Bionic Hand Controlled By Leap Motion

Will Cogley has been developing a bionic hand for years now most of his work has gone into the mechanical design. That hasn't been trivial, because his bionic hand is the same size as a real human hand and possesses all of the same movement capability. A lot of clever engineering went into making that happen, but it led Cogley to a new challenge: controlling all of the bionic hand's joints. He considered many possible solutions and then ultimately settled on using a Leap Motion hand tracker to control his bionic hand.

Like a human hand, Cogley's bionic hand does not have any "muscles" in its fingers. A human manipulates their fingers by flexing muscles in their palm and forearm. Doing so pulls on tendons, which cause the fingers to open and close. The bionic hand works in the same way, but with servos instead of muscles and cables instead of tendons. Each servo was modified for continuous rotation so it could perform like a winch to reel in its cable. The structure of the bionic hand (roughly equivalent to bones) was printed on a resin 3D printer to ensure quality and relatively tight tolerances.

This worked well, but it meant that Cogley had 17 individual servo motors to control — 15 for the fingers and thumb, plus another two for wrist movement. Trying to operate all of those independently would have been a nightmare and creating an algorithm to coordinate their movement in a natural way would have also been very difficult. So Cogley decided he would use his own hand as the input and simply make the bionic hand mimic his own movement.

To achieve that, Cogley first needed a way to monitor his hand movement. He chose a Leap Motion Controller 2 for that task. It is an affordable hand tracker that can monitor a user's hand movement and position in 3D space, in near real-time. Cogley connected that to Unity, which updates a 3D model to mirror the user's hand.

From there, Cogley just needed a way to make the bionic hand update to match the virtual hand. After trying multiple techniques to accomplish that himself, Cogley ended up settling for the Uduino plugin and was happy he did. That plugin takes data from Unity (the joint angles) and uses it to send commands to the Arduino Uno board that controls the bionic hand's servos.

This seems to work pretty well, though Cogley does still have some challenges to overcome before this project is finally complete.