Image forming system employing effective optical scan-line control device

Abstract

An optical scanning characteristic control method is applied to an optical scanning system in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam. The method comprising the steps of a) disposing a beam deflection control device on the light path of the beam before it is incident on the scanning surface; and b) controlling a beam deflection amount of the beam deflecting device provide to an incident beam so as to control a scanning characteristic of the optical scanning.

1. An optical scanning characteristic control method applied to an optical scanning system in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, said method comprising the steps:
 a) disposing a beam deflection control device on the light path of the beam before it is incident on the scanning surface, said beam deflection control device configured to cause an electric field distribution in a liquid crystal by applying electricity to an electrode formed on a side of a glass substrate; and   b) controlling a beam deflection amount of the beam deflecting device provided to an incident beam so as to control a scanning characteristic of the optical scanning, wherein   at least one resinous image-formation optical device is disposed in the optical scanning system;   the beam deflection control device comprises deflection areas configured by a series of a plurality, of deflection devices defined in a main scanning direction, and   the control of the scanning characteristic of the optical scanning is carried out individually for each of a plurality of ranges divided in the main scanning direction.   
     
     
       2. The method as claimed in  claim 1 , wherein:
 said beam deflection control device comprises a liquid crystal device by which refractive index thereof can be controlled electrically, and thus, the direction of the incident beam can be changed accordingly, and   laser beams corresponding to a plurality of colors have at least a single scanning image-formation device to pass through.   
     
     
       3. The method as claimed in  claim 1 , wherein:
 said beam deflection control device comprises a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in a subscanning direction;   said beam deflection control device is disposed between a beam deflecting device and the scanning surface;   the deflection amount in the subscanning direction of each beam deflection control unit is controlled for each scanning action so that scan line bending is corrected, and   laser beams corresponding to a plurality of colors have at least a single scanning image-formation device to pass through.   
     
     
       4. The method as claimed in  claim 1 , wherein:
 said beam deflection control device comprises a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in the main scanning direction;   said beam deflection control device is disposed between a beam deflecting device and the scanning surface;   the deflection amount in the main scanning direction of each beam deflection control unit is controlled for each scanning action so that a uniform velocity characteristic is corrected, and   laser beams corresponding to a plurality of colors have at east a single scanning image-formation device to pass through.   
     
     
       5. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, said device comprising:
 a beam deflection control device disposed on the light path of the beam before it is incident on the scanning surface, said beam deflection control device configured to cause an electric field distribution in a liquid crystal by applying electricity to an electrode formed on a side of a glass substrate, 
 wherein a beam deflection amount of the beam deflecting deflection control device provided to an incident beam is controlled so that a scanning characteristic of the optical scanning is controlled, 
 at least one resinous image-formation optical device is disposed in the optical scanning system, 
 the beam deflection control device comprises deflection areas configured by a series of a plurality of deflection devices defined in a main scanning direction, and 
 the beam deflection control device has liquid crystal deflection areas separated in a subscanning direction for respective laser beams corresponding to a plurality of colors, and the liquid crystal deflection areas are configured by a single laser beam transmitting member. 
 
     
     
       6. The optical scanning device as claimed in  claim 5 , wherein:
 said beam deflection control device comprises a liquid crystal device by which a refractive index thereof can be controlled electrically, and thus, the direction of the incident beam can be changed accordingly. 
 
     
     
       7. The optical scanning device as claimed in  claim 5 , wherein:
 said beam deflection control device comprises a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in a subscanning direction; 
 said beam deflection control device is disposed between a beam deflecting device and the scanning surface; and 
 the deflection amount in the subscanning direction of each beam deflection control unit is controlled for each scanning action so that scan line bending is corrected. 
 
     
     
       8. The optical scanning device as claimed in  claim 5 , wherein:
 said beam deflection control device comprises a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in the main scanning direction; 
 said beam deflection control device is disposed between a beam deflecting device and the scanning surface; and 
 the deflection amount in the main scanning direction of each beam deflection control unit is controlled for each scanning action so that a uniform velocity characteristic is corrected. 
 
     
     
       9. The optical scanning device as claimed in  claim 5 , further comprising a beam separating device separating a part of the beam before it is incident on the scanning surface,
 wherein: 
 said beam separating device directs the thus-separated beam part toward a detection surface which is optically equivalent to the scanning surface, and then, a scan line bending state on said detection surface, which is equivalent to the scan line bending occurring on the scanning surface, is detected. 
 
     
     
       10. The optical scanning device as claimed in  claim 9 , wherein:
 said beam separating device comprises said beam deflection control device, wherein: 
 a beam reflected by said beam deflection control device is directed toward said detection surface. 
 
     
     
       11. The optical scanning device as claimed in  claim 9 , further comprising a scanning position detection device which detects the position of scanning line on said detection surface,
 wherein: 
 said scanning position detection device comprises a number of optical sensors, which number is the same as the number of the beam deflection control units included in said beam deflection control device, said number of optical sensors being disposed at positions corresponding to the positions of the respective beam deflection control units and detecting the subscanning-directional positions of the optical spots. 
 
     
     
       12. The optical scanning device as claimed in  claim 5  comprising a multi-beam-type optical scanning device in which a light source device emits a plurality of beams and the scanning surface is scanned by the plurality of beams simultaneously. 
     
     
       13. The optical scanning device as claimed in  claim 5 , wherein:
 a plurality of light sources are provided; and 
 a scanning optical system defining a light path from each light source toward the respective scanning surface is configured so that a scan line drawn by an optical spot formed by the beam coming from each light source is substantially parallel to each other. 
 
     
     
       14. The optical scanning device as claimed in  claim 13 , wherein:
 the beam deflection control device is provided for each light source. 
 
     
     
       15. The optical scanning device as claimed in  claim 13 , wherein:
 the number of light sources is 3 or 4, and the beam emitted from each light source is modulated by image information for forming an image in a respective one of color components which thus form a color image in combination. 
 
     
     
       16. An image formation device which performs image formation by performing optical scanning of photosensitive bodies, comprising the optical scanning device claimed in  claim 15 ;
 wherein: 
 three or four photoconductive photosensitive bodies which provide the scanning surfaces to be optically scanned by the beams from the respective light sources are disposed in mutually parallel. 
 
     
     
       17. The optical scanning device as claimed in  claim 5 , wherein:
 a plurality of light sources are provided, and scanning optical systems defining light paths from the respective light sources toward the respective scanning surfaces are mutually equivalent; and 
 one of the scanning optical systems is regarded as a reference, and. the beam deflection control device is provided on the light path in each of the other scanning optical systems, is used for correcting the scanning characteristic of each of the other scanning optical systems for the scanning characteristic of the reference scanning optical system. 
 
     
     
       18. The optical scanning device as claimed in  claim 17 , wherein:
 the number of light sources is 3 or 4, and the beam emitted from each light source is modulated by image information for forming an image in a respective one of color components which thus form a color image in combination. 
 
     
     
       19. An image formation device which performs image formation by performing optical scanning of photosensitive bodies, comprising the optical scanning device claimed in  claim 18 ;
 wherein: 
 three of four photoconductive photosensitive bodies which provide the scanning surfaces to be optically scanned by the beams from the respective light sources are disposed in mutually parallel. 
 
     
     
       20. An image formation device which performs image formation by performing optical scanning of a photosensitive medium, comprising the optical scanning device claimed in  claim 5 . 
     
     
       21. The image formation device as claimed in  claim 20 , wherein said photosensitive medium comprises a photosensitive body having a photoconductivity. 
     
     
       22. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, said device comprising:
 a beam deflection control device disposed on the light path of the beam before it is incident on the scanning surface, wherein a beam deflection amount of the beam deflecting deflection control device provided to an incident beam is controlled so that a scanning characteristic of the optical scanning is controlled; 
 a beam separating device separating a part of the beam before it is incident on the scanning surface, wherein said beam separating device directs the thus-separated beam part toward a detection surface which is optically equivalent to the scanning surface, and then, a scan line bending state on said detection surface, which is equivalent to the scan line bending occurring on the scanning surface, is detected; 
 a scanning position detection device which detects the position of scanning line on said detection surface, wherein said scanning position detection device comprises a number of optical sensors, which number is the same as the number of the beam deflection control units included in said beam deflection control device, said number of optical sensors being disposed at positions corresponding to the positions of the respective beam deflection control units and detecting the subscanning-directional positions of the optical spots, wherein 
 a supporting member supporting the number of optical sensors is made of a material having a thermal expansion coefficient of not more than 1.0×10 −5 /° C. 
 
     
     
       23. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, said device comprising:
 a beam deflection control device disposed on the light path of the beam before it is incident on the scanning surface, 
 wherein a beam deflection amount of the beam deflecting deflection control device provided to an incident beam is controlled so that a scanning characteristic of the optical scanning is controlled, 
 a plurality of light sources are provided, and scanning optical systems defining light paths from the respective light sources toward the respective scanning surfaces are mutually equivalent; 
 one of the scanning optical systems is regarded as a reference, and, the beam deflection control device is provided on the light path in each of the other scanning optical systems, is used for correcting the scanning characteristic of each of the other scanning 
 optical systems for the scanning characteristic of the reference scanning optical system, and 
 a transparent member is provided on the light path of the reference scanning optical system for the purpose of correcting the difference in light path length caused by the existence of the beam deflection control device provided on the light path of each of the other scanning optical systems. 
 
     
     
       24. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, said device comprising:
 a beam deflection control device disposed on the light path of the beam before it is incident on the scanning surface, said beam deflection control device configured to cause an electric field distribution in a liquid crystal by applying electricity to an electrode formed on a side of a glass substrate, wherein   a beam deflection amount of the beam deflecting device provided to an incident beam is controlled so that a scanning characteristic of the optical scanning is controlled,   a plurality of light sources are provided, and scanning optical systems defining light paths from the respective light sources toward the respective scanning surfaces are mutually equivalent;   one of the scanning optical systems is regarded as a reference, and, the beam deflection control device is provided on the light path in each of the other scanning optical systems, is used for correcting the scanning characteristic of each of the other scanning optical systems for the scanning characteristic of the reference scanning optical system, and   each of the scanning optical systems comprises a lens system, and the lens system of the reference scanning optical system is made of a material having a thermal expansion coefficient of not more than 1.0×10 −5 /° C.   
     
     
       25. An optical scanning device in which a plurality of beams for respective color components for forming a color image in combination are deflected, are converged by a scanning and image-formation optical system, are directed to respective scanning surfaces individually and thus performing optical scanning of the scanning surfaces respectively, so as to write images of respective color components, comprising:
 a scan line correcting device which corrects a scan line bending, wherein:   a scan line bending on the beam of one color component is regarded as a reference scan line bending;   the scan line correcting device electronically corrects a scan line bending of the beam of each of the other color components for the reference scan line bending;   at least one resinous image-formation optical device is disposed in the optical scanning system;   the scan line correcting device comprises deflection areas configured by a series of a plurality of deflection devices defined in a main scanning direction,   laser beams corresponding to a plurality of colors have at least a single scanning image-formation device to pass through; and   the control of a scanning characteristic of the optical scanning is carried out individually for each of a plurality of ranges divided in the main scanning direction.   
     
     
       26. The optical scanning device as claimed in  claim 25 , wherein:
 one of the color components is black; and   the scan line bending of the beam of black is regarded as the reference scan line bending.   
     
     
       27. The optical scanning device as claimed in  claim 25 , wherein:
 said scan line correcting device comprises liquid crystal deflection devices each controllable individually arranged in a main scanning direction, is disposed on the light path of the deflected beam for which the scan line bending is to be corrected; and   according to the optical scanning action, a deflection amount provided to the beam is controlled in a subscanning direction for each liquid crystal deflection device.   
     
     
       28. The optical scanning device as claimed in  claim 27 , wherein:
 the scan line correcting device is configured in a manner such that the liquid crystal deflection devices thereof are combined together integrally for each deflected beam.   
     
     
       29. The optical scanning device as claimed in  claim 25 , wherein: the plurality of beams corresponding to the respective color components pass through at least one optical device in common of the scanning and image-formation optical system. 
     
     
       30. An image formation device for forming a color image from respective color-component images formed on respective scanning surfaces as a result of optical scanning thereof with beams of respective color components, comprising:
 the optical scanning device according to  claim 25  which performs optical scanning of the respective scanning surfaces.   
     
     
       31. The image formation device as claimed in  claim 30 , wherein:
 after starting a series of image formation processes, the scan line bending correction is performed by the scan line correcting device at least once during the thus-started series of processes.   
     
     
       32. An image formation device for forming a color image from respective color-component images formed on respective scanning surfaces as a result of optical scanning thereof with beams of respective color components, comprising:
 the optical scanning device according to  claim 25  which performs optical scanning of the respective scanning surfaces, wherein   after starting a series of image formation processes, the scan line bending correction is performed by the scan line correcting device at least once during the thus-started series of processes,   the correction operation performed by the scan line correcting device can be performed within an interval between successive sheets of paper on which color images are formed; and   the following requirements be satisfied:
   T A <0.8×(D/Y)
 
   where:   T A  denotes a required control time for the scan line correction operation;   D denotes a distance between adjacent sheets; and   V denotes a speed of each sheet being conveyed during the process.   
     
     
       33. An image formation device for forming a color image from respective color-component images formed on respective scanning surfaces as a result of optical scanning thereof with beams of respective color components, comprising:
 the optical scanning device according to  claim 25  which performs optical scanning of the respective scanning surfaces, wherein   a scan line deviation detecting device is provided for detecting a difference between the scan lines for the respective color components;   the scan line correcting device performs scan line correction based on the detection result of the scan line deviation detecting device; and   the following requirements be satisfied:
   Ts<10×(L/V)
 
   where:   Ts denotes a time required for the scan line deviation detection operation by said scan line deviation detecting device;   L denotes a length of sheet-shaped recording medium in a direction in which it is conveyed in the image formation process on which a color image is formed; and   V denotes a speed of the sheet-shaped recording medium being conveyed in the image formation process.   
     
     
       34. An optical scanning control method applied to an optical scanning system in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, said method comprising the steps:
 a) disposing a beam deflection control device on the light path of the beam before it is incident on the scanning surface, said beam deflection control device configured to cause an electric field distribution in a liquid crystal by applying electricity to an electrode formed on a side of a glass substrate;   b) controlling a beam deflection amount of the beam deflecting control device provided to an incident beam so as to control a scanning characteristic of the optical scanning: and   c) causing the incident beam to pass through the beam deflection control device without application of any beam deflection thereon when no correction of the current scanning characteristic is needed, wherein   at least one resinous image-formation optical device is disposed in the optical scanning system;   the beam deflection control device comprises deflection areas configured by a series of a plurality of deflection devices defined in a main scanning direction;   laser beams corresponding to a plurality of colors have at least a single scanning image-formation device to pass through; and   the control of the scanning characteristic of the optical scanning is carried out individually for each of a plurality of ranges divided in the main scanning direction.   
     
     
       35. The method as claimed in  claim 34 , wherein:
 said beam deflection control device comprises a liquid crystal device by which a refractive index thereof can be controlled electrically, and thus, the direction of the incident beam can be changed accordingly.   
     
     
       36. The method as claimed in  claim 34 , wherein:
 said beam deflection control device comprises a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in a subscanning direction;   said beam deflection control device is disposed between a beam deflecting device and the scanning surface; and   the deflection amount in the subscanning direction of each beam deflection control unit is controlled for each scanning action so that scan line bending is corrected.   
     
     
       37. The method as claimed in  claim 34 , wherein:
 said beam deflection control device comprises a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in the main scanning direction;   said beam deflection control device is disposed between a beam deflecting device and the scanning surface; and   the deflection amount in the main scanning direction of each beam deflection control unit is controlled for each scanning action so that a uniform velocity characteristic is corrected.   
     
     
       38. A beam deflection apparatus, comprising:
 a beam deflection control device configured for use in an optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, wherein:   said beam deflection control device is disposed on the light path of the beam before it is incident on the scanning surface, said beam deflection control device configured to cause an electric field distribution in a liquid crystal by applying electricity to an electrode formed on a side of a glass substrate;   a beam deflection amount of the beam deflecting device provided to an incident beam is controlled if necessary so that a scanning characteristic of the optical scanning is controlled;   at least one resinous image-formation optical device is disposed in the optical scanning system;   the beam deflection control device comprises deflection areas configured by a series of a plurality of deflection devices defined in a main scanning direction;   laser beams corresponding to a plurality of colors have at least a single scanning image-formation device to pass through; and   the control of the scanning characteristic of the optical scanning is carried out individually for each of a plurality of ranges divided in the main scanning direction.   
     
     
       39. The beam deflection control device as claimed in  claim 38 , comprising a liquid crystal device by which a refractive index thereof can be controlled electrically, and thus, the direction of the incident beam can be changed accordingly. 
     
     
       40. The beam deflection control device as claimed in  claim 38 , wherein:
 said beam deflection control device comprises a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in a subscanning direction;   said beam deflection control device is disposed between a beam deflecting device and the scanning surface; and   the deflection amount in the subscanning direction of each beam deflection control unit is controlled for each scanning action so that scan line bending is corrected.   
     
     
       41. An optical scanning device comprising the beam deflection control device claimed in  claim 40 . 
     
     
       42. The beam deflection control device as claimed in  claim 38 , wherein:
 said beam deflection control device comprises a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in the main scanning direction;   said beam deflection control device is disposed between a beam deflecting device and the scanning surface; and   the deflection amount in the main scanning direction of each beam deflection control unit is controlled for each scanning action so that a uniform velocity characteristic is corrected.   
     
     
       43. An optical scanning device comprising the beam deflection control device claimed in  claim 42 . 
     
     
       44. The beam deflection control device as claimed in  claim 38 , comprising:
 a first array of plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in a subscanning direction;   a second array of a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in the main scanning direction;   said first array and said second array are disposed in sequence between a beam deflecting device and the scanning surface;   the deflection amount in the subscanning direction of each beam deflection control unit of said first array is controlled for each scanning action so that a scan line bending is corrected; and   the deflection amount in the main scanning direction of each beam deflection control unit of said second array is controlled for each scanning action so that a uniform velocity characteristic is corrected.   
     
     
       45. The beam deflection control device a claimed in  claim 44 , wherein:
 said first array and said second array are configured in such a manner that these arrays are combined together integrally.   
     
     
       46. An optical scanning device comprising the beam deflection control device claimed in  claim 44 . 
     
     
       47. A beam deflection control device, comprising:
 a beam deflection device configured for use in an optical scanning device in which a plurality of beams for respective color components for forming a color image in combination are deflected, are converged by a scanning and image-formation optical system, are directed to respective scanning surfaces individually and thus performing optical scanning of the scanning surfaces respectively, so as to write images of respective color components, wherein:   said beam deflection control device acts as a scan line correcting device which corrects a scan line bending;   a scan line bending on the beam of one color, component is regarded as a reference scan line bending;   the scan line correcting device electronically corrects a scan line bending of the beam of each of the other color components for the reference scan line bending;   at least one resinous image-formation optical device is disposed in the optical scanning system;   the beam deflection control device comprises deflection areas configured by a series of a plurality of deflection devices defined in a main scanning direction;   laser beams corresponding to a plurality of colors have at least a single scanning image-formation device to pass through; and   the control of a scanning characteristic of the optical scanning is carried out individually for each of a plurality of ranges divided in the main scanning direction.   
     
     
       48. The beam deflection control device as claimed in  claim 47 , comprising:
 a plurality of individually controllable liquid crystal deflection devices arranged along the main scanning direction, and disposed on the light path of the beam to be corrected with respect to the scan line bending, each individually controllable liquid crystal deflecting device being controlled with respect to the deflection amount to be provided to the incident beam in the subscanning direction according to the optical scanning.   
     
     
       49. The beam deflection control device claimed in  claim 47 , wherein:
 the beam deflection control device is configured in such a manner that the respective beam deflection control devices provided for correcting the scan line bending of the beams for the respective color components to be corrected for the reference scan line bending are combined together integrally.   
     
     
       50. The beam deflection control device claimed in  claim 49 , wherein:
 the beam deflection control device comprising the integral combination of said respective beam deflection control devices for the beams for forming the respective color-component images further comprises, also in an integral combination manner, a portion through which the beam having said reference scan line bending passes without having any beam deflection applied thereto.   
     
     
       51. An optical scanning device in which a plurality of beams for respective color components for forming a color image in combination are deflected, are converged by a scanning and image-formation optical system, are directed to respective scanning surfaces individually and thus performing optical scanning of the scanning surfaces respectively, so as to write images of respective color components, comprising:
 the beam deflection control device claimed in  claim 47  configured to act as a scan line correcting device which corrects a scan line bending, wherein   a scan line bending on the beam of one color component is regarded as a reference scan line bending; and   the scan line correcting device corrects a scan line bending of the beam of each of the other color components for the reference scan line bending.   
     
     
       52. An image formation device which performs image formation by performing optical scanning on a photosensitive medium, comprising the optical scanning device claimed in  claim 51  performing the optical scanning. 
     
     
       53. An image formation device forming a color image in which a plurality of beams for respective color components for forming a color image in combination are deflected, are converged by a scanning and image-formation optical system, are directed to respective scanning surfaces individually and thus performing optical scanning of the scanning surfaces respectively, so as to write images of respective color components, the images of the respective color components being then combined on a sheet-shaped recording medium so that a color image is formed thereon, said image formation device comprising the optical scanning device claimed in  claim 51  performing the optical scanning of each scanning surface. 
     
     
       54. A beam deflection control device used in an optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam,
 wherein:   said beam deflection control device is used for adjusting the optical spot formed on the scanning surface:   said beam deflection control device comprises a plurality of beam deflection control units each individually controllable of a deflection amount provided to an incident beam, arranged along a main scanning direction, each beam deflection control unit configured to cause an electric field distribution in a liquid crystal by applying electricity to an electrode formed on a side of a glass substrate;   the deflection amount of each beam deflection control unit is controlled according to the optical scanning;   at least one resinous image-formation optical device is disposed in the optical scanning system;   the beam deflection control device comprises deflection areas configured by a series of a plurality of deflection devices defined in a main scanning direction;   laser beams corresponding to a plurality of colors have at least a single scanning image-formation device to pass through; and   the control of a scanning characteristic of the optical scanning is carried out individually for each of a plurality of ranges divided in the main scanning direction.   
     
     
       55. The beam deflection control  claim 54 , wherein:
 each beam deflection control unit comprises a liquid crystal device by which a refractive index thereof can be controlled electrically, and thus, the direction of the incident beam can be changed accordingly.   
     
     
       56. The beam deflection control device as claimed in  claim 54 , wherein:
 said beam deflection control device comprises a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in a subscanning direction.   
     
     
       57. The beam deflection control device claimed in  claim 56 , wherein:
 said beam deflection control device is configured so that the main-directional-length of each beam deflection control unit is so small that a difference in deflection amount between adjacent beam deflection control units be regarded as a substantially smooth variation.   
     
     
       58. The beam deflection control device as claimed in  claim 54 , wherein:
 said beam deflection control device comprises a plurality of beam deflection control units, arranged in a main scanning direction, each having a function of providing a deflection amount to the incident beam in a main scanning direction.   
     
     
       59. The beam deflection control device claimed in  claim 58 , wherein:
 said beam deflection control device is configured so that the main-directional-length of each beam deflection control unit is so small that a difference in deflection amount between adjacent beam deflection control units be regarded as a substantially smooth variation.   
     
     
       60. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, comprising the beam deflection control device claimed in  claim 54  adjusting the optical spot formed on the scanning surface. 
     
     
       61. The optical scanning device as claimed in  claim 60 , wherein:
 said beam deflection control device is disposed between an optical scanning device performing the optical scanning of the scanning surface and the scanning surface.   
     
     
       62. The optical scanning device as claimed in  claim 60  comprising a multi-beam-type optical scanning device in which a light source device emits a plurality of beams and the scanning surface is scanned by the plurality of beams simultaneously. 
     
     
       63. The optical scanning device as claimed in  claim 60 , wherein:
 a plurality of light sources are provided; and   a scanning optical system defining a light path from each light source toward the respective scanning surface is configured so that a scan line drawn by an optical spot formed by the beam coming from each light source is substantially parallel to each other.   
     
     
       64. The optical scanning device as claimed in  claim 63 , wherein:
 the beam deflection control device is provided for each light source.   
     
     
       65. The optical scanning device as claimed in  claim 63 , wherein:
 the number of light sources is 3 or 4, and the beam emitted from each light source is modulated by image information for forming an image in a respective one of color components which thus form a color image in combination.   
     
     
       66. An image formation device which performs image formation by performing optical scanning on a photosensitive medium, comprising:
 the optical scanning device claimed in  claim 60 .   
     
     
       67. The image formation device as claimed in  claim 66 , wherein:
 said photosensitive medium comprises a photoconductive photosensitive body on which an electrostatic latent image is formed as a result of the optical scanning performed by said optical scanning device; and   a toner image formed on said photosensitive body as a result of visualization of the electrostatic latent image is then transferred onto a sheet-shaped recording medium.   
     
     
       68. The image formation device as claimed in  claim 67 , wherein:
 the number of the photoconductive photosensitive bodies is 3 or 4 on which respective color-component images are formed as a result of optical scanning with beams previously modulated by image information for forming the respective color-component images from which a color image is formed in combination; and   the respective photoconductive photosensitive bodies are disposed in mutually parallel.   
     
     
       69. An image formation method applied to the image formation device as claimed in  claim 66 , comprising:
 detecting a scanning position of the optical spot with a scanning position detecting device; and   based on the detection result of the scanning position detecting device, determining a deflection amount of a respective beam deflection control unit.   
     
     
       70. The image formation method as claimed in  claim 69 , wherein:
 said step of determining is performed when a power supply to the image formation device is started.   
     
     
       71. The image formation method as claimed in  claim 69 , further comprising:
 said steps of detecting and determining are performed prior to commencement of a regular image formation process.   
     
     
       72. The image formation method as claimed in  claim 69 , further comprising:
 when successive image formation processes are performed in the image formation device in which a photoconductive photosensitive body is used as the photosensitive medium, determining whether or not a change of the deflection amount of the respective beam deflection control unit is needed, within a recording-medium conveyance time interval on successive conveyance of sheet-shaped recording media on each of which a toner image is transferred from the photoconductive photosensitive body.   
     
     
       73. The image formation method as claimed in  claim 72 , further comprising:
 when a change of the deflection amount on the respective beam deflection control unit is determined to be needed, performing an actual change of the deflection amount on the beam deflection control unit within the recording-medium conveyance interval same as that in which the optical spot scanning position detection is performed, or within the subsequent recording-medium conveyance interval.   
     
     
       74. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, comprising the beam deflection control device claimed in  claim 54  adjusting the optical spot formed on the scanning surface, wherein
 said beam deflection control device is disposed in a manner such that it is inclined with respect to a subscanning direction. 
 
     
     
       75. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, comprising:
 a liquid crystal beam deflection control device adjusting the optical spot formed on the scanning surface; and   a ghost light removal device blocking a diffracted beam occurring through said liquid crystal beam deflection control device which acts as a ghost light from reaching the scanning surface, wherein   said liquid crystal beam deflection control device is disposed between an optical deflection scanning device which performs the optical scanning of the scanning surface and the scanning surface, and   said ghost light blocking device comprises a slit opening long along a main scanning direction through which only a regular optical scanning beam is passed.   
     
     
       76. The An optical scanning device as claimed in  claim 75 , in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, comprising:
 a liquid crystal beam deflection control device adjusting the optical spot formed on the scanning surface; and 
 a ghost light removal device blocking a diffracted beam occurring through said liquid crystal beam deflection control device which acts as a ghost light from reaching the scanning surface, wherein 
 said liquid crystal beam deflection control device is disposed between an optical deflection scanning device which performs the optical scanning of the scanning surface and the scanning surface, and 
 said ghost light blocking device comprises a slit opening long along a main scanning direction through which only a regular optical scanning beam is passed, 
 wherein the following requirements be satisfied:
   L>(½)(b+Δ)/tan Θ
 
 
 where: 
 ‘b’ denotes a width in a subscanning direction of each beam deflected by the liquid crystal beam deflection control device; 
 ‘A’ ‘Δ’ denotes a width in the subscanning direction of the slit opening of the ghost light removal device; 
 ‘L’ denotes a distance between the liquid crystal beam deflection control device and the slit opening of the ghost light removal device; and 
 ‘Θ’ denotes an angle formed in the subscanning direction between the regular optical scanning beam obtained from the liquid crystal beam deflection control device and the ghost light which is nearest to said regular optical scanning beam with respect to the chief rays thereof. 
 
     
     
       77. The An optical scanning device as claimed in  claim 75 , in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, comprising:
 a liquid crystal beam deflection control device adjusting the optical spot formed on the scanning surface; and 
 a ghost light removal device blocking a diffracted beam occurring through said liquid crystal beam deflection control device which acts as a ghost light from reaching the scanning surface, wherein 
 said liquid crystal beam deflection control device is disposed between an optical deflection scanning device which performs the optical scanning of the scanning surface and the scanning surface, and 
 said ghost light blocking device comprises a slit opening long along a main scanning direction through which only a regular optical scanning beam is passed, 
 wherein: 
 said ghost light removal device is provided in such a manner that it is integrally combined with any one of optical devices disposed between the optical deflection scanning device and the scanning surface. 
 
     
     
       78. An image formation device which performs image formation by performing optical scanning on a photosensitive medium, comprising the optical scanning device claimed in  claim 75  performing the optical scanning. 
     
     
       79. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, comprising:
 a liquid crystal beam deflection control device adjusting the optical spot formed on the scanning surface; and   a ghost light removal device blocking a diffracted beam occurring through said liquid crystal beam deflection control device which acts as a ghost light from reaching the scanning surface, wherein   said ghost light blocking device comprising a slit opening long along a main scanning direction through which only a regular optical scanning beam is passed.   
     
     
       80. A new image formation device which performs image formation by performing optical scanning on a photosensitive medium, comprising the optical scanning device claimed in  claim 79  performing the optical scanning. 
     
     
       81. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, comprising:
 a liquid crystal beam deflection control device adjusting the optical spot formed on the scanning surface; and 
 a ghost light removal device blocking a diffracted beam occurring through said liquid crystal beam deflection control device which acts as a ghost light from reaching the scanning surface, wherein 
 said ghost light blocking device comprises a slit opening long along a main scanning direction through which only a regular optical scanning beam is passed, and 
 the following requirements by satisfied:
   L>(½)(b+Δ)/tan Θ
 
 
 where: 
 ‘b’ denotes a width in a subscanning direction of each beam deflected by the liquid crystal beam deflection control device; 
 ‘Δ’ denotes a width in the subscanning direction of the slit opening of the ghost light removal device; 
 ‘L’ denotes a distance between the liquid crystal beam deflection control device and the slit opening of the ghost light removal device; and 
 ‘Θ’ denotes an angle formed in the subscanning direction between the regular optical scanning beam obtained from the liquid crystal beam deflection control device and the ghost light which is nearest to said regular optical scanning beam with respect to the chief rays thereof. 
 
     
     
       82. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, comprising:
 a liquid crystal beam deflection control device adjusting the optical spot formed on the scanning surface; and 
 a ghost light removal device blocking a diffracted beam occurring through said liquid crystal beam deflection control device which acts as a ghost light from reaching the scanning surface, wherein 
 said ghost light blocking device comprises a slit opening long along a main scanning direction through which only a regular optical scanning beam is passed, and 
 said ghost light removal device is provided in such a manner that it is integrally combined with any one of the optical devices disposed between the optical deflection scanning device and the scanning surface. 
 
     
     
       83. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, said device comprising:
 a liquid crystal beam deflection control device disposed on the light path of the beam before it is incident on the scanning surface, said liquid crystal beam deflection control device configured to cause an electric field distribution in a liquid crystal by applying electricity to an electrode formed on a side of a glass substrate; and   a ghost light removal device configured to block a diffracted beam occurring through said liquid crystal beam deflection control device which acts as a ghost light from reaching the scanning surface, and including a slit opening long along a main scanning direction through which only a regular optical scanning beam is passed, wherein   a beam deflection amount of the liquid crystal beam deflection control device provided to an incident beam is controlled so that a scanning characteristic of the optical scanning is controlled to adjust the optical spot formed on the scanning surface,   at least one resinous image-formation optical device is disposed in the optical scanning system,   the liquid crystal beam deflection control device comprises deflection areas configured by a series of a plurality of deflection devices defined in a main scanning direction, and   the liquid crystal beam deflection control device includes liquid crystal deflection areas separated in a subscanning direction for respective laser beams corresponding to a plurality of colors, and the liquid crystal deflection areas are configured by a single laser beam transmitting member.   
     
     
       84. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, said device comprising:
 a liquid crystal beam deflection control device disposed on the light path of the beam before it is incident on the scanning surface, said liquid crystal beam deflection control device configured to cause an electric field distribution in a liquid crystal by applying electricity to an electrode formed on a side of a glass substrate; and   a ghost light removal device configured to block a diffracted beam occurring through said liquid crystal beam deflection control device which acts as a ghost light from reaching the scanning surface, and including a slit opening long along a main scanning direction through which only a regular optical scanning beam is passed, wherein   a beam deflection amount of the liquid crystal beam deflection control device provided to an incident beam is controlled so that a scanning characteristic of the optical scanning is controlled to adjust the optical spot formed on the scanning surface,   at least one resinous image-formation optical device is disposed in the optical scanning system,   the liquid crystal beam deflection control device comprises deflection areas configured by a series of a plurality of deflection devices defined in a main scanning direction,   the liquid crystal beam deflection control device includes liquid crystal deflection areas separated in a subscanning direction for respective laser beams corresponding to a plurality of colors, and the liquid crystal deflection areas are configured by a single laser beam transmitting member, and   the following conditions are satisfied:
   L>(½)(b+Δ)/tan Θ
 
   where:   ‘b’ denotes a width in a subscanning direction of each beam deflected by the liquid crystal beam deflection control device;   ‘Δ’ denotes a width in the subscanning direction of the slit opening of the ghost light removal device;   ‘L’ denotes a distance between the liquid crystal beam deflection control device and the slit opening of the ghost light removal device; and   ‘Θ’ denotes an angle formed in the subscanning direction between the regular optical scanning beam obtained from the liquid crystal beam deflection control device and the ghost light which is nearest to said regular optical scanning beam with respect to the chief rays thereof.   
     
     
       85. An optical scanning device in which a beam is deflected, and the deflected beam is converged and directed toward a scanning surface, so that optical scanning of the scanning surface is performed by an optical spot formed thereon by the deflected beam, said device comprising:
 a liquid crystal beam deflection control device disposed on the light path of the beam before it is incident on the scanning surface, said liquid crystal beam deflection control device configured to cause an electric field distribution in a liquid crystal by applying electricity to an electrode formed on a side of a glass substrate; and   a ghost light removal device configured to block a diffracted beam occurring through said liquid crystal beam deflection control device which acts as a ghost light from reaching the scanning surface, and including a slit opening long along a main scanning direction through which only a regular optical scanning beam is passed, wherein   a beam deflection amount of the liquid crystal beam deflection control device provided to an incident beam is controlled so that a scanning characteristic of the optical scanning is controlled to adjust the optical spot formed on the scanning surface,   at least one resinous image-formation optical device is disposed in the optical scanning system,   the liquid crystal beam deflection control device comprises deflection areas configured by a series of a plurality of deflection devices defined in a main scanning direction,   the liquid crystal beam deflection control device includes liquid crystal deflection areas separated in a subscanning direction for respective laser beams corresponding to a plurality of colors, and the liquid crystal deflection areas are configured by a single laser beam transmitting member, and   the ghost light removal device is integrally combined with any one of the optical devices disposed between the optical deflection scanning device and the scanning surface.