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Custom Forearm Crutch Handgrip with Integrated iPod Controller and Flashlight Adam McLaughlin, Jordan Tye, Lisabet Sizer, Mark Damplo University of Massachusetts Lowell The Design A custom forearm crutch handgrip with an integrated iPod controller and flashlight was designed and manufactured using Direct Digital Manufacturing (DDM) to be included in the final assembly of a crutch. The design is marketable to anyone in need of a forearm crutch, especially those with lifelong disabilities and those injured in the military. Approximately ten million pairs of crutches are sold in the United States per year1. Doctors are realizing the health benefits of forearm crutches over the tradition underarm style and are prescribing them more frequently. By modeling the grip after the user’s hand, the surface area of the hand in contact with the grip increases, spreading the pressure developed from leaning on the crutch. This not only alleviates pressure points common to a generic grip, but also makes the crutch more comfortable and desirable. The integrated iPod control allows the crutch user to listen to music and change songs or volume while walking without having to stop while the integrated flashlight adds safety. The large amount of customization and complexity needed to make the grip a perfect imprint of the user’s hand makes it an ideal fit for DDM. The grip is initially formed using a 3-D scanner. This process begins with a clay form that the user grips. This impression is scanned into a solid modeling program such as SolidWorks where it can be manipulated and modified to receive either the iPod controls or flashlight. Incorporated into the design are moving buttons and a hinge which are printed with the grip as one assembly. The Dimension SST 1200es Fused Deposition Modeler (FDM) used in the production builds a model consisting of both ABS and a support material, which is subsequently dissolved away. Testing and manufacturing iterations were done to obtain a reasonable Figure 1: Crutch Grips with clearance between the buttons and the hinge, and once the support material is Integrated iPod Controls and Flashlight dissolved, the buttons are fully functional. These built-in moving components remove assembly time that would otherwise be needed for a molded part. Environmental & Social Impact The major environmental impact this DDM product has is the more efficient use of materials compared with traditional methods. In the past, the way to make custom grips would start out the same way with an imprint. Then, a silicone mold would be made using about 1 gallon of silicone. The grips would then be cast using epoxy2. After this one use, the mold would either be thrown away or stored for an unlikely second use. In contrast, the DDM method uses far less material and the electronic files are far easier to store. Additionally, if any changes need to be made for comfort or aesthetics, the file can be manipulated easily, but the silicone molds would have to be remade. Additionally, the time it takes to print each grip is approximately 8 hours which is far less than 24 hours for curing silicone. The social impact of this product is the health benefit of using a crutch handle molded to one’s unique hand as opposed to using the generic smooth handle. The larger contact area of the grip reduces pressure on blood vessels and nerves in the hand. The benefits of this comfort also extend into long term effects, reducing the risk of carpal tunnel, as well as other permanent injuries to tendons or cartilage3. 1 http://www.popsci.com/bown/2010/innovator/leg 2 http://www.freemansupply.com/video.htm 3 http://www.disabledservices.net/crutch-‐gripstips/grip-‐crutch-‐handle/
Along with the health benefit, there is also added convenience with the integrated electronics. With the built-in iPod controls, crutch users now have the leisure of listening to music in their travels without getting wires tangled up around their crutch. Instead of having to stop and lean somewhere in order to control the iPod. They are able to change their songs on the move at the click of an easy-to-reach button, just as any other iPod user would. An integrated flashlight adds convenience and safety for the user allowing light for opening doors and seeing what lies on the ground ahead of the user. Component Integration The customized hand grip includes built-in electronics that control an iPod externally. Three buttons are included into the design. Two of the buttons control the volume up or down, while the middle button stops/plays the song with one click, or skips to the next song with two. These movable buttons press down onto stock click buttons stored inside a housing designed within the grip. A prototype was built utilizing the electronics of an already-existing iPod controller and an existing crutch. The flashlight design includes flexible buttons which depress stock off-on buttons inside the case. There are two buttons to control the dual LEDs, one pointing straight ahead and one pointing down at a 45 degree angle.
Figure 2: Interchangeable
Post-Processing Electronic Components Before the crutch grips can be delivered to a consumer, the electronics must be installed and a thin layer of rubber should be applied to the surface of the grip. The iPod controller requires the installation of three normally open momentary push buttons mounted behind the hinged door. These buttons must then be wired to the circuit board, which is located inside of the steel pipe of the crutch handle. Both the male and female ends of the headphone jacks should be run through the crutch; the female should be located near the cuff to allow for the headphone cord to be snaked up the sleeve and the male end should be located near the iPod holder. The flashlight requires the installation of a coin cell battery and holder, two off-on push buttons, and two ultra bright light emitting diodes. A light coating of rubber, such as Plasti-Dip, allows for a smooth, durable finish the preserves the contours of the grip. Innovative Aesthetics and Geometry Possible with DDM The most innovative feature of the custom handgrip is the ability to make a 3D scan of a unique hand mold and reprint that geometry with the same level of comfort as the original mold. Upon searching for similar products available in the market, the only similar idea found was a custom soft grip for crutches with a standardized hand imprint 4. This hand imprint was not personalized for each user, nor did it have any additional electronics built in. A patent search yielded similar results with the only similar idea being for a heat sensitive tape that wraps around grips. This tape is moldable when hot and stiffens when cooled5. This scan-and-reprint technology is much more hardware dependant, but results in an imprint that could be used in a variety of different ways. Cost Analysis A Dimension SST 1200es printer will be implored for this production. An initial investment of approximately $32,000 would be needed to purchase the machine along with an annual maintenance cost of about $8,000. A NextEngine 3-D scanner costs $2,995 and can be used to capture the hand’s geometry imprinted on clay. The hand imprint kit needed for the scanner costs about $5. The amount of material needed for a pair of grips to be produced is around $55 but is subject to change slightly based on the size of the user’s hand. The electronics 4 http://www.disabledservices.net/crutch-‐gripstips/grip-‐crutch-‐handle/ 5 US Patent #4785495
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Table 1. Summary of Cost Analysis. needed to make both the volume controller and flashlight come to Costs Amount Description approximately $10. An iPod Dimension FDM $32,000 Initial investments NextEngine 3D Scanner $2,995 holder that can be attached to the Maintenance & Overhead $8,000 For FDM and Scanner crutch is available for $15 and Hand Imprint Kit $5 Capture hand geometry crutches can be 3 Grip Material Per Pair $55 $260/in *11.52 in3 purchased for $39. The Labor $100 6.5 hrs*$13/hr labor needed to capture the 3D Electronics $10 iPod control & flashlight scan, adjust the imported image, iPod Holder $15 run the printer, and wire the part Bought from supplier Crutches $39 is approximately $100 if the Overall Producer Cost $224 Sum of material & labor employee is paid $13 an hour. Consumer Cost $640 After 65% markup Adding all of the costs together Profit Per Crutch $416 Consumer - producer cost and a 65% profit, the preliminary Crutches Made Per Year 390 260 work days*1.5 day consumer cost for a pair of Crutches made*profit - 1/5 Yearly Profit $147,241 crutches complete with custom investments & maintenance fitted handgrips, volume controller, and flashlight is $640. Assuming the printer prints at its maximum producing one and a half pairs of grips a day for 260 work days, this product would yield an annual profit of approximately $147,241 after one fifth of the investments and the yearly maintenance is taken out. The costs/benefit analysis is summarized in Table 1.
Conclusion The health benefits of a personalized molded handgrip are undeniable. With such a large amount of crutches sold, if this product could reach even just a small fraction of crutch users, the product would still be making a huge positive impact on the lives of disabled people. The DDM process also provides many benefits, including more efficient use of material and the ability to print moving parts already assembled. Also, due to the personalized nature of each hand grip produced, DDM is the perfect fit for the product. Additional photographs and presentation slides can be found on our website: http://faculty.uml.edu/bkim/capstone2011/crutch.htm Acknowledgments We acknowledge Prof. Byungki Kim and Prof. Stephen Johnston for their advice, Bobby Mullen and Jim Codair of J.F. Mullen for allowing us to use their 3D laser scanner, and Rapidform Inc. for software licensing.
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