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Articulating Arms Muscles Up

 

Improved portable-arm accuracies, features, and software lead more manufacturers to deploy shop-floor metrology

 

By Patrick Waurzyniak
Senior Editor

                       

Manufacturers increasingly are employing portable articulating arms for inspection purposes directly on the factory floor. With smaller, more accurate portable CMMs, manufacturing operations use the measurement devices for reverse-engineering parts, and for fast, accurate validation of part tolerances.

Today's portable CMMs now boast accuracies that are approaching traditional metrology lab equipment, yet the systems offer manufacturers the flexibility of performing on-line inspection tasks alongside machine tools on the shop floor. Portable CMMs can be found in many shop-floor applications in the automotive, aerospace, and heavy equipment industries where the equipment offers operators the immediate feedback needed to make quick, efficient decisions. Along with accuracies that in some cases reach 0.0002" (5µm), the latest portable CMMs feature more advanced networking capabilities and powerful new CAD-based 3-D software.

Portable articulating arms in North America predominantly come from two manufacturers, FARO Technologies Inc. (Lake Mary, FL) and Romer Cimcore Inc. (Farmington Hill, MI and Carlsbad, CA), which was purchased in August by Hexagon AB (Stockholm, Sweden). At the IMTS held in September, the companies recently demonstrated the latest in portable-arm offerings.

"What really started off as a need by a couple of aerospace companies to be able to come out of the CMM room really has developed into something much more far-reaching," notes Shaun P. Mymudes, FaroArm product manager at FARO Technologies, regarding portable CMMs' rising popularity. "Those early visionaries realized that when they're making things, they can't necessarily rely on traditional measurement methods, but they still have to make parts right."      

With portable CMMs like FARO Technologies' FaroArm articulating arm, manufacturers saw a way to not only get inspection data immediately, but also to do something with the data, Mymudes adds. "We call it 'action-ready' data, but even 15 years ago when they were envisioning this, they knew that articulating arms had advantages," he says. "When you take a part off the production line and put it in a temperature-controlled environment, it's not the same part anymore, because parts change with temperature." Fixturing also changes with temperature shifts, he says, adding one more variable for manufacturers.

Articulating arm accuracy is important for the many manufacturing applications relying upon portable measuring devices on the shop floor. In September, Romer introduced its Infinite portable CMM series, which is said to have a long list of exclusive features including new integrated wireless communications with a lithium-ion battery for extended portability, a digital video camera, the company's DOCS Lite (Digital Overlay Camera System) software for basic prismatic measuring, quick-change automatic probe identification, and Heidenhain rotary encoders built to Romer's specifications.

"There's more and more of a requirement for arms to be more accurate," notes Steve Ilmrud, Romer CimCore vice president, operations and engineering. "That's one of the things the industry is pushing, and the Infinite arm is the most accurate arm we've produced."     

Specifying custom Heidenhain rotary encoders helped boost accuracy on the Infinite series, Ilmrud notes. "These encoders are all machine-tool quality, the same type of encoders used in high-end machine tools, and Heidenhain has worked with us to co-design a specific encoder design for our needs. We have a widely spaced double-bearing design that allows us to have a rigid mechanical structure to get the accuracy we need."

The Romer Infinite CMM features the company's patented infinite rotation, and its new Wi-Fi (wireless 802.11b) connectivity enables users to connect the articulating arm to the Dell wireless laptop included with the CMM system without any cables. The Infinite series CMMs is lighter than its predecessors, and features include low-profile Zero-G counterbalance, a new universal mounting system that reduces the footprint and simplifies setups, next-generation electronics with on-board diagnostics, and carbon-fiber probes as standard equipment. The company also notes that Romer provides a NIST-traceable calibrated length standard with every arm to allow the operator to verify and document system performance for ISO or vendor requirements. Volumetric length accuracy for a 4' (1.2-m) Infinite arm is ±0.00054" (13.7 µm).

Romer also has an optional Infinite arm with seven axes for real-time laser-scanning inspection, or reverse-engineering. This model includes a new combination hard probe, laser-scanning probe assembly with infinite rotation that accommodates laser cameras manufactured by Perceptron (Munich, Germany), 3D Scanners (London, UK), Laser Design Inc. (LDI, Minneapolis, MN), and Kreon Technologies (Limoges, France). The handle of the combination probe assembly is removable to allow operation in tight confines, and all necessary wiring for third-party laser scanners is internal to the arm. The Infinite series arms are available in several measuring lengths in six and seven-axis configurations.

Visualizing parts with still images from the new digital video camera on the Romer system can help users see their parts more accurately while working with CAD models. An authorized reseller of the PowerInspect inspection package from Delcam plc (Birmingham, UK), Romer also has coupled its own DOCS software with the PowerInspect program. "I was a user for years, and one of the things that helps people is visualization of what they're trying to measure, of what they're trying to reverse-engineer," Ilmrud notes. "Oftentimes when you put a CAD model up, it's a wire-frame or a solid, and it's hard to really understand what you're looking at." To alleviate this, Romer added as a standard feature the new digital video camera, which is embedded in the arm's wrist.

"Our software allows the user to take visual images of their measuring environment and the part, and it enables them to capture that," he says. "When they capture geometric data, that data is overlaid on top of the visual images. We have a new term for this, called Trans-Projection, that was patented. The major benefits are to document the measuring part, as well as the measuring environment."

With Delcam's PowerInspect software, users can perform on-machine verification and off-line programming. The software offers inspection functions including comparison against all mainstream CAD formats, rapid alignment for complex free-form shapes, inspection of user-defined sections, and the ability to inspect along the edge of a part. With full geometric inspection capabilities, PowerInspect users can automatically create inspection features from CAD nominals. The package includes a step-by-step geometric dimensioning and tolerancing (GD&T) Wizard. The current version 3.05 software also adds real-time laser scanning with an optional, seamlessly integrated point-cloud add-on feature.

With Romer's DOCS software, Trans-Projection allows creating the overlay directly on the part's digital image. "Visualizing the part isn't that easy. It depends on the CAD view itself," says Ilmrud. "You can rotate the view, but having the ability to overlay that CAD data over the actual physical world can bring the picture home."

Aimed initially at tube inspection, the DOCS software and Trans-Projection capabilities are included with every Infinite series arm, and Ilmrud notes that Romer is considering licensing the Trans-Projection software to third-party developers in the future. "We've been in the tube-inspection market for the past 30 years, and this is our first new software in quite a few years to support the tube inspection market. Trans-Projection is one key, and the second is surface inspection of tubes."

The system can be used for inspecting tubes of varying sizes. "It's almost everything, from piano wire up to 6" [152-mm] tubing," Ilmrud says, "and it's for tubes of all sorts--for manifolds, brake lines, hydraulic lines, air lines, gas lines that are used in automotive, aerospace, heavy equipment, you name it, it's everywhere. With tubes now having all this surface definition, you're going to get a better result. It's more accurate and the data are available."

Wireless capabilities with the Infinite articulating arms mean no potential slip-ups on the shop floor, where operators often work in space-constrained workcells. "Sometimes you have applications where you're squirming around trying to get in and around things, always dealing with cable management, and you've got the umbilical cord to the arm which passes data back and forth, as well as the power cord.

"We have the world's first wireless arm, which uses the Wi-Fi standard 802.11b, and runs untethered for three hours on its rechargeable lithium-ion battery. When the arm is plugged in, it'll trickle-charge the batteries. When you unplug it, it has about a three-hour life cycle on it. That gives you the ability to roam around and not worry about any cables-either power cables or data cables."

Accuracy, flexibility, and reliability all factor into the performance of portable arms, which Mymudes notes have become much more rugged in recent years. "What's really come about to make the arms more viable is that they're getting more reliable and more durable," Mymudes says. "The focus is how to make a more useful device, and be able to use it on more parts. They really do have to chase the zeros. When the part comes off, it must be as accurate as possible."

As the market for portable arms matures, manufacturers have more confidence in the technology being able to perform metrology tasks previously in the realm of mainstream CMM equipment. Today's portable CMM equipment helps manufacturers cut scrap, and offers an accurate alternative to the metrology lab, Mymudes adds. "Oftentimes, you don't have to unchuck the part, and you can fix it right on the lathe," he says. "Accuracy has improved, and temperature compensation is a major reason."

With the latest equipment, each portable CMM includes electronics and composites in the tubes of the arm, Mymudes says. The company's FARO Gage line portable CMMs and FARO articulating arms feature advances including on-board lithium-ion batteries and USB connections. "Each joint in the arm has its own temperature compensation, which is patented, and the arms have to be light." Accuracy for the longer Platinum FaroArm starts at 0.0005" (12.7 µm). On the shorter portable CMMs mountable on a machine tool, the Gage and Gage-Plus respectively offer accuracies of 0.0004" (10.2 µm) and 0.0002" (5 µm).

CAD-based inspection software enables users to tackle complex reverse-engineering tasks that otherwise would be much more difficult. While Romer resells the PowerInspect software, FARO developed and has sold its own CAD-based software package, CAM2 Measure. Updated in April with version 4.0, CAM2 Measure adds some 250 new features including enhanced probe calibration, new measurement commands, new tubing functionality for round and rectangular tubes, and cross-section measuring.

Reverse-engineering tasks are greatly aided by such CAD-based software, Mymudes says. "Without it, you'd have to take an array of X-Y-Z locations of what you just measured, and try to dump them into some CAD model," he says. "It'd be a mess, whereas this way, you can actually make the part as you measure."

In the past, 3-D model sizes have presented problems, but this will be alleviated by the next version of CAM2, which Mymudes says will soon be released. "The big thing is that we used to use the ACIS kernel, which was limiting the CAD model size," he says. "You could not get a decent size model into it." Since purchasing Computer Aided Technology Systems (CATS) some time ago, Faro has acquired more expertise with CAD kernels, and now will be able to work with extremely large 3-D models. In addition, the company's software has enhanced its SPC capabilities, which are used for analyzing data from part inspections.

"This gives users quicker and easier reporting," Mymudes says of Faro's SPC database. "More assemblers demand data from the part. If you're doing periodic part inspections, you want to know that your process is controlled."

 

This article was first published in the November 2004 edition of Manufacturing Engineering magazine. 


Published Date : 11/1/2004

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