Independent, voluntary control of extra robotic limbs

Most of the wearable robots today assist their users by acting in parallel or in series to their natural limbs. We propose a different approach to wearable robotics, consisting of devices that provide users with additional, independent robotic limbs. We present a wearable robot prototype that can achieve these goals with an extremely light weight apparatus. In order to control additional robotic limbs as if they were part of the user's body, we need voluntary signals that are independent of natural limb motions and comfortable to measure. One suitable solution - explored in this study - is the use of muscle activation signals generated by the torso. We hypothesize that a human is competent to move the extra limbs voluntarily and independently without interfering with the natural arms and legs. We developed a wearable suit to measure these signals, and we tested three possible real-time control strategies linking torso muscle contraction to the motions of two simulated extra limbs. The experimental data show that the velocity control strategy yields the highest motion accuracy, minimum muscular effort, maximum independence from the natural limbs and the fastest learning rate. This control strategy has then been applied to the control of the physical robot prototype, worn by human subjects. All of the subjects achieved accurate (normalized tracking error <; 0.5), independent (normalized natural arm motions <; 0.15) control of the extra limbs.