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Measurement on the Move

Kip Hanson
By Kip Hanson Contributing Editor, SME Media
Arms with hard probes are generally used to measure parts measuring about three meters in diameter, while laser trackers can tackle much larger components, up to 160 meters across in some instances. (Provided by FARO Technologies)

Machinists from the Baby Boom generation learned how to inspect parts with little more than test indicators, a surface plate and that erstwhile standard of dimensional measuring equipment—a height gage from Cadillac Gage Co.

Those from Generation X mastered more advanced technology, first grappling with the principles of volumetric accuracy and probe selection on manual coordinate measuring machines (CMMs), then learning to program with dimensional measuring interface standard (DMIS) when their much-loved measuring devices became automated.

Along came Millennials and, most recently, Generation Z. From vision systems to digital comparators that would put their grandparents’ shadowgraphs to shame, there’s little that machinists can’t measure quickly, easily and, above all, accurately.

Roaming Free

One of the earliest of movable metrology systems was the portable CMM, aka the portable measuring arm. The first iterations began appearing in the mid-’80s, around the time preschool Millennials were jamming out to Fraggle Rock and watching KITT the talking car (from Knight Rider). We won’t get into the “who was first to market” discussion, except to say that portable arm CMM manufacturers Romer and FARO each contributed to the growth and popularity of these important devices, which have grown even more capable over the subsequent decades.

Stephan Amann is vice president of sales and marketing for the metrology devices business unit at Hexagon AB’s Manufacturing Intelligence unit, North Kingstown, R.I., which acquired the Romer brand in 2004. The event marked the start of a trend that continues to this day, he says, noting that shops of all kinds now bring portable inspection equipment onto the production floor in an attempt to improve quality and reduce downtime.

“The overall implementation and usage of metrology inside the manufacturing, design and engineering processes has come to life over the last 10 years,” Amann says. “Many manufacturers have realized that when they bring measuring arms and similar equipment directly into the production area, they can inspect and fix whatever deviation they might find right then and there, without having to bring the part into the quality room. This is why the latest model of our Absolute Arm has an IP54 rating, allowing it to be used in even very dirty environments.”

Portability means flexibility, he adds. The widespread availability of this and other inline, nearline and even offline metrology equipment means manufacturers are no longer dependent on traditional CMMs and gaging, nor limited by these devices’ relatively small measurement range. As a result, they can react more quickly to changes—in quality levels, production needs and customer demands.

Several metrology providers have taken a portable arm—once considered a niche and of limited capability—and enhanced it with 3D laser and structured light scanners for increased range and functionality. Hexagon also has equipped its arms with carbon-fiber construction for reduced weight, user-friendly displays, and software and advanced encoding systems that eliminate the need for referencing routines and annoying warm-up times. “The technology has improved dramatically over recent years,” Amann says.

An All-Around Arm

FARO Technologies Inc. Product Manager Leo Martinez cites similar improvements within the Lake Mary, Fla., company’s family of portable measuring arms. For example, the Quantum Max boasts eight axes of motion and an internal counterbalancing system that helps reduce operator fatigue. Such features were either unavailable or nearly impossible to deliver when FARO introduced its first product.

As a result of these advanced capabilities, portable arms have become a general-purpose measuring solution. “Granted, they’re not as accurate as a traditional CMM and probably never will be, but they’re easily sufficient for a wide range of applications, and are especially well suited to larger parts that are tough to move or that won’t fit on a fixed machine,” Martinez says.

Moving large components like this casting to the inspection room is both time-consuming and impractical. Portable measuring arms eliminate this problem. (Provided by Hexagon Manufacturing Intelligence)

For the latter, he points to a popular option that expands these capabilities even further. Rather than taking multiple points as is necessary when measuring with a stylus, a laser line-scanning head allows an operator to check even automobile-sized surfaces quickly and accurately. This is a go-to solution for carmakers who wish to model a “body-in-white,” designers looking to reverse engineer larger products and fabricating houses that need to inspect a weldment or sheet-metal enclosure.

Portable systems are also changing the way manufacturers operate CNC equipment. For instance, rather than removing a partially completed part from the machine tool and walking it over to the quality area for inspection on a CMM—a step that could result in many minutes to hours of downtime—a portable arm allows operators to measure even very complex part features that are still in the machine. There’s no loss of positioning, no need to refixture a part or “dial it back in,” and no waiting in line or downtime because someone forgot to program the CMM.

“Whether setting up a machine or troubleshooting a production issue, an arm gets you to the desired result very quickly,” Martinez says. “If you can avoid wasting several hours on a machining center or stamping press, the amount of additional productivity could easily add up to hundreds of thousands of dollars over time. More importantly, it might mean the difference between delivering good parts on time and scrapping a very expensive workpiece.”

Arms with hard probes and structured light scanning heads are generally used to measure parts three meters in overall diameter or smaller, he adds. “But we can also cover very large volumes with our laser-tracker product line, which has a range of up to 160 meters in total diameter. This opens the door to applications in the construction and geospatial industries, as well as the scanning of larger vehicles like farm equipment and aircraft. These capabilities are having a profound effect on numerous industries well beyond traditional manufacturing.”

Thanks to their advanced capabilities and extreme portability, measuring arms have become a general-purpose metrology solution. (Provided by FARO Technologies)

I Heard It on the X

Caitlin Considine has plenty of good things to say about in-machine measurement. She is a technical marketing engineer for quality and metrology systems at Keyence Corp. of America, Itasca, Illinois, and like her competitors, emphasizes the need to minimize downtime by keeping parts in the machine as much as possible. Her go-to approach to accomplish this, however, is far different than the solutions just described.

“Our XM-series of handheld probe CMMs continue to be a big hit with CNC machine shops, tool and die makers, and pretty much anyone who wants to shorten setup times and eliminate the errors that may result when workpieces are removed from the machine tool for inspection,” Considine says.

Keyence also continues to improve its products. The latest XM iteration includes a laptop with pre-installed measuring software, which Considine suggests improves portability and simplifies maintenance. It’s also wireless and has a swiveling head that follows the probe motion, increasing accuracy and measuring range alike. “It looks a little like R2-D2,” she laughs.

Star Wars references notwithstanding, metrology experts might greet the XM with skepticism. By using a high-resolution camera with a handheld probe that determines its position in space through triangulation, it seems unlikely that the system could offer any level of measuring precision. Yet, as Considine points out, looks can be deceiving: The XM promises +/-3 μm repeatability (0.00012") and accuracy of +/- 7μm (0.00027"), with a working range of 2000 × 1200 × 1000 mm (for the XM-5000).

Scaling Up

That range just got a lot bigger. Emily Rapp, Considine’s coworker and fellow technical marketing engineer, is excited to introduce the WM, a very big brother to the XM. It boasts accuracy similar to its sibling and works on the same triangulation technology, but with working envelopes that are vast by comparison.

“The WM can measure features up to 49 ft (15 m) away,” says Rapp. “And within its ideal measuring range of 15 x 12 ft (4.5 x 3.7 m), the volumetric accuracy is within a thousandth of an inch. Our customers have been pretty impressed with its capabilities.”

There is a caveat, albeit one that makes sense given the system’s optical nature: the handheld probe must maintain line of sight with the unit’s three cameras. In its original design, these were mounted to a head that sits on a movable stage, but to give the device greater flexibility, Keyence made it so the camera unit can be removed and placed on a nearby tripod or pole.

Mobile blue light 3D scanners like the ATOS Q quickly generate a geometric digital twin that can be used for many metrology needs. (Provided by Capture 3D)

Rapp notes that the WM is found in many different, often very large, applications. These include machinery and equipment alignment, measurement of assemblies and welded structures, precast concrete construction, energy components such as turbines and windmill vanes—and the list goes on. In each case, the operator can use a variety of stylii to measure hole position, flatness and parallelism, as well as perform “best-fit” calculations and compare the results to a CAD model.

“Some people refer to it as a wireless tape measure, but one with very high accuracy and GD&T capabilities,” she says. “Whatever you call it, it’s nice to have a single measurement tool that is mobile, doesn’t take up much space and only requires one person to operate it, no matter how big the workpiece.”

A Million Points of Light

As indicated earlier, manufacturers often use mobile metrology solutions for the reverse engineering of products. Alberto Griffa, regional sales manager at Capture 3D LLC, Santa Ana, Calif., a Zeiss company, suggests that the fastest way to accomplish this is with a 3D scanner and software that can convert the millions of points these devices collect into a virtual replica of the object.

The XM Series shop floor CMM from Keyence is said to simplify and speed up inspections, provide easy 3D and GD&T measurements, and is both portable and shop floor ready. (Provided by Keyence Corp.)

“It can be any type of part, from the cell phone sitting in your pocket to the car that you drove to the plant today,” Griffa says. “By scanning it and creating a dimensionally accurate digital representation, you’re able to perform all manner of tasks, whether it’s measuring, reverse engineering, finite element analyses, virtually assembling it with other scanned components or sending it to a 3D printer for prototyping. It’s really the starting point for everything.”

He recommends structured blue light 3D scanners, which are said to be less susceptible to poor lighting conditions and do a better job with highly reflective surfaces than the older, white light alternatives. Systems with “triple scan” capabilities allow users to peer into deep cavities and other features that would normally be inaccessible, and do so in less time, according to Griffa. “Scanning is line of sight, and if you can extend that through the use of two cameras as we do with our ATOS system, it means fewer measurements and greater accuracy,” he says.

When asked to quantify “greater accuracy,” Griffa responds with a question of his own. “How large is the scan area and what lenses will you use?” Using high-resolution cameras to measure a part that’s a few inches across is far different than scanning an airplane, he explains. In the first scenario, you’re probably looking at accuracies in the single-digit micron range. In the latter, accuracy might drop to the low double-digit microns, depending on the lenses, field of view and which blue light 3D scanner is used. “Providing exact figures is somewhat subjective, but in the majority of applications, 3D scanning offers excellent data quality.”

Excellent quality or not, what the user does with 3D scan data afterward is equally important. All structured light scanners require software to make sense of the massive point cloud, turning it into a collection of tiny triangles and then joining one to another through a process called polygonization. Griffa says this task can be accomplished inside Zeiss’ Quality Suite via Zeiss Inspect, which can export an STL file format for 3D printing, or if a solid model is needed, the company’s new reverse engineering software can be used.

“It requires a certain level of intelligence and no small amount of mathematical calculations to turn what is basically a huge blob of points into triangles, and from there into planes, lines, circles and freeform surfaces that can define any workpiece,” Griffa says. “However you get there, the end result is a digital twin that you can use for all manner of engineering and metrology needs.”

Hexagon’s Amann points out similar capabilities, reinforcing what he stated earlier about the relationship between portability and flexibility. “We have customers who are scanning parts with one of our structured light systems, importing the point cloud into their CAD software, and sending the toolpaths needed to replicate the part directly to a machining center,” he says. “On the design side, we can take that same point cloud and perform any kind of engineering simulation, whether it’s to analyze structural integrity, wind noise, fluid flow and so on.

“All this and more can be accomplished in an integrated measurement and software platform,” Amann continues. “Like I said, there have been some significant advancements over the past few years.”

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