Research On Position Retention Control Of Flexible Parallel Mechanism Used In Grating Tiling

The large-aperture diffraction grating is a kind of precise optical element and is widely used in such key areas as national defense and astronomy.With the increase of the size of the diffraction grating,the manufacturing difficulty is increased,the production cycle is increased,and the cost is rapidly increased.The small aperture grating has the advantages of easy fabrication,low cost,and easy access to higher quality.In engineering practice,mechanical splicing mechanisms are often used to splice small-size gratings into large-size gratings for application.In laser target engineering,the grating is required to remain in the same position for a long time.Therefore,the position retention of the grating splicing mechanism has become a key indicator of the performance of the evaluation device,which directly affects the stability of the optical path of the shooting range,and affects the shooting accuracy.In this paper,a comprehensive research on the mechanical parallel connection of the mechanical grating splicing flexible joint developed by Harbin Institute of Technology is carried out in order to improve the positional retention of the grating splicing mechanism and make the mechanism able to maintain long-term stability in engineering applications.In this paper,according to the requirement of grating splicing large stroke,large load,high precision and high position retention,the flexible parallel mechanism of 5TSP-PPS is designed and the finite element model of the mechanism is established.The grating splicing flexible parallel mechanism is a complex system with high coupling of force and displacement.Based on finite element simulation software,the motion accuracy and kinematic coupling of the mechanism are analyzed.The results show that the movement accuracy and kinematic coupling of the mechanism meet the design requirements.Combining experimental and practical engineering applications,the positional retention of the grating splicing device is analyzed from two aspects: vibration stability and long-term position drift.Firstly,modal analysis and random vibration analysis are performed to study the vibration stability of the mechanism.Then,the reasons for the long-term position drift of the grating splicing device are analyzed,and the position-keeping closed-loop control of the mechanism is proposed.Kinematics analysis is the basis for the study of position-preserving control.Through the spatial homogeneous coordinate transformation and vector operations,the inverse solution of the position of the mechanism is found and a motion control model is established.A high-precision position feedback element is used to sense the position and orientation changes of the grating,and a pose control model is established between the change of the position and orientation of the grating and the change of the measurement data of the feedback element.Finally,establish a closed-loop position control of the entire organization,develop control systems and software.In order to verify the effectiveness of the mechanism's position retention control,a high-precision displacement sensor was installed on the basis of the prototype of the grating splicing flexible parallel mechanism,and an experimental system was set up to test the mechanism's motion accuracy,position retention and other properties.The experimental results show that the motion accuracy and position retention of grating splicing mechanism can meet the actual application requirements.