Tuesday, July 27, 2010

A first finger

I began the telepresence hand design exercise using Andreas Maryanto's design as a starting point.

Andreas was kind enough to scan his design sketches for me which let me puzzle out the intricacies of his design.

Thanks to Google Translate my technical Bahasa Indonesia has improved dramatically.  :-)

I took inspiration from several other places as well.  Most notable was the Meka Robotics hand.

Their notion of using an elastic strip across the top of the fingers to return the hand to a rest state was very clever.  As well, their notion of making the hand a modular unit was also very interesting.  From these initial concepts I began to develop my own design.

To begin with, I own a personal Reprap-derived 3D printer.  A Reprap printer is the functional equivalent of quite an expensive machine shop.  It allows for a much freer design than either Andreas, cutting perspex or Meka, milling aluminum and plastic could hope for. After several false starts, I developed a joining approach which was rather easy to work with and print.  Here you can see half of a distal phalange.

The middle phalange...

The proximal phalange...

And the base knuckle and hand attachment of the finger...

I printed these parts without infill, as you can see in this printed and assembled distal phalange...

Here are a few pics of an assembled finger at various levels of flexure.

I use the Meka idea of a latex strip to return the finger to rest state except that I decided, for now at least, that rest state is going to be curled rather than extended.  The design I've evolved lets the latex strips mostly reside inside the phalanges.  The tendon in my design runs across the top of the finger and the servo driving the tendon pulls the finger into a fully extended state.  

This approach allows for the latex strips to determine the maximum degree of grip that the hand can deliver. This should let me avoid having to use fingertip pressure sensors to determine the degree of pressure exerted by the hand.  That is the theory, anyway.

My next step will be to install the latex strips and tendon.  After than I will be designing the hand/servo assembly.


  1. this looks quite nice -- what kind of precision / surface finish can you get from the reprap? In particular, what's the friction of the sleeve bearings you're building?

  2. The sleeves don't rattle and there isn't much friction. :-)