Research On Automatic Leveling Technology And Mechanical Properties Of Vehicle-mounted Theodolite

The vehicle-mounted measurement mode of theodolite has the characteristics of fast unfolding,fast withdrawal,fast measuring,etc.,which can greatly enhance the rapid response capability of the theodolite.This mode is the main mode of using the theodolite at present.However,there are still some core problems in the process of using the vehicle-mounted measurement mode,such as the theodolite leveling with high-precision,fast positioning/orientation with high-precision and platform shaking,which leads to the deterioration of the azimuth/pitch pointing angle.Therefore,in order to realize the vehicle-mounted measurement with high-precision,research on automatic leveling technology and mechanical properties of vehicle-mounted theodolite has been carried out in this dissertation,which is used to solve the problem of high-precision theodolite leveling and vehicle-mounted platform shaking.In order to realize the high-precision automatic leveling of the theodolite,the design and control of the two-stage self-leveling mechanism are studied.A graded selfleveling strategy is proposed to achieve automatic coarse leveling of the theodolite with the first-stage automatic leveling mechanism and automatic precise leveling of the theodolite with the second-stage automatic leveling mechanism.Firstly,through the analysis of physical modeling and geometric modeling of the first-stage automatic leveling mechanism,the leveling control process based on repeated positioning is proposed to realize the spatial motion path constraint of each equivalent contact center point in the process of leveling unfolding and withdrawal,which ensures the accurate docking of the fast locking mechanism interface when the platform falls back.The leveling control process provides critical support for the rapid withdrawal of the theodolite and improves the mobility of the theodolite.The static equilibrium equations of the legs and the "false leg" detection model are established,and a scheme based on the pressure monitoring of the legs is determined to ensure the stability of the theodolite support.Secondly,through the analysis of physical modeling and geometric modeling of the second-stage automatic leveling mechanism,the parallel leveling control strategy is proposed to realize the linkage of the leveling components.The leveling time and accuracy are tested to verify the high accuracy of the mechanism and the superiority of the parallel leveling control strategy over the serial one in terms of leveling time.In order to improve the support stability of the theodolite and decrease wobble error of the platform under the action of disturbance factors,the equivalent mechanical modeling method and structural optimization of the self-leveling mechanism are carried out.Firstly,the equivalent modeling method of screw joints based on stiffness calculation is proposed.With the solid model of the screw-coupled member,the equivalent virtual material parameters that can characterize the mechanical properties of the joint surface of the coupled joints is realized.The accuracy of the equivalent mechanical model is verified by the screw joints dynamics test.Secondly,the proposed equivalent mechanical modeling method of screw joints is used to develop the parametric modeling of the self-leveling mechanism,and the corresponding geometric and material parameters are determined,and then the equivalent mechanical modeling of each module itself is realized.Further,the core parameters of the self-leveling mechanism are identified based on the sensitivity analysis of the weak link.With the twist frequency as the optimization target,the approximate analytical expression between the core parameters and the twist frequency is established,which provides a model for the design and structural parameter optimization of the self-leveling mechanism,and finally realizes the mechanical performance optimization of the selfleveling mechanism.The results of the disturbance simulation analysis based on the wind loads and the theodolite driving torque show that after the mechanical performance optimization of the self-leveling mechanism,there is still a non-negligible platform wobble error caused by the disturbance factors.Therefore,the research of the vehicle-mounted platform wobble error measurement method is carried out.Firstly,a self-calibration optical noncontact measurement method is proposed,and a platform wobble error measuring device is designed.Secondly,a mathematical model of the platform wobble error measurement is established by using the ray-tracing method,and the approximate analytical expression between the wobble error and CCD image point deviation angle is obtained.Finally,the influence of the initial error of the measuring device on the measurement accuracy is analyzed by using the algebraic correction method based on the rigid body motion model,which provides a basis for the design and installation accuracy of the measuring device.Finally,an experimental platform is built to verify the accuracy of the vehiclemounted theodolite.Firstly,the proposed two-stage self-leveling mechanism and the graded self-leveling strategy are tested to verify their superiority in leveling accuracy,leveling efficiency and mechanical performance.Secondly,the automatic leveling test of the reflector verifies that under the high-precision leveling of the platform and the reflector,the designed wobble error measuring device can easily realize the automatic accurate alignment of the autocollimators and the reflectors,which effectively improve the measurement efficiency of the platform wobble error.Finally,the pointing accuracy test of the vehicle-mounted theodolite is conducted.By measuring the platform wobble error and error correction,the azimuth and pitch pointing angle errors can be significantly reduced and approximated to the pointing accuracy under fixed base conditions.