Review of recent advances on reactionless mechanisms and parallel robots

When parallel mechanisms are in motions, because the center of mass (CoM) is not fixed and angular momentum is not constant, vibration is often produced in the system. Shaking force and shaking moment balancing can usually be realized by making the CoM of mechanism fixed and angular momentum constant. There are generally two main ways for shaking force balancing and shaking moment balancing, balancing before kinematic synthesis and balancing at the end of the design process. For the balancing at the end of the design process, addition of counterweights and counter-rotations, addition of active dynamic balancing unit, and addition of auxiliary links are mostly used methods. The advances and problems on dynamic balancing of mechanisms are discussed in detail under the above two main categories here, and balancing through reconfiguration method is proposed, which can reduce the addition of mass and inertia. Fisher’s method belongs to the method of balancing before kinematic synthesis.