Dr. Ing. Rudolf Hell Gmbh

John A Kennedy, Jr

Walter I Hansen

A laser diode imagesetter having multiple resolution operating modes, includes means for stabilizing the optical output power from the semiconductor laser diode during the scan trace interval across a photosensitive material so as to maintain a high extinction ratio for the laser diode even when its driving current is changed to a different level in order to operate the imagesetter at a different resolution mode.

Laser diode output power stabilization in a laser imagesetter

Image setting apparatus is disclosed for producing two-dimensional image on photosensitive material. The apparatus includes a device for transporting the photosensitive material past an imaging line to provide a first dimension of the two-dimensional image, a controllable source of electromagnetic radiation (EMR) for producing a modulated EMR beam, a scanning device for converting the EMR beam into a scanning beam, and a scan lens in the path of the scanning beam to focus the beam spot on the photosensitive surface. The beam spot thus moves repeatedly along the imaging line to provide the other dimension of the two-dimensional image. According to the invention, the EMR source is controlled to switch the EMR beam on and off at a frequency which is adjusted to compensate for variations in the scanning speed of the beam spot along the imaging line.

Circuit for modulating a scanning beam in a text and graphics image

Image setting apparatus is disclosed for producing two-dimensional images on photosensitive material. The apparatus includes a device for transporting the photosensitive material past an imaging line to provide a first dimension of the two-dimensional image; a light source for producing a modulated beam of light; a scanning device for converting the light beam into a scanning beam; and a scan lens in the path of the scanning beam such that a focused beam spot moves linearly and repeatedly across the photosensitive material along the imaging line to provide the other dimension of the two-dimensional image. According to the invention, the device for transporting the photosensitive material past the imaging line includes a driving roller in contact with the photosensitive material, a stepper motor mechanically coupled to rotate the driving roller and a controllable circuit, connected to the coil of the stepper motor, for incrementing the motor in microsteps upon command. The current through the motor coils is so controlled that the stepper motor may be advanced at least two thousand substantially equal microsteps per revolution, thereby permitting correction of small repeatable errors in the advance of the photosensitive material and permitting the motor to be advanced in accordance with any desired image resolution.

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Ridge, NY, United States of America

John A Kennedy, Jr