Dominican Dog Prosthetic Project

Project Summary

In cooperation with Dr. Thomas at the McIntyre Veterinary Clinic in Roseau, we will be producing a prosthetic leg for injured animals on the island of Dominica and surrounding territories. The design will be open source and the modifications and methods for constructing it elucidated in detailed instruction sets so it can be used by other islands in the Caribbean chain.

It will be low cost and simple to manufacture custom designs using the 3D printing process. This will enable us to manufacture prosthetics for a wide variety of limb loss situations with the minimal amount of labor and tool investment. In order to do this we will scan the patient locally using a 3D scanner, modify the design remotely and then eventually manufacture the prosthetic inside of the veterinarian’s office.

The project will be carried out using the Design Process;

The Design Process

To that end…

Technological Requirements

3D Scanner

To begin we must acquire a 3D scan of the patient’s remaining limb. This will give us the data we need to reconstruct it on a computer and subsequently construct the prosthesis.

The scan must be accurate to within .5mm across 5cm. This is possible with two methods;

Structured light scanning (SLS) can be done with lasers or visible light.

These scanners project a known pattern of light on a scene. For example, using a single line or a pattern of dots.

In the case of the latter; dots that get smaller are determined to be further away and dots that get larger are closer to the camera. The scanner takes a picture of this distorted pattern and compares it against other pictures with other distortions and from that builds a 3D scan.

It is very inexpensive, is very fast and does not require a very powerful computer compared to photogrammetry. However most systems can’t be used outdoors or in areas with infrared lights as they will interfere with the structured light pattern.

Image by Audrey Penven.

Photogrammetry is the process of building a 3D model from 2D photos. It can be done with any camera, even an ordinary cell phone. This makes it excellent for use in situations where a more expensive scanning solution is out of unaffordable, the object is too remote or aerial scanning, where it’s impractical to use anything else.

A photogrammetry mesh.

An SLS scanner is ideal – it is relatively low cost and creates predictable results. However it would require an initial investment in a computer and the scanner itself – totally about $1,000 USD. Meanwhile, a photogrammetry approach can be done even with a low-cost cell phone or video recorder. However getting good results is almost an art and requires some not insignificant trial and error.

 

Determining which scanning approach will be our first objective. This is expected to take about a month from receiving the SLS scanner or from choosing to work with photogrammetry.

Software

The software used will be a combination of Rhino 3D, Grasshopper, Blender and Onshape. Eventually should volume warrant it a tailor-made Grasshopper script could be created. Below is an example of an automatic 3D scan segmentation script that I developed using Grasshopper 3D.

The first model will take about a month to create using manual tools, then another month to two months to design and develop an automatic script to do it in the future.

3D Printer

It is critical that we choose a machine that prioritizes low cost, high reliability and ease of use. This directs us to FFF printers like the Prusa Mk3 or Ender 3 machine. The initial prototype will most likely be printed on a machine we already have access to in the United States, but this project is truly only viable if a machine can be procured on-site.

Overall Project Plan

Overall the project is projected to take 3-6 months to complete. The breakdown is as follows;

Scan Workflow: ~1 month

Design: ~1 month

Prototyping/Testing/Implementation: ~ 1-3 Months*

*If a 3D printer can be procured for Dominica this would rapidly decrease the time needed.

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