Stiffness analysis of a 4-DOF hybrid robot

A semi-analytical approach for the stiffness modeling of a novel hybrid robot named Bicept is presented. The robot is composed of a 2-DOF planar parallel mechanism with two unconstrained active limbs and a properly constrained passive limb, plus a 2-DOF rotating head attached to the platform. The Bicept is a simplified 2D version of the well known Tricept robot, featuring low manufacturing cost and large workspace. The robot can be employed as a module to configure a robotic cell for automatic drilling or riveting in aircraft large structural components assembly by adding a translational motion along a long reference track. On the basis of the inverse position and deformation analyses, the stiffness modeling of the 2-DOF planar parallel mechanism within the Bicept is formulated by using the overall Jacobian and taking into account the compliances of all limb components and joints. Particular interest is placed upon the precise formulation of the bending stiffness matrix of the properly constrained passive lim