JP2014098762A - Aspherical optical element, image reader, and method for manufacturing aspherical optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aspherical optical element capable of highly accurately measuring the position of an optical effective surface having a non-rotationally symmetrical aspherical shape, in a rotational direction, with a simple configuration.SOLUTION: An aspherical optical element 100 includes an optical effective surface 101 formed of a non-rotationally symmetrical aspherical surface and a plurality of projecting parts or a plurality of recessed parts 102 and 103 provided in the front surface of the optical effective surface 101. In the optical effective surface 101, other parts except a part in which the plurality of projecting parts or the plurality of recessed parts 102 and 103 are provided are shaped to be continuous.

Description

  The present invention relates to an aspherical optical element, and is suitable for, for example, an imaging optical system provided in an image reading apparatus.

  In the aspherical optical element, it is required to measure the shape (aspherical amount) and decentering amount of the optically effective surface, the position of the optically effective surface when the aspherical optical element is incorporated in another member, and the like. Patent Document 1 discloses a transmissive diffractive optical element in which a protrusion is provided at the center of a diffractive surface, and the protrusion is used as a reference position for alignment and measurement of the center of the optical element. . Patent Document 2 discloses a technique in which a mirror surface is provided on the back surface (surface opposite to the reflection surface) of the reflective optical element, and the mirror surface is used for measuring the surface shape.

Japanese Patent Laid-Open No. 10-274705 JP 2009-271351 A

  Here, when the optically effective surface of the aspherical optical element is a non-rotationally symmetric aspherical surface, not only the shape of the aspherical surface but also the rotational direction of the optically effective surface in the aspherical optical element and the aspherical optical for other members It is necessary to precisely measure the position of the element in the rotational direction. In addition, the rotation direction here has shown the rotation direction (azimuth direction) centering on a surface normal.

  However, since the optical element described in Patent Document 1 has only one protrusion at the center, even if this structure is applied to an aspheric optical element having a non-rotationally symmetric aspherical surface, Sufficient accuracy cannot be obtained in measuring the position of the aspheric surface in the rotational direction. Moreover, in patent document 2, since the back surface of the reflective surface as an optical effective surface is used for measurement, position errors between a mold for forming the optical effective surface and a mold for forming the back surface, etc. Due to the influence, there is a problem that accuracy in measuring the shape and position of the optically effective surface is difficult to obtain.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an aspheric optical element that can measure the position in the rotational direction of an optically effective surface having a non-rotationally symmetric aspheric shape with a simple configuration with high accuracy.

  To achieve the above object, an aspherical optical element according to one aspect of the present invention includes an optically effective surface formed of a non-rotationally symmetric aspherical surface and a plurality of convex portions provided on the surface of the optically effective surface. Or a plurality of concave portions, and the optically effective surface has a continuous shape except for the portions provided with the plurality of convex portions or the plurality of concave portions.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  ADVANTAGE OF THE INVENTION According to this invention, the aspherical optical element which can measure the position of the rotation direction of the optical effective surface which has a non-rotationally symmetric aspherical shape with a simple structure with high precision can be provided.

1 is a schematic view of a main part of an aspheric optical element according to Example 1. FIG. 1 is a schematic diagram of an imaging optical system including an aspheric optical element according to Example 1. FIG. It is a figure explaining the additional wave-front shape by the aspherical optical element which concerns on Example 1. FIG. 3 is a flowchart showing a method for manufacturing the aspheric optical element according to the first embodiment. FIG. 6 is a schematic diagram of a main part of an aspheric optical element according to Example 2. 9 is a flowchart showing a method for manufacturing an aspheric optical element according to Example 2.

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

Example 1
FIG. 1 is a schematic diagram of a main part of an aspheric optical element 100 according to the first embodiment. The aspherical optical element 100 includes an optically effective surface 101 formed of a non-rotationally symmetric reflective aspherical surface, discontinuous portions 102 and 103 provided on the surface of the optically effective surface 101, and abutting portions 104a, 104b, and 105. , 106a, 106b and 106c. In this embodiment, “aspherical surface” indicates “a surface having an aspherical effect”.

  The optically effective surface 101 has a continuous shape except for the portions where the discontinuous portions 102 and 103 are provided. Each of the discontinuous portions 102 and 103 is provided at the center portion (surface vertex) and the peripheral portion of the surface of the optical effective surface 101 so that it can be detected when measuring the surface shape of the optical effective surface 101. The protrusion shape (convex portion) protrudes in the Z direction. The abutting portions 104a to 106b are portions serving as positioning references when the aspherical optical element 100 is incorporated into an imaging optical system or the like.

  FIG. 2 shows a configuration when the aspherical optical element 100 according to the present embodiment is incorporated in an off-axial imaging optical system. The off-axial imaging optical system converts light rays from the object point 201 into the first reflecting surface 202a of the reflective imaging element 202, the optical effective surface 101 of the aspherical optical element 100, and the second reflecting surface 202b of the reflective imaging element 202. , And are condensed on the image point 203.

  Here, the aspherical optical element 100 in the off-axial imaging optical system functions as a diaphragm having a power (refractive power) of substantially 0 (substantially non-power), and the difference in the angle of view and the focus shift contribute to the imaging performance. The wavefront of the luminous flux is changed so as to suppress the influence exerted. FIG. 3 shows a wavefront shape added to the light beam reflected by the optical effective surface 101 by the aspherical optical element 100 according to the present embodiment measured by an interferometer. This wavefront shape is optically effective. This corresponds to the aspherical shape of the surface 101. In FIG. 3, changes in the wavefront shape due to the discontinuous portions 102 and 103 are omitted.

  The optically effective surface 101 of the aspherical optical element 100 according to the present embodiment and the wavefront shape added by the aspherical optical element 100 are shapes that overlap with each other (10-fold symmetry) every time they are rotated 36 ° about the surface normal. Further, it has a ridge line and a valley part in the radial direction (Y direction) with respect to the center part (surface apex) of the wavefront, and has an unevenness of about ± 500 nm in the optical axis direction (Z direction) in the peripheral part. It should be noted that a surface having natural number of times symmetry with the surface normal as an axis, such as the optically effective surface 101 in this embodiment, is also a non-rotationally symmetric surface. That is, “a non-rotationally symmetric surface” indicates “a surface that does not have rotational symmetry that overlaps itself even when rotated at any angle about the surface normal.”

  The aspherical optical element 100 according to the present embodiment is assumed to be manufactured by injection molding having excellent mass productivity. A specific manufacturing method will be described based on the flowchart shown in FIG. First, in step S401, an aspherical surface (mirror surface) that is non-rotationally symmetric with respect to the piece is formed, and a plurality of recesses are formed on the aspherical surface, thereby producing a mold (mirror surface piece). In step S402, by using the mold, the optically effective surface 101 and the discontinuous portions 102 and 103 can be injection-molded simultaneously.

  Here, when the mold is manufactured in step S401, the aspherical surface is formed so as to have a continuous shape except for a portion where a plurality of recesses are formed. In addition, it is desirable to form the plurality of concave portions so that the discontinuous portions 102 and 103 have a protrusion shape that can be clearly detected by an interferometer or the like. Specifically, the height of the protrusions of the discontinuous portions 102 and 103 is at least about five times the wavelength generally used in measurement with respect to the optically effective surface 101 of the aspherical optical element 100 (in this embodiment, A recess is formed so as to be about 3 μm. Accordingly, each discontinuous portion can be clearly detected by a measuring instrument such as an interferometer (details will be described later).

  In this embodiment, a plurality of discontinuous portions (convex portions) having a protrusion shape (convex shape) are provided on the optically effective surface, but a configuration having a plurality of concave discontinuous portions (concave portions) is provided. Also good. In this case, a convex portion may be formed in the region where the aspherical surface of the piece is formed in step S401 so that the discontinuous portion has a concave shape that can be clearly detected by an interferometer or the like.

  Further, measurement of the shape (aspheric amount) and position of the optically effective surface 101 of the aspherical optical element 100, that is, an error with respect to the design value of the aspherical shape of the optically effective surface 101, and the optically effective surface of the aspherical optical element 100. The measurement of the amount of eccentricity 101 will be described.

  The aspherical shape of the optically effective surface 101 can be measured by observing interference fringes using an interferometer, and this method is one of the simplest methods. When using an interferometer, a method of measuring the position of the optically effective surface 101 in the aspherical optical element 100 by adjusting the spot diameter of the light beam emitted from the interferometer to the effective diameter size of the optically effective surface 101 can be considered. . However, in this method, a mask or a lens for converting the aperture of the interferometer is required in order to change the spot diameter of the light beam for each aspherical optical element.

  Therefore, in this embodiment, as shown in FIG. 4, the position of the optical effective surface 101 is measured using the discontinuous portions 102 and 103 provided in the aspherical optical element 100. Specifically, in step S403, in the wavefront shape obtained by the interferometer, the surface vertex of the optically effective surface 101 is determined based on the location of the wavefront changed by the discontinuous portion 102. Then, in step S404, based on the positional relationship between the discontinuous portion 102 and the discontinuous portion 103, that is, the distance between the wavefront change location due to the discontinuity portion 102 and the wavefront change location due to the discontinuity portion 103, the optical effective surface The length in 101 is measured. Thereby, the amount of eccentricity of the optically effective surface 101 can be obtained based on the measured position of the surface vertex and the length in the surface. Thus, by providing the discontinuous portions 102 and 103 on the optical effective surface 101, the position of the optical effective surface 101 can be easily measured without providing a mask or a lens for the interferometer.

  In addition, like the optically effective surface 101 of the aspherical optical element 100 according to the present embodiment, it is necessary to measure the position in the rotational direction (azimuth direction) with high accuracy in an aspherical surface that is not rotationally symmetric. Therefore, in step S405, the position of the optically effective surface 101 in the rotational direction is measured based on the positional relationship between the discontinuous portion 102 and the discontinuous portion 103. Specifically, the position of the optically effective surface 101 in the rotational direction is measured by using a straight line connecting the discontinuous portion 102 and the discontinuous portion 103 as a reference. Thus, according to the configuration of the present embodiment, even after the aspherical optical element 100 is incorporated into the imaging optical system or the like, the aspherical optical element 100 can be easily measured by measuring the wavefront using an interferometer or the like. It is possible to detect a positional deviation in the rotational direction about the optical axis direction of.

(Example 2)
Hereinafter, a second embodiment of the present invention will be described. The same or equivalent components as those of the first embodiment are denoted by the same reference numerals, and the description thereof will be simplified or omitted.

  FIG. 5 is a schematic diagram of a main part of an aspheric optical element 500 according to the second embodiment. The aspherical optical element 500 according to the present embodiment includes discontinuous portions 502 and 503 on the optical effective surface 501 and abutting portions 504a, 504b, 505, 506a, 506b and 506c. Here, the discontinuous portions 502 and 503 and the abutting portions 506a to 506c on the optical effective surface 501 side are formed of the same piece, and the abutting portions 506a to 506c have a convex shape. . According to the aspherical optical element 500 according to the present embodiment, the position of the optical effective surface 501 in the aspherical optical element 500 is determined not only by the measurement described in the first embodiment but also by using the abutting portions 506a to 506c. Can be sought.

  A specific method for manufacturing the aspherical optical element 500 according to the present embodiment will be described based on the flowchart shown in FIG.

  First, in step S601, similarly to step S401 in the first embodiment, an aspherical surface (mirror surface) that is non-rotationally symmetric with respect to the piece is formed, and a plurality of concave portions are formed on the aspherical surface, thereby obtaining a mold (mirror surface). ). Further, in the present embodiment, the concave portion is formed in a portion other than the region where the aspherical surface (mirror surface) is formed on the same surface of the piece. By using this die, the optically effective surface 501, the discontinuous portions 502 and 503, and the abutting portions 504 a to 506 c are integrally formed in step S <b> 602. It is possible to suppress the occurrence of errors due to the mold assembly. In this embodiment, the abutting portion is formed in a convex shape, but the abutting portion may be formed in a concave shape. That is, in step S601, a convex portion may be formed on a portion other than the region where the aspherical surface is formed on the same surface of the piece.

  Next, by measuring the distance dX between the discontinuous portion 502 and the abutting portion 505 shown in FIG. 5A, the amount of eccentricity of the surface apex of the optical effective surface 501 in the aspherical optical element 500 can be obtained. it can. Further, by measuring the height dZ of the abutting portions 506a to 506c with respect to the optical effective surface 501 in the vicinity of the discontinuous portion 502 shown in FIG. 5B, the optical effective surface 501 and the abutting portions 506a to 506c The relative position in the optical axis (surface normal) direction can be obtained.

  Thus, according to the aspherical optical element 500 according to the present embodiment, the amount of eccentricity of the optical effective surface 501 and the height in the optical axis direction are determined based on the positional relationship between the discontinuous portion 502 and the abutting portions 506a to 506c. It is possible to measure a position such as a high accuracy with a simple configuration. Note that, similarly to steps S403 to S405 in the first embodiment, measurement using only the discontinuous portions 502 and 503 (steps S604 to S606) may be further performed.

Further, when the aspherical optical element 500 is incorporated in the imaging optical system, the discontinuous portions 502 and 503 are prevented from affecting the imaging performance of the light flux and causing the occurrence of flare, the reduction in aperture efficiency, and the like. Therefore, it is preferable to design the area of each discontinuous portion in the XY cross section as small as possible. Specifically, it is preferable to design so that the areas of the discontinuous portions 502 and 503 are 1% or less of the area of the optical effective surface 501 in the XY cross section. The optically effective surface 501 according to the present embodiment has a circular shape with a diameter of 5.4 mm in the XY cross section, and its area is 22.9 mm ² . On the other hand, the area of the discontinuous portions 502 and 503 in the XY cross section is 0.2 mm ² which is about 1% of the area of the optically effective surface 501 and each discontinuous portion has a conical shape with a diameter of about 250 μm. Become.

(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.

  For example, in the measurement in each of the embodiments described above, a contact-type three-dimensional measuring instrument or the like may be used instead of the interferometer. Each of the discontinuous portions at that time can be measured if it has a height of about 3 μm as in the first embodiment. However, as a configuration suitable for a contact-type measuring instrument, the height of each discontinuous portion is 10 μm. It is desirable to set it above.

  Further, in each of the above-described embodiments, the configuration in which one discontinuous portion is provided in the central portion and the peripheral portion of the optically effective surface has been described. However, the number of discontinuous portions and the positions where the discontinuous portions are provided are in this configuration. It is not limited to. In other words, if the configuration has discontinuous portions at at least two locations on the optical effective surface, it is possible to measure the position of the optical effective surface in the rotational direction of the aspherical optical element.

  In addition, in steps S401 and S601 shown in FIGS. 4 and 6, each of the piece processing steps for forming the optically effective surface, the discontinuous portion, and the abutting portion may be performed in a reversed order. Furthermore, after an aspherical optical element is injection-molded in steps S402 and S602, the order of the measurement steps (steps S403 to S405 and steps S603 to S606) may be changed.

  The aspherical optical element according to each of the embodiments described above is a reflective optical element having an optically effective surface that is a reflective surface. However, the present invention is not limited to this, and the present invention is applied to a transmissive aspherical optical element. May be applied. In other words, in an aspherical optical element having an optically effective surface that is an aspherical surface as a transmitting surface (refractive surface), a plurality of discontinuous portions are provided on the optically effective surface, whereby the same method as in the above-described embodiments. The shape and position of the optically effective surface can be measured.

[Image reading device]
The aspherical optical elements according to the above-described embodiments may be applied to an imaging optical system provided in the image reading apparatus. That is, it is possible to configure an image reading apparatus including the imaging optical system having the aspherical optical element described above and a plurality of light receiving units. Here, when the aspherical optical element is incorporated into the imaging optical system, the position of the optically effective surface is measured by the method as described above, whereby highly accurate positioning can be performed. For example, a line sensor such as a CCD sensor or a CMOS sensor can be used as the plurality of light receiving units. In this configuration, the document is irradiated by illumination means including a light source, a plurality of light beams (reflected light or transmitted light) from the document are condensed by the imaging optical system, and received by the sensor surfaces of the plurality of light receiving units. be able to. Then, the original can be sequentially read by moving the relative position between the original and the imaging optical system by the driving unit.

100 Aspherical optical element 101 Optical effective surface 102, 103 Discontinuous portion

Claims (12)

An optically effective surface formed of a non-rotationally symmetric aspherical surface, and a plurality of convex portions or a plurality of concave portions provided on the surface of the optically effective surface,
An aspherical optical element characterized in that the optically effective surface has a continuous shape except for the portions provided with the plurality of convex portions or the plurality of concave portions.   The aspherical optical element according to claim 1, wherein one of the plurality of convex portions or the plurality of concave portions is provided at a central portion of the optically effective surface.   The aspherical optical element according to claim 1, further comprising a butting portion for positioning the aspherical optical element.   4. The aspherical optical element according to claim 1, wherein an area of each of the plurality of convex portions or the plurality of concave portions is 1% or less of an area of the optical effective surface. 5.   5. An imaging optical system having the aspherical optical element according to claim 1, illumination means for irradiating a document, and a light beam from the document collected by the imaging optical system is received. An image reading apparatus comprising: a plurality of light receiving units configured to move; and a driving unit configured to move a relative position between the imaging optical system and the document. A first step of manufacturing a mold, comprising: forming a non-rotationally symmetric aspherical surface with respect to a piece; and forming a plurality of concave or convex portions in a region of the piece where the aspherical surface is formed. When,
Second step of injection-molding an aspherical optical element having an optically effective surface formed of the aspherical surface and a plurality of convex portions or a plurality of concave portions provided on the surface of the optically effective surface by the mold. And having
In the first step, the aspherical surface is formed so that a portion other than a portion where the plurality of concave portions or convex portions are formed has a continuous shape.   A third step of measuring the position of the aspherical optical element or the optically effective surface in the rotational direction about the optical axis direction based on the positional relationship between the plurality of convex portions or the plurality of concave portions. The method for manufacturing an aspherical optical element according to claim 6. In the first step, one of the plurality of concave portions or the plurality of convex portions to be formed on the piece is formed at a central portion of a region where the aspheric surface of the piece is formed,
The method for manufacturing an aspherical optical element according to claim 6 or 7, wherein, in the second step, one convex portion or concave portion provided at a central portion of the optically effective surface is injection-molded.   The aspherical optical system according to claim 8, further comprising a fourth step of determining a surface vertex of the optical effective surface based on one convex portion or a concave portion provided at a central portion of the optical effective surface. Device manufacturing method.   Of the plurality of convex portions or the plurality of concave portions, based on the positional relationship between one convex portion or the concave portion provided at the center of the optical effective surface and the other convex portion or the concave portion, The method for manufacturing an aspherical optical element according to claim 9, further comprising a fifth step of measuring the length or the amount of eccentricity. The first step includes a step of forming a concave portion or a convex portion in a portion other than a region where the aspherical surface is formed on the same surface of the piece,
11. The method for manufacturing an aspheric optical element according to claim 6, wherein, in the second step, an abutting portion for positioning the aspheric optical element is injection-molded. 11. .   The method according to claim 11, further comprising a sixth step of measuring an amount of eccentricity of the optically effective surface based on a positional relationship between the plurality of convex portions or a plurality of concave portions and the abutting portion. Manufacturing method of spherical optical element.

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