Intelligent system for the detection of cracks in links on assembly lines

A group of researchers at the Public University of Navarre, together with Volkswagen Navarra, have designed an individual system for the intelligent detection of cracks in links in production assembly lines to which a detector of wear and tear in bolts has been incorporated.

The project is part of the joint working agreement that Volkswagen Navarra have had with the Public University of Navarre since 1997 and which has produced a number of results in the field of applied R+D. In this case in concrete, the research arose from the need to find a technological solution to one of the most common problems occurring in mass production assembly lines.

Inspection of links

These assembly lines are made up of chains of metal links to which the various devices or components forming part of the production process are fitted, the finished product being the article manufactured by the company in question. Given that the line moves at a more or less constant speed, the links are subject to stresses that are greater at some points than at others. This excess stress produces cracks and, in extreme cases, the link itself breaks up.

Until now the inspection of the line in order to detect cracks has been purely visual. However, this system is inefficient as the inspection is carried out while the line is in operation, the links moving at a speed that makes it difficult to identify a fine crack. On the other hand, if the ocular inspection is carried out when the production line is stopped, a proper inspection can take a considerable time.

Optoelectronic system

To solve this problem, researchers at the Public University of Navarre and Volkswagen Navarra worked on several hypotheses for detection systems of cracks in the links and finally opted for an optoelectronic system, one whereby a laser diode is located at an oblique angle to the link. The beam from this reflected from the link surface is received by a photodetector which converts this optical power into an electrical signal.

The basis for the detection is quite simple. The part (the link) moves horizontally at a more or less constant speed. When the part passes the optoelectronic system, there is a rise in the reflected light energy. But, if a crack exists, the reflection is irregular and there is a fall in this optical power, and this is registered by the detection system, thus indicating the presence of a crack.

The power values registered by the optical detector are transferred to a data acquisition card which digitalises and processes the information using a software programme.

The system has the great advantage that it avoids physical contact with the part under inspection. The only requirement is the correct design of the electronic device.
Although the system that is being presented today is a reality, the researchers at the Public University of Navarre and Volkswagen Navarra intend to continue theri joint R+D work with another project: instead of an individual system for each link the detection of cracks and of wear and tear in the bolts, a single system can be installed for each of the 12 production assembly lines that the Volkswagen plant has in Landaben (Pamplona). These would be interconnected by means of a wireless net and centralised at a PC with software for monitoring the state of each and every one of the links and bolts on the factory lines. The aim is that, when an event is detected (a broken link, a worn bolt, etc.) on any of the assembly lines, a brief message indicating the problem is sent to the mobile phone of the maintenance charge-hand.

The possibility of patenting the system is also being studied for its possible use in the rest of the Volkswagen group’s factories, in other vehicle companies as well as in all kinds of factories that have a similar problem.

Contact :
Iñaki Casado Redin
Nafarroako Unibertsitate Publikoa
inaki.casado@unavarra.es
(+34) 948 16 97 82