Part measurement, inspection and quality control
IN-SIGHT VISION SENSORS FROM COGNEX ENSURE 100% CONTROL AND A FAILURE RATE OF LESS THAN 10 PPM AT PHILIPS
The Philips factory at Chartres, France, specializing in automotive lighting systems, is one of the biggest factories in the world to manufacture indicator lamps. It supplies bulbs throughout the entire world. Philips Chartres subjects its production to 100% inspection and control. Each element of the bulb (the base, the filament, the glass and so on) is checked both for dimensional accuracy and appearance. Philips’ aim is to achieve a failure rate of less than 10 ppm. With a production rate of 8,000 bulbs per hour, only an industrial vision system would be capable of reliably carrying out this type of control.
Vision system control applications for glass products are always complex, because of the natural variations in shape of such components. As its industrial vision system requirements increased during 2000, Philips decided to test a number of different vision systems on the market, with the aim of selecting a solution that would become the standard for all future applications. The target was to cut training and maintenance costs for these systems. Philips eventually decided on Cognex In-Sight® vision systems, because of their ease of implementation and the performance of the vision tools. Today over 20 In-Sight systems have been installed at the Chartres factory.
Due to the cost of each of the bulb components, there is good financial justification for implementing an inspection system part way through the manufacturing process, to identify defect parts before additional value is added to them. This limits the reject rate of complete bulbs. For this reason the Chartres factory is equipped with both in-line and end-of-line inspection systems. In 2003 the T10 lamp production lines were equipped with a final inspection system to control lamp appearance. The initial objective was to guarantee that lamps have an optimum service life. A secondary aim is to ensure that these lamps during operation, have the perfect shape and geometry, enabling the OEM or automotive manufacturing client to fit them into vehicles automatically.
For this reason every part of the lamp has to be positioned within precise tolerances. The vision system must be capable of carrying out this inspection, but at the same time taking into account normal variations in the glass components. These variations can sometimes be fairly major, due to the nature of the glass material. The way the glass, the filament and the metal filament supports are assembled, means that each bulb has its own characteristics. At the inspection point each one will differ from the previous one, and from the following one. The bulb image will also vary depending on the colour of the glass used, or reflections from its metal parts. So it is a real challenge to the system to accept these major variations caused by the nature of the product, and to reject only those bulbs that really are faulty.
The application uses two Cognex In-Sight systems:
- the first inspects the lamp cap,
- the second inspects the cap + bulb assembly. (Here the camera uses a clever prism system, which means that the product can be inspected from two aspects.)
The images shown illustrate how the products being inspected can vary. The bulb shown in the left hand image is faulty, because it is too far out of centre. But, even though the metal filament is barely visible, the bulb inspected in the right hand image is OK. The full capability of Cognex vision tools, such as PatFind®, are required to reliably locate these check points and to make the right accept/reject decision.
Cognex vision tools meet the requirements of this application perfectly. The geometric tools (the detection of edges – straight line or arc of a circle – segments, construction lines, circles and intersections, the calculation of distances between points or between a point and a straight line) are used many times in this example. They allow the symmetrical axes of the product and the distances in relation to the axes to be calculated. They also enable many set-up operations to be made in an extremely flexibly manner, and the item’s dimensions to be recorded. The flexibility and robustness of the PatFind tool means that variations of the glass can be correctly taken into account, both with regard to geometry and the shade of colour.
Philips really appreciates the fact that Cognex systems are so easy to use. It has meant that their staff have mastered the vision systems quickly, and maintenance costs have been cut. “There’s no need for us to employ a machine vision system expert” said Jean Leriche, Industrial Projects Manager - “Our knowledge of the process has enabled us to optimise the application.”
Now that the system has been running for a few months, Philips is very satisfied with the operation of the system, and is encouraged to expand the vision system applications at its site. One example, is the use of networking facilities provided by the Ethernet interface incorporated into In-Sight 1000 and In-Sight 4000 sensors for tool optimisation, image recording of faulty products, and traceability. Projects are currently under way to study new applications on other products.