Design and Analysis of a Reconfigurable Hybrid Robot for Machining of Large Workpieces

Abstract

Large workpieces are important components of core equipment in aerospace and other fields, where the machining mainly focuses on the surfaces and inner cavities. However, there are no machining robots that can not only achieve high-precision surface machining, but also perform the machining of different inner cavities in a limited space. To fill this gap, a new reconfigurable hybrid robot (RHR) is proposed, called the 3PRR-3PSS-UPU RHR, for machining the surface and inner cavity of large workpieces (where P, P, R, S, and U stand for the actuated prismatic joint, passive prismatic joint, revolute joint, spherical joint, and universal joint, respectively). The proposed RHR consists of two parallel manipulators (PMs), in which one is a spatial 3PRR PM with one translational degree of freedom (DOF) and the other is a 3PSS-UPU reconfigurable PM (RPM) with different configurations of two rotational and one translational (2R1T) DOFs by using locking equipment, which is the main advantage of the designed robot. The inverse kinematics and singularities of two PMs are analyzed. The stiffness performance of the spatial 3PRR PM is compared with that of a moving slider with one translational DOF. By evaluating the workspace and motion/force transmissibility, the kinematic performance of two PMs is presented by using several local and global indices, followed by the dimensional optimization of link parameters. Based on the structural characteristics and excellent performance, it can be inferred that the 3PRR-3PSS-UPU RHR has great potential for machining of large workpieces.