MIT Wrist-Robot Adds Extra Fingers
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  • One hand is better than two

    R. Colin Johnson

    PORTLAND, Ore. — Ever try to get the lid off a jar with one hand, or open an envelope, or 1,000 other two-handed tasks? Well now you can, that is if you are wearing the new wrist-robot from the Massachusetts Institute of Technology (MIT). Still in the prototype stage, the wearable robot nevertheless offers a new paradigm in assistive robotics called "synergism."

    "It is well known that the motion of the human hand is controlled by synergy -- which is the idea that groups of muscles are activated together by a single control signal," said MIT doctoral candidate Faye Wu in a video about her presentation this week at Robotics: Science and Systems 2014 (July 22 through July 24, Berkeley, Calif.) "We want to extend the synergy-based control to wearable robots."

    MIT doctoral candidate Faye Wu shows that by following the motions of the fingers the two robotic fingers adjacent to thumb and pinky can help users perform tasks with one hand that would ordinarily take two.

    (Source: MIT)

    To do so, the wrist worn robot has a glove attached that measures the angle and orientation of each finger, then passes a control signal to the extra fingers to react synergistically. For instance, if a large object is being picked up, the normal fingers only need grasp its top while the longer robotic fingers grab its bottom portion.

    Because the user does not have to give explicit control signals to the new digits, the learning curve for working with extra fingers for assistance if not very steep.

    "We use a knife and fork, or we drive our car, and if you use these tools for a long time, they feel like and extension of your body. So that is exactly what we are trying to do with robotics. If you could have extra fingers or a extra arm and communicate with them very well, then you've got to feel too that they are an extension of your body," said Harry Asada, the Ford professor of engineering in MIT's Department of Mechanical Engineering.

    Asada's group is creating synergistic algorithms that allow extra robotic appendages to follow-along helping out with tasks that would be too difficult for one-hand, and someday an extra hand for tasks difficult with two-hands, or even an extra arm for tasks too difficult for two-arms. No explicit commands will be given to the robot, it just follows along helping out synergistically the way all your fingers cooperate to grasp something.

    Stirring a drink with one hand is easy if the robotic fingers hold the cup.

    (Source: MIT)

    Officially, the extra robotic fingers are called "supernumerary" because they consist of actuators linked together to exert forces of equal strength to actual human fingers. Through studying the way that humans grasp objects, the researchers found that synergistically there are only two basic algorithms used -- bringing the fingers together and twisting them inwards. Grasping most objects is just a combination of these two general patterns.

    The researchers hope that the bio-mechanical synergy of the other limbs will also follow a few basic patterns, but right now their next step is to add force into the mix. For instance, how do the fingers know to exert more force on small objects that are heavy or slippery? Secondly, different people use slightly different approaches to grasping objects, making the compiling of a library of those techniques a goal -- so that the robot can learn to recognize and assist more efficiently by picking the correct algorithm from the library for the person they are helping.

    The group is also working to downsize the mechanism so that it could fit inside a bracelet, with the extra fingers popping out when necessary, but then folding back up when no longer needed.

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