JP2015203747A - Imaging optical system, image reading device, and manufacturing method for image reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an imaging optical system which easily provides good imaging performance even with a reduced number of free-form surfaces acting as off-axial reflection surfaces; an image reading device; and a manufacturing method for the image reading device.SOLUTION: An imaging optical system includes first and second free-form surfaces acting as off-axial reflection surfaces, and a reflective aperture for guiding light rays from the first free-form surface to the second free-form surface, the first and second free-form surfaces being formed on a single optical element, where the reflective aperture and the optical element are configured to allow for changing relative positions thereof.

Description

  The present invention relates to an imaging optical system, an image reading apparatus, and an image reading apparatus manufacturing method, and is particularly suitable for an image scanner or a digital copying machine that can read an original image (monochrome image, color image, etc.) using a line sensor. It is a thing.

  2. Description of the Related Art Conventionally, an image reading apparatus that reads image information (original image) on an original surface uses a line sensor in which a plurality of light receiving elements are arranged in the main scanning direction. In this method, a light beam from a document image is condensed on a line sensor (CCD) surface by an image reading optical system, and the relative position between the document image and the line sensor is displaced in the sub-scanning direction to read the document image. is there. In an image reading apparatus that reads a color image as a document image, one line sensor for red, green, and blue that reads each color of R (red), G (green), and B (blue) is sub-scanned one by one. They are arranged side by side.

  When the image reading optical system consists of a normal refractive lens system, axial chromatic aberration, lateral chromatic aberration, etc. occur, so the image is formed on the red and blue line sensors with respect to the reference green line sensor. The defocused or misaligned line image is generated. Then, when each color image is superimposed and reproduced, the image becomes conspicuous in color bleeding and color misalignment, and when high aperture and high resolution performance is required, the request cannot be met.

  On the other hand, recently, it has also been proposed to construct an optical system in which aberrations are sufficiently corrected by introducing the concept of a reference axis and making an asymmetric aspherical surface in a non-coaxial optical system. In particular, an imaging optical system using a free-form surface (free-form surface mirror) that is a small number of off-axial reflecting surfaces is known (Patent Document 1). Also, an imaging optical system having a configuration that is easy to assemble by reducing the number of parts and simplifying the optical system by combining and integrating discontinuous off-axial free-form surfaces is known (Patent Document 2). .

JP 2003-57549 A JP 2006-259544 A

  However, in the prior art disclosed in the above-mentioned patent document, there is a problem that when the number of free curved surfaces that are off-axial reflecting surfaces is reduced, the degree of freedom gradually decreases and the eccentricity sensitivity increases, resulting in assembly. The accuracy has become very strict.

  An object of the present invention is to provide an imaging optical system, an image reading apparatus, and a method for manufacturing the image reading apparatus that can easily obtain good imaging performance while reducing the number of free-form surfaces that are off-axial reflecting surfaces. There is to do.

  In order to achieve the above object, an imaging optical system according to the present invention includes first and second free-form surfaces that are off-axial reflecting surfaces, and a light beam from the first free-form surface. The first and second free-form surfaces are formed in a single optical element, and the reflection diaphragm and the optical element are relative to each other. The position is configured to be changeable.

  In addition, an image reading apparatus according to the present invention includes an illuminating unit that illuminates a document image, the imaging optical system, and a line sensor provided on an imaging surface of the imaging optical system in one housing. The housing is moved in the sub-scanning direction.

  According to another aspect of the invention, there is provided a method for manufacturing the image reading apparatus, wherein the first and second free-form surfaces, which are off-axial reflecting surfaces, are integrally formed as a single optical element; An imaging optical system comprising a second free-form surface and a reflection stop that guides the light beam from the first free-form surface to the second free-form surface, and a central ray of the light beam incident on the reflection stop; When a plane including the central ray of the light beam reflected by the reflection diaphragm is used as a projection surface, the light beam reflected from the first free-form surface and reflected from the second free-form surface is projected onto the projection surface. A second step of disposing the imaging optical system intersecting with the light beam, a third step of displacing the relative positional relationship between the optical element and the reflection stop, and a line sensor for the imaging optical system. Direction or direction of the light beam reflected from the second free-form surface And having a, a fourth step of displacing in a direction perpendicular to.

  According to the present invention, there are provided an imaging optical system, an image reading apparatus, and a method for manufacturing the image reading apparatus that can easily obtain good imaging performance while reducing the number of free-form surfaces that are off-axial reflecting surfaces. can do.

1 is a sub-scanning sectional view of an image reading apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a main part when an optical path of the image reading apparatus according to the embodiment of the present invention is developed. (A) thru | or (c) are explanatory drawings of unitization in the manufacturing process of the image reading apparatus which concerns on embodiment of this invention. 6 is an explanatory diagram of a displacement direction in the manufacturing process of the image reading apparatus according to the first embodiment. FIG. FIG. 6 is a flowchart illustrating a manufacturing process of the image reading apparatus according to the first embodiment. (A), (b) is a graph which shows the sensitivity corresponding to the relative displacement which concerns on 1st Embodiment. It is explanatory drawing of the displacement direction in the manufacturing process of the image reading apparatus which concerns on 2nd Embodiment. FIG. 10 is a flowchart illustrating a manufacturing process of an image reading apparatus according to a second embodiment. It is a graph which shows the sensitivity corresponding to the relative displacement which concerns on 2nd Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<< First Embodiment >>
(Image reading device)
In FIG. 1, L is a light source (illuminating means), which comprises a fluorescent lamp, a xenon lamp, an LED array illumination system, and the like. CG is a document surface glass, on which a document image (monochrome image or color image) Obj is placed in the main scanning section (XZ plane). M1, M2, M3, M4, M5, and M6 are reflecting mirrors that sequentially form first, second, third, fourth, fifth, and sixth optical path folding reflecting surfaces (planes). An infrared light (IR) cut filter 7 removes unnecessary infrared light.

  Reference numeral 8 denotes an off-axial optical system, which will be described in detail later, and forms an image reading optical system together with the reflecting mirrors M1 to M6, and the light beam from the original image Obj illuminated by the light source L is disposed at a position corresponding to the image plane. The light is condensed on a line sensor LS as a reading unit. A CCD, CMOS, or the like is used as the line sensor LS. When a color image is a target, line sensors corresponding to R, G, and B are arranged in parallel in the Y direction (a direction perpendicular to the main scanning direction (X direction) that is the longitudinal direction of the line sensor). .

  CRG is a movable carriage (housing), and each member L, M1, M2, M3, M4, M5, M6, 7, 8, LS, etc. is housed in the housing. YZ plane) is extended in the main scanning direction (X direction) with respect to FIG. Then, with respect to the document image Obj, the carriage CRG is displaced in the sub-scanning direction (arrow A direction) with respect to the document image Obj, and the document image Obj is read two-dimensionally.

(Imaging optics)
1) Reference Axis and Off-Axial Optical System In order to clarify the configuration of the imaging optical system that is the image reading optical system according to the present embodiment, the reference axis and the off-axial optical system used in this specification will be described below. Define as follows. First, regarding the reference axis, if there is an axis having symmetry even in the optical system, and aberrations can be collected with good symmetry, the light beam passing on the axis having symmetry is used as the reference beam. The optical path of the reference beam is taken as the reference axis.

  If the optical system generally does not have a symmetry axis or if aberrations cannot be collected with good symmetry even if there is a partial symmetry axis, the optical path of the reference beam is And That is, out of the light rays that come from the center of the object surface (the center of the read range), the light rays that pass through the optical system in the order of the specified surface of the optical system and pass through the aperture center (pupil center) defined in the optical system It is set as a light beam, and the optical path of the reference light beam is used as a reference axis. The reference axis defined in this way generally has a bent shape, and finally reaches the center of the image plane.

  Next, at the point where the reference axis defined in this way intersects the curved surface, a curved surface whose surface normal does not coincide with the reference axis is defined as an off-axial curved surface, and an optical system including this off-axial curved surface is defined as an off-axial optical system. To do. Even when the reference axis is simply bent by the plane reflecting surface, the surface normal does not coincide with the reference axis, but the plane reflecting surface does not impair the symmetry of the aberration and is excluded from the target of the off-axial optical system. .

2) Description along the optical path In the present embodiment, the original image (object) Obj placed on the original table glass CG is illuminated with a light beam emitted from the light source L. Then, the first free light which is an off-axial reflecting surface is transmitted through the first to sixth reflecting mirrors M1 to M6 and the infrared light cut filter 7 for folding the light beam (diffuse reflected light beam) from the document image Obj. The light is incident on the curved surface 81.

  Then, the light beam reflected obliquely upward by the first free curved surface 81 is incident on the reflection diaphragm 82 and reflected obliquely downward, and then enters the second free curved surface 83 which is an off-axial reflective surface. Then, the light beam reflected by the second free-form surface 83 is emitted in parallel with the first free-form surface 81 and is condensed on the line sensor LS provided on the image formation surface of the image formation optical system.

  As described above, the imaging optical system according to the present embodiment includes the first to sixth reflecting surfaces M1 to M6, the first free curved surface (reflecting surface) 81, the reflecting stop (planar reflecting surface) 82, and the second free surface. A curved surface (reflection surface) 83 is provided. The first and second free curved surfaces 81 and 83 that are the reflecting surfaces of the curved mirror are a single optical element 80 that forms a free curved surface that is symmetric with respect to the reference axis in the main scanning direction and asymmetric in the sub scanning direction. As a single unit. The reflection surface of the reflection diaphragm 82 is a plane mirror.

3) Optical action In the present embodiment, the first and second free-form surfaces 81 and 83 are formed in a single optical element 80, and the relative position of the reflection stop 82 and the optical element 80 is changed. It is configured to be possible. Thereby, it is possible to easily obtain good imaging performance while reducing the number of free-form surfaces that are off-axial reflecting surfaces.

  Further, in the present embodiment, in order to make the imaging optical system compact in the sub-scanning section (YZ section), the optical path is first folded by the first to sixth reflecting mirrors M1 to M6. Further, the off-axial optical system 8 also has an optical path folded into a four-letter shape. That is, when a plane including the central ray of the light beam incident on the reflection diaphragm 82 and the central ray of the light beam reflected by the reflection diaphragm 82 is a projection surface, the first free-form surface 81 projected into the projection surface is used. The reflected light beam and the reflected light beam from the second free-form surface 83 intersect each other. Here, the direction of the surface normal of the first free-form surface 81 in the present embodiment is the vertical direction.

  Further, since the off-axial optical system 8 is composed of reflecting surfaces (first and second free-form curved surfaces and a reflective stop), chromatic aberration does not occur, and it is possible to widen the angle by the refractive power of the off-axial free-form surface. Become. In addition, it is easy to cancel the decentration aberrations by folding the optical path into a four-letter shape. Furthermore, the first and second free-form surfaces are each symmetrical with respect to the reference axis in the main scanning direction and asymmetrical in the sub-scanning direction, so that asymmetric aberrations due to decentering and various aberrations are corrected satisfactorily. In this way, good imaging performance can be obtained with a single optical element composed of a free-form surface and a small number of reflection diaphragms.

4) Tilt in the Sub-Scanning Section All the optical surfaces (reflection surfaces) of the imaging optical system according to the present embodiment are basically tilted in the same plane (YZ plane that is the sub-scanning section). Therefore, each axis of the coordinate system shown in FIG. 2 is determined as follows.
Z-axis: Reference axis passing through the origin (x, y, z = 0, 0, 0) toward the first surface Y-axis: Straight line passing through the origin and forming 90 ° counterclockwise with respect to the Z-axis in the tilt plane X axis: A straight line passing through the origin and perpendicular to each of the Z and Y axes. To express the surface shape of the i-th surface constituting the imaging optical system, the surface is represented by the coordinate system shown in FIG. Setting a local coordinate system with the origin at the point where the reference axis and the i-th surface intersect and expressing the surface shape of the surface in the local coordinate system is easier to understand for recognizing the shape. For this reason, in this embodiment, the surface shape of the i-th surface is represented by a local coordinate system. Further, the tilt angle in the sub-scan section (YZ plane) of the i-th surface is represented by an angle θi (unit: °) with the counterclockwise direction being positive with respect to the Z axis of the coordinate system shown in FIG. Therefore, in this embodiment, the origin of the local coordinates of each surface is on the YZ plane.

Further, there is no surface eccentricity in the XZ plane and the XY plane. Further, the y-axis and z-axis of the local coordinates (x, y, z) of the i-th surface are inclined by the angle θi in the YZ plane with respect to the coordinate system (X, Y, Z) shown in FIG. Specifically, it is set as follows.
z-axis: A straight line passing through the origin of the local coordinate and forming an angle θi in the counterclockwise direction in the YZ plane with respect to the Z-axis direction of the coordinate system shown in FIG. Straight line x-axis forming 90 ° in the counterclockwise direction in the YZ plane: A straight line passing through the origin of the local coordinate system and perpendicular to the YZ plane 5) Aspherical surface Also, the first and second free-form surfaces in this embodiment 81 and 83 have rotationally asymmetric aspherical surfaces, and their shapes are represented by the following equations.

  In the above formula, when x = 0, the shape on the sub-scanning direction axis is shown, and when y = 0, the shape on the main scanning direction axis is shown. The spherical surface has a shape represented by the following formula.

  Since the curved surface formula is only an even-order term with respect to x, the curved surface defined by the curved surface formula is a plane-symmetric shape with the yz plane as the symmetry plane.

  Here, it is difficult to directly calculate the focal length based on paraxial theory. Therefore, the converted focal length feq according to the following definition is used.

  Here, h1 is the incident height of a light beam that is parallel to the reference axis and incident infinitely on the reference axis on the first surface, and ak 'is an angle that the light beam makes with the reference axis when exiting from the final surface. Note that, by definition, when there are an odd number of reflecting surfaces, the sign of the focal length is expressed opposite to the normal sign.

  Next, the definition of the power (refractive power) in the main scanning direction of the first free-form surface 81 that is the most object-side (original image side) free-form surface in this embodiment will be described. Generally, it is known that when the curvature of a reflecting surface is r, the power φ of the reflecting surface is expressed as φ = −2 / r. Here, assuming that the curvature in the main scanning direction of the free-form surface on the most object side (original image side) is r1, the relational expression 1 / 2r1 = C20 is established.

  Therefore, when the second-order coefficient in the main scanning direction of the free-form surface on the most object side (original image side) in this embodiment is C20, the power φ1 of the first free-form surface 81 in the main scanning direction is φ1 = −4 ×. Defined as C20.

(Numerical example)
In the numerical examples shown below, Di is a scalar quantity representing the distance between the origins of the local coordinates between the i-th surface and the (i + 1) -th surface, and Ndi is the refractive index of the medium between the i-th surface and the (i + 1) -th surface. It is.
Document reading width = 305.0 Imaging magnification = −0.111
Document side NA = 0.177 Feq = 27.6

First off-axial free-form aspherical surface shape C02 = −4.70025E-03 C03 = 1.95452E-05 C20 = −5.06338E-3
C21 = 7.881725E-05 C22 = 2.80003E-06 C23 = 2.59571E-8
C41 = −1.32239E-07 C42 = −4.39348E−10 C43 = −3.54953E−10
C60 = -4.73343E-09 C61 = 2.38409E-10 C62 = 2.19191E-11
C80 = 5.63910E-12
Second off-axial free-form aspherical shape C02 = −7.52190E-03 C03 = 1.85322E-05 C20 = −8.03730E-03
C21 = −1.92907E-04 C22 = −2.43021E-05 C23 = 6.000834E-06
C41 = 2.76078E-07 C42 = 4.99962E-7 C43 = -6.18787E-7
C60 = −1.09008E−08 C61 = −7.46929E−10 C62 = −1.995926E−10
C80 = 2.17295E-11
(Unitization in manufacturing process of image reading device)
3A, 3 </ b> B, and 3 </ b> C are diagrams for explaining unitization in the manufacturing process of the image reading apparatus of the present embodiment. In FIG. 3A, the first holding member 84 is an X, Y, Z reference (803, 802, 801) of the single optical element 80 in which the first and second free curved surfaces 81, 83 are integrated. Each holding reference seating surface (842, 841, 843) corresponding to. And it hold | maintains so that each reference | standard of the single optical element 80 may contact | abut each holding | maintenance reference seat surface, for example, it adheres and fixes with UV hardening resin etc.

  Similarly, in FIG. 3B, the reflection diaphragm 82 is also abutted and fixed to each reference of the second holding member 85. The second holding member 85 restricts the movement of the first holding member 84 in the Y direction, and can be shifted in parallel only in the Z direction. Reference numeral 843 denotes an adhesive pool, which is fixed after adjusting the relative positional relationship between the first holding member 84 and the second holding member 85 that are configured so that the relative position can be changed in the manufacturing process described later. A unit (hereinafter, an imaging optical unit) is formed (FIG. 3C).

(Displacement direction in the image reading device manufacturing process)
FIG. 4 is a schematic view showing the displacement direction in the manufacturing process relating to the imaging optical unit described above. FIG. 5 is a flowchart showing the manufacturing process. Hereinafter, the manufacturing process of the image reading apparatus according to the present embodiment will be described with reference to FIGS. The manufacturing apparatus (adjusting apparatus) includes a transmission chart 1, a chart illumination optical system LC, a jig table glass CG, a jig mirror 2, a jig infrared cut filter 3, and a jig. Line sensor LS.

  Then, the relative positional relationship in the H direction (Z direction) between the single optical element 80 held by the first holding member 84 and the reflection diaphragm 82 held by the second holding member 85. The slide is adjustable. Further, the line sensor LS can be displaced in the arrow B direction (Z-axis direction) and the C direction (Y direction which is the sub-scanning direction) in the figure by a position adjusting mechanism (not shown).

  Items to be manufactured (adjusted) using this manufacturing apparatus (adjusting apparatus) include resolution, particularly field curvature in the main scanning direction and axial astigmatism. The former uses relative displacement in the H direction (Z direction) between the first holding member 84 and the second holding member 85, and the latter uses displacement in the C direction (Y direction which is the sub-scanning direction) of the line sensor LS.

  The transmission chart 1 includes a line pattern arranged in a direction (Y direction) perpendicular to the light receiving element arrangement direction (X direction) of the line sensor LS and a line pattern arranged at a certain angle in the X direction. Each pair is arranged at least at three locations in the main scanning direction. As an example of three places arranged in the main scanning direction, there are a central portion and both end portions in the main scanning direction. Then, the pattern of the transmission chart 1 is imaged on the line sensor LS by the off-axial optical system, and the resolving power is evaluated. The method for evaluating the resolving power is a known technique, and although the details are omitted here, the evaluation is performed based on the contrast of the monochrome line chart.

(Flowchart showing manufacturing process of image reading apparatus)
Hereinafter, the manufacturing process of the image reading apparatus according to the present embodiment will be described with reference to FIGS. First, the temporarily assembled off-axial optical system 8 is loaded on the adjustment base. The first holding member 84 is fixed by being sandwiched between claws on a stage that can move in parallel in the H direction (Z direction). The second holding member 85 is fitted and fixed to a jig-side reference pin based on the Z and Y references, and only the first holding member 84 can be displaced in parallel with the second holding member 85 on the stage. Fixed in state. In this case, the first holding member 84, the second holding member 85, and the line sensor LS are held at the design designation positions.

  Next, the chart illumination device LC is turned on, the transmission chart 1 is illuminated, and a chart image is formed on the line sensor LS by the off-axial optical system 8. Here, the resolving power is measured at a predetermined pitch while the line sensor LS is displaced by a predetermined range in the arrow B direction (Z direction), and the defocus characteristic of the resolving power is evaluated (step 1). In order to evaluate the defocus characteristic of the resolving power, both the main scanning direction and the sub-scanning resolving power are R at three positions in the main scanning direction corresponding to the chart pattern position (one central portion and two peripheral end portions). , G, B for each color.

  Next, based on the defocus data of the resolving power measured in Step 1, a main scanning image plane curvature amount, an axial ascent amount, and an axial depth center position, which will be described later, are calculated (Step 2).

   Next, based on the calculation result of the main scanning image plane curvature amount, the axial ascent amount, and the axial depth center position calculated in step 2, the following is performed. That is, the eccentricity adjustment amount (displacement amount) of the first holding member 84 in the arrow H direction (Z direction) and the eccentricity adjustment amount (displacement amount) of the line sensor LS in the arrow B direction and C direction are calculated from the sensitivity table. To do.

  6A shows the sensitivity when the first holding member 84 is eccentric (displaced) by 0.05 mm in the arrow H direction, and FIG. 6B shows the sensitivity of the line sensor LS by 0.05 mm in the arrow C direction. This is the sensitivity of the depth center change when (displaced). From these sensitivities, a correction amount necessary for manufacturing the image reading apparatus is calculated (step 3).

  Next, based on the calculated correction amount, the first holding member 84 is driven (displaced) in the arrow H direction and the line sensor LS in the C direction (step 4). Then, in the state after the position change, the defocus characteristic is measured again to determine whether it is within a predetermined standard (step 5). If the standard is satisfied in Step 5, the first holding member 84 and the second holding member 85 are fixed by a known method such as adhesion, and the first holding member 84 and the second holding member 85 are fixed. The relative position adjustment is completed (step 6). Thereby, the off-axial optical system 8 in which the curvature of field in the main scanning direction is sufficiently corrected is obtained.

  Thereafter, the off-axial optical system 8 and the line sensor LS are fixed by adhesion or the like while maintaining the eccentric state (displacement state) via the intermediate coupling member (STEP 7). In this way, the astigmatism amount of the main / sub image plane is sufficiently corrected by appropriately adjusting the decentering amount (displacement amount) of the line sensor LS with respect to the off-axial optical system 8 in the sub scanning direction (C direction). Can be unitized.

  Note that the transmission chart 1 may be prepared not by one (one type) but by a plurality (a plurality of types), and the defocus characteristic may be acquired and adjusted by using a chart having a resolution lower than a desired resolution. Further, when the main scanning image plane curvature amount and the axial ascent amount are large, it is assumed that the resolution at the peripheral image height is drastically reduced and the depth center cannot be calculated. In that case, the adjustment parameter can be determined at the same time by calculating the initial main scanning image plane curvature amount and the astigmatism amount with a low resolution chart different from the desired resolution. If the initial adjustment can be performed, the performance may be confirmed by returning to the original desired resolution chart.

  Then, the carriage unit is temporarily assembled as a unit in which the folding mirrors M1 to M6, the infrared light cut filter 7, the off-axial optical system 8 and the line sensor LS are coupled via the intermediate coupling member 9. Then, in addition to the line chart used in the unit adjustment described above, the performance is confirmed using a known geometric characteristic evaluation chart. If there is no problem, the assembly is completed.

(Method for manufacturing image reading apparatus)
As described above, the manufacturing method of the image reading apparatus according to the present embodiment includes the following steps. That is, first, the first and second free curved surfaces 81 and 83 which are off-axial reflecting surfaces are integrally formed as a single optical element 80. In addition, the imaging optical system includes first and second free curved surfaces 81 and 83, and a reflection stop 82, a light beam reflected from the first free curved surface projected onto the projection surface, and a second A second step of arranging an imaging optical system intersecting with the light beam reflected from the free curved surface. Here, a plane including the central ray of the light beam incident on the reflection diaphragm 82 and the central ray of the light beam reflected by the reflection diaphragm 82 is a projection surface.

  And the 3rd process of displacing the relative positional relationship of the single optical element 80 which consists of free-form surfaces, and the reflective stop 82 is provided. Specifically, the relative positional relationship in the direction of the light beam reflected from the second free-form surface 83 between the single optical element 80 having a free-form surface and the reflection stop 82 can be displaced. Furthermore, a fourth step of displacing the line sensor LS in the direction of the light beam reflected from the second free-form surface 83 or the direction perpendicular to the direction with respect to the off-axial optical system 8 which is an imaging optical system is provided.

(Effect of this embodiment)
By using an off-axial optical system 8 comprising two off-axis free-form surfaces and three surfaces of a reflective diaphragm, an imaging optical system that has a short optical path length and can be used for a carriage-integrated image reading apparatus is provided. it can. Further, it is possible to achieve an image reading apparatus with a simple configuration and no chromatic aberration and little occurrence of asymmetric aberration.

  Further, according to the present embodiment, by adjusting the relative positional relationship between the first and second free-form surfaces and the reflective diaphragm, it is possible to effectively adjust the main scanning field curvature and the asphalt, and as a result An image reading apparatus having good performance can be easily manufactured.

<< Second Embodiment >>
7 and 8 are explanatory diagrams of the displacement direction in the manufacturing process of the image reading apparatus according to the second embodiment of the present invention, and a flowchart showing the manufacturing process of the image reading apparatus according to the present embodiment. In FIG. 7, the same elements as those shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted. In this embodiment, the difference from the first embodiment is that, instead of adjusting the relative positional relationship between the first holding member 84 and the second holding member 85 by displacement in the H direction (Z direction), the relative position The relationship is adjusted by the displacement in the arrow V direction (Y direction which is the sub-scanning direction). Other configurations and optical actions are substantially the same as those of the first embodiment, and the same effects are obtained.

(Flowchart showing manufacturing process of image reading apparatus)
Hereinafter, the manufacturing process of the image reading apparatus of this embodiment will be described with reference to FIG. First, the temporarily assembled off-axial optical system 8 is loaded on the adjustment base. The first holding member 84 is fixed on a stage that can be translated in the V direction (Y direction). The second holding member 85 is fitted and fixed to a jig-side reference pin based on the Z and Y references, and only the first holding member 84 can be displaced in parallel with the second holding member 85 on the stage. Fixed in state. In this case, the first holding member 84, the second holding member 85, and the line sensor LS are held at the design designation positions.

  Next, the chart illumination device LC is turned on, the transmission chart 1 is illuminated, and a chart image is formed on the line sensor LS by the off-axial optical system 8. Here, the resolving power is measured at a predetermined pitch while the line sensor LS is displaced by a predetermined range in the arrow B direction (Z direction), and the defocus characteristic of the resolving power is evaluated (step 1). In order to evaluate the defocus characteristic of the resolving power, both the main scanning direction and the sub-scanning resolving power are R at three positions in the main scanning direction corresponding to the chart pattern position (one central portion and two peripheral end portions). , G, B for each color.

  Next, based on the defocus data of the resolving power measured in Step 1, a main scanning image plane curvature amount, an axial ascent amount, and an axial depth center position, which will be described later, are calculated (Step 2).

   Next, based on the calculation result of the main scanning image plane curvature amount, the axial ascent amount, and the axial depth center position calculated in step 2, the following is performed. That is, the eccentricity adjustment amount (displacement amount) of the first holding member 84 in the arrow V direction (Y direction) and the eccentricity adjustment amount (displacement amount) of the line sensor LS in the arrow B direction and C direction are calculated from the sensitivity table. To do.

  FIG. 9 shows the sensitivity when the first holding member 84 is eccentric (displaced) by 0.05 mm in the arrow V direction. The sensitivity when the line sensor LS is decentered (displaced) in the arrow C direction (sub-scanning direction) is the same as in the first embodiment. From these sensitivities, a correction amount necessary for manufacturing the image reading apparatus is calculated (step 3).

  Next, based on the calculated correction amount, the first holding member 84 is driven (displaced) in the arrow V direction and the line sensor LS in the C direction (step 4). Then, in the state after the position change, the defocus characteristic is measured again to determine whether it is within a predetermined standard (step 5). If the standard is satisfied in Step 5, the first holding member 84 and the second holding member 85 are fixed by a known method such as adhesion, and the first holding member 84 and the second holding member 85 are fixed. The relative position adjustment is completed (step 6). Thereby, the off-axial optical system 8 in which the curvature of field in the main scanning direction is sufficiently corrected is obtained.

  Thereafter, the off-axial optical system 8 and the line sensor LS are fixed by adhesion or the like while maintaining the eccentric state (displacement state) via the intermediate coupling member (STEP 7). In this way, the astigmatism amount of the main / sub image plane is sufficiently corrected by appropriately adjusting the decentering amount (displacement amount) of the line sensor LS with respect to the off-axial optical system 8 in the sub scanning direction (C direction). Can be unitized.

  Note that the transmission chart 1 may be prepared not by one (one type) but by a plurality (a plurality of types), and the defocus characteristic may be acquired and adjusted by using a chart having a resolution lower than a desired resolution. Further, when the main scanning image plane curvature amount and the axial ascent amount are large, it is assumed that the resolution at the peripheral image height is drastically reduced and the depth center cannot be calculated. In that case, the adjustment parameter can be determined at the same time by calculating the initial main scanning image plane curvature amount and the astigmatism amount with a low resolution chart different from the desired resolution. If the initial adjustment can be performed, the performance may be confirmed by returning to the original desired resolution chart.

  Then, the carriage unit is temporarily assembled as a unit in which the folding mirrors M1 to M6, the infrared light cut filter 7, the off-axial optical system 8 that is an imaging optical system, and the line sensor LS are coupled via the intermediate coupling member 9. Then, in addition to the line chart used in the unit adjustment described above, the performance is confirmed using a known geometric characteristic evaluation chart. If there is no problem, the assembly is completed.

(Method for manufacturing image reading apparatus)
As described above, the manufacturing method of the image reading apparatus according to the present embodiment includes the following steps. That is, first, the first and second free curved surfaces 81 and 83 which are off-axial reflecting surfaces are integrally formed as a single optical element 80. In addition, the imaging optical system includes first and second free curved surfaces 81 and 83, and a reflection stop 82, a light beam reflected from the first free curved surface projected onto the projection surface, and a second A second step of arranging an imaging optical system intersecting with the light beam reflected from the free curved surface. Here, a plane including the central ray of the light beam incident on the reflection diaphragm 82 and the central ray of the light beam reflected by the reflection diaphragm 82 is a projection surface.

  And the 3rd process of displacing the relative positional relationship of the single optical element 80 which consists of free-form surfaces, and the reflective stop 82 is provided. Specifically, the relative positional relationship in the direction orthogonal to the direction of the light beam reflected from the second free-form surface 83 between the single optical element 80 having a free-form surface and the reflection stop 82 can be displaced. Furthermore, a fourth step of displacing the line sensor LS in the direction of the light beam reflected from the second free-form surface 83 or the direction perpendicular to the direction with respect to the off-axial optical system 8 which is an imaging optical system is provided.

(Modification)
As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

(Modification 1)
In the above-described embodiment, the second holding member 85 is fixed, and using the first holding member 84 as a reference, the first holding member 84 is moved in the H direction (Z direction which is the reference axis direction) or V direction (Y which is the sub-scanning direction). Direction) was adjusted by shifting (parallel shift). However, conversely, the first holding member 84 is fixed, and using this as a reference, the second holding member 85 is moved in the H direction (Z direction which is the reference axis direction) or the V direction (Y direction which is the sub-scanning direction). Adjustment may be made by displacement (parallel shift), and the same effect can be obtained.

(Modification 2)
In the embodiment described above, the direction of the surface normal of the first reflective off-axial free curved surface 81 is the vertical direction, but the present invention is not limited to this, and the surface of the first reflective off-axial free curved surface 81 is The direction of the normal can be set to an arbitrary direction.

80 .. Off-axial free-form optical element, 81 .. First reflective off-axis free-form curved surface, 82 .. Reflective-type plane stop, 83 .. Second reflective off-axial free-form curved surface, Obj. LS line sensor array

Claims (10)

An imaging optical system comprising: first and second free curved surfaces that are off-axial reflecting surfaces; and a reflective diaphragm that guides a light beam from the first free curved surface to the second free curved surface,
The first and second free-form surfaces are formed in a single optical element;
The imaging optical system, wherein the reflection diaphragm and the optical element are configured such that relative positions thereof can be changed.   The light beams reflected by the first and second free-form surfaces intersect each other when projected onto a projection surface including the central ray of the light beam incident on the reflection stop and the central ray of the light beam reflected by the reflection stop. The imaging optical system according to claim 1, wherein:   The imaging optical system according to claim 2, wherein the reflection diaphragm and the optical element can change relative positions of each other in a projection plane.   The relative position of the reflection diaphragm and the optical element can be changed in the direction of the light beam reflected by the second free-form surface or in the direction perpendicular to the direction. The imaging optical system according to any one of the above.   The imaging optical system according to claim 1, wherein a direction of a surface normal of the first free-form surface is a vertical direction. Illumination means for illuminating the document image;
The imaging optical system according to any one of claims 1 to 5,
A line sensor provided on the imaging surface of the imaging optical system;
In one housing,
An image reading apparatus, wherein the housing is moved in a sub-scanning direction. A first holding member that holds the optical element, and a second holding member that holds the reflective diaphragm,
The first holding member can be displaced relative to the second holding member in a direction of a light beam reflected from the second free curved surface or in a direction perpendicular to the direction,
The image reading apparatus according to claim 6, wherein the first holding member, the second holding member, and the line sensor are fixed to a single coupling member.   The image reading apparatus according to claim 7, wherein the line sensor is displaceable in a direction of a light beam reflected from the second free-form surface or in a direction orthogonal to the direction. A first step of integrally forming first and second free-form surfaces, which are off-axial reflecting surfaces, as a single optical element;
An imaging optical system comprising: the first and second free curved surfaces; and a reflection diaphragm for guiding a light beam from the first free curved surface to the second free curved surface,
When a plane including the central ray of the light beam incident on the reflection diaphragm and the central ray of the light beam reflected by the reflection diaphragm is a projection surface,
A second step of disposing an imaging optical system projected onto the projection surface and intersecting with the light beam reflected from the first free curved surface and the light beam reflected from the second free curved surface;
A third step of displacing the relative positional relationship between the optical element and the reflective diaphragm;
A fourth step of displacing the line sensor with respect to the imaging optical system in a direction of a light beam reflected from the second free-form surface or a direction perpendicular to the direction;
A method for manufacturing an image reading apparatus, comprising:   The relative positional relationship in the direction of a light beam reflected from the second free-form surface of the optical element and the reflection stop in the third step or in a direction perpendicular to the direction can be displaced. A method for manufacturing the image reading apparatus according to claim 9.