Investigation Into Compliance Modeling And Design Methodology Of A Five Degree Of Freedom Hybrid Robot

This dissertation investigates into the theory and methodology for the design of a 5-DOF hybrid robot for high-speed machining, drilling and assembling processes of large aircraft components with particular focuses upon type synthesis, kinematic performance evaluation, compliance formulation, lightweight design, rigid body dynamic formulation and servomotor parameter estimation. The following contributions have been made.By taking the UPR-SPR and UP kinematic chains as the virtual chains, the type synthesis of 1T2 R positioning 3-DOF parallel mechanisms is investigated. The geometric conditions for generating the limb structures having 4-DOF and 5-DOF are formulated, leading to numerous redundantly actuated or overconstrained 3-DOF parallel mechanisms which could be used to configure 5-DOF hybrid robots by attaching a 2-DOF rotating head to the platform.The geometric conditions for achieving the analytical solution to the inverse kinematics of a planar symmetric 3-SPR parallel mechanism are investigated. Based upon the coordinate transformation technique, a dimensionally homogeneous overall Jacobian is developed. This lead to the development of a set of novel kinematic performance indices which are dimensionless, invariant with respect to the coordinate frame, and have a value of [0, 1]. The feasible domains of a set of dimensionless dimensions subject to the given kinematic and geometric constraints are obtained.By taking gravity and joint/link compliances into account, a semi-analytical approach for the deflection analysis of the proposed 5-DOF hybrid robot is developed. The approach can be implemented by three steps:(1) formulation of a linear map between the joint forces and the externally applied wrench;(2) establishment of a deflection model by taking into account those arising from the distributed gravity of the limbs;(3) formulation of the component compliance matrices in the joint space using a semi-analytical approach. The merit of this approach lies that the overall deflections caused by both the payload and gravity can be evaluated in an effective manner.A hierarchical approach for the lightweight design of the proposed 5-DOF hybrid robot is proposed using the criteria to match rigidities between two “generalized” components at different levels, i.e. between the 2-DOF rotating head and parallel mechanism at the system level; between the actuated and constraint rigidities at the limb level, and between the limb-body and joints at a realistic component level. Meanwhile, the constraints in terms of technological processes and the dimension correlations of components and joints, etc., are also considered. With these elaborate considerations, the design flow is developed by maximizing the lower order natural frequencies as well as by minimizing the weights of the limbs/subassemblies subject to the specified rigidity constraints attributed to them. The proposed approach simultaneously enables both the high static rigidities as well as high dynamic behaviors of the system to be achieved.The inverse rigid body dynamics of the 3-SPR parallel mechanism is modeled using the reaction wrenches and velocity twists applied upon the joints. Then, the method to estimate servomotor parameters is proposed by evaluating the peak torques and the average moments of inertia of the actuators, providing a theoretical foundation for the determination of servomotor specifications.The above-mentioned outcomes have successfully been employed for the design of a 5-DOF hybrid robot prototype, and laid a solid foundation for the development of a realistic machine for the use in aircraft industry.