Investigation On Modeling And Design Method Of A Hybrid Equipment Suitable For Friction Stir Welding

Driven by the requirement of multi-equipment mirror friction stir welding for large rocket storage tank,this thesis systematically investigates kinematic modeling,static compliance modeling,inverse rigid body dynamic modeling and hierarchical design method for a hybrid equipment with 3-PRS mechanism as the core module.The following results have been achieved:The hybrid equipment is disassembled into parallel module and long-stroke unit.Based on the vector chain method,Newton-Raphson method and screw theory,the position,velocity and acceleration model of the parallel core module are studied.Furthermore,motion of the long-stroke unit is incorporated to complete the kinematic model of the hybrid kinematic chain,which lays a solid foundation for subsequent modeling and design.By virtue of commercial CAE software and screw theory,starting from characterizing elasticity of the underlying parts,the static compliance model of the parallel module driving interface is constructed by assembling the parts in limb serially and assembling limbs in parallel according to the principle of static compliance matrix equivalent transformation rule.Additionally,the static compliance model of the hybrid equipment is derived hierarchically by sequentially connecting the moving platform part and long-stroke unit part.Taking the gravitational field into consideration,this model can predict static compliance and static deformation of the end-point rapidly at local configuration or throughout the whole workspace,which lays a foundation for static compliance performance design.Based on screw theory,the span rule of velocity and acceleration of each motion unit in the hybrid kinematic chain is studied.Guided by virtual work method and Newton-Euler method,an inverse rigid body dynamic model is derived to calculate the driving forces and internal wrenchs in all passive joints,which forms a powerful tool for the selection of servo motor and junction element.Based on kinematic model,static compliance model and inverse rigid body dynamics model,a hierarchical comprehensive performance design is completed in a hierarchical and progressive manner driven by the requirement the mirror friction stir welding of 2219 aluminum alloy with typical thickness: Firstly,force and orientation transmission matching performance are studied,and the dimentional parameter region is optimized.Secondly,static compliance constraints of the end-point is constructed based on the working condition,and it is decentralized to subsystems to reduce design complexity with the help of static compliance matching law.Thirdly,with kinematic performance,static compliance performance and mass property as a comprehensive aim,a multi-layer discrete point searching rule is established from subsystems to the equipment.In light of the rule,the optimal design parameters are obtained by traversing the discrete point set,thus the digital prototype of the equipment is integrated.Finally,with the requirements of typical acceleration/deceleration motion and working load,the servo motor selection is completed under the constraints of motor torque and speed.Thus,a set of hierarchical performance matching and integrated design method and process are formed.The outcome of this thesis not only provides a theoretical basis for guiding the design of aerospace friction stir welding hybrid equipment,but also enriches and develops the design theory and method for such kind of equipment.