| 摘要 |
<p>A register mark and a system for bringing a pair of register marks into alignment is disclosed. A first two-dimensional register mark (Fig. 1) comprises a plurality of dots of a first frequency, and a second two-dimensional register mark (Fig. 2) comprises a plurality of dots of a second, generally higher frequency. When the first and second register marks are overlaid, an interference pattern resulting from the difference in frequency is observed. The first and second register marks are in alignment when the interference pattern produces a maximum bright spot in the center of the register mark. A small relative movement of the first and second register marks results in a larger relative movement of center of the bright spot. The position of the bright spot indicates which direction and how much to move the second register mark in order to achieve image registration. It is preferred that the frequency of dots in each register mark is warped with distance from the center of the mark. The frequency of the dots of the second register mark is also warped with distance from the center, but overall has a generally higher frequency of dots as compared to the first register mark. In the resulting interference pattern the bright spot occurs unambiguously when the two register marks are in alignment. At misalignments of more than one dot width, the bright spot breaks up so that the overlaid register marks may serve as quick visual check of proper alignment. The register marks may be in a single dimension along a line. <IMAGE></p> |
