A novel slider-crank spring gravity balance module for 1-DOF rotary link and its application to serial manipulators

This paper presents a slider-crank spring gravity balance module for a rotary link and its application to serial manipulators. The spring is arranged in a slider-crank mechanism, its elastic energy is a quadratic function of the crank angle. The gravitational energy of a rotary link can be expressed as a quadratic function of half the link angle. It shows energies matched when the crank angle is half the link angle with a phase difference and the spring stiffness is a function of the link mass. Thus, the balance module is formed. In a serial manipulator, the gravitational energy of a remote link is expressed as the sum of quadratic functions of the angle of itself and preceding links. It can be matched by the elastic energy of the modules on the link itself and the preceding links respectively. Thus, the balance module can be applied to serial manipulators. Torque measurement tests for balancing a rotary link and a 2-DOF serial manipulator by balance modules are performed and show the driving torques are reduced by over 90 % by the balance module.