Optical scanner and image forming apparatus

• US 20050093955A1
• Filed: 08/27/2004
• Published: 05/05/2005
• Est. Priority Date: 08/29/2003
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Atsuumi, Hiromichi, Hayashi, Yoshinori, Izumi, Yasutaka
• Granted Patent: US 7,271,823 B2
• Time in Patent Office: Days
• US Class Current: 347/143
• CPC Class Codes: G02B 26/123 Multibeam scanners, e.g. using multiple light sources or beam splitters

Abstract

An optical scanner has a deflector, a coupling lens, a cylindrical lens, a plate through which light to and from the deflector pass, and an optical system which condenses the light deflected on a surface to be scanned. Bundles of light beams incident on the deflector have an angle between the bundles in a rotating plane of the deflector, and expressions 0.6<(θ1max−α)/(θ2+α)<1.4, and 0.6<(θ1min−α)/(θ2+α)<1.4, are satisfied, where θ1max and θ1min are maximum and minimum average angles of incidence on the deflecting surface, θ2 is a half-view angle, and α is an angle of inclination of the plate in the rotating plane with respect to a main scanning direction.

Claims

1. An optical scanner comprising:

a plurality of light sources;

a deflector including a deflecting-reflecting surface which deflects a plurality of bundles of light beams emitted from the plurality of light sources;

a coupling lens which couples the bundles of light beams emitted from the plurality of light sources;

a cylindrical lens which directs the bundles of light beams coupled by the coupling lens to the deflector;

a parallel plate through which the bundles of light beams incident on and deflected from the deflector pass; and

a scanning-imaging optical system which condenses the bundles of light beams deflected from the deflector on a surface to be scanned, wherein

the bundles of light beams incident on the deflector have an angle between the bundles in a rotating plane of the deflector, and

expressions

0.6<

(θ

1max−

α

)/(θ

2+α

)<

1.4

and

0.6<

(θ

1min−

α

)/(θ

2+α

)<

1.4

are satisfied, where θ

1max and θ

1min are maximum and minimum values of an average angle of incidence on the deflecting-reflecting surface in the rotating plane of the deflector, θ

2 is a half-view angle corresponding to an effective writing width, and α

is an angle of inclination of the parallel plate in the rotating plane of the deflector with respect to a main scanning direction.

2. The optical scanner according to claim 1, wherein an expression

(θ

1min−

α

)/(θ

2+α

)<

1.0<

(θ

1max−

α

)/(θ

2+α

)

is satisfied.

3. The optical scanner according to claim 1, wherein the parallel plate is tilted with respect to a sub-scanning direction.

4. An image forming apparatus which forms an electrostatic latent image on an image carrier by electrophotography, comprising an optical writing unit which performs optical writing on the image carrier and includes:

a plurality of light sources;

a deflector including a deflecting-reflecting surface which deflects a plurality of bundles of light beams emitted from the plurality of light sources;

a coupling lens which couples the bundles of light beams emitted from the plurality of light sources;

a cylindrical lens which directs the bundles of light beams coupled by the coupling lens to the deflector;

a parallel plate through which the bundles of light beams incident on and deflected from the deflector pass; and

a scanning-imaging optical system which condenses the bundles of light beams deflected from the deflector on a surface to be scanned, wherein

the bundles of light beams incident on the deflector have an angle between the bundles in a rotating plane of the deflector, and

expressions

0.6<

(θ

1max−

α

)/(θ

2+α

)<

1.4

and

0.6<

(θ

1min−

α

)/(θ

2+α

)<

1.4

are satisfied, where θ

1max and θ

1min are maximum and minimum values of an average angle of incidence on the deflecting-reflecting surface in the rotating plane of the deflector, θ

2 is a half-view angle corresponding to an effective writing width, and α

is an angle of inclination of the parallel plate in the rotating plane of the deflector with respect to a main scanning direction.

5. An optical scanner comprising:

a plurality of light sources;

a deflector including a deflecting-reflecting surface which deflects a plurality of bundles of light beams emitted from the plurality of light sources;

a coupling lens which couples the bundles of light beams emitted from the plurality of light sources;

a cylindrical lens which directs the bundles of light beams coupled by the coupling lens to the deflector;

a scanning-imaging optical system which condenses the bundles of light beams deflected from the deflector on a surface to be scanned; and

a parallel plate on an optical path between the deflector and the scanning-imaging optical system, wherein

at least a pair of bundles from among the bundles of light beams incident on the deflector has an angle between each other in a rotating plane of the deflector,

positions at which the pair of bundles pass through the parallel plate are separated by a distance in a sub-scanning direction, and

the parallel plate is tilted in the sub-scanning direction so that when the pair of bundles are reflected at an incidence plane of the parallel plate, one of the pair of bundles with a wider average angle of incidence on the deflecting-reflecting surface in the rotating plane of the deflector is reflected towards the other one of the pair with a smaller average angle of incidence.

6. The optical scanner according to claim 5, wherein the parallel plate is tilted with respect to the sub-scanning direction so that the other one of the pair with the smaller average angle of incidence does not enter the scanning-imaging optical system.

7. The optical scanner according to claim 5, wherein when an expression

2θ

1max−

2α

>

θ

2

is satisfied, where θ

1max is an average angle of incidence of the one of the pair of bundles with the wider average angle of incidence, α

is an angle of inclination of the parallel plate in the rotating plane of the deflector, and θ

2 is a half-view angle corresponding to an effective scanning width.

8. An image forming apparatus which forms an electrostatic latent image on an image carrier by electrophotography, comprising an optical writing unit which performs optical writing on the image carrier and includes:

a plurality of light sources;

a deflector including a deflecting-reflecting surface which deflects a plurality of bundles of light beams emitted from the plurality of light sources;

a coupling lens which couples the bundles of light beams emitted from the plurality of light sources;

a cylindrical lens which directs the bundles of light beams coupled by the coupling lens to the deflector;

a scanning-imaging optical system which condenses the bundles of light beams deflected from the deflector on a surface to be scanned; and

a parallel plate on an optical path between the deflector and the scanning-imaging optical system, wherein

at least a pair of bundles from among the bundles of light beams incident on the deflector has an angle between each other in a rotating plane of the deflector,

positions at which the pair of bundles pass through the parallel plate are separated by a distance in a sub-scanning direction, and

the parallel plate is tilted in the sub-scanning direction so that when the pair of bundles are reflected at an incidence plane of the parallel plate, one of the pair of bundles with a wider average angle of incidence on the deflecting-reflecting surface in the rotating plane of the deflector is reflected towards the other one of the pair with a smaller average angle of incidence.