A mechanism is reactionless or dynamically balanced when there is no shaking force and shaking moment applied to the base during mechanism movement. The theory for designing reactionless 2 degree-of-freedom (DOF) planar parallel manipulator is discussed in this paper. The legs of the manipulator are four-bar 2-DOF mechanisms with revolute joints. The dynamic balancing conditions of the manipulator are derived, considering that the time rate of the total linear and angular momentum have to be vanished. The dynamic balancing equations first are obtained and illustrated through a numerical example and finally verified by computer simulation using ADAMS software. پرونده مقاله