Monday, December 29, 2014

Catch up time!!

So, now that I've some time over Christmas break, I should start filling this blog up with my projects from the last few years and from my time in Boston so far!

First project is my masters thesis project.

For my masters thesis, I designed and manufactured a prosthetic hand that could be controlled by the residual muscles of the forearm. Why? Well currently there are commercially available hands that retail for in excess of $15,000 to give someone a hand that functions in a relatively realistic manner. This to me seemed like  rather steep price so I wanted to see if it was possible to make a prosthetic hand with similar functionality to the commercial ones, but for less than $1,000. My hand would not be as polished as the commercial ones but would at least feature a similar control methodology with an anatomically similar hand with individually controllable fingers and various grip patterns. CAD files and design files are available here.

The project consisted of two main chunks, the mechanical hand and the control electronics. For the hand, I was going the 3d print the hand on my reprap for the easy, flexibility and speed of prototyping. For the electronics, I was going to need some EMG sensors to read the muscle activity, a microcontroller for all the control and then some bidirectional motor drivers for the output. I also decided to incorporate force feedback for tactile feedback. Instead of force sensors, I decided to use current feedback to give me approximate force data. My design splurge on the hand was to include a clock face of RBG led's on the wrist to act as a watch but also a battery level monitor.

For the mechanical, I started with the design of the finger and worked back from there. I took some measurements of my hand and digits and averaged my index, ring and middle to make an "average finger". I wanted to use and average finger so that I could just copy and paste once I got one finger designed. I decided to use a capstan system which extends and flexes the finger. I used a stainless steel nylon coated wire from (link), motors from fingertech (link) and a tensioner mechanism to keep the wire from slipping on the capstan. This capstan system is similar to the one used in the open hand project though it was developed independently. It also allowed for a reduced number of spares. The shape of the fingers was quickly defined so the only thing that had to be done was find the correct internal profile to make the finger curl in the right manner (Start proximally to the palm then move distally). This took a number of iterations to get the correct as many of the initial profiles led to the distal segment curling first and moving inward. Anyway, after a number or prototypes I got it working satisfactorily.

Next I designed the palm to have an anatomical shape. The fingers were splayed by degrees and offset to match the anatomy of my hand. Small clips and nubs are used the limit any motion. The palm consists of two plates, one which holds the four fingers while the second acts as the palm and is the mount for the thumb. The thumb can adduct and abduct thanks to a servo mounted in the palm. The thumb itself is a modified finger, just being slightly wider than then the other fingers and a section shorter. 

The stump mount or sock is based on an article I'd seen here where old plastic bottles were thermoformed around a model of the stump. These socks are only suited for light to medium duty but that should be sufficient for the duty it would see. To mount the bottle to the hand, I made a split adapter that bolts together with 4 M4 bolts. One side interfaces with the bottle, the other with the PCB's.

The last part of the mechanical design was the wrist.Initially I wanted to have this joint actuated but due to limited time, I had to got with a fixed position wrist. The orientation can be changed by removing a M3 bolt and rotating it to one of 8 locating holes. A central M8 bolt acts to transfer forces through the wrist joint.

Tuesday, October 7, 2014

So yay, I now have a blog. However, I've work in the morning so I should probably get some sleep and work out all this in the AM......

List of up coming projects/write ups:

    • Masters thesis: Prosthetic hand with EMG control
    • Metric scooter
    • The Annals of the Atomic Chibi Jeep/Thing
    • Kossel XL printer
    • Travel/Foldey Kart or whatever I end up calling it.
    • Whatever else I end up building.