Dimensional Non-contact Optical Probe Study

Three-dimensional(3D) measurement has been increasingly applied in many scientific and engineering fields,for it provides more information of objects and works more efficiently. In modern industry,products of special materials and workpieces with smooth surface require 3D non-contact measurement,which can't be implemented by traditional touch probes.As a key component of 3D non-contact measuring instruments,probe plays an important role in 3D non-contact measurement.Contactless measurement is the development trend of probe.A 3D probe is designed in this paper and experiments on probe are carried out.The novel probe is based on 2D micro-vision probe.The XY axial measurement is done by microscope,while the Z axial height is measured by probe through auto-focus.A new method of optical design is presented to solve the problem that a microscope with both large field of view(FOV) and high resolution.The probe consists a primary and a secondary imaging system which are microscopes with different magnifications.The optical system parameters such as magnification and numerical aperture(NA) are calculated from the measuring range and resolution of the probe.In order to flatten the imaging field and achieve long work distance,the type of lens is specified.After estimating the initial data of lens,we use optical design software to optimize the lens data.The optimization makes the MTF of lens close to diffraction limit.After probe is assembled and adjusted,the performance is tested.The results indicate that the resolution of lens achieves requirement that is 1μm and depth of field is closed to theoretical estimating value.The calibration of primary microscope with standard gauge shows the pixel equivalent is 0.44μm at XY plane.And the distortion at the edge of FOV is less than 0.33%.There're several factors influencing on the precision of probe.In order to seek for the influence,experiments are carried out and results are analyzed theoretically.Some formularies are given to calculate the errors resulted from illumination intensity,tilting of probe and defocus,while XY axial sizes are measured.The experiments results show that illumination, texture of surface,tilting of probe and so on have influences on Z axial measurement.While Z axial measuring,operators should try to highlight the texture details of surface and avoid probe tilting.The measurement with probe shows that the expanded uncertainty is 0.07μm(k=2) at XY axial plane,while the 2σuncertainty is less than 5μm at Z axial height.It indicates that our probe achieves requirements.The performance of our probe could be improved if using higher precision guide and better microscopes.