Image formation device

Claim 2

An image formation device for forming an electrostatic latent image on a photosensitive body (7) by means of a laser beam, comprising: (a) a semiconductor laser (54) for generating a laser beam to form an electrostatic latent image on the photo­sensitive body (7); (b) a collimating lens (51) for arranging the laser beam from said semiconductor laser into a parallel beam; (c) flattening means (56, 57) for flattening the laser beam from said collimating lens (51); (d) scanning means (22) for scanning by deflecting the laser beam from said flattening means in the direction of main scanning; (e) first and second scanning lenses (24, 43) for co­operatively correcting the light path of the laser beam so as to move the laser beam from said scanning means (22) on the surface of said photosensitive body (7) at a constant speed; (f) said first scanning lens (24) being arranged on the side of the scanning means from the mid-point of the optical path length between the scanning means and the surface of the photosensitive body; (g) said second scanning lens (43) being arranged on the side of the photosensitive body from the mid-point of the optical path length between the scanning means and the surface of the photosensitive body; (h) said second scanning lens (43) having a power in the main scanning direction and a power in the sub-scanning direction which is strong at least several times the power in the main scanning direction.

Claim 3

The image formation device as claimed in claim 1, in which said second scanning lens is formed for giving its incidence surface a noncylindrical form to have power substantially in the main scanning direction alone and the power and the form of generatrix in the sub-scanning direction of its emission surface are functions of the image height in the main scanning direction, whereby the deviation from the fϑ characteristic due to the first scanning lens is principally corrected by the form of generatrix of the noncylindrical surface haveing power substantially in the main scanning direction and the other surface, while the bending in the sagittal image surface conjugated with the deflecting point of said scanning means is corrected by the power in the sub-scanning direction and the form of generatrix of the other surface.

Claim 4

The image formation device as claimed in claim 1, in which said second scanning lens is formed for giving its emission surface a noncylindrical form to have power substantially in the main scanning direction alone, and the power and the form of generatrix in the sub-scanning direction of its incidence surface are functions of the image height in the main scanning direction, whereby the deviation from the fϑ characteristic due to the first scanning lens is principally corrected by the form of generatrix of the noncylindrical surface that has power substantially in the main scanning direction and the other surface, while the bending in the sagittal image surface conjugated with the deflecting point of said scanning means is corrected by the power in the sub-scanning direction and the form of generatrix of the other surface.

Claim 5

The image formation device as claimed in claim 1, in which the curvature and the slope in the main scanning direction of said second scanning lens are functions of the image height in the main scanning direction, whereby it is possible to assign a surface slope that corrects the deviation from the fϑ characteristic due to the first scanning lens as a difference quantity, to the main scanning direction of the second scanning lens.

Claim 6

The image formation device as claimed in claim 1, in which said first scanning lens is arranged in the neighborhood of the deflector provided between said scanning means and the second scanning lens, and said second scanning lens is arranged in the neighborhood of the photosensitive body.

Claim 7

The image formation device as claimed in claim 5, in which said second scanning lens is formed so as to have the power in the main scanning direction which is a fraction of the power in the sub-scanning direction, whereby the beam deflection in the sub-scanning direction due to the deflector is corrected effectively by the power and the form of generatrix in the sub-scanning direction of the second scanning lens that is placed in the neighborhood of the photosensitive body.

Claim 8

The image formation device as claimed in claim 4, in which said second scanning lens is formed so as to have the curvature in the sub-scanning direction of at least either one of the incidence surface and the emission surface to be a function of the image height in the main scanning direction, thereby eliminating completely the bending of the sagittal image surface conjugated with the deflecting point of said scanning means by properly varying the power and the form of the second scanning lens in the sub-scanning direction at the image height.

Claim 9

The image formation device as claimed in claim 1, in which said second scanning lens is formed bar-like with plastic resin.

Claim 10

The image formation device as claimed in claim 1, in which said second scanning lens is formed so as to have the respective curvatures, for the image height in the main scanning direction, of the main scanning direction and the sub-scanning direction to be symmetric, thereby correcting distortions that are symmetric with respect to the optical axis of said first scanning lens and the bending curvature of the image surface.

Claim 11

The image formation device as claimed in claim 1, in which said second scanning lens is formed so as to have the reflecting surface of the laser beam provided on the scanning means and the position of the image height in the main scanning direction of the photosensitive body are to be mutually conjugate, by the cooperative action of the power and form in the sub-scanning direction of said second scanning lens with respect to those of the main scanning direction and said first scanning lens.

Claim 12

The image formation device as claimed in claim 1, in which said flattening means comprises a collimating lens unit mounted freely turnably, with the laser beam as the center, in a plane perpendicular to the laser beam emitted from said collimating lens.

Claim 13

The image formation device as claimed in claim 11, in which the collimating lens unit comprises a first and a second prism.

Claim 14

The image formation device as claimed in claim 12, in which said semiconductor laser, collimating lens, and first and second prisms are housed in one united body.

Claim 15

The image formation device as claimed in claim 1, in which said scanning means comprises a polygonal mirror for deflectively scanning in a prescribed scanning direction by means of the reflecting surfaces arranged on a rotating circle, and the laser beam reflecting surfaces are tilted to be out of the plane being perpendicular to said scanning direction.

Claim 16

The image formation device as claimed in claim 1, in which the second scanning lens is provided with a positioning member for positioning the main scanning direction.

Claim 17

The image formation device as claimed in claim 1, further comprising: detecting means for detecting the horizontally synchronized signal by receiving laser beam with a specified deflection angle.

Claim 18

The image formation device as claimed in claim 16, in which said detecting means comprises a horizontally synchronized signal detection element, a cylindrical lens that has power only in the main scanning direction and is provided on the side of the stage prior to the beam receiving plane of the detection element, and a cylindrical lens having power only in the sub-scanning direction which is perpendicular to the main scanning direction of the laser beam.

Claim 19

An image formation device for forming an electrostatic latent image on a photosensitive body by means of a laser beam, comprising: (a) a semiconductor laser (54) for generating a laser beam to form an electrostatic latent image on the photosensitive body (7), (b) a collimating lens (51) for arranging the laser beam from said semiconductor laser into a parallel beam; (c) a collimating lens unit (56, 57) mounted, freely turnably with the laser beam as the center, on a plane being perpendicular to the laser beam emitted from said collimating lens (51) in order to flatten the laser beam from said collimat­ing lens; (d) a polygonal mirror (22) for deflectively scanning in a specified scanning direction by means of the reflecting surfaces provided on the rotating circle in order to deflective­ly scan the laser beam from said collimating lens unit in the main scanning direction; (e) first and second scanning lenses (24, 43) for co­operatively scanning the optical path to move the laser beam from the polygonal mirror (22) over said photosensitive body (7) at a constant speed; (f) said first scanning lens (24) arranged on the side of the polygonal mirror from the mid-point of the optical path between the polygonal mirror and the photosensitive body, and (g) said second scanning lens (43) arranged on the side of the photosensitive body from the mid-point of the optical path between the scanning means and the photosensitive body and having a power in the main scanning direction and a power in the sub-scanning direction that is at least several times the power in the main scanning direction, both of the incidence and the emission surfaces of said second scanning lens being formed to be noncylindrical surfaces with power in the main scanning direction and the power and the form of generatrix in the sub-scanning direction of both surfaces of said second scanning lens are functions of the image height in the main scanning direction, whereby the deviation from the fϑ characteristic due to the first scanning lens is corrected principally by the form of generatrix of the noncylindrical surfaces having power in the main scanning direction and the bending of the image surface conjugated with a deflecting point of said scanning means is corrected principally by the power and the form of generatrix in the sub-scanning direction.

Claim 20

An image formation device for forming an electrostatic latent image on a photosensitive body by means of a laser beam, comprising: (a) a semiconductor laser (54) for generating a laser beam to form an electrostatic latent image on the photosensitive body (7), (b) a collimating lens (51) for arranging the laser beam from said semiconductor laser into a parallel beam; (c) a collimating lens unit (56, 57) mounted, freely turnably with the laser beam as the center, on a plane being perpendicular to the laser beam emitted from said collimating lens (51) in order to flatten the laser beam from said collimat­ing lens; (d) a polygonal mirror (22) for deflectively scanning in a specified scanning direction by means of the reflecting surfaces provided on the rotating circle in order to deflective­ly scan the laser beam from said collimating lens unit in the main scanning direction; (e) first and second scanning lenses (24, 43) for co­operatively scanning the optical path to move the laser beam from the polygonal mirror (22) over said photosensitive body (7) at a constant speed; (f) said first scanning lens (24) arranged on the side of the polygonal mirror from the mid-point of the optical path between the polygonal mirror and the photosensitive body, and (g) said second scanning lens (43) arranged on the side of the photosensitive body from the mid-point of the optical path between the scanning means and the photosensitive body and having a power in the main scanning direction and a power in the sub-scanning direction that is at least several times the power in the main scanning direction, both of the incidence and the emission surfaces of said second scanning lens being formed to be noncylindrical surfaces with power in the main scanning direction and the power and the form of generatrix in the sub-scanning direction of both surfaces of said second scanning lens are functions of the image height in the main scanning direction, whereby the deviation from the fϑ characteristic due to the first scanning lens is corrected principally by the form of generatrix of the noncylindrical surfaces having power in the main scanning direction and the bending of the image surface conjugated with a deflecting point of said scanning means is corrected principally by the power and the form of generatrix in the sub-scanning direction.