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This paper describes the design of a gravity balanced spatial orthosis. Previous works introduced planar mechanisms only and neglected friction. They relied on counterweight or auxiliary parallelograms. The main contributions of this paper are: (i) we succeed in designing a spatial (3D) mechanism and (ii) we analyzed the effects of friction. We designed a very simple system made with two pulleys and two springs in order to ensure gravity compensation. The system is in static equilibrium whatever its posture. It has three passive degrees of freedom at the shoulder and two at the elbow. A prototype of this orthosis is presented at the end of the paper.