Dynamic Model of a 3-dof Asymmetric Parallel Mechanism

Most research papers about parallel kinematic chain mechanisms investigate symmetric robot manipulators, in which all the limbs connecting the end-effector to the fixed based are composed by the same sequence of links and joints. Contrarily, in some manipulation tasks the velocity and stiffness requirements are anisotropic. In such cases, the asymmetric parallel kinematic chain mechanisms may offer advantages. This works’ main objective is to present the inverse dynamic modeling of a 3-dof asymmetric parallel chain mechanism, conceived as a robot manipulator for pickand-place operations. The type of kinematic structure of the mechanism constrains the motion of the end-effector to only three translations. First, a brief kinematic modeling is carried out. Then, the inverse dynamic modeling is developed by employing the virtual work principle, considering two assumptions: lumped and distributed masses. Based on the model equations, a motion simulation is performed. The same motion is also analyzed by using the ADAMS computing environment to validate the model equations. After the simulation, the results demonstrated a very good agreement between the analyzed variables provided by the dynamic model and those generated by ADAMS. One can also notice that the input torques calculated by the lumped-mass model are quite close to the torques evaluated by the distributed mass model, and might be sufficient for the future development of a motion control law for the mechanism.