On-line qualification of a micro probing system for precision length measurement of micro-features on precision parts

This paper presents on-line qualification of the effective diameter of the micro-stylus tip ball of a micro probing system for precision length measurement of micro-features on precision parts by utilizing a set of gauge blocks as the qualification artefact, which is composed by one calibrated gauge block and two supporting gauge blocks that are wrung together for a good mechanical stability. The qualification artefact is aligned side by side with the precision part to be measured for enabling a rapid transfer between the qualification step of the probe two-point tip ball diameter and the length measurement step of the precision part. Based on the proposed setup, on-line qualifications of a micro-stylus with a nominal tip ball diameter of 52.6 μm were carried out by using two methods referred to as Method A and Method B, respectively. Method A is operated by probing the opposite sides of the gap between the two supporting gauge blocks separated by the calibrated gauge block, and Method B is operated by probing the opposite sides of the calibrated gauge block supported by the two supporting gauge blocks. Intensive uncertainty analyses based on the experimental results and the geometrical models were carried out to compare the performances of these two methods. Method A, which was confirmed to be more accurate and faster than Method B, was then employed to measure the width of a micro-gap on a precision part with compensation of the determined effective two-point tip ball diameter.