Static balancing of a manipulator with hemispherical work space

This paper proposes a gravity compensator for the roll-pitch rotation which can be operated in hemispherical work space. The gravity compensator comprises two 1-dof gravity compensators and a bevel differential. It is revealed from analyses of energy and torque that the proposed gravity compensator can perform static balancing completely. The gravity compensation of a 4-dofs manipulator is briefly introduced for example. Experiments show that the proposed compensator can counterbalance the gravitational torques effectively and can be operated in hemispherical work space.