LAUSR

Roundness is a kind of form error in geometrical measurement in laboratory and industry and contributes significantly to the uncertainty of the measurement instruments using precision spheres, especially microspheres. A new radius and roundness measurement method for microspheres is proposed in this article. Using this method, not only can separate different run-out errors from the measuring results but also can obtain the true radii in different directions of the tested microsphere, which are necessary for the roundness evaluation according to ISO 1101. A new roundness measurement system has also been developed, which is mainly composed of two miniaturized Michelson interferometer (MI) systems, two elastic mechanisms, and a precision rotating stage. Repeated measurements have been performed using a ruby microsphere manufactured by Renishaw Corporation as the reference, which has a claimed diameter and a roundness of $700 ~\mu \text{m}$ and 130 nm, respectively. Experimental results show that the average radius of the tested microsphere is $349.99 ~\mu \text{m}$ with a maximum error of 65 nm and an expanded uncertainty of 94.0 nm ( $k $ = 2). The proposed method and system can be used in the precision contact measurements of parts with microcircular characteristics such as microspheres and microcylinders.