Creative Desighn And Theoretical Research On Novel Parallel Pointing Mechanism

Pointing mechanism are widely used in aerospace field,which has great requests for pointing precision and stability.Pointing mechanism usually can be affected by external distractions,which can be compensated by compensation mechanism in series.The distractions are usually can be compensated by adding a parallel compensation mechanism in series with pointing mechanism.However,there exists an intermediate mechanism,which increases the overall mass,the additional load and energy consumption of the mechanism.For the purpose of realizing the lightweight integrated design of pointing and disturbance compensation decoupling,this paper proposes configuration thought and synthesis method of serial-parallel kinematic equivalent mechanism without intermediate platform.The serial-parallel kinematic equivalent mechanisms with three symmetric chains are synthesized.The 3-RRCPR mechanism is adopted as the novel pointing mechanism configuration.The kinematics and dynamics model,the optimization design,the error analysis and the kinematic parameter calibration are studied.The main research contents of this paper are as follows:The synthesis method of the serial-parallel kinematic equivalent mechanism is studied.According to the serial-parallel mechanism formed by two parallel mechanisms,the composition principle,kinematic and constraint characteristics of the serial-parallel equivalent mechanism are analyzed.Based on screw theory,the kinematic equivalent condition is proposed.Further more,the synthesis method and process for serial-parallel kinematic equivalent mechanism is proposed.Serial-parallel kinematic equivalent mechanisms with three symmetric chains are synthesized.According to the proposed synthesis method,the symmetrical three-branch chains kinematic equivalent mechanisms with three degrees of freedom motion,four degrees of freedom of motion,five degrees of freedom of motion and six degrees of freedom are synthesized.The representative 3D model of the kinematic equivalent mechanisms with different freedom of motion are established and the application prospect of corresponding mechanisms are introduced.The kinematic and dynamic model of the novel parallel pointing mechanism are established.For the application requirements of precision pointing field,the synthesized 3-RRCPR mechanism was adopted as the configuration of the novel parallel pointing mechanism.According to the kinematic equivalent characteristic,the kinematic model of the novel parallel pointing mechanism is established by using the kinematic model of the3-RRR sub-mechanism and the 3-CPR sub-mechanism.Based on the kinematic model,the dynamic model of the novel parallel pointing mechanism is established.The optimization design is carried out and the physical prototype of the novel parallel pointing mechanism is developed.The novel 3-RRCPR parallel pointing mechanism is optimized by considering motion/force transformation index,reachable workspace and lightweight.The structural parameters of the mechanism are optimized based on the motion/force transformation index by using atlas method.Aiming at the problem of interference of links affecting mechanism reachable workspace,an interference analysis method is proposed.To reduce the interference space as much as possible,the links structure is designed.To reduce the weight of the novel parallel pointing mechanism,the lightness design of the links is carried out by using ANSYS software based on response surface method.According to the optimized mechanism parameters,kinematic and dynamic simulation is carried out through Adams software to verify the correctness of the theoretical model.The statics comparison of the novel 3-RRCPR mechanism and 3-RRR+3-CPR serial-parallel mechanism is carried out.After processing,manufacturing and purchasing of parts,building the control system,the physical prototype of the novel parallel pointing mechanism is developed.The error analysis and calibration are carried out.According to the kinematic equivalent characteristic,the closed-loop vector superposition method is proposed to establish the error model of the novel parallel pointing mechanism.The error analysis and sensitivity analysis of the mechanism are carried out.Based on the error model,the calibration model of kinematic parameters is established.The kinematic parameter calibration experiment is carried out through the laser tracker.The kinematic parameters of the mechanism are calibrated by the least square method.