Poka Yoke. quality technique for continuous improvement

A Poka Yoke (Japanese ポカヨケ, literally foolproof) is a device intended to prevent mistakes.

Some authors handle the poka yoke as an anti-fool system which guarantees the safety of the users of any machinery, process or procedure, where they are related, avoiding accidents of any kind, which would cause poorly manufactured parts if they continued in the process with it. consequent cost.

poka-yoke-best-practices

These devices were introduced to Toyota in the 1960s, by engineer Shigeo Shingo within what is known as the Toyota Production System (TPS).

Although Poka Yokes previously existed, it was not until their introduction in Toyota that they became a quality technique, now common.

Shingo affirmed that the cause of the errors was in the workers and the defects in the manufactured parts were produced by not correcting them. Consistent with such a premise, there were two possibilities or objectives to be achieved with the Poka-Yoke:

Somehow make human error impossible; for example, cables for recharging batteries for mobile phones and direct current devices. Highlight the mistake made in such a way that it is obvious to the one who made it; For example, when a worker has to mount two pushbuttons on a device by placing a spring under them; To avoid the lack of the latter in any of the pushbuttons, the worker was made to take two springs from the box where they were all stored before each assembly and put them on a tray or plate; Once the assembly was completed, the worker could immediately notice the oblivion with a simple glance at the tray, something impossible to do when observing the box where lots of springs were stacked.

PokaYoke techniques

Poka Yoke Techniques aim to eliminate defects in two possible states:

Before they occur (PREDICTION): It involves designing mechanisms that warn the operator when an error is going to be made so that they can avoid it (ALARM), that stop the chain when something wrong has been done (STOP) or that simply incorporate new ones elements to the job that make a certain error impossible or difficult (CONTROL). Once they have occurred (DETECTION): It is about designing mechanisms that warn when a defective product has been manufactured (ALARM), that stop the chain if this occurs (STOP) or that simply prevent that defective product from going to the next process (CONTROL).

Many of these techniques make 100% inspection possible by incorporating inexpensive mechanisms. Therefore, these techniques prevent human errors from being made in two areas of work: production activities (PREDICT and avoid production errors) and production monitoring activities (avoid DETECTION errors).

Types of Poka Yoke

There are three types of PokaYoke

Contact Type

The use of shapes, dimensions or some other physical properties to detect contact or non-contact of a particular part

Constant number

In case a number of movements or activities are not done, an error signal is triggered.

Of performance sequence

It ensures that the steps to be carried out are executed in the correct order.

V.gr.: the use of a checklist for pre-flight reviews or completing the filling of records in a logical sequence

Types of PokaYoke

Although there are no fixed rules, it all depends on the ingenuity of those responsible for the processes, some more mechanisms

common are:

Guide blocks and stops to avoid placing parts or tools incorrectly Alarms and light signals that warn of possible defects Limit switches to check the position of the parts or if they are removed before finishing the process Counters that measure if all operations have been done to all products Task checklists, to check all parts of the process have been completed

Types of errors

Mistakes	Examples
Forgetfulness errors	A worker may forget to assemble a part, to change tools
Errors due to ignorance or inexperience	Being can misuse a machine or tool due to ignorance or inexperience
Identification errors	An incorrect part can be assembled because it has not been seen well or because it is not easy to distinguish it from others
Voluntary errors	The operator may ignore rules or procedures thinking that nothing will happen
Inadvertent errors	The operator can be distracted and confuse different parts or tools with which he works
Slowness errors	The operator may take too long to perform certain tasks and causes the products to deteriorate (remove a product from a lathe in time)
Errors due to lack of standards	It is not clear what to do in each case and certain measures or tasks are carried out according to the operator's own judgment
Surprise mistakes	Sometimes a machine can malfunction without showing signs of anomalies
Intentional mistakes	Some operators may deliberately make mistakes (sabotage0

Three Golden Rules of PokaYoke

A foolproof system should consider the following:

PokaYoke implementation

Identify the problem of the operation or process that requires a Pokayoke (areas where there are a large number of errors or where a single error represents a high cost) Use the 5 whys or cause and effect analysis to get to the root cause of the problem Decide the type of PokaYoke to use and technique to attack the problem (there may be technical or economic reasons) Design a suitable PokaYoke Test it to see if it works (avoid high spending before you have completed this step) Once you have selected the type and technique of PokaYoke, make sure you have the tools, checklists, software,etc so that it works correctly and consistently Train everyone on how to use it After it has been operating for a while (the time period depends on the frequency of the activity) check the performance to make sure the errors have been eliminated

Take whatever steps are necessary to improve what you have done.

PokaYoke Benefits

When errors are avoided, waste is reduced and the process operates continuously Reinforces operational or sequential procedures Ensures quality at the source not at the result Eliminates decisions that lead to incorrect actions

The most convenient PokaYoke