JPH11125778A - Multibeam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an entirely new multibeam scanner constituted so that the bend of a scanning line inevitably caused when an optical scanner is designed can be corrected at the stage of design. SOLUTION: The optical scanner is constituted so that an optical scanning action is executed by deflecting luminous flux emitted from a light source side by an optical deflector 6 and condensing it on a surf ace to be scanned as a light spot by a scanning image forming optical system 7. Then, the optical system 7 is provided with a correcting reflection surface correcting the bend of the scanning line. Besides, the correcting reflection surface is decided so that the bend of the scanning line being inherent in the optical scanner is corrected by the inherent inclination thereof within a sub-scanning cross section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-beam scanning device.

[0002]

2. Description of the Related Art One of the problems in the optical scanning device is a problem of "scanning line bending". The scanning line is a trajectory drawn by the light spot condensed on the surface to be scanned on the surface to be scanned. Ideally, the scanning line is a straight line. . For scanning line bending,
There are "error causes" such as a manufacturing error and an assembly error of the optical scanning optical system, and "design causes" in which scanning line bending is inevitable in designing the optical system. Scan line bending due to error causes can be achieved by increasing the manufacturing accuracy and assembling accuracy of optical elements, or by taking into account manufacturing and assembly tolerances. Optical scanning optical system ''
Can be dealt with by designing.

As an example of the scanning line bending due to a design reason, a "concave mirror having an image forming function" as a scanning image forming optical system is used.
May be used. If the beam deflected by the optical deflector is made incident on such a concave mirror to form an optical spot on the surface to be scanned, the incident beam of the deflected beam is used to prevent the reflected beam from the concave mirror from returning to the optical deflector. It is necessary to shift the optical axis of the concave mirror with respect to the direction or to tilt the concave mirror. When the concave mirror is provided in this manner, the trajectory of the deflection beam moving on the concave mirror is shifted from the “plane including the optical axis of the concave mirror”, so that the scanning line is inevitably bent on the surface to be scanned. As a method of coping with the scanning line bending due to such a design cause, a method of effectively reducing the scanning line bending by using an auxiliary optical element, and a method of relatively reducing an optical deflector, a concave mirror, and a surface to be scanned. There is a method of adjusting the positional relationship.

In the method using an auxiliary optical element, it is difficult to sufficiently correct the scanning line bending. As a method for correcting the scanning line bending by adjusting the positional relationship of the optical system, a method disclosed in Japanese Patent Application Laid-Open No. 1-306813 is known. However, in this method, since the reflection surface shape of the concave mirror having the imaging function is limited to a parabolic surface, other attributes required for optical scanning, such as constant speed of optical scanning and stability of light spot diameter, and scanning line. It is difficult to balance bending correction. Recently, with the aim of speeding up optical scanning, a plurality of beams from the light source side having a plurality of light emitting sources are deflected by a common optical deflector, and the plurality of deflected beams are placed on the surface to be scanned in the sub-scanning direction. It is intended to realize a multi-beam scanning apparatus that performs simultaneous scanning of a plurality of lines by condensing a plurality of light spots separated from each other. The scanning line bending due to the above-mentioned "design cause" occurs, of course, also in the multi-beam scanning apparatus.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to realize a multi-beam scanning device capable of effectively correcting a scanning line bending which is inevitable in designing a multi-beam scanning device.

[0006]

According to the multi-beam scanning apparatus of the present invention, a plurality of beams from a light source having a plurality of light-emitting sources are deflected by a common optical deflector, and the plurality of deflected beams are shared by a common scanning beam. A multi-beam scanning apparatus that performs simultaneous scanning of a plurality of lines by condensing a plurality of light spots separated from each other in the sub-scanning direction on the surface to be scanned by an image optical system, and is characterized by the following points ( Claim 1). That is, a scanning image forming optical system that condenses each of a plurality of deflected beams as a light spot on a surface to be scanned has a correction reflecting surface that corrects a bending of a scanning line. The “correction reflection surface” is determined in accordance with the incident position of the one deflection beam so that the unique inclination in the sub-scan section corrects the scan line bending of the at least one deflection beam unique to the multi-beam scanning device. Have been. The “scanning line bending unique to the multi-beam scanning device” means “designed scanning line bending of each deflection beam in a state where an optical design is performed assuming that the correction reflection surface does not have a function of correcting the scanning line bending”. This is "inevitable scanning line bending" due to the design of the multi-beam scanning device. The “sub-scanning cross section” refers to a plane cross section orthogonal to the main scanning corresponding direction (direction corresponding to the main scanning direction on the optical path from the light source to the surface to be scanned) near the correction reflection surface. The “intrinsic inclination” of the corrected reflecting surface refers to the inclination from the inclination of the reflecting surface (reference inclination for installation of the corrected reflecting surface) when the corrected reflecting surface does not have the scan line curve correction function.

[0007] The "scanning optical system" may have a lens system in addition to the optical element having the correction reflection surface. For example,
A rotating polygonal mirror is used as the optical deflector, and the beam from the light source is used, and its chief ray is “the surface orthogonal to the rotation axis of the rotating polygonal mirror”.
When it is incident on the deflecting reflective surface so as to be inclined, the deflecting beam is deflected so as to follow the conical surface, but when such a deflecting beam is condensed as a light spot on the surface to be scanned by a lens system, the scanning line bends. Occurs. Such a scanning line curve can be corrected to a straight line by the correction reflection surface.

The scanning image forming optical system may include an "image forming mirror having an image forming function". The imaging function condenses each of the plurality of deflection beams on the surface to be scanned in the main scanning direction, and in the sub-scanning direction (direction corresponding to the sub-scanning direction on the optical path from the light source to the surface to be scanned). The image forming function may be such that, in cooperation with another optical element (for example, a long toroidal lens) or the like, each deflected beam is focused on the surface to be scanned. The imaging function may be such that each of the deflected beams is condensed as a light spot on the surface to be scanned (claim 3).
In the multi-beam scanning device according to the second or third aspect, "the reflection surface itself of the imaging mirror included in the scanning imaging optical system can be used as the correction reflection surface". At this time, the imaging mirror mirror surface forming the correction reflection surface has a surface shape such that “the center of curvature in the sub-scanning cross section and the center line of curvature connected in the main scanning corresponding direction becomes a three-dimensional curve”. Item 4).
At this time, the image forming mirror "is an image forming function that condenses each deflected beam as a light spot on the surface to be scanned by itself."
, The image forming mirror itself constitutes a scanning image forming optical system.

The correction reflecting surface may have a "non-circular shape" in the sub-scan section, and the "center of curvature" in this case refers to a paraxial center of curvature. “Paraxial” in this case refers to a range near the center axis of the correction reflection surface in the sub-scanning cross section, where Gaussian optics is substantially established. “The curvature center line is a three-dimensional curve” means that the curvature center line is not in the same plane. The curvature center line can be “asymmetrical in the main scanning corresponding direction without having a plane of symmetry orthogonal to the main scanning corresponding direction”. That is, in this case, a plane orthogonal to the main scanning direction (a plane parallel to the sub-scanning section) is set at an arbitrary position, and this plane is used as a mirror surface, and a mirror image of a curvature center line on one side of the plane is imagined. Sometimes, this mirror image does not overlap the curvature center line on the other side of the plane, no matter where the plane is.

In the multi-beam scanning device according to any one of the first to fifth aspects of the present invention, the scanning image forming optical system has a function of making the optical scanning by each deflected beam deflected at a constant angular velocity uniform. Have "(claim 6). The multi-beam scanning apparatus according to the present invention also provides a method of separating a plurality of beams from a light source side into a long line image in a main scanning corresponding direction by separating the beams from each other in a sub-scanning corresponding direction near a deflection reflecting surface of a common optical deflector. It has a common line image forming optical system, and the scanning image forming optical system has a function of making the vicinity of the starting point of deflection by the optical deflector and the position of the scanned surface geometrically conjugate in the sub-scanning corresponding direction. Have "(claim 7). In this way, it is possible to correct "surface tilt" in the optical deflector.

As the "optical deflector" common to a plurality of beams in the multi-beam scanning apparatus of the present invention, a rotating polygon mirror, a rotating single mirror such as a pyramidal mirror or a tenon mirror, a rotating two-plane mirror, and a galvanometer mirror Can be used. Alternatively, a rotating single-sided mirror is disclosed in JP-A-6-751.
Japanese Patent Application Laid-Open Publication No. 62-62103 discloses that "a lens having an incident surface and an exit surface as refracting surfaces is provided on a deflecting / reflecting surface, and a beam incident from the incident surface is reflected by the deflecting / reflecting surface to exit from the exit surface. A rotating lens mirror having at least one of the exit surfaces in a shape capable of performing aberration correction and constant-velocity correction, and performing the aberration correction function and the constant-velocity correction function of the rotary lens mirror in a scanning imaging optical system. It can also be used for correcting speed and aberration.

[0012]

FIG. 1 is a diagram showing an embodiment of a multi-beam scanning apparatus according to the present invention. Light source 1 is “2
A semiconductor laser unit using a monolithic semiconductor laser array having two laser light emitting units in close proximity, and each laser light emitting unit emits an independent beam.
The two beams from the light source 1 are coupled to the subsequent optical system by the coupling lens 2. Each of the coupled beams becomes a “parallel beam or a weakly divergent or weakly converging beam”. After passing through the aperture of the aperture 3, the beam periphery is cut off and subjected to a desired “beam shaping”. The beam is converged in the sub-scanning direction by a cylindrical lens 5 having a positive power only in the sub-scanning direction, and the light beam is focused for each beam in the vicinity of the deflecting and reflecting surface of the rotary polygon mirror 6 which is an "optical deflector" common to the two beams. As a long line image in the main scanning corresponding direction ". These line images are separated from each other in the sub-scanning corresponding direction. Each reflected beam from the deflecting reflecting surface is incident on an image forming mirror 7 which is a "scanning image forming optical system" while being deflected at a constant angular velocity with the rotation of the rotary polygon mirror 6 at a constant speed in an arrow direction. Then, the light is condensed as a light spot on the peripheral surface of the photoconductive photoconductor 10 whose peripheral surface matches the “scanned surface”, and the scanned surface (substantially, the photoconductor 10) is optically scanned.

That is, the image forming mirror 7 has a function of "condensing each beam deflected by the optical deflector 6 as a light spot on the surface to be scanned independently" (claims 2 and 3). further,
The imaging mirror 7 has a function of equalizing the optical scanning by the two deflection beams deflected at a uniform angular velocity, respectively (claim 6), and the vicinity of the starting point of the deflection by the optical deflector 6 and the scanning. The position of the surface 10 is referred to as “in the sub-scanning corresponding direction,
(A function to make a geometrical conjugate relationship). Therefore, the multi-beam scanning device shown in FIG. 1 has a function of correcting “surface tilt” of the rotary polygon mirror 6.

The "X, Y, Z directions" shown in FIG. 1 are orthogonal to each other, the Y direction is the main scanning corresponding direction (main scanning direction on the surface to be scanned), and the Z direction is the sub scanning corresponding direction (on the scanning surface). In the sub scanning direction), and a plane parallel to the XZ plane is a “sub scanning section”. On the optical path from the light source 1 to the rotary polygon mirror 6, the “direction without power” of the cylindrical lens 5 is the main scanning corresponding direction, and the “direction in which power acts” of the cylindrical lens 5 is the sub-scanning corresponding direction. Note that the cylindrical lens 5 can be replaced with a concave cylindrical mirror.

That is, in the multi-beam scanning apparatus shown in FIG. 1, a plurality of beams from the light source 1 are deflected by a common optical deflector 6 and a scanning and imaging optical system 7 common to the plurality of deflected beams is used in the sub-scanning direction. This is a multi-beam scanning device that converges a plurality of light spots on the surface to be scanned 10 and simultaneously scans a plurality of lines. The multi-beam scanning device is also a device for deflecting a plurality of beams from the light source 1 side at a constant angular velocity by the optical deflector 6 to perform a constant-speed multi-beam scanning. Are separated from each other in the sub-scanning direction in the vicinity of the deflecting and reflecting surface of the rotary polygon mirror 6 to form a long line image in the main scanning direction, and are deflected by the rotary polygon mirror 6 to form a scanning image forming optical system. 7 is a multi-beam scanning apparatus that converges a plurality of light spots on the surface to be scanned in the sub-scanning direction as a plurality of light spots and simultaneously scans a plurality of lines.

In FIG. 1, two deflecting beams deflected by a rotary polygon mirror 6 as an optical deflector are called first and second deflecting beams. Reference numerals 29a and 29a denote the beams when these deflected beams are directed to the substantially central portion of the imaging mirror 7.
The beam which is indicated by a ′ and enters the periphery of the imaging mirror 7 is indicated by reference numerals 29b and 29b ′. Deflection beam 29
a and 29b are "first deflection beams", which are incident on the imaging mirror 7 at the incident positions 7a and 7b. The deflecting beams 29a 'and 29b' are "second deflecting beams" and enter the imaging mirror 7 at the incident positions 7a 'and 7b'. The first deflecting beams 29a and 29b become reflected beams 30a and 30b when reflected by the imaging mirror 7, and the positions 31a and 31 on the photosensitive member 10 which is the surface to be scanned.
An image is formed as a light spot on b. The position 31a is “the center position of the writing area by the first deflection beam optical scanning”, and the position 31b is “the writing start side end” of the writing area. Similarly, the second deflection beams 29a ', 29
b ′ is reflected beam 3 when reflected by the imaging mirror 7.
0a ′, 30b ′, and the position 31 on the photoconductor 10
Images are formed as light spots on a 'and 31b'. Position 31
a 'is the "center position of the writing area by the optical scanning of the second deflection beam", and position 31b' is the "writing start side end" of the writing area.

FIG. 2 (a) is an explanatory view showing the state after the rotary polygon mirror 6 in FIG. 1 in a "state viewed from the Y direction". In order to avoid complication, the deflection beams 29a, 29b
And only their reflected light. The imaging mirror 7 has a tilt angle (also referred to as an off-axis angle) such that the reflected beam reaches the surface to be scanned without being “eclipsed” by the rotating polygon mirror 6:
β is given in the XZ plane. In this embodiment,
The reflection surface of the imaging mirror 7 is a “correction reflection surface”.

FIG. 2B shows a case where an imaging mirror 7 ′ having no scanning line bending correction function is used instead of the imaging mirror 7. When the imaging mirror 7 'having no scanning line bending correction function is used, the positions 7a and 7b
2B are positions 7a1 and 7b1 in FIG.
As shown. In the imaging mirror 7 ', since the tilt angle β is “the same everywhere” in the Y direction (perpendicular to the drawing), the beam 30a1 reflected at the position 7a1 also
The beam 30b1 reflected by b 'also travels in "substantially the same direction as the sub-scanning corresponding direction". Therefore, when the beam reflected by the imaging mirror 7 ′ reaches the surface 10 to be scanned, the position of the light spot is shifted in the sub-scanning direction according to the position of reflection on the imaging mirror 7 ′, resulting in “scanning line bending”. Occurs.

As shown in FIG. 2A, the imaging mirror 7 is provided with a tilt angle β, and the imaging mirror 7 moves the “first” in the main scanning corresponding direction (Y direction in FIG. 1). The reflection surface at the “deflection beam incident position” has “intrinsic inclination: Δβ (Y)” in the sub-scanning cross section, and the inclination in the sub-scanning cross section is “β + Δβ ( Y) ". The intrinsic inclination: Δβ (Y) changes according to the Y coordinate and is determined so as to “correct at least the scan line bending of the first deflection beam”. That is, the reflection surface of the imaging mirror 7 is a “correction reflection surface”.

When the incident position of the first deflection beam on the imaging mirror 7 is represented by the Y coordinate, the inclination of the reflection surface of the imaging mirror 7 in the sub-scanning section (XZ plane): β + Δβ (Y) is As shown in FIG. 3, it changes continuously in accordance with the Y coordinate, and the change in the inclination allows "at least the bending of the scanning line of the first deflection beam can be corrected". In other words, the reflection surface of the imaging mirror 7 is referred to as a “correction reflection surface”, and the intrinsic tilt Δβ (Y) in the sub-scanning cross section at the incident position of the first deflection beam on the correction reflection surface is “multi-beam scanning”. Scan line bend specific to the device (Δβ (Y) ≡0
Of the first and second deflecting beams, which would occur if the imaging mirror 7 'is used, is designed to correct at least the first deflecting beam. , And is determined according to the incident position of the first deflection beam. "

As described above, in the embodiment shown in FIG. 1, the "inherent tilt in the sub-scan section:
Δβ (Y) ”is set so as to correct at least the scanning line bending generated in the first deflection beam.
And the second deflected beams are close to each other, and the incident positions 7a and 7a 'and 7b and 7b' to the imaging mirror 7 are close to each other. The bending effect is extremely effective for the second deflection beam, and the scanning line bending of the second deflection beam is also effectively corrected.

The shape of the reflecting surface of the imaging mirror 7 can be expressed as follows. In FIG. 4, a coordinate system: x,
y and z are “coordinate systems fixedly set on the imaging mirror 7”. Coordinate system: x, y, and z are referred to as a “specific coordinate system”. y
The coordinates are the coordinates in the “longitudinal direction” of the reflecting surface of the imaging mirror 7, and the z coordinates are the coordinates in the “width direction” of the reflecting surface.
The x coordinate is orthogonal to the y, z coordinates. When the coordinate system: x, y, z is used, the shape of the reflection surface of the imaging mirror 7 is determined by “x = f (y, z)” using f as a function symbol. Shape in this unique coordinate system: x = f (y, z)
Is converted into a coordinate system fixed in the device space of the multi-beam scanning device, and the reflection surface shape represented by the coordinate system: X, Y, Z set in the multi-beam scanning device is obtained.

Here, for the sake of simplicity, it is assumed that the y direction is parallel to the main scanning corresponding direction (Y direction in FIG. 1). Then, the “sub-scan section” is parallel to the xz plane. In FIG. 4, the z direction and the x direction do not match the Z and X directions in FIG.

The image forming mirror 7 has an image forming function of forming an image of the deflected beam as a light spot on the surface to be scanned, and further has a constant scanning speed (so-called "fθ characteristic") and a correction of field curvature. Has functions for Therefore, the reflection surface shape of the imaging mirror 7 is “Y in the multi-beam scanning device”.
The direction is defined as “a shape that satisfactorily corrects constant velocity characteristics and curvature of field in the main scanning direction”, and the radius of curvature of the reflecting surface in the sub-scanning section (the paraxial radius of curvature for a non-circular shape) ) Changes in the Y direction so as to “correct the field curvature in the sub-scanning direction satisfactorily”. In FIG. 4, the intrinsic inclination: Δβ (y) in the imaging mirror 7 is “0 everywhere”.
, The line connecting the centers of curvature of the reflecting surfaces in the sub-scanning cross section is, for example, a curve (in the xy plane) like a curve (broken line) 20a in FIG. In FIG. 4, when an intersection between the reflection surface of the imaging mirror 7 and the xy plane is considered in an arbitrary sub-scanning section, the intersection is referred to as the “paraxial portion in the sub-scanning section”. ".

According to the first aspect of the present invention, the inherent inclination in the sub-scan section of the device space of the multi-beam scanning device is Δβ.
(Y) is “to correct the scan line bending inherent in the multi-beam scanning device for at least the first deflection beam,
It is determined according to the incident position (of the first deflection beam) ", and the center line of curvature connecting the centers of curvature is a curve as shown by reference numeral 20 in FIG. As is clear from the figure, the curve 20 is not on the same plane but is a "three-dimensional curve" (claim 4). In FIG. 4, curve 20b corresponds to curve 2
This is a “projection” in which 0 is projected on a plane parallel to the zy plane.

The embodiment shown in FIG. 1 has a problem of so-called "sag". That is, since the rotating polygon mirror 6 is "the rotation axis is apart from the deflecting / reflecting surface", as the rotating polygon mirror 6 rotates, as shown in FIG. 5, a "line image" is formed by a beam from the light source side. A shift occurs between the position: P and the deflecting reflection surface 6A. This “shift” is called “sag”, and FIG.
Is indicated by “ΔX”. With such “sag: ΔX”, the imaging position: P ′ of the light spot in the sub-scanning corresponding direction is changed to the scanning surface 1 by the vertical magnification of the imaging of the imaging mirror 7.
5, the spot diameter of the light spot in the sub-scanning direction changes according to the image height, as shown in FIG. In order to avoid this, the change in the radius of curvature (determining the imaging power of the imaging mirror 7 in the sub-scanning direction) in the sub-scanning cross section of the imaging mirror 7 is determined in consideration of the influence of the "sag". do it. As shown in FIG. 6, “sag: ΔX” is α according to the rotation angle of the rotary polygon mirror: ± α.
= 30 degrees (at this time, the light spot is formed asymmetrically around the central position 30a, 30a '(see FIG. 1) of the writing area), so that the influence of such sag is corrected. When the radius of curvature in the sub-scan section is changed, the change in the radius of curvature is asymmetric in the y direction. As a result, as shown in FIG. 4, the curvature center line 20 becomes an asymmetric curve in the main scanning corresponding direction (y direction).

[0027]

EXAMPLES Specific examples will be described below. The example is an example of the embodiment described with reference to FIGS. Each of the two beams coupled by the coupling lens 2 becomes a “light beam having a weak converging property”.
The rotating polygon mirror 6 used as the "optical deflector" has a number of deflecting / reflecting surfaces: 6, an inscribed circle radius: 12 mm, and a first from the light source side.
The angle formed by the principal ray of the incident beam and the principal ray of the deflected beam when the light spot of this beam converges on the central part (position 31a in FIG. 1) of the optical writing area is 60 degrees. The writing width by the optical scanning is ± 109 mm centering on the “center of the optical writing area (reference numerals 31a and 31a ′ in FIG. 1)”.

Embodiment FIG. 11 shows the "optical arrangement" of the embodiment. As shown in the figure, the radius of curvature of the i-th surface (lens surface, aperture surface, deflecting reflection surface, reflection surface of the imaging mirror) counted from the light source side (paraxial radius of curvature in a non-circular shape). , _Rmi , _rsi (i = 1 to 7): unit:
mm ", the i-th surface and the i + 1 th surface and the" d _i the surface interval on the optical axis (i = 1 to 6): Unit: mm ", on the incident side lens surface of the coupling lens from the light source The distance on the optical axis to be reached is “d ₀ (i = 0: unit: mm)”, and the imaging mirror 7
Is the distance from the scanning surface 10 to “d ₇ (i = 7: unit:
mm) ". Also, the refractive index of the material of the j-th lens counted from the light source side with respect to the used wavelength is represented by N _j (j = 1,
2).

In FIG. 11, the Y direction is the main scanning direction, and the X ″ direction is “the optical path from the light source to the reflecting surface of the imaging mirror 7 is linearly extended along the optical axis of the coupling lens 2. Direction ". The Z ″ direction is a direction orthogonal to the X ″ direction and the Y direction, and is parallel to the rotation axis direction of the rotary polygon mirror 6.

As for the image forming mirror 7, the inherent coordinate system: x, y, z (see FIG. 4) is shown in FIG. The imaging mirror 7 has a scanning line bending correction function as a “correction reflection surface”, and for this purpose, an inherent inclination: Δβ (y) is given. When the scan line bending correction function is not provided (Δ (y) ≡
0) "as a reference state, and in this reference state, the tilt angle (off-axis angle) when the imaging mirror 7 is provided is set to" β "so that" scanning line bending for each beam is minimized ".
(Unit: degree) ", and the shift amount in the main scanning corresponding direction is" η (unit: mm) ". The scanning line bending remaining in this state is "scanning line bending unique to the multi-beam scanning device". As is clear from FIG. 11A, the “Y direction which is the main scanning corresponding direction” and the “y direction in the unique coordinate system” are parallel to each other, and the shift amount η is the unique coordinate of the imaging mirror 7. Y of xz plane and "X" Z "plane" in the system
Direction (also y direction), tilt angle: β
As shown in FIG. 11B, “eigen coordinate axes:
the angle formed by z and the coordinate axis: Z ''. The “radius of curvature” is a “value in the xy plane and the xz plane in the unique coordinate system” for the imaging mirror 7. The x direction is a direction orthogonal to the y and z directions, and is a direction inclined clockwise from the X ″ direction by an angle: β. The “sub-scan section on the correction reflection surface” is represented by the tilt angle as described above:
FIG. 11 shows a “plane parallel to the X ″ Z ″ plane” when β · shift amount: η is given. The “reflection surface shape” of the imaging mirror 7 is specified as follows. First,
Considering “a state where intrinsic inclination: Δβ (y) ≡0” in the inherent coordinate system, “a shape in the xy plane” in this state is
The “curvature in the xz plane (reciprocal of the radius of curvature)” of the reflecting surface is
Coordinates parallel to the main scanning corresponding direction: specified as a function of y,
Next, in this state, an inherent inclination: Δβ (y) is given.

The "optical arrangement" _{i r mi r si d i η} β j N j 0 12.9325 1 ∞ ∞ 3.0 1 1.7122 (C lens) 2 -10.2987 -10.2987 14.46 3 ∞ ∞ 24.60 ( aperture) 4 ∞ 29.5 3.0 2 1.5112 (CY lens) 5 ∞ ∞ 53.2 6 ∞ ∞ 111.0 (deflection reflection surface) 7 -360.0 -131.0 160.0 0.45 2.5 (imaging mirror) On the “imaging mirror”, “C lens” is a coupling lens, “CY”
"Lens" is a cylinder lens.

The "shape of the xy plane" of the image forming mirror 7, known formulas known in connection with non-spherical ^{shape: x = (y 2 / r} m) / [1 + √ {1- (1 + K) ^{_{(y / r m) 2}}} ]
+ Ay ⁴ + By ⁶ + Cy ⁸ + Dy ¹⁰ + Ey ¹² + Fy ¹⁴ + G
y ¹⁶ +. . In, r _m, K, specifying the shape giving A-G. The shape of the xy plane of the reflecting surface of the imaging mirror _{7: r m = -360, K} = -0.82982, A = 9.4
7965E-11, B = 1.70228E-13, C
= -7.81309E-18, D = -3.272682E
-22, E = -3.18515E-25, F = 2.5
0390E-29, G = 1.51822E-33
.

The shape of the reflecting surface of the imaging mirror 7 in the xz plane is obtained by calculating the curvature Csn (y) in the sub-scanning cross section at the coordinate y in the above-mentioned unique coordinate system by the formula Csn (y) = (1 / r _s ) + Σ
_{b n · y ** n (n} = 1,2,3, ..) expressed in, r _s and the coefficient: giving b _n specifying the shape. Note that y ** n represents y raised to the nth power. The curvature in the sub-scan section of the reflecting surface of the imaging mirror 7: Csn (y): r s = -131.0, b 1 = 7.81955E-09,
_{b 2 = -6.70610E-8, b} 3 = 2.45171
_{E-11, b 4 = -5.84477E} -13, b 5 = -
3.61511E-15, b ₆ = 1.29274E-
_{16, b 7 = 6.73126E-19} , b 8 = -3.2
_{6120E-20, b 9 = -5.04102E} -23,
b ₁₀ = 2.54690E-24
.

The expression of Csn (y) includes odd-order terms, and y = 0
Is asymmetric with respect to In the above, "E-8" and the like are "powers", for example, "E-8" represents 10 to ⁸ , and this numerical value is applied to the numerical value before it.

In this way, the shape and arrangement of the optical system are determined except for the “intrinsic tilt” of the image forming mirror. The optical arrangement at this time is the “reference state”. Here, light source 1
The light source 1 is a semiconductor laser unit having a monolithic semiconductor laser array as described above, but has two independent semiconductor light emitting sources,
These have an emission wavelength of 780 nm and are separated from each other by 15 μm. Each light-emitting unit is disposed so as to be shifted in the negative direction (downward in the figure) in the Z ″ direction in FIG. 11B with respect to the optical axis of the coupling lens 2, and the position of the first light-emitting unit is Z ′. '= -1
5 μm, the position of the second light emitting unit is Z ″ = − 30 μm. In the arrangement of the reference state, the light source 1
And the curvature of field (dashed line in the main scanning direction, solid line in the sub-scanning direction), scanning line bending, and constant velocity characteristics (calculated by the formula of fθ characteristics) when the optical system is provided. FIG. 8 shows a beam (first deflection beam), and FIG. 10 shows a beam (second deflection beam) from the second light emitting unit. Although the curvature of field and the constant velocity characteristics are good for each beam, the scanning line curve is remarkably generated at 1.064 mm at the maximum for each beam. The scan line bend shown in FIGS. 8 and 10 is “scan line bend inherent to the multi-beam scanning device regarding the first and second deflection beams”.

In this embodiment, the incident position of the first deflecting beam on the imaging mirror 7 is designed in order to correct the scanning line bending of the first deflecting beam, which is a beam from the first light emitting source. Was set as follows.

The intrinsic inclination of the imaging mirror 7 in the xz plane: Δβ (y) (unit: degree) Δβ (y) indicates that the inclination in the x-axis direction in the xz plane is “positive”. As described above, in FIG. 11, the sub-scanning section (the plane section orthogonal to the main scanning corresponding direction (Y direction) in the apparatus space of the multi-beam scanning apparatus) is a plane parallel to the X "Z" plane. This surface is parallel to the xz surface in the eigen coordinate system x, y, z fixed to the imaging mirror 7, and y = Y−η, that is, Y = Since there is a relationship of y + η, the above-mentioned inherent inclination is ΔΔ in the optical scanning device space.
β (Y) = Δβ (y + η).

As described above, the curvature of field, the curvature of the scanning line, and the fθ characteristic when the imaging mirror 7 is given an inherent inclination are given by the first characteristic.
FIG. 7 shows a beam (first deflection beam) from the light emitting section of FIG.
FIG. 9 shows a beam (second deflection beam) from the second light emitting unit. The field curvature / constant velocity characteristics are in the case of the “reference state” described above as the “comparative example” (FIGS. 8 and 1).
As good as 0), the scan line bow has been reduced to a maximum of 0.001 mm for both the first and second deflected beams.

That is, in the design of the imaging mirror, the inherent inclination is set so as to correct the scan line bending of the first deflection beam. However, the "incident position of the first and second deflection beams on the imaging mirror" Are close to each other ", the effect of the scanning line bending correction works extremely effectively not only on the first deflection beam but also on the second deflection beam, and the scanning of the first and second deflection beams is performed. Both the line bends were corrected very well.

In the above-described embodiment, the scanning line curve inherent to the optical scanning device is corrected by only one correction reflection surface. However, two or more correction reflection surfaces are provided in the scanning image forming optical system. May be provided, and the scanning line bending correction effect may be distributed to the plurality of correction reflection surfaces, so that the scanning line bending is corrected synthetically by the plurality of correction reflection surfaces. Also,
In the embodiment described above, the shape in the sub-scanning cross section of the imaging mirror 7 is set to “arc shape”. However, when the incident positions of the beams incident on the correction reflecting surface are separated from each other, By making the shape in the sub-scanning cross section “non-circular shape”, it is also possible to determine the inherent inclination at each beam incident position so as to correct the scan line bending of each beam. Alternatively, instead of correcting the scan line bend of a specific beam among the plurality of beams, the inherent inclination of the corrected reflection surface is adjusted so that the scan line bend of each of the plurality of beams is “averagely corrected”. Can also be set.

In the embodiment described above, as is clear from FIGS. 7 and 9, since the scanning line bending is well corrected for any of the two beams, the light emitting portion of the light source is used. Even if one of them is used as a single beam scanning device, very good optical scanning can be performed. Further, even if the "third light emitting portion" is added at the position of Z "= 0 in the above embodiment, and three lines are simultaneously scanned by three beams, any of the three scanning lines simultaneously scanned is none. Scanning line bending is corrected extremely well. The state of occurrence of sag in FIG. 6 depends on the optical arrangement in the above embodiment. Also, FIGS.
The "Y value" in the table represents not the coordinates in the main scanning direction but the value of the "maximum image height" of the light spot.

[0042]

As described above, according to the present invention, a novel multi-beam inspection device can be realized. The multi-beam scanning device of the present invention (claims 1 to 7) has a correction reflection surface for correcting a scan line curve, and can correct a scan line curve unique to the multi-beam scan device with the correction reflection surface. Very good multi-beam scanning can be realized by the “scanning line with good linearity”. Claims 2 and 3
If the scanning image forming optical system has an image forming mirror as in the invention according to the fourth aspect, the reflecting surface of the image forming mirror can be used as a correction reflecting surface as in the invention according to the fifth aspect. The reflecting surface can independently design the function of satisfactorily correcting the constant velocity characteristics such as the fθ characteristic and the curvature of field, and the function of correcting the scanning line curvature, so that while maintaining the constant velocity characteristics and the curvature of field satisfactorily, Scanning beam bending of the beam can be corrected well.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining one embodiment of an optical scanning device of the present invention.

FIG. 2 is a diagram for explaining a scanning line bending correction function in the embodiment.

FIG. 3 is a diagram for explaining a specific inclination: Δβ (Y) in a sub-scanning cross section at an incident position of a deflected beam on a reflecting surface of an imaging mirror in the embodiment of FIG. 1;

FIG. 4 is a diagram showing that a three-dimensional curved line is used as a center line of curvature in the imaging mirror 7 of the embodiment shown in FIG. FIG. 7 is a diagram for explaining the characteristic coordinate system of FIG.

FIG. 5 is a diagram for explaining sag in the embodiment of FIG. 1;

FIG. 6 is a diagram showing a state of occurrence of sag in the embodiment of FIG.

FIG. 7 is a diagram showing the field curvature, scanning line curve, and fθ characteristics of the beam from the first light emitting unit in the example.

FIG. 8 is a diagram showing the field curvature, scanning line curve, and fθ characteristics for the comparative example of FIG. 7;

FIG. 9 is a diagram showing the field curvature, scanning line curve, and fθ characteristics of the beam from the second light emitting unit in the example.

FIG. 10 is a diagram showing the field curvature, scanning line curve, and fθ characteristics for the comparative example of FIG. 10;

FIG. 11 is a diagram for explaining an optical arrangement according to an example.

[Explanation of symbols]

Reference Signs List 1 semiconductor laser unit using semiconductor laser array as light source 2 coupling lens 3 beam shaping aperture 5 cylinder lens 6 rotating polygon mirror as optical deflector 7 imaging mirror 10 photoreceptor

Claims (7)

[Claims] A plurality of beams from a light source side having a plurality of light emitting sources are deflected by a common optical deflector, and the plurality of deflected beams are separated from each other in a sub-scanning direction by a common scanning image forming optical system. In a multi-beam scanning apparatus that simultaneously scans a plurality of lines by condensing light beams on a surface to be scanned as a light spot, a scanning imaging optical system that condenses each of a plurality of deflected beams as a light spot on the surface to be scanned Has a correction reflection surface for correcting the bending of the scanning line, and the correction reflection surface has a characteristic inclination in the sub-scanning cross section that corrects the scanning line bending of the multi-beam scanning device of at least one deflection beam. A multi-beam scanning device, wherein the multi-beam scanning device is determined according to the incident position of the one deflection beam. 2. The multi-beam scanning device according to claim 1, wherein the scanning image forming optical system includes an image forming mirror having an image forming function. 3. The multi-beam scanning apparatus according to claim 2, wherein the imaging mirror has an imaging function of condensing each of the plurality of deflection beams as a light spot on a surface to be scanned. Beam scanning device. 4. The multi-beam scanning device according to claim 2, wherein the reflecting surface of the imaging mirror is a correction reflecting surface, and a center of curvature in the sub-scanning section is connected to a main scanning corresponding direction. Is a three-dimensional curve. 5. The multi-beam scanning device according to claim 4, wherein the center line of curvature has no plane of symmetry orthogonal to the main scanning corresponding direction and is asymmetric in the main scanning corresponding direction. Scanning device. 6. A multi-beam scanning apparatus according to claim 1, wherein said multi-beam scanning apparatus has a function of equalizing the speed of light scanning by each deflection beam deflected at a uniform angular velocity. Scanning device. 7. A multi-beam scanning apparatus according to claim 1, wherein a plurality of beams from a light source side are separated from each other in a sub-scanning corresponding direction near a deflecting reflection surface of a common optical deflector. It has a common line image forming optical system that forms a long line image in the main scanning corresponding direction, and the scanning image forming optical system supports sub-scanning of the vicinity of the starting point of deflection by the optical deflector and the position of the surface to be scanned. A multi-beam scanning device having a function of establishing a geometrical conjugate relationship in a direction.