Research On Simultaneous Calibration Of Multi-node 3D Measurement System Based On Stereoscopic Target

The optical three-dimensional(3D)measurement technology based on phase calculation has the advantages of high precision,realizability,non-contact,simple system structure,good flexibility and so on.At present,3D measurement technology has been widely used in industrial testing,reverse engineering,surveying and mapping navigation,medical engineering and other fields.The traditional 3D measurement system is composed of a camera and a projector,which is easy to be limited by the field of view to cause visual blind area,and there will be a very obvious phenomenon of data loss.In order to solve the problem of complex topography measurement and expand the field of view of the system,this dissertation uses a multi-node system composed of double cameras and projectors for measurement.The measurement accuracy of the system depends on the calibration accuracy,while the traditional calibration method has complex steps and takes a long time,especially when calibrating each camera separately in the multi-node measurement system,and the cumulative error is introduced.In order to solve the above problems,this dissertation studies a calibration method based on a 3D target,and uses it to calibrate the twonode system and evaluate the accuracy.The main work of this dissertation includes the following aspects:First of all,aiming at the complex problem of multi-node system calibration,this dissertation constructs a 3D target,which is composed of two planes.Each target plane is attached with a pattern with known specifications,and the plane connection is marked with a special pattern to distinguish between the left and right sides.The system calibration experiment is carried out by using the stereo target,and the simultaneous calibration of the multi-node 3D measurement system is realized.For the measurement system used in this dissertation,the calibration time is reduced by half,and the calibration process is simplified.The accuracy evaluation experiments of the multi-node system are carried out.The results show that the depth(Z)and transverse(XY)can be calibrated accurately by using the stereo target,and the measured error is less than 0.053 mm.Then,in order to solve the problem of the deviation in the center extraction of the ring identification point,this dissertation studies the ring concentric model and corrects the center extraction error of the ring mark point on the stereo target by using the ring centrifugal deviation correction technology.the experimental results show that the accuracy of ring center extraction can be improved by 50%,which provides more accurate data for later system calibration.Finally,the plaster image with free surface is measured by the experimental system,and the point cloud data obtained by splicing different nodes in the same coordinate system are obtained to verify the effectiveness of the established volume target in the calibration process.In this dissertation,related experiments have been carried out for the two-node threedimensional measurement system.For the system with more than two nodes,the stereo target will simplify the calibration process to a greater extent and reduce the cumulative error of calibration one by one,which has application value in the calibration of multi-node system.