In this work, a comparative study of the energy needed to run a 3-degree of freedom (DOF) parallel manipulator (PKM) for two different configurations of the inputs and two different transformation matrices for a concrete trajectory is presented. The 3-PRS is a PKM of low mobility, i.e., it has less than 6-DOF and when the main motion takes place, unexpected motions in the constrained DOF appear. These are parasitic motions. As previous studies show, these parasitic motions lead to less accuracy and, therefore, they are not desired from the point of view of the kinematics. It would be of great interest to know if the parasitic motions affect the dynamics as well and, if so, in which way. Thus, with those parasitic motions in mind, the inverse kinematic problem of position, velocity and acceleration is solved. Once the accelerations of all the elements have been derived, the rigid solid dynamics and the results of force requirements and power consumption in inputs are analysed. The trajectory studied is a rotation about an axis in a plane Pu,v in a mobile reference frame and the parasitic expressions depend on the transformation matrix combination used. In this paper, the results for two of those transformation combinations are presented for two configurations of the inputs — in the first one, the inputs are in a horizontal plane, while in the second one they are vertical.

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