Elevator Pitch

Hello, my name is ____, and these are my partners ______. Our final robot mechanism design project was to create a minimally-actuated robotic hand. Now robotic hands are some of the most widely known and striking kinematic mechanisms because they use technology to recreate one of the most recognizable symbols of humanity. Our hand is how we interact with the world- by having a machine mimic it, we can mimic life itself. However, in an effort to capture the individual motion of human fingers, they often require many actuators to function, which is both expensive and very complex to design.

To tackle this issue, we aimed to design and manufacture a robotic hand that used only a single actuator. Our project was inspired by the work done by Park and colleagues from Kyung Hee University, who made a modular robotic hand with kinematic linkages for each finger. Each finger consists of seven links, with the first link acting as the metacarpal, or the palm bone, the second link acting as the flexor tendon, and the seventh link acting as the fingertip. 

With our project, a big hurdle we had to overcome was that, without any form of tactile sensing or individual motion of the fingers, it would be difficult to grip objects of a varying shape since the fingers would all close in the same manner. To get around this, we chose to connect our linear actuator to each finger with a compression spring. Our linear actuator is connected to a sliding link with four slots, each of which is connected to the actuating link of one finger with the spring. As the linear actuator extends, before a finger touches the object it will flex as normal, as the spring transmits the force directly to the finger's actuating link. However, when a finger touches the object, the compliance in the spring would allow that fingertip to remain in place by instead compressing the spring itself. This allows the four fingers to conform to the shape of whatever object they are holding, letting them hold onto irregular objects much like a real human hand. 

On the sliding joint, we also have a rack gear that connects to a pinion gear that drives the thumb linkage. The thumb is there primarily for stability, as it serves to support the object in the palm while the four main fingers actually grip it. Since the thumb is not parallel to the axis of the sliding link, it would normally be quite difficult to actuate it with a linear mechanism. By using a rack-and-pinion geartrain, we can convert the linear motion of the actuator into rotational motion, and then back again to transmit this force onto a different axis.

All of our mechanisms are placed into a 3D-printed housing, with a laser-cut acrylic screen to allow the mechanism to be visible in motion. In the wrist and forearm below the hand, we have our electronic components which include a motor driver, a battery, and a small Arduino microcontroller.

Overall, our mechanism was very successful. Our elegant design closely mimics the appearance of a real human hand, our sliding mechanism allows the whole thing to be controlled with a single piston, and our compression springs give it the flexibility and compliance needed to conform to real-life objects. Thank you for listening!