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CMMs: More Than Precision

By Michael C. Anderson Contributing Writer

Accuracy is just a starting point for modern CMM users, who have other ways in which their machines need to measure up.

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The new-generation CONTURA keeps the old version’s measurement accuracy but adds a wider range of capabilities.

The makers of coordinate measuring machines (CMMs) spent a long time in competition to reach the highest levels of repeatable measurement accuracy. That was once the finish line, with the distance between the competitors measured in microns. Now, however, measurement accuracy isn’t the end but rather the beginning for their customers.

That’s not to say measurement accuracy isn’t important—it’s most important. But once that first question of “is it accurate enough?” has been satisfactorily answered, a whole range of other questions occur to the user—speed, versatility, ease of use, integration into production, and more. The answers will have a direct impact on their return on investment. And how best to answer such questions is where CMM makers now compete.

Versatility in Sensors and Applications

For example, Carl Zeiss Industrial Metrology LLC, Maple Grove, Minn., has released a new generation of its CONTURA CMM. The series has been the company’s most popular bridge-style CMM even though it has about twice the measurement uncertainty of the company’s higher-end CMM, the Prismo (which has measurement uncertainty as low as 0.9+L/350 μm), according to David Wick, manager—product management, Zeiss Industrial Quality Solutions.

To keep up with changing user requirements, the new-generation CONTURA’s measurement uncertainty is…exactly the same as it has been.

“Customers told us that they were satisfied with the CONTURA’s measurement accuracy [so] they didn’t want to pay to have a CMM with better than that,” Wick said. “But those higher end machines also had capabilities unrelated to measurement uncertainty. Users told us they wanted a CONTURA able to use the range of probes and sensors that were available on the higher-end machine.”

In response, he said, the new CONTURA is equipped with the company’s multi-application sensor system (mass) technology, which enables switching between multiple types of sensor technology. The company likes to think of it as the equivalent of a Swiss Army knife—able, that is, to do a range of tasks that would have previously required multiple machines.

“With the mass technology, a large number of Zeiss sensors can be operated with high precision and quickly replaced on the same measuring instrument. Sensors with an articulating probe holder or fixed probe configuration, optical or tactile, passive or active—all can be swapped into place as needed,” Wick said.

This enables the flexibility to go from measurement tasks using tactile probes to chromatic white light sensors and triangulation lasers. Each sensor is equipped with an ID chip, which is automatically recognized by the machine when it is selected in the company’s Calypso measuring software.

“Job shops need to be able to make more types of parts than ever before and need to be able to guarantee the quality of the work,” Wick said. “And at the same time, every square foot of floor space is precious. More and more of them need the flexibility to, say, capture the surface topography of one part with a Dotscan white-light scanner, then check another part’s roughness with a Rotos probe, and later use LineScan to capture the entire surface of a form using point clouds to compare it with CAD data—all on the same CMM.”

The CONTURA’s capabilities can be further extended with options such as a flexible rotary table that can be put in place as needed for measurements in four axes; HTG (high temperature gradient), which uses floating glass ceramic scales to maintain measurement stability in a larger range of temperatures; and the ProMax E automated probe-changing magazine that moves into the measuring range and replaces the probe systems safely and accurately.

The optional Zeiss Smart Services range of digital services allows the performance of the device to be monitored while on the move in real time, Wick said.

Easy to Use by Operators

Hexagon Manufacturing Intelligence, North Kingstown, R.I., has similarly followed its customers’ priorities—away from the precision race and toward other priorities, namely, “how to make the customers’ lives easier,” said Ryan Toole, the company’s automated measurement solutions product manager. “We’ve shifted our focus from trying to get one more tenth of a micrometer out of the machine to improving the overall user experience.”

Toole pointed out that the status of a CMM in a manufacturing facility is different than a lathe or mill or other production equipment. “A CMM is not a profit generator—it’s a necessity for a business’s success but can’t be the engine of its success the way its actual manufacturing capabilities are.” If a job shop is like a great restaurant, containing the knowledge and capabilities to make fantastic entrees, the CMM’s status is somewhat akin to the dishwasher: needed, but not the star attraction.

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The shop floor-optimized Mitutoyo MiStar 555 features several Industry 4.0 integrations, including the company’s Smart Measuring System.

And there’s another impetus, namely the ongoing pressure on manufacturers to do more and better work with fewer, often less experienced, workers.

With that in mind, Hexagon has developed specialized equipment to simplify the measurement process. Toole said, “We want to make sure that the measurement tasks are as painless as we can make them.”

For example, TEMPO is the company’s off-the-shelf system for automated part loading, queuing and unloading. The system consists of a Universal Robots ISO 10218-1-certified collaborative robot that accesses parts from up to six drawers loaded with parts. Each 3.2 ft² (0.3 m²) drawer can hold up to 220 lb (100 kg). It’s designed to enable continuous CMM measurement for hours or days at a time without the need for human intervention.

A second example of labor-saving technology is the Eye-D camera system, which can be mounted to the bridge of a CMM and can recognize a part as well as the part’s position. “With Eye-D, the operator can simply place a part into the work volume of the CMM and click ‘detect’ on a control screen. With no further input from the operator, the system will first identify the part, and then calculate the part’s orientation in space,” Toole said. That latter task would previously require the operator to go into the CMM control software to enter the precise part location in the work volume—a time-consuming task. Once the Eye-D system has identified the part and its location, the system calls up the inspection program for the part and executes it.

The benefits are twofold, Toole said. First, it frees up time for the operator, who can place the part, press a button or two and go away and do other tasks while the inspection program runs. Second, none of this calls for an operator with expertise in programing or metrology.

“You can take anybody in your manufacturing facility and they could learn how to do this in seconds,” Toole said. “There’s almost no training involved.”

A third add-on lets that operator walk away from a working CMM with increased confidence. The Pulse sensor system attaches to the CMM and monitors for any environmental events or probe collisions that could affect data integrity. Vibration, temperature, humidity, air pressure, luminosity, and collision information are presented in one dashboard, accessible locally or remotely via PCs, smartphones, or tablet devices.

The Pulse system itself is four years old, Toole noted, but what’s new is its availability in a wireless version. This makes it easier to install—no pre-cabling required—and lets the sensors be placed in more, and more varied, positions on the machine for better understanding of environmental changes. “It uses a simple interface to give a complete picture of the CMM’s inspection activities and the actionable information needed to optimize measurement efficiency,” said Toole.

Integrating into the Smart Factory

According to Gene Hancz, product specialist for Mitutoyo America Corp., Aurora, Illinois, his company has focused on two priorities in its development of CMM technology. The first is the traditional one of offering high-accuracy measurements at optimal speed. For this, the company has two new and somewhat dissimilar general-purpose CMMs. The second priority is what they share in common: complete Industry 4.0 readiness.

One of the CMMs—introduced in 2019—is the MiSTAR 555, designed for use on the shop floor. “The 555 is compact, with an open-structure design that lets users place workpieces from its front, rear and right side. That makes it an easily accessible, walk-up inspection station,” Hancz said.

The modular control unit and PC are stored in the base of the main body structure, making the MiSTAR more compact, he said. It’s designed to be robust enough to work well in varying conditions, with accuracy assured at temperatures between 50 and 100o F (10–40o C). It also uses a scale detection system with a high resistance to airborne contaminants, eliminating the need for costly environmental controlled enclosures.

The other CMM—released this year—is the new V Series of the company’s CRYSTA-Apex line. Its starting points are accuracy and speed, Hancz said. “We believe the CRYSTA-Apex V’s accuracy is unmatched by any previous general-purpose measuring machine,” with a maximum permissible length measurement error of E0, mpe of 1.7 + 3L/1000 μm. The machine’s real-time temperature compensation system greatly contributes to measurement accuracy, he said.

Speed is maximized in a couple of ways. The CRYSTA-Apex V Series offers a maximum drive speed of 20.4 ips and a maximum acceleration of 2,309 G. More than that, users can freely set measurement paths along 3D forms, enabling intricate workpieces to be measured along their curved surfaces and contours. The series also features real-time correction of path errors caused by differences between the workpiece and design values—all of which increases throughput, Hancz said.

“Its high drive speed and acceleration, combined with a maximum measuring speed—the speed with which a tactile stylus traces over the workpiece—of 0.3 ips [7.6 mm/s], dramatically reduces the total measuring time,” Hancz said. Users aren’t limited to touch probes, he pointed out; the device can also use the company’s scanning and other non-contact probes.

The MiSTAR 555 and the CRYSTA-Apex V have differing priorities. What unites them is their readiness to function in a Smart Factory environment. Both feature several Industry 4.0 integrations, including the company’s Smart Measuring System (SMS), which enables monitoring the state of operation as required in a Smart Factory environment. The SMS Status Monitor retrieves current CMM status features using the MTConnect protocol. The SMS Condition Monitor provides a system that collects and evaluates different operational information, such as measuring, movement lengths, machine error, probe functions, and others for long-term preventative maintenance and machine use statistics.

“Machine monitoring is comparable to the OBD [on-board diagnostics] system used in automobiles,” Hancz said. “The OBD monitors the car’s vital system to maintain peak performance and alert the driver to potential system faults or failures. It also alerts the driver to routine maintenance actions that are due, such as oil changes, air filter and cabin filter replacement, and so on.” In the smart factory environment, pertinent data needs to be efficiently monitored, shared and acted upon, and it’s a Mitutoyo priority to ensure its CMMs are ready, he said.

Supplying the Smaller Job Shop

LK Metrology Inc., New Hudson, Mich., has started small—or, at least, compact. Until 2018, the company was the CMM development part of Nikon’s metrology business. When it was spun off that year, its engineers found themselves in the interesting position of having decades of hard-won experience but no name recognition at all. In the two years since then, the company has had to work to introduce—or rather reintroduce—itself to CMM users.

Joseph Szymanski, the company’s vice president of sales and marketing, said that the new entity understood it wouldn’t be able to instantly offer a varied line of CMMs for every kind of need—not in two years. It had to choose a field in which to first place a new flag. After much discussion with manufacturers, the company chose to develop a machine for use in small job shops—those with 10–50 employees.

“We saw a need for a machine that was versatile and accurate enough for use in a clean room but was engineered to be compact and robust to be kept right on an active shop floor,” Szymanski said.

The company’s initial offering is the Altera (the name was first used by Nikon in 2016)—a CMM line that strives to balance quality with the affordability needed by smaller shops in a space-saving design.

“We realized that in small job shops, a big limiting factor is floor space,” Szymanski said. To minimize the machine’s footprint “we’ve integrated the controller inside the actual frame of the machine,” rather than having it reside on a stand-alone computer desk. The controller interface is attached to a swiveling keyboard and monitor arm for easy movement on a crowded floor.

The Altera doesn’t skimp on quality in order to lower the price point, Szymanski said. “There are budget machines out there that use aluminum construction in order to save some upfront costs. We chose not to do that.” The CMM features an ultra-stable ceramic bridge and spindle guideway, with high-resolution 0.05-μm optical scales, he said. According to company literature, volumetric accuracies are as good as 0.7μm+L/600.

The machine also features granite dovetail table guideways with single-orifice, grooved, preloaded air bearings for precise motion control, and self-leveling vibration isolation for optimum performance in areas subject to high levels of low-frequency vibration. The guideways are protected from shop-floor contaminants and, if needed, complete machine enclosures are available.

Flexible CMMs Call for Flexible Probe Systems

As CMMs become more flexible to meet changing user requirements, the probes they control and depend on are necessarily evolving in tandem. That’s according to Andy Holding, marketing manager, CMM & gauging products division for Renishaw PLC, parent company of Renishaw Inc., West Dundee, Illinois.

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RFP fringe probe, a new addition to the Renishaw REVO five-axis, multi-sensor system, scans an aerospace component.

Holding offers the company’s RFP optical fringe probe, a new addition to its REVO five-axis, multi-sensor system, as an example.

RFP provides high-density data at a high capture rate to deliver highly accurate measurement of surface topology. The probe projects a fringe pattern onto the part surface and the probe’s camera captures the variation in fringe pattern to build a high-density point cloud of 3D surface data. The data cloud is then evaluated by the 3D metrology software to deliver inspection results.

“The RFP is a long way from being the first 3D fringe-based measurement system to be used on a CMM,” he acknowledged. “However, it is the first one that can readily be interchanged with tactile touch trigger and scanning probes, and surface roughness sensors,” through the shared use of an infinite positioning head.

“What this means is that the best sensor can be chosen for the feature rather than on a per-part basis,” he said. “And all of the data is collected automatically in a common part coordinate reference system. Because it’s on a CMM, there is very little constraint on the part size. For manufacturers that have already chosen the REVO system, the RFP fringe probe can simply be added to the range of sensors to provide non-contact 3D measurement capability.”

With the RFP, all surface data patches are collected in the part or CMM coordinate frame, so there is no need to overlap patches and no need for reference markers, he said. Also, no separate inspection stations, tripods or rotary tables are needed, “which reduces footprint and staff requirements across your inspection process,” he said.

Automatic exposure controls compensate for different surface materials, colors and textures, ensuring optimal data results without the need for matte coatings.

Growing the multi-sensor capability of the CMM provides the opportunity to remove dedicated pieces of equipment from production areas by transferring the measurement task to an existing CMM, Holding noted. “The significance of this shouldn’t be understated given the ongoing cost of maintaining each piece of capital equipment in good working order, plus the ongoing cost of occupying additional shop floor space,” he said.

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