Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Patent
1996-03-15
1998-09-15
Le, N.
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
358471, B41J 245, G01D 1514, H04N 140
Patent
active
058086560
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an arrangement and a process for generating a matrix image, composed of individual image points, on a photosensitive recording substrate, in particular in an electrophotographic printing device.
Description of the Related Art
In electrophotographic printing, character generation has until now taken place either via a laser-scan module or via LED rows. The latter, for reasons of constructional cost, are limited to resolutions up to about 600 dpi (dots per inch). In the case of laser-scan modules, although resolutions greater than 600 dpi have already been realized, for example for film exposure units, this has only been achieved at relatively low process speeds. The limiting effect is caused here by the necessary rotational speed of the polygonal mirror or of its drive motor which, in the case of resolutions above 600 dpi and process speeds over 0.5 m/s, would have to lie far above the rotational speeds of up to 100,000 rev/min which can be realized industrially today, or far above those of about 14,000 rev/min which are economically practical.
The rotational speed of the polygonal mirror can be calculated as ##EQU1## where:
f.sub.pol rotational speed of polygonal mirror
u process speed
1/R resolution
Z number of partial beams
M number of surfaces/polygonal mirror Example: M=10, Z=1, u=1 m/s, 1/R=1200 dpi, here there results a rotational speed of about 286,000 rev/min.
To avoid high rotational speeds, attempts have been made to operate with a plurality of partial beams in parallel. Thus, in the case of using a gas laser (HeNe laser or Ar laser), an acousto-optical deflector was used which permits a plurality of partial beams to be generated independently of each other (typically up to about 10). Such a process is technically very complicated and therefore also very cost-intensive, moreover in the case of very high requirements on the resolution and process speed, the number of partial beams which can be achieved in this way is still not sufficient.
Lasers with laser-scan modules contain, apart from the deflection unit comprising a polygonal rotary mirror, scanning optics. These generally comprise collimation optics which shape the laser beam emerging from the radiation source and expand it to the necessary diameter, as well as a lens system, arranged downstream of the polygonal rotary mirror and having an f.theta. characteristic, which is primarily used to correct the pyramidal error which occurs. This lens system has no imaging properties since, in the case of laser beam printers, the radiation source is not imaged, but the laser beams are simply a means of generating an image pattern on the recording substrate under the control, for example, of the acousto-optical deflector, the laser being subject to distortions on the path from the laser source to the target, that is to say to the recording substrate. In the case of conventional laser printers, generation of the character image actually only takes place on the photoconductor, using the known deflection means, differing for example from copying devices in which the original is imaged on the photoconductor as far as possible free of distortion with the aid of optics.
U.S. Pat. No. 404,571 discloses a laser scanner for the generation of a matrix image from individual image points on a photosensitive image drum of a printer, which has a laser diode array having a plurality of individually excitable laser diodes and a polygonal rotary mirror which guides the laser beams over the surface of the image drum. In the optical path between the laser diode array and the image drum there are arranged optics having a collimator lens and an f.theta. lens. These optics serve to focus the laser beams.
Moreover, it is disclosed by European Patent Document EP-A3-0 363 347 to use a laser diode array for the generation of characters on a recording medium by means of thermal changing of its surface. This laser diode array has a plurality of laser diodes which are driven in a phase-shifted man
REFERENCES:
patent: 4404571 (1983-09-01), Kitamura
patent: 4774524 (1988-09-01), Warbus et al.
patent: 5073041 (1991-12-01), Rastani
patent: 5274394 (1993-12-01), Corona et al.
patent: 5525810 (1996-06-01), Jewell et al.
Le N.
Nguyen Thinh
Oce Printing Systems GmbH
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