A 3D scanner will be implemented (Tuesday, 11/3) to model the 3D foot sole shape to provide customized arch support to the insole. 3D scanning will be a part of the pre-processing phase on the way to acquiring an STL file that can be used to print. 3D scanning will provide a way to acquire point cloud data from an insole in the user’s existing shoe. Reverse engineering will also be used to create an orthodic support based on the user’s foot dimensions. Consumers spend 100’s of dollars on custom orthodics which have rigid support structure in the medial arch to help collapsing ankles, which affect hip positioning and walking gait. The 3D scanner that is available is stationary, therefore directly scanning the foot is not possible due to positioning constraints. A cast of the foot will be crafted by first creating a mold using Aluminite molding resin. We’re only concerned with shape of the sole, therefore we only need enough resin to capture the medial arch. Since the resin is not safe for human touch, plastic wrap will be used. After the mold is made, a casting resin will be mixed and poured in to replicate the foot surface. This rubber part will be placed in the scanner to access the point cloud data.
Below is a preliminary CAD model of a solid insole mapping a 2D outline of the foot. Geomagic Design X can mesh the point cloud data from the foot cast into a triangular slicing format, such as an STL file. Thereafter, a 3D model for the rigid support material (PLA/ABS) will be created to enhance foot stability. The PLA structures will have to be adhered to the flat insole in the medial arch area. The thermoplastic elastomer material provides enough flexibilty to form over the arch support. Alternatively, the flexible flat insole can be heated to the glass transition temperature (~60 C) to make it leathery and formable.
NinjaFlex is a Thermoplastic Elastomer providing high flexibility properties. My3dmatter.com does an excellent job comparing the NinjaFlex material to other commerically available FDM flexible materials (http://my3dmatter.com/what-is-the-best-flexible-filament-for-my-3d-printing-needs/). The hardness is the lowest, as seen in the table below. This is desirable to provide sufficient comfort in the shoe, however typical foam insoles rate at a shore hardness of 30A-50A. One downside is the ‘C’ rating given for the processing quality. This grade is considered “fair” so further web browsing will be done to ensure adequate processing variables.
An S-shaped test sample was produced with the NinjaFlex filament to showcase the printing parameters and quality. The extruder temperature was set to 230 C and the print bed was set to 50 C, which are the max parameters suggested by the NinjaFlex website. Below is an image of the sample experiencing tensile strain and disconnecting at the outer edge layer. This could be a potential issue when stepping onto the 3D printed insole, which can experience forces up to 2.5x the body weight during high impact movements, such as running. However, since our 3D printed insole matches the exact dimensions of the actual shoe foam insole, high tensile stresses should not be a concern.
