A twin FBG probe and integration with a microhole-measuring machine for the measurement of microholes of high aspect ratios

To enhance the precision manufacture of the microholes of high aspect ratios, a fiber Bragg grating (FBG) probe with a twin fiber structure based on capillary-driven self-assembly fabrication method is developed for a micro-hole-measuring machine to do the high-precision measurement. The sensing principle of the twin FBG probe is investigated through analyzing the strain distribution within the probe under an axial or radial contact displacement. Then, the design and fabrication method of the twin FBG probe is demonstrated. To improve the accuracy of the measurement, both data processing method and measuring method are proposed. A data processing method for acquiring the triggering position with the transformation of the signal domain and multiple fitting is implemented to raise the accuracy of the triggering position. And a method for measuring the diameter of a microhole with perpendicular bisector of the chords and dichotomization scanning is utilized to enhance the determination accuracy of the diameter. Experimental and simulation results indicate that the data processing method and measuring method are robust, and the accuracy of the measurement can be improved.