OpenBionics - Prosthetic Hands

Nowadays most prosthetic hands cost dozens of thousands of USD. The OpenBionics initiative (www.openbionics.org) presents a new open-source design for highly functional prosthetic hands. The proposed hands cost less than 200$, weigh less than 300 gr and can be easily fabricated with off-the-shelf materials and rapid prototyping techniques (3D Printing).

A novel differential mechanism (based on the whiffletree) allows the user to block the motion of each finger independently and facilitates the execution of 144 different grasps with only 1 actuator. The design is based on parametric models of hand anthropometry studies, so it can easily be personalized to specific patients.

Personalized Design

Τhe use of parametric models derived from human hand anthropometry studies, allows for the development of personalized prostheses. The only parameters that we need in order to derive the finger phalanges lengths and the personalized finger base frames positions and orientations, are the human hand length (HL) and the human hand breadth (HB).

We have modified our CAD files in order to integrate the required parameters (HL & HB) for the replication of a personalized design. Firstly, you need to decide which hand you want to replicate (Right or Left). You can find below a quick guide for the production of the personalized design. The procedure is the same for both hands.

1. Open the part file "prostheticParameters.SLDPRT" which can be found @ Prosthetic-Hands\CAD\Left.
2. Make the "parametersSketch" file editable. You can see there, the parameters that you can change. Their values are reported in mm and NOT in inches.
3. Open the assembly file "AnthropomorphicHandAssembly.SLDASM" which can be found @ Prosthetic-Hands\CAD\Left\Assembly.
4. Go to the file "prostheticParameters.SLDPRT" and change the desired values (HL=hand length, HB=hand breadth & fingerWidth) according to this image and then save the file.
5. Go to the assembly file "AnthropomorphicHandAssembly.SLDASM" and rebuild it. All .SLDPRT files that are used in the assembly should be rebuilt.
6. If you want .STL files, you should open every rebuilt part and then choose "Save as .STL".

#Things to note:

1. The design has specific constraints, which cover the 95th percentile of the human hand and those are:
   Hand Length: 182 - 225 mm
   Hand Breadth: 82.5 - 110 mm.
2. Dimensions should be changed symmetrically. The mean HL/HB ratio is 2.2, so if your new assembly has errors it is probably either because you didn't measure correctly your hand values or because your hand construction is very far from the human mean value.
3. For editing our CAD files you should own Solidworks 2014 or a later version. In case that you don't have the required software, complete this webform in the OpenBionics website. We are currently in the process of preparing our designs with open-source CAD software.
4. Our approach is inspired by the Yale Open Hand project. More details can be found here.
5. An assembly guide for our prosthesis and a video tutorial will soon be available.