JP2006071893A - Optical scanner and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner made simply and compact and having superior environment stability of optical performance, and to provide an image forming apparatus using the same. <P>SOLUTION: The optical scanner is provided with a light source means, an incident optical means and a scanning optical means. The incident optical means makes a luminous flux incident in the main scanning cross section with a luminous flux width broader than the width of the deflection face of a deflection means, makes the luminous flux diagonally incident within the subscanning cross section. The scanning optical means has a first and a second focusing elements made of resin. The first focusing element has larger power in the main scanning cross section than in the subscanning cross section. At least one face of the incident optical means has a shape of a non-circular arc in the main scanning cross section, and the face on the side of the deflection means is composed of a concave meniscus shape. The power of the second focusing element is larger in the main scanning cross section than in the subscanning cross section. At least a face is a non-circular arc in the main scanning cross section respective elements are set to satisfy respective conditional formulas. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical scanning device and an image forming apparatus using the same, and in particular, after a light beam (light beam) emitted from a light source means is deflected by a polygon mirror as an optical deflector, it passes through a scanning optical means having fθ characteristics. Suitable for image forming apparatuses such as laser beam printers having an electrophotographic process, digital copying machines, multifunction printers (multifunction printers), etc., which scan the surface to be scanned and record image information. It is.

  Conventionally, an optical scanning device has been widely used as an image forming apparatus such as a laser beam printer having an electrophotographic process, a digital copying machine, or a multifunction printer.

  The optical scanning device converts a light beam emitted from a light source means such as a semiconductor laser into a substantially parallel light beam by a condensing lens (collimator lens) and guides it to a deflection surface (reflection surface) of an optical deflector composed of a polygon mirror (rotating polygon mirror). The light beam deflected by the optical deflector is scanned at a constant speed while spot-imaged on the surface to be scanned using a scanning optical means (fθ lens system).

  In this optical scanning device, a substantially parallel light beam emitted from the condenser lens in the sub-scan section orthogonal to the main scan section is condensed near the deflection surface of the optical deflector using a cylinder lens (cylindrical lens). Then, a so-called tilt correction optical system that re-images on the surface to be scanned by the scanning optical means may be used.

  On the other hand, in the main scanning section, an underfill optical system (hereinafter referred to as “UFS”) in which the light beam width of the substantially parallel light beam emitted from the condenser lens is made narrower than the deflection surface and all the light beams are reflected and deflected by the deflection surface. Has been used. While UFS can deflect and scan light energy without waste, it is necessary to enlarge the deflection surface to some extent, and the optical deflector tends to increase in size.

  In recent years, there has been a strong demand for improvement in printing speed in laser beam printers, digital copying machines, multifunction printers, etc. In order to improve printing speed, the optical deflector can be rotated at high speed or the deflection surface It is necessary to increase the number of faces.

  If the optical deflector is rotated at a higher speed in a large UFS, problems such as heat generation, noise, and electric power of the optical deflector occur. Further, when the number of deflection surfaces is increased, the size of the optical deflector is further increased, and similarly, problems such as heat generation, noise, and electric power of the optical deflector arise.

  On the other hand, there is an overfilled optical system (hereinafter also referred to as “OFS”) in which the light beam emitted from the light source means is incident on the deflection surface of the optical deflector in a state wider than the width of the deflection surface in the main scanning direction. It has been proposed (see Patent Documents 1 and 2).

  In OFS, the optical deflector itself is smaller than UFS, and further high-speed rotation and increase in the number of reflecting surfaces are possible. In OFS, a part of the light beam incident on the deflecting surface of the optical deflector in a state wider than the width of the deflecting surface in the main scanning direction is cut off by the deflecting surface. However, there is a problem that the output power of the light source is necessary because of lower than UFS, but in recent years, a high-power semiconductor laser has appeared, and this problem has been solved.

  On the other hand, in recent years, a color image forming apparatus has been proposed in which latent images written on a plurality of photoconductors are embodied as toners of different colors and a color image is formed by superimposing the images. Various optical scanning devices for writing image information on a plurality of photoconductors have been proposed (see Patent Documents 3 and 4).

  Patent Documents 3 and 4 show a system in which a plurality of light beams emitted from a plurality of light sources are deflected and scanned by a single optical deflector.

  On the other hand, various devices have been proposed as optical scanning devices that reduce the components of the scanning optical means to achieve compactness and cost reduction (see Patent Documents 5 and 6).

In Patent Documents 5 and 6, the scanning optical means is configured by using two plastic imaging elements (anamorphic lenses) having a non-arc-shaped optical surface.
Patent No. 3104618 JP-A-8-171070 JP-A-10-228148 JP-A-8-262352 JP 2000-98288 A JP 2000-19444 A

  However, the OFS has various problems as described below.

First, as the first issue,
Conventionally, OFS disclosed in Patent Documents 1 and 2 and the like is a scanning optical means that has two main scanning cylinder lenses that contribute to image formation in the main scanning direction (the shape in the main scanning direction is an arc), and a tilt correction optical system ( As a contribution to image formation in the sub-scanning cross section), the cylinder mirror obtains the image formation effect of the scanning light beam with a total of three optical elements.

  However, Patent Documents 1 and 2 have a problem that there are many components of the scanning optical means, and it is difficult to reduce the size and cost of the entire apparatus.

As a second issue,
The optical scanning device has a tendency to increase the focal length of the scanning optical means (imaging lens) because it cannot take a wide scanning angle of view. The reason why a wide scanning angle of view cannot be obtained is because OFS reflects and deflects a part of the incident light beam that is incident in a state wider than the width of the deflecting surface of the optical deflector in the main scanning direction. is there. As a result, there is a difference in light intensity between the central part and the peripheral part of the incident light beam due to the FFP (far-filled pattern) of the laser light source, and this causes uneven light intensity corresponding to the image height on the scanned surface. Distribution occurs. As the angle of view increases, the uniformity of the light intensity distribution is lost. For this reason, the OFS employs a method of suppressing the angle of view and ensuring the uniformity of the light intensity distribution. Specifically, the half angle of view of OFS is generally about 25 to 40 degrees, which is 30 to 40% smaller than UFS. As a result, it is necessary to increase the focal length of the scanning optical means in order to scan a predetermined scanning width, and as a result, the optical path length becomes inevitably long, and it is difficult to reduce the size of the entire apparatus. It was.

  In recent years, there is an increasing demand for miniaturization of an image forming apparatus equipped with an optical scanning device, and shortening of the optical path length of scanning optical means is an urgent issue.

As the third issue,
When adopting a so-called double path configuration in which at least a part of the scanning optical elements constituting the scanning optical means are allowed to enter the optical deflector in order to make the OFS compact, the environmental stability of the optical performance is a problem. Become.

  In the double path configuration, as disclosed in Patent Documents 1, 5, and 6, the light beam before entering the optical deflector (incident light beam) and the light beam after entering (scanning light beam) pass through the same scanning optical element. It is comprised as follows. That is, the optical path is set so that it is obliquely incident at a predetermined angle in the sub-scan section with respect to the normal line of the deflecting surface of the optical deflector, and the scanning optical element in the vicinity of the optical deflector is reciprocally passed.

  However, as described above, a scanning optical element made of plastic for cost reduction has a larger refractive index variation due to environmental variation (particularly temperature) than a glass scanning optical element. For this reason, it is known that the imaging performance of the scanning optical element fluctuates with environmental fluctuations, for example, the focus position shifts. In addition, since the incident light is obliquely incident on the deflection surface, the irradiation position also changes when the environment changes. Particularly problematic is that the double-pass scanning optical element contributes approximately twice to the optical characteristics because the light beam passes twice. In the conventional optical scanning apparatus, sufficient discussion and solution have not been found in this respect.

As the 4th subject,
In the method of scanning using a single light deflector from a plurality of light sources as in Patent Document 4, by changing the height of the light beam incident on the light deflector, the incident angle, etc. within the sub-scan section, Optical path separation is performed after deflection scanning. For this reason, on the common scanning optical element, the light beam passes through positions separated in the sub-scanning direction.

  Assuming that the incident light path has a double-pass configuration as described above, the light beam passage position in the sub-scan section of the scanning optical element to be double-passed is different because the light beam height of the incident light beam and the light beam height of the scanning light beam are different for each light source. Is off-axis further away from the optical axis in the sub-scanning direction. For this reason, if the power in the sub-scanning section of the scanning optical element that is double-passed is large, the aberrations deteriorate due to passing off the axis, and the optical performance changes greatly when the environment changes as described above. The problem that it will guide arises.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning device that achieves a simple and compact configuration and has good environmental stability of optical performance, and an image forming apparatus using the same.

The optical scanning device of the invention of claim 1
In an optical scanning apparatus comprising: an incident optical unit that guides a light beam emitted from a light source unit to a deflecting unit; and a scanning optical unit that guides a light beam deflected by the deflecting unit onto a surface to be scanned.
The incident optical means causes the light beam emitted from the light source means in the main scanning section to enter the deflecting surface with a light beam width wider than the width of the deflecting surface of the deflecting means, and the deflecting surface in the sub-scanning section. Is incident from an oblique direction,
The scanning optical means includes first and second imaging elements made of resin,
The first imaging element has a power in the main scanning section that is greater than a power in the sub-scanning section, and at least one surface has a non-arc shape in the main scanning section, and the surface on the deflection means side is concave. The meniscus shape of
In the second imaging element, the power in the sub-scanning section is larger than the power in the main-scanning section, and at least one surface has a non-arc shape in the main-scanning section,
The focal length in the main scanning section of the first imaging element is G1m,
The focal length in the main scanning section of the second imaging element is G2m,
The combined focal length in the main scanning section of the first imaging element and the second imaging element is Fθm,
When the focal length in the sub-scan section of the second imaging element is G2s,
0.87 <G1m / Fθm <0.97
−12.5 <G2m / Fθm <−5.0
-40.2 <G2m / G2s <-17.5
It is characterized by satisfying the following conditions.

The invention of claim 2 is the invention of claim 1,
Both the light beam incident on the deflecting means and the light beam deflected by the deflecting means pass through the first imaging element, and the power in the sub-scan section of the first imaging element is substantially equal. It is zero, and at least one surface in the sub-scan section of the second imaging element has a convex shape whose curvature gradually changes from on-axis to off-axis.

The invention of claim 3 is the invention of claim 1,
The first imaging element has a symmetrical shape with respect to the optical axis of the first imaging element in the main scanning cross section, and the principal ray of the light beam incident on the deflecting means and the first coupling element. The optical axis of the image element and the rotation axis of the deflecting means are in the same plane.

The invention of claim 4 is the invention of claim 3,
The second imaging element has a symmetric shape with respect to the optical axis of the second imaging element in the main scanning section, and the second imaging element is coupled to the optical axis of the first imaging element. The optical axis of the image element is in the same plane.

The invention of claim 5 is the invention of any one of claims 1 to 4,
When the distance from the deflection surface of the deflection means to the scanned surface is TC and the distance from the deflection surface of the deflection means to the incident surface of the second imaging element is Sg2, 0.5 <Sg2 / TC
It is characterized by satisfying the following conditions.

An optical scanning device according to a sixth aspect of the present invention comprises:
Incident optical means provided for each of the light beams that causes a plurality of light beams emitted from a plurality of light source means to enter the deflecting means, and scanning for guiding the plurality of light beams deflected by the deflecting means onto the corresponding scanned surface An optical scanning device comprising:
The incident optical means provided for each light beam causes the light beam emitted from the corresponding light source means to enter the deflecting surface with a light beam width wider than the width of the deflecting surface of the deflecting means in each main scanning section. ,
The light beam emitted from the corresponding light source means in the sub-scan section is incident on the deflection surface from an oblique direction,
The scanning optical means includes first and second imaging elements made of resin,
The first imaging element has a power in the main scanning section that is greater than a power in the sub-scanning section, and at least one surface has a non-arc shape in the main scanning section, and the surface on the deflection means side is concave. The meniscus shape of
In the second imaging element, the power in the sub-scanning section is larger than the power in the main-scanning section, and at least one surface has a non-arc shape in the main-scanning section,
The focal length in the main scanning section of the first imaging element is G1m,
The focal length in the main scanning section of the second imaging element is G2m,
The combined focal length in the main scanning section of the first imaging element and the second imaging element is Fθm,
When the focal length in the sub-scan section of the second imaging element is G2s,
0.87 <G1m / Fθm <0.97
−12.5 <G2m / Fθm <−5.0
-40.2 <G2m / G2s <-17.5
It is characterized by satisfying the following conditions.

The invention of claim 7 is the invention of claim 6,
The plurality of light beams incident on the deflecting unit and the plurality of light beams deflected by the deflecting unit pass through a common first imaging element, and are within a sub-scanning section of the first imaging element. The power is substantially zero, and at least one surface in the sub-scan section of the second imaging element has a convex shape whose curvature gradually changes from on-axis to off-axis.

The invention of claim 8 is the invention of claim 7,
The plurality of light beams incident on the deflecting unit and the plurality of light beams deflected by the deflecting unit pass through different positions of the first imaging element in the sub-scan section.

The invention of claim 9 is the invention of claim 7,
The second imaging element is provided for each of a plurality of light beams deflected by the deflecting unit and passed through the first imaging element.

The invention of claim 10 is the invention of claim 6,
The first imaging element has a symmetrical shape with respect to the optical axis of the first imaging element in the main scanning section, and the principal rays of a plurality of light beams incident on the deflecting means, and the first The optical axis of the imaging element and the rotation axis of the deflecting means are in the same plane.

The invention of claim 11 is the invention of claim 10,
The second imaging element has a symmetric shape with respect to the optical axis of the second imaging element in the main scanning section, and the second imaging element is coupled to the optical axis of the first imaging element. The optical axis of the image element is in the same plane.

The invention of claim 12 is the invention of any one of claims 6 to 11,
When the distance from the deflection surface of the deflection means to the scanned surface is TC and the distance from the deflection surface of the deflection means to the incident surface of the second imaging element is Sg2, 0.5 <Sg2 / TC
It is characterized by satisfying the following conditions.

An image forming apparatus according to the invention of claim 13
13. The optical scanning device according to claim 1, a photosensitive member disposed on the surface to be scanned, and a static beam formed on the photosensitive member by a light beam scanned by the 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. Yes.

An image forming apparatus according to a fourteenth aspect is provided.
13. An optical scanning device according to claim 1, and a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device. It is said.

A color image forming apparatus according to a fifteenth aspect of the present invention provides:
Each of the optical scanning devices according to any one of claims 1 to 12 is arranged on a surface to be scanned, and has a plurality of image carriers that form images of different colors.

The invention of claim 16 is the invention of claim 15,
It is characterized by having a printer controller that converts color signals input from an external device into image data of different colors and inputs them to each optical scanning device.

  According to the present invention, it is possible to achieve a simple and compact configuration by appropriately setting each element constituting the optical scanning device and satisfying at least one of the conditional expressions. An optical scanning device having good stability and an image forming apparatus using the same can be achieved.

  It is also possible to reduce fluctuations in the irradiation position on the photosensitive drum surface during manufacture and use of the apparatus, abrupt deterioration of aberrations, and deterioration of the spot image formation state. An optical scanning device capable of exhibiting image performance and 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 a main part in the main scanning direction of Embodiment 1 of the present invention, and FIG. FIG.

  Here, the main scanning direction is a direction perpendicular to the rotation axis of the deflection means (the direction in which the light beam is reflected and deflected (deflection scanning) by the deflection means), and the sub-scanning direction is a direction parallel to the rotation axis of the deflection means. Indicates. The main scanning section indicates a plane parallel to the main scanning direction and including the optical axis of the scanning optical system. The sub-scanning cross section indicates a cross section perpendicular to the main scanning cross section.

  In the figure, reference numeral 1 denotes light source means, which comprises a single light emitting portion, for example, a semiconductor laser. In the present embodiment, the light source means 1 is composed of a single light emitting section. However, the present invention is not limited to this, and it may be composed of light source means having a plurality of light emitting sections.

  A light beam conversion element (condenser lens) 2 converts the light beam emitted from the light source means 1 into a substantially parallel light beam (or a divergent light beam or a convergent light beam). Reference numeral 8 denotes an aperture stop (aperture), which regulates a beam shape by regulating a passing light beam. A cylinder lens (cylindrical lens) 3 has a predetermined power (refractive power) only in the main scanning direction. Reference numeral 4 denotes a correction element (anamorphic lens) having a diffraction grating on the exit surface 4b, which has a negative power in the main scanning section, a positive power in the sub-scanning section, and has passed through the condenser lens 2. The light beam is formed as a substantially linear image on a deflection surface (reflection surface) 5a of a polygon mirror 5 to be described later in the sub-scan section.

  Each element such as the condenser lens 2, the aperture stop 8, the cylinder lens 3, the correction element 4, the first imaging lens 61 described later, and the like constitute one element of the incident optical means 71.

  Reference numeral 5 denotes an optical deflector having a plurality of (eight in this embodiment) deflecting surfaces, which is composed of a polygon mirror (rotating polygon mirror), and is driven at a constant speed in the direction of arrow A in the figure by driving means (not shown) such as a motor. It is rotating at.

  In this embodiment, the light beam emitted from the light source means 1 is incident on the deflection surface 5a by the incident optical means 71 with a light beam width wider than the width of the deflection surface 5a of the polygon mirror 5 in the main scanning section (OFS). ).

  Reference numeral 6 denotes an fθ lens system as a scanning optical means having a condensing function and an fθ characteristic, and has first and second resin-made imaging lenses (imaging elements) 61 and 62. The light beam based on the image information reflected and deflected by the polygon mirror 5 is imaged in a spot on the photosensitive drum surface 7 as the scanned surface in the main scanning section, and the deflecting surface 5a of the polygon mirror 5 in the sub-scanning section. And a photosensitive drum surface 7 are optically substantially conjugate to provide a tilt correction function.

  The first and second imaging lenses 61 and 62 made of resin in this embodiment are manufactured by a known molding technique in which a mold is filled with a resin and taken out from the mold after cooling. As a result, it can be manufactured more simply and at a lower cost than a conventional OFS imaging lens using a glass lens.

  As shown in Table 1 described later, the first imaging lens 61 mainly has power in the main scanning section, and the lens surface shape is an aspherical shape expressed by a function of the given expression. The power of the first imaging lens 61 in the main scanning section is greater than the power in the sub-scanning section, and at least one surface (incident surface and exit surface in this embodiment) is non-circular in the main scanning section. The shape is a meniscus shape having a concave surface on the polygon mirror 5 side. The shape in the main scanning section is symmetric with respect to the optical axis L of the first imaging lens 61.

  Note that the incident surface and the exit surface of the first imaging lens 61 are formed with substantially the same non-power having the same curvature in the sub-scan section as shown in Table 1. However, the present invention is not limited to this. Both surfaces may be formed in a flat cylinder shape in the sub-scan section. The first imaging lens 61 is mainly responsible for imaging in the main scanning section with respect to the incident light beam.

Here, when the power is φ,
0 ≦ | φ | <0.001
Say.

  The second imaging lens 62 is an anamorphic lens mainly having power in the sub-scan section as shown in Table 1 described later. The lens surface shape is an aspherical shape expressed by a function of the given equation. The power of the second imaging lens 62 in the sub-scanning section is greater than that in the main-scanning section, and the incident surface has an arcuate shape and the exit surface has a non-arc shape in the main-scanning section. . The shape of the second imaging lens 62 in the main scanning section is symmetrical with respect to the optical axis L, and the power in the main scanning direction near the axis is substantially non-power.

Here, when the power is φ,
0 ≦ | φ | <0.001
Say.

  The incident surface in the sub-scan section of the second imaging lens 62 has a substantially flat surface with a very gentle curvature, and the exit surface has a convex shape whose curvature gradually changes from on-axis to off-axis. It consists of a symmetric shape. The second imaging lens 62 is mainly responsible for image formation in the sub-scanning section and correction of slight distortion in the main scanning section for the incident light beam.

  In this embodiment, a light beam (incident light beam) Li incident on the polygon mirror 5 passes through the first imaging lens 61, and a light beam (scanning light beam) Lo deflected by the polygon mirror 5 is again the first imaging lens. A double-pass configuration that is incident on 61 is adopted.

  Reference numeral 8 denotes a photosensitive drum surface as a surface to be scanned, and the spot scans the surface at a constant speed.

  Each element of the reference numerals 1 to 8 constitutes one element of the scanning optical system.

  In this embodiment, the divergent light beam emitted from the light source means 1 is converted into a substantially parallel light beam by the condenser lens 2.

  In the main scanning section, the light beam converted into a substantially parallel light beam is regulated by the aperture stop 8 as it is, converted into a substantially convergent light beam by the cylinder lens 3, and the correction element 4 and the first imaging lens 61. Is again converted into a substantially parallel light beam, and enters the deflection surface 5a from the center of the deflection angle of the polygon mirror 5 or from the substantially center (front incidence). At this time, the light flux width of the substantially parallel light flux is set to be sufficiently larger than the facet width of the deflection surface 5a of the polygon mirror 5 in the main scanning direction (OFS).

  Next, in the sub-scan section, the light beam converted into a substantially parallel light beam is converted into a convergent light beam by the correction element 4, passes through the first imaging lens 61, enters the deflecting surface 5 a of the polygon mirror 5, An image is formed in the vicinity of the deflection surface 5a as a substantially line image (a line image elongated in the main scanning direction). At this time, the light beam incident on the deflecting surface 5a is obliquely incident on the deflecting surface 5a at a predetermined angle (θ = 1.5 °) (obliquely incident optical system).

  In this embodiment, as apparent from FIG. 1, the optical axis L of the first imaging lens 61 coincides with the principal ray of the light beam incident on the polygon mirror 5. Further, the rotation center O of the polygon mirror 5 is an extension of the optical axis L of the first imaging lens 61. As a result, the optical axis L of the first imaging lens 61, the principal ray of the incident light beam, and the rotation center O of the optical deflector 5 are configured in the same plane (in the sub-scanning section). The optical axis L of the first imaging lens 61 and the optical axis L of the second imaging lens 62 are configured in the same plane (in the main scanning section).

  In the polygon mirror 5, the incident light beam is deflected so as to be partly cut off by the deflecting surface 5 a so as to be partly cut off by the deflecting surface 5 a wider than the width of the deflecting surface 5 a in the main scanning direction, and guided to the fθ lens system 6. Therefore, different portions of the light beam incident on the polygon mirror 5 are used according to the image height on the scanned surface 7. For example, the central portion of the incident light beam to the polygon mirror 5 is used for the light beam guided to the center portion on the scanned surface 7, and the peripheral portion of the incident light beam to the polygon mirror 5 is used for the light beam guided to the peripheral portion. is there.

  The light beam reflected and deflected by the deflecting surface 5a of the polygon mirror 5 is imaged on the photosensitive drum surface 7 via the first imaging lens 61 and the second imaging lens 62, and the polygon mirror 5 is By rotating in the direction of arrow A, the photosensitive drum surface 7 is optically scanned in the direction of arrow B (main scanning direction). As a result, an image is recorded on the photosensitive drum surface 7 as a recording medium.

  Next, Table 1 shows specifications (numerical values) of the optical scanning device according to the present embodiment.

  However, the expression is defined as follows.

  ・ Lens surface shape (toric shape). . . An aspherical shape whose main scanning direction can be expressed by a function up to the 10th order, the intersection point with the optical axis as the origin, the optical axis direction as the x axis, the axis perpendicular to the optical axis in the main scanning plane, the y axis, and the sub scanning plane When the axis perpendicular to the optical axis is the z axis, the bus direction corresponding to the main scanning direction is

(Where R is the radius of curvature, and K, B ₄ , B ₆ , B ₈ , and B ₁₀ are aspheric coefficients)
The sub-scanning direction (the direction including the optical axis and orthogonal to the main scanning direction) and the sub-line direction are

Where 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)
· Diffraction grating . . . Diffraction surface represented by a secondary phase function whose main scanning direction is up to the 10th order and whose sub-scanning direction varies depending on the position in the main scanning direction φ = mλ = b ₂ Y ² + b ₄ Y ⁴ + c ₂₂ Y ² Z ² + d ₂ Z ² + d ₄ Z ⁴
(However, m is the diffraction order: + 1st order diffracted light is used.)
In Table 1,
G1m is the focal length of the first imaging lens 61 in the main scanning direction,
G2m is the focal length of the second imaging lens 62 in the main scanning direction,
Fθm is a combined focal length of the first imaging lens 61 and the second imaging lens 62 in the main scanning direction,
G1s is the focal length of the first imaging lens 61 in the sub-scanning direction,
G2s is the focal length of the second imaging lens 62 in the sub-scanning direction,
TC is the distance from the deflecting surface 5a of the polygon mirror 5 to the scanned surface 8,
Sg2 is the distance from the deflecting surface 5a of the polygon mirror 5 to the incident surface of the second imaging lens 62,
dZg2 is the separation distance of the optical axis in the sub-scan section of the second imaging lens 62 with respect to the first imaging lens 61;
It is said.

  The first and second imaging lenses 61 and 62 do not necessarily have to be function expressions as shown in the above equations 1 and 2, but may be known expressions.

  The optical deflector 5 in this embodiment is an 8-sided polygon mirror inscribed in φ13.72, and the width of the deflecting surface 5a in the main scanning direction is 5.25 (mm). In OFS, the width of the deflecting surface 5a serves as a stop in the main scanning direction. The stop in the sub-scanning direction is 8 shown in FIG. The diaphragm 8 is easy to configure if provided on the optical path from the light source means 1 to the polygon mirror 5.

  As described above, the light beam incident on the deflection surface 5a of the polygon mirror 5 is obliquely incident on the deflection surface 5a at an incident angle of 1.5 ° in the sub-scan section. Therefore, in order to satisfactorily correct the rotation of the spot caused by the oblique incidence and the linearity of the scanning line on the scanned surface 7, the second imaging lens 62 is sub-scanned with respect to the first imaging lens 61. It is desirable that the distance dZg2 between the optical axes in the cross section be 5.8 (mm).

In this embodiment, the focal length in the main scanning section of the first imaging lens 61 is G1m,
The focal length in the main scanning section of the second imaging lens 62 is G2m,
The combined focal length in the main scanning section of the first imaging lens 61 and the second imaging lens 62 is Fθm,
When the focal length in the sub-scan section of the second imaging lens 62 is G2s
0.87 <G1m / Fθm <0.97 (1)
−12.5 <G2m / Fθm <−5.0 (2)
-40.2 <G2m / G2s <-17.5 (3)
Satisfy the following conditions.

When the distance from the deflecting surface 5a of the polygon mirror 5 to the scanned surface 7 is TC and the distance from the deflecting surface 5a of the polygon mirror 5 to the incident surface of the second imaging lens 62 is Sg2, 0.5 < Sg2 / TC (4)
Satisfy the following conditions.

More preferably, the above conditional expressions (1), (2), (3), (4)
0.89 <G1m / Fθm <0.96 (1a)
−12.3 <G2m / Fθm <−5.1 (2a)
-40.0 <G2m / G2s <-17.7 (3a)
0.52 <Sg2 / TC <0.7 (4a)
It is good to do.

  Next, the technical meaning of each of the conditional expressions (1) to (4) will be described.

  Conditional expression (1) and conditional expression (2) indicate the power (1 / focal length) in the main scanning section of the first imaging lens 61 and the second imaging lens 62 constituting the fθ lens system 6 respectively. This is a condition for defining the ratio of the power (1 / focal length) of the entire lens system 6. The power arrangement is uneven (positive / negative), and conditional expression (1) indicates that the first imaging lens 61 bears a power slightly larger than the power of the entire fθ lens system 6. Conditional expression (2) indicates that the second imaging lens 62 has a gentle concave power.

  By arranging in this way, the distance from the optical deflector 5 to the scanned surface 7 is reduced and a compact configuration is achieved. For example, in Patent Documents 5 and 6 described above, the distance from the optical deflector 5 to the scanned surface 7 is 443 to 494 (mm), but this embodiment realizes compactness of about 329 (mm) and about 70%. ing.

  If the upper limit value of the conditional expression (1) or the lower limit value of the conditional expression (2) is exceeded, the distance from the optical deflector 5 to the scanned surface 7 increases, and it is difficult to achieve the compactness of the entire apparatus. Absent. If the lower limit value of the conditional expression (1) or the upper limit value of the conditional expression (2) is exceeded, the power of the first imaging lens 61 and the second imaging lens 62 becomes too large and the image plane is increased. Since it is difficult to correct curvature and distortion, it is not good. If the lower limit value of conditional expression (1) is exceeded, the power of the first imaging lens 61 becomes too large, resulting in a large power fluctuation due to environmental fluctuations, and a double focus fluctuation in a double pass. So not good.

  Conditional expression (3) is a condition for defining the power ratio (1 / focal length ratio) in the main scanning section and the sub-scanning section of the second imaging lens 62. The power in the sub-scan section is set to about 17 to 40 times the power in the main scan section. As described above, the distance of the optical axis in the sub-scan section of the second imaging lens 62 is set to dZg2 with respect to the first imaging lens 61, and 1.5 ° with respect to the deflection surface 5a of the optical deflector 5. The rotation of the spot and the linearity of the scanning line on the surface to be scanned 7 that are generated by oblique incidence at an incident angle of 5 are corrected well. For this reason, if the power in the sub-scanning section is too strong with respect to the power in the main scanning section of the second imaging lens 62 (that is, exceeds the upper limit value of the conditional expression (3)), the wavefront aberration is remarkably deteriorated. It's not good because it gets worse and can't correct the rotation of the spot. If the power in the sub-scanning section is too weak (that is, the lower limit value of conditional expression (3) is exceeded) with respect to the power in the main scanning section of the second imaging lens 62, the linearity of the scanning line is improved. It is not good because it becomes difficult to correct.

  Conditional expression (4) is a condition for defining the ratio of the distance from the optical deflector 5 to the second imaging lens 62 and the optical deflector 5 to the scanned surface 7. In the optical scanning apparatus of the present embodiment, the fθ lens system 6 is composed of a first imaging lens 61 mainly having power in the main scanning section and a second imaging lens 62 having mainly power in the sub-scanning section. Therefore, the focus fluctuation that occurs when the fθ lens system 6 is heated is caused by the first imaging lens 61 for the focus in the main scanning section, and the second imaging for the focus in the sub-scanning section. This is due to the lens 62.

  Therefore, in FIG. 3, the distance from the polygon mirror 5 to the scanned surface 7 is fixed to 329 (mm), which is the same as in Table 1, and the positions of the first imaging lens 61 and the second imaging lens 62 are changed. It shows the focus fluctuation when the optimized fθ lens system 6 is heated. In FIG. 3, the distance (329 mm) from the polygon mirror 5 to the scanned surface 7 is normalized to 1 on the horizontal axis, and the distance from the polygon mirror 5 to each imaging lens is shown on the vertical axis. The position of the imaging lens 61 and the focus variation ΔM / dT in the main scanning section, and the position of the second imaging lens 62 and the focus variation ΔS / dT in the sub-scanning section are shown.

  According to FIG. 3, the focus fluctuation ΔM / dT in the main scanning section does not change so much with respect to the position of the first imaging lens 61.

  On the other hand, it can be seen that the focus fluctuation ΔS / dT in the sub-scan section changes very greatly with respect to the position of the second imaging lens 62. Therefore, if it is intended to reduce the focus fluctuation due to the temperature change, if the position of the second imaging lens 62 is set to 0.5 or more, the focus fluctuation ΔS / dT in the sub-scanning section and the focus in the main scanning section. The variation ΔM / dT can be made substantially equal or less.

  Further, if the position of the second imaging lens 62 is 0.7 or less, the focus fluctuation ΔS / dT in the sub-scanning section and the focus fluctuation ΔM / dT in the main scanning section become approximately the same, and the main and sub-focusing positions. Astigmatism (AS) does not occur due to the fluctuation, and the spot shape is kept good.

  Even in a spot shape that is usually circular or elliptical, when astigmatism (AS) occurs, the spot shape becomes a pincushion-shaped distortion, and side lobes also occur, and good printing performance becomes difficult.

  As described above, in the present embodiment, each element is appropriately set as described above, and at least one of the conditional expressions is satisfied, whereby a simple and compact configuration can be achieved, and the optical performance can be achieved. An optical scanning device with good environmental stability can be obtained. In addition, it is possible to reduce the irradiation position on the photosensitive drum surface during the manufacture and use of the apparatus, and the deterioration of the imaging state of the spot due to abrupt deterioration of aberrations. Demonstrating performance.

  In the present embodiment, the first imaging lens 61 constituting the fθ lens system 6 has a double-pass configuration, but the present invention is not limited to this, and a single-pass configuration may be used.

  FIG. 4 is a sectional view (sub-scanning sectional view) of the main part in the sub-scanning direction according to the second embodiment of the present invention. In the figure, the same elements as those shown in FIG.

  This embodiment differs from the first embodiment described above in that two scanning optical systems 73 and 73 shown in the first embodiment are arranged upside down in the sub-scan section and arranged. Other configurations and optical actions are substantially the same as those in the first embodiment, and the same effects are obtained.

  That is, in this embodiment, the light source means 1 · 1 to the correction elements 4 · 4 are provided separately for each light beam, and are arranged in two upper and lower stages in the sub-scan section. The optical axes L1 and L1 of both the incident optical means 72 and 72 have a relative angle of 3 ° in the sub-scan section, and the angle of the light beam incident on the deflecting surface 5a of the polygon mirror 5 is ± 1.5 °. It arranges so that. The upper and lower optical paths of the incident optical means 72 and 72 intersect at the rear of the correction elements 4 and 4 as shown in FIG. 4, and then pass through the common first imaging lens 61 and pass through the single polygon mirror 5. Reaches the deflection surface 5a. In this embodiment, two light beams are incident on the deflecting surface 5a of the polygon mirror 5 at positions separated in the sub-scanning direction.

  Then, the two light beams deflected by the polygon mirror 5 pass again through the first imaging lens 61 (double path configuration), and after passing through the second imaging lenses 62 and 62 provided on the respective optical paths, The light is guided onto the corresponding scanned surfaces 7 and 7 respectively. Thus, image recording is performed on the photosensitive drum surfaces 7 and 7 as recording media.

  As described above, in this embodiment, the scanning optical systems 73 and 73 are arranged in two upper and lower stages in the sub-scan section as described above, so that the polygon mirror 5 and the driving system (not shown) of the polygon mirror 5 and the first The plurality of scanning surfaces 7 and 7 can be scanned by sharing the imaging lens 61, thereby reducing the number of parts and reducing the cost.

  In the present embodiment, two incident light beams incident on the polygon mirror 5 and two scanning light beams deflected by the polygon mirror 5 that pass through the first imaging lens 61 are in the sub-scan section. Each imaging lens 61 is configured to pass through different positions. That is, the four light beams are configured to pass off-axis away from the optical axis L3 of the first imaging lens 61.

  In the present embodiment, as shown in Table 1 above, both lens surfaces 61a and 61b of the first imaging lens 61 are set to have the same very low curvature in the sub-scan section, and the power thereof is substantially zero (non-power) ). For this reason, even though four light beams pass through the first imaging lens 61 at different locations in the sub-scan section, that is, off-axis away from the optical axis L3, the aberrations are hardly deteriorated as though they pass through the parallel plate. No (strictly speaking, minor coma occurs equally in each optical path). Further, since the power of the first imaging lens 61 is substantially zero, it is possible to reduce the deterioration of the optical performance at the time of temperature rise despite the double pass configuration.

  If the first imaging lens 61 is provided with a curvature so as to have power in the sub-scanning section, it is influenced by spherical aberration as it moves away from the optical axis L3, and a large coma aberration is generated as a light beam. In addition, there is a problem that the irradiation position varies because the refractive angle of the optical path shifts due to the variation of the refractive index of the material at the time of temperature rise.

  In the present embodiment, as described above, the power in the sub-scanning section of the first imaging lens 61 is made substantially zero, so that the influence of such spherical aberration and environmental fluctuations can be avoided.

  Next, a third embodiment of the present invention will be described.

  The present embodiment is different from the first embodiment described above in that some specifications of the optical scanning device are made different. Other configurations and optical actions are substantially the same as those in the first embodiment, and the same effects are obtained.

  Next, Table 2 shows specifications of the optical scanning device according to the third embodiment.

  The optical deflector 5 in this embodiment is an 8-sided polygon mirror inscribed in φ13.72, and the width of the deflecting surface 5a in the main scanning direction is 5.25 (mm). In OFS, the width of the deflecting surface 5a serves as a stop in the main scanning direction.

  In this embodiment, the light beam incident on the deflecting surface 5a of the polygon mirror 5 is obliquely incident on the deflecting surface 5a at an incident angle of 1.6 ° in the sub-scan section. Therefore, in order to satisfactorily correct the rotation of the spot caused by the oblique incidence and the linearity of the scanning line on the scanned surface 7, the second imaging lens 62 is sub-scanned with respect to the first imaging lens 61. The separation distance dZg2 of the optical axes in the cross section is desirably 5.92 (mm).

  Next, a fourth embodiment of the present invention will be described.

  The present embodiment is different from the first embodiment described above in that some specifications of the optical scanning device are made different. Other configurations and optical actions are substantially the same as those in the first embodiment, and the same effects are obtained.

  Next, Table 3 shows specifications of the optical scanning device according to the fourth embodiment.

  The optical deflector 5 in this embodiment is an 8-sided polygon mirror inscribed in φ13.72, and the width of the deflecting surface 5a in the main scanning direction is 5.25 (mm). In OFS, the width of the deflecting surface 5a serves as a stop in the main scanning direction.

  In this embodiment, the light beam incident on the deflection surface 5a of the polygon mirror 5 is obliquely incident on the deflection surface 5a at an incident angle of 1.7 ° in the sub-scan section. Therefore, in order to satisfactorily correct the rotation of the spot caused by the oblique incidence and the linearity of the scanning line on the scanned surface 7, the second imaging lens 62 is sub-scanned with respect to the first imaging lens 61. It is desirable that the separation distance dZg2 of the optical axes in the cross section is 6.2 (mm).

[Image forming apparatus]
FIG. 5 is a cross-sectional view of the main 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, third, and fourth 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 108 disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in the paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 5), 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. 5). 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, and the sheet conveyed from the transfer unit. The unfixed toner image on the paper 112 is fixed by heating 112 while applying pressure at the pressure contact portion between the fixing roller 113 and the pressure roller 114. 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. 5, 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 the higher the recording density is, the higher the image quality is required, the configurations of the first to fourth embodiments of the present invention are more effective in an image forming apparatus of 1200 dpi or more.

[Color image forming apparatus]
FIG. 6 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 in which four optical scanning devices are arranged in parallel and image information is recorded on a photosensitive drum surface as an image carrier. In FIG. 6, 60 is a color image forming apparatus, 11, 12, 13, and 14 are optical scanning devices having any of the configurations shown in the first, third, and fourth embodiments. Each of the photosensitive drums 31, 32, 33, and 34 is a developing unit, and 51 is a conveyance belt.

  In FIG. 6, the color image forming apparatus 60 receives R (red), G (green), and B (blue) color signals 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 devices 11, 12, 13, and 14, respectively. From these optical scanning devices, light beams 41, 42, 43, and 44 modulated according to each image data are emitted, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are caused by these light beams. Scanned in the main scanning direction.

  The color image forming apparatus in this embodiment has four optical scanning devices (11, 12, 13, and 14) arranged in each color of C (cyan), M (magenta), Y (yellow), and B (black). Correspondingly, image signals (image information) are recorded on the photosensitive drums 21, 22, 23, and 24 in parallel, and a color image is printed at high speed.

  As described above, the color image forming apparatus in this embodiment uses the light beams based on the respective image data by the four optical scanning devices 11, 12, 13, and 14, and the photosensitive drums 21 and 22 respectively corresponding the latent images of the respective colors. , 23, 24 on the surface. 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 60 constitute a color digital copying machine.

Main scanning sectional view of Embodiment 1 of the present invention Sub-scan sectional view of Embodiment 1 of the present invention The figure which shows the focus fluctuation | variation at the time of temperature rising of Example 1 of this invention. Sub-scan sectional view of Embodiment 2 of the present invention FIG. 3 is a sub-scan sectional view showing an embodiment of the image forming apparatus 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.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source means 2 Condensing lens 3 Cylinder lens 4 Correction | amendment element 5 Deflection means 6 Scanning optical means 61 1st image formation lens 62 2nd image formation lens 7 Surface to be scanned 8 Aperture 71, 72 Incident optical means 73 Scanning optical system 11, 12, 13, 14 Optical scanning device 21, 22, 23, 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 51 Conveyor belt 52 External device 53 Printer controller 60 Color image forming apparatus 100 Optical scanning device 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 (16)

In an optical scanning apparatus comprising: an incident optical unit that guides a light beam emitted from a light source unit to a deflecting unit; and a scanning optical unit that guides a light beam deflected by the deflecting unit onto a surface to be scanned.
The incident optical means causes the light beam emitted from the light source means in the main scanning section to enter the deflecting surface with a light beam width wider than the deflection surface width of the deflecting means, and the deflecting surface in the sub-scanning section. Is incident from an oblique direction,
The scanning optical means includes first and second imaging elements made of resin,
The first imaging element has a power in the main scanning section that is greater than a power in the sub-scanning section, and at least one surface has a non-arc shape in the main scanning section, and the surface on the deflection means side is concave. The meniscus shape of
In the second imaging element, the power in the sub-scanning section is larger than the power in the main-scanning section, and at least one surface has a non-arc shape in the main-scanning section,
The focal length in the main scanning section of the first imaging element is G1m,
The focal length in the main scanning section of the second imaging element is G2m,
The combined focal length in the main scanning section of the first imaging element and the second imaging element is Fθm,
When the focal length in the sub-scan section of the second imaging element is G2s,
0.87 <G1m / Fθm <0.97
−12.5 <G2m / Fθm <−5.0
-40.2 <G2m / G2s <-17.5
An optical scanning device characterized by satisfying the following conditions.   Both the light beam incident on the deflecting means and the light beam deflected by the deflecting means pass through the first imaging element, and the power in the sub-scan section of the first imaging element is substantially equal. 2. The light according to claim 1, wherein at least one surface in the sub-scan section of the second imaging element is formed of a convex shape whose curvature gradually changes from on-axis to off-axis. Scanning device.   The first imaging element has a symmetrical shape with respect to the optical axis of the first imaging element in the main scanning cross section, and the principal ray of the light beam incident on the deflecting means and the first coupling element. 2. The optical scanning device according to claim 1, wherein the optical axis of the image element and the rotation axis of the deflecting unit are in the same plane.   The second imaging element has a symmetric shape with respect to the optical axis of the second imaging element in the main scanning section, and the second imaging element is coupled to the optical axis of the first imaging element. 4. The optical scanning device according to claim 3, wherein the optical axis of the image element is in the same plane. When the distance from the deflection surface of the deflection means to the scanned surface is TC and the distance from the deflection surface of the deflection means to the incident surface of the second imaging element is Sg2, 0.5 <Sg2 / TC
The optical scanning device according to claim 1, wherein the following condition is satisfied. Incident optical means provided for each of the light beams that causes a plurality of light beams emitted from a plurality of light source means to enter the deflecting means, and scanning for guiding the plurality of light beams deflected by the deflecting means onto the corresponding scanned surface An optical scanning device comprising:
The incident optical means provided for each light beam causes the light beam emitted from the corresponding light source means to enter the deflecting surface with a light beam width wider than the width of the deflecting surface of the deflecting means in each main scanning section. ,
The light beam emitted from the corresponding light source means in the sub-scan section is incident on the deflection surface from an oblique direction,
The scanning optical means includes first and second imaging elements made of resin,
The first imaging element has a power in the main scanning section that is greater than a power in the sub-scanning section, and at least one surface has a non-arc shape in the main scanning section, and the surface on the deflection means side is concave. The meniscus shape of
In the second imaging element, the power in the sub-scanning section is larger than the power in the main-scanning section, and at least one surface has a non-arc shape in the main-scanning section,
The focal length in the main scanning section of the first imaging element is G1m,
The focal length in the main scanning section of the second imaging element is G2m,
The combined focal length in the main scanning section of the first imaging element and the second imaging element is Fθm,
When the focal length in the sub-scan section of the second imaging element is G2s,
0.87 <G1m / Fθm <0.97
−12.5 <G2m / Fθm <−5.0
-40.2 <G2m / G2s <-17.5
An optical scanning device characterized by satisfying the following conditions.   The plurality of light beams incident on the deflecting unit and the plurality of light beams deflected by the deflecting unit pass through a common first imaging element, and are within a sub-scanning section of the first imaging element. 7. The power is substantially zero, and at least one surface in the sub-scan section of the second imaging element has a convex shape whose curvature gradually changes from on-axis to off-axis. Optical scanning device.   The plurality of light beams incident on the deflection unit and the plurality of light beams deflected by the deflection unit pass through different positions of the first imaging element in a sub-scan section. 8. The optical scanning device according to 7.   8. The optical scanning device according to claim 7, wherein the second imaging element is provided for each of a plurality of light beams deflected by the deflecting unit and passed through the first imaging element.   The first imaging element has a symmetrical shape with respect to the optical axis of the first imaging element in the main scanning section, and the principal rays of a plurality of light beams incident on the deflecting means, and the first 7. The optical scanning device according to claim 6, wherein the optical axis of the imaging element and the rotation axis of the deflecting means are in the same plane.   The second imaging element has a symmetric shape with respect to the optical axis of the second imaging element in the main scanning section, and the second imaging element is coupled to the optical axis of the first imaging element. The optical scanning device according to claim 10, wherein the optical axis of the image element is in the same plane. When the distance from the deflection surface of the deflection means to the scanned surface is TC and the distance from the deflection surface of the deflection means to the incident surface of the second imaging element is Sg2, 0.5 <Sg2 / TC
The optical scanning device according to claim 6, wherein the following condition is satisfied.   13. The optical scanning device according to claim 1, a photosensitive member disposed on the surface to be scanned, and a static beam formed on the photosensitive member by a light beam scanned by the 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. Image forming apparatus.   13. The optical scanning device according to claim 1, and a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device. An image forming apparatus.   13. A color image comprising a plurality of image carriers, each of which is disposed on a surface to be scanned of the optical scanning device according to claim 1 and forms images of different colors. Forming equipment.   16. A color image forming apparatus according to claim 15, further comprising a printer controller that converts color signals input from an external device into image data of different colors and inputs the image data to each optical scanning device.