JP2012230396A - Optical scanning device and image forming apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact optical scanning device by which routing of a light path is facilitated and the height of the device in the sub-scanning direction can be reduced, and an image forming apparatus using the optical scanning device.SOLUTION: A transmission type imaging optical element and a reflection type optical element composing an imaging optical system are arranged in that order in an optical path between a light deflector and a scanned surface. In the case where, in a sub-scanning cross-section, the angle formed between the principal ray of a luminous flux reflected by the reflection type optical element and the normal of the reflection type optical element is θ, the optical scanning device satisfies the condition of θ≤45°. The transmission type imaging optical element, which is a resin lens, is arranged opposite an optical path reflected by the reflection type optical element relative to the principal ray of a luminous flux on which the outer-shape center line is made incident so as not to interfere with the optical path reflected by the reflection type optical element, within the sub-scanning cross-section. The ratio of a physical distance from the outer-shape center line to the incident principal ray with respect to the outer-shape height of a holding frame is within a predetermined range.

Description

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

  Conventionally, a plurality of optical scanning devices having a light source means, a deflecting means, an imaging optical system, etc. are provided, and light beams emitted from the plurality of optical scanning devices are guided onto a plurality of corresponding image image carriers, respectively. Various color image forming apparatuses for forming images have been proposed.

  The main configuration and optical action of the conventional color image forming apparatus will be described with reference to FIGS.

  The color image forming apparatus in FIG. 12 has an independent image carrier (hereinafter referred to as “photosensitive drum”) 20 for each color of yellow, magenta, cyan, and black. The photosensitive drum 20 is obtained by applying a photosensitive layer to a conductor, and forms an electrostatic latent image by a light beam (laser light) emitted from an optical scanning device.

In FIG. 12, reference numeral 21 denotes an optical scanning device (scanning optical device) that emits a light beam based on image information sent from an image reading device or a personal computer (not shown). A developing unit 22 forms a toner image on the photosensitive drum with toner frictionally charged on the photosensitive drum, and an intermediate transfer belt 23 conveys the toner image on the photosensitive drum to a transfer sheet. Reference numeral 24 denotes a paper feed cassette for storing paper on which a toner image is formed, and reference numeral 25 denotes a fixing device that adsorbs the toner image transferred onto the paper to the paper by heat. 26 is a paper discharge tray on which the fixed transfer paper is stacked, and 27 is a cleaner for cleaning the toner remaining on the photosensitive drum.
In FIG.
In the image formation, an electrostatic latent image is formed on the photosensitive drum charged by the charger by irradiating the photosensitive drum with a light beam emitted from the optical scanning device based on the image information. Thereafter, a toner image is formed on the photosensitive drum by adhering the frictionally charged toner in the developing unit 22 to the electrostatic latent image. The toner image is transferred from the photosensitive drum onto an intermediate transfer belt, and the toner image is transferred again to a sheet conveyed from a paper feed cassette provided at the lower part of the main body, whereby an image is formed on the sheet. The image transferred onto the paper is fixed with toner by the fixing device 25 and is stacked on the paper discharge tray 26.

  FIG. 13 is a sub-scan sectional view showing the image forming unit of FIG. In FIG. 13, the image forming unit includes two optical scanning devices (scanning optical devices) SR and SL, and the two optical scanning devices SR and SL are configured symmetrically with respect to the optical deflector 28. Therefore, the symbol in the figure shows only one side (optical scanning device SR) and will be described.

  The optical scanning device in the figure includes a rotating polygon mirror 28 (hereinafter also referred to as “polygon mirror”) that deflects and scans a light beam (laser light) emitted based on image information, a constant speed scanning of the light beam and a photosensitive drum. It passes through two fθ lenses 29 and 30 that form an image in a spot shape. The light flux that has passed through the fθ lenses 29 and 30 passes through a plurality of reflecting mirrors 31a to 31d that reflect in a specific direction and a dustproof glass 32 that protects the optical scanning device from dust. Then, an electrostatic latent image is formed on the surface of the photosensitive drum by the light flux that has passed through the dust-proof glass 32.

  With this type of optical scanning device, as the image forming apparatus becomes more compact, a method of scanning and exposing four photosensitive drums with one polygon motor unit has come to be used as shown in FIG. This system has two optical scanning devices SR and SL that irradiate a plurality of light beams on the opposing surfaces of the polygon mirror 28, respectively. Each of the optical scanning devices SR and SL deflects and scans two light beams that are vertically shifted by a predetermined distance on the deflection surface (reflection surface) of the polygon mirror 28, respectively.

  In addition, two fθ lenses 29 and 30 are provided in order to form the light beams of the upper and lower optical paths on the photosensitive drum, respectively. The two fθ lenses 29 and 30 each have the same lens surface in two upper and lower stages. For the production, two lenses may be bonded together or integrally molded as a molded lens.

  This upper and lower two-stage optical scanning device requires a deflecting surface for deflecting and scanning the light beam for each optical path, and a thick polygon mirror or a two-stage polygon mirror is used. This method tends to increase the load on the motor that drives the large polygon mirror.

  On the other hand, FIG. 14 shows a color image forming apparatus using a thin polygon mirror. In FIG. 14, the image forming unit has two optical scanning devices SR and SL, and the two optical scanning devices SR and SL have a symmetrical configuration with respect to the optical deflector 33. Shows only one side (optical scanning device SR) and will be described.

  In this method, the polygon mirror 33 is made thin (oblique incidence optical system) by causing each light beam to be incident (obliquely incident) on the deflection surface 33a of the polygon mirror 33 within the sub-scan section.

  Each light beam is deflected and scanned by the polygon mirror 33 and then passes through two common fθ lenses 35 and 36. The one light beam U transmitted through the fθ lenses 35 and 36 is guided to the photosensitive drum 38a via the two reflecting mirrors 34a and 34c and the single concave mirror 34b. The other light beam L transmitted through the fθ lenses 35 and 36 is guided to the photosensitive drum 38b via the two reflecting mirrors 34d and 34f and the single concave mirror 34e.

In the figure,
Separation of the optical path of the light beam is performed by a reflection mirror 34d disposed in the middle of the optical path. A plurality of reflecting mirrors 34c, 34f arranged on the upper side of the optical box are reflected by the reflecting mirror 34d so that the light beam L deflected and scanned on the lower side in the figure intersects with the light beam U deflected and scanned on the upper side in the figure. To the photosensitive drum 38b.

  As described above, in FIG. 14, a plurality of reflecting mirrors are used to guide a plurality of light beams to the corresponding photosensitive drum surfaces (see Patent Documents 1 to 6).

JP 2004-21133 A JP 2000-231074 A JP 2005-338573 A JP 7-287180 A Japanese Patent Laid-Open No. 62-267419 JP 2004-317790 A

  The conventional color image forming apparatus described above has the following various problems.

  The first problem is that a large number of reflecting mirrors are required to guide the light beam to the photosensitive drum. For example, in FIG. 13, three reflecting mirrors 31b, 31c, and 31d are used in the same optical path. Also in FIG. 14, three reflecting mirrors 34a, 34b, 34c (34d, 34e, 34f) are used in the same optical path.

  As a result, the apparatus becomes complicated due to an increase in the number of parts, and a space for storing the mirror is required, resulting in an increase in the size of the entire apparatus.

  On the other hand, Patent Document 1 proposes a method of reducing the height of the optical scanning device in the sub-scanning direction and reducing the number of reflection mirrors.

  In this method, the optical path is changed so as to avoid the imaging lens while devising the optical path and taking into consideration the size of the imaging lens.

  Patent Document 3 proposes a method for reducing the height of the optical scanning device in the sub-scanning direction. In Patent Document 3, attention is paid to the reflection angle of the reflection mirror, the distance from the imaging lens to the reflection mirror, and the height of the imaging lens, and attempts to reduce the height of the apparatus. In particular, the height of the imaging lens is limited to 6 to 10 mm, so that the reflection angle of the optical path can be reduced.

  However, in a resin lens (hereinafter also referred to as “resin lens”) that has come to be generally used in an imaging lens, the following problems occur when the height of the imaging lens is lowered. .

  In a resin lens molded by a mold, if the height of the lens is lowered with respect to the thickness in the optical axis direction of the lens, cooling proceeds from the up and down direction of the lens at the time of cooling immediately after taking out from the mold. As a result, the refractive index distribution and the birefringence distribution inside the lens are likely to occur within the sub-scan section (in the lens height direction). As a result, the imaging performance in the sub-scanning direction is remarkably increased. Therefore, it is practically difficult to reduce the lens height as proposed in Patent Document 3.

  As another problem, in the oblique incidence optical system as shown in FIG. 14, the light beam is obliquely incident on the fθ lens (imaging lens) in the sub-scanning section, thereby deteriorating aberrations, and spot imaging. There are problems that the performance deteriorates and the scanning lines on the surface to be scanned are curved.

  On the other hand, in Patent Document 6, as shown in FIG. 10 of Example 3 of the same publication, the power distribution in the sub-scanning direction of the two-piece fθ lens is concentrated on the second fθ lens, and the second fθ lens is focused on the light flux. Are shifted in the sub-scan section. This realizes a reduction in aberration deterioration and a reduction in scanning line bending amount.

  Regarding the routing of the optical path, as shown in FIG. 13 of the publication, the optical path is arranged so as to surround the lens.

  In Patent Documents 4 and 5, as in Patent Document 6, a part of the fθ lens is shifted with respect to the light beam in the sub-scan section.

  These are for the purpose of avoiding the surface reflection ghost of the imaging lens, and it is assumed that any shifted imaging lens has a power in the sub-scanning direction and has a power.

  Patent Documents 4 and 5 do not sufficiently discuss an approach for downsizing the entire apparatus.

  In Patent Document 2, there are cases in which the imaging lens is tilted by about 1 ° to 4 ° in order to prevent ghosting, and cases in which the scanning light beam is obliquely incident in the sub-scan section in order to separate the optical path after being double-passed through the imaging lens. Disclosure. Similar to Patent Document 6, an attempt is made to define the reflection angle of the cylinder mirror in order to reduce the imaging performance of the spot due to oblique incidence and to reduce the scanning line curvature.

  However, Patent Document 2 does not sufficiently discuss the handling of the optical path for downsizing the entire apparatus.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a compact optical scanning device that can easily handle optical paths and reduce the height of the device in the sub-scanning direction, and an image forming apparatus using the same.

An optical scanning device according to the present invention includes an optical deflector that deflects and scans a light beam emitted from a light source means, and an imaging optical that forms an image on the scanned surface by the light beam deflected and scanned by the deflection surface of the optical deflector. A light beam incident on the deflecting surface of the optical deflector is incident perpendicularly to the deflecting surface in the sub-scan section, and the optical deflector deflects the optical deflector. The light beam incident on the surface is incident at an angle with respect to the optical axis of the imaging optical system in the main scanning section, and in the optical path between the optical deflector and the scanned surface. A transmission type imaging optical element and a reflection type optical element constituting the imaging optical system are arranged in order from the optical deflector, and the light beam reflected by the reflection type optical element in the sub-scan section is arranged. When the angle formed by the principal ray and the normal of the reflective optical element is θ,
θ ≦ 45 °
The transmission imaging optical element is a resin lens, and the transmission imaging optical element interferes with an optical path reflected by the reflection optical element in the sub-scan section. So that the center line of the outer shape of the transmissive imaging optical element is located on the opposite side of the optical path reflected by the reflective optical element with respect to the principal ray of the light beam incident on the transmissive imaging optical element. And the height of the outer shape of the holding frame that holds the transmissive imaging optical element is H (mm) in the sub-scan section, and the incident surface of the transmissive imaging optical element from the outer center line When the physical distance to the principal ray of the light beam incident on is dZ (mm),
0.05 <dZ / H <0.3 is satisfied.

  An image forming apparatus using the optical scanning device also constitutes another aspect of the present invention.

  According to the present invention, it is possible to achieve a compact optical scanning apparatus and an image forming apparatus using the same, which can easily handle the optical path and reduce the height of the apparatus in the sub-scanning direction.

Sub-scan sectional view of Embodiment 1 of the present invention Main scanning sectional view of Embodiment 1 of the present invention FIG. 3 is an enlarged view of a sub-scan sectional view of Embodiment 1 of the present invention. Enlarged view of sub-scanning sectional view of Embodiment 2 of the present invention The enlarged view of the subscanning sectional view of Example 3 of the present invention. Main scanning sectional view of Embodiment 4 of the present invention Main scanning sectional view of Embodiment 5 of the present invention Main-scan sectional view of Embodiment 6 of the present invention Enlarged view of sub-scanning sectional view of Embodiment 7 of the present invention Cross-sectional view of essential parts of the image forming apparatus of the present invention Sectional drawing of the principal part of the color image forming apparatus of this invention Cross-sectional view of main parts of a conventional image forming apparatus Cross-sectional view of main parts of a conventional image forming apparatus Cross-sectional view of main parts of a conventional image forming apparatus

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

[Example 1]
FIG. 1 is a sectional view (sub-scanning sectional view) of the main part in the sub-scanning direction of Embodiment 1 of the present invention, and FIG. 3 is a cross-sectional view (sub-scanning cross-sectional view) of a main part in the sub-scanning direction of a part of FIG.

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

  1 to 3, the image forming apparatus includes two optical scanning devices (scanning optical devices) SR and SL, and the two optical scanning devices SR and SL are symmetrical with respect to the optical deflector 5. The configuration and the same optical action will be described below, focusing on the optical scanning device SR.

  In the figure, reference numeral 1 denotes a light source means, which consists of a semiconductor laser. A condensing lens (collimator lens) 2 converts the divergent light beam emitted from the light source means 1 into a parallel light beam. The condensing lens 2 may convert the incident light beam to a convergent light beam or a divergent light beam as well as a parallel light beam.

  Reference numeral 3 denotes an aperture stop which shapes the beam shape by limiting the passing light flux. A cylindrical lens 4 has a specific power only in the sub-scan section (sub-scan direction), and a light beam that has passed through the aperture stop 3 is deflected on the deflecting surface (reflection) of the deflecting means 5 described later in the sub-scan section. Surface) 51 as a line image.

  The condensing lens 2 and the cylindrical lens 4 may be integrally configured as one optical element (anamorphic lens). Each element such as the condensing lens 2, the aperture stop 3, and the cylindrical lens 4 constitutes one element of an incident optical system (condensing optical system) LA, and the light beam from the light source means is incident on the deflecting means 5. ing.

  Reference numeral 5 denotes an optical deflector (polygon mirror) as a deflecting unit, which has a six-surface configuration, and deflects and scans the light beam from the light source unit 1. The rotating optical deflector 5 rotates on the surface to be scanned 11 in the main scanning direction by rotating at a constant speed in a predetermined direction by a motor (not shown).

  LB is an imaging optical system (fθ lens system). The imaging optical system LB in the present embodiment has a plurality (two in this embodiment) of imaging optical elements (transmissive imaging optical elements) that guide the light beam from the optical deflector 5 to the scanned surface 8 ( The first and second imaging lenses 6 and 8) are included.

  The imaging optical system LB binds a light beam based on image information deflected and scanned by the rotating optical deflector 5 to a spot on the photosensitive drum surface 11 as a scanned surface in the main scanning section (main scanning direction). I am letting you image. Further, surface tilt compensation is performed by optically conjugating the deflection surface 51 of the optical deflector 5 and the photosensitive drum surface 11 that rotate in the sub-scan section.

  Reference numerals 7 and 9 denote first and second reflection mirrors (reflection type optical elements) for bending the optical path, respectively, and are disposed in the optical path between the optical deflector 5 and the scanned surface 11. Of the first and second reflecting mirrors 7 and 9, the first reflecting mirror 7 that is optically closest to the optical deflector 5 is between the first and second imaging lenses 6 and 8 (two imaging lenses). (Between optical elements).

  In this embodiment, optical means the direction in which the light beam travels.

  10 is a cover glass, and 11 is a photosensitive drum surface as a surface to be scanned.

  Reference numeral 61 denotes an outline center line of a holding frame (not shown) for holding an imaging lens as an optical element, 14 denotes a light beam (scanned light beam) deflected and scanned by the deflecting surface 51, and 15 denotes a first mirror 7. An optical path reflected by 67 and 67 is a gate.

  The optical scanning device in this embodiment is a so-called deflection in-plane scanning system that scans in a plane perpendicular to the deflection surface of the optical deflector (polygon mirror) 5 in the sub-scan section as shown in FIG. For this reason, as shown in FIG. 2, the incident optical system LA from the light source means 1 to the cylindrical lens 4 is arranged in the paper surface which is a deflection surface.

  In this embodiment, as can be seen from FIG. 2, the same optical scanning devices (scanning optical devices) SR and SL are arranged on the left and right with the optical deflector 5 interposed therebetween, and a plurality of optical deflectors 5 are used in common. The surface to be scanned is scanned.

  Next, Table 1, Table 2, and Table 3 show the specifications of the optical scanning device in Example 1 of the present invention.

Polygon mirror circumscribed circle = φ40
Number of polygon mirror deflection surfaces = 6
Angle between the incident optical system and the optical axis of the imaging optical system = 70 °
Reflection point on polygon mirror of polygon mirror center (0,0) = (15.05,8.71)
Distance between polygon mirror center and first reflection mirror = 85
Incident angle between the normal of the first reflecting mirror and the incident light flux = 7.3 °
Distance from first mirror to second mirror = 140
Incident angle between the normal of the second mirror 9 and the incident light flux = 62.3 °

  However, the expression is defined as follows.

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

(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, and D ₂ , D ₄ , D ₆ , D ₈ and D ₁₀ are coefficients)
In the table,
The focal length of the first imaging lens in the main scanning direction is G1m,
The focal length of the second imaging lens in the main scanning direction is G2m,
The combined focal length of the first imaging lens and the second imaging lens in the main scanning direction is fθm,
The focal length of the first imaging lens in the sub-scanning direction is G1s, and the power is φ1
The focal length of the second imaging lens in the sub-scanning direction is G2s, and the power is φ2
The combined focal length of the first imaging lens and the second imaging lens in the sub-scanning direction is fθs, and the power is φall.
The distance from the polygon mirror to the scanned surface is TC,
It is said.

In the table, the display of “e−X” means “× 10 ^−X ”.

  In this embodiment, the divergent light beam emitted from the semiconductor laser 1 is converted into a parallel light beam by the condenser lens 2, the light beam (light quantity) is limited by the aperture stop 3, and is incident on the cylindrical lens 4.

  Out of the convergent light beam incident on the cylindrical lens 4, it exits as it is in the main scanning section and enters the deflecting surface 51 of the optical deflector 5. Further, in the sub-scan section, a line image (line image elongated in the main scanning direction) is formed on the deflecting surface 51 of the optical deflector 5 that further converges and rotates.

  At this time, the light beam emitted from the incident optical system LA is incident perpendicularly to the deflection surface of the optical deflector 5 in the sub-scan section and is condensed on the deflection surface 51.

  Then, the light beam deflected and scanned by the deflecting surface 51 of the optical deflector 5 passes through the first imaging lens 6, is reflected by the first reflecting mirror 7, passes through the second imaging lens 8, and passes through the second reflecting mirror. 9, and is imaged in a spot shape on the photosensitive drum surface 11. As a result, an image is recorded on the photosensitive drum surface 11 as a recording medium.

  Next, the optical action of the imaging optical system LB composed of the first and second imaging lenses 6 and 8 will be described.

  In this embodiment, the first and second imaging lenses 6 and 8 are made of resin (plastic).

  The imaging optical system LB forms an image of the light beam deflected and scanned by the optical deflector 5 on the scanned surface 11 to form a beam spot, and scans the scanned surface 11 at a constant speed. The resin-made imaging lens is manufactured by a known molding technique in which a mold is filled with a resin and is taken out of the mold after cooling. Thereby, it can manufacture easily from the conventional imaging lens which uses a glass lens.

  As shown in Table 1, the first imaging lens 6 mainly having power (refractive power) in the main scanning direction has an aspherical shape whose lens surface shape is expressed by a function of the given equation.

  In the present embodiment, the first of the optical path 15 reflected by the first reflecting mirror 7 and the holding frame (not shown) of the imaging optical element that holds each of the plurality of imaging lenses is the closest to the outer periphery. The imaging lens 6 (imaging optical element A) has a smaller power in the sub-scanning direction than that in the main scanning direction. The first imaging lens 6 is a meniscus lens (meniscus lens) whose main scanning cross section is a non-arc and has a concave surface facing the optical deflector 5 side.

  The shape of the first imaging lens 6 in the main scanning section is symmetric with respect to the optical axis. Further, although the entrance surface and the exit surface have non-power with the same curvature with respect to the sub-scanning direction, for example, a cylinder shape in which both surfaces are flat in the sub-scanning direction may be used. It is mainly responsible for image formation in the main scanning direction with respect to the incident light beam.

  The holding frame is integrally formed with the imaging optical element by molding. The holding frame may be formed separately from the imaging optical element.

  One second imaging lens 8 is an anamorphic lens having power mainly in the sub-scanning direction as shown in Table 1. The lens surface shape is an aspherical shape expressed by a function of the given equation.

  The second imaging lens 8 has a larger power in the sub-scanning direction (within the sub-scanning section) than a power in the main scanning direction (within the main-scanning section), and the incident surface of the main scanning section has an arc. The surface has a non-arc shape. The shape in the main scanning section is symmetric with respect to the optical axis, and the main scanning direction on the axis is non-power. The shape of the sub-scanning cross section is a flat surface with a very gentle curvature of the entrance surface, and a convex shape in which the exit surface gradually changes in curvature from on-axis to off-axis, and is symmetrical with respect to the optical axis. It is mainly responsible for image formation in the sub-scanning direction and correction of slight distortion in the main scanning direction for the incident light flux.

  The imaging relationship in the sub-scanning direction by the imaging optical system LB including the first and second imaging lenses 6 and 8 is a so-called surface tilt correction system in which the deflection surface 51 and the surface to be scanned 7 are conjugated. It has become.

  The imaging optical system LB is not necessarily a function expression as shown in Table 1, and may be a known expression. In order to further improve the imaging performance, the shape may be asymmetric with respect to the optical axis.

  In this embodiment, as shown in FIG. 3, a light beam (scanned light beam) 14 deflected and scanned by the deflecting surface 51 is incident on the first imaging lens 6 and then reflected by the first reflecting mirror 7.

  In the present embodiment, in the sub-scan section, the first imaging lens 6 holds the imaging optical element holding frame (not shown) with respect to the center line (principal ray) of the light beam incident on the first imaging lens 6. ) Is arranged so as to be located on the opposite side of the reflected optical path 15.

  That is, in this embodiment, the first imaging lens 6 is shifted by a distance (shift amount) dZ, which will be described later, in a direction perpendicular to the scanning light beam 14, thereby causing interference between the reflected optical path 15 and the first imaging lens 6. Is avoiding. By avoiding this interference, the reflection angle θ at the first reflecting mirror 7 can be reduced, which contributes to a reduction in the height of the apparatus in the sub-scanning direction.

  As shown in Table 1, the curvature radius r of the first imaging lens 6 in the sub-scanning direction is 1000, and the apex thereof is configured to coincide with the outer shape center line 61.

In this embodiment, when the angle formed by the principal ray of the light beam reflected by the first reflecting mirror 7 and the normal line of the reflecting mirror 7 is θ,
θ ≦ 45 ° (3)
Satisfy the following conditions.

  Conditional expression (3) defines the reflection angle θ reflected by the first reflecting mirror 7. If the upper limit of conditional expression (3) is exceeded, it will not be possible to contribute to downsizing of the entire device. That is, when the reflection angle θ exceeds 45 degrees, the angle formed by the principal ray of the scanning light beam 14 and the reflected optical path 15 exceeds 90 degrees, and the compactness in the horizontal direction is lost. Therefore, the reflection angle θ is preferably set to 45 degrees or less.

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

θ ≦ 30 ° (4)
In this embodiment, as shown in Table 1 above,
θ = 7.3 °
It is. This satisfies conditional expression (3) and further conditional expression (4).

In this embodiment, the height of the outer shape of the holding frame of the imaging optical element that holds the first imaging lens 6 is H, and the physical distance from the outer shape center line 61 to the principal ray of the incident light beam (scanning light beam) 14 When the distance (shift amount) is dZ,
0.05 <dZ / H <0.5 (5)
Satisfy the following conditions.

  Conditional expression (5) relates to the ratio of the distance from the outer shape center line 61 to the incident light beam 14 and the height of the outer shape. If the conditional expression (5) is deviated, it becomes difficult to route the optical path, and it becomes difficult to reduce the height of the apparatus in the sub-scanning direction.

  More preferably, the conditional expression (5) should be set as follows.

0.07 <dZ / H <0.3 (6)
In this embodiment, H = 13.0
dZ = 1.5
Therefore,
dZ / H = 0.115
It is. This satisfies conditional expression (5) and further conditional expression (6).

  In this embodiment, as can be seen from FIG. 3, the height of the apparatus in the sub-scanning direction can be reduced by reducing the angle θ. In order to avoid interference between the reflected optical path 15 and the first imaging lens 6 at this time, the first imaging lens 6 may be shifted in a direction perpendicular to the scanning light beam 14. As the shift amount dZ is increased, the height reduction effect increases. However, the maximum shiftable amount is ½ of the lens height H, which determines the upper limit of the conditional expression (5).

  Further, in a resin lens molded by a mold, if the height of the lens is lowered with respect to the thickness in the optical axis direction of the lens, cooling proceeds from the vertical direction of the lens at the time of cooling immediately after taking out from the mold. As a result, the refractive index distribution and the birefringence distribution inside the lens are likely to occur within the sub-scan section (in the lens height direction). It is known that this effect becomes more significant as the distance from the central axis of the lens outer shape increases, and that the deterioration rapidly starts from about 2/3 from the outer shape center toward the outer edge. Therefore, if importance is attached to the imaging performance of the apparatus, it is important to set dZ / H <0.3.

  This is defined by the upper limit of conditional expression (6). The lower limits of conditional expressions (5) and (6) define the lower limit of the shift amount of the first imaging lens 6. If the shift amount is small, the interference between the reflected optical path 15 and the first imaging lens 6 is insufficiently prevented, and the position of the reflected optical path 15 and the position of the first imaging lens 6 due to tolerances at the time of assembly are determined. Interference occurs when it swings.

In this embodiment, as described above, the power in the sub-scanning direction of the first imaging lens 6 is smaller than the power in the main scanning direction. At this time, the width of the light beam reflected by the first reflection mirror 7 is La, and the distance from the first imaging lens 6 to the first reflection mirror 7 is L. Further, the reflection angle formed between the principal ray of the light beam reflected by the first reflection mirror 7 and the normal line of the first reflection mirror 7 is θ, and the height of the outer shape of the holding frame of the imaging optical element is H. The shift amount dZ of the first imaging lens 6 at this time is
5 <dZ (7)
It is good to do.

  Conditional expression (7) is a condition for defining the shift amount dZ of the first imaging lens 6. If the conditional expression (7) is not satisfied, the interference between the reflected optical path 15 and the first imaging lens 6 will be insufficiently prevented in the same manner as in the conditional expression (5), and the reflected optical path 15 due to tolerances during assembly or the like. And the position of the first imaging lens 6 are interfered with each other.

In this embodiment, when the power in the sub-scanning section of the first imaging lens 6 (imaging optical element C) is φi and the power in the sub-scanning section of the imaging optical system LB is φall,
| Φi / φall | ≦ 0.01 (1)
Satisfy the following conditions.

  Conditional expression (1) expresses the ratio between the power (1 / focal length) of the first imaging lens 6 constituting the imaging optical system LB in the sub-scanning direction and the power (1 / focal length) of the imaging optical system LB. It is a condition for prescribing. That is, conditional expression (1) defines that the power ratio of the first imaging lens 6 is set to be smaller than a predetermined amount. When the power ratio of the first imaging lens 6 increases beyond the upper limit value of the conditional expression (1), aberrations occur when the power ratio of the first imaging lens 6 is shifted in parallel to the optical axis as described above. It deteriorates, resulting in deterioration of the spot diameter and curvature of the scanning line.

In this embodiment, as shown in Table 1 above,
| Φi / φall | = 8.8E-05
It is. This satisfies the conditional expression (1).

  More preferably, the conditional expression (1) should be set as follows.

0.00001 ≦ | φi / φall | ≦ 0.0050 (1a)
In this embodiment, when the curvature radii of the first image forming lens 6 on the optical deflector side and the scanned surface side are R1 and R2, respectively.
| 1 / R1 | + | 1 / R2 | <0.0071 (1 / mm) (2)
Satisfy the following conditions.

  Conditional expression (2) is a condition for defining the curvature in the sub-scanning direction of the first imaging lens 6 constituting the imaging optical system LB. That is, conditional expression (2) defines that the curvature in the sub-scanning direction of the entrance surface and exit surface of the first imaging lens 6 is set to be smaller than a predetermined amount. When the curvature in the sub-scanning direction of the entrance surface and exit surface of the first imaging lens 6 exceeds the upper limit value of the conditional expression (2), the power ratio of the first imaging lens 6 is set to the optical axis as described above. On the other hand, when the parallel shift is performed, the aberration is deteriorated, and the spot diameter is deteriorated and the scanning line is curved.

In this embodiment, as shown in Table 1 above,
| 1 / R1 | + | 1 / R2 | = 2.0E-03 (1 / mm)
It is. This satisfies the conditional expression (2).

  More preferably, the conditional expression (2) should be set as follows.

0.0010 (1 / mm) <| 1 / R1 | + | 1 / R2 | <0.0035 (1 / mm) (2a)
As described above, in this embodiment, among the imaging lenses constituting the imaging optical system LB, the first imaging lens 6 having a very small power in the sub-scanning direction is shifted in the sub-scanning section with respect to the scanning light beam 14. It is a feature.

  The power in the sub-scanning direction of the first imaging lens 6 may be zero (non-power).

  Further, as described above, the curvature of the first imaging lens 6 is very gentle, and Fresnel reflected light generated on the lens surface of the first imaging lens 6 returns to the optical deflector 5 even if it is shifted within the sub-scanning section.

  Therefore, in this embodiment, the distance between the optical deflector 5 and the first imaging lens 6 is sufficiently set, and the thickness of the optical deflector 5 in the height direction is set to 2 mm or less, so that the Fresnel reflected light is affected as flare or ghost light. It is configured so as not to affect. Furthermore, the lens surface of the first imaging lens 6 may be coated.

  In the present embodiment, as described above, the first imaging lens 6 (imaging optical element C) having the smallest or zero power in the sub-scanning direction among the first and second imaging lenses 6 and 8. ) With respect to the scanning light beam 14 within the sub-scan section. Thus, in this embodiment, the influence on the deterioration of the aberration and the scanning line curve is reduced.

  In the present embodiment, the first imaging lens 6 is shifted by the distance dZ = 1.5 mm in the sub-scanning direction, so that the fluctuation of the scanning line curve is negligible at about 1 μm or less.

  In the present embodiment, as described above, the first reflecting mirror 7 is provided so as to be positioned in the optical path between the first imaging lens 6 and the second imaging lens 8. Thereby, in this embodiment, both the horizontal direction and the vertical direction are made compact.

  If the first reflecting mirror 7 is provided behind the second imaging lens 8, the width in the horizontal direction is increased. If the first reflecting mirror 7 is provided in the optical path between the first imaging lens 6 and the optical deflector 5, it is compact in the horizontal direction but cannot be compact in the vertical direction. Therefore, in order to make the horizontal and vertical directions compact, it is preferable to provide the first reflecting mirror 7 in the optical path between the first imaging lens 6 and the second imaging lens 8.

  In this embodiment, as shown in FIG. 1, optical scanning devices (scanning optical devices) SR, SL having the same configuration on the left and right sides with respect to the plane including the rotation axis of the optical deflector 5 with the optical deflector 5 interposed therebetween. And a plurality of scanned surfaces are scanned using the optical deflector 5 in common.

  However, the reflection angles of the second reflecting mirror 9 are different from each other in each of the optical scanning devices SR and SL as shown in FIG. The reflection angle at the second reflecting mirror 9 may be set as appropriate according to the arrangement of the image forming apparatus.

  As described above, in this embodiment, by adopting the above-described configuration, interference between the light beam reflected by the first reflecting mirror 7 and the first imaging lens 6 can be avoided, so that the number of reflecting mirrors used can be reduced. A compact optical scanning device can be configured. In this embodiment, the power in the sub-scanning direction of the first imaging lens 6 to be shifted is suppressed to be low, so that the deterioration of aberration due to the shift can be suppressed and the spot imaging state can be maintained well.

  In this embodiment, the gate portion (gate) 67 of the first imaging lens 6 is provided in the same direction in both the left and right imaging optical systems LB as shown in FIG. By providing the gate portion 67 in this way, the same parts can be used for the left and right imaging lenses 6 and 8.

  In this embodiment, the light source means (multi-beam light source) having a plurality of light emitting portions (light emitting points) may be used.

[Example 2]
FIG. 4 is a sub-scan sectional view of the main part of the second embodiment of the present invention. In the figure, the same elements as those shown in FIG.

  In this embodiment, the difference from the first embodiment is that the end face 62 of the outer peripheral portion of the holding frame of the imaging optical element that holds the first imaging lens 6 is formed in a tapered shape along the optical path 15. It is. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in this embodiment, the end face (inclined portion) 62 of the outer peripheral portion of the holding frame (not shown) of the imaging optical element that holds the first imaging lens 6 is formed in a tapered shape along the optical path 15. The height of the apparatus in the sub-scanning direction is reduced.

  In general, a resin lens molded by a mold employs a technique in which a taper is provided at the outer end of the lens that is parallel to the lens optical axis direction in order to reduce mold release deformation when the resin lens is removed from the mold.

  In this embodiment, the inclination direction of the draft taper is configured along the optical path 15 reflected by the first reflecting mirror 7.

  With this configuration, it is easy to avoid interference between the optical path 15 reflected by the first imaging lens 6 and the first reflection mirror 7, and the reflection angle θ reflected by the first reflection mirror 7 is further reduced. This is effective in reducing the height of the apparatus in the sub-scanning direction.

[Example 3]
FIG. 5 is a main scanning sectional view of the main part of Embodiment 3 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 a reference surface 63 for positioning in the main scanning section is provided outside the effective area of the lens surface (optical surface) of the first imaging lens 6. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in this embodiment, the reference surface 63 for positioning in the main scanning section is provided outside the effective area of the lens surface of the first imaging lens 6, and the receiving portion 12 as a position reference is provided on the reference surface 63.

  As can be seen from FIG. 5, the receiving portion 12 is provided outside the effective portion of the first imaging lens 6 in the main scanning direction. The receiving portion 12 is provided on a frame (not shown) and serves as a position reference for the first imaging lens 6 in the main scanning direction.

  Conventionally, the position reference in the main scanning direction is generally provided above and below the central portion in the scanning direction of the first imaging lens 6 in FIG. If it is provided above and below the part, it will interfere with the optical path 15 reflected by the first reflecting mirror 7.

  Therefore, in the present embodiment, the above-described conventional problem is solved by providing the reference surface 63 for positioning in the main scanning section outside the effective range of the lens surface of the first imaging lens 6.

[Example 4]
FIG. 6 is a main scanning sectional view of the main part of Embodiment 4 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 a reference pin 64 for positioning in the main scanning section is provided outside the effective area of the lens surface of the first imaging lens 6. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in this embodiment, the reference pin 64 as a position reference for positioning in the main scanning section is provided outside the effective area of the lens surface of the first imaging lens 6.

  The reference pin 64 is configured to be fitted into a reference hole of a frame body (not shown). As can be seen from FIG. 6, the reference pin 64 is provided outside the effective portion of the first imaging lens 6 in the main scanning direction, and serves as a position reference for the first imaging lens 6 in the main scanning direction.

  Conventionally, the position reference in the main scanning direction is generally provided above and below the central portion in the scanning direction of the first imaging lens 6 in FIG. If it is provided above and below the part, it will interfere with the optical path 15 reflected by the first reflecting mirror 7.

  Therefore, in this embodiment, the above-described conventional problem is solved by providing the reference pin 64 for positioning in the main scanning section outside the effective range of the lens surface of the first imaging lens 6.

[Example 5]
FIG. 7 is a main scanning sectional view of the main part of Embodiment 5 of the present invention. In the figure, the same elements as those shown in FIG.

  The present embodiment is different from the above-described first embodiment in that a reference protrusion 65 that determines a reference position in the main scanning section is provided on the incident surface side of the first imaging lens 6. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in this embodiment, the reference projection 65 that determines the reference position in the main scanning section is provided on the incident surface side of the first imaging lens 6.

  The reference protrusion 65 is configured to fit into a reference hole or a reference pin of a frame (not shown). As can be seen from FIG. 7, the reference protrusion 65 is provided on the incident surface side of the first imaging lens 6.

  Conventionally, the position reference in the main scanning direction is generally provided above and below the central portion in the scanning direction of the first imaging lens 6 in FIG. If it is provided above and below the part, it will interfere with the optical path 15 reflected by the first reflecting mirror 7. Further, even if the reference projection 65 is provided on the exit surface side, it easily interferes with the reflected optical path 15.

  Therefore, in this embodiment, the above-described conventional problem is solved by providing the reference projection 65 for determining the reference position in the main scanning section on the incident surface side of the first imaging lens 6.

[Example 6]
FIG. 8 is a sub-scan sectional view of the main part of Embodiment 6 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 a concave reference portion 66 that determines the reference position in the main scanning section is provided on the outer periphery of the first imaging lens 6. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in this embodiment, a concave reference portion 66 that determines the reference position in the main scanning section is provided on the outer periphery of the first imaging lens 6.

  The reference hole 66 is configured to engage with the reference pin 13 of the frame.

  Conventionally, the position reference in the main scanning direction is generally provided above and below the central portion in the scanning direction of the first imaging lens 6 in FIG. If it is provided above and below the part, it will interfere with the optical path 15 reflected by the first reflecting mirror 7.

  Therefore, in this embodiment, the above-described conventional problem is solved by providing a concave reference portion 66 for determining the reference position in the main scanning section on the outer peripheral portion of the first imaging lens 6.

[Example 7]
FIG. 9 is a sub-scan sectional view of the main part of Embodiment 7 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 the second imaging lens 8 having the shortest distance between the optical path 15 reflected by the first reflecting mirror 7 and the outer peripheral portion of the holding frame of the imaging optical element. (Also referred to as imaging optical element B) is provided between the first imaging lens 6 and the first reflection mirror 7.

  Further, in the sub-scan section, the optical axis 82 of the second imaging lens 8 and the outer shape center line 81 of the holding frame of the imaging optical element are configured to be inconsistent.

  Further, the configuration is such that the outer shape center line 81 of the holding frame of the imaging optical element is reflected and positioned opposite to the optical path 15 with respect to the center line (principal ray) of the light beam incident on the second imaging lens 8. is there.

  Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in the present embodiment, the second imaging lens 8 having the shortest distance between the optical path 15 reflected by the first reflecting mirror 7 and the outer periphery of the holding frame of the imaging optical element is referred to as the first imaging lens 6. It is provided in the optical path between the first reflection mirror 7. The second imaging lens 8 is a lens having power in the sub-scanning direction and optically closest to the scanned surface 11.

  Furthermore, in this embodiment, the optical axis 82 of the second imaging lens 8 and the outer shape center line 81 of the holding frame of the imaging optical element are configured to be inconsistent in the sub-scan section. Further, in the present embodiment, the outer center line 81 of the holding frame of the imaging optical element is reflected and positioned opposite to the optical path 15 with respect to the principal ray of the light beam incident on the second imaging lens 8. Yes.

  Next, Tables 4, 5, and 6 show the specifications of the optical scanning device according to Example 7 of the present invention.

Polygon mirror circumscribed circle = φ40
Number of polygon mirror deflection surfaces = Angle between the optical axes of the 6-plane incidence optical system and the imaging optical system = 70 °
For polygon center (0,0), reflection point on polygon of image center beam = (15.05,8.71)
Distance between polygon center and first reflection mirror = 152
Incident angle between the normal of the first reflecting mirror and the incident light flux = 7.1 °

  The expression in this embodiment is the same as the expression in the first embodiment. In addition, the definition of the parameter of each element in the table is the same as in the first embodiment.

  Next, the optical action of the imaging optical system LB composed of the first and second imaging lenses 6 and 8 in this embodiment will be described.

  In this embodiment, the first and second imaging lenses 6 and 8 are made of resin (plastic).

  The imaging optical system LB forms an image of the light beam deflected and scanned by the optical deflector 5 on the scanned surface 11 to form a beam spot, and scans the scanned surface 11 at a constant speed. The resin-made imaging lens is manufactured by a known molding technique in which a mold is filled with a resin and is taken out of the mold after cooling. Thereby, it can manufacture easily from the conventional imaging lens which uses a glass lens.

  As shown in Table 2 above, the first imaging lens 6 mainly having power in the main scanning direction has an aspherical shape whose lens surface shape is expressed by a function of the given equation.

  The first imaging lens 6 has a meniscus-shaped lens (meniscus lens) whose power in the main scanning direction is larger than that in the sub-scanning direction, the main scanning section is non-circular, and the concave surface is directed to the optical deflector 5 side. ).

  The shape of the first imaging lens 6 in the main scanning section is symmetric with respect to the optical axis. Further, although the entrance surface and the exit surface have non-power with the same curvature with respect to the sub-scanning direction, for example, a cylinder shape in which both surfaces are flat in the sub-scanning direction may be used. It is mainly responsible for image formation in the main scanning direction with respect to the incident light beam.

  One second imaging lens 8 is an anamorphic lens having power mainly in the sub-scanning direction as shown in Table 2. The lens surface shape is an aspherical shape expressed by a function of the given equation.

  In the second imaging lens 8, the power in the sub-scanning direction is larger than the power in the main scanning direction, the incident surface of the main scanning section is an arc, and the other surface is a non-arc shape. The shape in the main scanning section is symmetric with respect to the optical axis, and the main scanning direction on the axis is non-power. The shape of the sub-scanning cross section is a flat surface with a very gentle curvature of the entrance surface, and a convex shape in which the exit surface gradually changes in curvature from on-axis to off-axis, and is symmetrical with respect to the optical axis. It is mainly responsible for image formation in the sub-scanning direction and correction of slight distortion in the main scanning direction for the incident light flux.

  The imaging relationship in the sub-scanning direction by the imaging optical system LB including the first and second imaging lenses 6 and 8 is a so-called surface tilt correction system in which the deflection surface 51 and the surface to be scanned 7 are conjugated. It has become.

  The imaging optical system LB is not necessarily a function expression as shown in Table 2, and may be a known expression. In order to further improve the imaging performance, the shape may be asymmetric with respect to the optical axis.

  In this embodiment, as shown in FIG. 9, the scanning light beam 14 deflected and scanned by the deflection surface 51 passes through the first imaging lens 6 and the second imaging lens 8 and is then reflected by the first reflecting mirror 7. .

  In FIG. 9, reference numeral 81 denotes an outer shape center line of a holding frame (not shown) of the imaging optical element, and 82 denotes an optical axis of the imaging optical system LB.

  In the present embodiment, as described above, the second imaging lens 8 has the outer center of the holding frame of the imaging optical element with respect to the principal ray of the light beam incident on the second imaging lens 8 in the sub-scan section. The line 81 is arranged so as to be reflected and located on the opposite side of the optical path 15.

  In other words, in this embodiment, the second imaging lens 8 is shifted by a distance (shift amount) dZ in the direction perpendicular to the scanning light beam 14 to avoid interference between the reflected optical path 15 and the second imaging lens 8. doing. By avoiding this interference, the reflection angle θ at the first reflecting mirror 7 can be reduced, which contributes to a reduction in the height of the apparatus in the sub-scanning direction.

  As shown in Table 2, the curvature radius r of the second imaging lens 8 in the sub-scanning direction is 1000, and the optical axis 82 connecting the vertices does not coincide with the outer shape center line 81.

In this embodiment, as shown in Table 2, the angle θ formed between the normal line of the first reflecting mirror 7 and the principal ray of the scanning light beam 14 is
θ = 7.1 °
It is. This satisfies conditional expression (3) and further conditional expression (4).

In this embodiment, the height H of the outer shape of the holding frame of the imaging optical element that holds the second imaging lens 8 and the distance dZ from the outer shape center line 81 to the principal ray of the incident light beam (scanning light beam) 14 are ,
H = 12.0
dZ = 1.7
Therefore,
dZ / H = 0.142
It is. This satisfies conditional expression (5) and further conditional expression (6).

  In this embodiment, as can be seen from FIG. 9, the height in the sub-scanning direction of the apparatus can be reduced by reducing the angle θ. In order to avoid interference between the reflected light path 15 and the second imaging lens 8 at this time, the second imaging lens 8 may be shifted in a direction perpendicular to the scanning light beam 14. As the shift amount dZ is increased, the height reduction effect increases. However, the maximum shiftable amount is ½ of the lens height H, which determines the upper limit of the conditional expression (5).

  Further, in a resin lens molded by a mold, if the height of the lens is lowered with respect to the thickness in the optical axis direction of the lens, cooling proceeds from the vertical direction of the lens at the time of cooling immediately after taking out from the mold. As a result, the refractive index distribution and the birefringence distribution inside the lens are likely to occur within the sub-scan section (in the lens height direction). It is known that this effect becomes more significant as the distance from the central axis of the lens outer shape increases, and that the deterioration rapidly starts from about 2/3 from the outer shape center toward the outer edge. Therefore, if importance is attached to the imaging performance of the apparatus, it is important to set dZ / H <0.3.

  This is defined by the upper limit of conditional expression (6). The lower limits of conditional expressions (5) and (6) define the lower limit of the shift amount of the second imaging lens 8. If the shift amount is small, the interference between the reflected optical path 15 and the second imaging lens 8 is insufficiently prevented, and the position of the reflected optical path 15 and the position of the second imaging lens 8 are affected by tolerances during assembly. Interference occurs when it swings.

  In the present embodiment, the second imaging lens 8 having power in the sub-scanning direction is configured by decentering the outline center line 81 and the optical axis 82 by a distance dZ, and the principal ray of the scanning light beam 14 and the optical axis 82 are coincident with each other. It is arranged. As a result, while the reflected light path 15 and the second imaging lens 8 are prevented from interfering with each other, the principal ray of the scanning light beam 14 and the optical axis 82 coincide with each other, so that the aberration is deteriorated and the scanning line is curved. It is suppressed.

  The inventions of the second to sixth embodiments described above may be incorporated in the second imaging lens 8 of the present embodiment.

[Image forming apparatus]
FIG. 10 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 (optical scanning device) 100 having the configuration shown in any of the first to seventh 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 a paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 10), 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. 10). The fixing device includes a fixing roller 113 having a fixing heater (not shown) therein and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113. Then, the sheet 112 conveyed from the transfer unit is heated while being pressed by the pressure contact portion between the fixing roller 113 and the pressure roller 114 to fix the unfixed toner image on the sheet 112. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and the fixed paper 112 is discharged out of the image forming apparatus.

  Although not shown in FIG. 10, 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 seventh embodiments of the present invention are more effective in an image forming apparatus of 1200 dpi or more.

[Color image forming apparatus]
FIG. 11 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 (scanning optical devices) are arranged in parallel and image information is recorded on a photosensitive drum surface as an image carrier in parallel. In FIG. 11, 60 is a color image forming apparatus, 61, 62, 63, and 64 are optical scanning apparatuses having any of the configurations shown in the first to seventh embodiments, and 71, 72, 73, and 74 are image carriers. The photosensitive drums 31, 32, 33 and 34 are developing units, and 51 is a conveyor belt. In FIG. 11, there are a transfer device (not shown) for transferring the toner image developed by the developing device to the transfer material, and a fixing device (not shown) for fixing the transferred toner image to the transfer material. doing.

  In FIG. 11, 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 61, 62, 63 and 64, 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 71, 72, 73, and 74 are emitted by these light beams. Scanned in the main scanning direction.

  The color image forming apparatus in this embodiment has four optical scanning devices (61, 62, 63, 64) arranged in each color of C (cyan), M (magenta), Y (yellow), and B (black). It corresponds. In parallel, image signals (image information) are recorded on the surfaces of the photosensitive drums 71, 72, 73, and 74, and color images are 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 61, 62, 63, 64, and the corresponding photosensitive drums 71, 72 corresponding to the latent images of the respective colors. , 73, 74 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.

1 Light source means 2 Condensing lens (collimator lens)
3 Aperture 4 Cylindrical lens 5 Deflection means LA Incident optical system LB Imaging optical system 6 First imaging lens 8 Second imaging lens 7 First reflection mirror 9 Second mirror 10 Cover glass 11 Scanned surfaces 61 and 81 Center of outline Line 15 Reflected light path 61, 62, 63, 64 Optical scanning device 21, 22, 23, 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 51 Conveying belt 52 External device 53 Printer controller 60 Color image forming apparatus 100 Optical scanning apparatus 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

Claims (10)

An optical scanning device comprising: an optical deflector that deflects and scans a light beam emitted from a light source means; and an imaging optical system that forms an image on the scanned surface by the light beam deflected and scanned by the deflection surface of the optical deflector. There,
The light beam incident on the deflection surface of the optical deflector is incident perpendicularly to the deflection surface in the sub-scan section,
The light beam incident on the deflection surface of the optical deflector is incident at an angle with respect to the optical axis of the imaging optical system in the main scanning section,
In the optical path between the optical deflector and the surface to be scanned, a transmissive imaging optical element and a reflective optical element constituting the imaging optical system are arranged in order from the optical deflector,
In the sub-scan section, when the angle formed by the principal ray of the light beam reflected by the reflective optical element and the normal line of the reflective optical element is θ,
θ ≦ 45 °
Is satisfied,
The transmissive imaging optical element is a resin lens,
In the sub-scan section, the transmission type imaging optical element has an outer center line of the transmission type imaging optical element so that it does not interfere with the optical path reflected by the reflection type optical element. Is disposed so as to be located on the opposite side of the optical path reflected by the reflective optical element with respect to the principal ray of the light beam incident on the light beam, and
In the sub-scan section, the height of the outer shape of the holding frame that holds the transmissive imaging optical element is H (mm), and the main light flux incident on the incident surface of the transmissive imaging optical element from the outer center line When the physical distance to the light beam is dZ (mm),
0.05 <dZ / H <0.3
An optical scanning device characterized by satisfying the following conditions. In the sub-scan section, when the angle formed by the principal ray of the light beam reflected by the reflective optical element and the normal line of the reflective optical element is θ,
θ ≦ 30 °
The optical scanning device according to claim 1, wherein the following condition is satisfied. When the power in the sub-scan section of the transmissive imaging optical element is φi, and the power in the sub-scan section of the imaging optical system is φall,
| Φi / φall | ≦ 0.01
The optical scanning device according to claim 1, wherein the following condition is satisfied. When the radius of curvature in the sub-scanning direction of the entrance surface of the transmissive imaging optical element is R1 (mm) and the radius of curvature of the exit surface of the transmissive imaging optical element in the sub-scanning direction is R2 (mm),
| 1 / R1 | + | 1 / R2 | <0.0061 (1 / mm)
The optical scanning device according to claim 1, wherein the following condition is satisfied.   5. The transmission imaging optical element according to claim 1, wherein the transmission imaging optical element has a reference protrusion for determining a reference position in a main scanning section on the incident surface side of the transmission imaging optical element. An optical scanning device according to claim 1.   In the sub-scanning section, the transmissive imaging optical element has a concave reference portion that determines a reference position in the main scanning section on the outer periphery in the sub-scanning direction of the transmissive imaging optical element. The optical scanning device according to claim 1, wherein:   In the sub-scanning section, the end face of the outer peripheral portion in the sub-scanning direction of the holding frame that holds the transmissive imaging optical element has a tapered shape along the optical path reflected by the reflective optical element. The optical scanning device according to any one of claims 1 to 6.   8. An optical scanning device, wherein two image forming optical systems according to claim 1 are arranged in the sub-scan section with the optical deflector interposed therebetween.   9. The optical scanning device according to claim 1, a photosensitive member disposed on the surface to be scanned, and a static image 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.   9. 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.