Browse Prior Art Database

Scan Angle Multiplying and Twisted Mirrors for Bar Code Scanner or Laser Printer

IP.com Disclosure Number: IPCOM000107305D
Original Publication Date: 1992-Feb-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 6 page(s) / 232K

Publishing Venue

IBM

Related People

Cato, RT: AUTHOR

Abstract

This article describes an algorithm for designing curved mirrors to be used in flying spot scanners or laser printers. It is well known that curved mirrors can be used to multiply the scan angle of a scanning laser beam (much more than a planar mirror); however, it is not known how to do this without distorting the shape and size of the "flying spot" (of non-paraxial beams). When planar mirrors are used, the maximum scan angle multiplication possible is two. The mirrors described here can have scan-angle multiplications of 4 or even higher. The algorithm described here does this with the added feature of allowing the shape of the path of the "flying spot" or focal point to be controlled. In scanners this would allow better utilization of the depth of field.

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Scan Angle Multiplying and Twisted Mirrors for Bar Code Scanner or Laser Printer

       This article describes an algorithm for designing curved
mirrors to be used in flying spot scanners or laser printers.  It is
well known that curved mirrors can be used to multiply the scan angle
of a scanning laser beam (much more than a planar mirror); however,
it is not known how to do this without distorting the shape and size
of the "flying spot" (of non-paraxial beams).  When planar mirrors
are used, the maximum scan angle multiplication possible is two. The
mirrors described here can have scan-angle multiplications of 4 or
even higher.  The algorithm described here does this with the added
feature of allowing the shape of the path of the "flying spot" or
focal point to be controlled.  In scanners this would allow better
utilization of the depth of field.  In laser printers it would allow
the laser's focal point to closer match the shape of the medium it is
scanning.

      The algorithm described here designs "acylindrical" mirrors.
These are mirrors that would be produced if the contour of an
aspherical lens were extruded in one dimension, in the same way that
cylindrical lenses are spherical lenses extruded in one dimension.
This approach simplifies the algorithm in that the majority of the
calculations are done in two-dimensional space.  When the contour of
the mirror is obtained, the acylindrical mirror is extruded from the
contour.

      Classical cylindrical surfaces are used for the starting point.
A model of the scanner optics is set up that establishes the spatial
relationships of the planar faced deflector, the scan-angle
multiplying mirror (SAMM), and the desired PATH of the "flying spot".
An initial radius is chosen for the cylindrical starting segment of
the SAMM.  This radius is what ultimately determines the scan-angle
multiplication factor of the SAMM.  Trial and error has shown that it
is best to use a rather large value (300 mm).  The path of the spot
can be any curve that is constantly bending in one direction (not
necessarily constant radius, but not bending back on the opposite
direction).  For convenience, a large radius circle was used.  (A
line can be used.)

      The focal point of the scanning laser beam is established at
the start of the desired path of the spot. From this point two rays
are drawn back to the edges of the spherical starting segment of the
SAMM.  The distance between edges of the starting segment of the SAMM
is established from experience with focused laser beams; we have in
the past focused an approximately 3 mm diameter laser beam to form
the "flying spot".  Hence, the distance between edges of the starting
segment of the SAMM is established at 3 mm.  The intersection point
of the top ray and the starting segment of the SAMM is called the 1ST
PIVOT POINT.

      The two rays from the spot to the SAMM are then reflected off
the SAMM using conventional spherical optical...