At various times throughout the manufacturing process, medical device and orthopaedic implant manufacturers need to carry out a wide range of inspections and measurements of the parts that they produce. Operators in the orthopaedic industry, for example, may check hip stems against a template many times during the grinding and polishing process. Like many manufacturers across a wide range of industries, they have traditionally used optical comparators to check parts directly on the shop floor.
Traditional Optical Comparators
Optical comparators are robust, versatile measurement and inspection devices, and up until now, they have been the easiest way to quickly compare a part to its drawing to allow the user to make a pass/fail determination.
Optical comparators, however, require overlays, also known as templates or Mylars ™, to allow operators to verify that parts are in tolerance. Overlays present a number of problems: they must be physically stored and managed, they cannot be used simultaneously by multiple operators, and they need to be re-calibrated periodically. Beside every comparator, there needs to be a storage cabinet with the Mylars for all of the different parts that can be produced in a given environment, including a polishing cell. The 30" optical comparators have a large footprint as well, and they take up floor space. Optical comparators also cannot provide any type of record of the inspection and measurement operations.
To allow manufacturers to overcome the limitations of traditional optical comparators, VISIONx (Pointe-Claire, Quebec, Canada) developed the Vision- Gauge® Digital Optical Comparator (patents pending). This system has been adopted by a number of leading medical device and orthopaedic implant manufacturers as an improved way to quickly and accurately check parts directly on the shop floor throughout the manufacturing process and collect complete device history. Many medical device manufacturers are using the VisionGauge Digital Optical Comparator to make sure that various implants meet specifications. Common examples include hip and knee implants, medical instruments, craniomaxillofacial implants, bone screws, and other spinal implants.
The VisionGauge works directly with the part’s CAD data and does not require the production, storage, retrieval, and management of overlays.
At the heart of the VisionGauge Digital Optical Comparator is a high-resolution imaging system that projects a geometrically accurate image of a part on a quad-monitor array. The image is obtained using a high-pixel-count camera and high-precision optical lenses. The system’s software takes the video images produced by the hardware components and increases their accuracy by carrying out fine mathematical image corrections in real-time, and at full video frame rate.
In the past, with traditional optical comparators, medical manufacturers had to use lower magnification systems to be able to inspect and measure larger components. The VisionGauge system includes an encoded stage to accurately move the part in front of the imaging system, and inspect different zones along the part. Because the stage has high-resolution glass scales, the CAD overlay “tracks the part” and moves along with it. As a result, large parts can be compared to their CAD data beyond the system’s optical field-of-view, across the entire stage travel.
When templates are used, the operator determines if a part passes or fails. One operator may deem a part acceptable, while another finds it unacceptable. The digital optical comparator employs software- based programs to determine pass/fail decisions. The system projects an accurate representation of the part, and the program can check to a very high sub-pixel accuracy. While traditional optical comparators require extremely large, difficult-to-manufacture lenses to project the image of the part onto a 30" screen, the optical comparator system projects an image onto a camera’s small sensor, which is less than 1" across.
Furthermore, these lenses can be manufactured with a much larger depth of field, so that the entire object is in focus at once. The lenses also allow a greater working distance between the part and the lens, which benefits medical manufacturers as the parts that they produce have complex geometries. Traditional optical comparators, with their shallow depth of field, require that the operator refocus them constantly to accommodate these complex medical parts. The extended depth of field keeps manufacturers from making frequent adjustments.
The VisionGauge can be set up to automatically capture a high-resolution image of a part with its CAD overlay, as well as with automatically computed deviations from nominal, the auto pass/fail result, measurements of critical dimensions, and annotations. This information can be time/date stamped and easily linked to job and lot number. The VisionGauge can also export all of its measurements, statistics, and results to other applications, such as Microsoft Excel®.
The technology can be set up to automatically read-in the correct overlay when the operator scans in the barcode on the router that accompanies the parts. As a result, multiple operators in the polishing cells can share a single machine, and part changeover and settings recall can be done quickly.
The resulting gains in productivity, time, and floor space represent significant benefits for medical manufacturers. VISIONx has now seen two traditional optical comparators being replaced by a single VisionGauge in polishing cells.
Today’s medical device and orthopaedic implant manufacturers need to meet ever-tighter tolerances, ensure 100% product conformity, and collect complete device history and product documentation. By replacing traditional optical comparators with the Vision- Gauge Digital Optical Comparator, medical device and orthopaedic manufacturers have been able to meet these increasing demands and at the same time reduce their inspection costs.
This article was written by Patrick Beauchemin, president of VISIONx. For more information, Click Here .