Reconfigurable mass parameters to cross direct kinematic singularities in parallel manipulators

Some authors have suggested the concept of adding active masses to some links so as to allow us to control the location of their center of mass and other dynamic properties for serial manipulators. This paper investigates the possibility of following a desired trajectory that contains direct kinematic singularity configurations using reconfigurable mass parameters in parallel manipulators. To illustrate the concept, an actuated mass is added to each of the two branches of a 2-RPR planar parallel manipulator. The dynamic model of this manipulator is developed using the principle of virtual work. The model is then used to compute the required displacements, velocities and accelerations of the active masses over time as to allow the manipulator to successfully cross singular configurations. Numerical examples are presented to support the idea.