Optical: systems and elements – Mirror – Plural mirrors or reflecting surfaces
Reexamination Certificate
2000-06-06
2001-03-13
Sikder, Mohammad (Department: 2872)
Optical: systems and elements
Mirror
Plural mirrors or reflecting surfaces
C359S851000, C359S852000, C359S853000, C359S854000, C359S855000, C359S877000
Reexamination Certificate
active
06199990
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to mirror assemblies in a laser scanning machine, and, more particularly, to mirror assemblies for optical path reversal in an electrophotographic machine.
2. Description of the Related Art
In order to provide a color electrophotographic printer with a same printing speed as a monochrome electrophotographic printer, it is known to substantially simultaneously produce the images on each respective electrophotographic drum for each of the colors of the printer. This is known as “tandem color laser electrophotographic architecture” and requires four laser print image lines to be respectively generated by cyan, magenta, yellow and black printheads, all of which must be packaged in a reasonably sized machine housing.
In order to minimize the size of a tandem color laser printer system, a compact laser printhead is required. Meeting this compactness objective requires folding the optical path back over top (or under) the mirror motor. To accomplish this, a 180° reversal of the optical path is achieved by a set of mirrors mounted as a pair, which are oriented at an angle of approximately 90° relative to each other. This 90° mirror set is located between the scanning polygon mirror and the first f-theta lens. In order to avoid undesirable bow and spot distortions occurring at the image plane, it is critical that the scanned laser beam pass through the desired optical axis of each lens. Thus, extreme care must be taken to physically align the source of the laser beam and/or the lens such that the scanned laser beam passes through the desired optical axis of the lens. Further, the laser beam and/or the lens must be provided with a shiftable mounting in order to perform such alignment.
What is needed in the art is a method of reversing a laser beam between a scanning mirror and a lens in an electrophotographic machine Such that a physical alignment procedure does not need to be performed on the source of the laser beam and/or the lens.
SUMMARY OF THE INVENTION
The present invention provides a method of reversing a laser beam and aligning the reversed laser beam with the optical axis of a lens without having to physically align either the source of the laser beam or the lens.
The invention comprises, in one form thereof, a method of reversing a laser beam in a machine. A pair of reflective surfaces are oriented at an angle of approximately 90° relative to each other. The laser beam is directed in a first direction such that the laser beam sequentially impinges upon a first of the reflective surfaces, reflects off of the first reflective surface, impinges upon a second of the reflective surfaces, and reflects off of the second reflective surface in a second direction substantially parallel to and opposite the first direction. A pivot axis is substantially parallel to each of the reflective surfaces. Each of the reflective surfaces is pivoted about the pivot axis by a substantially equal angle to thereby change a position of the laser beam after reflecting off of the second reflective surface.
An advantage of the present invention is that the laser beam can be aligned with the optical axis of a lens without having to physically align either the source of the laser beam or the lens.
Another advantage is that the alignment procedure can be performed quickly, resulting in minimal assembly time.
Yet another advantage is that only minimal changes occur in the length of the optical path, and hence, no translation of the reversing mirrors is required.
REFERENCES:
patent: 4266847 (1981-05-01), Menke
patent: 5341207 (1994-08-01), Tank et al.
Chee Christopher Gregory
Moore Susan Marie
Ward II Earl Dawson
Lexmark International Inc.
Sanderson Michael T.
Sikder Mohammad
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