| 摘要 |
<p>Planar light sources (41, 39) are directed at an article (3) on either side of the optical axis so that the trace of each light beam defines a line, on either side of the optical axis, whose form is dependent on the shape of the surface of the article. To determine whether the article is in focus, the distance between the two lines is measured. To determine whether the article is in correct pitch, the distance between each line and the optical axis is measured and compared. To determine whether the article has drifted, the distances between the ends of the lines and the optical axis are measured and compared.</p> |
