Multi-beam scanning device and image forming system and method using the same

• US 6,198,562 B1
• Filed: 12/03/1999
• Issued: 03/06/2001
• Est. Priority Date: 03/03/1999
• Status: Expired due to Term

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Hayashi, Yoshinori, Kawamura, Atsushi
• Primary Examiner(s): Schuberg, Darren
• Application Number:
  US09/454,148
• Time in Patent Office: 459 Days
• Field of Search: 359/196, 359/204, 359/205, 359/216, 359/217, 359/218, 359/219, 347/233, 347/241, 347/243, 347/244
• US Class Current: 359/204.1
• CPC Class Codes: G02B 26/123 Multibeam scanners, e.g. using multiple light sources or beam splitters

Abstract

A multi-beam scanning device includes a plurality of light sources which emit multiple beams. A plurality of coupling lenses couple the multiple beams from the light sources. A converging lens device converts the coupled beams into converging beams, the converging beams being elongated in a direction corresponding to a main scanning direction and converging only in a direction corresponding to a sub-scanning direction, at least two of the converging beams forming a difference angle therebetween. A rotary deflector has a reflection surface rotated about a fixed rotation axis. The reflection surface deflects the converging beams while the reflection surface is rotated. A scanning lens device scans an image surface in the main scanning direction at a substantially uniform velocity by focusing each deflected beam into a beam spot on the image surface. The multi-beam scanning device is configured to satisfy desired conditions to allow the multi-beam scanning device to achieve excellent optical characteristics without using a polarization beam splitter. Further, an image forming system and method which uses such a multi-beam scanning device is provided.

Claims

1. A multi-beam scanning device comprising:

a plurality of light sources which emit multiple beams, the plurality of light sources including a first light source which emits a first beam, and a second light source which emits a second beam;

a plurality of coupling lenses which couple the multiple beams from the light sources, the plurality of coupling lenses including a first coupling lens which couples the first beam, and a second coupling lens which couples the second beam;

a converging lens device which converts the coupled beams from the coupling lenses into converging beams, the converging beams being elongated in a direction corresponding to a main scanning direction and converging only in a direction corresponding to a sub-scanning direction that is substantially perpendicular to the main scanning direction, the converging beams which correspond to the first and second beams forming a difference angle that is largest among difference angles formed by all of the converging beams;

a rotary deflector having a reflection surface which is rotated about a fixed rotation axis, the reflection surface deflecting the converging beams from the converging lens device while the reflection surface is rotated; and

a scanning lens device which scans an image surface in the main scanning direction at a substantially uniform velocity by focusing each of the deflected beams from the rotary deflector into a beam spot on the image surface,

wherein said multi-beam scanning device is configured to satisfy the conditions;

2. The multi-beam scanning device according to claim 1, wherein, when first image points corresponding to outermost peripheries of one of the multiple beams are located at positions S1(+) and S1(−

) on the image surface relative to the sub-scanning direction and second image points corresponding to outermost peripheries of a different one of the multiple beams are located at positions S2(+) and S2(−

) on the image surface relative to the sub-scanning direction, said positions of said first and second image points satisfy the condition;

3. The multi-beam scanning device according to claim 1, wherein, when first image points corresponding to outermost peripheries of one of the multiple beams are located at positions M1(+) and M1(−

) on the image surface relative to the main scanning direction and second image points corresponding to outermost peripheries of a different one of the multiple beams lie at positions M2(+) and M2(−

) on the image surface with respect to the main scanning direction, said positions of said first and second image points satisfy the condition;

4. The multi-beam scanning device according to claim 1, wherein the plurality of light sources include the first light source and the second light source.

5. The multi-beam scanning device according to claim 1, wherein the scanning lens device comprises a single scanning lens element.

6. The multi-beam scanning device according to claim 1, wherein the scanning lens device includes at least two scanning lens elements.

7. The multi-beam, scanning device according to claim 1, wherein the scanning lens device includes at least one scanning lens element which is shifted and/or tilted within a scanning plane that is substantially perpendicular to the rotation axis.

8. A multi-beam scanning device comprising:

a plurality of light sources which emit multiple beams, the plurality of light sources including a first light source which emits a first beam, and a second light source which emits a second beam;

a plurality of coupling lenses which couple the multiple beams from the light sources, the plurality of coupling lenses including a first coupling lens which couples the first beam, and a second coupling lens which couples the second beam;

a converging lens device which converts the coupled beams from the coupling lenses into converging beams, the converging beams being elongated in a direction corresponding to a main scanning direction and converging only in a direction corresponding to a sub-scanning direction that is substantially perpendicular to the main scanning direction, the converging lens device including a substantially cylindrical lens, the converging beams which correspond to the first and second beams forming a difference angle that is largest among difference angles formed by all of the converging beams;

a rotary deflector having a reflection surface which is rotated about a fixed rotation axis, the reflection surface deflecting the converging beams from the cylindrical lens while the reflection surface is rotated, the reflection surface spaced at a constant distance from the rotation axis; and

a scanning lens device which scans an image surface in the main scanning direction at a substantially uniform velocity by focusing each of the deflected beams from the rotary deflector into a spot on the image surface,

wherein said multi-beam scanning device is configured to satisfy the conditions;

9. The multi-beam scanning device according to claim 8, wherein, when first image points corresponding to outermost peripheries of one of the multiple beams are located at positions S1(+) and S1(−

) on the image surface relative to the sub-scanning direction and second image points corresponding to outermost peripheries of a different one of the multiple beams are located at positions S2(+) and S2(−

) on the image surface relative to the sub-scanning direction, said positions of said first and second image points satisfy the condition;

10. The multi-beam scanning device according to claim 8, wherein, when first image points corresponding to outermost peripheries of one of the multiple beams are located at positions M1(+) and M1(−

) on the image surface relative to the main scanning direction and second image points corresponding to outermost peripheries of a different one of the multiple beams lie at positions M2(+) and M2(−

) on the image surface with respect to the main scanning direction, said positions of said first and second image points satisfy the condition;

11. The multi-beam scanning device according to claim 8, wherein the plurality of light sources include the first light source and the second light source.

12. The multi-beam scanning device according to claim 8, wherein the scanning lens device comprises a single scanning lens element.

13. The multi-beam scanning device according to claim 8, wherein the scanning lens device includes at least two scanning lens elements.

14. The multi-beam, scanning device according to claim 8, wherein the scanning lens device includes at least one scanning lens element which is shifted and/or tilted within a scanning plane that is substantially perpendicular to the rotation axis.

15. A multi-beam scanning device comprising:

a plurality of light source means for emitting multiple beams, the plurality of light source means including a first light source which emits a first beam, and a second light source which emits a second beam;

a plurality of coupling lens means for collimating the multiple beams from the light source means, the plurality of coupling lens means including a first coupling lens which couples the first beam, and a second coupling lens which couples the second beam;

converging lens means for converting the coupled beams from the coupling lenses into converging beams, the converging beams being elongated in a direction corresponding to a main scanning direction and converging only in a direction corresponding to a sub-scanning direction that is substantially perpendicular to the main scanning direction, the converging beams which correspond to the first and second beams forming a difference angle that is largest among difference angles formed by all of the converging beams;

rotary deflector means having a reflection surface which is rotated about a fixed rotation axis, for deflecting the converging beams from the converging lens means while the reflection surface is rotated; and

scanning lens means for scanning an image surface in the main scanning direction at a substantially uniform velocity by focusing each of the deflected beams from the rotary deflector into a beam spot on the image surface,

wherein said multi-beam scanning device is configured to satisfy the conditions;

16. An image forming system comprising:

a multi-beam scanning device; and

a photoconductive medium having an image surface, wherein the photoconductive medium is electrostatically charged, an electrostatic image is formed on the photoconductive medium when subjected to a multi-beam scanning by the multi-beam scanning device, and the electrostatic image is transformed into a viewable image by a development of the electrostatic image using a toner,

said multi-beam scanning device including;

a plurality of light sources which emit multiple beams, the plurality of light sources including a first light source which emits a first beam, and a second light source which emits a second beam;

a plurality of coupling lenses which couple the multiple beams from the light sources, the plurality of coupling lenses including a first coupling lens which couples the first beam, and a second coupling lens which couples the second beam;

a converging lens device which converts the coupled beams from the coupling lenses into converging beams, the converging beams being elongated in a direction corresponding to a main scanning direction and converging only in a direction corresponding to a sub-scanning direction that is substantially perpendicular to the main scanning direction, the converging beams which correspond to the first and second beams forming a difference angle that is largest among difference angles formed by all of the converging beams;

a rotary deflector having a reflection surface which is rotated about a fixed rotation axis, the reflection surface deflecting the converging beams from the converging lens device while the reflection surface is rotated; and

a scanning lens device which scans the image surface of the photoconductive medium in the main scanning direction at a substantially uniform velocity by focusing each of the deflected beams from the rotary deflector into a spot on the image surface,

said multi-beam scanning device being configured to satisfy the conditions;

17. A method of forming an image on an image surface of a photoconductive medium in an image forming system, the method comprising the steps of:

providing a multi-beam scanning device including a plurality of light sources which emit multiple beams, the plurality of light sources including a first light source which emits a first beam, and a second light source which emits a second beam, a plurality of coupling lenses which couple the multiple beams from the light sources, the plurality of coupling lenses including a first coupling lens which couples the first beam, and a second coupling lens which couples the second beam, a converging lens device which converts the coupled beams from the coupling lenses into converging beams, the converging beams being elongated in a direction corresponding to a main scanning direction and converging only in a direction corresponding to a sub-scanning direction that is substantially perpendicular to the main scanning direction, the converging beams which correspond to the first and second beams forming a difference angle that is largest among difference angles formed by all of the converging beams, a rotary deflector having a reflection surface which is rotated about a fixed rotation axis, the reflection surface deflecting the converging beams from the converging lens device while the reflection surface is rotated, and a scanning lens device which scans the image surface of the photoconductive medium in the main scanning direction at a substantially uniform velocity by focusing each of the deflected beams from the rotary deflector into a spot on the image surface, said multi-beam scanning device being configured to satisfy the conditions (1) θ

²β

²·

A/L<

0.0005; and

(2) Ø

>

tan<sup>−

1</sup>[(Ø

1+Ø

2)/2L1], where A is a constant distance between the reflection surface and the rotation axis, θ

is the largest difference angle measured in terms of radians, Ø

1 is an effective diameter of the first coupling lens through which the first beam passes, Ø

2 is an effective diameter of the second coupling lens through which the second beam passes, β

is a transverse magnification of the scanning lens device in the sub-scanning direction, L1 is the smaller one of a first distance between the first coupling lens and the reflection surface and a second distance between the second coupling lens and the reflection surface; and

L is a distance between the reflection surface and the image surface; and

forming an electrostatic image on the image surface of the photoconductive medium by subjecting the photoconductive medium to a multi-beam scanning of said multi-beam scanning device, in order to transform the electrostatic image into a viewable image by a development of the electrostatic image using a toner.