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CMMs in the Wide World of Metrology

Bruce Morey
By Bruce Morey Senior Technical Editor, SME Media

There are numerous alternatives to the now venerable coordinate measuring machine, or CMM. Sensors like video cameras, structured light systems and handheld laser scanners have come of age. These sensors collect data in ways far different than the traditional tactile probe-equipped CMM. Some see these as encroaching on its turf. Has the heyday of the CMM come and gone?

Apparently not. “The state of the CMM market is solid and growing,” said David Wick manager of product management of Zeiss Industrial Quality Solutions, Maple Grove, Minn. Zeiss offers a wide array of CMMs, including standard bridge-style CMMs, models designed for the shop floor, and horizontal arm versions along with others capable of measuring airplane-sized parts.

“Although the CMM market is mature in its traditional automotive powertrain and aerospace segments, we see the market growing in medical applications,” he explained. And it is growing in small industrial operations where people are looking for a basic, first machine to get into metrology with a CMM, according to Wick.

New entry-level SPECTRUM CMM from ZEISS with the latest scanning technology

However, even with these first-time users, CMM operation has evolved. Automatic CNC-driven CMMs were long regarded as complex, even finicky machines, needing a climate-controlled room and programming from experts. Many of today’s first-time users still sequester their CMM purchases in special rooms, according to Wick. “But you don’t have people in lab coats just sitting there waiting for jobs to come in and get measured,” he explained. Owners now use CMMs to both measure and act as tools for teaching metrology to technicians, key operators, and machinists. “So, anybody can come in at any time and check something out,” he said.

Zeiss saw that this group of industrial applications could benefit from a machine targeting its needs. In response, Zeiss created a new line of CMMs called Spectrum. “Many small potential customers wanted access to the Zeiss software and the Zeiss sensors, so we developed a machine at a different price point,” Wick explained. It is equipped with a Zeiss VAST XXT and XDT scanning probes, fitted onto an articulating RDS-C5 CAA holder. It enables more positions for probe head rotation, reduces calibration time and increases operation time dramatically, according to Zeiss.

This evolution of the CMM from something sequestered to something accessible is a tribute both to todays’ more robust designs and their software. “People trust the software today,” Wick stated. That, combined with especially robust designs, has led to their use on the shop floor. “Our customers tell us that CMMs are proven both in special [temperature and humidity controlled] rooms and for at-line measurement,” he said. Zeiss products for both applications include its DuraMax, GageMax and CenterMax line of measuring devices.

CMMs Feed the Digital Thread

Michael Mariani, director of strategic business development, business unit manager-automated measurement systems, Hexagon Manufacturing Intelligence, North Kingstown, R. I., agreed that the CMM market is robust, but for slightly different reasons. “[The CMM market] is an integral part of the digital thread initiative in product development, manufacturing, and product lifecycle,” he explained. “You can design, simulate performance, and simulate production processes, but you always want to tie that to actual validation,” he said. “Anything that calls itself Industry 4.0 needs measurement data.”

To get that data, he sees more CMMs moving out of specialized rooms and more tightly integrated into the production process, providing their data in more flexible and useful ways. Hexagon now designs its special-purpose CMMs to be easy to operate in such conditions. These ease-of-use features include cantilevered architectures for easy access, power from easy-to-find 110-V outlets, and no shop air connections required for operation.

But does feeding data for smart manufacturing require a CMM? In some instances, yes. It is a question of the level of accuracy required, as well as the nature of the part itself, according to Mariani. The tolerances and accuracies of a CMM are—in general, depending on the design—still superior to what is available from other sensor sources. Structured light and laser scanners might be faster. Portable CMM arms might be more versatile. But CMMs remain the gold standard for accuracy, according to Mariani. “You could measure a gear with a [structured light] system, but the uncertainty of that data set probably isn’t appropriate for a gear that’s used in an automotive transmission,” he explained.

Productivity for the Long Term

Many times, metrology devices, including CMMs, are thought of as a necessary evil, an expense that must be endured to prove products meet specs. That is changing, according to Gene Hancz, CMM product specialist for Mitutoyo America Corp., Aurora, Illinois. “I see two groups of users, the traditional group that sees inspection equipment as something they must endure,” he said. “But there is a growing group of users that see its value going to the production floor.” In high production scenarios, he sees many more CMMs integrated into production lines, feeding data to keep control over manufacturing processes. This could include feeding statistical process control applications as well as automatically feeding offsets to CNC cutting machines to adjust for tool wear or compensate for temperature changes.

Many CMMs, such as Mitutoyo’s new MiSTAR 555, have movement architectures that allow greater freedom of access, including with robots or automated systems. (Provided by Mitutoyo)

One of the biggest advantages of CMMs is also their large size, according to Hancz. “On the large sizes, we’re talking upwards of three to seven meters on a single axis. You aren’t going to do that with a [portable CMM arm.] You aren’t going to do that with a vision system yet,” he said.

“Now the CMMs are being integrated into inline/nearline use where it’s automatically being fed by a part handling system,” he said. “It is not necessarily a robot; it could be a simple conveyor that goes right under the CMM.”

To help feed that kind of scenario, Mitutoyo offers a variety of architectures that fit the needs of fast production rates. One is its compact MACH Ko-ga-me 3D CNC measuring system. It is designed with a small footprint for easy mounting in difficult spots, even inside a CNC machining center enclosure. He also noted that CMMs with cantilever arm architectures are popular right now for shop floor CMMs. “They offer an open-air design on three sides. It makes it very easy for operators to use it that way or to incorporate part handling systems,” he said. The Mitutoyo MiSTAR 555 is an example of this application.

Sturdy Structures, More Sensors

The expanding suite of sensors available on many CMMs is also a factor. It is more common to see suppliers offer CMMs with laser scanners, vision systems and other non-contact metrology used in conjunction with tactile probes.

For example, in January Hexagon launched its first blue light laser scanning sensor, the HP-L-5.8, for creating point clouds. The blue light is better for measuring from dark or shiny surfaces, according to Hexagon. Designed to protect the sensor from collisions and vibrations, it is offered not only on the company’s smaller CMMs but also in other applications where accessibility is restricted. It turns a CMM into a multisensor machine that can switch easily between tactile probing or laser scanning within a single part program, according to the company.

In January, Hexagon launched its first blue light laser scanning sensor, the HP-L-5.8, for creating point clouds. It can be equipped on CMMs, demonstrating the range of sensors available to add to tactile probing. (Provided by Hexagon Manufacturing Intelligence)

“People, in general, want to measure more and they want richer data sets,” said Mariani from Hexagon. That is why they want more than touch or scanning analog probes, and why CMMs continue to remain relevant.

Eric Hayes agrees the market for CMMs remains strong. He is the director of metrology solutions in North America for LK Metrology Inc., Brighton, Mich. In 2018, LK Metrology was relaunched as an independent CMM manufacturer after several years as a division of Nikon Metrology. It also acquired the CAMIO CMM software product as well. First established as a CMM company in 1963, it traces its technical heritage back to the early days of CMMs. “As new technology is available, companies find they still need to rely on their CMMs,” he said. “They provide a better level of accuracy and flexibility, especially when compared to some of the handheld devices.”

CMMs, such as LK Metrology’s new ALTERA SCANtek 5, remain relevant as the standard inspection equipment used to correlate other inspection equipment. (Provided by LK Metrology.)

How have CMMs kept up with the technical competition that today is quite a bit more varied than in 1963? He pointed to improvements in the basic structures with a wider range of architectures and more temperature stable platforms that have allowed for better CMM accuracies. Most of LK Metrology’s machines feature a ceramic bridge along with spindles and air bearings, which provide a very stiff and stable platform for utilizing the newer sensor technologies.

Versatility in sensors also keeps them relevant, with articulating heads from Renishaw that give newer models five-axis movements. Hayes was also quick to point out that LK Metrology still offers non-contact laser scanning heads from Nikon on its CMMs despite their corporate separation, as well as surface finish probes and vision systems. According to the company, by employing different tip arrangements and knuckle joints, detailed surface finish analyses can be combined with other CMM measurements in a single operation, the basic output being Ra, Rz, RMS and raw data.

LK Metrology announced in April a new product in its Altera CMM line it called the SCANtek 5. It features Renishaw’s REVO-2 scanning system and multisensor technology to offer manufacturers a five-axis solution for inspecting the dimensional accuracy and surface finish of components. The machine features a scanning speed of 500 mm/sec. It is available with a variety of standard measuring volumes, from 800 x 700 x 600 mm to 6,000 x 2,000 x 1,000 mm, with larger options available upon request.

CMMs today also feature many more accessories, including rotary tables, racks for multiple probes, flexible fixtures and automation, according to Hayes. While acknowledging that many of today’s CMMs are robust enough to operate on shop floors, “if you really want the utmost accuracy you’re going to want to perform the measurements in a controlled environment,” he said.

Adding CMMs to Sensors

Not only have companies that provided traditional CMMs added some newly available sensors, conversely, companies that pioneered some of those alternatives—such as 2D machine vision—have begun offering versions of their own CMMs. So it is with Quality Vision International (QVI), Rochester, N.Y., with its FlexPoint CMM offerings.

The CMM is a mainstay for metrology professionals, especially as many of them are now equipped with more sensors than tactile probes, like this FlexPoint model from QVI. (Provided by QVI)

“Traditional CMMs have been around forever because they have a place in the metrology market,” said Tom Groff, chief technology officer and senior vice president of product development for QVI. He explained in detail why CMMs have probably the best inherent accuracy for measuring parts of any size—three independent linear axes, built into a stable and rigid platform. Solid-granite platforms, air bearings and sensor-driven temperature compensation create a transport system where high accuracy is possible over a relatively large measuring volume.

In contrast, the advantage of video sensors and laser scanners over CMMs equipped only with tactile probes is their ability to measure detailed features with high throughput. “Video sensors can be faster and often collect a denser data set on small features of contrast with a high level of accuracy,” he said. Point lasers can scan surfaces with high accuracy by taking advantage of the CMM stage accuracy. “Line lasers offer the highest throughput by scanning larger datasets with minimal stage motion, with some compromise in accuracy. Without high-accuracy transport, all sensors are adversely affected,” noted Groff.

While some of these newer measurement systems have replaced the traditional CMM, in many cases they have not, he said. At the same time, many users of CMMs are starting to recognize that a tactile probe is not going to do everything they need it to do. “Parts are getting more complex, and features are getting smaller. Not necessarily the parts, but the features on the parts are getting smaller,” Groff said. A tactile probe, either touch trigger or scanning analog, cannot access these features, or capture enough data because the tactile probe has access and speed limitations. “There are a variety of reasons why a video camera or a laser is a better tool to measure something,” he said.

Putting non-contact sensors on the CMM 3D transport gives users the best of both worlds—access to non-contact sensors with high accuracy. QVI’s decision was driven by demand. “We had a lot of requests from customers with larger parts that wanted to measure features as small and detailed as what they could with our smaller multisensor machines,” he said. QVI’s FlexPoint series of CMMs are offered both in a benchtop version and a bridge-style floor model. The Flexpoint has options for Renishaw TP20, TP200 and SP25 tactile probes, as well as video, laser probes, or interferometry probes housed in a multisensor cluster at the end of an articulating head attached to the CMM drive mechanism.

While the alternative sensors are a key element of the FlexPoint CMM, “most customers order it starting with a tactile probe and then add video or lasers,” he said. “You could order it with any of those sensors, but it seems that people treat the tactile probe as the primary sensor due to familiarity and get the additional sensors to take advantage of the increased capability or throughput.”

The Future: Limits and Strengths

The future of CMMs means recognizing their limitations as much as their strengths. Even companies that have solid CMM offerings are expanding. “You can’t see inside a part [with a CMM], so Zeiss developed a CT scanner to see inside parts,” said Wick. Through acquisition and development, it also now offers optical metrology systems, vision systems, and 3D scanning systems based on structured light.

In April, Zeiss announced it was acquiring GOM, one of the leaders in providing structured light sensors and automation systems built around them for inline metrology applications. While not abandoning CMMs, Zeiss is certainly adapting to offer an ecosystem of measurement. It is one of many tools an emerging metrology ecosystem.

Integration will also be important. According to Hexagon’s Mariani, “You will see CMMs get closer to the manufacturing process, see more sensor technologies, and an improvement in complementary technologies to integrate them into production workflows,” such as increased automation and a continuing emphasis on integrating CMMs in workcells.

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