Background & Motivation

The subject of our proposed project are those who have undergone stroke/injury, and have lost some of the motor skills and strength in their hands, requiring therapy. The majority of today’s therapeutic workout devices for the hand involve training and strengthening of the extrinsic hand muscles.  These are the muscles located in the back of the forearm and have long tendons connecting them to the bones in the hand, where they exert their action.  However, the intrinsic hand muscles, a smaller set of muscles isolated within the hand itself, are often left neglected. 

The motivation for our project is to design a therapeutic workout device for the human hand, targeting those who need to rehabilitate the strength of the intrinsic muscles in the hand.  Specifically, the targeted motion begins with the user’s hand in a fully-curled position, with all of the joints of the finger fully flexed and the tips of the fingers buried in the palm of the hand.  The device will be designed to assist in the unfurling of the fingers and fully extending all joints until the fingers are pointing outwards and form an approximate 90° angle with the palm of the hand.  The device will only be used for the four fingers and not the thumb, as flexion and extension of the thumb occur out of plane in relation to the other fingers and would require additional design considerations.

Our initial assumptions for the project were that this fingertip motion can be modeled as pure sliding. We chose this because the problem then is solved by simple mechanisms learned in lecture, while also achieving the highest desired range of motion. In addition, we also assumed that the motion of the fingertip is related to the angle of the MCP (knuckle) joint. That is, we assumed that at the fully curled position of the finger, the angle of the MCP is roughly parallel with the palm, and when the finger is fully extended, the MCP angle is perpendicular with the palm. The below image demonstrates roughly demonstrates the motion and dimensions we were dealing with.

Overlaid image showing intrinsic motion and rough working dimensions

With these assumptions in mind, we sought to create a first prototype to achieve this motion.