LED head allows color-on-color package inspection
LED head allows color-on-color package inspection
Despite advances in parallel processing, digital cameras, and imaging software, machine-vision color systems are still in their infancy. However, widespread demands exist, especially in the packaging industry, to inspect products for color consistency and registration, such as in color-on-color printing. One expensive method to satisfy this need is to couple high-resolution color cameras with imaging systems that are capable of performing color analysis. Another more affordable method, recently proposed by Advanced Illumination (Stockbridge, VT), uses a specialized multicolor light-emitting-diode (LED) light head to increase the reflected contrast ratios of color objects so that they can be inspected by low-cost monochrome vision systems.
Dubbed the 4236C, the 4-in.-diameter LED light head contains a ring of 36 focused red, green, and blue LEDs for illuminating an object. Because an equal number of color LEDs are used in the light head, the resultant light, after diffusion, becomes white.
"The red, green, and blue LEDs used in the light head," says Bill Thrailkill, company president, "result in a white-light system that is four to six times brighter than those that use white LEDs and that produces the same spectral characteristics as xenon light."
Benefits of such lighting include an operational lifetime of up to ten years, no bulb replacement, and no lighting recalibration. Better yet, the light head provides distinct advantages where color packages need to be rapidly inspected. Operated under the direction of the company`s ELS 3000 microprocessor-based control unit, all the red, green, and blue LEDs can be pulse-controlled between 1 and 300 ms. "In production-line packaging systems for example, says Thrailkill, "pulsing the light head at 100 ms would allow 500 parts to be inspected per second."
The key to color inspection, however, is that the intensity and the pulsewidth of individual sets of color LEDs can be controlled. In packages, such as for toothpaste, where color type is printed on color backgrounds, decreasing the intensity of the red light component might increase the contrast of reflected yellow type printed on a red background. Because of this, monochrome-based machine-vision systems can be used to detect and process the images, thereby eliminating the need for more expensive color-based systems. According to Thrailkill, the 4236C is the first in a line of products that will include domelight and spotlight versions.