A Novel Method and Exoskeletons for Whole-Arm Gravity Compensation

We present a new method for providing gravity compensation to a human or robot arm. This method allows the arm to be supported in any orientation, and also allows for the support of a load held in the hand. We accomplish this with a pantograph, whereby one portion of the linkage duplicates the arm's geometry, and another portion of the linkage contains a scaled copy of the arm. Forces applied to the scaled copy are transferred back to the original arm. We implement these concepts with two exoskeletons: the Panto-Arm Exo, a low-profile exoskeleton that supports the arm's weight, and the Panto-Tool Exo that supports a mass held in the hand. We present two linkages used for pantographs, and analyze how different linkage dimensions and their positioning relative to the body affect the forces providing gravity compensation. We also measured the effect of the Panto-Arm exoskeleton on fourteen subjects' arm muscles during static holding tasks and a task in which subjects drew horizontal and vertical lines on a whiteboard. Even though the Panto-Arm Exo linkage geometry and forces were not optimized, it reduced the Mid Deltoid by 33-43% and the Biceps Brachii by up to 52% in several arm postures.