| Large-size truss structures are widely used in railway stations,theaters,large-span factories,aerospace launches and other occasions.It has the characteristics of large scale(usually reaching the order of 100 meters),high position accuracy,and long service life.Restricted by manufacturing and transportation factors,large-size truss structures are often realized at the construction site through segmented splicing or mechanical unfolding,and its assembly accuracy puts forward extremely high requirements for the accurate measurement of trusses.At the same time,during the truss run,it will inevitably undergo deformation due to heat and gravity.For safety considerations,it is necessary to conduct online inspection of the truss structure during its assembly and service stage to ensure its installation accuracy and safe operation.Based on the analysis of the characteristics of the truss structure,the principle proposes a laser scanning measurement plan for the large-size truss structure.The two-dimensional scanning device is used to drive the laser distance sensor,and the corresponding data processing method is used to realize the end of the large-size truss structure.Measurement of space torsion angle and horizontal offset.To this end,the detailed research was developed as following:1.The limitation factors of the large-size truss structure on the measurement technology are studied,and the laser scanning measurement scheme is proposed.The system realizes ranging by detecting the transmission time of the pulsed laser beam between the sensor and the measured target,and at the same time,the pulse echo intensity is collected for the identification of the target surface characteristics,and then the spatial coordinate position of the target at the corresponding node of the truss is obtained,and the truss geometry is realized Indirect measurement of size,spatial torsion angle and horizontal offset;a two-dimensional rotating scanning system is designed to achieve highprecision scanning through a precision turntable driven by a motor.2.According to the surface topography characteristics of the target at the truss node,it is divided into plane type and arc surface type for separate processing,and their own data processing methods are established.Considering the accuracy requirements and realtime requirements of truss inspection comprehensively,the least square method is used to fit the target characteristic straight line to avoid time-consuming calculation methods such as iterative method.The planar target mainly measures the spatial position of its edge line segment and the normal vector of the plane.The arc surface target mainly measures the spatial position of its center line segment.Through the identification and calculation of the respective key feature information of the target,the spatial position of the truss node is indirectly obtained.3.Select the pulse time-of-flight laser ranging sensor of the laser scanning measurement system,and according to the measurement error source of the sensor,its system error,the distance to the measured target,the reflection characteristics of the target surface,and the laser divergence angle and other influencing factors The experimental analysis is carried out to determine the measurement error and fluctuation range caused by various factors.A two-dimensional rotating scanning device was built,the source of positioning error was analyzed,and the error equation including the assembly error was established.According to the equation,the calibration scheme of the scanning measurement system not relying on other measurement tools was determined,and the experiment was verified.At the same time,the measurement software of the laser scanning measurement system was developed.4.Using the laser scanning measuring device to measure the simulated target,the measurement results of the torsion angle and horizontal offset of the simulated target are obtained,and the reasons for the errors are analyzed from the aspects of hardware factors and scanning resolution. |
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