Conventional prosthetic devices substitute lost human limbs with mechanical proxies to enable amputees perform daily chores. We present an alternative approach that may replace or supplement traditional upper-limb prostheses by utilizing and enhancing the functionality of the remaining healthy limb with a new type of wrist-mounted robot: the Supernumerary Robotic (SR) Fingers. These SR Fingers are naturally and implicitly coordinated with the motion of the human fingers to provide assistance in a variety of prehensile tasks that are usually too difficult to carry out with a single hand, such as grasping a large/oddly shaped object or taking the lid off a jar. A novel control algorithm, termed “Bio-Artificial Synergies”, is developed so the SR Fingers can share a work load and adapt to diverse task conditions just like the real fingers do. Through grasp experiments and data analysis, postural synergies were found for a seven-fingered hand comprised of two SR Fingers and five human fingers. The synergy-based control law was then extracted from the experimental data using Partial Least Squares Regression (PLSR) and tested on the SR Finger prototype on a number of common tasks to demonstrate the usefulness and effectiveness of this new class of prosthetic device.

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