Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-12-20
2001-09-11
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S203100, C359S216100, C347S233000, C347S235000
Reexamination Certificate
active
06288818
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an optical scanning apparatus which linearly scans an image surface of a photoconductive medium in a main scanning direction by exposing the photoconductive medium to a light beam pattern so as to produce an image on the image surface. The optical scanning apparatus of the present invention is applicable to an optical writing module for use in image forming systems such as digital copiers, printers or facsimiles.
(2) Description of the Related Art
An image forming system, such as digital copier, printer or facsimile, which reproduces an image with a large size, such as A0 A1 size, is known. Generally, the image forming systems of this kind are provided with an optical scanning apparatus. The optical scanning apparatus linearly scans an image surface of a photoconductive medium in a main scanning direction by exposing the photoconductive medium to a light beam pattern so as to produce an image on the image surface. In order to achieve the reproduction of large-size copies, it is needed for the optical scanning apparatus to enlarge the effective scanning range on the image surface so as to cover the desired size.
When it is intended to enlarge the effective scanning range of the optical scanning apparatus, one may encounter some technical restrictions of optical systems in the optical scanning apparatus. Currently, the dominant optical scanning apparatus which is adapted to reproduce large-size copies employs a light-emitting diode (LED) array as the light source. The LED array can be easily configured to match the desired size. However, the LED optical scanning apparatus is bulkier and more expensive than an laser-diode (LD) optical scanning apparatus, and there is no denying that the image quality created by the LED optical scanning apparatus is lower than the image quality created by the LD optical scanning apparatus.
Hence, there is the demand for an LD optical scanning apparatus which is configured in a compact, inexpensive structure and produces a large-size image on an image surface of a photoconductive medium with an improved image quality. The LD emits a laser beam and it is widely used as the light source of the image forming system.
As disclosed in Japanese Laid-Open Patent Applications No.61-11720 and No.6-208066, there is known an LD optical scanning apparatus which linearly scans an image surface of a photoconductive medium in a main scanning direction by exposing the photoconductive medium to a light beam pattern so as to produce a large-size image on the image surface.
In order to ensure an elongated scanning range of the light beam on the image surface of the photoconductive medium so as to cover the desired size (such as A0 A1 size), the above-mentioned optical scanning apparatus utilizes a combination of two optical writing modules. Each of the two writing modules includes a rotary polygonal mirror provided as a rotary deflector, and the two polygonal mirrors are rotated independently of each other when scanning the image surface along the same scanning line. Because of the use of the two polygonal mirrors, it is difficult for the above optical scanning apparatus to synchronize the timings of the rotation of the two rotary deflectors with a suitable accuracy. This causes some distortion in the reproduced image to be produced by the above optical scanning apparatus at connecting portions between the two halves of each main scanning line.
As disclosed in Japanese Laid-Open Patent Application No.8-72308, there has been proposed an LD optical scanning apparatus that is adapted to eliminate the above problem. The optical scanning apparatus of this type employs a combination of two optical writing modules and a synchronizing mechanism. The synchronizing mechanism is provided for synchronizing the timings of the rotation of the two rotary deflectors in the writing modules. The two rotary deflectors are synchronously rotated by the mechanism when scanning the image surface along the same scanning line. However, because of the use of multiple laser beams deflected by the two rotary deflectors, it is difficult to improve the image quality at connecting portions between the two halves of each main scanning line in the image created by the above optical scanning apparatus. Further, the above optical scanning apparatus requires the synchronizing mechanism which will make the entire system configuration bulky and expensive.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide an improved optical scanning apparatus which is configured in a compact, simple and inexpensive structure and ensures good image quality at the connecting portions between the halves of each main scanning line while producing a large-size image on an image surface of a photoconductive medium.
The above-mentioned objects of the present invention are achieved by an optical scanning apparatus which scans an image surface of a photoconductive medium along a main scanning line by focusing and deflecting a light beam onto the image surface, so as to produce an electrostatic image on the image surface, the optical scanning apparatus including: a plurality of light sources which emit first and second beams; first and second coupling lens units which respectively couple the first and second beams emitted by the plurality of light sources; a rotary deflector, having pairs of mutually-opposite reflection surfaces, which deflects the first beam, coupled by the first coupling lens unit, in a first direction by one of the reflection surfaces, and deflects the second beam, coupled by the second coupling lens unit, in a second direction opposite to the first direction, by another of the reflection surfaces; and first and second imaging units which scan the image surface along a first half of the main scanning line by focusing and deflecting the first beam, deflected by the rotary deflector, into a first spot on the image surface, and scan the image surface along a second half of the main scanning line by focusing and deflecting the second beam, deflected by the rotary deflector, into a second spot on the image surface, such that the first and second halves form a substantially straight scanning line on the image surface.
According to one aspect of the present invention, the optical scanning apparatus includes only a single rotary deflector which is shared by the first and second imaging units in order to scan the image surface of the photoconductive medium along one of the first and second halves of the main scanning line by focusing and deflecting the light beam, deflected by the rotary deflector, into a spot on the image surface. The first and second halves of the main scanning line by the first and second imaging units form a substantially straight scanning line with no discontinuity on the image surface when the rotary deflector is rotated. The optical scanning apparatus of the present invention is effective in ensuring good image quality at connecting portions between the halves of each main scanning line while producing a large-size image on the image surface of the photoconductive medium. As the present invention does not require a mechanism which synchronizes the timings of the rotation of plural rotary deflectors required by a conventional optical scanning apparatus, it is possible that the optical scanning apparatus of the present invention be configured in a compact, simple and inexpensive structure.
The above-mentioned objects of the present invention are achieved by an optical scanning apparatus which scans an image surface of a photoconductive medium along a main scanning line by focusing and deflecting a light beam onto the image surface, so as to produce an electrostatic image on the image surface, the optical scanning apparatus including: a plurality of light sources which emit first and second beams; first and second coupling lens units which respectively couple the first and second beams emitted by the plurality of light sources; a rot
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Phan James
Ricoh & Company, Ltd.
LandOfFree
Optical scanning apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical scanning apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical scanning apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2483699