Research On Attitude Adjustment Mechanism Based On Double-Layer 3-UPU Hybrid Parallel Mechanism

The traditional Stewart type parallel posture adjustment mechanism has a limited working space,the posture adjustment at the output end is not flexible enough,and the control algorithm is complicated.The hybrid linkage mechanism is easy to solve and control,and has a broad application prospect in the machinery industry.In order to meet the flexible,fast,and precisely controlled attitude adjustment requirements of small astronomical telescopes,this paper proposes a hybrid attitude adjustment mechanism made up of two 3-UPU parallel mechanisms connected in series,which is analyzed for kinematics,stiffness,and attitude Error analysis,and prototype development and experiment.The spatial geometric constraint relationship and the spatial coordinate transformation of the mobile platform and the rotating platform of the hybrid attitude adjustment mechanism are used.The kinematics model of the hybrid linkage attitude adjustment mechanism was established,and the position,velocity and acceleration of the attitude adjustment mechanism were solved numerically.The limit posture of the hybrid linkage mechanism during single-degree-of-freedom movement is obtained.The Rodriguez formula is used to solve the problem of transcending equations in the positive solution of the kinematics of the rotating platform.A virtual prototype model was established in Adams,and the kinematics simulation of the hybrid attitude adjustment mechanism was carried out;the fifth degree polynomial trajectory planning function was constructed,and the attitude adjustment trajectory planning simulation of the hybrid mechanism was carried out.The comparative analysis of the virtual prototype simulation results and the theoretical results was carried out,and the results were basically the same.However,when there are assembly errors in the virtual prototype,there will be small accompanying movements during the simulation,which will affect the accuracy of posture adjustment.Using the conservation coordinate stiffness matrix formula and the maximum eigenvalue of the stiffness matrix as the stiffness evaluation index,the angular stiffness and linear stiffness projection of the hybrid stance adjustment mechanism on the working space are analyzed;the mechanism is statically analyzed using Ansys In mechanical simulation,the error between the simulation result and the theoretical stiffness calculation result is 10%,which verifies the correctness of the theoretical stiffness model.The results show that the maximum eigenvalues of the linear and angular stiffness of the posture adjustment mechanism during the posture adjustment process are symmetrically distributed along the working space,and the stiffness is the smallest at the limit position;the modal analysis is performed on the hybrid linkage mechanism to determine the adjustment The resonance frequency band of the attitude mechanism analyzes that the moving platform of the rotating platform deforms most during the resonance process,and has two vibration forms of radial vibration and bending vibration.The motion differential method is used to model the pose error of the hybrid posture adjustment mechanism.The influence of the structural error of the posture adjustment mechanism on the posture error is analyzed.The analysis shows that the driving rod length error is the main influencing factor that affects the posture error of the posture adjustment mechanism.The posture error verification is carried out by establishing a parameterized model in Adams.A prototype of a two-layer 3-UPU hybrid attitude adjustment mechanism was developed,and the rotation angle experiment of the rotation platform of the hybrid attitude adjustment mechanism was completed.The results show that the experimental results are basically consistent with the trajectory planning simulation results,and the maximum error of the precision measurement of the rotating platform is 0.24 arc minutes.