Inspection:

Inspection is a method to identify the defects. During Inspection, defective products are segregated and ensured that they are not reaching the customers. However, Inspection will not reduce defects as Inspection is done after the process. Defects are originating in the process, so unless we take steps to eliminate defects, Inspection has to be continued.

Three Types of Inspection:

1. Judgemental Inspection:

In this type of inspection, the defects are segregated / classified and then recorded in the database. The information / data is not shared with the previous stage for reducing the defects. In many small and medium enterprises in India, this is the type of inspection you would find. People would rarely use the data and take decisions to reduce the defects.

2. Informative Inspection

In type of inspection, the data related to defects is shared with the previous stages so that they can take some corrective actions in the future. There are 3 types of inspection in Informative Inspection

2A: Statistical Quality Control:

Here the data related to defects are analysed and corrective actions are taken. People use Quality Circles, 7 QC tools and other quality principles and do projects to reduce the defects.

2B: Successive Check

In this type of inspection, in a production line, the internal customer who is receiving the product, does a 100% inspection every time before he/she starts the process. Only if the product is OK, the process will be continued, else the product is returned to the internal supplier and information is passed.

This inspection is not done in batches, it is done for each product that is coming out of the previous process. Defects are identified immediately and informed to the previous stage. So by Successive Check, we can reduce the defects, but cannot bring it to Zero Defects (at least 1 product becomes defective – during inspection)

2C: Self Check

In this type of inspection, 100% inspection is carried out by the process owner, before the product is sent to the next process. This inspection is done for each product (not in batches). So once a defect is identified, corrective actions are taken immediately. In this case also, we can reduce the defects, but cannot bring it to Zero Defects (at least 1 product becomes defective – during inspection)

3. Source Inspection

In this type of Inspection, all the parameters are checked before the process starts (for each cycle). Whenever a parameter is out of specification, the process would not be started, thus preventing the defects from arising. For each cycle, this checking is done and thus defective products would not be produced. Only with Source Inspection, we can eliminate defects. i.e. achieving ZERO QC.

How to Implement Source Inspection?

Pokayoke helps in implementing Source Inspection. Along with Source Inspection, PokaYoke helps in achieving ZERO QC. i.e. no need for Quality Control as pokayoke prevents any defects from arising.

Pokayoke (Mistake Proofing) are simple tools which prevents the defects from arising. The best Pokayoke projects are done at the source inspection level. If doing at source inspection level involves high cost/technology, create pokayoke projects at Self Check stage or Successive Check stage.

For our easy understanding, we can classify any pokayoke device into 3 categories

1. Operating Level – Type of Inspection (Source Inspection / Successive Check or Self Check)
2. How the system works – Setting Methods
3. How the system communicates to the user – Regulatory Function

We have explained the first point in the previous paragraph.

2. Setting Methods / How does the Pokayoke system works?

This is how the pokayoke device works/identifies the OK and NOT OK products. There are 3 types of Setting Methods:

2A: Contact Method:

Here the device use physical contact to identify the Ok & NOT OK components. For e.g. a pen drive can be used only in 1 direction. If you try to insert in the wrong direction, due to physical contact/design, the pen drive would not get inserted.

Sometimes, we can also use non-contact type sensors to identify the mistakes. However, we still classify them under the Contact Method. For e.g. we have sensors in the press machines, which will stop if the operator inserts their hand in the danger zone. Though there is no physical contact of the hand, the sensor identifies this and stops the machine to prevent hand injury.

2B: Fixed Value Method:

This type of Pokayoke devices use a fixed value to identify whether the process is completed or not. For e.g. in an assembly process, there are 10 screws to be tightened. Frequent customer complaints indicate that the operator misses out 1 or 2 screws. So a pokayoke device can be designed in such a way that it counts ’10’ and gives a green signal to send it to the next station. If the 10 screws are not completed, the product cannot be sent to the next stage. In this type, the device uses a count /value to determine the process.

2C: Motion Step Method:

This type of PokaYoke device allows the user to complete the process in a sequence. For. e.g. Imaging in an assembly process, there is a bolt to be tightened, a warranty card to be inserted and then a Quality Check sticker has to be pasted (in the same order). Frequent customer complaints are that warranty cards are missing in the product. So we can design a pokayoke device in such a way that once the process starts, the box containing the bolts open (and the remaining boxes are closed), then the box containing the warranty cards open (remaining boxes are closed), and finally the QC sticker box is opened. During the process, only box will be in open condition. So the operator can only proceed in a sequence. This is called Motion Step Method

3. Regulatory Function

This is how the pokayoke device communicates to the user. There are 2 types in Regulatory function.

3A: Control Method:

In this case the device shuts down the machine / process. There is no byepassing the system. This method is used in critical applications where the bypassing results in big damages / high cost / life threatening situations. For e.g. in Lifts, if there is an overload situation, the lift will not move till the time the load brought down to the limit. Another example is a pen drive where you can insert it wrongly.

3B: Warning Method:

In this case the device gives a warning light /sound to indicate the user that there is something wrong. Here the user chooses how to respond to the warning. Warning methods are used in regular situations (where the process is not very critical). Example: Low Fuel Indicator in automobiles is a warning that the fuel is low. However, the user can ignore this and can fill the fuel later.