Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-09-10
2001-04-24
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S204200, C359S197100, C359S201100, C359S203100, C359S241000, C347S241000
Reexamination Certificate
active
06222663
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to scanning operations used for high speed printing in which images based on text, image or graphics data or a combination of them are transferred to paper. More particularly, this invention is concerned with scanners used for high speed, high resolution, electronic printers. Such scanners generally use a polygon disk with multiple facets that are partially illuminated by a single or multi-beam light source.
BACKGROUND OF THE INVENTION
In recent years, high speed electronic printing has improved both in quality and in the speed with which the printing is accomplished. However, those skilled in this particular art are continuously searching for ways to further increase the speed of the printers. The faster the printer can operate, the more marketable it is.
Higher speeds must not adversely effect the resolution, contrast and overall quality of the printed material. Presently available printers often use scanners comprising a rotating polygon disk with partially illuminated facets to direct light at a drum having a photo sensitive layer for transferring data to be printed. While single beam scanners are used for slow speed printing, for high speed printing, a multiple beam light source is generally used. However, the duty cycle of the polygon facets in the presently available scanners operating in an under scanned mode is about 50% as a result of a minimum beam size constraint imposed by optical resolution requirements and limitations on the polygon diameter due to its high rotational speed.
In the past those skilled in the art have attempted to increase the speed of the scanner, thereby increasing the speed at which the printers operate by increasing either the rotational speed of the polygon disk, by increasing the number of polygon facets, or by increasing the number of light beams from the source. It has been found that the possibility of increasing each of these parameters is technologically limited or highly expensive. For example, increasing the speed of rotation of the scanners has been frustrated by inertial facet deformation and air friction forces. The same frustration was met in attempting to increase the number of polygon facets. As the number of light beam sources is increased, optical aberrations caused by off-axis light sources cause innumerable problems. Thus, in the art as known, attempts at increasing the speed of the scanning process may have reached a limit.
SUMMARY OF THE INVENTION
The present invention seeks to increase the speed of operation of printers which utilize polygon scanners by increasing the scanning capability of the scanners by about a factor of two. The present invention accomplishes this increase in capacity by increasing the duty cycle of the polygon by almost a factor of two. This increase in duty cycle is accomplished, in a preferred embodiment of the invention, by providing an improved polygon scanner that uses a plurality of rotating multi-faceted polygon disks, rather than a single disk. Preferably each of the disks has the same number of facets and all of the disks are mounted on the same axis. Furthermore the disks preferably rotate together about the axis.
In a preferred embodiment of the invention the facets of the two stacked polygon disks are mounted out of phase, i.e. the facets of one polygon is rotated by one-half a facet angle with respect to the other polygon.
Data modulated beams of energy such as light waves are directed at the facets and reflected therefor to scan across a photosensitive surface of a rotating drum or a belt.
In a preferred embodiment of the invention, a first beam or group of beams is directed toward one of the disks and a second beam or group of beams is directed toward the other disk. The beams which are reflected from the facets enter on a combiner in which both sets of beams are made to sweep (scan) the same line (or lines, for multibeam scanners). In order to avoid confusion, when the term “beam” is used herein, the term includes a group of multiple beams which are swept together.
Since the beams reflected from the two polygons are “out of phase,” one or the other of the beams, but generally not both, sweeps the line at any one time. Since the duty cycle of each of the beams is the same as in a polygon scanner of the prior art, utilizing two beams doubles the sweep duty cycle of the system.
In a preferred embodiment of the invention a first optical system splits a data modulated beam or beams into two sets of beams and directs the sets of beams to available facets of each of said plurality of disks. A second optical system recombines the beam components and directs the reconstructed beam onto the photo-sensitive surfaces of the drum or other photosensitive surfaces causing an image based on the data to be provided on the photosensitive surface.
More particularly, an improvement of preferred embodiments of the uses a uni-axis double disk arrangement polygon with the scanning operation performed by interlacing the beam components between an upper and a lower polygon disk. The two identical polygon disks are mounted having an angular shift (where two disks are used) of &Dgr;&phgr;=180°/N (wherein N is the number of facets) on the same motor shaft so that the useful parts of the scanning cycle are alternated between the two disks. Accordingly, since the useful duty cycle for each disk is 50% or less, there is no time overlap while scanning with the two disks; synergistically the same multi-source beam and rotational drive system is used for scanning with both disks.
A first beam splitter is preferably used to illuminate the upper polygon disk and the lower polygon disk from one or preferably a plurality of light sources. A second beam splitter is provided between the polygon and an F-Theta lens system, as known in the art, for directing the reflected data modulated beams to the optical symmetry plane of the F-Theta lens. The addition of the second beam splitter between the scanner and the F-Theta lens avoids off-axis operation of the F-Theta lens and improves the resultant image quality. The beam splitters are preferably designed so that the upper and lower channels are optically identical so that the interlaced scanning lines and focal spots are identical.
The preferred method and apparatus as described above are based on utilizing almost the entire polygon disk duty cycle by interlacing between two uni-axis polygon disks.
It should be understood that the upper and lower scanned beams alternatively sweep the moving drum or belt allowing for twice the scanning speed for the same number of parallel scanned beams.
A preferred embodiment the invention uses polarizing beam splitters for dividing an incoming beam into upper and lower channels which are P- polarized and S-polarized. The beam or beams, prior to the scanner, is preferably provided with a circular polarization or a linear polarization having equal P and S components.
In addition, it is within in the scope of the present invention to utilize methods of splitting the beam other than using polarizing beam splitters. For example, wave length selected beam splitting can be accomplished, as well many other well-known methods of optically filtering. In certain of the preferred embodiments of the invention, semi-transparent mirrors can be used, with generally decreased efficiency.
In an alternative preferred embodiment of the invention, the (two) polygon disks can be illuminated by separately generated beams rather than by single beam which is split.
While the present invention is described in the context of scanning a photoreceptor drum of a printer or the like, the scanned surface may be any surface which reacts to light, referred to herein as a photosensitive surface. Additionally, the present invention is also applicable to a document scanner. In this application, the system sweeps a surface to be read and the reflection from that surface is read by a photo-detector. In this case the beams are not data modulated, however, the light reflected from the document being scanned is modulated.
The
Amir Gideon
Breen Craig
Livne Haim
Malobani Itzhak
Plotkin Michael
Assaf Fayez
Fenster & Company Patent Attorneys Ltd.
Indigo N.V.
Schuberg Darren
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