50 Years of Quality: A Look Back at Laser Measurement
How to Use Laser Measurement Confidently, June 2001Using laser measurement in dimensional applications results in fast, accurate and traceable results, provided that the measurement uncertainties are correctly factored into the equation.
Lasers are inherently accurate because the wavelength of light, which is the basis of a laser system, has a high resolution that is linear and provides a stable reference for dimensional measurement. The most common laser-based measuring system couples the wavelength of light to the part to be measured by using a fringe counting laser interferometer to detect linear motion of a probe that contacts the part. Although various methods are used for laser measurement, including interferometry, triangulation and scanning, the interferometry method is typically more accurate than the other methods.
Laser Measurement Takes Hold, August 2002The original application of laser measurement in automotive manufacturing was a single station at the end of a body-in-white assembly line that checked each part and prevented any defective parts from continuing in the process. However, because the in-process station measures every assembly being produced, it also becomes a barometer of the manufacturing process itself. The information is critical for root cause determination and variation reduction.
Most defective parts are not anomalies but rather the result of some change in the manufacturing process. When defective parts are detected, the most important question to answer is, “What is the origin of this error?”
To more quickly determine the answer, manufacturers over the past decade have installed more measurement systems in their processes to aid root cause analysis. Instead of a single station to measure the body-in-white assembly, many automakers measure the completed underbody, body sides, framed body, doors and hoods. This step has helped manufacturers more quickly isolate problems at the subassembly level.
But even that is no longer enough. Each subassembly is made up of numerous individual components that are assembled and welded together.
The current trend is to strive for complete “diagnosability” of manufacturing processes to support very fast root cause determination. To do so requires the distribution of sensors throughout a manufacturing process rather than at a dedicated measurement station. For instance, some Audi assembly plants in Germany contain more than 25 laser measurement stations in their body assembly processes. Analytical models have been developed recently that determine what features to measure and where to measure them to obtain the most useful information with the smallest investment in equipment.
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Lasers, a Practical Tool for Inspection, November 2005It’s no wonder that laser measurement has been moving into manufacturing in a big way lately. Laser scanners are fast and accurate measurement devices that lend themselves to automation. They can collect a cloud of datum points automatically on contours and features in a matter of minutes and then send the points to software for comparison against known values. Consequently, they are making it practical to make many more measurements and conduct more thorough inspections than before-and often do them in less time.
Because they fulfill the needs created by the demand for full-surface inspection, faster data collection and greater automation, laser scanners are now busy at work inspecting a variety of parts across many industries. They are checking parts small enough to fit in one’s hand, measuring engine castings in automobile factories, and providing important feedback for the Boeing 787 and Joint Strike Fighter programs.
Despite these recent successes, laser scanning has been slow to catch on in factories. Sure, lasers have found inspection applications there all along, but their most common industrial use has been in design studios, where they caught on as reverse engineering and modeling tools from their earliest days in the 1980s. The situation has changed, however, over the past five years or so. In fact, Jim Clark at Metris USA Inc. (Rochester Hills, MI) reports that most of the laser scanners that Metris sells now are for inspection.
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Lasers Pinpoint Measurement, November 2006In the future, as computers get faster, laser measurement will further ensure quality by producing more data per second from scanners. Increased competition should force prices to decrease. There will be a wider range of localizing devices, improved software and higher speeds of data acquisition. Devices should become lighter and smaller, have higher accuracies and distance capabilities, and enhanced automated feature recognition.
According to Martin Dumberger, vice president of Micro-Epsilon (Raleigh, NC), semiconductor-based laser triangulation is currently about as fast and as accurate as it can get. “More economical systems will be introduced that will have more features for the dollar,” he says. “Laser sensors with less than 0.03% linearity are at their limits of what is physically possible in spot penetration. So there will be even more sophisticated systems with even higher integration of intelligence to improve the performance.”
Until now the majority of laser scanners have been manually operated and flexible. Giles Gaskell, director of business development at NVIsion Inc. (Wixom, MI), says this is ideal for design and development environments, but less so for in-line applications. He forecasts increasing numbers of in-line contact measurement solutions available in the future.
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