Laser photocomposition system and method

Abstract

Type characters are formed on a photo-sensitive surface by projecting a laser beam directly onto the photo-sensitive surface while moving the beam rapidly upwardly and downwardly, moving the beam steadily in a horizontal direction, and blanking the beam at selected times during the vertical movements. The horizontal movement gives horizontal dimensions to the characters and proportionally spaces them from one another to form composed lines of characters. The blanking of the beam is accomplished by providing a barrier near the optical path of the beam, and using an acousto-optic modulator to rapidly deflect the beam out of its path and against the barrier. A programmed computer is used to store information regarding the start and the stop of each blanking interval for each vertical stroke forming each of the characters of a substantial number of fonts of characters. An optical-electric feedback system is used to indicate the precise position of the laser beam relative to the photo-sensitive surface. This feedback arrangement includes a beam splitter for capturing a portion of the laser beam and projecting it onto an optical grating which is located in a fixed spatial relationship to the photo-sensitive surface. A photo-electric detector is used to detect the position of the laser beam and provide an electrical signal to time the operation of the vertical scanning and blanking devices. The speed of the machine preferably is increased by detecting the height of the characters in a line to be composed and, if the maximum height of any character is below a pre-determined level, then reducing the vertical scan distance traveled by the laser beam while increasing the horizontal and vertical scan rates.