Method for accurate control of a light beam in phototypesetting and other applications

Apparatus for controlling a light beam to write picture elements on an image surface comprising means for writing a sufficient number of adjacent stripes, one stripe at a time, to fill the image surface, including means for deflecting the light beam across the stripe, having therein means for causing said light beam to deflect in a plurality of strokes having lengths approximately equal to the width of the stripe and means for simultaneously moving the light beam along the length of the stripe at a velocity lower than that provided thereto in said strokes,

• means for measuring two-dimensional position coordinates of the beam on the image surface, including a plurality of rulings situated in the vicinity of the writing area of the image surface, as a function of signals, which themselves are functions of positions of indicia in said rulings, and means for deflecting the light beam along a ruling while writing on the surface and for providing said signals to said means for measuring two-dimensional position coordinates;
• said means for deflecting including means for deflecting said beam across said ruling indicia, for registering the resulting signal, and for modulating the beam during said strokes responsive thereto so as to cause the writing to be positioned correctly on the image surface.