Structural Design Method And Kinematics Analysis Of A Class Of Reconfigurable Parallel Mechanisms

With the rapid development of science and technology, and the requirements of reconfigurablity, adaptability for mechanisms used in modern production, structural design and analysis of reconfigurable parallel mechanisms (RPMs) have attracted substantial interests in the research community of mechanism and robot. This dissertation carries out the research on RPMs in terms of structural design and kinematics analysis. A class of novel RPMs is presented, followed by the design and analysis of a RPM used in modern manufacturing process with multi-task requirement.To address the problems that the RPMs having been proposed in the current stage are relatively few and the existed RPMs suffer from the disadvantage of unsatisfactory actuation scheme, a new method for structural design of RPMs is proposed. By intergrating singular closed-loop chains and serial limbs with fixed degrees of freedom (DOFs), hybrid limbs and subsequently, parallel mechanisms with reconfigurability are constructed. The configuration and motion of the hybrid limbs are changeable due to the singularity characteristic of the included closed-loop chains, resulting in the reconfiguration and mobility variation of the RPMs. In order to make the reconfigurable hybrid limbs having an expected motion characteristic, we identify a possible motion condition for the feasible serial limb with fixed DOFs, namely, two rotational and two translational motion. Structural synthesis and enumeration of this kind of limbs are conducted based on Lie group theory.On the aspect of constructing RPMs that utilize the constraint singularity of closed-loop chains, three existed kinematotropic chains and a novel kinematotropic chain with special link length condition are concerned. The requirements of constructing reconfigurable hybrid limbs and parallel mechanisms based on those four kinematotropic chains are discussed, respectively. The corresponding design results are given. The obtained RPMs have the ability to work in four operation modes with 3-DOFs. We furhter analysis the kinematic decoupled characteristic of a special RPM, and verify its reconfigurability through motion simulation. To illustrate the design of RPMs that utilize the limb singularity of closed-loop chains, four planar metamorphic mechanisms are proposed, and subsequently, used in the construction of reconfigurable hybrid limbs and parallel mechanisms, resulting in a series of RPMs that is capable of performing ten operation modes from three to six DOFs. The acutations of all the proposed RPMs can be mounted on the fixed bases, which will benefit the dynamic performance of the mechanisms.A novel multi-diamond kinematotropic chain, which is the variation of the diamond kinematotropic chain is presented. Reconfigurable hybrid limbs and RPMs are obtained by integrating the multi-diamond kinematotropic chain with serial limbs. The kinematics and stiffness of a planar type RPM are analyzed, and compared with that of a fixed-DOF parallel mechanism, demonstrating that in addition to the reconfigurability, the RPMs can exhibit some other advantages in terms of kinematics and performance.To accommodate the multi-task requirement in modern manufacturing process, a series of RPMs that has four operation modes is proposed. Unified model for position analysis and the overall Jacobian matrix of a representative RPM are established. Motion simulations associated with different operation modes are performed to verify the validity of the direct position solutions. Workspace and singularity analysis of the RPM are conducted. A prototype of the RPM is built on which several motion and manufacturing experiments are carried out.