Research And Application Of Matched Filters In BTC Measuring Lenses

The demand for accuracy on optical image measurement is higher and higher due to the modern industrial development. Compares to traditional optical system, Bi-Telecentric(BTC) optical system has notable features including low distortion and large depth of field, which was effectively applied in precision measuring geometric variables in recent years. However, when performing ultra-precision measurement, there are also some limitations. For example, in order to obtain a large depth of field, the power of optical resolution will be limited. In addition, when measuring geometry, confocal on the boundary tends to drift due to the size of the object, the slope of the signal on the boundary will therefore change, limiting the precision(micron or even submicron) of boundary detection. Due to this problem, it is important to perform a detailed study on this kind of system’s boundary condition, in practical engineering application, it could provide a way to compensate the depth of residual.The theoretical and experimental studies described above are based on a due telecentric optical lens used on an ultra-precision optical grinding machine system. This paper is based on the Fourier transform theory, combined with related simulation software as major mathematical modeling tools to create experimental system simulation and experimental study. The main work can be divided into follows:First of all, by reading through extensive literature survey and in-depth study, reviewing the current application features of telecentric optical system in industrial measurement and possible ways to improve, then provide an in-depth analysis on the structure of the BTC optical system.Secondly, targeting BTC optical system in ultra-precision optical system, design a function specifically for measuring precision of contour such as diameter measurement, and output an evaluation criteria for the system. Analysis calculate the coherent transfer function of this optical system; non-coherent transfer function; modulate coherent function and cutoff frequency of the system.Thirdly, On the basis of determining the implementation of the double telecentric optical system wave filter, simulating and designing the wave filter to improve measurement performance of this system from two aspects: Firstly, for diffraction-limited problem with this system, combined with the optical ultra-resolution technology that is breaking through diffraction limit and the traditional ring-type super-resolution amplitude pupil filter, to achieve its ultimate resolution break through; Secondly, for accurate boundary measurement such as detecting diameter, designing and optimizing boundary detection wave filter, analyzing different impact on accuracy when measuring different diameter caused by varies of pupil size and wave filter, along with simulation and experiment.Super-resolution pupil filters are applied on BTC image measurement system so that the limitation of the maximum resolution is increased by 3 lp/mm. In the diameter measurement for BTC image measurement system, it determines diameter measurement’s confocal point under different pupil and different filter; while providing different diameter measurement, it also provides drift of confocal point under specific filter pore size.