Tuesday, January 14, 2014

prosthetic hand: cable tensioner

David Orgeman from e-NABLE had posted the first three images from above about a mechanism to tighten the cables for the hands that people are making. Gregg Dennison had also posted images of the hand he built with a tensioner designed by Jorge Zuniga. I couldn't sleep last night so I thought I'd take a quick stab at a solution for tensioning the cables. My first thought was to use hanger bolts. I went over the MCMaster Carr and grabbed a CAD model of a hanger bolt and then got to work sketching out a possible solution. What you see above is my first attempt at this. 

There are five, interior threaded, barrels (each one has a round recess in the end that sits into a round nub in the housing. These barrels also sit into a slot in the housing. These barrels are snapped in and then a stop nut is put on top of this. This stop nut allows locking of the barrel once desired tension is achieved. The hanger bolt is inserted into the end with the cable already attached and knotted. Then the stop nut is loosened, the barrel turned, to pull the hanger bolt into the housing deeper and achieve desired tension, and then the stop nut is locked down. I printed all of the components just to check size and approximate fit. Obviously the threaded hanger bolt is too small to print. Right now I have it set at an 8-32 bolt. In the final version, I would be tempted to make the barrels and lock nut on my lathe and use a pre-made hanger bolt.  Also the threaded barrels are difficult to turn, but I do think this design might be a direction that I could follow if I wanted to make it a bit easier to tune the tension of the cables. The barrels could be accessible from the end of the housing, so you would stick an allen wrench in the back end of the barrel to tension the cable. I'm just thinking out loud here...

Anyway, just a quick exercise to see what I could come up with to solve David's issue. Side-note: I used Jorge's cable tensioner mounting pattern so this could be used with existing hands that use his design. 

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