Research On Multi-camera Calibration In Fringe Projection 3D Measurement System

Fringe projection measurement technology,with its high precision,non-contact property,has been the hot spot in the field of three-dimensional measurement.Multi-camera is the direction of development in visual application.The combination of both will generate new measuring means with a wider range of measurement,and thus promote the development and application of computer vision theory.In this paper,the key technologies such as calibration and measurement of multi-camera fringe projection measurement system are studied.New methods is proposed for some problems,and a physical system is built on the basis of research results.The main innovations are as follows:1.A multi-camera calibration method based on fringe projection is proposed.It is difficult to obtain constraint information about the system's structure because the field of view of cameras is not overlapped.This airticle uses the projector as an auxiliary device to provide additional information.Projector can project encoding fringe patterns to the planes for calibration,meanwhile cameras capture these fringe images,then decoding the images can restore the mapping relationship between the projection plane and calibration plane.Because the projector can be seen as the camera's inverse system,projector calibration could be work.we can resolve the position of the cameras and projector according to the external parameters after calibrating them.Finally,optimizing the results using the method based on the reconstruction bias.It can proved that the method uses a projector to construct a large virtual target for calibration,which subtracts the cost of making a large target and has a high degree of flexibility.The experimental results show that the method has high accuracy.2.The improved methods are proposed in the traditional fringe projection measurement system.First,the circular pattern has the distortion under the perspective projection transformation,resulting in low center position accuracy,meamwhile the black region would cause a large error in unwrapping phase.Secondly,the projector has serious distortion and its calibration depends on the camera,therefore the inverse camera method has limitations.Finally,traditional single-camera fringe projection measurement system has small measurement range,also can't solve the self-occlusion.In order to solve the above problems,this paper uses the diagonal intersections of white squares in the checkerboard pattern as control points,and improving the accuracy of calibration.Also a two-plane model is proposed to describe the projector.The model simplifies the calibration of the projector,only need solve the mapping between the projection plane and at least two calibration planes.The above methods are applied to a multi-camera fringe projection measurement system,which improves the applicability of the original system.