Device adapted for adjustment of scan position of light beam

• US 20040223195A1
• Filed: 02/17/2004
• Published: 11/11/2004
• Est. Priority Date: 02/17/2003
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Nomura, Yujiro
• Granted Patent: US 7,652,786 B2
• Time in Patent Office: Days
• US Class Current: 358/509
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 26/085 the reflecting means being moved or deformed by electromagnetic means
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G02B 26/105 with one or more pivoting mirrors or galvano-mirrors G02B26/101 takes precedence
• CPC Class Codes: G06K 15/1219 Detection, control or error compensation of scanning velocity or position, e.g. synchronisation G06K15/1223 takes precedence
• CPC Class Codes: H04N 1/1135 for the main-scan only
• CPC Class Codes: H04N 1/12 using the sheet-feed movement or the medium-advance or the drum-rotation movement as the slow scanning component, e.g. arrangements for the main-scanningsheet-feed movement by translatory movement of a flat picture-bearing surface H04N1/1008; main-scanning using oscillating or rotating mirrors H04N1/113; using multi-element arrays H04N1/19

Abstract

An optical scanning device 65 is adapted to bring a deflector mirror plane 651 into independent pivotal motions about a first axis and a second axis perpendicular to each other. A mirror driver section including a first axis driver and a second axis driver is so controlled as to bring the deflector mirror plane 651 into pivotal motion about the first axis thereby deflecting a light beam L for scanning along a main scan direction. On the other hand, the deflector mirror plane 651 is pivotally moved about the second axis thereby to adjust the scanned beam L for its position on a photosensitive member 2 with respect to a subscan direction. Thus, even if the scanned beam is deviated from a reference scan position with respect to the subscan direction due to component tolerances or assembly errors, such a deviation can be corrected.

Claims

What. What is claimed is:

1. An exposure device for scanning a light beam on a surface of a latent image carrier along a main scan direction, comprising:

a light source section for emitting a light beam;

an inner movable member having a deflector mirror plane;

an outer movable member for pivotally supporting said inner movable member about a first axis;

a support member for pivotally supporting said outer movable member about a second axis different from said first axis; and

a mirror driver section for driving said inner movable member into pivotal motion about said first axis and said outer movable member into pivotal motion about said second axis,

wherein said mirror driver section drives said deflector mirror plane into pivotal motion about a main-scan deflection axis defined by either one of said first axis and said second axis thereby scanning the light beam from said light source along said main scan direction, and also drives said deflector mirror plane into pivotal motion about a subscan direction axis defined by the other axis thereby adjusting said scanned beam for its position with respect to said subscan direction different from said main scan direction.

2. An exposure device as claimed in claim 1, wherein said first axis is said main-scan deflection axis, whereas said second axis is said subscan deflection axis.

3. An exposure device as claimed in claim 1, wherein said first axis is said subscan deflection axis, whereas said second axis is said main-scan deflection axis.

4. An exposure device as claimed in claim 1, wherein said light source section emits a single light beam.

5. An exposure device as claimed in claim 1, wherein said light source section emits plural light beams parallel with one another.

6. An exposure device as claimed in claim 1, wherein said inner movable member, said outer movable member and said support member are formed of monocrystalline silicon.

7. An exposure device as claimed in claim 1, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis in a resonant mode.

8. An exposure device as claimed in claim 1, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis by way of an electrostatic attractive force.

9. An exposure device as claimed in claim 1, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said subscan deflection axis in a non-resonant mode.

10. An exposure device as claimed in claim 1, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said subscan deflection axis by way of an electromagnetic force.

11. An exposure device as claimed in claim 1, further comprising:

a first optical system disposed between said light source and said deflector mirror plane and operative to converge the light beam from said light source in said subscan direction thereby linearly focusing the light beam on said deflector mirror plane; and

a second optical system disposed between said latent image carrier and said optical scan means and operative to focus the scanned beam from said optical scan means on the corresponding latent image carrier.

12. An image forming apparatus comprising:

a latent image carrier;

exposure means having the same arrangement as the exposure device as claimed in claim 1;

and

control means for controlling said exposure means thereby irradiating the scanned beam on said latent image carrier to form a latent image thereon while adjusting the scanned beam for its position on said latent image carrier with respect to said subscan direction.

13. An image forming apparatus as claimed in claim 12, further comprising storage means for storing deviation information indicative of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said exposure means based on said deviation information stored in said storage means.

14. An image forming apparatus as claimed in claim 12, further comprising first detection means for sensing an amount of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said exposure means based on said amount of light deviation determined by said first detection means.

15. An image forming apparatus as claimed in claim 12, further comprising:

development means for forming a toner image by developing the latent image formed on said latent image carrier;

transfer means for forming a color image by superimposing the toner images on top of each other on a transfer medium, the toner images formed on said latent image carriers; and

storage means for storing correction information necessary for correcting registration deviations,

wherein said control means controls said exposure means based on said correction information stored in said storage means.

16. An image forming apparatus as claimed in claim 12, further comprising:

development means for forming a toner image by developing the latent image formed on said latent image carrier;

transfer means for forming a color image by superimposing the toner images on top of each other on a transfer medium, the toner images formed on said latent image carriers; and

second detection means for obtaining information on the registration deviations,

wherein said control means controls said exposure means based on said detection information obtained by said second detection means.

17. An image forming apparatus comprising:

a plurality of latent image carriers;

exposure means having the same arrangement as the exposure device as claimed in claim 1;

and

control means for controlling said exposure means thereby irradiating the scanned beam on said latent image carrier to form a latent image thereon while selectively switching the scanned beam to any one of said plural latent image carriers for irradiation with said scanned beam.

18. An image forming apparatus as claimed in claim 17, wherein said control means controls said exposure means thereby accomplishing switchable selection of a latent image carrier and adjusting the scanned beam for its position on the selected latent image carrier with respect to said subscan direction.

19. An image forming apparatus as claimed in claim 17, further comprising storage means for storing deviation information indicative of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said exposure means based on said deviation information stored in said storage means.

20. An image forming apparatus as claimed in claim 17, further comprising first detection means for sensing an amount of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said exposure means based on said amount of light deviation determined by said first detection means.

21. An image forming apparatus as claimed in claim 17, further comprising:

development means for forming a toner image by developing the latent image formed on said latent image carrier;

transfer means for forming a color image by superimposing the toner images on top of each other on a transfer medium, the toner images formed on said latent image carriers; and

storage means for storing correction information necessary for correcting registration deviations,

wherein said control means controls said exposure means based on said correction information stored in said storage means.

22. An image forming apparatus as claimed in claim 17, further comprising:

development means for forming a toner image by developing the latent image formed on said latent image carrier;

transfer means for forming a color image by superimposing the toner images on top of each other on a transfer medium, the toner images formed on said latent image carriers; and

second detection means for obtaining information on the registration deviations,

wherein said control means controls said exposure means based on said detection information obtained by said second detection means.

23. An exposure device for scanning plural light beams on a surface of a latent image carrier along a main scan direction, comprising:

a light source section for emitting M light beams parallel with one another (M denoting a natural number of M≧

2);

M inner movable members each having a deflector mirror plane for reflecting the light beam from said light source section;

an outer movable member for pivotally supporting each of said M inner movable members about each subscan deflection axis;

a support member for pivotally supporting said outer movable member about a main-scan deflection axis different from said subscan deflection axis; and

a mirror driver section for driving said M inner movable members into pivotal motion about said subscan deflection axes and said outer movable member into pivotal motion about said main-scan deflection axis,

wherein said mirror driver section pivotally moves said deflector mirror planes about said main-scan deflection axis thereby scanning said M light beams from said light source section along said main scan direction, and also pivotally moves said M deflector mirror planes about said subscan deflection axes for deflecting said M light beams via said M deflector mirror planes thereby adjusting said M scanned beams for their positions with respect to said subscan direction.

24. An exposure device as claimed in claim 23, wherein said mirror driver section is capable of controlling a distance between said M scanned beams by driving each of said M inner movable members into independent pivotal motion about said subscan deflection axis.

25. An exposure device as claimed in claim 23, wherein said inner movable member, said outer movable member and said support member are formed of monocrystalline silicon.

26. An exposure device as claimed in claim 23, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis in a resonant mode.

27. An exposure device as claimed in claim 23, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis by way of an electrostatic attractive force.

28. An exposure device as claimed in claim 23, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said subscan deflection axis in a non-resonant mode.

29. An exposure device as claimed in claim 23, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said subscan deflection axis by way of an electromagnetic force.

30. An exposure device as claimed in claim 23, further comprising:

a first optical system disposed between said light source and said deflector mirror plane and operative to converge the light beam from said light source in said subscan direction thereby linearly focusing the light beam on said deflector mirror plane; and

a second optical system disposed between said latent image carrier and said optical scan means and operative to focus the scanned beam from said optical scan means on the corresponding latent image carrier.

31. An image forming apparatus comprising:

a latent image carrier;

exposure means having the same arrangement as the exposure device as claimed in claim 23;

and

control means for controlling said exposure means thereby irradiating the scanned beam on said latent image carrier to form a latent image thereon while adjusting the scanned beam for its position on said latent image carrier with respect to said subscan direction.

32. An image forming apparatus as claimed in claim 31, further comprising storage means for storing deviation information indicative of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said exposure means based on said deviation information stored in said storage means.

33. An image forming apparatus as claimed in claim 31, further comprising first detection means for sensing an amount of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said exposure means based on said amount of light deviation determined by said first detection means.

34. An image forming apparatus as claimed in claim 31, further comprising:

development means for forming a toner image by developing the latent image formed on said latent image carrier;

transfer means for forming a color image by superimposing the toner images on top of each other on a transfer medium, the toner images formed on said latent image carriers; and

storage means for storing correction information necessary for correcting registration deviations,

wherein said control means controls said exposure means based on said correction information stored in said storage means.

35. An image forming apparatus as claimed in claim 31, further comprising:

development means for forming a toner image by developing the latent image formed on said latent image carrier;

transfer means for forming a color image by superimposing the toner images on top of each other on a transfer medium, the toner images formed on said latent image carriers; and

second detection means for obtaining information on the registration deviations,

wherein said control means controls said exposure means based on said detection information obtained by said second detection means.

36. An image forming apparatus comprising:

a plurality of latent image carriers;

exposure means having the same arrangement as the exposure device as claimed in claim 23;

and

control means for controlling said exposure means thereby irradiating the scanned beam on said latent image carrier to form a latent image thereon while selectively switching the scanned beam to any one of said plural latent image carriers for irradiation with said scanned beam.

37. An image forming apparatus as claimed in claim 36, wherein said control means controls said exposure means thereby accomplishing switchable selection of a latent image carrier and adjusting the scanned beam for its position on the selected latent image carrier with respect to said subscan direction.

38. An image forming apparatus as claimed in claim 36, further comprising storage means for storing deviation information indicative of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said exposure means based on said deviation information stored in said storage means.

39. An image forming apparatus as claimed in claim 36, further comprising first detection means for sensing an amount of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said exposure means based on said amount of light deviation determined by said first detection means.

40. An image forming apparatus as claimed in claim 36, further comprising:

development means for forming a toner image by developing the latent image formed on said latent image carrier;

transfer means for forming a color image by superimposing the toner images on top of each other on a transfer medium, the toner images formed on said latent image carriers; and

storage means for storing correction information necessary for correcting registration deviations,

wherein said control means controls said exposure means based on said correction information stored in said storage means.

41. An image forming apparatus as claimed in claim 36, further comprising:

development means for forming a toner image by developing the latent image formed on said latent image carrier;

transfer means for forming a color image by superimposing the toner images on top of each other on a transfer medium, the toner images formed on said latent image carriers; and

second detection means for obtaining information on the registration deviations,

wherein said control means controls said exposure means based on said detection information obtained by said second detection means.

42. An image forming apparatus comprising:

a latent image carrier rotated in a subscan direction;

a light source for emitting a light beam;

optical scan means operative to deflectively scan the light beam from said light source along a main scan direction substantially perpendicular to said subscan direction and to irradiate said scanned beam on said latent image carrier; and

control means for controlling said light source and said optical scan means thereby forming a latent image on said latent image carrier,

wherein said optical scan means includes a fine adjustment mechanism for deflecting the light beam from said light source or the scanned beam along said subscan direction, and

wherein said control means controls said fine adjustment mechanism thereby adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction.

43. An image forming apparatus as claimed in claim 42, wherein said optical scan means comprises:

an inner movable member having a deflector mirror plane for reflecting the light beam from said light source;

an outer movable member for pivotally supporting said inner movable member about a first axis;

a support member for pivotally supporting said outer movable member about a second axis different from said first axis; and

a mirror driver section for driving said inner movable member into pivotal motion about said first axis and said outer movable member into pivotal motion about said second axis,

wherein said mirror driver section drives said deflector mirror plane into pivotal motion about a main-scan deflection axis defined by either one of said first axis and said second axis thereby scanning the light beam from said light source along said main scan direction, and also drives said deflector mirror plane into pivotal motion about a fine adjustment axis defined by the other axis thereby adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction.

44. An image forming apparatus as claimed in claim 43, wherein said inner movable member, said outer movable member and said support member are formed of monocrystalline silicon.

45. An image forming apparatus as claimed in claim 43, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis in a resonant mode.

46. An image forming apparatus as claimed in claim 43, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis by way of an electrostatic attractive force.

47. An image forming apparatus as claimed in claim 43, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said fine adjustment axis in a non-resonant mode.

48. An image forming apparatus as claimed in claim 43, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said fine adjustment axis by way of an electromagnetic force.

49. An image forming apparatus as claimed in claim 43, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

50. An image forming apparatus as claimed in claim 42, wherein said optical scan means comprises:

a polygon mirror having a plurality of deflector mirror planes for reflecting the light beam and driven into rotation about a main-scan deflection axis perpendicular to said main scan direction thereby defectively scanning the light beam along said main scan direction via said deflector mirror planes; and

a fine adjustment mirror having a fine adjustment reflector plane for reflecting the light beam and pivotally moved about a fine adjustment axis perpendicular to said subscan direction for adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction,

wherein either one of said polygon mirror and said fine adjustment mirror is disposed at the site of said light source for reflecting the light beam from said light source, whereas the other mirror operates to reflect the light beam from said one mirror.

51. An image forming apparatus as claimed in claim 50, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

52. An image forming apparatus as claimed in claim 42, wherein said optical scan means comprises:

a main-scanning pivotal mirror having a deflector mirror plane for reflecting the light beam and pivotally moved about a main-scan deflection axis perpendicular to said main scan direction thereby deflectively scanning the light beam along said main scan direction via said deflector mirror plane; and

a fine adjustment mirror having a fine adjustment reflector plane for reflecting the light beam and pivotally moved about a fine adjustment axis perpendicular to said subscan direction for adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction,

wherein either one of said main-scanning pivotal mirror and said fine adjustment mirror is disposed at the site of said light source for reflecting the light beam from said light source, whereas the other mirror operates to reflect the light beam from said one mirror.

53. An image forming apparatus as claimed in claim 52, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

54. An image forming apparatus as claimed in claim 42, further comprising storage means for storing deviation information indicative of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said fine adjustment mechanisms based on said deviation information stored in said storage means.

55. An image forming apparatus as claimed in claim 42, further comprising detection means for sensing an amount of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said fine adjustment mechanisms based on said amount of light deviation determined by said detection means.

56. An image forming apparatus for forming a color image by repeating the following processing for each of N different colors (N denoting a natural number of N≧

2) and superimposing toner images of said N colors on top of each other on a transfer medium, the processing including the steps of forming a latent image on a latent image carrier rotated in a subscan direction by scanning a light beam thereon along a main scan direction perpendicular to said subscan direction;

forming a toner image by developing the latent image; and

transferring the toner image to said transfer medium, the apparatus comprising;

a light source for emitting a light beam;

optical scan means operative to defectively scan the light beam from said light source along said main scan direction and to irradiate the scanned beam on said latent image carrier, and

control means for controlling said light source and said optical scan means thereby forming the latent image on said latent image carrier,

wherein said optical scan means includes a fine adjustment mechanism for deflecting the light beam from said light source or the scanned beam along said subscan direction, and

wherein said control means adjusts said scanned beam for its position on said latent image carrier with respect to said subscan direction by controlling said fine adjustment mechanism, thereby correcting relative registration deviations of the individual toner images on said transfer medium.

57. An image forming apparatus as claimed in claim 56, wherein said optical scan means comprises:

an inner movable member having a deflector mirror plane for reflecting the light beam from said light source;

an outer movable member for pivotally supporting said inner movable member about a first axis;

a support member for pivotally supporting said outer movable member about a second axis different from said first axis; and

a mirror driver section for driving said inner movable member into pivotal motion about said first axis and said outer movable member into pivotal motion about said second axis,

wherein said mirror driver section drives said deflector mirror plane into pivotal motion about a main-scan deflection axis defined by either one of said first axis and said second axis thereby scanning the light beam from said light source along said main scan direction, and also drives said deflector mirror plane into pivotal motion about a fine adjustment axis defined by the other axis thereby adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction.

58. An image forming apparatus as claimed in claim 57, wherein said inner movable member, said outer movable member and said support member are formed of monocrystalline silicon.

59. An image forming apparatus as claimed in claim 57, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis in a resonant mode.

60. An image forming apparatus as claimed in claim 57, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis by way of an electrostatic attractive force.

61. An image forming apparatus as claimed in claim 57, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said fine adjustment axis in a non-resonant mode.

62. An image forming apparatus as claimed in claim 57, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said fine adjustment axis by way of an electromagnetic force.

63. An image forming apparatus as claimed in claim 57, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

64. An image forming apparatus as claimed in claim 56, wherein said optical scan means comprises:

a polygon mirror having a plurality of deflector mirror planes for reflecting the light beam and driven into rotation about a main-scan deflection axis perpendicular to said main scan direction thereby defectively scanning the light beam along said main scan direction via said deflector mirror planes; and

a fine adjustment mirror having a fine adjustment reflector plane for reflecting the light beam and pivotally moved about a fine adjustment axis perpendicular to said subscan direction for adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction,

wherein either one of said polygon mirror and said fine adjustment mirror is disposed at the site of said light source for reflecting the light beam from said light source, whereas the other mirror operates to reflect the light beam from said one mirror.

65. An image forming apparatus as claimed in claim 64, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

66. An image forming apparatus as claimed in claim 56, wherein said optical scan means comprises:

a main-scanning pivotal mirror having a deflector mirror plane for reflecting the light beam and pivotally moved about a main-scan deflection axis perpendicular to said main scan direction thereby defectively scanning the light beam along said main scan direction via said deflector mirror plane; and

a fine adjustment mirror having a fine adjustment reflector plane for reflecting the light beam and pivotally moved about a fine adjustment axis perpendicular to said subscan direction for adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction,

wherein either one of said main-scanning pivotal mirror and said fine adjustment mirror is disposed at the site of said light source for reflecting the light beam from said light source, whereas the other mirror operates to reflect the light beam from said one mirror.

67. An image forming apparatus as claimed in claim 66, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

68. An image forming apparatus as claimed in claim 56, further comprising storage means for storing deviation information indicative of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said fine adjustment mechanisms based on said deviation information stored in said storage means.

69. An image forming apparatus as claimed in claim 56, further comprising detection means for sensing an amount of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said fine adjustment mechanisms based on said amount of light deviation determined by said detection means.

70. An image forming apparatus including N latent image carriers (N denoting a natural number of N≧

2) rotated in a subscan direction and designed to form a color image by the steps of;

forming a latent image on each of said N latent image carriers by scanning a light beam thereon along a main scan direction substantially perpendicular to said subscan direction;

forming a toner image by developing the latent image with a toner of a color corresponding to the latent image carrier; and

superimposing the toner images of said N colors on top of each other on a transfer medium, the apparatus comprising;

a light source for emitting a light beam;

optical scan means operative to defectively scan the light beam from said light source along said main scan direction and to guide said scanned beam along said subscan direction thereby selectively switching said scanned beam to any one of said N latent image carriers for irradiation with said scanned beam; and

control means for controlling said light source and said optical scan means thereby forming the latent images on said N latent image carriers,

wherein said optical scan means includes a fine adjustment mechanism for deflecting the light beam from said light source or the scanned beam along said subscan direction, and

wherein said control means adjusts said scanned beam for its position on said latent image carrier with respect to said subscan direction by controlling said fine adjustment mechanism, thereby correcting relative registration deviations of the individual toner images on said transfer medium.

71. An image forming apparatus as claimed in claim 70, wherein said optical scan means comprises:

an inner movable member having a deflector mirror plane for reflecting the light beam from said light source;

an outer movable member for pivotally supporting said inner movable member about a first axis;

a support member for pivotally supporting said outer movable member about a second axis different from said first axis; and

a mirror driver section for driving said inner movable member into pivotal motion about said first axis and said outer movable member into pivotal motion about said second axis,

wherein said mirror driver section drives said deflector mirror plane into pivotal motion about a main-scan deflection axis defined by either one of said first axis and said second axis thereby scanning the light beam from said light source along said main scan direction, and also drives said deflector mirror plane into pivotal motion about a fine adjustment axis defined by the other axis thereby adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction.

72. An image forming apparatus as claimed in claim 71, wherein said inner movable member, said outer movable member and said support member are formed of monocrystalline silicon.

73. An image forming apparatus as claimed in claim 71, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis in a resonant mode.

74. An image forming apparatus as claimed in claim 71, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis by way of an electrostatic attractive force.

75. An image forming apparatus as claimed in claim 71, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said fine adjustment axis in a non-resonant mode.

76. An image forming apparatus as claimed in claim 71, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said fine adjustment axis by way of an electromagnetic force.

77. An image forming apparatus as claimed in claim 71, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

78. An image forming apparatus as claimed in claim 70, wherein said optical scan means comprises:

a polygon mirror having a plurality of deflector mirror planes for reflecting the light beam and driven into rotation about a main-scan deflection axis perpendicular to said main scan direction thereby defectively scanning the light beam along said main scan direction via said deflector mirror planes; and

a fine adjustment mirror having a fine adjustment reflector plane for reflecting the light beam and pivotally moved about a fine adjustment axis perpendicular to said subscan direction for adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction,

wherein either one of said polygon mirror and said fine adjustment mirror is disposed at the site of said light source for reflecting the light beam from said light source, whereas the other mirror operates to reflect the light beam from said one mirror.

79. An image forming apparatus as claimed in claim 78, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

80. An image forming apparatus as claimed in claim 70, wherein said optical scan means comprises:

a main-scanning pivotal mirror having a deflector mirror plane for reflecting the light beam and pivotally moved about a main-scan deflection axis perpendicular to said main scan direction thereby deflectively scanning the light beam along said main scan direction via said deflector mirror plane; and

a fine adjustment mirror having a fine adjustment reflector plane for reflecting the light beam and pivotally moved about a fine adjustment axis perpendicular to said subscan direction for adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction,

wherein either one of said main-scanning pivotal mirror and said fine adjustment mirror is disposed at the site of said light source for reflecting the light beam from said light source, whereas the other mirror operates to reflect the light beam from said one mirror.

81. An image forming apparatus as claimed in claim 80, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

82. An image forming apparatus as claimed in claim 70, further comprising storage means for storing deviation information indicative of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said fine adjustment mechanisms based on said deviation information stored in said storage means.

83. An image forming apparatus as claimed in claim 70, further comprising detection means for sensing an amount of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said fine adjustment mechanisms based on said amount of light deviation determined by said detection means.

84. An image forming apparatus comprising:

N latent image carriers (N denoting a natural number of N≧

2) rotated in a subscan direction;

N exposure means each provided in correspondence to each of said N latent image carriers and operative to scan a light beam on the corresponding latent image carrier along a main scan direction substantially perpendicular to said subscan direction thereby forming a latent image thereon; and

control means for controlling said N exposure means thereby forming the latent images on said N latent image carriers, respectively, and designed to form a color image by forming toner images by developing the individual latent images on said N latent image carriers with toners of colors individually corresponding to the respective latent image carriers and superimposing the toner images of said N colors on top of each other,

wherein each of said exposure means comprises;

a light source for emitting a light beam; and

optical scan means which deflectively scans the light beam from said light source along said main scan direction for irradiating the scanned beam on said latent image carrier, and which includes a fine adjustment mechanism for deflecting the light beam from said light source or the scanned beam along said subscan direction,

wherein said control means adjusts said scanned beams for their positions on said latent image carriers with respect to said subscan direction by controlling said fine adjustment mechanism, thereby correcting relative registration deviations of the individual toner images on said transfer medium.

85. An image forming apparatus as claimed in claim 84, wherein said optical scan means comprises:

an inner movable member having a deflector mirror plane for reflecting the light beam from said light source;

an outer movable member for pivotally supporting said inner movable member about a first axis;

a support member for pivotally supporting said outer movable member about a second axis different from said first axis; and

a mirror driver section for driving said inner movable member into pivotal motion about said first axis and said outer movable member into pivotal motion about said second axis,

wherein said mirror driver section drives said deflector mirror plane into pivotal motion about a main-scan deflection axis defined by either one of said first axis and said second axis thereby scanning the light beam from said light source along said main scan direction, and also drives said deflector mirror plane into pivotal motion about a fine adjustment axis defined by the other axis thereby adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction.

86. An image forming apparatus as claimed in claim 85, wherein said inner movable member, said outer movable member and said support member are formed of monocrystalline silicon.

87. An image forming apparatus as claimed in claim 85, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis in a resonant mode.

88. An image forming apparatus as claimed in claim 85, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis by way of an electrostatic attractive force.

89. An image forming apparatus as claimed in claim 85, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said fine adjustment axis in a non-resonant mode.

90. An image forming apparatus as claimed in claim 85, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said fine adjustment axis by way of an electromagnetic force.

91. An image forming apparatus as claimed in claim 85, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

92. An image forming apparatus as claimed in claim 84, wherein said optical scan means comprises:

a polygon mirror having a plurality of deflector mirror planes for reflecting the light beam and driven into rotation about a main-scan deflection axis perpendicular to said main scan direction thereby defectively scanning the light beam along said main scan direction via said deflector mirror planes; and

a fine adjustment mirror having a fine adjustment reflector plane for reflecting the light beam and pivotally moved about a fine adjustment axis perpendicular to said subscan direction for adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction,

wherein either one of said polygon mirror and said fine adjustment mirror is disposed at the site of said light source for reflecting the light beam from said light source, whereas the other mirror operates to reflect the light beam from said one mirror.

93. An image forming apparatus as claimed in claim 92, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

94. An image forming apparatus as claimed in claim 84, wherein said optical scan means comprises:

a main-scanning pivotal mirror having a deflector mirror plane for reflecting the light beam and pivotally moved about a main-scan deflection axis perpendicular to said main scan direction thereby defectively scanning the light beam along said main scan direction via said deflector mirror plane; and

a fine adjustment mirror having a fine adjustment reflector plane for reflecting the light beam and pivotally moved about a fine adjustment axis perpendicular to said subscan direction for adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction,

wherein either one of said main-scanning pivotal mirror and said fine adjustment mirror is disposed at the site of said light source for reflecting the light beam from said light source, whereas the other mirror operates to reflect the light beam from said one mirror.

95. An image forming apparatus as claimed in claim 94, further comprising a third optical system for focusing the light beam, scanned by said optical scan means along said main scan direction, on the latent image carrier,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

96. An image forming apparatus as claimed in claim 84, further comprising storage means for storing deviation information indicative of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said fine adjustment mechanisms based on said deviation information stored in said storage means.

97. An image forming apparatus as claimed in claim 84, further comprising detection means for sensing an amount of light deviation from a predetermined reference scan position on said latent image carrier with respect to said subscan direction,

wherein said control means controls said fine adjustment mechanisms based on said amount of light deviation determined by said detection means.

98. An image forming apparatus including N latent image carriers (N denoting a natural number of N≧

2) each formed with a linear latent image on its surface by scanning a single light beam thereon along a main scan direction, the apparatus comprising;

a light source for emitting a single light beam; and

optical scan means operative to deflect the light beam from said light source for scanning along said main scan direction and to guide said scanned beam along a subscan direction different from said main scan direction, thereby selectively switching the light beam to any one of said N latent image carriers for irradiation with said scanned beam.

99. An image forming apparatus as claimed in claim 98, wherein said optical scan means comprises:

an inner movable member having a deflector mirror plane for reflecting the light beam from said light source;

an outer movable member for pivotally supporting said inner movable member about a first axis;

a support member for pivotally supporting said outer movable member about a second axis different from said first axis; and

a mirror driver section for driving said inner movable member into pivotal motion about said first axis and said outer movable member into pivotal motion about said second axis,

wherein said mirror driver section drives said deflector mirror plane into pivotal motion about a main-scan deflection axis defined by either one of said first axis and said second axis thereby scanning the light beam from said light source along said main scan direction, and also drives said deflector mirror plane into pivotal motion about a switch axis defined by the other axis thereby selectively switching said scanned beam to any one of the latent image carriers for irradiation with said scanned beam.

100. An image forming apparatus as claimed in claim 99, wherein said inner movable member, said outer movable member and said support member are formed of monocrystalline silicon.

101. An image forming apparatus as claimed in claim 99, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis in a resonant mode.

102. An image forming apparatus as claimed in claim 99, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis by way of an electrostatic attractive force.

103. An image forming apparatus as claimed in claim 99, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said switch axis in a non-resonant mode.

104. An image forming apparatus as claimed in claim 99, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said switch axis by way of an electromagnetic force.

105. An image forming apparatus as claimed in claim 99, further comprising:

a first optical system disposed between said light source and said optical scan means and operative to converge the light beam from said light source in said subscan direction thereby linearly focusing the light beam on said deflector mirror plane; and

a second optical system disposed between each of said N latent image carriers and said optical scan means and operative to focus the scanned beam from said optical scan means on the corresponding latent image carrier.

106. An image forming apparatus as claimed in claim 99, further comprising a third optical system for focusing the light beam, scanned by said deflector mirror plane along said main scan direction, on the latent image carrier to which the scanned beam is guided by said deflector mirror plane,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

107. An image forming apparatus as claimed in claim 98, wherein said optical scan means comprises:

a polygon mirror having a plurality of deflector mirror planes for reflecting the light beam and driven into rotation about a main-scan deflection axis perpendicular to said main scan direction thereby defectively scanning the light beam along said main scan direction via said deflector mirror planes; and

a switching pivotal mirror having a switching reflector plane for reflecting the light beam and pivotally moved about a switch axis perpendicular to said subscan direction for switching the light beam to any one of the latent image carriers for irradiation with the light beam,

wherein either one of said polygon mirror and said switching pivotal mirror is disposed at the site of said light source for reflecting the light beam from said light source, whereas the other mirror operates to reflect the light beam from said one mirror.

108. An image forming apparatus as claimed in claim 107, further comprising:

a first optical system disposed between said light source and said deflector mirror plane and operative to converge the light beam from said light source in said subscan direction thereby linearly focusing the light beam on said deflector mirror plane; and

a second optical system disposed between each of said N latent image carriers and said deflector mirror plane and operative to focus the scanned beam from said deflector mirror plane on the corresponding latent image carrier.

109. An image forming apparatus as claimed in claim 107, further comprising a third optical system for focusing the light beam, scanned by said deflector mirror plane along said main scan direction, on the latent image carrier to which the scanned beam is guided by said deflector mirror plane,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

110. An image forming apparatus as claimed in claim 98, wherein said optical scan means comprises:

a main-scanning pivotal mirror having a deflector mirror plane for reflecting the light beam and pivotally moved about a main-scan deflection axis perpendicular to said main scan direction thereby deflectively scanning the light beam along said main scan direction via said deflector mirror plane; and

a switching pivotal mirror having a switching reflector plane for reflecting the light beam and pivotally moved about a switch axis perpendicular to said subscan direction for switching the light beam to any one of the latent image carriers for irradiation with the light beam,

wherein either one of said main-scanning pivotal mirror and said switching pivotal mirror is disposed at the site of said light source for reflecting the light beam from said light source, whereas the other mirror operates to reflect the light beam from said one mirror.

111. An image forming apparatus as claimed in claim 110, further comprising:

a first optical system disposed between said light source and said deflector mirror plane and operative to converge the light beam from said light source in said subscan direction thereby linearly focusing the light beam on said deflector mirror plane; and

a second optical system disposed between each of said N latent image carriers and said deflector mirror plane and operative to focus the scanned beam from said deflector mirror plane on the corresponding latent image carrier.

112. An image forming apparatus as claimed in claim 110, further comprising a third optical system for focusing the light beam, scanned by said deflector mirror plane along said main scan direction, on the latent image carrier to which the scanned beam is guided by said deflector mirror plane,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

113. An image forming apparatus as claimed in claim 98 designed to form images of different N colors on said N latent image carriers, respectively, the apparatus further comprising:

storage means for storing N image data items representative of images of said N colors; and

control means which reads out a 1-line image data piece, equivalent to one scan stroke of the scanned beam, from the image data item of a color stored in said storage means and then, modulates said scanned beam based on the 1-line image data piece for forming a linear latent image on a latent image carrier corresponding to the color of interest,

wherein said control means serially reads out the 1-line image data pieces one by one from said storage means as selectively switching a reading source of the 1-line image data piece among said N image data items and then, in association with each 1-line image data piece thus read, switches a target of the scanned beam guided by said optical scan means for establishing correspondence between the latent image carrier and the color component of the read data.

114. An image forming apparatus including N latent image carriers (N denoting a natural number of N≧

2) each formed with M linear latent images on its surface by scanning M light beams (M denoting a natural number of M≧

2) thereon along a main scan direction, the apparatus comprising;

light source means for emitting the M light beams parallel with one another; and

optical scan means operative to deflect the M light beams from said light source means for scanning along said main scan direction and to guide said M scanned beams along a subscan direction different from said main scan direction, thereby selectively switching said M scanned beams to any one of said N latent image carriers for irradiation with said M scanned beams.

115. An image forming apparatus as claimed in claim 114, wherein said optical scan means comprises:

an inner movable member having a deflector mirror plane for reflecting the M light beams from said light source means;

an outer movable member for pivotally supporting said inner movable member about a first axis;

a support member for pivotally supporting said outer movable member about a second axis different from said first axis; and

a mirror driver section for driving said inner movable member into pivotal motion about said first axis and said outer movable member into pivotal motion about said second axis,

wherein said mirror driver section pivotally moves said deflector mirror plane about a main-scan deflection axis defined by either one of said first axis and said second axis thereby scanning the M light beams from said light source means along said main scan direction, and also pivotally moves said deflector mirror plane about a switch axis defined by the other axis thereby selectively switching said M scanned beams to any one of the latent image carriers for irradiation with said M scanned beams.

116. An image forming apparatus as claimed in claim 115, wherein said inner movable member, said outer movable member and said support member are formed of monocrystalline silicon.

117. An image forming apparatus as claimed in claim 115, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis in a resonant mode.

118. An image forming apparatus as claimed in claim 115, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis by way of an electrostatic attractive force.

119. An image forming apparatus as claimed in claim 115, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said switch axis in a non-resonant mode.

120. An image forming apparatus as claimed in claim 115, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said switch axis by way of an electromagnetic force.

121. An image forming apparatus as claimed in claim 115, further comprising:

a first optical system disposed between said light source and said optical scan means and operative to converge the light beam from said light source in said subscan direction thereby linearly focusing the light beam on said deflector mirror plane; and

a second optical system disposed between each of said N latent image carriers and said optical scan means and operative to focus the scanned beam from said optical scan means on the corresponding latent image carrier.

122. An image forming apparatus as claimed in claim 115, further comprising a third optical system for focusing the light beam, scanned by said deflector mirror plane along said main scan direction, on the latent image carrier to which the scanned beam is guided by said deflector mirror plane,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

123. An image forming apparatus as claimed in claim 114, wherein said optical scan means comprises:

M inner movable members each having a deflector mirror plane for reflecting the light beam from said light source means;

an outer movable member for pivotally supporting each of said M inner movable members about each switch axis;

a support member for pivotally supporting said outer movable member about a main-scan deflection axis different from said switch axis; and

a mirror driver section for driving said M inner movable members into pivotal motion about said switch axes and said outer movable member into pivotal motion about said main-scan deflection axis,

wherein said mirror driver section pivotally moves said deflector mirror planes about said main-scan deflection axis thereby scanning the M light beams from said light source means along said main scan direction, and also pivotally moves said M deflector mirror planes about said switch axes for deflecting said M light beams via said M deflector mirror planes, respectively, thereby selectively switching said M scanned beams to any one of the latent image carriers for irradiation with said scanned beams.

124. An image forming apparatus as claimed in claim 123, wherein said mirror driver section is capable of controlling a distance between said M scanned beams by driving each of said M inner movable members into independent pivotal motion about said each subscan deflection axis.

125. An image forming apparatus as claimed in claim 123, wherein said inner movable member, said outer movable member and said support member are formed of monocrystalline silicon.

126. An image forming apparatus as claimed in claim 123, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis in a resonant mode.

127. An image forming apparatus as claimed in claim 123, wherein said mirror driver section drives said deflector mirror plane into pivotal motion about said main-scan deflection axis by way of an electrostatic attractive force.

128. An image forming apparatus as claimed in claim 123, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said switch axis in a non-resonant mode.

129. An image forming apparatus as claimed in claim 123, wherein said mirror driver section positions said deflector mirror plane by pivotally moving the same about said switch axis by way of an electromagnetic force.

130. An image forming apparatus as claimed in claim 123, further comprising:

a first optical system disposed between said light source and said optical scan means and operative to converge the light beam from said light source in said subscan direction thereby linearly focusing the light beam on said deflector mirror plane; and

a second optical system disposed between each of said N latent image carriers and said optical scan means and operative to focus the scanned beam from said optical scan means on the corresponding latent image carrier.

131. An image forming apparatus as claimed in claim 123, further comprising a third optical system for focusing the light beam, scanned by said deflector mirror plane along said main scan direction, on the latent image carrier to which the scanned beam is guided by said deflector mirror plane,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

132. An image forming apparatus as claimed in claim 114, wherein said optical scan means comprises:

a polygon mirror having a plurality of deflector mirror planes for reflecting the light beams and driven into rotation about a main-scan deflection axis perpendicular to said main scan direction thereby deflectively scanning the M light beams along said main scan direction via said deflector mirror planes; and

a switching pivotal mirror having a switching reflector plane for reflecting the light beams and pivotally moved about a switch axis perpendicular to said subscan direction for switching the light beams to any one of the latent image carriers for irradiation with the light beams,

wherein either one of said polygon mirror and said switching pivotal mirror is disposed at the site of said light source means for reflecting the M light beams from said light source means, whereas the other mirror operates to reflect the M light beams from said one mirror.

133. An image forming apparatus as claimed in claim 132, further comprising:

a first optical system disposed between said light source means and said deflector mirror plane and operative to converge each of the M light beams from said light source means in said subscan direction thereby linearly focusing the individual light beams on said deflector mirror plane; and

a second optical system disposed between each of said N latent image carriers and said deflector mirror plane and operative to focus the M scanned beams from said deflector mirror plane on the corresponding latent image carrier.

134. An image forming apparatus as claimed in claim 132, further comprising a third optical system for focusing the M light beams, scanned by said deflector mirror plane along said main scan direction, on the latent image carrier to which the M scanned beams are guided by said deflector mirror plane,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

135. An image forming apparatus as claimed in claim 114, wherein said optical scan means comprises:

a main-scanning pivotal mirror having a deflector mirror plane for reflecting the light beams and pivotally moved about a main-scan deflection axis perpendicular to said main scan direction thereby defectively scanning the light beams along said main scan direction via said deflector mirror plane; and

a switching pivotal mirror having a switching reflector plane for reflecting the light beams and pivotally moved about a switch axis perpendicular to said subscan direction for switching the light beams to any one of the latent image carriers for irradiation with the light beams,

wherein either one of said main-scanning pivotal mirror and said switching pivotal mirror is disposed at the site of said light source means for reflecting the M light beams from said light source means, whereas the other mirror operates to reflect the light beams from said one mirror.

136. An image forming apparatus as claimed in claim 135, further comprising:

a first optical system disposed between said light source means and said deflector mirror plane and operative to converge each of the M light beams from said light source means in said subscan direction thereby linearly focusing the individual light beams on said deflector mirror plane; and

a second optical system disposed between each of said N latent image carriers and said deflector mirror plane and operative to focus the M scanned beams from said deflector mirror plane on the corresponding latent image carrier.

137. An image forming apparatus as claimed in claim 135, further comprising a third optical system for focusing the M light beams, scanned by said deflector mirror plane along said main scan direction, on the latent image carrier to which the M scanned beams are guided by said deflector mirror plane,

wherein said third optical system comprises a single lens and has a distortion characteristic that the scanned beam deflected based on a swinging characteristic intrinsic to said deflector mirror plane is moved on the surface of each latent image carrier at a constant speed, the third optical system specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

138. An image forming apparatus as claimed in claim 114 designed to form images of N different colors on said N latent image carriers, respectively, the apparatus comprising:

storage means for storing N image data items representative of images of said N different colors; and

control means which reads out M 1-line image data pieces, each equivalent to one scan stroke of the scanned beam, from the image data item of a color stored in said storage means and then, modulates said M scanned beams based on the 1-line image data set for forming M linear latent images on a latent image carrier corresponding to the color of interest,

wherein said control means serially reads out the 1-line image data sets from said storage means as selectively switching a reading source of the 1-line image data set among said N image data items and then, in association with each 1-line image data set thus read, switches a target of the M scanned beams guided by said optical scan means for establishing correspondence between the latent image carrier and the color component of the read data set.

139. An image forming apparatus comprising:

N latent image carriers (N denoting a natural number of N≧

2);

a light source for emitting a light beam;

optical scan means operative to deflect the light beam from said light source for scanning along a main scan direction and to guide said scanned beam in a subscan direction different from said main scan direction thereby selectively switching said scanned beam to any one of said N latent image carriers for irradiation with said scanned beam; and

storage means for storing image data items representative of images of N colors; and

control means which reads out a 1-line image data piece, equivalent to one scan stroke of the scanned beam, from the image data item of a color stored in said storage means and then, modulates said scanned beam based on the 1-line image data piece for forming a linear latent image on a latent image carrier corresponding to the color of interest,

wherein during an image forming operation limiting the number of usable colors to (N-1) or less, said control means serially reads out 1-line image data pieces from an image data item of said limited color stored in said storage means and based on each 1-line image data piece thus read, forms a latent image on a latent image carrier corresponding to the color of the read data.

140. An image forming apparatus as claimed in claim 139, wherein said N colors include black, and

wherein during an image forming operation using the limited color of black alone, said control means sets a target of said scanned beams guided by said optical scan means to a latent image carrier corresponding to black.

141. An image forming apparatus comprising:

N latent image carriers (N denoting a natural number of N≧

2);

light source means for emitting M light beams parallel with one another;

optical scan means operative to deflect the M light beams from said light source means for scanning along a main scan direction and to guide said M scanned beams along a subscan direction different from said main scan direction, thereby selectively switching the M scanned beams to any one of said N latent image carriers for irradiation with said scanned beams;

storage means for storing image data items representative of images of N colors; and

control means which reads out M 1-line image data pieces, each equivalent to one scan stroke of the scanned beam, from the image data item of a color stored in said storage means and then, modulates said M scanned beams based on the 1-line image data set for forming M linear latent images on a latent image carrier corresponding to the color of interest,

wherein during an image forming operation limiting the number of usable colors to (N-1) or less, said control means serially reads out sets of M 1-line image data pieces from an image data item of said limited color stored in said storage means and based on each 1-line image data set thus read, forms a latent image on a latent image carrier corresponding to the color of the read data.

142. An image forming apparatus as claimed in claim 141, wherein said N colors include black, and

wherein during an image forming operation using the limited color of black alone, said control means sets a target of said scanned beams guided by said optical scan means to a latent image carrier corresponding to black.

143. An image forming method performed by an image forming apparatus comprising N latent image carriers (N denoting a natural number of N≧

2) each formed with a linear latent image on its surface by scanning a light beam thereon along a main scan direction, and capable of forming latent images corresponding to different N colors on said N latent image carriers, respectively, by deflecting the light beam from the light source for scanning along said main scan direction while switching a target of the scanned beam to any one of said N latent image carriers,

the method wherein during a color-image forming operation using said N colors, 1-line image data pieces, each equivalent to one scan stroke of the scanned beam, are serially read out from image data items of said N colors as a reading source stored in the storage means while the light beam is modulated based on each 1-line image data piece thus read for forming a linear latent image on a latent image carrier corresponding to the read data, and

wherein during an image forming operation limiting the number of usable colors to (N-1) or less, 1-line image data pieces, each equivalent to one scan stroke of the scanned beam, are serially read out from an image data item of the limited color as a reading source stored in the storage means while the light beam is modulated based on each 1-line image data piece thus read for forming a linear latent image on a latent image carrier corresponding to the read data.

144. An image forming method performed by an image forming apparatus comprising N latent image carriers (N denoting a natural number of N≧

2) each formed with M linear latent images (M denoting a natural number of M≧

2) on its surface by scanning M light beams thereon along a main scan direction, and capable of forming latent images corresponding to different N colors on said N latent image carriers, respectively, by deflecting the M light beams from the light source for scanning along said main scan direction while switching a target of each scanned beam group to any one of said N latent image carriers,

the method wherein during a color-image forming operation using said N colors, sets of M 1-line image data pieces, each equivalent to one scan stroke of the scanned beam, are serially read out from image data items of said N colors as a reading source stored in storage means while said M light beams are modulated based on each 1-line image data set thus read for forming linear latent images on a latent image carrier corresponding to the read data, and

wherein during an image forming operation limiting the number of usable colors to (N-1) or less, sets of M 1-line image data pieces, each equivalent to one scan stroke of the scanned beam, are serially read out from an image data item of the limited color as a reading source stored in the storage means while said M light beams are modulated based on each 1-line image data set thus read for forming linear latent images on a latent image carrier corresponding to the read data.

145. An image forming apparatus comprising a plurality of latent image carriers, each scanned with a light beam along a main scan direction substantially perpendicular to a subscan direction as rotated in said subscan direction thereby to be formed with a latent image on its surface, the apparatus comprising:

a light source section for emitting the light beam;

optical scan means operative to deflect the light beam from said light source section via a pivotal deflector mirror plane thereby scanning the light beam along said main scan direction and to selectively switch said scanned beam to any one of said plural latent image carriers for irradiation with said scanned beam;

an optical focusing system having the following arrangement for focusing said scanned beam on the surface of each latent image carrier; and

control means for controlling said light source section and said optical scan means thereby forming the latent image on each of the latent image carriers,

wherein said optical scan means includes a fine adjustment mechanism for deflecting the light beam from said light source section or the scanned beam along said subscan direction,

wherein said control means controls said fine adjustment mechanism thereby adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction, and

wherein said optical focusing system comprises a single lens and is specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

146. An image forming apparatus comprising:

a plurality of latent image carriers rotated in a subscan direction;

a plurality of exposure means each provided in correspondence to each of said N latent image carriers and operative to scan a light beam on each corresponding latent image carrier along a main scan direction substantially perpendicular to said subscan direction thereby forming a latent image thereon; and

control means for controlling said N exposure means thereby forming latent images on said N latent image carriers, respectively,

wherein each of said exposure means comprises;

a light source section for emitting the light beam;

optical scan means operative to defectively scan the light beam from said light source section along said main scan direction and to deflect the light beam from said light source section or the scanned beam along said subscan direction by means of a fine adjustment mechanism; and

an optical focusing system having the following arrangement for focusing said scanned beam on the surface of each latent image carrier;

wherein said control means controls said fine adjustment mechanism thereby adjusting said scanned beam for its position on said latent image carrier with respect to said subscan direction, and

wherein said optical focusing system comprises a single lens and is specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

147. An image forming apparatus designed to form images of N different colors on N latent image carriers (N denoting a natural number of N≧

2), respectively, the apparatus comprising;

a light source for emitting a single light beam;

optical scan means operative to deflect the light beam from said light source via a pivotal deflector mirror plane thereby scanning the light beam along a main scan direction and to guide said scanned beam in a subscan direction different from said main scan direction thereby selectively switching said scanned beam to any one of said N latent image carriers for irradiation with said scanned beam;

an optical focusing system having the following arrangement for focusing said scanned beam on the surface of the each latent image carrier;

storage means for storing N image data items representative of images of said N different colors; and

control means which reads out a 1-line image data piece, equivalent to one scan stroke of the scanned beam, from the image data item of a color stored in said storage means and then, modulates said scanned beam based on the 1-line image data piece for forming a linear latent image on a latent image carrier corresponding to the color of interest,

wherein said control means serially reads out the 1-line image data pieces one by one from said storage means as selectively switching a reading source of the 1-line image data piece among said N image data items and then, in association with each 1-line image data piece thus read, switches a target of the scanned beam guided by said optical scan means for establishing correspondence between the latent image carrier and the color component of the read data, and

wherein said optical focusing system comprises a single lens and is specified that opposite sides in a tangential plane are formed in mutually different non-arcuate shapes in a manner to correct for tangential field-curvature aberration in the light beam at any position on the surface of each latent image carrier, and that sagital curvatures at positions on the non-arcuate curve of at least either one of said opposite sides in the tangential plane are varied non-correlatively of the tangential curvature in order to correct for sagital field-curvature aberration in the light beam.

148. An exposure device operative to deflect a light beam from a light source along a main scan direction via deflection means and to guide the deflected light beam to a scanned surface thereby scanning the light beam on the scanned surface,

wherein said deflection means is disposed at place below a scan position of the light beam on said scanned surface, and

wherein said deflection means comprises a movable member and a support member which are integrally formed, the movable member having a deflector mirror plane for reflecting the light beam from said light source, the support member pivotally supporting said movable member about a pivotal axis substantially perpendicular to said main scan direction, and drives said movable member into pivotal motion about said pivotal axis thereby scanning said light beam along said main scan direction.