Coordinate Measuring Machines

byKennedy Smith It's a bit inaccurate to call new developments in coordinate measuring machine technology "trends." Unlike your favorite suit or dress from 1985--which you'd likely never consider wearing again and have probably given to Goodwill by now--a CMM is not something you just toss out and replace as times (and fashions) change. In fact, once a new CMM breakthrough is introduced, it tends to stick around for the long haul. The economics of CMMs are simply such that frequent changes aren't feasible; CMMs are made to stay put, to be improved upon and to be honed to reach their optimum capabilities.

Think of CMM technology as an antique house. Say your home was built in the 1850s, well before electrical outlets, dishwashers, microwaves, dryers, central heating and air, lawn sprinklers, and all the other amenities we've come to expect in a house were available. As time went on and these appliances were invented, the former inhabitants of your home gradually installed them, reworking certain aspects of the house to fit their needs. large moving bridge cmm

This is the way CMMs improve over time. Their basic structure has remained constant, while parts have become more accurate, several functions have been integrated into one machine, and the latest software has added new usability.

The CMM of the Future Several of the leading CMM manufacturers have speculated about what's on the horizon in terms of CMM improvements. Here's what some have predicted: "On the accuracy side, there will be improvements in the uncertainty of optical master calibration by at least an order of magnitude, after which we can promote even higher specifications."--Art Whistler of Werth America "There will soon be dynamic mapping of CMM parametric errors with built-in sensors. When practical, it becomes possible to actively compensate for these errors in real time."--Larry Magganio, CMM systems analyst at Mitutoyo America Corp. "Adaptable measuring and inspection strategies in the production environment is steadily gaining momentum. Inspection on the production floor closes the gap on feedback for shorter production cycles, which calls for measuring systems that can operate under the most extreme environmental conditions and still achieve high accuracy."-- Chris Grow of Carl Zeiss "I expect that you will see more advancement in noncontact probing technology. Laser-based noncontact probes in use today have some real advantages in the amount of data that can be acquired and the speed with which data can be acquired. But they are not as accurate as contact-type probes."--Jeff Walker of LK Metrology "You'd really like to measure everything without touching it. It's faster, quicker and cleaner, and you don't scratch the parts. But the technology hasn't been there. It's starting to get to the point where it may become mainstream soon."--Dave Genest of Brown & Sharpe "We'll see multisensor machines where the CMM can use more than two types of probes. In the CMM software, I envision part programming becoming even easier; soon it will be just a matter of bringing in a CAD file and telling the CMM which feature to measure and the software does the rest."--Colin Robinson of the L.S. Starrett Co. The foundation

The CMM of the Future

Several of the leading CMM manufacturers have speculated about what's on the horizon in terms of CMM improvements. Here's what some have predicted:

"On the accuracy side, there will be improvements in the uncertainty of optical master calibration by at least an order of magnitude, after which we can promote even higher specifications."--Art Whistler of Werth America

"There will soon be dynamic mapping of CMM parametric errors with built-in sensors. When practical, it becomes possible to actively compensate for these errors in real time."--Larry Magganio, CMM systems analyst at Mitutoyo America Corp.

"Adaptable measuring and inspection strategies in the production environment is steadily gaining momentum. Inspection on the production floor closes the gap on feedback for shorter production cycles, which calls for measuring systems that can operate under the most extreme environmental conditions and still achieve high accuracy."-- Chris Grow of Carl Zeiss

"I expect that you will see more advancement in noncontact probing technology. Laser-based noncontact probes in use today have some real advantages in the amount of data that can be acquired and the speed with which data can be acquired. But they are not as accurate as contact-type probes."--Jeff Walker of LK Metrology

"You'd really like to measure everything without touching it. It's faster, quicker and cleaner, and you don't scratch the parts. But the technology hasn't been there. It's starting to get to the point where it may become mainstream soon."--Dave Genest of Brown & Sharpe

"We'll see multisensor machines where the CMM can use more than two types of probes. In the CMM software, I envision part programming becoming even easier; soon it will be just a matter of bringing in a CAD file and telling the CMM which feature to measure and the software does the rest."--Colin Robinson of the L.S. Starrett Co.

Many CMM features haven't changed since their initial development, which is why CMMs pretty much look the same as they did 30 years ago. "I think the hardware is no longer that important," states Dave Genest, director of marketing and corporate communications at Brown & Sharpe. "There haven't been a lot of technological breakthroughs with the materials or the look."

Jeff Walker, marketing manager at LK Metrology Systems Inc., notes that the use of temperature-stable materials, such as granite, carbon fiber and ceramics, has remained consistent throughout the CMM's history. Certain materials may have been replaced by more usable or economically feasible products, but the concept behind the material being very stable has always been there.

If it ain't broke, don't fix it

Despite constant improvements in CMM technology, there are few instances in which replacing your old CMM with a new one is called for. For many practical reasons, companies opt to keep the CMMs they already have and upgrade when needed. "For example, a properly maintained air bearing machine will not wear out during its useful life," comments Art Whistler of Werth America Inc. "A motor may need replacing, but the fundamental machine should last a long time."

Additionally, a coordinate measurement system is not a light investment, and, if companies have had continued success with their current system, they see no reason to spend time and money in buying and learning how to use a new one.

"It's amazing to see how many hot or 'to die for' products go unused," says Whistler. "We never get very far away from a solid, sound, intrinsically accurate mechanical system, in spite of advances in software error compensation."

"It's conceivable that you could have a machine that's 20 years old," adds Genest. "You could have upgraded it five times, and it still gives you the same performance as it did."

Along with an occasional part replacement, upgrades also tend to come in the form of software. According to Chris Grow, vice president of marketing at Carl Zeiss IMT Corp., customers tend to want the latest version of software more frequently than the latest hardware. "The software and applications world of metrology is far more dynamic. We survey our customers and use their feedback to constantly revise and update our software."

Walker at LK Metrology agrees, noting that customers most often want the most advanced software, probing technology and controls--in that order. As factories move toward a paperless environment, they want to obtain and store their data electronically with more efficiency. CMM technology is adapting to this particular need.

Software aside, new features for CMMs differ depending on the CMM developer and its customers' needs, but all of the new CMMs boast improved accuracy and usability.

Mahr Federal Inc.'s MarVision Multiscope 222 www.mahrfederal.com LK Metrology's Ultra CMM www.lk-cmm.com Brown & Sharpe's Global CMM www.brownandsharpe.com Werth America Inc.'s Video-Check Multisensor CMM www.werthamerica.com L.S. Starrett Co.s Aurora www.starrett.com Mitutoyo America Corp.'s Legex CMM www.mitutoyo.com CE Johansson's Saphir CMM www.cejmetrology.com In response to customers' needs to integrate several functions into one machine, Mahr Federal's new MarVision Multiscope 222 3-D CMM accommodates multiple sensing technologies, including touch-probe, vision and laser sensors.

Brown & Sharpe's Global CMM

Werth America Inc.'s Video-Check Multisensor CMM

L.S. Starrett Co.s Aurora

Mitutoyo America Corp.'s Legex CMM

CE Johansson's Saphir CMM

Temperature control is also an important factor, which has recently led CEJohansson to develop thermal expansion sensors that can read the CMM's reaction to environmental changes in real time. "Conventional practice has been to limit the use of a CMM to a temperature- and humidity-controlled environment," notes Beth Graham, the company's marketing director. "By utilizing Invar rods--made from a nickel alloy material--and thermal expansion sensors, we are able to compensate for changes in temperature."

An increasing interest in noncontact measurement is also leading to new CMM development. Werth distributes CMMs with touch probes, but the company mainly develops video and laser sensors. Werth's Fiber Probe is a fiber-optic thread microprobe made to detect tiny features using styli as small as 25 microns. The Werth Zoom for video measuring has linear guides, instead of traditional rotating helical movement, which can be programmed for variable working distances from 50 to 180 mm, allowing access to deep interior features not possible with conventional lenses. And, the company's Foucault Laser allows the user to integrate a laser into the primary video sensor rather than position it with an offset from the video sensor, resulting in no loss of range between sensors because they cover a common area.

The latest improvements and changes

In the last decade or so, several developments have led to improved CMM functionality. These include:

Software. Graphically driven software capable of storing and retrieving a wealth of information has been greatly improved. According to metrology experts, this is an area that will continue to become more accurate, user-friendly, affordable and standardized.

Accuracy and affordability. According to Brown & Sharpe, a machine that was within the 10 micron range of accuracy 10 years ago, may now be in the five to six micron range. Ultra-high-accuracy machines a decade ago were in the one to two micron range and have remained there since. This may be a sign that improvements in accuracy have reached a plateau, allowing a move toward value-oriented high-accuracy machines.

"There's a couple-micron difference now between a half-million dollar, ultra-high-accuracy machine and something that you pay $80,000 or $100,000 for," notes Genest. "So those extra couple microns have become more expensive."

The user. One of the most influential elements in directing new CMM technology is the ways in which CMM users have changed. Ten years ago, the CMM operator was a quality engineer. Now, however, many more manufacturing engineers are operating CMMs, as the quality responsibility has shifted from the end-user to an engineer working midprocess. There is less need at the end of the line to determine whether things go right or wrong because manufacturers determine that as they make the product. Consequently, new versions of software are being developed with the manufacturing engineer in mind, rather than the quality engineer.

Location. Because the focus has shifted from quality control to process control, CMMs are starting to be located on the shop floor, whereas they once may have been housed in a more controlled environment. This shift has led to development of CMMs that are tolerant of less environmentally controlled areas.

Of course, it's dangerous to say that any piece of machinery has reached its optimum performance, as there's usually room to improve. Given that there are dozens of CMM manufacturers, hundreds of different CMMs and a number of different software programs that run the machines, a major concern is standardization of CMMs.

"The CMM industry lags the machine tool and robotics industries in terms of standardization," notes Walker. "Our customers are telling us they want standardization in language and a more standard communications interface to permit interchanging software between machines, beginning at the CAD level through the CMMs, all the way to reporting and analysis."

Whistler believes that educating users on the principles of coordinate metrology is key in improving CMMs. "This doesn't mean they need to learn how to run their machines, but they need a statistical sense for how features are produced from data points, and the relationship of data density and geometric ratios to results and repeatability."

Because the people running CMMs are more often manufacturing and production experts, there is a call for systems that work fast and are simple to operate. "Manufacturing and production people don't have as much time as quality engineers," states Genest. "They're there to make parts, to make money, so they need systems that are even simpler."

Although there are several different ideas of how to improve CMM technology, Genest notes that one idea is becoming more common among major metrology development companies: If speed is what you're after, you need a scanning machine. This thought has led CMM developers

to produce more affordable scanning machines with ever-increasing accuracy. Where there once was a "scanning vs. nonscanning" market, there is now the idea that continuous measurement is simply a must. Many believe that improvements in this area will be the next big wave in CMM technology.

There is also a race among metrology companies to become the benchmark in noncontact measurement. As Genest puts it, "The competition right now is to be the noncontact version of the Renishaw Touch Trigger probe, where you become the de facto standard."

Walker agrees, adding, "When noncontact probes can match the accuracy of contact probes, they will dominate."

It's difficult to visualize what your home will look like 10 years from now. Some things are certain, however. You'll still have a door, windows, a kitchen, a bathroom, and perhaps a pool in the backyard. But the structure won't change so dramatically that your house won't be recognizable as a house.

It's the same when trying to picture a 2012 model CMM. A decade of improvements in accuracy and usability will set it apart from the 2002 models, but you'll still be able to recognize it as a measuring machine. If improvements in CMM technology continue the way they have in the past, their structure, function and usefulness will remain sound and virtually unchanged.

Kennedy Smith is Quality Digest's assistant editor. E-mail her at ksmith@qualitydigest.com . Letters to the editor regarding this article can be sent to letters@qualitydigest.com .

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