Medical Device Link.

Originally Published EMDM January/February 2004

ENGINEERING INSIGHT

The FineScan takes a finely detailed image of the stent, any part of which can then be automatically inspected.

It has been said that any type of quality control procedure relying on operator expertise is only 80% accurate. When the device being inspected is something as critical as a stent, however, a 20% error rate is not acceptable. A contract stent manufacturer, seeking to add value to its OEM services, found an optical inspection instrument that not only reduced the potential for human error but substantially accelerated the QC process.

Laserage Technology Corp. (Waukegan, IL, USA) manufactures precision tubes, including stents; connectors; and various other items for medical device OEMs. The company typically accommodates 20 to 60 individual jobs with lot sizes ranging from 50 to more than 5000 per production run. “We need to inspect as-cut stents using approved and validated procedures as required by FDA and our customers,” notes business unit manager Dan Capp.

As stents have decreased in size and cutting patterns become more intricate, conventional optical equipment has not always been up to the task of adequately inspecting the products. Laserage had been using an array of optical comparators, tool microscopes, and automated CNC vision systems, which all require a high level of operator expertise. Standard automated optical systems with a camera use a stepping process to take multiple small photo segments; the engineer must write fairly complex CNC inspection routines and then piece together the images like a jigsaw puzzle to complete a full stent inspection. While this technique is acceptable for some of the larger stent diameters, it lacks the repeatable accuracy required to inspect extremely small stents or those with intricate patterns. It also is not suited for performing a 100% point inspection. Because the instrument requires considerable operator expertise, labor costs can be significant and there is potential for human error.

In sourcing a new inspection tool, Laserage identified speed, accuracy, and fast changeover capability as key criteria. The ability to offer its customers 100% inspection of the product—performing thousands of measurements at once as opposed to having an operator look at a handful of critical points—was also an attractive proposition. The FineScan system from Visicon Inspection Technologies (Napa, CA, USA) fulfilled these requirements.

How It Works

The system comprises a high-resolution digital camera, rotating gem spindle, light source, and proprietary software bundle. Once the unit has been programmed, the inspection process is fully automatic with the exception of the loading and unloading of the stents. All inspection data are saved within the system software.

“We take a single scan and from that we look at the entire image, using pattern matching to do inspections. What used to take minutes, now takes seconds,” says Dan Freifeld, president of Visicon.

The operator places the stent over a transparent mandrel. Light is projected through the stent, which is automatically rotated 360°. The camera, mounted above the mandrel assembly, takes photos of the part as it spins underneath, producing a finely detailed and perfectly registered digital image. Gauges programmed by the user tell the system software which points require inspection. The system can be programmed to perform inspection routines on a single location or the entire device pattern. The inspection data are output in a table format, which can be exported to Excel or SPC programs.

Capp concedes that learning the mechanics of the FineScan system and programming it was no walk in the park. “It’s a challenge,” he says. “The most critical part is getting the lighting right, especially for very small stents with dense patterns.” But the effort was worth it, he adds. 

Laserage has benefited from the system’s speed as well as the ease with which on-the-fly changeovers can be made. Being able to offer OEMs the capability of taking thousands of measurements in under a minute with 100% accuracy adds substantial value to the company’s services, adds Capp. “One plus that I didn’t expect is that I can use the digital output from the FineScan as a descriptor,” says Capp. “I put images into procedures and e-mail them to customers to show them specific areas of concern in their design. I don’t know of any other inspection system that can provide a detailed digital image of the entire stent surface,” explains Capp.

Joyce Laird

Copyright ©2003 European Medical Device Manufacturer