Fast and high-precision roundness metrology of small cylinders with a confocal chroma-line sensor

Roundness measurements are essential for improving the product quality of cylindrical parts in industrial manufacturing. To address the challenge of precision roundness metrology for small cylindrical workpieces, which are difficult to measure accurately using traditional methods, this paper proposes a surface coordinate scanning and reconstruction method. The cross-sectional circle of a small cylindrical workpiece (with a diameter of 3 mm and length of 50 mm) is equally divided into 24 segments for scanning by a confocal chroma-line sensor. Each segment's coordinate points form an arc, the radius and center coordinates of which are fitted using the least squares method. The 24 characterized arc profiles are then stitched into an integrated roundness profile. Compared with other methods, this approach achieves higher measuring efficiency and eliminates motion error, as both the optical probe of the confocal chroma-line sensor and the measured workpiece remain static during scanning. The roundness error of the small cylindrical workpiece is evaluated to be 0.2 μm, consistent with results from commercial instruments.