This paper focuses on optimum force balancing of a planar parallel manipulator, articulated with revolute joints, with a combination of a proper distribution of link masses and two springs connected to the driving links. After conducting the static force analysis of the mechanism, the force balancing is formulated as an optimization problem such that a mean-square root of the sum-squared values of bearing and spring forces is minimized throughout an operation range of the manipulator, provided that a set of balancing constraints consisting of balancing conditions and the sizes of some inertial and geometric parameters are satisfied. The minimization of bearing forces and spring forces adds to the life of bearings and springs, transmits less shaking force and moment to the ground, decreases wear in the mechanism components and consequently reduces the actuation burden on the actuators when the manipulator is in motion. Optimization results indicate that the proposed optimization approach is systematic, versatile and easy to implement for the optimal balancing of the parallel manipulator and other kinematic chains.
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