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Optical Metrology in Three Dimensions

Bruce Morey
By Bruce Morey Senior Technical Editor, SME Media

Basic trends in modern manufacturing are driving growth in 3D optical metrology. “One is the highly complex and high-tech material that manufacturers are using today. For example, in the aerospace turbine blade market, they simply cannot touch the part like they used to—the surface finish of the material is too readily affected by any kind of contact metrology. Or, the materials are thin and flexible and too easily deformed,” said Cliff Bliss, national sales manager of Hexagon Manufacturing Intelligence (North Kingstown, RI). In these growing cases, only noncontact will do.

The Cube-R from Creaform offers an automated solution for its MetraSCAN 3D-R scanners in a 4.1 × 4.1 × 3.1 m turnkey solution with a flexible shop-floor configuration.

Another trend is a switch in thinking, according to Bliss. Metrology is no longer viewed as a cost but as a cost-saving investment. Manufacturers no longer want only to prove the quality of the supplied part or product. “They are using metrology data to generate cost savings by improving their process and [the design of] the part itself,” he said. Using metrology to provide corrections during the manufacturing process means near-line or even in-line collection.

Automation and Optical

The speed and accuracy of 3D optical techniques, especially laser scanners and white-light or structured-light systems make them ideal for automation. Hexagon offers a wide array of noncontact, optical sensing, including Romer arms equipped with laser scanners for hand-held use, the AICON suite of structured light systems, and the WLS series of optical scanners. “The WLS systems are especially good for production-floor applications, while the AICON series of products are better for controlled environment applications, like a quality lab,” he said. In fact, 3D optical systems are proving so useful, that Bliss believes that in the long run, their market share will continue to steadily increase as companies realize their full benefits.

What might be most exciting is that new industries are discovering the usefulness of such “high tech” metrology systems. “Industries that use wood as their prime material, such as cabinet making and furniture making, are discovering that tape measures and hand metrology tools are no longer adequate,” said Bliss. “Now they are going to Romer arms with laser scanners and other noncontact measurement technologies because they need accurate measurements in their process control today.” Other newcomer industries include appliance makers, like refrigerators and dryers. “Ten years ago, they didn’t really measure these things. They used to think that if the eyeball liked them they’re good enough,” said Bliss. Now that appliances are getting expensive, consumers are demanding higher quality. “They are saying if I’m paying $3000 for a refrigerator the doors better fit,” he said.

Existing Markets, More Growth

“3D metrology equipment sales are growing,” agreed Jérôme-Alexandre Lavoie, product manager for Creaform (Levis, QC, CN). “The need for increased productivity, increased traceability, and the need for remote decision making have led companies to adopt devices capable of extracting more information on each part with a dream of controlling 100% of dimensions on 100% of all parts.” He noted that today the fastest scanner in the world can take up to millions of points per second, making it ideal for automated in-line production.

He sees the primary industries for 3D optical metrology in aerospace and automotive. In these industries especially, the costs of poor quality control are easily quantifiable. “It varies between 15 to 20% up to 40% of the total operational cost in the worst case,” said Lavoie. “Optimizing these costs can have serious impact on profitability. To know where there is a problem in a manufacturing process, quality control can be key.” He noted that applications like body-in-white and stamped parts inspection are extremely demanding for automated quality control inspection.

With a color projection, the AICON StereoScan neo features visualizing deviations from the CAD following the measurement on the surface of the scanned object.

Ian Scribner, portable 3D scanning product sales manager for Carl Zeiss Industrial Metrology Technology LLC (Maple Grove, MN), agrees that automotive manufacturing is a prime market for automated 3D optical metrology. He jokes that his customers always “want more information faster,” driving the selection of 3D optical systems.

Zeiss offers two flavors of such devices, the Comet white-light system and its T-Scan laser scanner. “The scanning head of our T-Scan laser is an optically tracked laser system,” explained Scribner. “The Comet, on the other hand, is a unique blue-light system that features a mono camera and a mono source projector featuring LED lights.”

Scribner also elaborated on both expectations and cautions.

“More of our customers want automated, noncontact systems either in the production line—for 100% inspection—or as close to the production line as possible [for sampling inspections],” he stated. “But there are constraints that must be evaluated.” These include its level of coverage in noncontact, how accurate it is, and if it is fast enough to meet the needs of the application. “It is difficult to optimize all three. Sometimes you must choose to optimize only two—sometimes only one,” he said. Interestingly, he claims his customers typically are willing to sacrifice optimizing accuracy in favor of speed.

That is because, he said, most sheetmetal applications require measuring accuracies in the range of 100–150 µm (0.004″). “The first question customers typically ask is if it is accurate enough for their job, the second question is if it can be automated,” said Scribner. “First comes trust, then comes automation,” he stated.

Another question is long-term value. It is difficult for any customer to buy a sensor that is intended to be stagnant. They need a future upgrade path and that includes automation, he said.

Another important factor Scribner points out is what, exactly, are the most important measurements his customers in automotive sheetmetal really need. “For our in-line or at-line systems, they want us to find feature size and accuracy, not necessarily its absolute location on the part. There are other ways and places in their production for them to do that,” he said.

The nice thing about scanning systems is that they have so much data they can easily determine feature size and accuracy. A scanning system can tell if a hole is round, its diameter, and its concentricity, or if the feature is meeting print.

Extraction of features points to another caution. “It is easy to get mesmerized by point cloud data or color maps created by comparisons to CAD data,” he said. Operators need to understand there is more work to get the full utility from the data, to get those feature characteristics. “Data capture is just the start of the process, tip of the iceberg. The rest is feature interrogation,” he said.

With the help of both more affordable suppliers and easier to use software that can display GD&T callouts, shown here, advanced metrology equipment is becoming pervasive, according to a spokesman from Exact Metrology Inc.

Enablers—Education and Computers

Matthew Martin, applications engineer for Exact Metrology (Cincinnati, OH), points to a couple of key reasons he thinks 3D optical metrology is growing. He too sees that every year the market is getting bigger, and attributes this to the education new engineers and technicians are getting for a good measure of that growth. “Now we are selling to the universities and STEM programs in high school,” he said. “They are no longer solely relying on traditional hand measurements in their classes and programs.” That is creating a class of knowledgeable end-users who know the benefits of 3D optical systems and can put it to good use.

Another is cheaper, more powerful computing, a fundamental enabler in this industry as in many others. For him, that means collecting and processing data is getting faster and cheaper. The sensing devices themselves are getting cheaper, in part fueled by cheaper electronics and sensing chips. This goes hand in hand with customers demanding more from inspections. “For example, clients are always wanting higher accuracy and better resolution with the scan data,” he said.

It also affects what buyers of parts want. Because they know the price is dropping and capability increasing, customers and downstream users now demand detailed inspections from even smaller suppliers, such as mom-and-pop machine shops. “They might not have had that technology even seven years ago, but certainly can afford it now,” he said.

The other enabler for automation is the growing intelligence of the metrology software. Exact Metrology has a broad view of metrology, providing contract measurement and scanning services, metrology equipment solutions, as well as offering hardware and software rentals. One of the more popular software programs they provide to clients is PolyWorks from InnovMetric. “PolyWorks can now do repeat inspections on the fly on a variety of scanners,” he said. That means that once a user has programmed the first part, as say part of a First Article Inspection, they can run the program repeatedly for subsequent parts. “Because of the turnaround time, we can now measure every single part rather than a sample batch as we used to do in the past,” he said.

“The emerging market is 100% inspection with 3D optical metrology, enabled by speed,” he said. “They knew they were always able to collect the data, now they can do something with it because of faster computing speed.”

Automation Off the Shelf

For Frank Stone, national sales engineering manager for Capture 3D Inc. (Santa Ana, CA), the demand for GOM ATOS blue-light scanners and systems that they re-sell in North America has grown exponentially over the last eight years. They have also seen continued adoption throughout all industries ranging from product development, manufacturing planning, and now production.

“What we are seeing is more and more companies replacing CMMs with our blue systems,” he stated, echoing what a few others interviewed for this article noted. “A lot of that has to do with the data quality and the intuitive analysis capabilities you get from scanned, optical data,” he said. There are other reasons. “One of the nice things about CMMs is that they can be programmed,” he said, which is why their line of commercial-off-the-shelf ScanBox automated inspection solutions is so useful. According to the company, an ATOS ScanBox includes an ATOS 3D scanner, robot, rotary stage, software, in a safety house that can be programmed by the user. The program can be stored and used multiple times, quick and easy.

The Rogers Innovation Diffusion curve is a well-accepted approach to understanding the demographics of potential users. Geoffrey Moore pioneered the idea of a ‘Chasm’, where innovations can quickly die if they do not cross into wide-spread acceptance into Early Majority. Anecdotal evidence shows 3D Optical at or near the Chasm, with some thinking it is beyond.

The Scan Boxes come in different sizes to match the part, from the 4105 for smaller parts (think medical) to the Series 8 which can fit in a whole body-in-white car chassis. “The GOM Virtual Measuring Room software means you can program these systems just like a CMM, including offline programming using CAD data and a measurement plan,” he said. But the optical-driven speed means that anywhere there is a CMM on the shop floor it is a candidate for eventual replacement by an automated 3D optical sensor, according to Stone.

“The key element is that we do not need to put our scan boxes in a controlled environment,” he said, making them ideal for the shop floor. He believes these are more flexible than a CMM, able to go into quality rooms or in-line or anywhere in-between.

He also notes that the level of automation and the ability for true “hands off” operation is growing in response to the reported availability in skilled labor (and lack thereof). “They want what I call a Kiosk Mode, a pushbutton operation programmed offline for many different parts. They can download it, take it to the shop floor, and with barcode or RFID readers drop in a fixture, read it, pull up a CAD model, push a button and then have the robot run the sequence of measuring,” he said. When complete, the program provides a quality report without intervention or interpretation by the user. An intelligent feature in the Virtual Measuring Room is that it can automatically program the robot moves simply from the CAD model as input. “An operator can program the robot but they’re going to be much slower at it than what the software can do,” he said.

Their latest offering is the ScanBox In-Line, tailored for integration directly into a production line. “It is not an enclosed box and features a PLC interface so that it can act with a robot that a customer may already have, even a cobot,” he explained.

Creaform has also launched a pre-packaged solution with its CUBE-R automated metrology systems. They announced it in April 2018—an accelerated release from their original plan, according to Lavoie from Creaform. A complete turnkey automated dimensional inspection solution, it puts Creaform’s MetraSCAN 3D-R metrology scanner into a turnkey system, including offline programming solution. The company reports that it is targeting dimensional measurement of parts ranging from 1 to 3 m with metrology-grade volumetric accuracy in real-life shop-floor conditions.

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