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High-Speed And High-Resolution Laser Printer

IP.com Disclosure Number: IPCOM000101263D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 4 page(s) / 142K

Publishing Venue

IBM

Related People

Leas, JM: AUTHOR [+2]

Abstract

Current laser printers scan with a single laser shining on a rotating drum and discharging photoconductors on the drum in a pattern representing the figure or text to be printed. The beam is rapidly swept across the drum by a facet of a rotating polygonal mirror. Each sweep prints one line. For typical resolution, at least 300 dots per inch (dpi) are needed. Print speed depends on factors, such as mirror rotation rate, the number of facets on the mirror, drum rotation rate, and the resolution specifications. Print speed is limited by the fact that the laser forms one spot at a time.

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High-Speed And High-Resolution Laser Printer

       Current laser printers scan with a single laser shining
on a rotating drum and discharging photoconductors on the drum in a
pattern representing the figure or text to be printed. The beam is
rapidly swept across the drum by a facet of a rotating polygonal
mirror.  Each sweep prints one line.  For typical resolution, at
least 300 dots per inch (dpi) are needed.  Print speed depends on
factors, such as mirror rotation rate, the number of facets on the
mirror, drum rotation rate, and the resolution specifications.  Print
speed is limited by the fact that the laser forms one spot at a time.

      This article provides a design for a faster, higher resolution,
simpler, and more reliable laser printer.   The rotating mirror is
eliminated.  Semiconductor chips, each with an array of lasers with
the beams aimed perpendicularly to the surface of the chip form the
image on the rotating drum.  The page is created as the drum rotates
under the lasers.

      Referring to Figs. 1 and 2, a rotating drum 11 is placed in
close proximity to a circuit board 13 which extends across the entire
width of the drum.  On the circuit board 13, a series of chips with a
two- dimensional array of lasers is mounted.  The lasers emit
perpendicular to the surface of the chips 13.  Multiple beams from
the laser arrays form all the spots needed to create a line.
Subsequent lines of the page are illuminated as the drum rotates.

      While it is known that printers may also be fabricated by
aligning standard bar lasers or bar light-emitting diodes above one
edge of the drum, in such a configuration, horizontal resolution is
limited to a required spacing between the light emitters.  This
restriction on resolution can be ameliorated by the use of the
two-dimensional arrays as suggested in this article.

      The resolution can be improved by staggering the columns of
lasers on the laser array chips.  This allows spots on the drum to be
more closely packed than are lasers on the chips.  With a staggered
array, flash timing must be electronically correlated with drum
rotation to produce a line.  Staggering can be achieved by tilting
each chip 15 with respect to the direction of motion of the drum 11.

      In addition to improving resolution, tilting also eliminates a
concern that there might be gaps in the printing corresponding to the
edges of the chips.

      This concern arises since the lasers cannot be formed too close
to the edges of a chip and since chips must have a small space
between them to account for thermal expansion. A tilted row of chips
with a two-dimensional array of lasers can accommodate the needed
chip-edge gaps while the space between spots on the drum remains
small.

      While each individual chip can be tilted, staggering can most
simply be accomplished by mounting the printed circuit board at an
angle above the drum....