The recorded brain signals are then used to control a physical or virtual device that carries out a task according to the user's intent.
The first step we took when designing the prosthetic hand was to decide on the best control mechanism for finger movement. The goal for our design was to minimize the number of actuators necessary to control the movement of the finger and simplify the equations needed to describe the motion of the finger.
The first proposal, which was the tension controlled model, consisted of the three joints of the finger, with a cable attached to a fixed point on each link of the finger which was run back through the finger to an actuator mechanism at the hand or behind the wrist. For this model, each joint would have a compliant mechanism which forced the resting state of the links to be in the bent position.
The second approach for this design has the complaint mechanisms such that the resting state for the links is in the straightened positions. A second design proposal included the use of pneumatic systems to drive the bending or unbending of the fingers. In this proposal small tubes could be used to fill with either air or liquid to actuate the finger. The noise would create the same discomfort for the user as non life-like prosthetics.
The third proposal for the finger design wa...
In this proposal small tubes could be used to fill with either air or liquid to actuate the finger. The noise would create the same discomfort for the user as non life-like prosthetics.
The third proposal for the finger design was a pulley system to control each joint independently. Pulley's would be placed at each joint in the finger, and would be independently controlled by its own wire. Therefore, when the actuator is active, the fingers will bend and hold their positions. When the actuator becomes inactive, the compliant mechanism would return the fingers to their straightened positions.
In the designs described above, a pulley at each joint in the finger would have a cable wrapped around it just enough for it to actuate the exact number of degrees of rotation required at that joint. It may be possible to use flexinol in place of the motors, but testing would need to be completed to confirm that overheating does not occur and that temperatures of the prosthesis do not rise above the melting point of the prosthetic skin covering. One aspect of this design that we later incorporated into our final design was the knuckle joint. This piece had to be designed so that it could provide space for the pulley to rotate as well as allow the finger to rotate side to side. This piece also had to allow for the actuating cables to pass through it on its path to the motors.
The third, and final, approach to the design of the finger uses a four bar mechanism to control the movement of the finger, and compliant mechanisms to move the finger back to its resting state at the straight position. In this design, the four bar linkage is placed between the two upper joints on the finger. From our preliminary research, we had determined the