Design of a novel X-type gravity compensation unit for the passive waist exoskeleton

Abstract Gravity compensation, widely employed in mechanisms such as manipulators and exoskeletons, serves to minimize unnecessary energy consumption. Enhancing the performance of gravity compensation mechanisms (GCMs) is therefore of significant practical importance. One promising approach is the development of novel design methodologies. Existing GCMs utilizing cable-pulley units exhibit limitations in terms of structural compactness and efficiency. To address these issues, this paper proposes an innovative X-type gravity compensation unit featuring an adjustable cable sequencing arrangement. The application of this unit to a passive waist exoskeleton (PWE) is further introduced. Given the potential influence of pulley size and positioning on the actual spring elongation, a pulley-angle error model is established to analyze the effect of varying pulley positions. Simulations confirm the validity of the model and demonstrate that pulley size is a non-negligible factor in system performance. Finally, an experimental platform is constructed to evaluate the performance of the PWE. Experimental results indicate a notable improvement in exoskeleton performance attributable to the unique design of the X-type unit.