Initial Designs and First Prototype

Inspiration

We looked into simple four bar mechanisms and existing exoskeletons in the market. We started looking at the spider hand created by a student at Lehigh University. It was a simple four bar mechanism that was actuated by the wrist motion.

Source of inspiration

(Source: http://3dprint.com/83807/spiderhand-mobility-assist/)

Initial Design

Our first model was similar to this mechanism. The mechanism mainly actuated the proximal phalanges.  This device included only straight links and focused mainly on the actuation of one single finger. We wanted to perfect the motion of one finger so that we could replicate the linkages for the rest of the fingers. We began with a simple four bar mechanism that used straight bars and two plastic rings to secure the device to the fingers.

Problems we encountered with this model

• From testing this first device, we found that there was no actual force applied on the intermediate and distal phalanges. This was problematic as we were unable to obtain the full motion that we desired in order to complete our task. 
• One of the issues was that the range of motion was limited by the links as the shape of the device link would not allow the finger to curl around objects.
• The rings also had to fit perfectly on the hand so that the force would be transmitted efficiently.
• All these factors contributed to a lack of range of motion and a need to further develop our ideas.

This led us to our first redesign that had a triangular link to allow the fingers to have a more natural range of motion, as seen in the figure below. However, the problem of transmitting enough force and contact with the ring surface prevailed.

First Redesign

First Prototype

After our first few iterations, we decided that actuation directly from the wrist only mechanically did not provide enough range of motion for the fingers to close. We then moved on to having a link going to each phalange in the hand. This meant that we needed to add more links which led us to having two separate linkages that would ideally be controlled by the same motor through one shaft. In this version of the design, we included curved links that had three contact points past each joint of the finger in order to transmit force to all of the links of the finger and cause the hand to close and open effectively. This led us to our first functional prototype as seen below:

First Prototype for a Single Finger

Problems we encountered with this model

• Hand would become too crowded with links.

• Hard to attach links to the distal phalanges in the hand. Would not be practical to attach a full hand’s worth of links

• Attaching all links onto one rotating shaft would prevent each phalange to get full range of motion. This would keep us from closing the entire hand and could potentially damage the links as well.