The venerable Coordinate Measuring Machine is still going strong, with manufacturers exploiting its automation capabilities to ease labor problems
For CMMs, the good times continue to roll. “One of the surprising things that has happened in just the last three to four years is the sheer volume of CMMs that we are shipping,” said Angus Taylor, president of Hexagon Manufacturing Intelligence, North America (North Kingstown, RI). “The market seems to be really exploding.”
The question is why now?
There are a number of reasons. Today’s CMMs tolerate a wider range of temperatures and vibrations. They are sturdier, smaller and measure more accurately. They measure faster than ever. Also, shop floors aren’t what they used to be. “The manufacturing plants themselves are getting cleaner,” said Taylor. Today’s precision machining and manufacturing demand cleaner environments. In doing so, it also makes them friendlier for CMMs.
Perhaps most importantly, it may just get down to people.
“Manufacturers are not finding enough skilled people, so they are now looking at CMMs as being an automated measuring system,” Taylor explained. “One person can produce measurement programs for 20 [computer controlled] CMMs.” That reduces the skill set of the operator to knowing how to load and unload parts, perhaps using precision fixtures, and how to pull up the right measurement program. Hexagon offers three CMMs for the shop floor, the 4.5.4SF, the 7.10.7SF, and its newest addition, the TIGO SF.
With bar codes and robotic material handling, even loading/unloading could be automated.
“There is also a trend towards metrology as being part of the [manufacturing] operation,” said Michael Mariani, director of strategic development, Hexagon Manufacturing Intelligence. That means metrology devices integrated into a closed-loop manufacturing cell, such as the one recently demonstrated by Hexagon. The demo shows parts being machined and then moved by a robot to a CMM. The CMM then automatically provides information on how to adjust the machining operation, if needed, to maintain tolerances.
Sensors and Growth
CMMs are growing more useful as suppliers offer more sensors. That diversity is reflected in Hexagon’s own suite of probes. The company provides touch probes, scanning probes, and surface roughness measurements, as well as its HP-O optical sensor based on interferometric laser technology.
Sensors and probes are the main business of Renishaw PLC (West Dundee, IL, and New Mills, Gloucestershire, UK), the inventor of the touch-trigger probe that made CMMs so popular in the first place. Adding to its PH10 three-axis probe, the company invented the five-axis and fast-moving PH20 and Revo heads to improve CMM throughput. The company does this by allowing local movement while the CMM mechanism remains stationary, moving less mass while collecting data faster. It also means less system stiffness and more error, forcing slower measurements.
Probes and sensors do not always need to be on CMMs. They can be in flexible gaging like the Renishaw Equator or in machine tools themselves. Still, a CMM must provide assurance that a product is being accurately manufactured. Machine tools can drift out of tolerance, according to Michael Litwin, Renishaw’s CMM products business manager. “You want traceability to a NIST standard artifact. You still need that CMM as an independent check,” he said.
The company recognizes that even its industry-standard touch and scanning analogue probes cannot satisfy all needs. In February 2018, Renishaw introduced its SFP2 surface finish measurement probe for use with its REVO five-axis measurement system on CMMs. “This makes surface-finish inspection an integral part of CMM measurement and enabling switching between scanning and surface finish measurement,” he said. The SFP2 is a skidded probe with a 2-μm radius diamond stylus tip. The company said that its surface measurement capability ranges from 6.3 μm to 0.05 μm (250 μin. to 2 μin.) as measured in Ra.
Renishaw also introduced a vision system for use on its Revo-2 head, the RVP vision probe. According to Litwin, it measures features from 2D images using edge detection. Three-dimensional data is derived by capturing several images from different angles along with postprocessing. “It provides another avenue of measuring features where tactile measurements are not suitable,” he said. “This includes small cooling holes in turbine blades or sheet metal parts with complex 3D geometry.”
“CMMs are typically for large features but not necessarily larger volumes. Many markets are driving smaller features and capabilities that require non-contact technologies,” said Nate Rose, new product development manager, Quality Vision International Inc. (Rochester, NY).
He noted that the newest five-axis machine tools and additive manufacturing systems allow parts to have complex, intricate features whose dimensions and positions need to be verified. “Sometimes those features are best measured with an optical, noncontact sensor as part of the larger tactile probing for collecting points for analysis,” he said.
That is why QVI offers its video systems, line scan lasers, Rainbow white light sensors and TeleStar laser probes in addition to Renishaw TP20, TP200, and SP25 contact probes on its line of CMMs.
“The VersaFlex multisensor head allows simultaneous use of up to three sensors on a PH10 so they can reach features in virtually any orientation,” said Rose. “Smaller features are sometimes not conducive to tactile methods when location of that feature is not controlled. Having the vision sensor active on the VersaFlex has allowed us to find the feature first, set it as a reference, then measure with tactile. Point laser sensors allow for high-resolution surface profiles.”
Like other CMM OEMs, Wenzel America Ltd. (Wixom, MI) offers tactile probes from Renishaw along with two sensors of its own. Wenzel’s Phoenix sensor uses structured light—sometimes called white light technology—to capture a 3D point cloud. This white light sensor is light enough to be mounted on a CMM probe head. The company’s other sensor is the Shapetracer laser line scanner that also mounts on a standard Renishaw probe head.
Machines and Integration
CMMs exist in manufacturing ecosystems. “What we are seeing is a change in the ownership of the metrology equipment,” said Drew Shemenski, president of Wenzel America. “The real shift we have seen is from a machine that is in the lab controlled by a quality group to the manufacturing team. They are now in charge of the equipment and are the owners of it.”
In May, Wenzel introduced its SF 87 shop-floor CMM. Shemenski emphasized that this machine is multisensor capable and ready for all of Wenzel’s and Renishaw’s probes. The company claims the CMM’s measuring volume of 800 x 700 x 700 mm aligns with common sizes of metal-cutting and forming machines. It also boasts high travel speeds and accelerations to speed up measuring, according to the company. To further enhance its shop-floor readiness, it features a temperature stable structure and dirt resistant guides and scales. The measuring space is accessible from three sides and is integrated with other automation with the optional Wenzel Automation Interface.
“The CMM market today is strong,” agreed Gene Hancz, product specialist, CMM for Mitutoyo America Corp. (Aurora, IL). Mitutoyo offers CMMs in bridge, arm and horizontal varieties, as well as standard, high accuracy and ultra-high accuracy. “The standard accuracy bridge CMM is the workhorse of our machines,” he said.
Has he seen a change in how CMMs are used? “Most definitely, continuing to the shop floor,” he stated. “Whether it be a walk-up machine [for general use] or integrated into a robotic cell.” The integrated installations he has seen range from the simple with manual placement to the fully automated, with robotic cells that automatically feed and execute parts measuring programs.
Like other suppliers of CMMs, Mitutoyo offers CMMs for shop-floor deployment, such as the Mach series in three distinct models. The Mach-3A is a horizontal arm designed for in-line measurement. A horizontal arm saves space. The Mach-V series is designed to be used in a manufacturing line and provides pre/post feedback to a machine tool for machining adjustments.
An interesting approach to offering CMMs is the Mach Ko-Ga-Me, a mountable CMM. “You can mount it on any fixture design, even inside a CNC milling machine,” explained Hancz. It has a measuring range of only 120 x 120 x 80 mm with movements as fast as 340 mm/second with up to 2 μms of accuracy, making the mountable CMM ideal for small parts.
“Probe technology keeps expanding, and we offer anything that is available,” said Hancz. “Our most popular is the Renishaw SP25 scanning analog probe, collecting data at up to 100 mm/second.” Mitutoyo also offers a skidded type surface roughness measurement probe. The CMM Surftest probe is derived from Mitutoyo’s SJ-210/310 series of portable surface finish units. Five different probes are available: Standard, small-hole, extra small-hole, deep-groove, and gear-tooth detectors.
“There is increasing demand in the medical and aerospace segments, and especially for multisensor systems,” said David Wick, manager of product management for Carl Zeiss Industrial Metrology LLC (Maple Grove, MN). Zeiss introduced a roughness measurement probe, the Rotos sensor, in April. This adds to its suite of CMM touch, scanning, and optical non-contact sensors. The noncontact sensors include camera sensors and a confocal white light sensor.
The Rotos surface measurement probe is a skidless contact surface texture sensor with LVDT detector and two continuous rotating/tilting axes. Depending on the measuring machine and the particular stylus, Zeiss says it measures Ra roughness values down to 0.03 µm at speeds ranging from 0.25 to 1.0 mm/s.
Zeiss also offers a line of CMMs for shop-floor production. These are the GageMax, the CenterMax, and the DuraMax. Wick said the DuraMax has expanded into four separate models—DuraMax LTE, DuraMax CNC, DuraMax CNC with a rotary table, and the DuraMax HTG. The HTG is for use in environments that get up to 100°F (38°C). The CMMs are equipped with a scanning probe and feature small footprints and easy accessibility to the measuring volume.
The CenterMax is a bridge-style CMM that Wick said is especially useful in high-volume production of highly engineered parts, such as automotive powertrain and aerospace parts. “We added our new surface roughness measurement probe [the Rotos] to the CenterMax. [Now] with one set-up, our users can measure features like diameters and bores, and then measure critical surface roughness,” he said.
One Probe, One Machine
With customers finding utility in CMMs equipped with a combination of sensors, Alicona Corp. (Bartlett, IL) has taken a slightly different tack—finding more uses for a single sensor. The core of the company’s technology is a noncontact sensor that exploits focus variation.
This technique provides high-resolution surface data using limited depth of focus. The technique is similar to but more advanced than confocal imaging or optical sectioning, since it also provides color data. It measures both surface form and roughness. It is especially useful in production settings, according to the company.
Alicona has adapted it as an alternative means to measure form and geometry, expanding its use. Since it lacks range, the company needed to be able to move it precisely over a large object to measure form. That is why Alicona mounted its 3D Focus-Variation measuring instrument onto a precision three-axis stage called the µCMM coordinate measuring machine. The addition of a motorized rotation unit, the advanced Real3D Rotation Unit, provides a five-axis system, if desired. The company publishes accuracy data of EMPE = (0.8 + L/600) μm according to the ISO10360:8 specifications.
“With our sensor’s unique features, we can refrain from following a strategy now becoming very common in the CMM world, namely integrating multiple sensors into one CMM frame. The features of focus variation lets us use one single sensor. [It also provides] a more robust, less fragile, more user-friendly [device] than if you have to fiddle around with multiple sensors,” said Scherer.
CMMs in Context
Zeiss’ Wick sees a bigger future for CMMs. “New tools and expanded multisensor capabilities will grow, of course, but how they fit into the ecosystem is becoming important,” he said. “Especially in Europe there are many examples where customers are working their CMMs together with nearby machine tools to exchange information.”
While a CMM that can provide offsets to a machining center is useful, he also thinks there are additional opportunities for further integration and machine collaboration. Worldwide, he is not seeing many full Smart Factory implementations that incorporate CMMs into something one might call Industry 4.0.
“In the U.S. we are even farther behind,” he said. But that may be changing soon. “What I would expect to happen in the coming year or two is that CMMs vendors will offer more automation options on their machines. Perhaps an add-on box to let you talk to a ProfiNet or ProfiBus,” he said. With that information exchange at the machine level will come the Smart Factory.
Wenzel’s Shemenski sees that upstream integration of how CMMs are programmed will also become more important. “Model-based design technology that incorporates attaching GD&T to CAD models early in the program is becoming real. There are kinks to be worked out, and upstream designers need to recognize it as a growth in their responsibilities, but it is a trend to watch,” he said.
What this will open up is the automation of creating measurement programs—as long as valid GD&T is attached to valid CAD models. “An exciting trend is creating measurement programs automatically from CAD models with attached GD&T,” agreed Hancz. Every OEM supplier interviewed for this article has metrology software for creating parts programs for their CMMs. While at present it is a capability not often used, the next trend could well be how designers begin thinking differently of GD&T in upstream design processes. Stay tuned.