. One begins to wonder if the effort to mistake proof this process would grind the whole thing to a halt. In this respect, waste is sometimes seen as the lubricant that keeps the whole thing going. You could achieve zero waste, but the cost of going from 99.9% perfect to 100% perfect would put you out of business and drive your employees nuts. As a perfectionist, conceding to this view would be terribly difficult for me, but I’m trying to explore possible future states here…

Shingo explained that traditional ‘long cycle’ inspection systems wait until an error in action produces a defective item. The defective item is then found by inspecting the output. His concept of source inspection uses the ‘short cycle’ inspection system. In this system the action itself is checked 100% using mechanical means. If an error occurs, immediate action is taken to correct it before a defect is produced. With this methodology we can guarantee zero defects to the final customer.

The basic system is simple;
The Poka-Yoke methods/devices should be designed to detect deviation from the standard actions and outputs required to satisfy the customer’s requirements. *
This can be done in three ways;
a) Physical contact.
b) Fixed values.
c) Motion steps.
In some cases at the original design stage the part can be made a Poka-Yoke device by ensuring it can only be assembled/used in the correct way.

They should also check for deviation in the 3M’s of actions and items;
Missing. Action or item not there.
Misplaced Action or item there, but in wrong position.
Malformed. Action or item are there but wrong, size, shape, colour, temp etc.
When designing Poka-Yoke devices they must check for specific deviations in the 3M’s using; a, b and c. This can be done with a ‘what can go wrong’ 3 M’s analysis.

The Poka-Yoke device should then;

1) Control the operation. Stop the process when an error or defect occurs.
2) Warn the operator. Signal to the operator that an error or defect has occurred.

They should be applied at the following check points;

1) The source action. (source check) This is the ideal as it gives zero defects.

2) Output of the action. (self check) This is our second choice as the output will be defective if the PY device is activated, but it will not be passed to the internal customer.

3) Before the next process. (successive check). At this stage the item will be defective if the PY device is activated, but it cannot go to the final customer.

With this system in place it is now possible to consistently achieve;
‘Zero Defects in our activities and production processes’.
This was Shingo’s original goal in 1965.
If applied to safety it is possible to achieve ‘Zero Accidents’. I do not understand why this methodology is not more widely used in this area.

The most impressive example of Shingo’s system I have experienced was on an assembly line for inlet manifolds in Japan. We were allowed to work on the line and challenged to produce a defective assembly. It was impossible to produce one, and we had some very talented people trying.

Once our front line people understand this system they become some of the best designers of Poka-Yoke devices.

Poka-yoke should be seen as the device for implementing Shingo’s zero defects system.
The goal is to identify deviation from the desired conditions or actions in any situation.
A good example is the selector stick on an automatic car gearbox. If the stick is not in the park position the poke-yoke switch is not activated and the engine will not start. Zero defects in all situations.

Shingoe pointed out to me that this would be impossible to achieve with statistical techniques.

Thanks for your question. Shigeo Shingo stipulated three rules for poka-yoke devices, the third of which was “low-cost”, perhaps anticipating the diminishing returns argument prevalent then as now. His book, “Zero Quality Control” has many examples of low-cost devices, and my experience has also been that frontline employees can become very good at devising low-cost poka-yokes. In fact, I’ve never seen an instance where the cost of prevention was greater than the cost of rework, sorting or scrap; not to mention the impact on employee morale when problems are not fixed, or the customer who is on the receiving end of the ‘occasional’ defect.

I have, however, seen many instances where defects were not addressed in the name of diminishing returns, and subsequently many problems that were not reported because they were deemed to be too small. When the principle, ‘pass no defects’ is replaced with ‘pass no costly defects’, we have chosen our level of stagnation, friendly neither to employee or customer. One notable example comes to mind. Here is the link:

http://philosophia.uncg.edu/phi361-metivier/module-2-why-does-business-need-ethics/case-the-ford-pinto/

Regards,
Bruce

One will of course argue that every mistake has many hidden costs, or that it reveals deeper root causes that are symptomatic of waste elsewhere, etc. But can you envision a situation where the cost of perfection is too high, and therefore there is a tolerable level of mistake-making?