Research On Microscale Dimensional Measurement Using Four Cores Fiber Bragg Grating Probe

With the development of modern precision manufacturing, the requirement of themicro devices with characteristics of complexity and high aspect ratio is increasingurgently. However, conventional dimension measurement can hardly be used to inspectthe manufacturing quality of these devices. Relatively backward measurement methodshave seriously restricted the development of precision manufacturing technology. Atpresent, micro coordinates measuring machine with new tactile probe sensor hasbecome one of the most effective means in high-precision measurement of micro partswith high aspect ratio. But conventional probes, have problems such as shadowingeffect, limited probing space and forces, absence of multi-dimensional tactile sense andmulti-decoupling capacity, that hardly meet the requirements of dimensionalmeasurement on precision machining.For the above problems, a probe based on fiber grating is proposed, this probe isfabricated by four cores fiber and has the sensitivity on both axial and radial contactdisplacement, and it also has decoupling capacity. In this paper, sensing mechanism,sensing system, simulation methods, packaging and manufacturing technique of fourcores fiber grating probe is thoroughly investigated, and performance of the probe isverified by experiments. The main research works are followings:1. Studying the sensing mechanism of four cores fiber grating probe. A sensingmodel of four cores fiber grating probe is established to analyze the relationship ofcontact displacement, probe parameters and the reflection spectra of the fiber grating.The effects of environment perturbation on the probe have been evaluated by ANSYS.Random vibration model and fluid-solid coupling model have been built to analyze theinfluence of basement vibration and air flow, and then the rationality of the design ofprobe structure can be verified.2. Design sensing system and research of simulation methods. According to thecharacteristics and application of the probe, four cores fiber grating sensing system isdesigned including by broadband light source, optical signal amplifier, measurementsystem based on optical wavelength and optical power interrogation system, the systemalso have been optimized by OptiSystem. Then a modified transmission matrix methodis utilized to run the simulation of the sensing system. The model of optical powerinterrogation system is built to analyze its best matched initial condition to make itworking in linear mode.3. Research on packaging and manufacturing technology of four cores fiber gratingprobe. Packaging of the fan-out of four cores fiber grating probe by erosion-coupling method is experimentally studied, and a model is built using BeamPROP to analyze theinsertion loss caused by the alignment errors. Then, a three-dimensional opticalwaveguide manufactured by femtosecond Laser is utilized to package the fan-out offour cores fiber grating probe to achieve low-loss transmission among differentchannels of the probe. Inscribing grating on four cores fiber by the method ofPhase-Mask technique using an UV excimer Laser exposure and manufacturing spheretip of the probe by the fusion method using an Electric Discharge Machining (EDM) areinvestigated respectively to make a four cores fiber grating probe.4. Performance verification experiments. Rotation and tilt calibration experiment isconducted to match the coordinate system of the probe and the measurement system.Then, performance of the four cores fiber grating probe interrogated by opticalwavelength and power sensing system are experimentally tested. Experiments resultsindicate that a radial sensitivity of6.41pm/μm, axial sensitivity of24.87pm/μm, andthree-dimensional measurement decoupling capacity is verified; a radial measuringrange of±5μm with a resolution of30nm, an axial measuring range of3μm with aresolution of8nm, a radial tactile stability of65nm within1minutes and98nm within10minutes, and a axial tactile stability of19nm within1minutes and28nm within10minutes can be achieved by an optimized optical power interrogation system working inlinear and sensitive mode. A micro hole in an injection plate of a rocket engine ismeasured by four cores fiber grating probe, and the measurement uncertainty isestimated. Experiment results indicate that the mean diameter of the hole is267.3μmwith an expanded uncertainty of0.4μm for k=2.The research of this paper enriches the knowledge of existing probes. It provides anew method for micro-scale dimensional measurement.