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Advances in Medical Metrology

Bruce Morey
By Bruce Morey Senior Technical Editor, SME Media

While medical device manufacturers continue to refine their offerings, matching the right metrology device to the manufacturing process is getting more complex

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Intricate, small medical devices such as these biomedical connectors are a challenge to measure. Photo courtesy OGP/QVI

Sometimes, too many choices can be a problem. That might be the case today for manufacturers of medical devices, who are facing a host of challenges and opportunities. Devices are small and getting smaller. Their complexity is increasing. End users are demanding tighter tolerances.

In response, metrology providers are devising clever sensors, probes, and software. A short list would include advanced handheld tools, coordinate measuring machines, vision stations, laser scanners, surface roughness instruments, and even CT scanners that can peer into a device with metrology-level accuracy. There is a lot to choose from.

“The challenge right now is communicating the importance of education, fundamentals, and available technology throughout organizations, including management,” said Joyce Rotger, CEO of Visional Technology LLC (San Juan, Puerto Rico).

Integration and re-seller companies like Visional Technology can help with that, providing metrology devices, support, and services. They can give perplexed customers a broad view into the market. Other issues the industry faces are knowing how to validate metrology devices and implement them to the best advantage, according to Rotger. “Many also have issues replicating measurements that their suppliers are making, compounding the need for greater education,” she said.

One of the advantages of a company like Visional Technology is the multiple product lines it represents, in its case Starrett, Zeiss, Mitutoyo, Artec, and Geomagic. Visional Technology also performs metrology services, including routine outsourcing, First Article inspections, and helping manufacturers install statistical process control (SPC). This base gives the company the broad understanding of the field needed to educate users.

Rotger also pointed out that, beyond education, how a company organizes itself can have an impact on how well it can absorb metrology. “Often, companies do not implement measurement systems taking a holistic approach. These companies want to implement a [new measuring program] quickly, in a month or so,” she explained. They need to understand part dimensions, the environment where the equipment resides, and how knowledgeable their teams are.

“Naturally, they want a return-on-investment quickly, but in so doing they forget that an improved quality program is a stage in a journey, not an event,” Rotger continued. Once metrology devices are purchased and installed, it is common for users to encounter unanticipated issues, either in collecting, interpreting, or reporting data. Companies need to anticipate issues and plan to work through them. She stressed that the purpose of a quality measurement program is to find failures, not simply confirm all products are good.

More importantly, a manufacturing process must first be stable before a measurement program can yield benefits. Many companies, in her experience, rush to automate before stabilizing their production processes, causing avoidable headaches in a rush to get ROI.

These issues will grow in urgency as the medical industry moves towards greater personalization of devices. This includes using new materials, even transparent materials that are difficult to scan. It means creating parts from reverse engineering. It will also mean creating 3D-printed parts of individual devices like orthopedic implants from metrology-level data taken from the patient. All are a challenge.

Easy and Accurate

Education takes a different turn with Mark Arenal, general manager for Starrett Kinemetric Engineering Inc. (Laguna Hills, CA). He agreed there is a wide selection of metrology equipment available today, and added that some customers are more open than others to new technology. “In general, I see two groups of users, one [of which] tends to stay with tried-and-true equipment they are familiar with,” he said. “Others are seeking new equipment to provide them with advanced data.”

Those who want new technology are driven by trends familiar to many industries—a changing, dynamic workforce, the need to improve processes with more data, and the simple desire to lower costs. In these cases, manufacturers are switching from Go/No-Go methods. Go/No-Go is easily obtainable from standard devices like optical comparators equipped with overlays or even fixed gages. New metrology solutions provide richer, variable data sets that can head off problems or point to cost savings—not to mention eliminating operator variability common with overlays on comparators.

“While they want better data, they also want easy-to-use systems,” Arenal said. “Competent operators will get up to speed quicker and be more effective when a shorter learning curve is possible.” That means metrology devices that require less training and are more reliable. Accessible service and support is also important, he said.

A device that meets these needs is Starrett’s HVR100-Flip bench top vision measurement system. Arenal described it as a digital optical comparator with a large field of view (FOV) that can be used in either a vertical or horizontal orientation. It is useful in many applications, from flat parts to turned and threaded parts, as well as parts with complex shapes like orthopedic joint implants. The main operator interface displays a live video image with touch-screen enabled software measurement tools and a graphical digital display of measurements. A part image can be resized using pan and pinch zoom.

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Selecting the right metrology equipment for medical device manufacturing means balancing accuracy, speed, ease of use and cost. Starrett’s HVR100-Flip is designed for versatility as well.

Easy to use means the MetLogix M3 software on the FLIP system allows measurements to be taken by touching a feature on the monitor screen. The company also offers its HDV Horizontal Digital Video Comparators that “combine the best features of a horizontal optical comparator and a vision metrology system for added versatility,” according to Starrett. The company also offers a range of multisensor and vision systems.

Another key trend Arenal noted is the growing utility of 3D measurements for medical manufacturing, a trend in line with most other industries.

“More things are getting manufactured with rapid prototyping and integrated manufacturing methods. Metrology will [need to respond] by capturing complete 3D data very rapidly, with higher resolution,” he said.

CT Scanning and Medical

Perhaps the ultimate in 3D sensing is CT Scanning, said Kevin Legacy, director X-Ray solutions for Carl Zeiss Industrial Metrology LLC (Maple Grove, MN).

“CT and X-Ray have become, in the last three to four years, an important part of the process in all aspects of medical device manufacturing,” he said. This is true from R&D to production and all phases in between.

To match these needs, Zeiss has developed a comprehensive portfolio of X-ray-based inspection machines. Legacy explained that Zeiss recently acquired Bosello High Technology srl (Cassano Magnago, Italy), a provider of 2D X-ray inspection equipment used in non-destructive testing. “We have many medical customers that rely on just simple 2D X-ray to do 100% inspection on their parts, looking for the presence of certain defects quickly,” he said.

The next in capability is the Versa line of what might be called X-ray-based microscopes that deliver CT information—from the assembly to the raw materials. “These are the highest in resolution and contrast, delivering sub-micron accuracy,” he said, and are targeted for R&D groups.

For near-line or quality room work, Zeiss offers its Metrotom CT scanner. “This CT scanner is like a CMM except it uses X-rays, perfect for medical device manufacturers looking to validate the dimensional tolerances of devices inside and out,” Legacy said. The smaller size of most medical devices is an ideal match for the scanning volumes of CT scanners.

“Finally, we are seeing more medical companies wanting to go full-on in a production line,” said Legacy. “They want to use CT for 100% inspection, where they are making millions of parts. For this application, we have a product called Volumax.” He noted that by taking advantage of fixturing methods and measuring multiple parts at the same time, manufacturers can effectively get Takt times down to seconds with Volumax.

CT is limited in its penetration length by the density of materials, with plastics being easiest to scan and dense metals the most difficult. Many critical medical devices are made of plastic, making CT ideal for those applications. But even in metals, the growing use of 3D printing in medical makes application of CT scanning easier.

“Certain parts, like orthopedic implants, actually benefit from higher porosity,” Legacy explained. “That porosity is good for CT scanning because it effectively shortens penetration depth and provides better data,” he said.

Parts, Measuring and GD&T

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Multiple sensors solve many problems in medical device metrology, such as this VersaFlex package from OGP/QVI.

Shape alone affects choice of metrology sensor. “Medical devices must fit into or mold to the human body and have organic surfaces and curves,” said Tom Groff, vice president for North American sales for OGP, a brand of QVI (Rochester, NY). In just the last few years he has seen several much smaller medical devices emerging for use by doctors in surgery or in measuring ever smaller parts of the body (think flowmeters in blood vessels). “We are even starting to measure dental implants,” he said. “These measurements are not easily done with traditional metrology equipment.”

Enter multisensor metrology equipment. A multisensor system usually incorporates video, laser scanners, and tactile sensors. “Those three complement each other and are good for measuring odd shapes and small features,” he said. For especially fine measurements, OGP offers interferometric laser probes with sub-micron accuracies.

For medical parts, the company’s FlexPoint series of multisensor systems built around a CMM is a good choice. It is offered in a variety of configurations, from a small benchtop system to large bridge-style CMMs up to 2 m, according to Groff. FlexPoint incorporates sensors, laser scanners, and white light sensors, as well as tactile probes.

Another device Groff said is important for medical devices is the QVI Fusion 400, with a large FOV multisensor measurement system. “Many medical parts measure less than 3” [76.2 mm] and the large field of view on the Fusion is good for these parts, especially if you want to just walk up and get some measurements without writing a program,” he said. Ease of use is paramount, and nothing is simpler than a walk-up metrology device.

However, it is not just measuring—it is matching evolving tolerances and specifications to reporting as well. GD&T is getting more complex. To report deviations, software must map measurements to a complex CAD surface. “Our ZONE3 metrology software package is designed to make that easy, as well as make it easy to demonstrate compliance to standard FDA regulations and 21 CFR Part 11,” he said, referring to the governing regulations for medical device manufacturing. New additions to the ZONE3 include managing authorizations, tracking users by electronic signatures, and providing approved inspection reports. “Customers are especially attracted to color surface maps and histograms that provide a quick, accurate visual of their part,” he said.

Looking to the future, he sees a big impact from current trends in smart manufacturing, Industry 4.0 and the desire to digitally integrate design information with production information. “We are beginning to see GD&T attached to CAD data using Model-Based Definition [MBD],” he said. “ZONE3 supports product manufacturing information, and aids in efficient CAD programming. I think using the model to define how to measure, manufacture and design will improve communications between those departments.”

While predicting the utility of MBD, he also noted that the industry has much work to do before it can recognize the full benefit of Industry 4.0. Still, there is a lot of focus on it from multiple facets—including medical metrology.

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