JP5094221B2 - Optical scanning device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to an optical scanning device and an image forming apparatus using the same, and is suitable for an image forming apparatus such as a laser beam printer, a digital copying machine, or a multi-function printer (multi-function printer) having an electrophotographic process.

  Conventionally, an optical scanning device is used in an image forming apparatus such as a digital copying machine or a laser beam printer (LBP).

  In this optical scanning device, as a means for reducing the size of the entire apparatus or as a means for separating a plurality of light beams when a plurality of light beams are scanned by the same optical deflector, sub-scanning is performed on the deflection surface of the optical deflector. An oblique incidence optical system that makes a light beam incident from an oblique direction within a cross section is used. As a result, the entire apparatus can be reduced in size, and the spatial separation of a plurality of light beams can be performed efficiently.

  Various types of optical scanning devices using such a method have been proposed (see Patent Document 1).

  In the conventional optical scanning device, the oblique incident angle of the light beam in the sub-scanning direction is set large with respect to the deflection surface of the optical deflector. Thus, the distance between the light beams is increased so that the optical path separation by the optical path separation mirror (optical path separation means) is facilitated.

  24A and 24B are cross-sectional views (sub-scanning cross-sectional views) in the sub-scanning direction of the optical scanning device proposed in Patent Document 1, respectively.

  24A and 24B, the sub-scan section of the entire first optical system including the first and second lenses G1 and G2 close to the optical deflector 5 so that the light beam can be separated efficiently even when the oblique incidence angle is small. The power (refractive power) is negative.

  Accordingly, when two light beams incident on the deflection surface S at slightly different angles in the sub-scanning direction are emitted from the first optical system, the distance between the light beams and the angle θ3 after passing through the second lens G2. Will spread further. As a result, the light separating mirror 10b. The distance between the light beams is obtained so that the light beam can be separated at 10c.

In FIGS. 24A and 24B, reference numerals 11a, 11b, 11c, and 11d denote reflection mirrors for bending the optical path, and 9 denotes a photosensitive drum surface (photosensitive drum) as a surface to be scanned. G3 is a third lens. θ1 is the reflection angle of the principal ray from the deflection surface S, and θ2 is the angle after passing through the first lens G1.
JP 2003-57585 A

  In general, in an optical scanning device, if the oblique incident angle of a light beam in the sub-scanning direction is increased with respect to the deflection surface, it becomes more susceptible to processing errors and mounting errors of the optical deflector (polygon mirror). The pitch unevenness of the scanning lines is greatly generated. Further, since the light beam deflected by the deflecting surface passes through a position away from the optical axis of the imaging lens in the sub-scanning cross section, scanning line bending and rotation of the imaging spot are greatly generated.

  In Patent Document 1, a sufficient distance between the light beams is obtained on the light beam separation mirrors 10b and 10c so that the light beam can be separated. However, since the third lens G3 is disposed in the optical path after the light beam is separated by the light beam separation mirrors 10b and 10c, if a mounting error of the light beam separation mirrors 10b and 10c occurs, the third lens G3 is disposed in the light path after the light beam separation. A light beam shift occurs on the lens G3. As a result, scanning line bending and imaging spot rotation occur. Further, since the third lens G3 closest to the scanning surface 9 in the optical path is disposed at a position away from other optical elements, it is difficult to make the optical scanning device compact.

  The present invention is an optical scanning apparatus that is less susceptible to mounting errors of deflecting means and light beam separating means, and that can effectively perform spatial separation of light beams and can obtain a compact and high-quality image. An object is to provide an image forming apparatus used.

The optical scanning device according to the first aspect of the present invention includes a plurality of light source means and incident optics for causing a plurality of light beams emitted from the plurality of light source means to enter the same deflection surface of the deflection means from different directions in the sub-scan section. the optical scanning apparatus having a system, and a imaging optical system Ru is imaged on the same deflecting surface deflection scanned plurality of light beams with mutually different scan plane of said deflecting means,
The imaging optical system has, as an optical element having an imaging function, a first imaging optical element whose power in the sub-scanning direction is negative in order from the deflection surface side of the optical path of the plurality of light beams, and sub-scanning Having only a second imaging optical element with positive directional power,
In the optical path between the second imaging optical element and the surface to be scanned, a reflection mirror that reflects the light beam deflected and scanned by the same deflection surface of the deflection unit is disposed ,
In the sub scanning cross section, the angle between the optical reference axis of the imaging optical system after the principal ray of the light beam has passed through the exit surface of the second imaging optical element when scanning the center of the surface to be scanned and θs2 The optical surface of the second imaging optical element performs at least one of shift decentering in the sub-scanning direction or tilt decentering with the main scanning direction as the rotation axis so that the condition of 0 (deg) ≦ θs2 is satisfied. It is characterized by.

A second aspect of the invention is characterized in that, in the first aspect of the invention, a plurality of light beams deflected and scanned by the same deflection surface of the deflecting means pass through the first and second imaging optical elements.

According to a third aspect of the present invention, in the first or second aspect of the present invention, in the sub-scan section, the optical path length from the deflection surface of the deflection means to the scanned surface is L1, and the second imaging optical element from the deflection surface to the second scanning optical element. When the optical path length to the exit surface is L2,
2 ≦ (L1 / L2) ≦ 4
It is characterized by satisfying the following conditions.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, each of the light source means has a plurality of light emitting portions.

According to a fifth aspect of the present invention, there is provided an image forming apparatus according to any one of the first to fourth aspects, a photoconductor disposed on the surface to be scanned, and a light beam scanned by the optical scanning apparatus. A developing unit that develops the electrostatic latent image formed on the photoconductor as a toner image, a transfer unit that transfers the developed toner image to a transfer material, and the transferred toner image as a transfer material. And a fixing device for fixing.

  According to the present invention, there is provided an optical scanning device which can obtain a compact and high-quality image which is not easily affected by the mounting error of the deflecting unit and the light beam separating unit and which can effectively perform the spatial separation of the light beam. An image forming apparatus using the same can be achieved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a sectional view (main scanning sectional view) of the main scanning direction of the optical scanning apparatus according to the first embodiment of the present invention, and FIG. It is a figure (sub scanning sectional drawing), and has expanded and showed the optical path.

  In the following description, the main scanning direction (Y direction) is a direction perpendicular to the rotation axis of the deflecting unit and the optical axis (X direction) of the imaging optical system (the direction in which the light beam is deflected and scanned by the deflecting unit). is there. The sub-scanning direction (Z direction) is a direction parallel to the rotation axis of the deflecting unit. The main scanning section is a plane including the optical axis of the imaging optical system and the main scanning direction. The sub-scan section is a section that includes the optical axis of the imaging optical system and is perpendicular to the main scan section.

  The optical reference axis C0 means that the principal ray of the light beam emitted from the incident optical system is deflected and scanned by the deflection surface of the optical deflector and is incident on the center of the scanned surface. An axis that passes through the point of incidence on the deflection surface and is perpendicular to the deflection surface.

  In the figure, reference numerals 1a and 1b denote light source means each made of a semiconductor laser.

  Reference numerals 2a and 2b respectively denote aperture stops, which form divergent light beams emitted from the plurality of light source means 1a and 1b into a specific beam shape. Reference numerals 3a and 3b denote condensing lenses (collimator lenses), which convert divergent light beams that have passed through the aperture stops 2a and 2b into parallel light beams (or convergent light beams). Reference numerals 4a and 4b denote lens systems (cylindrical lenses) each having a refractive power (power) only in the sub-scanning direction (within the sub-scanning cross section).

  Each element of the light source means 1a, 1b, aperture stops 2a, 2b, condenser lenses 3a, 3b, and cylindrical lenses 4a, 4b constitutes one element of the incident optical system LA.

  The incident optical system LA guides a plurality of light beams emitted from the plurality of light source units 1a and 1b to the same deflection surface 5a of the deflection unit 5 to be described later at different angles in the sub-scan section.

  The condensing lens 3a (3b) and the cylindrical lens 4a (4b) may be constituted by one optical element (anamorphic lens).

  An optical deflector 5 as a deflecting means is composed of a polygon mirror (rotating polygonal mirror) having a circumscribed circle diameter of 34 mm and a five-sided configuration, and is driven in the direction of arrow A in the figure by a driving means (not shown) comprising a motor. It is rotating at a constant speed (equal angular speed).

Reference numeral 6 denotes an imaging optical system having a light condensing function and an fθ characteristic described later. The imaging optical system 6 in this embodiment is an imaging optical element (an optical element having an imaging function) having different powers in the main scanning direction (in the main scanning section) and in the sub-scanning direction (in the sub-scanning section). First and second imaging lenses (first imaging optical element, second imaging optical element) (also referred to as scanning lenses) 6a and 6b are provided.

  The first and second imaging lenses 6a and 6b in this embodiment are made of a plastic material, and a plurality of light beams based on image information deflected and scanned by the same deflecting surface 5a of the optical deflector 5 are different from each other to be scanned. Are imaged on the photosensitive drum surfaces 7a and 7b. In addition, the first and second imaging lenses 6a and 6b have a conjugate relationship between the deflection surface 5a of the optical deflector 5 and the photosensitive drum surfaces 7a and 7b in the sub-scan section, so that the deflection surface 5a Compensate for trouble.

  The first imaging lens 6a has a positive power in the main scanning section and a negative power in the sub-scanning section on the optical axis of the first imaging lens 6a.

  The second imaging lens 6b has a negative power in the main scanning section and a positive power in the sub-scanning section on the optical axis of the second imaging lens 6b.

  Here, the fθ characteristic means that a light beam incident at an angle of view (scanning angle) θ is on the image plane (on the scanned surfaces 7a and 7b), the height from the optical axis is Y, and the constant is f. , Y = f × θ. That is, the scanning width (scanning speed) scanned per unit angle of view is equal over the entire scanning surface. The constant f is called an fθ coefficient. When the incident light beam to the imaging optical system 6 is a parallel light beam, the constant f has the same value as the paraxial focal length f of the imaging optical system 6.

  Reference numeral 7 (7a, 7b) denotes a photosensitive drum surface (photosensitive drum) as a surface to be scanned.

  In FIG. 1 and FIG. 2, a light beam separation mirror as a light beam separation means and a reflection mirror that bends the optical path are omitted.

  In the present embodiment, two divergent light beams modulated and emitted from the two light source means 1a and 1b according to image information are regulated by the corresponding aperture stops 2a and 2b, and are converted into parallel light beams by the collimator lenses 3a and 3b. The light is converted and enters the cylindrical lenses 4a and 4b. Out of the light beams incident on the cylindrical lenses 4a and 4b, they are emitted as they are in the main scanning section. In the sub-scan section, the light beams converge to form a line image (a line image elongated in the main scanning direction) on the same deflection surface 5a of the optical deflector 5 at different angles. The two light beams deflected and scanned by the deflecting surface 5a of the optical deflector 5 are spot-formed on the different photosensitive drum surfaces 7a and 7b via the first and second imaging lenses 6a and 6b. To do.

  Incidentally, the light beam from the light source means 1a incident obliquely from above in the sub-scan cross section with respect to the deflecting surface 5a of the optical deflector 5 is reflected obliquely downward, and the light beam incident from obliquely below from the light source means 1b is reflected. Reflected obliquely upward.

  Then, by rotating the optical deflector 5 in the direction of arrow A, the photosensitive drum surfaces 7a and 7b are optically scanned in the direction of arrow B (main scanning direction). Thus, image recording is performed on the photosensitive drum surfaces 7a and 7b as recording media.

  In this embodiment, it is assumed that the printing width corresponding to the A3 size is scanned, and the effective scanning width on the scanned surface 7 is 310 mm to constitute the optical system. However, the present invention is not limited to this, and larger and smaller sizes can be handled.

  The shape of the refracting surfaces of the first and second imaging lenses 6a and 6b in this embodiment is expressed by the following shape expression. When the intersection with the optical axis is the origin, the optical axis direction is the X axis, the axis orthogonal to the optical axis in the main scanning plane is the Y axis, and the axis orthogonal to the optical axis in the sub scanning plane is the Z axis, The bus direction corresponding to the scanning direction is

... (a)
(Where R is the radius of curvature of the generatrix on the optical axis, and K, B ₄ , B ₆ , B ₈ , and B ₁₀ are aspheric coefficients)
It is expressed by the following formula.

  The sub-scanning direction (direction including the optical axis and orthogonal to the main scanning direction) corresponds to the sub-line direction,

... (b)
It is expressed by the following formula.

  Here, a radius of curvature (sub-wire curvature radius) r ′ in the sub-scanning direction at a position Y away from the optical axis in the main scanning direction is

r ′ = r ₀ (1 + D ₂ Y ² + D ₄ Y ⁴ + D ₆ Y ⁶ + D ₈ Y ⁸ + D ₁₀ Y ¹⁰ )
(Where r ₀ is the radius of curvature on the optical axis on the optical axis, and D ₂ , D ₄ , D ₆ , D ₈ and D ₁₀ are coefficients)
It is expressed by the following formula.

  Note that the radius of curvature r 'outside the optical axis is defined in a plane perpendicular to the main scanning plane, including the normal of the bus at each position. The polynomial in the shape expression is expressed by a function up to the 10th order, but the order may be higher or lower. If the surface shape expression itself is an expression having the same degree of freedom of surface expression, the effect of the present invention can be obtained without any problem.

Tables 1 and 2 show the numerical values of the optical arrangement of the optical element of Example 1 and the surface shape of the imaging optical element (imaging lens) in this example. In Table 2, the first surface is the entrance surface of the first imaging lens 6a, the second surface is the exit surface of the first imaging lens 6a, the third surface is the entrance surface of the second imaging lens 6b, The fourth surface is the exit surface of the second imaging lens 6b. In addition, E-x means ^{10 -x.}

  Here, the aspheric coefficients B4u to B10u and D2u to D10u are coefficients that specify the shape on the anti-light source means 1 side with the optical axis of the lens surface in the main scanning section and the sub-scanning section. The aspheric coefficients B4l to B10l and D2l to D10l are coefficients that specify the shape of the light source means 1 with the optical axis of the lens surface in the main scanning section and the sub-scanning section.

  In this embodiment, the light beam emitted from the light source means 1 is incident on the deflection surface 5a of the optical deflector 5 at an angle with respect to the optical axis of the imaging optical system 6 in the main scanning section. The entrance / exit (sag) of the deflection surface accompanying the rotation of the lens occurs asymmetrically on the scanning start side and the end side.

  In order to satisfactorily compensate for the asymmetrical sag, the curvature of field and the variation in spot diameter are asymmetrically changed in the main scanning direction with respect to the optical axis, the first and second imaging lenses 6a and 6b are both It has a surface in which the radius of curvature in the sub-scanning direction changes asymmetrically along the main scanning direction with respect to the optical axis.

  As shown in Table 2, the aspherical coefficients B4u to B10u and B4l to B10l in the main scanning section of the second surface and the fourth surface are different, and the shape in the main scanning section is axially within the effective diameter of the lens surface. It turns out that it changes asymmetrically centering on the optical axis toward the off-axis.

  Further, the second surface, the third surface, and the fourth surface have different aspherical coefficients D2u to D10u and D2l to D10l in the sub-scanning cross section, and the curvature in the sub-scanning surface is on the axis within the effective diameter of the lens surface. It turns out that it changes asymmetrically centering on the optical axis toward the off-axis.

  In this embodiment, the entrance surface (first surface) and the exit surface (second surface) of the first imaging lens 6a are aspherical surfaces expressed by functions up to the 10th order in the main scanning section (main scanning direction). It is formed in a shape (non-arc shape). In the sub-scan section (sub-scan direction), the incident surface (first surface) is formed in a planar shape, and the exit surface (second surface) is formed in a spherical shape whose curvature changes in the main scan direction.

  The incident surface (third surface) and the exit surface (fourth surface) of the second imaging lens 6b are formed in an aspherical shape (non-arc shape) expressed by a function up to the 10th order in the main scanning section. Yes. Then, the power in the sub-scanning section decreases from on-axis to off-axis in the main scanning direction, so that the field curvature in the sub-scanning direction is well adjusted.

  In the present embodiment, as described above, the material of the first and second imaging lenses 6a and 6b is formed of a plastic material (resin). However, the material is not limited to the plastic material, and may be a glass material.

  FIG. 3 is a diagram showing the geometric aberration in the present embodiment.

  It can be seen from FIG. 3 that each aberration is adjusted to a level where there is no practical problem. It can also be seen that the change in the sub-scan magnification due to the image height is suppressed to 2% or less. As a result, a change in the spot shape in the sub-scanning direction due to the image height is suppressed, and good imaging performance can be obtained. Note that the change in the sub-scanning magnification due to the image height is preferably 10% or less. More preferably, it is 5% or less.

  Next, means and effects for achieving the object of the present embodiment will be described with reference to FIGS.

  FIG. 4 is a sub-scan sectional view of an image forming apparatus provided with two optical scanning devices of the present embodiment described above. In FIG. 4, the same elements as those shown in FIGS. 1 and 2 are denoted by the same reference numerals.

  In FIG. 4, S1 and S2 are first and second stations, respectively, and correspond to the optical scanning device described above.

  7 is a photosensitive drum (scanned surface) as a recording medium, and 7a, 7b, 7c, and 7d are photosensitive drums (scanned surfaces) as recording media for C, M, Y, and B colors, respectively.

  Reference numeral 8a denotes a light beam separation mirror (reflection mirror) as a light beam separation means, which is composed of a plane mirror, and is the first of the first and second imaging lenses 6a and 6b, which is disposed closest to the scanned surface 7 in the optical path. 2 in the optical path between the second imaging lens 6b and the surface 7 to be scanned.

  The light beam separation mirror 8a in this embodiment separates a plurality (two) of light beams deflected and scanned by the same deflection surface 5a (5b) into a plurality of light beams.

  Reference numerals 8b and 8c are reflection mirrors as reflection members, each of which is made of a plane mirror. The light beams that have passed through the first and second imaging lenses 6a and 6b are folded back to the corresponding photosensitive drums 7a, 7b, 7c, and 7d. Yes. The reflecting mirrors 8a, 8b, and 8c may have power in the main scanning section or the sub-scanning section.

  Reference numeral 5 denotes an optical deflector (polygon mirror) as a deflecting means as described above, and is used in common by the first and second stations S1 and S2.

  In FIG. 4, the above-described optical scanning device (station) is arranged so as to be symmetrically distributed on both sides about the rotation axis of the optical deflector 5 and arranged in four colors (C, M, Y, B). The image forming apparatus can be mounted on the image forming apparatus.

  In the first station S1, two light beams emitted from two light source means (not shown) are obliquely applied to the deflection surface 5a of the optical deflector 5 from the vertical direction of the optical reference axis C0 in the sub-scan section. Incident incidence is performed at an incident angle θs0. In the second station S2, two light beams emitted from two light source means (not shown) are obliquely applied to the deflecting surface 5b of the optical deflector 5 from the vertical direction of the optical reference axis C0 in the sub-scan section. Incident incidence is performed at an incident angle θs0.

  Then, the light beams incident obliquely from above to the deflecting surfaces 5a and 5b are reflected obliquely downward, and the light beams incident from obliquely below are reflected obliquely upward, and the corresponding reflecting mirrors 8a, 8b, and 8c are reflected by the imaging optical system 6. The optical path is separated through

  A color image is formed by guiding the separated four light beams onto the corresponding photosensitive drum surfaces (C, M, Y, B) 7a, 7b, 7c, and 7d.

  As described above, in FIG. 4, a plurality of optical scanning devices (stations) are provided so as to share the optical deflector 5 included in the optical scanning device. A plurality of light beams from the plurality of optical scanning devices S1 and S2 are guided to different deflection surfaces 5a and 5b of the optical deflector 5 for each optical scanning device. A plurality of light beams in each of the optical scanning devices S1 and S2 are incident on different scanned surfaces 7a, 7b, 7c, and 7d to form a color image.

  In this embodiment, the first and second imaging lenses 6a and 6b are arranged on the light deflector 5 side of the light beam separation mirror 8a. Therefore, the light beams deflected and scanned by the same deflecting surface 5a (5b) pass through all the first and second imaging lenses 6a and 6b, and then are optically separated by the light beam separation mirror 8a. , 8c to the corresponding photosensitive drum surfaces 7a, 7b, 7c, 7d.

  In this embodiment, since the imaging lens is not disposed after the light beam separation mirror 8a in the optical path, even if an attachment error of the reflection mirrors 8a, 8b, 8c occurs, the scanning line curve and the rotation of the imaging spot do not occur. .

  In this embodiment, since two light beams deflected and scanned by the same deflection surface 5a (5b) pass through the same first and second imaging lenses 6a and 6b, the number of imaging lenses. Thus, the imaging optical system 6 can be configured.

  Since the first and second stations S1 and S2 have the same configuration and optical action, only the first station S1 will be described below.

  FIG. 5 is a cross-sectional view (sub-scanning cross-sectional view) of a main part in which a part of the first station S1 in FIG. 4 is extracted.

  In this embodiment, as described above, it is necessary to separate the light beams in the optical path in order to guide the plurality of light beams deflected and reflected by the same deflecting surface 5a of the optical deflector 5 to the plurality of scanned surfaces 7a and 7b, respectively. For this purpose, the light beam is obliquely incident on the same deflecting surface 5a of the optical deflector 5 within the sub-scan section.

  However, if the oblique incident angle of the light beam in the sub-scanning direction is made large with respect to the deflection surface 5a, it becomes susceptible to processing errors and mounting errors of the optical deflector 5 as deflection means, and the scanning line on the scanned surface 7 The pitch unevenness is greatly generated. Further, since the light beam passes through a position away from the optical axis of the imaging lens in the sub-scanning section, the scanning line curve and the rotation of the imaging spot become large. Therefore, in this embodiment, the oblique incident angle θs0 (γ) is set to 1.8 (deg).

  In this embodiment, since the oblique incident angle in the sub-scanning direction is small, the distance Ld1 in the sub-scanning direction between the marginal rays closer to the optical reference axis C0 of the two light beams on the exit surface 6a2 of the first imaging lens 6a. Is only 0.8 mm.

  However, since the power in the sub-scanning section of the first imaging lens 6a is negative, two light beams incident on the deflection surface 5a at slightly different angles in the sub-scanning direction are the first imaging lens 6a. When the light exits from the exit surface 6a2, the distance and angle of each other increase.

  The distance Ld2 in the sub-scanning direction between the marginal rays closer to the optical reference axis C0 of the two light fluxes on the exit surface 6b2 of the second imaging lens 6b extends to 2.16 mm.

  Since the power in the sub-scan section of the second imaging lens 6b is positive, the distance and angle of the two light fluxes whose distances and angles spread from each other pass through the second imaging lens 6b. It narrows.

Therefore , the second imaging is performed by decentering the exit surface 6b2 of the second imaging lens 6b in the sub-scanning direction, that is, performing at least one of shift eccentricity and tilt eccentricity so as to satisfy the conditional expression (2) described later. The second imaging lens 6b can be emitted without reducing the interval between the two light beams incident on the lens 6b.

  In this embodiment, the exit surface 6b2 of the second imaging lens 6b is shifted decentered by 1.1 mm in the sub-scanning direction on the same side as the side through which the light beam passes with respect to the optical reference axis C0.

  As a result, the distance Md in the sub-scanning direction between the marginal rays closer to the optical reference axis C0 of the two light fluxes at the reflection point of the ray separation mirror 8a after exiting the exit surface 6b2 of the imaging lens 6b is 2.78 mm. Sufficient space is secured to arrange the beam separation mirror.

  The shift eccentricity in the sub-scanning direction referred to here indicates a state where the optical reference axis C0 and the optical axis of the lens surface do not coincide with each other in the sub-scanning section.

  In this embodiment, the lens surface is shifted in the sub-scanning direction in the sub-scanning section, but the same effect can be obtained by tilting the lens surface in the sub-scanning section with the main scanning direction as the rotation axis. .

  The same effect can be obtained even if the lens surface of the second imaging lens 6b is shifted in the sub-scanning direction in the sub-scanning section and the lens surface is tilted with the main scanning direction as the rotation axis.

  In this embodiment, although the oblique incident angle θs0 is as small as 1.8 (deg) as described above, a sufficient space can be secured for arranging the light separating mirror 8a in the sub scanning direction at the light separating position. It becomes easy to separate.

  Further, by shifting and decentering the exit surface 6b2 of the second imaging lens 6b in the sub-scanning direction, the light beam passes through a position close to the optical axis of the imaging lens in the sub-scanning cross section, so that the scanning line curve or connection is reduced. It becomes easy to reduce the rotation of the image spot.

  FIG. 6 is a diagram showing a scanning line bending amount on the surface to be scanned 7, and FIG. 7 is a diagram showing an imaging spot on the surface 7 to be scanned.

  By shifting and decentering the exit surface 6b2 of the second imaging lens 6b in the sub-scanning direction, the light beam passes through a position close to the optical axis of the second imaging lens 6b in the sub-scanning section. And the rotation of the imaging spot is suppressed. Therefore, the color misregistration becomes inconspicuous in the color image forming apparatus equipped with the optical scanning device of this embodiment.

  FIG. 8 is a diagram schematically showing the optical path of the principal ray of the light beam in the sub-scan section of FIG.

  In this embodiment, the principal ray of the light beam when scanning on the optical axis of the imaging optical system 6 on the surface to be scanned 7 is deflected and scanned by the optical deflector 5 in the sub-scan section, and then the optical reference axis C0. Is defined as θs0. The angle θs0 is equal to the oblique incident angle γ described above.

Further, an angle formed with the optical reference axis C0 after passing through the first imaging lens 6a having a negative power is defined as θs1. Further, the angle formed with the optical reference axis C0 after passing through the second imaging lens 6b disposed closest to the scanned surface 7 in the optical path is defined as θs2. then,
θs0 <θs1 (1)
0 (deg) ≦ θs2 (2)
Satisfy the following conditions.

  If the conditional expression (1) is not satisfied, it is not good because effective light separation using the refraction of the imaging lens in the sub-scan section is not performed. Further, if the conditional expression (2) is not satisfied, the distance between the two light beams that is secured when the two light beams enter the second imaging lens 6b is determined after the light beams exit the second imaging lens 6b. Since it becomes narrow, effective beam separation cannot be performed.

Each angle θs0, θs1, and θs2 in this embodiment is
θs0 = 1.8deg
θs1 = 3.05deg
θs2 = 0.23deg
It is. When these values are applied to conditional expressions (1) and (2),
θs0 (1.8 (deg)) <θs1 (3.05 (deg))
0 (deg) ≤ θs2 (0.23 (deg))
This satisfies the conditional expressions (1) and (2).

2, the optical path length from the deflecting surface 5a of the optical deflector 5 to the scanned surface 7 is L1, and the optical surface (lens surface) closest to the scanned surface 7 from the deflecting surface 5a. ) Let L2 be the distance to (exit surface) . then,
2 ≦ (L1 / L2) ≦ 4 (3)
Satisfy the following conditions.

  Here, the deflection surface 5a is based on the position at which the light beam enters the center of the scanned surface 7 in the main scanning section.

  Conditional expression (3) defines the position of the second imaging lens 6b closest to the scanned surface 7 in the optical path. When the upper limit value of conditional expression (3) is exceeded, the imaging magnification in the sub-scanning direction increases, and the influence of focus movement in the sub-scanning direction due to shift decentering of the optical element and surface tilt of the deflecting surface of the optical deflector 5 is scanned. It will occur greatly on the surface 7. If the lower limit of conditional expression (3) is exceeded, the position of the second imaging lens 6b closest to the scanned surface 7 in the optical path is arranged on the scanned surface 7 side, so the lens back becomes shorter and the toner cartridge is removed. It is not good because the space to arrange becomes narrow.

The distances L1 and L2 in this embodiment are
L1 = 248.3mm
L2 = 69.0mm
It is. When these values are applied to conditional expression (3),
(L1 / L2) = 3.6
This satisfies the conditional expression (3).

  More preferably, the conditional expression (3) should be set as follows.

2.8 ≦ (L1 / L2) ≦ 3.8 (3a)
In this embodiment, since the power in the sub-scanning section of the first imaging lens 6a is negative, the sub-scanning section of the imaging optical system 6 is compared with the case where the power in the sub-scanning section is positive or non-power. The image forming magnification can be kept small. As a result, it is possible to suppress the occurrence of a large influence on the scanned surface 7 due to the focus movement in the sub-scanning direction and the surface tilt of the deflecting surface of the optical deflector 5.

  In this embodiment, only the lens surface closest to the light separation mirror 8a in the optical path, that is, the exit surface 6b2 of the second imaging lens 6b is shifted in the sub-scanning direction, but only the entrance surface 6b1 is shifted. The same effect as described above can be obtained by shifting the eccentricity. Alternatively, the same effect as described above can be obtained by shifting the both surfaces 6b1 and 6b2 to be eccentric.

  In the present embodiment, as described above, the first imaging lens 6a has a negative power in the sub-scanning section, so that the distance in the sub-scanning direction between the two light fluxes passing through the second imaging lens 6b can be reduced. The distance in the sub-scanning direction of the two light beams at the reflection point of the light beam separation mirror 8a is separated.

  However, the present invention is not limited to this, and negative power is applied to the second imaging lens 6b closest to the scanning surface 7 in the sub-scan section so that the two light fluxes at the reflection point of the light separation mirror 8a in the sub-scan direction. The distance may be separated.

  Thus, in this embodiment, as described above, it is difficult to be affected by the mounting error of the optical deflector 5 and the light beam separation mirror 8a, and the light beam can be separated efficiently. As a result, in this embodiment, it is possible to achieve an optical scanning apparatus and a color image forming apparatus that can obtain a high-quality image with a compact configuration and no deterioration in image performance in a color LBP and a color copying machine.

  In the present embodiment, the plurality of light source means 1a and 1b are configured by a single light emitting unit. However, the present invention is not limited thereto, and may be configured by a plurality of light emitting units.

  In this embodiment, the imaging optical system 6 is constituted by two imaging optical elements (imaging lenses), but is not limited thereto, and may be constituted by two or more imaging optical elements.

  9 is a sectional view (main scanning sectional view) of the main scanning direction of the optical scanning apparatus according to the second embodiment of the present invention, and FIG. 10 is a sectional view of the main section of the optical scanning apparatus according to the second embodiment of the present invention. It is a figure (sub scanning sectional drawing), and has expanded and showed the optical path. 9 and 10, the same elements as those shown in FIGS. 1 and 2 are denoted by the same reference numerals.

  This embodiment is different from the first embodiment in that the distance L1 from the deflecting surface 5a of the optical deflector 5 to the scanned surface 7 is set longer. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in the figure, reference numeral 61 denotes an imaging optical system having a condensing function and an fθ characteristic, and the first and second imaging lenses 61a and 61b having different powers in the main scanning section and the sub-scanning section. have.

  The first and second imaging lenses 61a and 61b are made of a plastic material, and two light beams based on image information deflected and scanned by the same deflecting surface 5a of the optical deflector 5 are used as different scanning surfaces. An image is formed on the drum surfaces 7a and 7b. In addition, the first and second imaging lenses 61a and 61b are in a troublesome state of the deflection surfaces by providing a conjugate relationship between the deflection surface 5a of the optical deflector 5 and the photosensitive drum surfaces 7a and 7b in the sub-scan section. Compensation.

  The first imaging lens 61a in this embodiment has a positive power in the main scanning section on the optical axis of the first imaging lens 61a, and a negative power in the sub-scanning section. Yes.

  The second imaging lens 61b has a negative power in the main scanning section and a positive power in the sub-scanning section on the optical axis of the second imaging lens 61b.

  Tables 3 and 4 show the numerical values of the optical arrangement of the optical element of Example 2 and the surface shape of the imaging optical element (imaging lens) in this example.

  In this embodiment, the entrance surface (first surface) and the exit surface (second surface) of the first imaging lens 61a are aspherical surfaces expressed by functions up to the 10th order in the main scanning section (main scanning direction). It is formed in a shape (non-arc shape). In the sub-scan section (sub-scan direction), the incident surface (first surface) is formed in a planar shape, and the exit surface (second surface) is formed in a spherical shape whose curvature changes in the main scan direction.

  The entrance surface (third surface) and the exit surface (fourth surface) of the second imaging lens 61b are formed in an aspherical shape (non-arc shape) expressed by a function up to the 10th order in the main scanning section. Yes. Then, the power in the sub-scanning section decreases from on-axis to off-axis in the main scanning direction, so that the field curvature in the sub-scanning direction is well adjusted.

  In the present embodiment, the material of the first and second imaging lenses 61a and 61b is formed from a plastic material (resin) as described above. However, the material is not limited to a plastic material, and may be a glass material.

  FIG. 11 is a diagram showing the geometric aberration in the present embodiment.

  It can be seen from FIG. 11 that each aberration is adjusted to a level where there is no practical problem. It can also be seen that the change in the sub-scan magnification due to the image height is suppressed to 2% or less. As a result, a change in the spot shape in the sub-scanning direction due to the image height is suppressed, and good imaging performance can be obtained. Note that the change in the sub-scanning magnification due to the image height is preferably 10% or less. More preferably, it is 5% or less.

  Next, means and effects for achieving the object of the present embodiment will be described with reference to FIGS.

  FIG. 12 is a sub-scan sectional view of an image forming apparatus provided with two optical scanning devices (stations) according to this embodiment. In FIG. 12, the same elements as those shown in FIGS. 4 and 9 are denoted by the same reference numerals.

  The configuration and optical action of the image forming apparatus in this embodiment are the same as those in the first embodiment.

  Since the first and second stations S1 and S2 have the same configuration and optical action, only the first station S1 will be described below.

  FIG. 13 is a cross-sectional view (sub-scanning cross-sectional view) of a main part in which a part of the first first station S1 in FIG. 12 is extracted.

  In this embodiment, as described above, it is necessary to separate light beams in the optical path in order to guide a plurality of light beams scanned on the same deflecting surface 5a of the optical deflector 5 to the plurality of scanned surfaces 7a and 7b, respectively. For this purpose, the light beam is obliquely incident on the same deflecting surface 5a of the optical deflector 5 within the sub-scan section.

  However, if the oblique incident angle in the sub-scanning direction is increased with respect to the deflecting surface 5a, it becomes susceptible to processing errors and mounting errors of the optical deflector 5 as the deflecting means, and the scanning line pitch unevenness on the surface to be scanned 7 becomes uneven. Will occur greatly. Further, since the light beam passes through a position away from the optical axis of the imaging lens in the sub-scanning section, the scanning line curve and the rotation of the imaging spot become large. Therefore, in this embodiment, the oblique incident angle θs0 (γ) is set to 2.2 (deg).

  In this embodiment, since the oblique incidence angle in the sub-scanning direction is small, the distance Ld1 in the sub-scanning direction between the marginal rays closer to the optical reference axis C0 of the two light beams on the exit surface 61a2 of the first imaging lens 61a. Is only 1.34 mm.

  However, since the power in the sub-scanning section of the first imaging lens 61a is negative, two light beams incident on the deflecting surface at slightly different angles in the sub-scanning direction are incident on the first imaging lens 61a. When the light exits from the exit surface 61a2, the distance and the angle are increased.

  The distance Ld2 in the sub-scanning direction between the marginal rays closer to the optical reference axis C0 of the two light beams on the incident surface 61b1 of the first imaging lens 61b extends to 3.72 mm.

  Since the power in the sub-scanning section of the second imaging lens 61b is positive, the two light beams whose distances and angles are widened pass through the second imaging lens 61b, so that the distances and angles of each other are increased. It narrows.

  Therefore, the second imaging lens 61b can be moved without reducing the interval between the two light beams incident on the second imaging lens 61b by shifting and decentering the exit surface 61b2 of the second imaging lens 61b in the sub-scanning direction. The light is emitted.

  In this embodiment, the exit surface 61b2 of the second imaging lens 61b is shifted and decentered by 1.2 mm in the sub scanning direction on the same side as the side through which the light beam passes with respect to the optical reference axis C0.

  As a result, the distance Md in the sub-scanning direction between the marginal rays closer to the optical reference axis C0 of the two light fluxes at the reflection point of the ray separation mirror 8a after exiting the exit surface 61b2 of the imaging lens 61b is 4.28 mm. Become. As a result, a sufficient space for arranging the light beam separation mirror is secured.

  In this embodiment, although the oblique incident angle θs0 is as small as 2.2 (deg) as described above, it is possible to secure a sufficient space for arranging the light separating mirror 8a in the sub-scanning direction at the light separating position. It becomes easy to separate.

  In addition, by shifting and decentering the exit surface 61b2 of the second imaging lens 61b in the sub-scanning direction, the light beam passes through a position close to the optical axis of the imaging lens in the sub-scanning cross section, so that the scanning line curve or connection is reduced. It is possible to reduce the rotation of the image spot.

  FIG. 14 is a diagram showing the amount of scanning line curvature on the surface to be scanned, and FIG. 15 is a diagram showing imaging spots on the surface to be scanned.

  By shifting and decentering the exit surface 61b2 of the second imaging lens 61b in the sub-scanning direction, the light beam passes through a position close to the optical axis of the second imaging lens 61b in the sub-scanning section. Curvature and rotation of the imaging spot are suppressed. Therefore, the color misregistration becomes inconspicuous in the color image forming apparatus equipped with the optical scanning device of this embodiment.

  In this embodiment, the distance from the deflecting surface 5a of the optical deflector 5 to the scanned surface 7 is set to be longer, so that a wider toner cartridge space can be secured.

  In this embodiment, the principal ray of the light beam when scanning on the optical axis of the imaging optical system 61 on the surface to be scanned 7 is deflected and scanned by the optical deflector 5 in the sub-scanning section, and the optical reference axis C0. The formed angle θs0 is set as follows. Further, the angle θs1 formed by the principal ray of the light beam and the optical reference axis C0 after passing through the first imaging lens 61a having a negative power is set as follows. Further, an angle θs2 formed by the principal ray of the light beam and the optical reference axis C0 after passing through the second imaging lens 61b disposed closest to the scanning surface 7 in the optical path is set as follows.

θs0 = 2.2deg
θs1 = 3.96deg
θs2 = 0.15deg
When these values are applied to conditional expressions (1) and (2),
θs0 (2.2 (deg)) <θs1 (3.96 (deg))
0 (deg) ≤ θs2 (0.15 (deg))
This satisfies the conditional expressions (1) and (2).

In this embodiment, the optical path length L1 from the deflecting surface 5a of the optical deflector 5 to the scanned surface 7, and the distance L2 from the deflecting surface 5a to the lens surface closest to the scanned surface 7 are:
L1 = 266.2mm
L2 = 71.9mm
It is. When these values are applied to conditional expression (3),
(L1 / L2) = 3.7
This satisfies the conditional expression (3).

  Furthermore, since the power in the sub-scanning section of the first imaging lens 61a is negative, the imaging optical system 61 is connected in the sub-scanning direction as compared with the case where the power in the sub-scanning section is positive or non-power. The image magnification can be kept small. As a result, it is possible to suppress the occurrence of a large influence on the scanned surface 7 due to the focus movement in the sub-scanning direction and the surface tilt of the deflecting surface of the optical deflector 5.

  Thus, in this embodiment, as described above, it is difficult to be affected by the mounting error of the optical deflector 5 and the light beam separation mirror 8a, and the light beam can be separated efficiently. As a result, in this embodiment, it is possible to achieve an optical scanning apparatus and a color image forming apparatus that can obtain a high-quality image with a compact configuration and no deterioration in image performance in a color LBP and a color copying machine.

  FIG. 16 is a sectional view (main scanning sectional view) of an essential part of the optical scanning device according to the third embodiment of the present invention in the main scanning direction, and FIG. It is a figure (sub scanning sectional drawing), and has expanded and showed the optical path. 16 and 17, the same elements as those shown in FIGS. 1 and 2 are denoted by the same reference numerals.

  This embodiment differs from the first embodiment described above in that the distance L1 from the deflecting surface 5a of the optical deflector 5 to the scanned surface 7 is set longer, and the first closest to the optical deflector 5 in the optical path. The negative power in the sub-scan section of the imaging lens 62a is further strengthened. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in the figure, 62 is an imaging optical system having a condensing function and fθ characteristics, and the first and second imaging lenses 62a and 62b having different powers in the main scanning section and the sub-scanning section. have.

  The first and second imaging lenses 62a and 62b are made of a plastic material, and two light beams based on image information deflected and scanned by the same deflecting surface 5a of the optical deflector 5 are exposed as different scanning surfaces. An image is formed on the drum surfaces 7a and 7b. In addition, the first and second imaging lenses 62a and 62b have a conjugate relationship between the deflecting surface 5a of the optical deflector 5 and the photosensitive drum surfaces 7a and 7b in the sub-scan section, so Compensation.

  The first imaging lens 62a in the present embodiment has a positive power in the main scanning section on the optical axis of the first imaging lens 62a, and a negative power in the sub-scanning section. Yes.

  The second imaging lens 62b has a negative power in the main scanning section and a positive power in the sub-scanning section on the optical axis of the second imaging lens 62b.

  Tables 5 and 6 show the numerical values of the optical arrangement of the optical element of Example 3 and the surface shape of the imaging optical element (imaging lens) in this example.

  In this embodiment, the entrance surface (first surface) and the exit surface (second surface) of the first imaging lens 62a are aspherical surfaces expressed by functions up to the 10th order in the main scanning section (main scanning direction). It is formed in a shape (non-arc shape). In the sub-scan section (sub-scan direction), the incident surface (first surface) is formed into a spherical shape, and the exit surface (second surface) is formed into a spherical shape whose curvature changes in the main scanning direction.

  The entrance surface (third surface) and the exit surface (fourth surface) of the second imaging lens 62b are formed in an aspherical shape (non-arc shape) expressed by a function up to the 10th order in the main scanning section. Yes. Then, the power in the sub-scanning section decreases from on-axis to off-axis in the main scanning direction, so that the field curvature in the sub-scanning direction is well adjusted.

  In the present embodiment, the first and second imaging lenses 62a and 62b are made of a plastic material (resin) as described above. However, the material is not limited to a plastic material, and may be a glass material.

  FIG. 18 is a diagram showing geometric aberration in the present embodiment.

  It can be seen from FIG. 18 that each aberration is adjusted to a level where there is no practical problem. It can also be seen that the change in the sub-scan magnification due to the image height is suppressed to 2% or less. As a result, a change in the spot shape in the sub-scanning direction due to the image height is suppressed, and good imaging performance can be obtained. Note that the change in the sub-scanning magnification due to the image height is preferably 10% or less. More preferably, it is 5% or less.

  Next, means and effects for achieving the object of the present embodiment will be described with reference to FIGS.

  FIG. 19 is a sub-scan sectional view of an image forming apparatus provided with two optical scanning devices (stations) according to this embodiment. 19, the same elements as those shown in FIGS. 4 and 16 are denoted by the same reference numerals.

  The configuration and optical action of the image forming apparatus in this embodiment are the same as those in the first embodiment.

  Since the first and second stations S1 and S2 have the same configuration and optical action, only the first station S1 will be described below.

  FIG. 20 is a cross-sectional view (sub-scanning cross-sectional view) of a main part in which a part of the first two stations S1 in FIG. 19 is extracted.

  In this embodiment, as described above, it is necessary to separate light beams in the optical path in order to guide a plurality of light beams deflected and scanned by the same deflecting surface 5a of the optical deflector 5 to the plurality of scanned surfaces 7a and 7b, respectively. For this purpose, the light beam is obliquely incident on the same deflecting surface 5a of the optical deflector 5 within the sub-scan section.

  However, if the oblique incident angle in the sub-scanning direction is increased with respect to the deflecting surface 5a, it becomes susceptible to processing errors and mounting errors of the optical deflector 5 as the deflecting means, and the scanning line pitch unevenness on the surface to be scanned 7 becomes uneven. Will occur greatly. Further, since the light beam passes through a position away from the optical axis of the imaging lens in the sub-scanning section, the scanning line curve and the rotation of the imaging spot become large. Therefore, in this embodiment, the oblique incident angle θs0 (γ) is set to 1.8 (deg).

  In this embodiment, since the oblique incidence angle in the sub-scanning direction is small, the distance Ld1 in the sub-scanning direction between the marginal rays closer to the optical reference axis C0 of the two light beams on the exit surface 62a2 of the first imaging lens 62a. Is only 0.91 mm.

  However, since the power in the sub-scanning section of the first imaging lens 62a is negative, two light beams incident on the deflecting surface at slightly different angles in the sub-scanning direction are incident on the first imaging lens 62a. When exiting from the exit surface 62a2, the distance and angle of each other will increase.

  The distance Ld2 in the sub-scanning direction between the marginal rays closer to the optical reference axis C0 of the two light beams on the incident surface 62b2 of the second imaging lens 62b extends to 3 mm.

  Since the power in the sub-scan section of the second imaging lens 62b is positive, the two light beams whose distances and angles are widened pass through the second imaging lens 62b, so that the distance and angle of each other are increased. It narrows.

  Therefore, the second imaging lens 62b can be moved without reducing the interval between the two light beams incident on the second imaging lens 62b by shifting and decentering the exit surface 62b2 of the second imaging lens 62b in the sub-scanning direction. The light is emitted.

  In this embodiment, the exit surface 62b2 of the second imaging lens 62b is decentered by 1.4 mm in the sub scanning direction on the same side as the side through which the light beam passes with respect to the optical reference axis C0.

  As a result, the distance Md in the sub-scanning direction between the marginal rays closer to the optical reference axis C0 of the two light beams at the reflection point of the light separation mirror 8a after exiting the exit surface 62b2 of the imaging lens 62b is 3.95 mm. Become. As a result, a sufficient space for arranging the light beam separation mirror is secured.

  In this embodiment, although the oblique incident angle θs0 is as small as 1.8 (deg) as described above, a sufficient space can be secured for arranging the light separating mirror 8a in the sub scanning direction at the light separating position. It becomes easy to separate.

  In the present embodiment, the shape of the incident surface 62a1 of the first imaging lens 62a in the sub-scan section is a spherical shape with the concave surface facing the optical deflector 5, so that it is in the optical path compared to the first embodiment. The negative power in the sub-scan section of the first imaging lens 62a closest to the optical deflector 5 is further increased. For this reason, the light beam emitted from the first imaging lens 62a advances in a direction away from the optical reference axis C0, so that the light beam separation on the light beam separation mirror 8a is facilitated.

  Also, by shifting and decentering the exit surface 62b2 of the second imaging lens 62b in the sub-scanning direction, the light beam passes through a position close to the optical axis of the imaging lens in the sub-scanning section, thereby reducing the scanning line curvature. It becomes possible to do.

  FIG. 21 is a diagram showing the amount of scan line bending on the surface to be scanned.

  By shifting and decentering the exit surface 62b2 of the second imaging lens 62b in the sub-scanning direction, the light beam passes through a position close to the optical axis of the second imaging lens 62b in the sub-scanning section. Curving is suppressed. Therefore, the color misregistration becomes inconspicuous in the color image forming apparatus equipped with the optical scanning device of this embodiment.

  In this embodiment, the angle θs0 formed by the principal ray of the light beam when scanning on the optical axis of the imaging optical system 62 on the surface to be scanned 7 is deflected by the optical deflector 5 with the optical reference axis C0 in the sub-scan section. Is set as follows. Further, the angle θs1 formed by the principal ray of the light beam and the optical reference axis C0 after passing through the first imaging lens 62a having a negative power is set as follows. Further, the angle θs2 formed by the principal ray of the light beam and the optical reference axis C0 after passing through the second imaging lens 62b disposed closest to the scanning surface 7 in the optical path is set as follows.

θs0 = 1.8deg
θs1 = 4.63deg
θs2 = 0.28deg
When these values are applied to conditional expressions (1) and (2),
θs0 (1.8 (deg)) <θs1 (4.63 (deg))
0 (deg) ≤ θs2 (0.28 (deg))
This satisfies the conditional expressions (1) and (2).

In this embodiment, the optical path length (distance) L1 from the deflecting surface 5a of the optical deflector 5 to the scanned surface 7, and the optical path from the deflecting surface 5a to the optical surface (lens surface) closest to the scanned surface 7 The long (distance) L2 is
L1 = 248.4mm
L2 = 69mm
It is. When these values are applied to conditional expression (3),
(L1 / L2) = 3.6
This satisfies the conditional expression (3).

  Furthermore, since the power in the sub-scanning section of the first imaging lens 62a is negative, the imaging optical system 62 is connected in the sub-scanning direction as compared with the case where the power in the sub-scanning section is positive or non-power. The image magnification can be kept small. As a result, it is possible to suppress the occurrence of a large influence on the surface to be scanned due to the focus movement in the sub-scanning direction or the tilting of the deflecting surface of the optical deflector 5.

  Thus, in this embodiment, as described above, it is difficult to be affected by the mounting error of the optical deflector 5 and the light beam separation mirror 8a, and the light beam can be separated efficiently. As a result, in this embodiment, it is possible to achieve an optical scanning apparatus and a color image forming apparatus that can obtain a high-quality image with a compact configuration and no deterioration in image performance in a color LBP and a color copying machine.

[Image forming apparatus]
FIG. 22 is a cross-sectional view of an essential part in the sub-scanning direction showing an embodiment of the image forming apparatus of the present invention. In the figure, reference numeral 104 denotes an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. The code data Dc is converted into image data (dot data) Di by a printer controller 111 in the apparatus. The image data Di is input to the optical scanning unit 100 having the configuration shown in any one of the first to third embodiments. The light scanning unit 100 emits a light beam 103 modulated in accordance with the image data Di, and the light beam 103 scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction.

  The photosensitive drum 101 serving as an electrostatic latent image carrier (photoconductor) is rotated clockwise by a motor 115. With this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction perpendicular to the main scanning direction with respect to the light beam 103. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface. The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with the light beam 103 scanned by the optical scanning unit 100.

  As described above, the light beam 103 is modulated based on the image data Di, and by irradiating the light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. The electrostatic latent image is developed as a toner image by a developing unit 107 disposed so as to contact the photosensitive drum 101 further downstream in the rotation direction of the photosensitive drum 101 than the irradiation position of the light beam 103.

  The toner image developed by the developing unit 107 is transferred onto a sheet 112 as a transfer material by a transfer roller (transfer unit) 108 disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in a paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 22), but can be fed manually. A paper feed roller 110 is provided at the end of the paper cassette 109, and feeds the paper 112 in the paper cassette 109 into the transport path.

  As described above, the sheet 112 on which the unfixed toner image has been transferred is further conveyed to a fixing device behind the photosensitive drum 101 (left side in FIG. 22). The fixing device includes a fixing roller 113 having a fixing heater (not shown) therein and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113. Then, the sheet 112 conveyed from the transfer unit is heated while being pressed by the pressure contact portion between the fixing roller 113 and the pressure roller 114 to fix the unfixed toner image on the sheet 112. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and the fixed paper 112 is discharged out of the image forming apparatus.

  Although not shown in FIG. 22, the print controller 111 controls not only the data conversion described above, but also controls each part in the image forming apparatus including the motor 115 and a polygon motor in the optical scanning unit described later. I do.

The recording density of the image forming apparatus used in the present invention is not particularly limited. However, considering that higher recording density requires higher image quality, the configurations of the first to third embodiments of the present invention are more effective in an image forming apparatus of 1200 dpi or more.
(Color image forming device)
FIG. 23 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention.

  This embodiment is a tandem type color image forming apparatus that scans four beams by an optical scanning device and records image information on a photoconductor as an image carrier in parallel. 23, reference numeral 100 denotes a color image forming apparatus, 11 denotes an optical scanning device having any one of the configurations shown in the first to third embodiments, 21, 22, 23 and 24 denote photosensitive drums as image carriers, Reference numerals 32, 33, and 34 denote developing units, and 51 denotes a conveyance belt.

  In FIG. 23, R (red), G (green), and B (blue) color signals are input to the color image forming apparatus 60 from an external device 52 such as a personal computer. These color signals are converted into C (cyan), M (magenta), Y (yellow), and B (black) image data (dot data) by a printer controller 53 in the apparatus. These image data are input to the optical scanning device 11. The optical scanning device 11 emits light beams 41, 42, 43, and 44 that are modulated in accordance with each image data, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are mainly formed by these light beams. Scanned in the scanning direction.

  The color image forming apparatus in this embodiment scans four beams by the optical scanning device 11, and each corresponds to each color of C (cyan), M (magenta), Y (yellow), and B (black). In parallel, image signals (image information) are recorded on the surfaces of the photosensitive drums 21, 22, 23, and 24, and color images are printed at high speed.

  In the color image forming apparatus according to the present embodiment, as described above, the optical scanning device 11 forms the latent images of the respective colors on the corresponding photosensitive drums 21, 22, 23, and 24 using the light beams based on the respective image data. doing. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 52, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 100 constitute a color digital copying machine.

Sectional drawing of a sub-scanning essential part of the optical scanning device according to the first embodiment of the present invention. FIG. 3 is a main scanning sectional view of the optical scanning device according to the first embodiment of the present invention. FIG. 3 is a sub-scan sectional view of the optical scanning device according to the first embodiment of the present invention. The figure which shows the uniformity of the geometrical aberration and subscanning magnification of Example 1 of this invention FIG. 2 is a diagram when the optical scanning device according to the first exemplary embodiment of the present invention is mounted on a color image forming apparatus. The figure which shows the scanning line curvature amount of Example 1 of this invention. The figure which shows the spot shape of Example 1 of this invention. FIG. 2 is a sub-scanning principal ray optical path diagram of the optical scanning device according to the first embodiment of the present invention. Cross-sectional view of the sub-scanning main part of the optical scanning device according to the second embodiment of the present invention. FIG. 6 is a main scanning sectional view of the optical scanning device according to the second embodiment of the present invention. FIG. 5 is a sub-scan sectional view of the optical scanning device according to the second embodiment of the present invention. The figure which shows the uniformity of the geometrical aberration of Example 2 of this invention, and a subscanning magnification. FIG. 5 is a diagram when the optical scanning device according to the second exemplary embodiment of the present invention is mounted on a color image forming apparatus. The figure which shows the scanning line curvature amount of Example 2 of this invention. The figure which shows the spot shape of Example 2 of this invention. Cross-sectional view of the sub-scanning essential part of the optical scanning device according to the third embodiment of the present invention. FIG. 5 is a main scanning sectional view of an optical scanning device according to a third embodiment of the present invention. FIG. 5 is a sub-scan sectional view of the optical scanning device according to the third embodiment of the present invention. The figure which shows the uniformity of the geometric aberration of Example 3 of this invention, and a subscanning magnification. FIG. 6 is a diagram when the optical scanning device according to the third exemplary embodiment of the present invention is mounted on a color image forming apparatus. The figure which shows the scanning line curvature amount of Example 3 of this invention. 1 is a schematic view of a main part of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. Sub-scan sectional view of a conventional optical scanning device

Explanation of symbols

1a, 1b Light source means 2a, 2b Aperture stop 3a, 3b Focusing lens (collimator lens)
4a, 4b Lens system (anamorphic lens)
5 Deflection means (polygon mirror)
6a, 61a, 62a First imaging lens 6b, 61b, 62b Second imaging lens 7, 7a, 7b, 7c, 7d Scanned surface (photosensitive drum surface)
8a, 8b, 8c Folding mirror C0 Optical reference axis θs0, θs1, θs2 Angle formed by optical reference axis and principal ray LA, LB Incident optical system 6, 61, 62 Imaging optical system 11 Optical scanning device 21, 22, 23 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 51 Conveying belt 52 External device 53 Printer controller 60 Color image forming apparatus 100 Optical scanning unit 101 Photosensitive drum 102 Charging roller 103 Light beam 104 Image forming apparatus 107 Developing device 108 Transfer roller 109 Paper cassette 110 Paper feed roller 111 Printer controller 112 Transfer material (paper)
113 Fixing Roller 114 Pressure Roller 115 Motor 116 Paper Discharge Roller 117 External Equipment

Claims (5)

A plurality of light source means, an incident optical system for allowing a plurality of light beams emitted from the plurality of light source means to enter the same deflection surface of the deflection means from different directions in the sub-scan section, and the same deflection surface of the deflection means in the optical scanning device having an imaging optical system which Ru is imaged a plurality of light beams different in surface to be scanned from one another which is deflected and scanned in, the,
The imaging optical system has, as an optical element having an imaging function, a first imaging optical element whose power in the sub-scanning direction is negative in order from the deflection surface side of the optical path of the plurality of light beams, and sub-scanning Having only a second imaging optical element with positive directional power,
In the optical path between the second imaging optical element and the surface to be scanned, a reflection mirror that reflects the light beam deflected and scanned by the same deflection surface of the deflection unit is disposed ,
In the sub scanning cross section, the angle between the optical reference axis of the imaging optical system after the principal ray of the light beam has passed through the exit surface of the second imaging optical element when scanning the center of the surface to be scanned and θs2 The optical surface of the second imaging optical element performs at least one of shift decentering in the sub-scanning direction or tilt decentering with the main scanning direction as the rotation axis so that the condition of 0 (deg) ≦ θs2 is satisfied. An optical scanning device characterized by the above.
However, in the sub-scanning cross section, the θs2 is a direction rather away from the optical reference axis of the imaging optical system is positive. 2. The optical scanning device according to claim 1, wherein a plurality of light beams deflected and scanned by the same deflecting surface of the deflecting unit pass through the first and second imaging optical elements. In the sub-scan section, when the optical path length from the deflecting surface of the deflecting means to the scanned surface is L1, and the optical path length from the deflecting surface to the exit surface of the second imaging optical element is L2,
2 ≦ (L1 / L2) ≦ 4
The optical scanning device according to any one of claims 1 or 2, characterized by satisfying the following condition. Each of the said light source means has a some light emission part, The optical scanning device as described in any one of Claim 1 thru | or 3 characterized by the above-mentioned. An optical scanning apparatus according to any one of claims 1 to 4, a photosensitive member disposed on said surface to be scanned, which is formed on said photosensitive member by a light beam scanned by said optical scanning device A developing device that develops an electrostatic latent image as a toner image, a transfer device that transfers the developed toner image onto a transfer material, and a fixing device that fixes the transferred toner image onto the transfer material. An image forming apparatus.