Advanced Imaging


Advanced Imaging Magazine

Updated: January 12th, 2011 10:01 AM CDT

Lights! Camera! Action!

Illumination better come first when planning machine vision system
microscopic illumination
© Courtesy Volpi
Illumination is one of the most crucial aspects of any application. New users need to allot plenty of planning time.
lighting equipment
© Courtesy Mercron
Engineers have to make sure of the details. Figuring out lighting needs is one of their most difficult tasks.
Monster backlight from Spectrum
© Courtesy Spectrum Illumination
Pick the proper lighting before getting too far into the project. This is a Monster backlight from Spectrum.

By Barry Hochfelder

Biederman mentions a problem he often runs into: thinking that one single geometry of light will do the application. "You have to think about the size of the object and the speed," he adds. "In bottling applications, it's really difficult to do 1,200 a minute. You need outstanding lighting and control—geometry, the angle the light hits the object—how it gets delivered. A customer will say, ‘I've got this object and I need to see 30 different things on it. I need a bunch of lights, sequenced, and I need different wave lengths, color and positioning.' Oftentimes it's not a single-camera presentation. People find problems they didn't think they had. They want to assemble some parts together, then realize that, ‘Oh, this part is out of spec.' It all comes back to knowledge."

The Trend

"Traditionally, halogen coupled with fiber optic was the default lighting," says Varley. "For the longest time, that's all we did. The benefits are very intense light and it's controllable. There are some subtle differences, especially in whites. The limitations are bulb life, which is in the 100s, maybe 1,000 or 2,000 hours. That's a big detriment. If something is fine-tuned, the replacement is not exact, so you need another calibration procedure.

"It does have its uses," he adds. "The intensity is great and it's a cold light source. Heat is not transmitted through the fibers. If you're looking at biological samples, for example, with an LED the heat is under the sample. With this, cold light is under the sample."

Eventually, though, people started to turn to LEDs. It started with small, classic LEDs of 3mm or 5mm. They have longer life and different varieties of wave length. Control is pretty quick. Instead of a ½-inch or ¾-inch fiber bundle going through the machine, you had them in the power cord instead, Varley says. There was no routing of the cable, replacement of the bulbs or outside power supply. You lose light snaking through. With this, you're not losing light. That was the first change from halogen/fiber optic.

"What we're starting to see emerge is a combination," he adds. "Instead of halogen/fiber optic, we're using an LED source with fiber optic delivery. You get the long life of LED and separation of heat from the point of illumination. You get better light. We see that as the current trend and it's going to continue. There's long life and the color availability of LEDs, separation of heat from the object [because of the fiber device] and pretty consistent control and light source."

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