Supernumerary Robotic Fingers: An Alternative Upper-Limb Prosthesis

Abstract

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.