JP3717656B2 - Optical scanning device and scanning imaging lens - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an optical scanning device and a scanning imaging lens.And image forming apparatusAbout.
[0002]
[Prior art]
An optical scanning device that performs light scanning by deflecting a light beam from the light source side at a constant angular velocity by an optical deflector and condensing the deflected light beam as a light spot on a surface to be scanned is an image of a digital copying machine, various printers, etc. Widely known in connection with forming equipment.
Conventionally, such an optical scanning device generally has an optical arrangement in which the light beam from the light source side and the surface on which the deflected light beam is deflected and swept are on the same plane, and has the following problems. .
That is, first, “the floor area of the optical scanning device” is increased.
Second, a rotating polygon mirror is the most common optical deflector, but the rotational axis of the rotating polygon mirror is away from the deflection reflection surface, so the incident position of the light beam from the light source side on the deflection reflection surface is small. A so-called “sag” is generated in which the deflection reflection surface is displaced with the rotation of the deflection reflection surface, and the deflection starting point of the deflected light beam fluctuates. Since the “direction of the deflected light beam to be realized” and the “direction of the incident light beam from the light source side to the deflecting / reflecting surface” form an angle of about 60 degrees, for example, the sag is asymmetrical on both sides of the image height: 0 in the optical scanning region. In view of the influence of sag, it is necessary to asymmetrically correct curvature of field and “constant velocity characteristics such as fθ characteristics”, which makes it difficult to design a scanning imaging optical system.
[0003]
As an optical arrangement that can solve these problems at once, the light beam from the light source side is incident on the deflection reflection surface of the optical deflector from the direction obliquely intersecting the rotation axis of the deflection reflection surface, and is deflected at an equal angular velocity. An optical arrangement that condenses the deflected light beam as a light spot on the surface to be scanned and makes the light scanning symmetrical with respect to a plane including the incident direction from the light source side to the deflecting reflection surface and the rotation axis. Conceivable.
In this way, since the optical system part from the light source to the optical deflector and the optical system part after the optical deflector can be laid out vertically, the floor area of the optical scanning device can be reduced and the optical scanning device Compactness can be achieved. Even if sag is generated, it occurs symmetrically with an image height of 0, so that it is easy to correct constant velocity characteristics and field curvature.
[0004]
However, such an optical arrangement has the following problems.
That is, since the light beam from the light source side is incident on the deflection reflection surface of the optical deflector so as to cross the rotation axis of the deflection reflection surface obliquely, the deflection light beam is deflected so as to sweep the conical surface. The “position where the light beam is incident on the subsequent optical system” fluctuates in the sub-scanning corresponding direction (direction corresponding to the sub-scanning direction on the optical path from the light source to the scanned surface) with the deflection. For this reason, the locus of the light spot on the surface to be scanned is not a straight line, and so-called “scanning line bending” occurs.
[0005]
[Problems to be solved by the invention]
The present invention is an optical scanning device having an optical arrangement in which a light beam from the light source side is incident on a deflection reflection surface of an optical deflector from a direction obliquely intersecting with a rotation axis of the deflection reflection surface. It is an object of the present invention to realize favorable optical scanning by making the fluctuation of the spot diameter good and effectively reducing the scanning line bending.
[0006]
[Means for Solving the Problems]
The scanning imaging lens according to the present invention is such that the light beam from the light source side is incident on the deflecting reflecting surface from a direction obliquely intersecting with the rotation axis of the deflecting reflecting surface at an incident angle: θ, and the main scanning is performed in the vicinity of the deflecting reflecting surface. Form a line image that is long in the corresponding direction, deflect the reflected light beam from the deflecting reflecting surface symmetrically with respect to the plane formed by the principal ray of the incident light beam on the deflecting reflecting surface and the rotation axis, and This is a “scanning imaging lens used in an optical scanning device that is focused as a light spot on a surface to be scanned by a scanning imaging lens and performs optical scanning of the surface to be scanned”, and is composed of a single lens.
[0007]
The scanning imaging lens according to claim 1 has the following characteristics.
The center axis of the incident side lens surface is x₁The axis and the direction corresponding to the main scan are y₁X is the axis₁y₁The in-plane shape is a non-arc shape.
The center axis of the exit side lens surface is x₂The axis and the direction corresponding to the main scan are y₂X is the axis₂y₂The in-plane shape is a non-arc shape.
The incident side lens surface (deflecting / reflecting surface side lens surface) and / or the exit side lens surface (scanned surface side lens surface) are “WT surfaces”.
The “WT surface” is the following surface. For example, when the incident-side lens surface is a WT surface, the coordinates relating to this lens surface: x₁y₁Z is the coordinate axis orthogonal to₁X is the axis₁z₁Radius of curvature in a plane cross section parallel to the surface: r₁Is y₁Coordinate axis function: r₁(y₁) As a change.
x₁Axis and x₂The axes form a finite angle with each other in a plane including them. That is, these x₁, X₂The axes are in the same plane, but the directions are different from each other. x₁Axis and x₂Considering the limit where the angle formed by the axis is reduced, x₁Axis and x₂The axes coincide with each other and become the same straight line, but this straight line corresponds to an “optical axis” in a normal lens.
[0008]
For the following description, coordinate axes are set in the device space of the optical scanning device as follows.
That is, the rotation axis of the deflecting / reflecting surface is the Z-axis, the axis perpendicular to the Z-axis in the plane including the principal ray of the light beam incident on the deflecting / reflecting surface and the Z-axis is the X-axis, and the X-axis and Z-axis are The orthogonal axis is the Y axis. In this way, the principal ray of the light beam from the light source side is incident on the deflecting / reflecting surface in the XZ plane. The incident light beam has an incident angle of θ. , It means that it is inclined by an angle θ relative to a plane parallel to the XY plane. The “main scanning corresponding direction” refers to a direction corresponding to the main scanning direction on the optical path from the light source to the surface to be scanned. The Y-axis direction corresponds to the main scanning corresponding direction, and the light flux from the light source side is the Y-axis direction. The image is formed as a long line image. Further, the deflected light beam is deflected symmetrically with respect to the XZ plane.
[0009]
The scanning imaging lens according to claim 1 is arranged in the optical scanning device as follows.
As mentioned above, y₁Axis and y₂Since the axis "corresponds to the main scan", the scanning imaging lens has its y₁Axis and y₂The axis is made parallel to the Y axis. And the above x₁Axis and x₂A plane containing the axis is matched to the XZ plane.
Incident to the chief ray of the deflected light beam (angle: θ with respect to the XY plane) in the plane formed by the principal ray of the incident light beam on the deflecting reflecting surface and the rotation axis of the deflecting reflecting surface, that is, the XZ plane. Side lens surface is x₁Angle the axis: α₁Just tilted, and x₁The axis is displaced in a direction parallel to the rotation axis of the deflecting reflecting surface (Z-axis direction): Δ₁Is displaced only. The exit lens surface is x₂The angle of the axis with respect to the chief ray of the deflected light beam: α₂Just tilt, and x₂The axis is displaced in the Z direction: Δ₂Only displaced and deployed.
At this time, the angle: α₁, Α₂, Displacement amount: Δ₁, Δ₂Are used as correction parameters for scanning line bending, field curvature, and light spot diameter variation.
That is, the scanning imaging lens is designed so that the lens shape (lens surface shape, thickness) and lens material (refractive index) satisfy the conditions required for the scanning imaging lens.₁, Α₂, Δ₁, Δ₂Is also used as a correction parameter in the design.
[0010]
  As described above, in the scanning imaging lens according to claim 1, at least one of the incident-side lens surface and the exit-side lens surface is a WT surface. Of course, “both the incident-side and exit-side lens surfaces are WT surfaces. (Claim 2).
  The scanning imaging lens according to claim 1, wherein x ₁ Axis and x ₂ The focal length in the plane including the axis (in the XZ plane in the optical scanning device) is f _Z When, angle: α ₁ , Α ₂ However, for the incident angle: θ, the condition:
(1) 0.8 <| α ₁ /Θ|<2.5
(2) 0.8 <| α ₂ /Θ|<2.5
Is satisfied, displacement amount: Δ ₁ , Δ ₂ And focal length: f _Z But the condition:
(3) 1 × 10 ^-2 <| Δ ₁ / F _Z | <1 × 10 ^-1
(4) 1 × 10 ^-2 <| Δ ₂ / F _Z | <1 × 10 ^-1
Satisfied.
[0011]
Conditions (1) and (2) are conditions for effectively correcting scanning line bending and effectively suppressing fluctuations in the light spot diameter.
In the case of an optical scanning device of the type that “the light beam from the light source side is incident on the deflecting / reflecting surface from a direction obliquely intersecting with the rotation axis of the deflecting / reflecting surface at an incident angle: θ” Although the scan line is slightly bent, the incident angle: θ needs a predetermined amount in order to separate the incident light beam and the reflected light beam.
Angle: α₁, Α₂Should be proportional to θ, and its proportionality factor is the angle: α₁, Α₂The ranges of conditions (1) and (2) are good.
If the lower limits of the conditions (1) and (2) are exceeded, a sufficient scanning line bending correction effect cannot be realized.
When the upper limit of the conditions (1) and (2) is exceeded, coma aberration in the sub-scanning direction becomes excessive at the intermediate to peripheral image height of the light spot, the wavefront aberration is deteriorated, and compared with the image height at the center. Thus, the light spot diameter increases from the intermediate to the peripheral image height.
[0012]
When the scanning imaging lens is “tilted” in the range of the conditions (1) and (2), as described above, the scanning line bending is effectively corrected, but coma aberration occurs due to the inclination of the lens. . Conditions (3) and (4) are conditions for effectively correcting this coma.
If the lower limits of the conditions (3) and (4) are exceeded, the coma due to the tilt cannot be canceled, the wavefront aberration is deteriorated, and the fluctuation of the light spot diameter becomes large.
When the upper limit of the conditions (3) and (4) is exceeded, higher-order field curvature increases in the sub-scanning corresponding direction (the direction corresponding to the sub-scanning direction on the optical path from the light source to the scanned surface), and the light spot Since the image plane rapidly tilts toward the scanning imaging lens at the peripheral image height, the light spot diameter in the sub-scanning direction rapidly increases at the peripheral image height.
[0013]
  Claim 3The scanning imaging lens has the following characteristics.
  When the optical axis is the x-axis and the direction corresponding to the main scanning is the y-axis, both the incident-side lens surface and the exit-side lens surface have a non-arc shape in the xy plane.
  The incident side lens surface and / or the exit side lens surface is a WT surface.
  The x-axis is tilted by an angle: α with respect to the principal ray of the deflected light beam in the XZ plane, and the incident side lens surface is displaced in the Z-axis direction by an amount of displacement: Δ₁The exit lens surface is displaced in the x-axis direction in the z-axis direction: Δ₂, Respectively displaced and deployed, angle: α, displacement: Δ₁, Δ₂Are used as correction parameters for scanning line bending, field curvature, and light spot diameter variation.
    That is, the scanning imaging lens according to claim 4 is the same as the scanning imaging lens according to claim 1, wherein the axis x₁, X₂Match and become the optical axis (x-axis).
[0014]
  In the scanning imaging lens according to claim 3, when the focal length in the plane: XZ plane formed by the principal ray of the light beam incident on the deflection reflection surface and the rotation axis of the deflection reflection surface is fZ, the angle: α is For incident angle: θ, conditions:
(5) 0.8 <| α / θ | <2.5
Is satisfied, displacement amount: Δ ₁ , Δ ₂ And focal length: f _Z Is:
(6) 1 × 10 ^-2 <| Δ ₁ / F _Z | <1 × 10 ^-1
(7) 1 × 10 ^-2 <| Δ ₂ / F _Z | <1 × 10 ^-1
Satisfied.
[0015]
The condition (5) is a condition for effectively correcting the scanning line bending and effectively suppressing the fluctuation of the light spot diameter, as in the above conditions (1) and (2). If the upper limit is exceeded when the bending correction effect cannot be realized, the coma aberration in the sub-scanning direction becomes excessive at the intermediate to peripheral image height of the light spot, the wavefront aberration is degraded, and compared to the image height at the center. Thus, the light spot diameter increases from the intermediate to the peripheral image height.
The conditions (6) and (7) are conditions for effectively correcting the coma due to the tilt of the lens as in the conditions (3) and (4). The lower limits of the conditions (6) and (7) are If it exceeds, the coma aberration due to the tilt cannot be canceled, the wavefront aberration is deteriorated, and the fluctuation of the light spot diameter increases, and if the upper limit of the conditions (6) and (7) is exceeded, the higher order in the sub-scanning corresponding direction And the image surface rapidly falls to the scanning imaging lens side at the peripheral image height of the light spot, so that the light spot diameter in the sub-scanning direction rapidly increases at the peripheral image height.
[0016]
  Claims 1-3Any of the scanning imaging lenses according to any one of (1) may have a “function for equalizing the optical scanning of the surface to be scanned with a deflected light beam deflected at a constant angular velocity” (see FIG.Claim 4).
  Also,Claims 1-4Any of the scanning imaging lenses according to any one of the above-mentioned items collects the deflected light beam formed in the “long line image in the main scanning correspondence direction” in the vicinity of the deflection reflection surface as a light spot on the surface to be scanned. With respect to the sub-scanning corresponding direction, it has a function of having a conjugate relationship between the vicinity of the deflecting reflection surface position and the scanned surface position. The paraxial magnification in this conjugate relationship: m is a condition:
  (8) 2 <| m | <6
It is preferable to satisfy (Claim 5).
  That is, when the lower limit is exceeded, the arrangement of the scanning imaging lens approaches the surface to be scanned, so the scanning imaging lens becomes longer in the Y direction, making it difficult to process and increasing costs.
  On the other hand, if the upper limit is exceeded, the error in the X-axis direction on the deflecting / reflecting surface is “m”.²Since it is propagated to the surface to be scanned by “double”, high accuracy is required for the positional accuracy and surface accuracy of the deflecting / reflecting surface, which causes an increase in cost.
[0017]
  The optical scanning device according to the present invention is described as follows: “Because the light beam from the light source side is incident on the deflection reflection surface from a direction obliquely intersecting with the rotation axis (Z axis) of the deflection reflection surface at an incident angle: θ, and in the vicinity of the deflection reflection surface And forming a line image that is long in the direction corresponding to the main scanning (Y-axis direction), and the reflected light beam from the deflection reflection surface is formed on the plane (XZ plane) formed by the principal ray of the incident light beam on the deflection reflection surface and the rotation axis. An optical scanning device that deflects light symmetrically and condenses a deflected light beam as a light spot on a surface to be scanned by a scanning imaging lens to perform optical scanning on the surface to be scanned.
  Claim 6The described optical scanning device has the following characteristics.
  That is, as a scanning imaging lens, the aboveClaim 1 or 2Using the scanning imaging lens described above, the material and shape and angle of the scanning imaging lens: α₁, Α₂, Displacement amount: Δ₁, Δ₂With this adjustment, the curvature of field, the curve of the scanning line, and the variation of the light spot diameter are suppressed within allowable ranges.
  Claim 7This optical scanning device has the following characteristics.
  That is, as a scanning imaging lens, the aboveClaim 3Using the described scanning imaging lens, the material and shape of the scanning imaging lens, the angle: α, and the displacement: Δ₁, Δ₂With this adjustment, the curvature of field, the curve of the scanning line, and the variation of the light spot diameter are suppressed within allowable ranges.
  theseClaim 6 or 7In the described optical scanning device, the scanning imaging lens can have a “function for making the optical scanning of the surface to be scanned constant by the deflected light beam deflected at a constant angular velocity” (Claim 8), Paraxial magnification in the conjugate relationship in the sub-scanning corresponding direction: m is the condition:
  (8) 2 <| m | <6
Can be configured to satisfy (Claim 9).
  The image forming apparatus of the present inventionClaims 6-9The optical scanning device described in any one of (1) is used (Claim 10).
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram for explaining one embodiment of an optical scanning device according to the present invention. In FIG. 1A, reference numeral 10 is a semiconductor laser as a “light source”, reference numeral 15 is a coupling lens, reference numeral 20 is an aperture, reference numeral 25 is a cylindrical lens, reference numeral 30 is a rotating polygon mirror as an “optical deflector”, Reference numeral 31 denotes a deflection reflection surface, reference numeral 30AX denotes a rotation axis of the deflection reflection surface 31 (rotation axis of the rotary polygon mirror 30 itself), reference numeral 40 denotes a scanning imaging lens, and reference numeral 50 denotes a surface to be scanned (actually photoconductive. 1 shows the photosensitive surface of the photosensitive member.
[0019]
The light beam emitted from the semiconductor laser 10 is coupled to the subsequent optical system by the coupling lens 15. The coupled light beam can be a parallel light beam, a converging light beam, or a divergent light beam, depending on the optical characteristics of the subsequent optical system.
When the coupled light beam passes through the aperture 20, the peripheral light beam portion is removed and so-called “beam shaping” is performed. The beam-shaped light beam is focused in the direction corresponding to the sub-scanning by the cylindrical lens 25, and is formed as a long line image in the direction corresponding to the main scanning at the position of the deflection reflection surface 31. The reflected light beam from the deflecting reflecting surface 31 becomes a deflected light beam deflected at a constant angular velocity as the rotating polygon mirror 30 rotates at a constant speed, and a light spot is formed on the scanned surface 50 by the scanning imaging lens 40. Is optically scanned.
In FIG. 1A, the “Z axis” is set so as to coincide with the rotation axis 30AX of the rotary polygon mirror 30, and the X and Y directions are determined as shown in the figure. Then, the light beam (the principal ray) incident on the deflecting / reflecting surface 31 from the semiconductor laser 10 side and the rotation axis 30AX are in the same plane, that is, in the “XZ plane”. The Y direction becomes the “main scanning corresponding direction”.
[0020]
  FIG. 1B shows the state of FIG. 1A viewed from the Y direction, and the surface of FIG. 1B is an “XZ plane”. As shown in (b), the principal ray of the light beam from the semiconductor laser 10 side enters the deflecting / reflecting surface 31 with an incident angle: θ with respect to the rotation axis 30AZ of the deflecting / reflecting surface 31 in the XZ plane. . That is, the incident angle: θ is an angle formed by the principal ray of the incident light beam with respect to a plane (XY plane) orthogonal to the rotation axis 30AX. In FIG. 1B, the incident angle: θ is represented as θ (−), indicating that the incident light beam is incident from the “negative side” in the Z direction with respect to the plane orthogonal to the rotation axis 30AX. Yes.
  As is clear from FIG. 1A, the optical scanning of the surface to be scanned 50 is performed substantially symmetrically with respect to the XZ plane, that is, “symmetrical with respect to the XZ plane” as the rotary polygon mirror 30 rotates.
  That is, the optical scanning device according to the embodiment shown in FIG. 1 “deflects and reflects the light beam from the light source 10 side in a direction that obliquely intersects with the rotation axis (Z axis) of the deflecting reflection surface 31 at an incident angle: θ. The light beam is incident on the surface 31, and is formed into a line image in the vicinity of the deflection reflection surface in the main scanning correspondence direction (Y direction), and the reflected light beam from the deflection reflection surface 31 is combined with the principal ray of the incident light beam on the deflection reflection surface and the above-mentioned Light is deflected symmetrically with respect to the plane (XZ plane) formed by the rotation axis, and the deflected light beam is condensed as a light spot on the scanned surface 50 by the scanning imaging lens 40, and optical scanning of the scanned surface 50 is performed. Optical scanning device "Claims 6, 7), The scanning imaging lens 40 isClaim 1 or 2When the scanning imaging lens is the optical scanning device according to claim 6, the scanning imaging lens 40 isClaim 3When the scanning imaging lens is describedClaim 7The described optical scanning device is obtained.
[0021]
FIG. 2 is a view for explaining the shape of the scanning imaging lens according to claim 1 and the arrangement in the optical scanning device.
The lens 40A used as the scanning imaging lens 40 in the embodiment of FIG. 1 is configured by a single lens, and the center axis of the lens 40A on the incident side lens surface 41A is x.₁Axis, direction corresponding to main scanning (direction orthogonal to the drawing) is y₁X is the axis₁y₁The in-plane shape is a non-arc shape. The center axis of the exit side lens surface 41B is x.₂The axis and the direction corresponding to the main scan are y₂X is the axis₂y₂The in-plane shape is a non-arc shape.
The incident side lens surface 41A and / or the emission side lens surface 41B are WT surfaces, and x₁Axis and x₂The axes form a finite angle with each other in a plane including these (XZ plane in the drawing). With respect to the principal ray FL of the deflected light beam in the plane (XZ plane) formed by the principal ray of the incident light beam on the deflecting reflection surface and the rotation axis (Z axis) of the deflecting reflection surface, the incident side lens surface 41A has x₁Angle the axis: α₁Tilt only (-) and x₁Amount of displacement in the direction parallel to the rotation axis of the deflecting reflecting surface: Δ₁And the exit side lens surface 41B is x₂Angle the axis: α₂Tilt only (-) and x₂Amount of displacement in the direction parallel to the rotation axis of the deflecting reflecting surface: Δ₂Only displaced and deployed. These angles: α₁, Α₂, Displacement amount: Δ₁, Δ₂However, it is used as a correction parameter for scanning line bending, field curvature, and light spot diameter variation.
[0022]
  FIG.Claim 3It is a figure for demonstrating the shape of the description scanning imaging lens, and arrangement | positioning in an optical scanning device.
  The lens 40B used as the scanning imaging lens 40 in the embodiment of FIG. 1 is formed of a single lens, and the optical axis is the x axis and the direction corresponding to the main scanning (the direction orthogonal to the drawing) is the y axis. When the incident side lens surface 42A and the emission side lens surface 42B are both non-arc-shaped in the xy plane.
  The incident-side lens surface 42A and / or the exit-side lens surface 42B is a WT surface, and is within a plane (XZ plane) formed by the principal ray of the incident light beam on the deflection reflection surface and the deflection reflection surface rotation axis (Z axis). The x-axis is inclined by an angle α (−) with respect to the principal ray FL of the deflected light beam, and the incident-side lens surface 42A is displaced in a direction parallel to the rotation axis of the deflecting / reflecting surface: Δ₁Only, the exit side lens surface 42B has a displacement amount Δ₂Only deployed with each displaced. These angles: α, displacement: Δ₁, Δ₂Are used as correction parameters for scanning line bending, field curvature, and light spot diameter variation.
  In the description based on FIGS. 2 and 3, the angle: α₁, Α₂(−) Attached to indicates that the clockwise angle with respect to the principal ray FL is negative, and (+) attached to the angle θ indicates that the counterclockwise angle with respect to the X axis is positive. It means an individual to do. Incident angle: θ, tilt angle: α in the embodiment described above₁, Α₂, Displacement amount: Δ₁, Δ₂It should be noted that, of course, an optical arrangement in which the sign is reversed as a whole is also possible.
[0023]
【Example】
Hereinafter, three specific examples will be given.
[0024]
Each example is an example of the embodiment shown in FIG.
The semiconductor laser as the light source 10 has an emission wavelength of 780 nm. The coupling lens 15 has a focal length of 9 mm and NA = 0.3, the coupling action is a “collimating action”, and the coupled light beam becomes a “substantially parallel light beam”. The aperture 20 has a circular aperture with an aperture diameter of 3 mm, the cylindrical lens 25 is a “plano-convex lens” with a focal length of 60 mm in the sub-scanning corresponding direction, and the light flux from the light source side is near the surface to be scanned. The line image is substantially parallel in the main scanning direction, condensed in the sub-scanning direction, and has a long line image as a whole in the main scanning direction (Y direction).
In such an optical system layout, the allowable range of curvature of field is within ± 1 mm in both the main and sub scanning directions, the allowable range of bending of the scanning line is within 0.1 mm, and the variation of the light spot diameter is in both the main and sub scanning directions. The lens surface shape and tilt angle of the scanning imaging lens 40 are set to 3.5 μm or less so that the performance within the allowable range is realized.₁, Α₂, Displacement amount: Δ₁, Δ₂Was determined according to the incident angle: θ.
[0025]
In the following, description will be given on specifying the shape of the scanning imaging lens and the deployment position.
In the first embodiment, the scanning imaging lens according to the third aspect is used, and in the second and third embodiments, the one according to the fifth aspect is used.
In any of the first to third embodiments, the lens surface of the scanning imaging lens is a “WT surface”. The “non-arc shape” of each surface is a well-known formula:
x (y) = (y²/ R) / [1 + √ {1- (1 + K) (y / R)²}] A₀・ Y²+ A ・ y^Four+ B · y⁶+ C ・ y⁸+ D · y^Ten+. . .
, Paraxial radius of curvature: R and constants: K, A₀, A, B, C, D,. Specify and give. When the scanning imaging lens is as defined in claim 5, “x” in this equation is a coordinate matched with the optical axis, and “y” is a coordinate corresponding to the main scanning direction. Further, when the scanning imaging lens is the one described in claim 3, “x, y” is “x” for the incident side lens surface.₁, Y₁”And“ x for the exit side lens surface ”₂, Y₂Is used.
In addition, a WT surface which is a “special toric surface” is specified, and the Y function shape of the radius of curvature in a plane parallel to the XZ plane: r_i(y) is an even degree polynomial:
r_i(y) = a + b · y²+ C ・ y^Four+ D · y⁶+ E ・ y⁸+ F · y^Ten+ G · y¹²+. . Each coefficient in: a, b,. . . , G. . To identify. i is i = 1 for the entrance-side lens surface and i = 2 for the exit-side lens surface.
[0026]
  In each example, the refractive index of the material of the scanning imaging lens (with a wavelength of 780 nm)lightN780 ”in the XZ plane (in the xz plane, x₁z₁Surface or x₂z₂Lens thickness (scanning imaging lens)Claim 1 or 2Y₁Axis origin and y₂The distance from the axis origin) is d (0).
[0027]
Further, with respect to the principal ray of the deflected light beam in the XZ plane (straight line in FIG. 12: FL),₁The state in which the axes are aligned is referred to as the “reference state”, and in this reference state, the distance in the X-axis direction where the incident side lens surface is located is set to “S (0)”, and the exit side lens surface and the scanned surface The distance in the X-axis direction is “l (0)”. The unit of the quantity having the dimension of distance is “mm”.
[0028]
Example 1
S (0) = 45.5, d (0) = 13.2, l (0) = 172.2, n₇₈₀= 1.52441, θ (+) = 0.0806 rad
Incident side lens surface: WT surface
x₁y₁In-plane non-arc shape
R = 208.373, K = -6.077E + 1, A₀= -1.879E-4, A = -5.031E-7,
B = 1.261E-10, C = -4.089E-14, D = 2.987E-18
r₁(y₁)
a = -165.05, b = 5.579E-2, c = -2.019E-4, d = 5.043E-7,
e = -8.302E-10, f = 6.326E-13, g = -1.831E-16
Exit lens surface: WT surface
x₂y₂In-plane non-arc shape
R = -152.69, K = 0.9840, A₀= -4.044E-4, A = -7.295E-7,
B = 1.495E-10, C = -7.287E-140, D = 5.104E-18
r₂(y₂)
a = -19.833, b = -6.700E-4, c = 1.093E-6, d = 6.400E-10,
e = -3.381E-12, f = 3.126E-15, g = -9.374E-19
α₁= 0.122 rad α₂= 0.1145rad,
Δ₁= -2.429 mm, Δ₂=-1.927 mm.
[0029]
  Changes in spherical aberration (wavefront aberration) according to Example 1 due to image height are shown below.
    Image height Wavefront aberration (RMS)
    (mm) (λ = 780nm)
      0 0.0086
    35 0.0149
    58 0.0129
    82 0.0173
    93 0.0133
  105 0.0122
  Parameter values for conditions (1) to (4) and (8):
    ｜ α₁/Θ|=1.51
    ｜ α₂/Θ|=1.42
    | Δ₁/ F_Z| = 5.83E-2
    | Δ₂/ F_Z| = 4.62E-2
    | M | = 3.10
    (F_Z= 41.7)
  FIG. 4 is a graph of field curvature (solid line is the sub-scanning direction, broken line is the main scanning direction), scanning line bending, linearity, and fθ characteristics related to Example 1.Show. Scan line curveThe curvature of field, linearity, and fθ characteristics are corrected well as well as the burrs.
  In the above data notation, for example, “E-9” is “10^-9"Means. The same applies hereinafter.
[0030]
Example 2
S (0) = 45.5, d (0) = 13.0, l (0) = 176.8, n₇₈₀= 1.52441, θ (+) = 0.0806 rad
Incident side lens surface: WT surface
Non-arc shape in xy plane
R = 207.192, K = -6.044E + 1, A₀= -1.396E-4, A = -5.034E-7,
B = 1.258E-10, C = -4.098E-14, D = 2.917E-18
r₁(y₁)
a = -161.55, b = 5.924E-2, c = -2.016E-4, d = 3.759E-7,
e = -6.073E-10, f = 4.929E-13, g = -1.540E-16
Exit lens surface: WT surface
Non-arc shape in xy plane
R = -152.94, K = 0.9844, A₀= -3.655E-4, A = -7.305E-7,
B = 1.493E-10, C = -7.292E-14, D = 5.102E-18
r₂(y₂)
a = -19.862, b = -7.272E-4, c = 1.087E-6, d = 1.215E-9,
e = -4.674E-12, f = 5.502E-15, g = -1.690E-18
α = 0.1306 rad
Δ₁=-2.247 mm, Δ₂= -1.694 mm.
[0031]
  Changes in spherical aberration (wavefront aberration) according to Example 2 due to image height are shown below.
    Image height Wavefront aberration (RMS)
    (mm) (λ = 780nm)
      0 0.0144
    35 0.0153
    58 0.0141
    82 0.0154
    93 0.0121
  105 0.0129
  Parameter values for conditions (5) and (6) to (8):
    | Α / θ | = 1.62
    | Δ₁/ F_Z| = 5.36E-2
    | Δ₂/ F_Z| = 4.04E-2
    | M | = 3.19
    (F_Z= 41.9)
  FIG. 5 shows curvature of field (solid line in the sub-scanning direction, broken line in the main scanning direction), scanning line bending, linearity, and fθ characteristics for Example 2.The figure is shown. Scan line bendIn addition, the field curvature, linearity, and fθ characteristics are corrected well.
[0032]
Example 3
S (0) = 46.3, d (0) = 11.5, l (0) = 174.8, n₇₈₀= 1.52441, θ (+) = 0.0605 rad
Incident side lens surface: WT surface
Non-arc shape in xy plane
R = 205.770, K = -5.691E + 1, A₀= -3.317E-5, A = -5.027E-7,
B = 1.255E-10, C = -4.056E-14, D = 3.090E-18
r₁(y₁)
a = -168.84, b = 6.330E-2, c = -2.024E-4, d = 3.754E-7,
e = -4.920E-10, f = 3.226E-13, g = -8.142E-17
Exit lens surface: WT surface
Non-arc shape in xy plane
R = -154.17, K = 1.092, A₀= -1.841E-4, A = -7.253E-7
  B = 1.527E-10, C = -7.271E-14, D = 5.090E-18
r₂(y₂)
a = -19.761, b = -8.503E-4, c = 1.064E-6, d = 3.593E-9,
e = -2.381E-12, f = 2.117E-15, g = -5.788E-19
α = 0.985rad
Δ₁=-2.146 mm, Δ₂= -1.132 mm.
[0033]
  Changes in spherical aberration (wavefront aberration) according to Example 3 due to image height are shown below.
    Image height Wavefront aberration (RMS)
    (mm) (λ = 780nm)
      0 0.0197
    35 0.0195
    58 0.0210
    82 0.0198
    93 0.0205
  105 0.0175
  Parameter values for conditions (5) and (6) to (8):
    | Α / θ | = 1.63
    | Δ₁/ F_Z| = 5.16E-2
    | Δ₂/ F_Z| = 2.72E-2
    | M | = 3.18
    (F_Z= 41.6)
  FIG. 6 is a diagram of field curvature (solid line in the sub-scanning direction, broken line in the main scanning direction), scanning line bending, linearity, and fθ characteristics related to Example 3.Show. Scan line bendIn addition, the field curvature, linearity, and fθ characteristics are corrected well.
[0034]
  That is, in the first embodiment, as the optical scanning device, the light beam from the light source side is incident on the deflection reflection surface from a direction obliquely intersecting with the rotation axis of the deflection reflection surface at an incident angle: θ, and deflected and reflected. A line image that is long in the main scanning direction is formed near the surface, and the reflected light beam from the deflecting reflecting surface is deflected symmetrically with respect to the plane formed by the principal ray of the incident light beam on the deflecting reflecting surface and the rotation axis. In the optical scanning device that collects the deflected light beam as a light spot on the surface to be scanned by the scanning imaging lens and performs optical scanning of the surface to be scanned, as the scanning imaging lens,Claim 2The scanning imaging lens material, shape, and angle: α₁, Α₂, Displacement amount: Δ₁, Δ₂By adjusting this, the curvature of field, the curve of the scanning line, and the fluctuation of the light spot diameter are suppressed within the allowable range, respectively (Claim 6In the second and third embodiments, the light scanning device allows the light beam from the light source side to be incident on the deflection reflection surface from a direction obliquely intersecting with the rotation axis of the deflection reflection surface at an incident angle: θ. A line image that is long in the main scanning direction is formed near the reflecting surface, and the reflected light beam from the deflecting reflecting surface is symmetrical with respect to the plane formed by the principal ray of the incident light beam on the deflecting reflecting surface and the rotation axis. In an optical scanning device that deflects and deflects a deflected light beam as a light spot on a scanned surface by a scanning imaging lens and performs optical scanning of the scanned surface, as a scanning imaging lens,Claim 3Using the described scanning imaging lens, the material and shape of the scanning imaging lens, the angle: α, and the displacement: Δ₁, Δ₂With this adjustment, the curvature of field, the curve of the scanning line, and the fluctuation of the light spot diameter are suppressed within the allowable range, respectively (Claim 7).
  In each of the embodiments, the scanning imaging lens has a function of “constant speed of optical scanning of the surface to be scanned with a deflected light beam deflected at a constant angular velocity” (Claim 8), Paraxial magnification in a conjugate relationship in the sub-scanning corresponding direction: m satisfies the condition (8) (Claim 9).
[0035]
【The invention's effect】
  As described above, according to the present invention, a novel scanning imaging lens and an optical scanning device are provided.And image forming apparatusCan be realized.
  As described above, the scanning imaging lens of the present invention has an angle: α or α₁, Α₂And Δ₁, Δ₂Is used as a correction parameter for scanning line bending and field curvature, etc., and the scanning line bending of the oblique-incidence type optical scanning device is effectively corrected and fluctuations in field curvature and light spot diameter are effectively suppressed. Good optical scanning can be realized.
    In addition,Claim 1 or 2The described scanning imaging lens can be easily and inexpensively manufactured by plastic molding.
  Further, as described above, the optical scanning device of the present invention has an optical arrangement in which the light beam from the light source side is incident on the deflection reflection surface of the optical deflector from a direction obliquely intersecting the rotation axis of the deflection reflection surface. Since the floor area of the optical scanning device can be reduced and the generated sag is symmetrical on both sides of the image height 0 of the light spot, it can be said that the scanning imaging lens includes a special toric surface (WT surface). It can be realized as a relatively easy-to-manufacture lens that is optically symmetric in the scanning direction. By using this scanning imaging lens, it is possible to satisfactorily correct scanning line bending and image plane strength, and to reduce fluctuations in the light spot diameter. Thus, good optical scanning can be realized.
  Also,Claims 4 and 8In this invention, the scanning line bending is effectively corrected, the light spot shape is appropriately maintained, the field curvature and the light spot diameter can be corrected satisfactorily, and the constant speed of the optical scanning can be realized,Claims 5 and 9In this invention, the positional accuracy and surface accuracy of the deflecting / reflecting surface can be moderated without increasing the length of the scanning imaging lens.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining one embodiment of the present invention.
FIG. 2 is a diagram for explaining the shape of a scanning imaging lens according to claim 1 and the state of deployment to an optical scanning device;
[Fig. 3]Claim 3It is a figure for demonstrating the shape of this scanning imaging lens, and the deployment state to the optical scanning device.
4 is a diagram illustrating field curvature, scanning line bending, linearity, and fθ characteristics according to Example 1. FIG.
5 is a diagram illustrating field curvature, scanning line bending, linearity, and fθ characteristics according to Example 2. FIG.
6 is a diagram illustrating field curvature, scanning line bending, linearity, and fθ characteristics according to Example 3. FIG.
[Explanation of symbols]
  10 Semiconductor laser
  15 coupling lens
  25 Cylindrical lens
  30 rotating polygon mirror
  31 deflection reflective surface
  30AX Rotation axis of deflecting reflecting surface
  40 Scanning imaging lens
  50 surface to be scanned

Claims (10)

A light beam from the light source side is incident on the deflection reflection surface from a direction obliquely intersecting with the rotation axis of the deflection reflection surface at an incident angle: θ, and is formed into a line image in the vicinity of the deflection reflection surface in a main scanning corresponding direction. The reflected light beam from the deflecting reflecting surface is deflected symmetrically with respect to the plane formed by the principal ray of the incident light beam on the deflecting reflecting surface and the rotation axis, and the deflected light beam is covered by the scanning imaging lens. A scanning imaging lens for use in an optical scanning device that collects light as a light spot on a scanning surface and performs optical scanning of the scanned surface,
Composed of a single lens,
When the center side axis is the x ₁ axis and the direction corresponding to the main scanning is the y ₁ axis, the shape in the x ₁ y ₁ plane is a non-arc shape.
Per exit side lens surface, when the center axis x ₂ axis, a direction corresponding to the main scanning and y ₂ axes, the shape of the x ₂ y ₂ surfaces are non-arcuate shape,
The incident side lens surface and / or the exit side lens surface is a WT surface,
The x ₁ axis and the x ₂ axis form a finite angle with each other in a plane including them,
The incident side lens surface tilts the x ₁ axis by an angle α ₁ with respect to the chief ray of the deflected light beam in the plane formed by the principal ray of the incident light beam on the deflecting reflection surface and the rotation axis, and x _One axis is displaced in the direction parallel to the rotation axis of the deflecting reflecting surface by a displacement amount: Δ ₁
The injection-side lens surface angle of x ₂ Axis: alpha ₂ with only inclined, x ₂ axis displacement in a direction parallel to the rotational axis of the deflecting reflection surfaces: that is deployed displaced by delta _2,
When the focal length in a plane including the x ₁ axis and the x ₂ axis is f _Z ,
The angle: α ₁ , α ₂ is relative to the incident angle: θ:
(1) 0.8 <| α ₁ /θ|<2.5
(2) 0.8 <| α ₂ /θ|<2.5
The above-mentioned displacement amounts: Δ ₁ and Δ ₂ and the focal length: f _Z are the conditions:
(3) 1 × 10 ⁻² <| Δ ₁ / f _Z | <1 × 10 ⁻¹
(4) 1 × 10 ⁻² <| Δ ₂ / f _Z | <1 × 10 ⁻¹
Satisfied,
A scanning imaging lens characterized in that the angles: α ₁ , α ₂ and displacements: Δ ₁ , Δ ₂ are used as correction parameters for scanning line bending, field curvature, and light spot diameter fluctuation. The scanning imaging lens according to claim 1.
A scanning imaging lens, wherein both the incident-side and exit-side lens surfaces are WT surfaces. A light beam from the light source side is incident on the deflection reflection surface from a direction obliquely intersecting with the rotation axis of the deflection reflection surface at an incident angle: θ, and is formed into a line image in the vicinity of the deflection reflection surface in a main scanning corresponding direction. The reflected light beam from the deflecting reflecting surface is deflected symmetrically with respect to the plane formed by the principal ray of the incident light beam on the deflecting reflecting surface and the rotation axis, and the deflected light beam is covered by the scanning imaging lens. A scanning imaging lens for use in an optical scanning device that collects light as a light spot on a scanning surface and performs optical scanning of the scanned surface,
Composed of a single lens,
When the optical axis is the x-axis and the direction corresponding to the main scanning is the y-axis, the incident side lens surface and the exit side lens surface are both non-arc shapes in the xy plane,
The incident side lens surface and / or the exit side lens surface is a WT surface,
The x-axis is inclined by an angle α with respect to the chief ray of the deflected light beam in the plane formed by the principal ray of the incident light beam on the deflecting reflection surface and the rotation axis, and the incident side lens surface is x-axis. displacement in a direction parallel to the rotational axis of the deflecting reflective surface: only delta _1, the exit side lens surface displacement in the direction parallel to the axis of rotation of the deflecting reflective surface in the x-axis: only delta _2, are respectively displaced Deployed,
When the focal length in the plane formed by the principal ray of the incident light beam on the deflecting reflecting surface and the rotation axis is f _Z ,
The angle: α is relative to the incident angle: θ.
(5) 0.8 <| α / θ | <2.5
The above-mentioned displacement amounts: Δ ₁ and Δ ₂ and the focal length: f _Z are the conditions:
(6) 1 × 10 ⁻² <| Δ ₁ / f _Z | <1 × 10 ⁻¹
(7) 1 × 10 ⁻² <| Δ ₂ / f _Z | <1 × 10 ⁻¹
Satisfied,
A scanning imaging lens, wherein the angle: α and the displacements: Δ ₁ and Δ ₂ are used as correction parameters for scanning line bending, field curvature, and light spot diameter fluctuation. The scanning imaging lens according to any one of claims 1 to 3 ,
What is claimed is: 1. A scanning imaging lens having a function of equalizing the speed of optical scanning of a surface to be scanned by a deflected light beam deflected at a constant angular velocity. The scanning imaging lens according to any one of claims 1 to 4 ,
With respect to the sub-scanning corresponding direction, it has a function of having a conjugate relation between the vicinity of the deflecting reflection surface position and the scanned surface position, and the paraxial magnification m in the conjugate relation is the condition:
(8) 2 <| m | <6
A scanning imaging lens characterized by satisfying A light beam from the light source side is incident on the deflection reflection surface from a direction obliquely intersecting with the rotation axis of the deflection reflection surface at an incident angle: θ, and is formed into a line image in the vicinity of the deflection reflection surface in a main scanning corresponding direction. The reflected light beam from the deflecting reflecting surface is deflected symmetrically with respect to the plane formed by the principal ray of the incident light beam on the deflecting reflecting surface and the rotation axis, and the deflected light beam is Focused as a light spot on the surface to be scanned,
In the optical scanning device that performs optical scanning of the scanned surface,
The scanning imaging lens according to claim 1 or 2 is used as a scanning imaging lens, and an image is obtained by adjusting the material and shape of the scanning imaging lens and the angles: α ₁ , α ₂ and displacements: Δ ₁ , Δ _2. An optical scanning device characterized in that surface curvature, scanning line bending, and variation in light spot diameter are suppressed within allowable ranges. A light beam from the light source side is incident on the deflection reflection surface from a direction obliquely intersecting with the rotation axis of the deflection reflection surface at an incident angle: θ, and is formed into a line image in the vicinity of the deflection reflection surface in a main scanning corresponding direction. The reflected light beam from the deflecting reflecting surface is deflected symmetrically with respect to the plane formed by the principal ray of the incident light beam on the deflecting reflecting surface and the rotation axis, and the deflected light beam is In an optical scanning device that collects light as a light spot on a surface to be scanned and performs optical scanning of the surface to be scanned.
The scanning imaging lens according to claim 3 is used as the scanning imaging lens, and the field curvature and scanning line curve are adjusted by adjusting the material and shape of the scanning imaging lens and the angle: α and the displacements: Δ ₁ and Δ _2. An optical scanning device characterized in that the variation of the light spot diameter is suppressed within an allowable range. The optical scanning device according to claim 6 or 7 ,
An optical scanning device characterized in that the scanning imaging lens has a function of making the optical scanning of the surface to be scanned with a deflected light beam deflected at a constant angular velocity constant. The optical scanning device according to claim 6, 7 or 8 ,
The scanning imaging lens has a function of making the vicinity of the deflecting / reflecting surface position and the scanned surface position conjugate with respect to the sub-scanning corresponding direction, and the paraxial magnification in the conjugate relation: m is the condition:
(8) 2 <| m | <6
An optical scanning device characterized by satisfying An image forming apparatus that forms an image using the optical scanning device according to claim 1 .

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