提高光栅莫尔条纹信号质量的滤波方法

Filtering method of improving quality of grating Moiré fringe

针对莫尔条纹信号的质量问题提出一种相位差滤波法。将指示光栅上四场裂相方式中每场细分为多个不同相位的行组合,利用行组合间的不同相位排列关系来消弱高次谐波的分量,从而提高莫尔条纹信号的质量。首先,介绍了莫尔条纹的傅里叶级数表达式,对莫尔条纹的各次谐波特性进行了分析。然后,以指示光栅的图案设计为例,阐明该滤波方法消除二次、三次和四次谐波的过程。最后,通过仿真和实验,验证了该滤波方法对削弱高次谐波的有效性。实验结果表明,该滤波方法可将莫尔条纹信号的三次谐波削弱4.9%,在20μm内测量精度提高了0.5μm。另外,该方法仅改变指示光栅的刻划图案,不增加制造成本和体积,实用性强,易于工业生产。

A filtering method,phase-difference filtering,was presented to improve the quality of grating Moiré fringe.Each field of the 4 field scanning reticle was devided into multi-lines with different phases to suppress the high harmonic generations and to improve the signal quality of the Moire fringe.Firstly,the Fourier series expression of Moiré fringe was introduced and various harmonic generations of the Moiré fringe were analyzed.Then,the filtering method to eliminate the second,third and fourth harmonic generations was illustrated with the designed grating patterns.Finally,the validity of the method to inhibit the high harmonic generations was verified through simulations and experiments.Experimental results indicate that the third harmonic generation of the Moiré fringe signal can be reduced by 4.9% and the accuracy can be improved by 0.5 μm with the period of 20 μm.The method is effective,low cost,without increasing the system size and easy to be used in industrial productions.