Scanning-free Confocal Profilometry Based On The Principle Of Single-pixel Imaging

Translucent and metal objects are widely used in engineering,and obtaining their threedimensional(3D)profiles is very important to the supervision of engineering quality.However,when the traditional fringe projection profilometry is used to measure such objects,subsurface scattering and refraction will occur on translucent objects,and mutual reflection will occur on the surface of metal objects,resulting in low contrast of fringe images captured by the camera.Therefore,the 3D profiles of these objects cannot be reconstructed by the conventional fringe projection profilometry.In order to address the influence of subsurface scattering,refraction and inter-reflection on 3D profile measurement results and obtain high quality 3D profiles of translucent and metal objects,this paper proposed a scanning-free confocal profilometry based on the principle of single-pixel imaging.In the principle part,this paper firstly introduced the single-pixel imaging technology,and focused on the principle of Fourier single-pixel imaging.Different from traditional imaging techniques,the image reconstructed by single-pixel imaging reflected the field of view of the projection unit.According to this characteristic,this paper explained that the optical signal emitted by conjugated obect points and non-conjugated object points can be distinguished based on the principle of single-pixel imaging.To extract the optical signal from conjugated obect points,confocal imaging was introduced and its imaging principle was introduced.However,the traditional confocal imaging needs mechanical scanning,resulting in low imaging efficiency.To improve the imaging efficiency,we proposed a method to calibrate the conjugated mapping relationship between camera pixels and projector pixels in advance.Then combined with the principle of single-pixel imaging,the optical signal emitted by conjugated points can be extracted without mechanical scanning and formed a confocal image.Next,this paper introduced the method of calibrating the conjugated mapping relationship between camera pixels and projector pixels in detail.Finally,this paper introduced the method of reconstructing the 3D profile of the object according to the extracted optical signal emitted by the conjugated points.In the experimental part,this paper first built the system of experiment and calibrated the conjugated mapping relationship between the camera pixels and the projector pixels by the method described above.Afterwards,the 3D profiles of the diffuse reflection,translucent and metal objects were measured respectively by the proposed method.These results were compared with the reconstruction results of traditional fringe projection profilometry,showing that the 3D profiles of translucent and metal objects obtained by the proposed method proposed is more accurate than that of conventional fringe projection profilometry.Finally,the 3D profile of a small ball with known size was measured by the proposed method,demonstrating that the accuracy of the proposed method is within 0.3 mm.The scanning-free confocal profilometry based on the principle of single-pixel imaging proposed in this paper provides a new technical solution for measuring the 3D profiles of translucent and metal objects.