Measurement of micropore by resonant probe with microsphere

A micro–nano coordinate measuring machine (CMM) is an instrument for high-precision measurement of micro-precision parts. The top of its probe is a microsphere with a diameter of tens to hundreds of micrometres. When the probe microsphere touches the part for measurement, its accuracy is affected by the surface morphology of the microsphere. A tuning fork resonant probe used for micro–nano CMMs is used to measure the contour of the micropore in automotive fuel injection nozzles in this study. Combined with the self-made optical fiber microsphere cross-sectional circle parameters at the top of the tuning fork probe, precise measurement of micropore diameter and roundness is achieved. During the experiment, the microsphere and micropore were measured by two independent systems, and thus, the error caused by the initial measurement angle of the microsphere and micropore is evaluated. The experimental results indicate that the measured micropore diameter is 194.542 µm and the roundness is 2.551 µm. The error caused by the initial measurement angle evaluated by the cubic Hermitian interpolation method can be ignored relative to the measurement results. The micropore structure parameters are precisely measured by the resonant probe combined with the morphology information of its top microsphere in this study, providing a research method for improving the measurement accuracy of micro–nano CMMs by combining microsphere morphology features.