Color Sensors Displace Older Methods

Users Begin Looking Into Color Sensors for More Sophisticated Capabilities, but Still See Benefits of Contrast Sensors

By Jim Montague

Remember when Judy Garland landed in Oz, and the movie went from black and white (B+W) to brilliant color? Well, that's what's been happening to the world of photoelectric sensors lately. Many users formerly satisfied with B+W, grayscale or contrast sensing want more complex and sophisticated capabilities, and they're looking for color sensors to provide them — and do it fast on production lines without having to pull samples for analysis. But, that's not the end of the story because innovations give contrast sensors some more colorful capabilities, too.

SEE ALSO: Color Sensors Gain on Vision Systems

"Our users are getting into some very small areas to view colors, such as on pencils and carpeting, and so they're benefiting from using a true color sensor, which can look at the whole spectrum, perform CIELab calculations internally, set up algorithms, and automatically distinguish even very small color values and shade differences without sending a sample to a lab," says Joe Poelmann, applications engineering at Balluff. CIELab are standards from the International Commission on Illumination (CIE) for accurately determining visible colors.

Bill Letterle, senior engineer and project manager at EMX Industries, notes evolving user needs for their sensors. "In the past year, we've had customers that want to look at colors from items that produce their own light, such as LEDs and newly welded seams, so we developed a sensor that looks exclusively at light from the outside world."

Colors finally can be used for measurement and object sorting, which could reduce the need for some other types of sensors.

Even with the biggest, more-sophisticated and costly color line and area scanners, such as those made by Teledyne Dalsa Industrial Products, users still want improved camera speed, better color response and more sensitivity, according to Bill Dawson, Teledyne's strategic development director. "We can put more lines of sensors across moving webs or conveyor belts, and integrate them for greater sensitivity, but we're now at the high end of what multiple, 100-megabyte cables can do."

To inspect and differentiate what's going by on a conveyor in 20 ms, Teledyne Dalsa recently released a small, smart color camera with a high-performance microprocessor, Ethernet networking and programming via the Internet. It works with Teledyne's software to monitor colors, but it can also measure the size and shape of colored objects. This means that colors finally can be used for measurement and object sorting, which could reduce the need for some other types of sensors.

Nick Tebeau, manager of the Vision Solutions Group at machine-vision integrator Leoni Engineering Products and Services, says many firms that do sample testing with colorimeters would like to do color line testing, but it's been too costly or the right technology just hasn't been available until now. "More manufacturers are making three-charge coupled device (3ccd) cameras such as Trilinear-style line scanners, which have three sensors or patterns across a line, one each for red, green and blue. This improves their color spatial resolution and clarity over regular cameras such as Bayer pattern-types with 1ccd that have one sensor for all RGB," Tebeau says. "On the other hand, most potential users look at processes with colored objects and assume they need a color sensor, and this isn't true. If you're dealing with two or even three different primary colors, you could still be able to use a monochrome sensor. Even if you're trying to tell the difference between red, half red and not red, you can still do monochrome, but if you're looking at shades, then you'll need a color sensor."

Steve Kinney, technical presales director at JAI, adds his firm makes cameras with color sensors, including its 3ccd cameras, which have three sensors and channels and used to have three chips, but now use one field-programmable gate array (FPGA) to do all the data processing. "For a lot of discrete manufacturers, it's still new to use color at all, but the use of color sensors in machines and automation has been increasing," Kinney says.

While contrast sensors can't escape their binary, on-off nature and perform true RGB sensing, they can use improved networking and switching to gain more sophisticated, color-like functions, according to Michael Turner, photoelectric sensing product manager at Pepperl+Fuchs. "One innovation in contrast sensing is adding IO Link to sensors, which allows us to go inside and add 0 to 250 possible RGB color codes. This enables the sensor to pick out the best contrast, and match the best RGB value to a golden example," says Turner. "When we use contrast sensors to check granola bar wrappers, we usually need to look at just two colors anyway, and so contrast sensors mean we can do it faster, more affordably and at greater distances."

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