Optical scanner and image forming apparatus

• US 7,271,823 B2
• Filed: 08/27/2004
• Issued: 09/18/2007
• Est. Priority Date: 08/29/2003
• Status: Expired due to Fees

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Atsuumi, Hiromichi, Hayashi, Yoshinori, Izumi, Yasutaka
• Primary Examiner(s): Pham; Hai
• Assistant Examiner(s): Wright; Kainoa
• Application Number:
  US10/927,226
• Publication Number:
  US 20050093955A1
• Time in Patent Office: 1,117 Days
• Field of Search: 347/233, 347241-244, 347/256, 347/260, 347/261
• US Class Current: 347/241
• 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, each of which produces a bundle of light beams;

a deflector including a deflecting-reflecting surface which deflects a plurality of the 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, wherein each individual light beam of each of the bundles of light beams from a respective one of the plurality of light sources is incident on the deflecting-reflecting surface of the deflector with an angle of incidence, wherein the average of the angles of incidence of the individual light beams of each of the bundles of light beams is an average angle of incidence for the respective bundle of light beams, and wherein the average angles of incidence for the bundles of light beams from the plurality of light sources have values between a maximum and a minimum value;

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

0.6<

(θ

1min−

α

)/(θ

2+α

)<

1.4

and

(θ

1min−

α

)/(θ

2+α

)<

1.0<

(θ

1max−

α

)/(θ

2+α

)

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 the parallel plate is tilted with respect to a sub-scanning direction.

3. 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, each of which produces a bundle of light beams;

a deflector including a deflecting-reflecting surface which deflects a plurality of the 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, wherein each individual light beam of each of the bundles of light beams from a respective one of the plurality of light sources is incident on the deflecting-reflecting surface of the deflector with an angle of incidence, wherein the average of the angles of incidence of the individual light beams of each of the bundles of light beams is an average angle of incidence for the respective bundle of light beams, and wherein the average angles of incidence for the bundles of light beams from the plurality of light sources have values between a maximum and a minimum value;

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

0.6<

(θ

1min−

α

)/(θ

2+α

)<

1.4

and

(θ

1min−

α

)/(θ

2+α

)<

1.0<

(θ

1max−

α

)/(θ

2+α

)

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.

4. An optical scanner comprising:

a plurality of light sources, each of which produces a bundle of light beams;

a deflector including a deflecting-reflecting surface which deflects the plurality of bundles of light beams emitted from the plurality of light sources, wherein each individual light beam of each of the bundles of light beams from a respective one of the plurality of light sources is incident on the deflecting-reflecting surface of the deflector with an angle of incidence, and wherein the average of the angles of incidence of the individual light beams of each of the bundles of light beams is an average angle of incidence for the respective bundle of light beams;

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, whereby one of the pair of bundles is reflected at an incidence plane of the parallel plate with a wider average angle of incidence and the other one of the pair of bundles is reflected at the incidence plane of the parallel plate with a smaller average angle of incidence,

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, the one of the pair of bundles with a wider average angle of incidence is reflected towards the other one of the pair with a smaller average angle of incidence,

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,

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.

5. 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, each of which produces a bundle of light beams;

a deflector including a deflecting-reflecting surface which deflects the plurality of bundles of light beams emitted from the plurality of light sources, wherein each individual light beam of each of the bundles of light beams from a respective one of the plurality of light sources is incident on the deflecting-reflecting surface of the deflector with an angle of incidence, and wherein the average of the angles of incidence of the individual light beams of each of the bundles of light beams is an average angle of incidence for the respective bundle of light beams;

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, whereby one of the pair of bundles is reflected at an incidence plane of the parallel plate with a wider average angle of incidence and the other one of the pair of bundles is reflected at the incidence plane of the parallel plate with a smaller average angle of incidence,

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, the one of the pair of bundles with a wider average angle of incidence is reflected towards the other one of the pair with a smaller average angle of incidence,

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,

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-imagine optical system.