Over the past decade, technological improvements have seen 3D laser scanning become an increasingly important alternative to tactile measurement in an expanding range of measurement applications.
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The success of laser scanning owes as much to under-the-hood technologies that improve the usability and flexibility of scanning as it does to improvements like points/mm, laser line length, and data acquisition rate.
Managing optical exposure settings is one capability that doesn’t make the headlines, but it’s critical for the usability of a laser scanner and the accuracy and efficiency of data capture. This article looks at the development and advantages of a set of optical algorithms created by Hexagon, called SHINE, which has transformed the usability and performance of 3D laser scanning in both portable metrology and traditional coordinate measuring machines (CMMs).
Optical challenges
Modern high-performance 3D laser scanners can now acquire more than a million points in a second, covering an entire object instead of just a few key features, and in much less time.
The movement from tactile measurement toward scanning has, however, brought its own set of challenges. The first is simply that laser scanners are optical instruments, so they have optical challenges just like any camera—especially when scanning a variety of surface textures, colors, and reflectivities.
For instance, you can overexpose the scan—analogous to using a flash when you shouldn’t. If you’ve put too much power into the laser, or possibly opened the aperture of the camera too much, or both of those things, then you will overexpose the scan data, and that creates noise.
A good way to visualize noise is to take the example of scanning a perfectly flat surface. If you overexpose the scan, the scan data of that plane will look a bit like an orange peel. The problem is when you look at the orange peel, you don’t know which data points are the right ones. Are they the ones at the peaks, in the valleys, or in the middle? So, it’s crucial to get exposure settings right.
The evolution of laser scanning
3D laser scanning began with first-generation line scanners that required a user to manually define and input optical exposure settings, limiting scanning to one type or color of material in one pass. And with this came a training need: You had to teach people how to do this.
A second generation of scanners introduced automatic exposure adjustment based on the surface color detected by the scanner’s camera, similar to how a camera can automatically adjust to the brightness of the subject. Although this was a significant improvement, it required the entire scan line to be always be on the same surface color because every point on the line was measured at the same exposure setting.
Of course, many customers said, “Well, hold on a minute. My part isn’t just black, it’s black and white, and often other colors as well.” So, the optical settings that you would use for, say, dark blue, would be completely different to the settings you’d use to scan a yellow part. You could get the scanner to set itself up on each of those different colors, but this was far from ideal. Very often, when you looked at the scan data, you might see a small step in the data where the different settings had been used.
With the next-generation, “flying-dot” scanning concept, the scanner could adjust the exposure setting for every single point along the laser line, enabling it to scan any material in any orientation. However, the mechanics and motorization needed within the scanner to make this type of scanning possible was a bit delicate and also made it relatively slow.
Ideally, what the user wanted was a scanner that was rugged, easy to use, and could scan any surface with minimal setup.
Easing user experience with intelligent data collection
When Hexagon started to develop the next generation of scanning technology, our first requirement, the driving force, was that we wanted the scanner to be set up so it could scan 95% of parts, on most surfaces, without the operator having to intervene.
Earlier, with typical laser scanners, because the operator needed to choose appropriate settings for the part’s surface, you frequently saw a marked difference in measurement quality according to the skill and experience level of the operator. You could ask two people to scan a part, and one of them would give you orange peel, and the other would give you good data.
We wanted to make precision measurement reliable and user-friendly, regardless of the operator’s experience, so they could just walk up, take the measuring arm, and scan the part without having to go into any menus to see what the scanner was doing.
And because we wanted to use a fixed laser rather than flying-dot (with its inherent drawbacks), we needed intelligence in how the scan data would be collected by the sensor—meaning different parameters for each point along the laser line—so you could accurately and efficiently scan each surface and color, including that juncture between a blue and yellow surface, for example.
Full performance all the time
It’s also important that the full performance of a scanner is available to the user all the way through its working envelope.
When we looked closely at the technologies available and how scanner performance was often being advertised, we discovered that some of the most eye-catching performance claims—higher frame rates, higher scan frequency (points per second), lines per second, and so on—came with many caveats in the small print. To achieve those top figures, all sorts of settings would have to be activated. You might have to shorten the focal length of the camera substantially, or the camera might not look at the entire laser line but only at the middle 50% of the line. In many cases, this meant a scanner was more difficult to use because its working envelope was much narrower.
Hexagon engineers knew that wasn’t good enough; that’s not what we wanted. Nor is it what the user needs or expects—they’re likely to feel short-changed.
We wanted a scanner to guarantee its full performance all the way through its working envelope. It doesn’t matter if the part is some really tough, shiny black-plastic carbon fiber or machined aluminum, or a complex-shaped turbine blade with surface features smaller than a millimeter. The full performance of the scanner should be available to the user—all of the performance, all of the time—which brings us to algorithms and SHINE, Hexagon’s latest scanner performance improvement.
What is SHINE?
SHINE stands for systematic high intelligence noise elimination. It is a set of algorithms—a patented type of high dynamic range (HDR) technology—that allows measurement of surfaces of different colors and levels of glossiness in a single scan pass. By capturing data at three different exposure levels applied to each point along a measured scan line, all surface information is captured using the optimum settings at all times: one low-level exposure captures light or matte surfaces; a second high-level exposure captures high-gloss and dark surfaces; and a medium-level exposure is used for other surface types. The SHINE algorithm then determines which of those three readings provides the most useful data at any particular point.
Because SHINE ensures that the scanner is always operating in its optimum configuration, the range of surfaces that can be scanned is wider than with conventional scanners. This smart selection of the optimum exposure level also allows for much cleaner data collection, because any noise created by scanning a surface at an unoptimized exposure setting is eliminated.
Having fully automatic settings means improved reproducibility; different users will get the same result, making for a much more consistent metrology tool. SHINE also saves time, because there’s no need to run trials on the part before starting the measurement job.
Empowering users
Hexagon wants its products to be for anyone. They should be easy to operate, deliver accurate results, and allow you to find the engineering problem. That’s it. As manufacturing complexity grows and quality demands continue to rise, this technology simplifies inspections, improves data quality, and enhances productivity. It enables less-trained users to perform high-precision measurements, which is particularly valuable in the face of metrology skills shortages, and where machine operators are tasked with quality inspections. We’ve delivered scanners that are positioned to solve the challenges of almost any application in manufacturing inspection.
SHINE is embedded in Hexagon’s current generation Absolute Scanner range of laser scanners for portable measuring arms and laser trackers, and is also used in the HP-L-10.10 range of scanners for CMMs.
Comments
Scanning made simple!
Great article! Thanks Hexagon!
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