SCHOTT solutions no. 2/2010 > Machine Vision

The SCHOTT “High Brightness LED Light Line”, a high quality illumination solution for industrial image processing, is used at the Albuquerque, New Mexico, U.S.A. site to inspect solar panel cover glasses for possible edge chips, cracks, foreign material and other material ­defects prior to assembly. Photo: SCHOTT/K. Malone

Spotlight on Quality


SCHOTT develops highly specialized lighting solutions for complex machine vision applications – and draws the appropriate expertise from its own production requirements.


Thilo Horvatitsch

Lighting is simultaneously the most important and most ­underestimated component in a machine vision system. It often makes the difference between the success or failure of the whole application,” emphasizes Carl Van Dommelen. The Business Manager is driving SCHOTT’s business forward in North America with lighting solutions for industrial image processing and often holds training courses on machine vision. With the type of automated quality inspections that are used in manufacturing, cameras and computers are able to monitor whether razor-thin semi-conductor components have been applied properly to silicon plates or the surfaces of wooden panels meet stringent quality requirements.
The SCHOTT “High Brightness LED Light Line”, a high quality illumination solution for industrial image processing, is used at the Albuquerque, New Mexico, U.S.A. site to inspect solar panel cover glasses for possible edge chips, cracks, foreign material and other material ­defects prior to assembly. Photo: SCHOTT/K. Malone
How these products are illuminated determines the quality of the resulting image information and therefore the entire test. This is anything but trivial. Different lighting components and techniques are needed depending on the optical properties of the part being inspected, such as the geometry, surface reflectance, and color of the product. The production environment and process speed also play a key role. Heat, dust, water and oil can negatively affect how a light source or even the entire system functions. “You need to take all of these factors into account and have a lot of experience with these types of applications in order to be successful,” Carl Van Dommelen explains. As leading suppliers of optics and lighting solutions, SCHOTT and its Japanese partner Moritex not only have this type of expertise, but their know-how continues to grow because their own production environments require advanced solutions like these. For instance, the SCHOTT Solar subsidiary decided to use the company’s own high-brightness LED line lights in its production process. “The expertise in the area of technology and applications that we have in our own ranks was only one reason,” says Michael Jacquorie, Chief Operating ­Officer at the SCHOTT Solar production facility in Albuquerque, New Mexico. An excellent reason, however, because it is extremely important that even the smallest of defects that occur during manufacturing of solar cells be detected. A solar module is made up of several cells. If only one of them has a defect, then the entire module cannot be used or will fail. Considering the stringent requirements for quality in the solar industry, with warranty periods of between 20 and 25 years, this can cost the manufacturer a lot of money or even its reputation.

In Albuquerque, the line lights are being used to inspect cover glasses for solar panels for possible edge chips, cracks, foreign material or other material defects before assembly. The “High Brightness LED Light Line” installed here can be adapted to suit a specific customer and allows for inspection widths of between 300 mm and 3 meters. With inspection widths of 1.8 meters, this met the requirements at SCHOTT Solar just perfectly. In addition, the very even light distribution and compact design of the line light allowed it to integrate in a way that saves space. The standard module is used in diffuse applications for so-called dark-field illumination. The light hits the glass panes from the side at a very low angle and highlights the edges and material structures quite powerfully. In this case, scratches can easily be seen against a dark background.
LED Light Line products are also used for reflective applications – here, for surface testing of solar cells at the SCHOTT Solar German site in Alzenau. Photo: SCHOTT
The LED line light is also ideal for testing the surface of solar cells in reflective applications. With what is known as the “fingerprint” inspection, the thin line of light passes over the front side metallization on the cell surface in a precise manner and thus provides the necessary high contrast for the inspection of the metal structures. The working distance between the inspected object and the light source can also be custom set between 50 – 100 mm once it has been installed. With “line scanning”, the high luminous intensity of up to 400 kilolux allows for high throughput speeds in time with the speed of the production line – a significant advantage for the growth-oriented solar ­industry. A similar system has also been installed at SCHOTT ­Solar’s German site in Alzenau.

Technical solutions like these can be tailored to meet different needs, from the use of different colored leds to housing designs, and they are also capable of adapting to harsh environmental conditions. Here, the LED also shows its strengths as a long-lasting light source that can be combined with CCD cameras quite well. Of course, there are always challenges. To help light-emitting diodes stand up to their arch enemy, heat, SCHOTT has developed an optimized temperature management system that uses air or water cooling to improve the service life and light output of the LEDs. “We are constantly working to improve the efficiency, performance, light intensity and homogeneity,” Carl Van Dommelen notes. And the next development is already knocking on the door: SCHOTT is planning to introduce new types of LEDs in the near future that offer twice or three times the light intensity.
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