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Is Infrared the Best Way to Address Safety Questions?
by Winn Hardin, Contributing Editor - AIA Posted 11/19/2013
When it comes to safety concerns—particularly in industrial and other settings where strobing can be an issue—using infrared and other non-visible wavelengths of light might seem like a no-brainer. But whether or not companies choose to do so depends on a number of factors, including the complexity of implementing such a solution and the other available options. Here we look at several cases where infrared might and might not aid in addressing questions about safety.
Flashing lights are everywhere in machine vision applications, from intelligent transport systems to line inspections. But the strobing effect these produce can raise safety concerns—for example, the possibility of inducing epileptic seizures and any hazards that might arise as a result of a worker having spots in his or her eyes.
To avoid the risks of strobing with visible light, customers are increasingly turning to non-visible wavelengths. “The safety [regulations] at some of the facilities can get pretty tough; you can barely get a laser in the door,” says Matt Pinter, a Design Engineer at Muskegon, Michigan-based Smart Vision Lights. “Strobing lights can get blasted by the safety people at some of these companies.”
For this reason, Smart Vision Lights will try to steer customers toward solutions in the infrared. Indeed, some customers—particularly automotive companies, where there will be workers all around the flashing lights—already know before selecting a system that they want to work with non-visible wavelengths.
Moving into the non-visible range can help address safety concerns in a variety of scenarios, not just in manufacturing. The “easiest and most obvious” of these is intelligent transport systems, or ITS, says Steve Kinney, Director of Technical Pre-Sales and Support at JAI Inc., USA, in San Jose, California. “Most people recognize that, ‘Hey, if I want to take a picture of this guy as he blows through my tollbooth, I can’t be flashing a strobe in his face.’”
Even when it’s not a matter of a flashing a light in someone’s face—in nighttime situations, where you might want to light an air section with a series of high-speed, high-power strobes—you run the risk of causing an accident.
In cases such as these, Kinney notes, “near-infrared is one of the keys to safety.”
But using infrared or near-infrared light isn’t always the clear-cut answer in seeking to address strobing. In some application areas, companies and customers are divided as to what approach to take.
This is the case with inspections on assembly lines. In some applications, you might be scanning anywhere from 30 to 100 items per second. So if a strobe light is being used to freeze the motion, the light is flashing at a rate of up to 100 Hz.
“If you’re using something fast or bright like a Xenon lamp or even a high-power white LED strobe, then you’re getting strobe effects,” Kinney says. “And then you’re facing a bunch of OSHA safety issues.”
More and more, customers are requesting that strobing be designed so it cannot be seen, says Jim Roberts, National Sales Manager at Mettler Toledo – CI Vision in Aurora, Illinois. The question is, how best to achieve this?
Using infrared isn’t always the answer. “Honestly, it’s much more common to use an enclosure in a solution because you get the added benefit of totally eliminating ambient light,” according to Roberts.
In fact, Mettler prefers to use enclosures, and for a number of reasons. “Anytime they have an opportunity to separate their controlled lighting solution from the ambient environment, vision companies prefer to do it,” Roberts says. “It’s really a multifaceted gain for a turnkey supplier.” In addition to avoiding the risks of strobing, enclosures help prevent people from touching the equipment while also minimizing the effects of ambient light or sunlight.
|IR vs. UV
Companies sometimes turn to other non-visible wavelengths—UV, for instance—when seeking to address strobing. Each of these has its advantages and disadvantages.
One example: Infrared offers considerably higher quantum efficiency. It takes about 4 volts to run a UV LED at 350 mA, or a little more than a watt. But a 350-mA infrared LED requires only about 1.3 V, which results in almost a third of the wattage. “IR is very efficient so you can pack a lot of LEDs around the camera,” says Smart Vision Lights’ Pinter. “You don’t need a heat sink and you don’t need special packaging because the wattage is so low. UVs are like little heaters because they take 4 V for the same size chip.”
Of course, complete enclosure isn’t always going to be practical; sometimes, using infrared is going to be the best option.
Kinney notes, for example, that machine vision is being used more and more often during the final stages of assembly—to inspect everything about an object, to probe it almost like a human would before it goes out the door. And in such cases, it’s often necessary to use infrared light. “A lot of these things are happening on open conveyers where it’s a real burden to contain all the light,” he says. Here, as in the traffic applications, infrared strobes fit the bill.
“You’ll likely still put some containment around them, but you don’t have to worry about it being completely light-tight,” Kinney adds. “You can just block off the major parts of the equipment and still not worry about workers’ eyes.”
Of course, safety concerns aren’t always related to strobing. Oftentimes, companies want to monitor certain areas in a plant to make sure workers don’t get too close to a robot or another piece of equipment. Some have suggested using machine vision and infrared cameras for this instead of the more conventional light curtains. The system can tag a person who crosses into an area and, if he or she gets too close, stop the robot to avoid the person interfering and possibly getting hurt.
But Kinney, for one, isn’t convinced this is the best approach. For starters, conventional light curtains don’t have all the complexity of a camera-based system. “There’s the camera, there’s the software, there’s the logic, and what if it doesn’t meet the fail-safe requirement?” he asks. Customer preferences can (and often do) change, of course, but for now it seems infrared isn’t the most practical solution for monitoring areas.
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