Structure Synthesis and Stiffness Analysis of a Parallel Metamorphic Mechanism With a Reconfigurable Joint

Abstract The traditional riveting of aircraft surfaces heavily relies on manual operation, which greatly affects the production efficiency of the aircraft. This article proposes a metamorphic riveting mechanism that can be employed as a motion adjustment cell for riveting rivets on aircraft surfaces. First, a reconfigurable double rotational (rD) joint is proposed, which can change the direction of the traditional universal joint axis. Subsequently, a metamorphic riveting mechanism is obtained by incorporating the rD joint, which may change its degrees-of-freedom (DoFs) from 2 to 4. To fulfill the riveting requirements, two integrated riveting mechanisms with different DoFs are presented as cases. In configuration 1, a 2-DoF mechanism can achieve the primary screw-riveting motion. In configuration 2, a 4-DoF mechanism can be used to adjust the pose of the drill bit. Then, by determining the type of constraint force screw in different configurations, the parasitic motion, kinematics, and stiffness equations for the metamorphic mechanism are established. Finally, a numerical example is provided to investigate the mechanical performance of the mechanism during the riveting process. The stiffness distribution results guide further optimization of the mechanism design. This mechanism is expected to replace traditional manual riveting operations, providing a theoretical basis for achieving integrated manufacturing.