| 摘要 |
In an apparatus for forming an image in a radiation sensitive layer (6) and comprising an array (16) of light valves (18-22) and a corresponding array (40) of converging elements (46) the positions of radiation spots (204) formed by these arrays (16,40) are monitored and their positions determined by means of a sensing module, which is arranged below the plane of the spots. The module is provided with a slit plate (182) showing pair of slits (186,188) and with position encoders (190,192,194,196) and the plate carrying the converging elements is provided with tracking configurations (171,173,175,177) and alignment marks (198).
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