Stiffness modeling for a class of reconfigurable PKMs with three to five degrees of freedom

Reconfigurability of manufacturing systems is becoming important as production requires more agility to adapt to the fast-changing product cycle. The technology trend is moving toward developing full-scale reconfigurable systems including both software and hardware flexibility. Selecting a machine tool design that will best suit the forecasted rigidity and precision requirements for various tasks can be a difficult and costly exercise. This problem can be alleviated by using a reconfigurable parallel mechanism that consists of standard six-DOF actuated legs, which can be efficiently configured into the most suitable number of degrees of freedom required for given tasks. The mechanism includes several identical actuated legs distributed around the platform and one passive leg located in the center of the platform. The degrees of freedom of the system depend on the passive leg. Different degrees of freedom of the passive leg can be used to obtain new configurations with the required degrees of freedom. From this point of view, reconfigurable parallel mechanisms introduce a new dimension to flexible automation in terms of hardware flexibility compared to conventional industrial robots. In this paper, a kinetostatic model for parallel mechanisms with prismatic actuators is introduced for stiffness analysis of reconfigurable parallel kinematic machines. The geometric model of this class of mechanisms is first introduced. An example is given to illustrate the results of stiffness analysis.