Keep it Covered: Specifying Enclosures for Vision Systems
| By: Winn Hardin, Contributing Editor
Whenever machine vision systems operate in a harsh environment, the system requires an enclosure that protects the investment within. But when it comes to protection, one size does not fit all. An enclosure on an automotive inspection line will have different specifications and regulatory compliance requirements than does process monitoring in a corrosive environment like a petrochemical plant. With this in mind, machine vision enclosure manufacturers are listening closely and doing their best to educate customers on their specific needs as they relate to protective enclosures, delivering solutions that are safe, robust, cost-effective, and fully integrated.
Protection on the Factory Floor
A food and beverage manufacturing facility may be more hygienic than hazardous, but it still takes a beating thanks to the high-temperature, high-pressure washdowns with harsh cleaners needed to keep food-preparation areas safe.
Machine vision enclosures for food processing applications typically are made of type 316 stainless steel, which offers increased corrosion resistance and strength at elevated temperatures. The enclosures also must have food contact–rated gaskets and must be designed to eliminate moisture traps where liquids might collect. What's more, enclosures must be built without glass since it could shatter on impact, creating the risk of shards falling onto the food processing line.
While nearly all industrial enclosures are designed to an Ingress Protection (IP) rating, enclosures in food preparation and packaging applications require IP65, IP66, and IP66K ratings to withstand water jets of increasing pressure. According to Chris McGeary, more manufacturers are asking for even higher-rated enclosures.
"Most food lines are sterilized regularly with a high-temperature pressure washer with some type of cleaning fluid in the spray," says McGeary, President of Allison Park Group, Inc. (APG; Allison Park, Pennsylvania), which specializes in industrial enclosures for machine vision systems. "[Today], companies with food processing lines are selecting IP69K rating, and that will cover anything that they throw at it."
The IP69K rating test method specifies a spray nozzle dispensing 176°F water at 1160–1450 psi at a flow rate of 4 gallons per minute. The nozzle is placed within 4–6 inches of the tested device, which is rotating once every 12 seconds.
APG regularly modifies its off-the-shelf enclosures according to the needs of the application. "We've made enclosures with acrylic viewports, but it turns out that on some food lines, the chemical used in the cleaning process attacks the acrylic, so you put in a polycarbonate window instead," McGeary says. "In some cases it might be a hot environment, so we need to add a provision for cooling in the enclosure."
In another instance, a food application operating amid potentially explosive gases or dust would require a custom solution that includes an off-the-shelf explosion-proof housing as well as a pressurization system that keeps positive pressure within the enclosure.
The "get tough" trend is also being adopted by other manufacturing industries, such as automotive. Instead of choosing machine vision enclosures that only meet the NEMA 12 standard for designs that keep dust and dripping water at bay, customers are specifying IP65 because it stands up to the pressure of a garden hose, McGeary says.
The Harsh and the Hazardous
As a general rule, thermal imaging applications can pose the greatest challenge to the engineers tasked with protecting sensitive machine vision technology. "Most thermal cameras are inherently in rough industrial environments with a lot of heat exposure, or they might be in hazardous locations requiring explosion-proof installations," says Markus Tarin, Certified Vision Professional Advanced and President and CEO of MoviTHERM (Irvine, California).
Thermal imaging is commonly used in remote condition monitoring and process control of critical industrial assets where a temperature anomaly could signal a dangerous situation. For example, infrared cameras can remotely monitor flare stacks, which burn off gas waste in harsh and hazardous industrial locations like petroleum refineries and gas processing plants. Thermal cameras also are exposed to a lot of heat in industries such as steel, requiring that enclosures be cooled via air or liquid.
Because enclosures for thermal cameras have a unique set of operational requirements, Tarin encourages customers to shop for a turnkey machine vision enclosure solution. "On the surface, designing an enclosure seems fairly straightforward, but many people do not understand all the technical intricacies required," Tarin says. "It can be a daunting task to get the camera integrated properly into an enclosure."
As part of its integration services, MoviTHERM calibrates thermal cameras to account for transmission losses on the viewing glass, as well as performs thermal calculations to determine the correct type of cooling (and engineering those options in-house when applicable).
Conversely, some enclosures require a heating element. "We have designed special high-powered heating systems for applications in Alaska, where conditions can be below the camera's minimum operating temperature," Tarin says. "We've also done heaters to make sure the viewing glass doesn't fog up or freeze over."
Thermal camera enclosure manufacturers often offer other add-ons appropriate to the application. These include a sunshield for enclosures with direct exposure to sunlight, an automated windshield wiper that cleans the viewing window of dust and debris, and an air barrier surrounding the viewing glass that blows a steady stream of compressed air to prevent particles from settling.
Explosion Containment and Prevention
Thermal cameras operating in explosive atmospheres represent another challenging area that a qualified integrator can help navigate. Industry standards and regulations like Europe's ATEX directive and UL FM in the U.S. mandate that equipment be designed to minimize the occurrence and severity of accidental explosions. This can be accomplished with explosion-proof ("ex-proof") enclosures, which prevent any explosion transmission from the inside of the protection system to the outside. Another method, explosion prevention, uses a purge and pressurization system to ensure that hazardous particles or gases have been eliminated from the enclosure.
"Customers can't just buy an ex-proof enclosure and put their own camera in it," Tarin says. "You need to be certified to integrate these things. The user is not allowed to ever open up that enclosure because as soon as they do, they lose the certification for that application."
To meet growing demand for condition monitoring in explosion-hazard environments with extreme climate conditions, AT - Automation Technology GmbH (Bad Oldesloe, Germany) recently added several features to its IRCamSafe Ex ex-proof enclosure. The product, which integrates an infrared camera, heater, and interface controller and is ATEX certified, accommodates cameras with an extended operating temperature range of –40°C to +60°C. AT also enlarged the protection window and added a sensor to measure the viewport's temperature.
The Complete Package
According to MoviTHERM's Tarin, buying trends in the enclosure sector act as a microcosm of how U.S. customers currently specify their entire vision system: They're looking for a one-stop shop. "They really don't care about the individual components so much as what the end solution can do for them," he says.
However, companies do care about cost and lead time. "We see customers who, if they can't get something off-the-shelf, they would rather not do it at all and wait it out for another year or two to see if somebody comes up with something," Tarin says. "They don't want to pay custom engineering charges for enclosure projects. But they want a complete turnkey solution at an off-the-shelf price."