A 2-dof gravity compensator with bevel gears

This paper presents a 2-dof gravity compensator used for roll-pitch rotations, which are often applied to the shoulder joint of a service or humanoid robot. The 2-dof gravity compensator is comprised of two 1-dof gravity compensators and a bevel differential. The rollpitch rotations are decoupled into two rotations on the moving link by the bevel differential; the two 1-dof gravity compensators are applied to the two rotations. The spring coefficients are determined through energy and torque analyses in order to achieve complete static balancing. The experiment results indicate that the proposed gravity compensator effectively counterbalances the gravitational torques and can also be operated in the hemispherical work space.