Inspection machine design

Inspection machine design　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　8233　　

　Here,I would like to explain as an example of the case 　where an equipment　 which 　inspects　 whether the fluid inside an industrial commodity does not leak to the exterior,　 and to explain introduction of inspection equipment.

　　　　About the external leak testing using a helium, please refer this site. (In Japanese only, D　etailed document is charged.) http://www.webstore.jsa.or.jp/webstore/Com/FlowControl.jsp

Selection of inspection method

There are some methods for achieving the purpose of this inspection.
There is a method of judging whether compressed air pressure　 put in a product falls.
Another method of judgment is that there is leakage vacuum level falls after expelling air from inside the product.
A third method of judgment is to charge gas into the product, and confirm leakage around the product.

The method quoted at the end has various means.

Inspection products are charged inside with a gas　and are sunk in water. After a while it is visually inspected by existence of the surrounding bubble of a product 　　This was a very popular inspection method in the 70's.

　There was already a method of the inspection with halogen gas detector in those days. However, when the surrounding atmosphere of a product is polluted, the inspection by this equipment cannot be conducted correctly.
Because some halogen gas is contained in　atmosphere to some degree, (For example, in automobile exhaust gas) it is uncertain to judge accurately.

　In around 1978, a machine which has equipped with helium gas detector was installed on another site of the company which I worked for. Afterwards, a similar machine was installed at our site, too.
　　This machine　was a troublemaker.　 The troubles came one after another 　and it had not been possible to use　 in production line for a long time.

　The machine had worked as a result of one year or more of our efforts.
But it was equipment hard to maintain,still

Because I had taken charge of another　product line, I was not involved in the air-tight　inspection　 by helium 　machine　anymore.

Similar machines were continued to be installed　by my colleagues though I　 had 　had a hard experience myself.　Meanwhile, I　 had 　installed　 some leak inspection machines which equipped halogen leak detectors. These machines replace the air to fresh air around the product. The maintenance for them was a little easier than the helium ones, but these machines were very expensive, too.

In around 1995, some leak inspection machines that had been improved and designed to be compact in size, were installed on another site. seeing those machines, I 　completely changed 　view 　about 　helium leak　ｔestings.*

We had used to order this kind of machines from specific companies, but I decided that we would design by ourselves since that time.

Eleven inspection machines were made since then. Four is equipment completely automated by using handling robots. Two of them were designed for the factory in China
All those machines charge helium gas inside of products and add gas at high pressure, and to detect helium gas the machines make surroundings of the products in a vacuum.　　　One machine which has been using for 15　years was modified for other products 5 years ago, these 11 machines are still being　used in the production line, as far as I know.

It is necessary to decide which method to　select in consideration of the kind and pressure of the fluid in those products and the accuracy which the products are demanded by their users.

Anyway, it is necessary to select a method which takes the shortest time with the lowest cost possible. The technology is always advanced. You are not to neglect gathering information .

　My　experiences contained both some examples good and bad　things. I 　dare describe　them because you might obtain something from bad　experiences.

It is necessary to consider human characteristic.

The technology that makes inspection results be accurate is important. However, there is an important thing to be　considered as well as judging leakage accurately.

In a good product, it is general that frequency where defective products generate is low. Workers occasionally decrease their powers of attention to find defective products when the incidence is extremely low. Moreover, they might be accustomed to the processing at the good products and not the defective products. nbsp;As measures against these diminished attentions, workers are told beforehand that defect of products sometimes are thrown in the line. It will be confirmed when they are surely discovered.

Another way to protect human’s error is that　the afterward inspection can be restarted by confirming the defective product was put on the defective products reservoir by a sensor when the product was judged as a defective one.

The judgment of the inspection　can　be automated, but workers might fail to remove the defective product.

It is a sure method preventing this trouble　by using a handling robot. However, sometimes detaching to the inspection machine by the robot is difficult. So, we have to rely on workers' hands.It becomes a repetition, but it is necessary to confirm whether to have been processed surely as a defective one when manually processing. Mixing defec　tive products in to good ones can not be prevented by only the method in the production line where the name of the inspection personnel is recorded.

Needless to say, check the result of　judgments by comparing the number of input products with the total of good products and defective products .

Where is the inspection process put?

When the product is inspected in the processes may influence productivity.

First of all, it is necessary to examine whether there is something that gives a bad influence for the inspection in the series of process.

In an airtight inspection, even if it is a small amount, the leaking part is closed when the inside includes water and oil, etc. For instance, if there is a process of injecting oil internally for lubrication, the inspection should be done befor　e it. When very little helium that leaks outside is detected, surroundings of the product should be made a vacuum. It takes a time long if there is a drop of water on the surface. After the process of airtight, these processes where water adheres should be done if it is possible.Thus,the timing of inspection　effects the　 accuracy and　 required time . The order of the manufacturing process of the product should be decided by thinking about these things.

Next, the defective percentage in the inspection processes should be considered.　The item that becomes the most defective in the inspection items should be previously inspected.
Do not take useless time on the product that becomes defective sooner or later.In general, an inspection process where a lot of defects are found is given priority to be done, and processes where few defects are found are done next

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