Page 217 - The Toyota Way Fieldbook

Chapter 8. Build a Culture That Stops to Fix Problems 193

Figure 8-10. Lock and key error-proofing device

using a quarter-inch steel plate over the front of the QDs that had
unique slots milled for each separate color (Figure 8-10). Then he
made a sleeve that was attached to each paint line with a pin config-
uration that would fit the slot. Just like a lock and key! The prototype
was installed at one station to test and to verify ease of use. After
modifications, matching sets were made for each paint station (all
were identical lock/key configurations).
Of course, this method is not completely mistake proof. In fact, it’s possi-
ble to defeat the method for any system that is developed (think about
computer hackers breaking into “secure” systems). In this case, if the pins
were broken or removed, the device would be ineffective. To counter
this possibility the team leader added a check of the pins to the daily
preshift inspection to verify that everything was in correct working order.

The cost of this simple solution was about $200 for material and labor,
and the sleeves only added a few ounces of weight to the operator—
not a significant ergonomic impact. The device effectively prevented
the problem with zero recurrences.

There are some key points that support the effort of mistake proofing. The
key determinant of your success is your mind-set. Error-proofing techniques
and tools are simple and easy to apply. The greatest challenge is in discovering
the root cause and using your imagination to effectively eliminate it.
There is a hierarchy when it comes to the mistake-proofing effort. The highest
order is to prevent the occurrence of the error completely. But complete elimina-
tion is not always feasible or practical. Any system or device that is installed can
be bypassed if desired. If a prevention device is installed that is problematic or
cumbersome, people will tend to “work around” it. If you create a cure that is
worse than the disease, people will sidestep your cure.
If it’s not possible to completely prevent the error (most of the time), then try
to detect the error as it occurs. Detection devices or methods are more common