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Measuring the dimensions of medical device components with speed, precision and accuracy is becoming an increasingly important and a dramatically more complex challenge for the industry. The popularisation of nitinol and other metals with “shape memory,” the miniaturisation of devices and the development of new surface modification technologies such as laser micromachining are all contributing to a more intricate landscape when components are viewed underneath a microscope. Added to this, several fields, most notably cardiology and orthopaedics, have experienced an explosion in the number and variety of device designs. Where once one a few basic models of hip implants, knee implants and stents existed, there are now hundreds and in some cases, thousands of competing designs, each with subtle differences in construction that can affect performance and longevity.
To meet the greater demands of component measurement in today’s market, many device manufacturers are turning to automated video measurement systems that are capable of rapidly analysing the most intricate structures with unsurpassed reliability. Although these systems were once shunned for their operational complexity, some of the next generation video measuring machines (VMM) that feature new software packages and design layouts are putting these systems back within the technical reach of every operator. By reliably determining the coordinate measurement of sample components, manufacturers can reduce waste, improve engineering processes (Six Sigma) and, in turn, reduce manufacturing costs to compete better in their markets.
VMM in cardiology
Although the cardiovascular device market is characterised by an enormous variety of products, it is most well known for the use of stents for the expansion and support of occluded blood vessels. In recent years, the microstructures of stent designs have become highly intricate, multilayered systems. The elaborate designs of these devices require measurement systems that are capable of determining minute variances in the xyz planes as well as the capability to determine the consistency of material thickness; that is, measuring whether the centre of the stent tube is concentric or if there is a drift in the centre that could indicate misalignment of production machinery.
Using high intensity white light emitting diode light sources and advanced charged-coupled device imaging, the latest VMMs provide precise measurements of part coordinates and edge details down to a resolution of 0.1 µm (near the possible limit in visible light wavelengths) in a fraction of the time needed by manual systems. A few systems also have the option for independent laser focusing. Using a noncontact sensor and red semiconductor laser light, these systems can achieve submicrometer resolution of z-axis measurements to detail surface substructures. The laser is also used to guide rapid changes in magnification levels to distinguish and image multiple layers within objects.
Some new systems also have the benefits of software packages tailored to the needs of the medical device industry. In addition to having multiple user settings for novice and advanced operators, these packages include teaching wizards to guide new users through various metrology functions and intelligent process “memories.” These enable the machine to recognise familiar objects and automatically run previously defined measurement routines to minimise the amount of user interaction required.
VMM in orthopaedics
In contrast to cardiology, the orthopaedics industry is characterised by larger plastic, metal and ceramic components. Although laser-guided measurement of surface finish and roughness is again important in this field, particularly for articulating, weight bearing surfaces, manufacturers must also be concerned with how their implants endure wear over many years of use. Implants removed from patients undergoing revision surgery are a unique source of this type of information, but adequately measuring the dimensions of these uneven shapes can be problematic for traditional measuring systems.
For these applications, users will require a VMM system that is capable of working with a touch probe. This enables contact surface probing of components, the detection of side coordinates and true three-dimensional (3D) analysis of complicated parts in cases where vision probing cannot be used. Ideally, the machine will also include a computer aided design (CAD) interface, which allows the system to create a 3D virtual representation of the sample object and to compare this with the original CAD design data. In this manner, manufacturers can gain detailed analysis of the wear of their components and make empirically determined design changes to successive generations of each implant.
Improved manufacturing
Of course, the use of VMM systems for component measurement and analysis is by no means exclusive to cardiology and orthopaedics. Throughout the medical device industry their use is rapidly gaining momentum as manufacturers tap into their potential to improve design performance, reduce lead times and minimise waste. As medical devices become more complex in design, so the need will increase for systems that are capable of measuring their features for continuous improvement in their manufacture.
Phil Wilson is a Video Measurement Specialist and Paul Gough is a Video Measurement Specialist at Nikon UK Ltd, Kingston-on-Thames, UK. For more information on metrology and VMM systems in medical device manufacturing, visit: www.nikoninstruments.eu.
