JP2010049060A - Scanning optical apparatus and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a scanning optical apparatus which attains a highly precise printing and is high in environmental stability, and to obtain an image forming apparatus using the scanning optical apparatus. <P>SOLUTION: The scanning optical apparatus includes: a deflection means which deflects a luminous flux emitted from a light source means and having a wavelength λ (mm); and an imaging optical system which images the deflected luminous flux on a face to be scanned. At least one of imaging optical elements of the imaging optical system is formed by bonding an optical element made of a glass material and an optical element made of a resin material to each other. The face in contact with the air of the optical element made of the resin material has an aspherical shape. The variation in the Newton number of the width D (mm) of luminous flux, which is made incident on the optical element made of the resin material, satisfies (the equation (1)) when the shape of the imaging optical element is varied so that the amount of sag F(h) of the aspherical shape varies to the amount of sag expressed by F'(h)=F(h)+0.005×äT(h)-T(0)}, where the amount of sag of the aspherical shape with respect to the distance h from the optical axis of the imaging optical element is expressed by F(h), the thickness of the optical element made of the resin material is expressed by T(H), and N in the equation 1 shoes the refractive index of the material of the optical element made of the resin material for the wavelength λ, dF(h)/dh stands for the first derivative of F(h) at h, and d<SP>2</SP>F(h)/dh<SP>2</SP>show the second derivative of F(h) at h, respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  Conventionally, a scanning optical device has been used in a laser beam printer (LBP), a digital copying machine, a multifunction printer, and the like. In this scanning optical device, a light beam (light beam) light-modulated and emitted from a light source means in accordance with an image signal is periodically deflected by an optical deflector composed of, for example, a rotating polygon mirror (polygon mirror). The deflected light beam is focused in a spot shape on the surface of a photosensitive recording medium (photosensitive drum) by an imaging optical system having fθ characteristics, and image recording is performed by optically scanning the surface.

  FIG. 14 is a schematic view of the main part of a conventional scanning optical device.

  In the same figure, the divergent light beam emitted from the light source means 91 is converted into a parallel light beam by the collimator lens 92, and the light beam is limited by the stop 93 and is incident on the cylindrical lens 94 having a predetermined refractive power only in the sub-scanning direction. Yes. Out of the parallel light flux incident on the cylindrical lens 94, it exits as it is in the main scanning section. In the sub-scan section, the light beam is converged and formed as a substantially linear image on the deflecting surface (reflecting surface) 95a of the optical deflector 95 composed of a rotating polygon mirror.

  Then, the light beam deflected by the deflecting surface 95a of the deflecting means 95 is guided to the photosensitive drum surface 98 as the scanned surface through the imaging optical system 96 having the fθ characteristic. Then, by rotating the deflecting means 95 in the direction of arrow A, the photosensitive drum surface 98 is optically scanned in the direction of arrow B to record image information.

  In the above scanning optical device, in order to adjust the timing for starting image formation on the surface of the photosensitive drum 98 before scanning the surface of the photosensitive drum 98 with the light spot, a synchronous detection BD ( a beam detector) sensor-99 is provided.

  This BD sensor 99 is a BD light beam (synchronous detection light beam) that is a part of the light beam reflected and deflected by the optical deflector 95, that is, outside the image forming area before scanning the image forming area on the surface of the photosensitive drum 98. The light flux is scanned while scanning the area.

  This BD light beam is reflected by a BD mirror 97 for synchronous detection, condensed by a BD lens (not shown) for synchronous detection, and enters a BD sensor 99. A BD signal (synchronization signal) is detected from the output signal of the BD sensor 99, and the image recording start timing on the surface of the photosensitive drum 98 is adjusted based on the BD signal.

  The imaging optical system 96 in the figure is configured such that the deflecting surface 95a of the optical deflector 95 and the photosensitive drum surface 98 are in a conjugate relationship within the sub-scan section, thereby correcting surface tilt of the deflecting surface 95a. is doing.

  In such a scanning optical apparatus, a scanning optical apparatus capable of high-definition printing for the light printing industry such as POD (Print On Demand) has recently been demanded. In order to perform high-definition printing, it is conceivable to reduce the spot diameter using a laser having a short wavelength (for example, a red laser or a blue laser). Here, the image plane depth is generally expressed as follows.

(Depth of image plane) = a × λ × (F number) ² (Formula A)
However, a is a proportionality constant, λ is the wavelength (mm) of the light source, and the F number is the F number (FNo) on the exit side of the imaging optical system.

  It is clear that the depth of field becomes smaller than that of (Formula A) when the wavelength is shortened. When the refractive index of the optical system changes due to environmental changes such as temperature changes, and the curvature of field in the main scanning direction varies, as described above, the depth of field is very narrow. There is a problem that the printing characteristic is deteriorated due to rapid enlargement.

  Therefore, an optical system having a strong power (refractive power) in the main scanning direction conventionally uses a glass lens so that a change in refractive index is small with respect to environmental fluctuations.

By the way, in order to perform high-definition printing, the imaging optical system has
(1) Almost no curvature of field,
(2) fθ characteristics (partial magnification) are good,
That is required. In order to satisfy this requirement, for example, the lens shape may be aspherical.

  However, in the case of glass lenses, a special polishing process is required to make the surface shape an aspherical surface, which is not suitable for mass production. Therefore, it has been dealt with by increasing the number of glass lenses having a spherical surface or a cylindrical shape. (See Patent Document 1).

In recent years, a glass lens is coated with an ultraviolet curable resin, and the lens is irradiated with ultraviolet rays while holding the resin with a mold having an aspherical shape. Techniques that can be brought about (replica molding) are known. (See Patent Document 2).
JP-A-3-43708 JP 2001-91878 A

  However, when this manufacturing method is used in an imaging optical system for a scanning optical device, the following concerns are raised.

  Since UV curable resin has a higher water absorption rate than resins used for optical lenses (acrylic resin (PMMA), olefin resin, etc.), the shape change due to moisture absorption is larger than that of resin molded lenses, so the effect on optical performance is considered. It is necessary to do. Therefore, it is necessary to optimize the shape of the UV curable resin to be applied.

  An object of the present invention is to provide a scanning optical device capable of high-definition printing and having high environmental stability and an image forming apparatus using the same.

A scanning optical device according to a first aspect of the present invention comprises:
A light source unit, a deflection unit that deflects and scans a light beam having a wavelength λ (mm) emitted from the light source unit, and an imaging optical system that forms an image on the scanning surface by the light beam deflected and scanned by the deflection unit. In a scanning optical device,
At least one imaging optical element of the imaging optical system is formed by bonding an optical element made of a glass material and an optical element made of a resin material, and the surface of the optical element made of the resin material that comes into contact with air is It consists of an aspheric shape,
When the aspherical sag amount with respect to the distance h from the optical axis of the imaging optical element is F (h), and the thickness of the optical element made of the resin material is T (h),
The sag amount F (h) of the aspheric shape is
F ′ (h) = F (h) + 0.005 × {T (h) −T (0)}
When the shape changes to the sag amount F ′ (h) expressed by the equation, the change amount of the Newton number in the light beam width D (mm) incident on the optical element made of the resin material satisfies the following (Equation 1) It is characterized by.

(Where N is the refractive index at the wavelength λ of the material of the optical element made of a resin material,
dF (h) / dh is the first derivative of F (h) at h,
d ² F (h) / dh ² represents the second order derivative of F (h) at h. )

The image forming apparatus of the invention of claim 2
The scanning optical device according to claim 1, a photoconductor disposed on the surface to be scanned, and an electrostatic latent image formed on the photoconductor by a light beam scanned by the scanning optical device is used as a toner image. The image forming apparatus includes a developing device that develops, 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.

The image forming apparatus of the invention of claim 3
The scanning optical apparatus 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 scanning optical apparatus.

According to a fourth aspect of the present invention, there is provided a color image forming apparatus.
Each of the plurality of image carriers is arranged on a surface to be scanned of the scanning optical device according to the first aspect and forms an image of a different color.

The invention of claim 5 is the invention of claim 4,
It has a printer controller that converts color signals input from an external device into image data of different colors and inputs them to each scanning optical device.

  According to the present invention, it is possible to achieve a scanning optical device capable of high-definition printing and having high environmental stability and an image forming apparatus using the same.

  The scanning optical apparatus of the present invention includes a light source means, a deflection means for deflecting a light beam having a wavelength λ (mm) emitted from the light source means, and a light beam deflected and scanned by the deflection means to form an image on a surface to be scanned. It has an image optical system.

  In the imaging optical system, at least one imaging optical element is formed by bonding an optical element made of a glass material and an optical element made of a resin material, and the surface of the optical element made of a resin material that is in contact with air is not It consists of a spherical shape.

Then, the aspherical sag amount with respect to the distance h from the optical axis of the imaging optical element is F (h), and the thickness of the optical element made of a resin material is T (h). At this time,
The sag amount F (h) of the aspherical surface of an optical element made of a resin material is
F ′ (h) = F (h) + 0.005 × {T (h) −T (0)}
When the shape changes to the sag amount F ′ (h) expressed by the equation, the change amount of the Newton number in the beam width D (mm) incident on the optical element made of the resin material satisfies the following (Equation 1). ing.

(Where N is the refractive index at the wavelength λ of the material of the optical element made of a resin material,
dF (h) / dh is the first derivative of F (h) at h,
d ² F (h) / dh ² represents the second order derivative of F (h) at h. )

  Of the optical elements to be joined, the aspherical optical element is made of a resin material and the other is made of a glass material.

  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 part in the main scanning direction of the scanning optical apparatus according to the first embodiment of the present invention.

  In the following description, the sub-scanning direction (Z direction) is a direction parallel to the rotation axis of the deflecting means. The main scanning section is a section whose normal is the sub-scanning direction (direction parallel to the rotation axis of the deflecting means). The main scanning direction (Y direction) is the direction in which the light beam deflected and scanned by the deflecting means is projected onto the main scanning section. The sub-scanning cross section is a cross section whose normal is the main scanning direction.

  In the figure, reference numeral 1 denotes light source means, for example, a semiconductor laser.

  Reference numeral 3 denotes a collimator lens (plano-convex lens) having a positive refractive power (power), which converts light emitted from the light source means 1 into a parallel light flux. In this embodiment, the image forming position in the main scanning direction is adjusted by moving the collimator lens 3 in the optical axis direction.

  Reference numeral 7 denotes a spherical lens having a negative refractive power, which converts the light beam converted into a parallel light beam by the collimator lens 3 into a divergent light beam. In this embodiment, the image forming position in the main scanning direction is adjusted by moving the spherical lens 7 in the optical axis direction. The mounting seat surface of the spherical lens 7 has a shape machined into a plane parallel to the optical axis of the incident optical system described later.

  Reference numeral 2 denotes an aperture stop, which regulates a beam shape by regulating a passing light beam.

  Reference numeral 4 denotes a cylindrical lens having a positive refractive power in the sub-scanning direction, and the light beam that has passed through the aperture stop 2 is formed as a substantially line image on a deflection surface 5a of an optical deflector 5 to be described later within the sub-scanning section. . In this embodiment, the imaging position in the sub-scanning direction is adjusted by moving the cylindrical lens 4 in the optical axis direction. The mounting seat surface of the cylindrical lens 4 has a shape machined into a plane parallel to the optical axis of the incident optical system described later.

  Each element of the collimator lens 3, the spherical lens 7, the aperture stop 2, the cylindrical lens 4, and the first imaging lens 61 described later constitutes an element of the incident optical system LA.

  In the main scanning section, the spherical lens 7, the cylindrical lens 4, and a first imaging lens 61 described later constitute an afocal system. Further, the incident optical system LA makes the scanning optical device (scanning optical system) compact by bending the optical path by the reflecting mirror 10.

  An optical deflector (polygon mirror) 5 as a deflecting means is rotated at a constant speed in the direction of arrow A in the figure by a driving means (not shown) such as a motor.

  Reference numeral 6 denotes an imaging optical system having an fθ characteristic, which includes first and second imaging lenses 61 and 62 as imaging optical elements.

  The first imaging lens 61 is a cemented lens (hereinafter referred to as a “replica lens”) 6b which is a spherical lens 6a as an optical element composed of a glass material and a lens (hereinafter referred to as “replica lens”) 6b which is composed of a resin material. "Replica aspherical lens").

  The surface of the replica lens 6b of this embodiment that contacts the air has an aspherical shape. The first imaging lens 61 mainly corrects curvature of field in the main scanning direction and maintains an excellent fθ characteristic.

  The first imaging lens 61 also constitutes a part of the incident optical system LA as described above.

  The second imaging lens 62 is a plastic lens, and is composed of an anamorphic lens having different powers in the main scanning direction and the sub-scanning direction, and mainly corrects field curvature in the sub-scanning direction.

  8 is a photosensitive drum surface as a surface to be scanned, and 9 is a dustproof glass.

  In this embodiment, a light beam having a wavelength λ (mm) that is light-modulated and emitted from the semiconductor laser 1 is converted into a parallel light beam by the collimator lens 3. Next, the light is converted into divergent light by the spherical lens 7, and the light beam is limited by the aperture stop 2 and is incident on the cylindrical lens 4 of the incident system. Of the light beam incident on the cylindrical lens 4, the light beam in the sub-scan section converges, passes through the first imaging lens 61, enters the deflecting surface 5 a of the optical deflector 5, and is almost lined in the vicinity of the deflecting surface 5 a. An image is formed as an image (line image elongated in the main scanning direction). At this time, the light beam incident on the deflecting surface 5a is shifted from the sub-scan section including the rotation axis of the optical deflector 5 and the optical axis of the imaging optical system 6 to a plane perpendicular to the rotation axis (rotation plane of the optical deflector 5). On the other hand, the incident light is incident at an oblique incident angle θ / 2 = 0.8 degrees to separate the incident light beam and the deflected light beam.

  The light beam in the main scanning section diverges and is converted into a parallel light beam by passing through the first imaging lens 61, and is incident on the deflecting surface 5 a from approximately the center of the deflection angle of the optical deflector 5. The beam width of the parallel beam at this time is set so as to be sufficiently wider than the facet width of the deflecting surface 5a of the optical deflector 5 in the main scanning direction (overfilled optical system).

  The light beam deflected and reflected by the deflecting surface 5 a of the optical deflector 5 is guided to the photosensitive drum surface 8 through the first and second imaging lenses 61 and 62 and the dust-proof glass 9. Then, by rotating the optical deflector 5 in the direction of arrow A, the photosensitive drum surface 8 is optically scanned in the direction of arrow B (main scanning direction). Thereby, an image is recorded on the photosensitive drum surface 8 as a recording medium.

  Here, the inventor conducted an experiment on how the shape of the replica aspherical lens 61 in which the spherical lens 6a and the replica lens 6b are joined changes due to moisture absorption.

  FIG. 2 shows the result of measuring the surface shape of the replica aspherical lens (test lens) before and after being left for 1 day in an environment of 60 ° C. and 80%. In FIG. 2, the lens coordinates correspond to the distance from the optical axis. The same applies to each figure below.

  The thickness of the replica lens (replica resin) is shown in FIG. FIG. 4 shows the amount of change in the surface shape during moisture absorption with respect to the thickness of the replica lens.

  From each figure, it is expected that the shape change due to moisture absorption depends on the thickness of the replica lens. This is presumably because the replica lens has a thin thickness of about 0.15 mm and is in close contact with the spherical lens, so that expansion in the radial direction is restricted by close contact and is expanded only in the thickness direction.

  Further, in this experiment, the average amount of change in the thickness direction due to moisture absorption of the replica lens was about 0.5% with respect to the thickness of the replica lens, which almost coincided with the water absorption rate (volume expansion coefficient) of the resin.

  S (h) is the sag amount with respect to the lens apex of the spherical lens, T (h) is the thickness of the replica lens, and h is the distance h from the optical axis of the replica aspheric lens. The sag amount of the aspherical shape (sag amount with respect to the lens apex) is F (h). At that time, the sag amount F (h) can be expressed as follows.

F (h) = S (h) + {T (h) −T (0)} (Formula B)
Next, the change F ′ (h) in the sag amount of the aspherical shape with respect to the lens apex of the replica aspherical lens when the replica lens absorbs water, the expansion due to water absorption of the replica lens is only a change in the thickness direction as described above. . Further, since the water absorption of a general replica lens is 0.5%, it can be expressed as follows.

F ′ (h) = S (h) + {T (h) −T (0)} × 1.005 (Formula C)
From (Formula B) and (Formula C), F ′ (h) can be expressed as follows using F (h).

F ′ (h) = F (h) + 0.005 × {T (h) −T (0)} (Formula D)
When the sag amount of the replica aspherical lens changes from F (h) to F ′ (h), the local R at the coordinate h changes to change the power at the coordinate h. The change amount m of the Newton number with respect to the beam width D (mm) passing through the lens can be expressed as follows from the change of the local R.

Where r (h) is the local R of F (h) at h, dF (h) / dh is the first derivative at h of F (h), and d ² F (h) / dh ² is F (h) The second derivative at h, r ′ (h), represents the local R of F ′ (h) at h. DF '(h) / dh is the first derivative of F' (h) at h, and d ² F '(h) / dh ² is the second derivative of F' (h) at h (calculation of local R For the formula, refer to “Differential integration” (Academic Books Publisher) p.55-p.57).

  When the local R of the replica aspheric lens is r (h), the focal length of the imaging optical system at this time is f, and the local R of the replica aspheric lens becomes r '(h) by moisture absorption, so that the imaging optical system Where f + Δf and the refractive index of the replica resin material at the wavelength λ is N. At that time, the following relationship holds.

  Since Δf is smaller than f, (Equation F) can be rewritten as follows.

  By combining (Equation G) and (Equation E), the fluctuation amount Δf of the focal length of the imaging optical system due to the change in the local R can be rewritten as follows.

  When the incident light beam enters the polygon mirror in parallel with the main scanning direction, the focal length variation Δf is equal to the main scanning focus variation, and f / D is the exit F number (Fno) of the imaging optical system. ). From this, the focus change amount ΔM in the main scanning direction due to the change in the local R is expressed as follows.

ΔM = 4mλ (N−1) × (Fno) ² (Formula I)
Here, assuming that the spot diameter on the photosensitive drum is w ₀ , the spot diameter w at a position x away from the photosensitive drum position can be expressed as follows, where the wavelength is λ.

If the allowable range is up to 20% of the spot diameter at the beam waist position, if the upper limit value of x satisfying w ≦ 1.2w ₀ is the focal depth W, (Formula J)

Since w ₀ is generally 1.64λ × Fno, it is substituted into (Formula F), and the depth of focus W can be expressed as follows.

  Here, even if the focus in the main scanning direction is changed due to the shape change due to moisture absorption, it is necessary to suppress the focus fluctuation amount to 10% or less of the focal depth in order not to affect the optical performance. Accordingly, when the focus change amount ΔM in (Expression I) is set to be 1/10 or less of the focal depth W in (Expression L), the change m of the Newton number in the light beam width from (Expression I) and (Expression L). Must meet the following conditions:

  In order to satisfy (Formula M), the surface shape of the replica aspherical surface must satisfy the following (Formula 1) in combination with (Formula E).

  As described above, the expression (Expression 1) defines a surface shape and a refractive index that do not cause a problem in optical performance even if the shape of the optical element surface changes due to moisture absorption.

  Table 1 shows the optical arrangement and shape of each lens in the optical system of Example 1 and the characteristics of the glass material used.

  In each table shown below, the first surface is the lens entrance surface, and the second surface is the lens exit surface.

  FIG. 5 shows the field curvature at each image height on the surface to be scanned in the optical system of Example 1, and FIG. 6 shows the fθ characteristics at each image height in the optical system of Example 1. FIG. 7 shows spot shapes at an image height of 160 mm, 100 mm, and 0 mm on the surface to be scanned in the optical system of Example 1 (5%, 10%, 13.5%, 36.8%, and 50% with respect to the peak light amount). Contour lines). FIG. 8 shows spot diameters in the main scanning direction and the sub-scanning direction when the image plane position is defocused.

  The surface shape of the replica aspheric lens in the present embodiment is expressed by the following shape expression.

  When the intersection of each lens surface and the optical axis is the origin, the optical axis direction is x-axis, and the radial coordinate is h, the shape when cut along the plane passing through the optical axis is

(Where R is the radius of curvature, and k, B ₄ , B _6, B ₈ and B ₁₀ are aspheric coefficients)
The surface shape of the anamorphic lens is expressed by the following expression.

  The intersection of each lens surface and 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 section is the y axis, and the axis orthogonal to the optical axis in the sub scanning section is the z axis The bus direction corresponding to the main scanning direction is

(Where R is the radius of curvature, and k, E ₄ , E ₆ , E ₈ , and E 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

here
r ′ = r ₀ (1 + F ₂ Y ² + F ₄ Y ⁴ + F ₆ Y ⁶ + F ₈ Y ⁸ )
(Where r ₀ is the radius of curvature of the sub-wire on the optical axis, and F ₂ , F ₄ , F ₆ and F ₈ are coefficients)
Incidentally, 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. Table 2 shows various numerical values of the scanning optical device according to this embodiment. In the table below, “E−x” indicates “10 ^−x ”.

  FIG. 9 shows the thickness of the replica lens at each lens coordinate.

The thickness T (h) of the replica lens in this embodiment is defined by the following mathematical formula. Where t is the thickness (T (0)) of the optical axis of the lens, and G ₄ , G ₆ , G ₈ , and G ₁₀ are aspheric coefficients, and can be expressed as follows.

  As is apparent from FIG. 9, the thickness of the replica lens increases uniformly from the on-axis to the off-axis. When moisture absorption occurs in this replica lens, it is considered that about 0.5% of the thickness of the replica portion expands in the thickness direction. FIG. 10 shows a focus change in the main scanning direction when the shape changes due to moisture absorption.

As shown in FIG. 10, the focus in the main scanning direction changes by 0.13 mm at the maximum off-axis due to moisture absorption. From FIG. 8, the minimum spot diameter w _{0 in} the main scanning direction is about 44 μm, and the image plane depth W that allows the spot diameter to be 1.2 times the minimum spot, that is, 53 μm, is ± 2.34 mm. Since the amount of focus fluctuation due to moisture absorption is suppressed to 1/10 or less of the image plane depth, it is considered that the influence on the optical performance is small.

  The sag amount F (h) of the replica lens and the sag amount F ′ (h) of the replica lens after moisture absorption can be expressed as follows from (Equation 2) and Tables 2 and 3.

  In the effective scanning area of ± 160 mm, the effective area of the replica lens is ± 32.7 mm. FIG. 11 shows the result of calculating the left side of (Expression 1) using the above two expressions.

Here, the width D of the light beam passing through the replica lens is D = 7.636 mm, the refractive index N of the material of the replica lens is 1.512935, and the wavelength of the light beam is λ = 0.67 × 10 ⁻³ mm.

  As is clear from FIG. 11, all the calculation results in the effective range of the replica lens are 0.14 or less, and it is understood that (Equation 1) is satisfied.

  In this embodiment, the replica lens has a rotationally symmetric shape, but the same effect can be obtained with a cylindrical shape or an anamorphic shape. In this embodiment, the imaging optical system is an overfilled optical system. However, the same effect can be obtained by using an underfilled optical system.

  In this embodiment, the oblique incidence optical system is used in the sub-scan section, but the same effect can be obtained by using the oblique incidence optical system in the main scan section.

  In this embodiment, the imaging optical system is configured by two imaging lenses. However, the present invention is not limited to this. For example, the imaging optical system may be configured by one imaging lens or three or more imaging lenses.

As described above, in this embodiment, by setting each element so as to satisfy the conditional expression (1) as described above, it is possible to obtain an image with good environmental stability and always good.
[Image forming apparatus]
FIG. 12 is a cross-sectional view of an essential part 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. This image data Di is input to an optical scanning unit (scanning optical device) 100 having the configuration shown in the first embodiment. The light scanning unit 100 emits a light beam 103 modulated according to the image data Di, and the light beam 103 scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction.

  A photosensitive drum 101 serving as an electrostatic latent image carrier (photosensitive member) is rotated clockwise by a motor 115. With this rotation, the photosensitive surface of the photosensitive drum 101 moves with respect to the light beam 103 in the sub-scanning direction orthogonal to the main scanning direction. 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 a 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. This electrostatic latent image is developed as a toner image by a developing device 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 that constitutes one element of the transfer unit disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. Transcribed. The paper 112 is stored in a paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 12), but can be fed manually. A paper feed roller 110 is disposed 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. 12). 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, thereby fixing 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. 12, the print controller 111 controls not only the data conversion described above but also each part in the image forming apparatus including the motor 115 and a polygon motor in the optical scanning unit. .

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 configuration of the first embodiment of the present invention is more effective in an image forming apparatus of 1200 dpi or more.
[Color image forming apparatus]
FIG. 13 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 scanning optical devices are arranged in parallel and image information is recorded on a photosensitive drum surface as an image carrier. In FIG. 13, reference numeral 60 denotes a color image forming apparatus, 11, 12, 13, and 14 scanning optical devices each having the structure shown in the first embodiment, 21, 22, 23, and 24, photosensitive drums as image carriers, Reference numerals 31, 32, 33 and 34 denote developing devices, and 51 denotes a conveyor belt.

  In FIG. 13, 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 K (black) image data (dot data) by a printer controller 53 in the apparatus. These image data are input to the scanning optical devices 11, 12, 13, and 14, respectively. From these scanning optical devices, light beams 41, 42, 43, 44 modulated according to each image data are emitted, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, 24 are caused by these light beams. Scanned in the main scanning direction.

  The color image forming apparatus in this embodiment has four scanning optical devices (11, 12, 13, and 14), each of which is different from C (cyan), M (magenta), Y (yellow), and K (black). It corresponds to each color. Then, image signals (image information) are recorded on a plurality of photosensitive drums 21, 22, 23, and 24 in parallel, and color images are printed at high speed.

  As described above, the color image forming apparatus in this embodiment uses the four scanning optical devices 11, 12, 13, and 14 and the corresponding photosensitive drums 21 and 22 respectively corresponding to the latent images of the respective colors by using the light beams based on the respective image data. , 23, 24 on the surface. Thereafter, a single full color image is formed by multiple transfer onto the 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 in Embodiment 1 of the present invention Diagram showing surface shape of replica lens before and after moisture absorption experiment Diagram showing thickness of replica lens used in moisture absorption experiment The figure which shows the ratio which the shape changed by the moisture absorption experiment to the thickness of the replica lens The figure which shows the curvature of field in Example 1 of this invention The figure which shows the distortion aberration in Example 1 of this invention. Spot shape on scanned surface in Embodiment 1 of the present invention Defocus characteristic of spot diameter in Example 1 of the present invention The thickness of the replica lens in Example 1 of the present invention The figure which shows the amount of focus movement of the main scanning direction by the moisture absorption in Example 1 of this invention. Calculation result of left side of (Formula 1) in Example 1 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. Schematic diagram of main parts of a conventional scanning optical device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source means 2 Aperture stop 3 Collimator lens 4 Cylindrical lens 5 Deflection means (rotating polygon mirror)
DESCRIPTION OF SYMBOLS 6 Imaging optical system 61 1st imaging lens 62 1st imaging lens 6a Spherical lens 6b Replica lens 7 Spherical lens 8 Surface to be scanned 9 Dust-proof glass 10 Reflection mirror 11, 12, 13, 14 Scanning optical 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 device 100 Scanning optical device 101 Photosensitive drum 102 Charging roller 103 Light beam 104 Image forming device 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 light source unit, a deflection unit that deflects and scans a light beam having a wavelength λ (mm) emitted from the light source unit, and an imaging optical system that forms an image on the scanning surface by the light beam deflected and scanned by the deflection unit. In a scanning optical device,
At least one imaging optical element of the imaging optical system is formed by bonding an optical element made of a glass material and an optical element made of a resin material, and the surface of the optical element made of the resin material that comes into contact with air is It consists of an aspheric shape,
When the aspherical sag amount with respect to the distance h from the optical axis of the imaging optical element is F (h), and the thickness of the optical element made of the resin material is T (h),
The sag amount F (h) of the aspheric shape is
F ′ (h) = F (h) + 0.005 × {T (h) −T (0)}
When the shape changes to the sag amount F ′ (h) expressed by the equation, the change amount of the Newton number in the light beam width D (mm) incident on the optical element made of the resin material satisfies the following (Equation 1) A scanning optical device.
(Where N is the refractive index at the wavelength λ of the material of the optical element made of a resin material,
dF (h) / dh is the first derivative of F (h) at h,
d ² F (h) / dh ² represents the second order derivative of F (h) at h. )
  The scanning optical device according to claim 1, a photoconductor disposed on the surface to be scanned, and an electrostatic latent image formed on the photoconductor by a light beam scanned by the scanning optical device is used as a toner image. An image forming apparatus comprising: a developing device that develops; a transfer device that transfers a 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 comprising: the scanning optical apparatus 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 scanning optical apparatus.   A color image forming apparatus comprising: a plurality of image carriers, each of which is disposed on a surface to be scanned of the scanning optical apparatus according to claim 1 and forms images of different colors.   5. The color image forming apparatus according to claim 4, further comprising a printer controller that converts color signals input from an external device into image data of different colors and inputs the data to each scanning optical device.