Tilt error corrective scanning optical system

Abstract

A tilt error corrective scanning optical system for use in a laser scanning machine such as a laser printer. The system comprises a linear image forming optical device for causing a beam to form a linear image on a deflecting device, and a scanning image forming optical device for causing the beam deflected by the deflecting device to form an image on a scanned object. The scanning image forming optical device includes a first lens disposed between the deflecting element and the scanned object, and a second lens disposed at a side of the first lens opposed to the scanned object. The second lens includes a toric surface opposed to the scanned object. A surface of the second lens opposed to the deflecting element, a surface of the first lens opposed to the scanned object or a surface of the first lens opposed to the deflecting element defines a cylindrical surface having a refracting power in a direction perpendicular to a scanning plane.

What is claimed is: 
     
       1. A tilt error corrective scanning optical system for a system having deflecting means for deflecting and reflecting a beam of light, comprising: a linear image forming optical device for causing a beam emitted from a light source to form a linear image on a deflecting and reflecting surface of said deflecting means, and   a scanning image forming optical device for causing the beam reflected and deflected by said deflecting means to form an image on a scanned object, said scanning image forming optical device consisting of a first lens disposed between said deflecting means and said scanned object, and a second lens disposed at a side of said first lens opposed to said scanned object, wherein said first lens includes a cylindrical surface, and said second lens includes a toric surface.   
     
     
       2. A tilt error corrective scanning optical system as claimed in claim 1, wherein said first lens has a negative refracting power in a direction perpendicular to a scanning plane. 
     
     
       3. A tilt error corrective scanning optical system as claimed in claim 2, wherein said cylindrical surface of said first lens is defined on a surface of said first lens opposed to said deflecting means. 
     
     
       4. A tilt error corrective scanning optical system as claimed in claim 3, wherein said second lens defines a concave surface opposed to said deflecting means. 
     
     
       5. A tilt error corrective scanning optical system as claimed in claim 2, wherein said cylindrical surface of said first lens is defined on a surface of said first lens opposed to said scanned object. 
     
     
       6. A tilt error corrective scanning optical system as claimed in any one of claims 2 through 5, wherein said first lens per se as a whole has a negative refracting power in a direction parallel to the scanning plane. 
     
     
       7. A tilt error corrective scanning optical system as claimed in claim 6, wherein said first lens satisfies the following condition:   |f1H/f1V|>2     wherein f1H is a focal length of said first lens in the direction parallel to the scanning plane, and f1V is a focal length of said first lens in the direction perpendicular to the scanning plane.   
     
     
       8. A tilt error corrective scanning optical system as claimed in claim 1, wherein said scanning image forming optical device is so arranged that the deflecting and reflecting surface and said scanned object are set in an optical conjugate relationship. 
     
     
       9. A tilt error corrective scanning optical system for a system having deflecting means for deflecting and reflecting a beam of light, comprising: a linear image forming optical device for causing a beam emitted from a light source to form a linear image on a deflecting and reflecting surface of said deflecting means, and   a scanning image forming optical device for causing the beam reflected and deflected by said deflecting means to form an image on a scanned object, said scanning image forming optical device consisting of a first lens disposed between said deflecting means and said scanned object, and a second lens disposed at a side of said first lens opposed to said scanned object, wherein said first lens comprises a cylindrical lens having no refracting power in a direction parallel to a scanning plane, and said second lens includes a toric surface.   
     
     
       10. A tilt error corrective scanning optical system as claimed in claim 9, wherein said first lens has a negative refracting power in a direction perpendicular to the scanning plane. 
     
     
       11. A tilt error corrective scanning optical system as claimed in claim 10, wherein said first lens includes a cylindrical surface on a surface of said first lens opposed to said deflecting means to have a negative refracting power in the direction perpendicular to the scanning plane. 
     
     
       12. A tilt error corrective scanning optical system as claimed in claim 11, wherein said second lens includes a surface opposed to said deflecting means and having a negative refracting power. 
     
     
       13. A tilt error corrective scanning optical system as claimed in claim 9, wherein said scanning image forming optical device is so arranged that the deflecting and reflecting surface and said scanned object are set in an optical conjugate relationship. 
     
     
       14. A tilt error corrective scanning optical system for a system having deflecting means for deflecting and reflecting a beam of light, comprising: a linear image forming optical device for causing a beam emitted from a light source to form a linear image on a deflecting and reflecting surface of said deflecting means, and   a scanning image forming optical device for causing the beam reflected and deflected by said deflecting means to form an image on a scanned object, said scanning image forming optical device consisting of a first lens disposed between said deflecting means and said scanned object, and a second lens disposed at a side of said first lens opposed to said scanned object, wherein said first lens includes a first cylindrical surface having an axis extending perpendicular to a scanning plane and a second cylindrical surface having an axis extending parallel to the scanning plane, and said second lens includes a toric surface.   
     
     
       15. A tilt error corrective scanning optical system as claimed in claim 14, wherein said first lens has a negative refracting power in a direction perpendicular to the scanning plane. 
     
     
       16. A tilt error corrective scanning optical system as claimed in claim 15, wherein said second cylindrical surface is defined on a surface of said first lens opposed to said deflecting means to have a negative refracting power. 
     
     
       17. A tilt error corrective scanning optical system as claimed in claim 15, wherein said second cylindrical surface is defined on a surface of said first lens opposed to said scanned object to have a negative refracting power. 
     
     
       18. A tilt error corrective scanning optical system as claimed in claim 17, wherein said first lens has a negative refracting power in a direction parallel to the scanning plane. 
     
     
       19. A tilt error corrective scanning optical system as claimed in any one of claims 15 through 18, wherein said first lens satisfies the following condition:   |f1H/f1V|>2     wherein f1H is a focal length of said first lens in the direction parallel to the scanning plane, f1V is a focal length of said first lens in the direction perpendicular to the scanning plane.   
     
     
       20. A tilt error scanning optical system as claimed in claim 16, wherein said first lens has a negative refracting power in a direction parallel to the scanning plane. 
     
     
       21. A tilt error scanning optical system as claimed in claim 12, wherein said first lens has a negative refracting power in a direction parallel to the scanning plane. 
     
     
       22. A tilt error corrective scanning optical system as claimed in claim 14, wherein said scanning image forming optical device is so arranged that the deflecting and reflecting surface and said scanned object are set in an optical conjugate relationship. 
     
     
       23. A tilt error corrective scanning optical system for a system having deflecting means for deflecting and reflecting a beam of light, comprising: a linear image forming optical device for causing a beam emitted from a light source to form a linear image on a deflecting and reflecting surface of said deflecting means, and   a scanning image forming optical device for causing the beam reflected and deflected by said deflecting means to form an image on a scanned object, said scanning image forming optical device consisting of a first lens disposed between said deflecting means and said scanned object, and a second lens disposed at a side of said first lens opposed to said scanned object, wherein said first lens includes a cylindrical surface having an axis extending perpendicular to a scanning plane and a second lens includes a cylindrical surface having an axis extending parallel to the scanning plane, and a toric surface.   
     
     
       24. A tilt error corrective scanning optical system as claimed in claim 23, said cylindrical surface of said second lens is defined on a surface of said second lens opposed to said deflecting means to have a negative refracting power in a direction perpendicular to the scanning plane. 
     
     
       25. A tilt error corrective scanning optical system as claimed in claim 24, wherein said first lens has a negative refracting power in a direction parallel to the scanning plane. 
     
     
       26. A tilt error corrective scanning optical system as claimed in claim 23, wherein said scanning image forming optical device is so arranged that the deflecting and reflecting surface and said scanned object are set in an optical conjugate relationship. 
     
     
       27. A tilt error corrective scanning optical system for a system having deflecting means for deflecting and reflecting a beam of light, comprising: a linear image forming optical device for causing a beam emitted from a light source to form a linear image in a deflecting and reflecting surface of said deflecting means, and   a scanning image forming optical device for causing the beam reflected and deflected by said deflecting means to form an image on a scanned object, said scanning image forming optical device consisting of a first lens disposed between said deflecting means and said scanned object, and a second lens disposed at a side of said first lens opposed to said scanned object, wherein said first lens includes a toric surface opposed to said scanned object, and any one of the remaining surfaces, that is to say, a surface of said second lens opposed to said deflecting means, a surface of said first lens opposed to said scanned object and a surface of said first lens opposed to said deflecting means further defines a cylindrical surface having a refracting power in a direction perpendicular to a scanning plane.   
     
     
       28. A tilt error corrective scanning optical system as claimed in claim 21, wherein said scanning image forming optical device is so arranged that the deflecting and reflecting surface and said scanned object are set in an optical conjugate relationship. 
     
     
       29. A tilt error corrective laser beam printer comprising: a laser beam source for emitting a laser beam modulated in accordance with image data,   a collimator lens for shaping the laser beam into parallel rays,   a linear image forming optical device for converging the laser beam in parallel rays into a line,   deflecting means for reflecting and deflecting the laser beam converged into a line toward a scanned object, and   a scanning image forming optical device for causing the laser beam reflected and deflected by a deflecting and reflecting surface of said deflecting means to form an image on said scanned object, said scanning image forming optical device consisting of a first lens disposed between said deflecting means and said scanned object, and a second lens disposed at a side of said first lens opposed to said scanned object,   wherein said first lens includes a cylindrical surface, and said second lens includes a toric surface.   
     
     
       30. A laser beam printer as claimed in claim 29 wherein said linear image forming optical device comprises a cylindrical lens. 
     
     
       31. A tilt error corrective scanning optical system as claimed in claim 29, wherein said scanning image forming optical device is so arranged that the deflecting and reflecting surface and said scanned object are set in an optical conjugate relationship. .Iadd. 
     
     
       32.  A scanning optical system for use in a laser printer comprising: a semiconductor laser;   a collimator lens receiving laser light from said semiconductor laser and emitting substantially parallel light rays;   a cylindrical lens having a curvature in a cross section taken in a first direction normal to a main scan direction, said cylindrical lens receiving said parallel light rays emitted by said collimator lens and images said laser light at a focusing point in said cross section taken in said first direction;   a deflector which deflects light rays transmitted by said cylindrical lens, said deflector being disposed on a downstream side of said cylindrical lens with respect to said light rays; and   an anamorphic scanning lens unit which converges light rays deflected by said deflector at a point on a scanning surface;   wherein said anamorphic scanning lens unit has a two-element composition comprising, in order from a side nearest said deflector;   a first lens having a negative lens element with a concave spherical surface on a side facing said deflector and a concave cylindrical surface on a side facing said scanning surface, said concave cylindrical surface having a curvature in said cross section taken in said first direction, and   a second lens having a planar surface on a side facing said deflector and a convex toric surface on a side facing said scanning surface, said convex toric surface having a stronger curvature in said cross section taken in said first direction. .Iaddend. .Iadd.   
     
     
       33.  A scanning optical system for use in a laser printer as claimed in claim 32, wherein said deflector is a polygonal mirror. .Iaddend. .Iadd. 
     
     
       34.  A scanning optical system for use in a laser printer comprising: a semiconductor laser;   first means for focusing the light from said laser onto a focusing point in a first dimension while leaving the light unfocused in a second dimension normal to said first dimension;   a deflector which deflects light rays transmitted by said first means, said deflector being disposed on a downstream side of said first means with respect to light rays; and   an anamorphic scanning lens unit which converges light rays deflected by said deflector at a point on a scanning surface;   wherein said anamorphic scanning lens unit has a two-element composition comprising, in order from a side nearest said deflector;   a first lens having a negative lens element with a concave spherical surface on a side facing said deflector and a concave cylindrical surface on a side facing said scanning surface, said concave cylindrical surface having a curvature in a cross section taken in a direction normal to said first dimension, and   a second lens having a planar surface on a side facing said deflector and a convex toric surface on a side facing said scanning surface, said convex toric surface having a stronger curvature in said cross section taken in said direction normal to said first dimension. .Iaddend. .Iadd.35. A tilt error corrective scanning optical system having a deflecting means for deflecting and reflecting a beam of light, comprising:   a linear image forming optical device for causing the beam emitted from a light source to form a linear image in a direction and reflecting surface of said deflecting means, said linear image being parallel to a direction normal to a first dimension and   an anamorphic scanning lens unit which converges the beam deflected by said deflecting means at a point on a scanning surface;   wherein said anamorphic scanning lens unit has a two-element composition comprising, in order from a side nearest said deflecting means;   a first lens having a negative lens element with a concave spherical surface on a side facing said deflecting means and a concave cylindrical surface on a side facing said scanning surface, said concave cylindrical surface having a curvature in a cross section taken in a direction normal to said first dimension, and   a second lens having a planar surface on a side facing said deflecting means and a convex toric surface on a side facing said scanning surface, said convex toric surface having a stronger curvature in said cross section taken in said direction normal to said first dimension. .Iaddend.