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We propose a design method for a gravity compensator using the space mapping method and joint constraints. The pose of a mechanism can be described with various joint angle sets (i.e., joint spaces). When constraints exist between joint angle sets, a gravity compensator for a mechanism can be derived from the gravity compensator of a base joint space using constraints. Thus, it is not necessary to recompute the whole design equation. A slider-crank mechanism was adopted as an example and various gravity compensators were obtained using the space mapping method. Investigations of various gravity compensators proved that their design equations can be derived from the base joint space by applying mapping relations between joint spaces (i.e., constraints). The results of simulations show that the obtained gravity compensators effectively counterbalance the gravitational force and the total potential energy is invariant for all poses. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]