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Scanning to Achieve the Human Touch

Wed, 01/14/2009 - 9:26am
Kristine Spangard

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The Project: Fabricate artificial finger prostheses with lifelike accuracy for partial finger amputees.
The Solution: Use a laser scanning system that enables a 3D digital CAD model to be created so that custom solutions may be designed.



Kristine Spangard, M.S., is a technical communicator, specializing in writing about laser scanning, biomechanics, and medical topics. She can be reached at 952-252-3405 or kspangard@laserdesign.com.

Top Row: Hand with prosthesis showing the underlying mechanics of the articulating finger.
Second Row: Showing the realistic finger articulation of the prosthetic device worn on the hand.
Bottom Row: Incredibly lifelike finger prosthesis.
A company that designs and fabricates active-function artificial finger prostheses for partial finger amputees contacted Larry Carlberg, GKS Service Bureau Manager about doing scans of two small hand casts for which they were creating prosthetic devices. The devices are body-powered, lightweight, and allow users to regain complete control of the flexion and extension movements of an artificial finger. The owner needed 3D digital CAD model files that are used in manufacturing to create custom prosthetics more cost effectively for a larger market.

To scan the casts, Carlberg used the Laser Design Surveyor 3500 laser scanning system. The scanning setup is automated to capture 360° of the casts' geometry using the integrated rotary stage and native data collection software. The multiple scans are then merged into a single point cloud.

Each cast took approximately one-half hour to scan. Compared to manually measuring, "the process of laser scanning cut 60% off the amount of time to make enough accurate measurements of the casts to create a CAD model," said the prosthetics company owner. "With over 600 different variations of each finger-hand configuration, plus six different hand sizes, getting the correct measurements is incredibly labor intensive. The speed and accuracy of laser scanning allows me to standardize assemblies and sizes and make all the parts interchangeable. In the future, this will reduce costs, increase availability, and make the process easier and faster for the benefit of the amputees."

"I can't think of an alternative to 3D laser scanning that would provide similar results. The geometry is too amorphous to capture without laser scanning," Carlberg added.

Hand prosthesis with four lifelike articulated fingers.
"The output we delivered is highly accurate since we create the solid models directly from scan data. The accuracy of the point data is 0.002? or 0.05 mm of the actual hand cast. To achieve a model of free-form shapes with this kind of accuracy is impossible by any other means. With such an accurate definition of the actual hand, the company can fit a prosthetic device perfectly."

The owner agrees. "In the past, hand prosthetics relied heavily on a fabricator's artistic ability. They were visually realistic but not functional with articulation and mobility. Technology is catching up with the need for the prosthetic to look and act realistically. Today, the realistic look and movement can all be created through measuring and duplicating technologies. It is quicker, cheaper, and provides better access to people all around the world."

"The files were imported as solids into SolidWorks, and I was able to do cross-sections and use the side views, which is essential to creating custom prosthetic finger assemblies," said the owner.

GKS's expert metrologists made the 3D scanning process quick, accurate, and cost-effective from start to finish, eliminating completely time-consuming manual measurement. Laser scanning brings the custom fabrication process for prosthetic fingers several steps closer to being an off-the-shelf product.

Online
For additional information on the technologies and products discussed in this article, see MDT online at www.mdtmag.com and the following websites:

www.gks.com
www.laserdesign.com
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