Warning: This device has not been printed nor tested and it may not perform as described. It is provided here at this time for others to share in the research and development. It should not be considered ready for the average e-NABLE volunteer to fabricate for a recipient.

The The Whippletree tensioner https://www.youmagine.com/designs/adaptive-grip-mechanism-for-prosthetic-hand  has evolved to using pegs as pulleys and thus eliminates most of the knot-tying associated with assembling the e-NABLE hands.   It also provides an improved adaptive grip in which the fingers each move appropriately to grip oddly shaped objects. When the whippletree is used without this ratchet mechanism, the degree to which the fingers are flexed when the wrist is in it’s neutral (straight) position will be determined by the length of the tendons, and some adjustment may be needed in the system. The 2-way Ratchet Tensioner provides a means for the user to easily make this adjustment anytime during use.

For instance, a user can place the Raptor Reloaded Hand (with this specially equipped gauntlet) on a bicycle handlebar with the wrist in a comfortable position, then pull back on the tensioner handle until the fingers tighten around the handlebar. With this adjusted starting position, flexion or extension of the wrist causes further flexion or extension of the fingers in the normal way.

This device also addresses a design concern where 3-jointed digits (like the human hand) require more displacement of the tendon cords (more flexion of the wrist in a wrist-actuated device) than do the 2-jointed digits on the regular Raptor, Raptor Reloaded and Cyborg Beast hands provided by e-NABLE. It is expected that the 2-Way Ratchet Tensioner will enable more people to comfortably use 3-jointed fingers like the Flexy-Hand and Falcon Hand.  

Small o-rings pull the ratchet pawl toward the ratchet surface.  It will be necessary to cut away a bit of material to fit the o-rings onto the bracket. (An overhang could have been a problem if it were printed open there.)

I'm working in tinkercad and it is an untested work in progress.  I just made it public.  

https://www.tinkercad.com/things/eDQnWC4OI9M-2-way-ratchet-tensioner  

All are welcome to duplicate and build on the design but give attribution to Raptor Reloaded by e-NABLE https://www.youmagine.com/designs/raptor-reloaded-by-e-nable for the hand and gauntlet design.  Please provide feedback on what you learn.

Prior Art:

Raptor Reloaded Hand  https://www.youmagine.com/designs/the-raptor-hand-by-e-nable#!design-documents 

Whippletree  http://www.thingiverse.com/thing:392970  and https://www.youmagine.com/designs/adaptive-grip-mechanism-for-prosthetic-hand 

Simplified Movement Printer Sheet Stack Edge Guide US Patent No.: 7,527,259 B2 https://www.google.com/patents/US7527259?dq=7527259B2&hl=en&sa=X&ei=osTXVK-JC4GyggSvloLYCg&ved=0CB0Q6AEwAA