2011

Benefits of a Fully Digital Comparator for Inspection of Orthopedic Implants

This system offers advantages over traditional optical comparators, including the ability for multiple operators to compare parts to the CAD file at any one time.

Manufacturers of orthopedic implants take great care to ensure that their products are of the highest quality. One way they do this is by performing numerous inspection operations at various stages throughout the manufacturing process. These have great value — however, they also represent considerable expense. Until recently, implant manufacturers reaped only a small fraction of the potential benefits of these efforts mainly because, in the end, few records of the inspection operations remained. Those that did exist were of poor and irregular quality. This is reasonable, considering in-process inspections are performed on the shop floor by system operators, whose primary function is to manufacture parts. Most inspection records consisted of a few checkmarks on a paper report indicating that the required inspection had indeed been performed successfully. These records do not do justice to industry-wide, high-quality standards.

altFurthermore, the FDA, in CFR 820.184, requires that medical device manufacturers maintain device history records (DHRs) which contain the complete production history of a finished product and demonstrate that it is manufactured in accordance with the Device Master Record (DMR) and all appropriate regulatory requirements. A DHR documents that all operations, processes, etc. described in the DMR have been completed for all finished devices manufactured. They include: date(s) of manufacture, quantity manufactured, quantity released for distribution, device identification(s) and control number(s) used, primary identification label and labeling used for each production unit and finally, any acceptance records that demonstrate the device is manufactured in accordance with the DMR.

Because of these regulations, many orthopedic implant manufacturers are using a drop-in optical comparator replacement to carry out shop floor inspection operations. This system allows automatic, electronic collection of high-quality device history. When an operator scans a barcode on the router that accompanies the parts requiring inspection, the computer not only loads the correct CAD file, but also all of the relevant information such as job numbers, work order, or operator identifier, and links it to the inspection step. The system can then be used to quickly obtain high-resolution imagery of the part and its CAD file overlay and a time/date stamp. All of this is accomplished on the shop floor as the parts are being inspected at different stages of the manufacturing process. The quality of the information collected is increased, while the cost of collecting more complete information is reduced.

A system like VisionGauge® that works directly with the part’s CAD data, instead of Mylars™ or overlays like traditional optical comparators, provides an added value for implant manufacturers. Only one operator at a time can use an overlay, whereas multiple operators can share CAD data simultaneously. Overlays require printing, which can introduce inaccuracies since no printer is perfect. The part’s CAD data, on the other hand, is its mathematical definition; there are no errors when CAD data is used on the system. Unlike overlays, CAD data never need to be recalibrated. Historically, if a part needed to be inspected at multiple magnifications, i.e. an overall inspection at 5× and then a more detailed inspection of tighter tolerance features at 20×, multiple overlays were required. The system uses the same CAD data regardless of the magnification. Other drawbacks with overlays include the cost and space required to store them. These problems are completely avoided by using direct CAD data.

The system is available in industry standard 5×, 10×, 20×, 50×, and 100× magnifications so that operators can continue to apply existing inspection procedures at the same magnification. Additionally, as a fully digital system, it can use the readings from its high-accuracy glass scales to have the CAD overlay “track the stage motion” and move with the part. This enables the user to compare parts to the CAD drawing beyond the system’s optical field-of-view, across the system’s entire stage travel.

Another shortcoming of traditional optical comparators is their large footprint, due to their internal optical path, which is very long and includes many optical elements such as lenses, prisms, and mirrors. The digital technology of this system requires only one very high-resolution lens and camera assembly, thus its footprint is reduced. Since no overlays are used, storage cabinets previously used to house overlays can be eliminated, resulting in a remarkable amount of free floor space. The system has been designed with casters and can be moved without requiring recalibration. It’s possible to move it to a line when new production starts and then when the process is controlled, relocate the system elsewhere.

The system is available in horizontal and vertical configurations. Knee and hip implants for example, are generally inspected on horizontal systems. Vertical configurations are typically used for craniomaxillofacial implants. For bone screws, some manufacturers use horizontal configurations, while others use a vertical configuration. The decision to use one or the other is generally based on fixturing considerations. The hardchrome plated stage, made from hardened tooling steel, has industry standard dual dovetail grooves that make it compatible with existing mounting fixtures, and a drop-in replacement for traditional optical comparators.

The system produces a very high contrast image with clear, crisp edges even in full daylight. There is no need for curtains or any type of shielding to isolate the display from ambient illumination. The high-resolution camera and lens produce a very geometrically accurate image that has less distortion than an image on a traditional optical comparator. Furthermore, the software carries out high-order, real-time image corrections on the live video stream. A highresolution, digital system is also able to carry out fully automated, operator-independent measurements with more accuracy and greater repeatability than any human operator.

The system is able to recall part settings with a single click of the mouse or joystick button. Therefore, part changeovers are much faster, which increases the throughput of each machine. Some operators report that they are able to attain twice the throughput of a traditional comparator.

Also important to note is that all illumination is LED-based. LEDs produce a very stable illumination over a rated life of 10 years. Stable illumination ensures results that are extremely repeatable and will remain so for the life of the system. Other benefits of LED illumination include no bulbs to change, lower power consumption, and little heat generation. The advanced, high-quality illumination produces exceptional image clarity even on surfaces and materials that have historically been considered difficult to work with, such as plastics and reflective materials. The system is available with transmitted (back) and/or reflected (front) illumination.

This technology was done by VISIONx Inc., Quebec, Canada. For more information, visit http://info.hotims.com/34459-198.