3D Printed Below Knee Prosthesis

Designed November, 2018 @ Cleveland State University by Michael Frawley, Julie Profeta

Prototyped April, 2019 @ Case Western Makerspace

View the Model Here, View the Paper Here


The Amputee Coalition of America estimates that there are over 2 million persons living with lower limb amputations in America, with the number expected to double by 2050.

A big problem when it comes to powered prosthetic devices is cost. On the lower end, a powered prosthesis can cost around $20,000 (often out of pocket) for the patient, while higher end units can cost upwards of $70,000.

The motivation of this project was to create an inexpensive, fully active prosthesis that utilizes 3D printed components and "off the shelf" hardware to reduce costs. The prosthesis is driven by a NEMA 23 motor and geared power transmission system, which are controlled using an Arduino Uno. Foot sensors placed on the patient's foot are used with the Arduino Uno to time the stepping gait of the wearer.

The design constraints of the device were as follows:

  • 110 kg (242 lbs.) wearer

  • Device must weigh less than 5 kg (11 lbs.)

  • Total cost must be below $1,000

Results

After several months of design work and prototyping, the project was a complete success. All design constraints were met and a unique approach to mechanical design was adapted to further reduce weight of the prosthesis (which weighed in at 4.8 kg):

Prior to this project, I only had limited exposure to topological optimization of mechanical design through the Ansys software package, but I never had the opportunity to apply it to a real design. Using SolidWorks 2018 Simulation coupled with a Topology Study performed within the Simulation package, a new approach can be used when designing mechanical structures: generative design. Initially, the result of a Topology Study created this from the original model:

Using the results of the Topology Study, the model can be amended to include the removal of areas of material. The new design can be simulated again with the given loading (of the wearer's weight) to ensure the design will still function without failure.

This approach to design can be particularly useful when using additive manufacturing such as 3D printing, selective laser sintering, and other AM technologies as the designer does not have to consider designing for manufacturability (machine tool paths, tolerances, etc.). In conclusion, this project was a fantastic success which gave me a great amount of experience with generative design and innovation.