Poka-yoke / Mistake-Proofing
Poka-yoke builds mistake-proofing into a process or equipment, so a human error either CANNOT be made or is detected the moment it happens — before it becomes a defect. The principle: people err; the process must catch it.
The failure mode is precisely understood: which action, under which circumstances, with which consequence
Those who work in the process are part of the design — they know the bypass options best
What is done wrong (wrong part, wrong direction, forgotten step, wrong quantity)? When does it happen (start-up, switch, variant, stress)? The anatomy of the error decides the solution’s type — a forgetting requires something other than a mix-up.
Level 1 (best): the error physically cannot be made — asymmetric plugs, guide pins, fixtures that only accept the correct part. Level 2: the error is detected instantly — a sensor, counter, weight check that stops the process or warns on the spot. Always aim for level 1 first; level 2 is the compromise.
The best poka-yokes are trivially simple: a guide bar, a stop, a template, a colour code, a counter. Brainstorm with those who do the work — and prefer the solution that can’t be bypassed over the one that is technically elegant.
Actively try to make the error with the safeguard in place — in all the ways a pressured colleague might. If it can be bypassed under pressure, the design must be tightened; bypassability discovered after commissioning is in practice never discovered.
The safeguard is written into the standard and the FMEA (detection/occurrence score is adjusted), and its function is checked in the daily/weekly routine — a defective sensor “temporarily” bypassed is a classic with a long history of harm.
How it goes wrong in practice — and this is where most implementations part ways.
A warning note is not poka-yoke — it is a reminder, and reminders lose to busyness. The standard distinguishes hard: physically impossible or instantly detected; everything else is something else.
The sensor is disconnected in a pressured situation and never reconnected. A bypass must be visible (andon/board) and time-limited with an owner — otherwise the safeguard is an illusion in the statistics.
An 80,000-kroner solution where an 80-kroner guide bar would have caught the error. Complexity is itself a source of error — simplicity is a quality property.
The method only works when it becomes daily routines and leadership behaviour. The operations check shows in 4 minutes where your operations stand — and what should come first.