Methodology for analysis and synthesis of inherently force and moment-balanced mechanisms: theory and applications

Abstract

A mechanism or robotic manipulator that is dynamically balanced does not cause base vibrations when moving at high speeds. A balanced mechanism does not perturb equipment mounted on the same base, the floor, and machines placed nearby, therefore dynamic balance improves the accuracy of a machine, reduces cycle times, and reduces the required size, mass, and stiffness of base frames and floors. For robotic end-effectors dynamic balance is advantageous because of dynamic decoupling. A balanced mechanism also remains stationary in any position which is advantageous for realizing safe and energy efficient large motion of objects. Since commonly dynamic balancing of multi-degree-of-freedom mechanisms is considered after the kinematic synthesis of a mechanism, profitable solutions without excessive mass, inertia, and complexity addition are hardly found. In this work a methodology was developed that considers dynamic balance as a design principle in the synthesis of dynamically balanced mechanisms. New mechanisms were found where all elements contribute to the motion as well as to the dynamic balance. Such mechanisms were named inherently dynamically balanced mechanisms. Two methods for the synthesis of inherently dynamically balanced mechanisms were proposed which consider dynamic balance prior to the kinematic synthesis, the ‘method of linearly independent linear momentum’ and the ‘method of principal vector linkages’. Also a method was found by which the loop closure relations of general planar closed kinematic chains can be considered implicitly. For that purpose the mass of an element with general center-of-mass is modeled with one virtual equivalent mass and two real equivalent masses. For the first time a high-speed inherently dynamically balanced parallel manipulator was designed, built, and tested, showing that with dynamic balance the performance of the manipulator can be improved significantly. New multi-degree-of-freedom balanced kinematic mechanism solutions were synthesized for various applications such as a balanced grasper, a balanced bascule bridge without counter-mass, and balanced movable architecture.