JP4767255B2 - Measuring method of optical axis eccentricity of front and back surfaces of lens - Google Patents

Description

  The present invention particularly relates to a method for measuring the optical axis eccentricity of front and back surfaces of an aspheric lens.

  Many aspheric lenses are mass-produced by a molding technique using a mold. A lens having both surfaces of a sphere-plane or a sphere-sphere has a rotationally symmetric shape with respect to the normal vector at any point on any surface, so that it is rotationally symmetric around any surface. There is an axis that becomes and becomes the optical axis. However, since an aspherical lens has only one rotationally symmetric axis, an aspherical-aspherical or spherical-aspherical lens must be processed so that the rotationally symmetric axes on both sides coincide with each other during molding. Therefore, in order to improve processing accuracy, it is indispensable to quantitatively measure the eccentricity of the aspheric lens.

  According to a molding technique using a mold, the eccentricity of the optical axis can be suppressed to an accuracy of several tens of micrometers. Conventionally, the decentration measurement of the aspherical lens is performed by optically evaluating the shake of the focus image with respect to the outer periphery using an autocollimator as disclosed in Japanese Patent Application Laid-Open No. 5-340838. It has been broken.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in such a conventional method using an autocollimator, the shape error cannot be quantitatively evaluated, so that the processing of the mold cannot be corrected from the obtained result. In addition, according to the recent trend toward downsizing and increasing the NA of aspherical lenses, an allowable eccentricity level of several micrometers or less is required, and the method using an autocollimator cannot cope with accuracy. Therefore, the surface shape of the aspheric lens is actually precisely measured, and the optical axis centers and inclinations of the front and back surfaces of the aspheric lens are obtained from the obtained shape data, and the relative eccentricity of both surfaces is less than a micrometer. There is a need to determine quantitatively at the level.

  The present invention has been made by paying attention to such a conventional technique. By accurately measuring the shape of the front and back surfaces of the aspherical lens, the relative eccentricity of both surfaces of the aspherical lens can be measured in micrometers. It is possible to provide a measurement method that can be obtained quantitatively at a level.

According to the first technical aspect of the present invention, there is provided a method for measuring the amount of optical axis eccentricity on both the front and back surfaces of an aspherical lens on a holder having three or more reference points fixed to each other. Fixing the position of an aspheric lens having a second surface and measuring the one-dimensional surface shape of the first surface at a predetermined pitch in the first direction and the second direction of the holder with respect to the first surface Measuring the first position of the reference point on the first surface side at the position of the holder when measuring the one-dimensional surface shape of the first surface, with respect to the second surface , Measuring the one-dimensional surface shape of the second surface at a predetermined pitch in the first direction and the second direction of the holder, and the position of the holder when measuring the one-dimensional surface shape of the second surface 2nd position of the reference point on the second surface side Measuring, and based on the measured first position and second position, the surface shape of the first surface of the aspheric lens and the surface shape of the second surface of the aspheric lens are the same three-dimensional The surface shape of the first surface and the surface shape of the second surface are aspherically fitted with a predetermined surface shape by describing in the coordinate system, and the optical axis deviation is determined from the vertex position and the inclination of the optical axis at the best fitting. see containing and calculating the core volume, measuring the first and second positions of the reference point, the first direction and the illumination light transmitted through the pinhole of each said reference point Taking an image from a third direction orthogonal to the direction of 2 through the optical system, measuring the position of the pinhole in the first direction and the second direction, and focusing on the pinhole of the optical system Based on the alignment position And measuring the position of the third direction of the serial reference point and said free Mukoto.

According to the second technical feature of the present invention, the method of measuring the optical axis eccentricity on both the front and back surfaces of the aspherical lens includes a first reference point, a second reference point, and a third reference point that are fixed to each other. And a holder having a fourth reference point, wherein the first reference point and the second reference point are arranged along a first direction, and the third reference point and the fourth reference point are the first reference point. One arranged along a second direction orthogonal to one direction, fixing an aspherical lens having a first surface and a second surface to the holder, and each reference point on the first surface side Detecting a first position of the first surface, setting a common reference coordinate based on the first direction and the second direction, and detecting a first vertex position of the first surface by the common reference coordinate Describing and detecting the first vertex position of the first surface by the reference coordinates Describing, reversing the holder, detecting a second position of each reference point on the second surface side, associating it with the common reference coordinates, and second of the second surface and it detects the vertex positions described in association with the reference coordinate, looking contains and calculating the amount of eccentricity from said first vertex position and a second vertex positions, a first of said reference point Measuring the position and the second position means that the illumination light transmitted through the pinhole at each reference point is imaged through an optical system from a third direction orthogonal to the first direction and the second direction. Measuring the position of the pinhole in the first direction and the second direction, and determining the position of the reference point in the third direction based on the focus position of the optical system with respect to the pinhole. and measuring characterized by containing Mukoto.

FIG. 1 is a schematic diagram showing the structure of a laser probe type non-contact three-dimensional measuring apparatus for measuring an aspheric lens. FIG. 2 is a perspective view showing a lens holder holding an aspheric lens. 3 is a cross-sectional view taken along the line SA-SA in FIG. FIG. 4 is an enlarged cross-sectional view of an aspheric lens. FIG. 5 is a plan view of an aspheric lens. FIG. 6 is a cross-sectional view of the lens holder showing the measurement state of the aspheric lens surface. FIG. 7 shows the detection of the apex of the aspheric lens surface. FIG. 8 is an enlarged cross-sectional view showing the inclination of the optical axis of the aspheric lens. FIG. 9 is a perspective view showing a lens holder that holds an aspheric lens according to the second embodiment. FIG. 10 shows the measurement of the surface of the aspheric lens according to the second embodiment. FIG. 11 shows vertex detection on the surface of an aspheric lens according to the second embodiment. FIG. 12 illustrates vertex detection on the surface of an aspheric lens according to a modified embodiment.

  Embodiments of a switching power supply apparatus according to the present invention will be described below in detail with reference to the drawings.

  The present invention provides a measurement method capable of quantitatively determining the relative eccentricity of both surfaces of an aspheric lens at a level of micrometer or less by precisely measuring the shape of the front and back surfaces of the aspheric lens. be able to. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Example 1
1-7 is a figure which shows one Example of this invention. FIG. 1 is a diagram showing the structure of a laser probe type shape measuring instrument according to this embodiment. In FIG. 1, X and Y are two directions orthogonal on a horizontal plane, and Z is a vertical direction. FIG. 1 is also schematically illustrated.

<Common reference point and common reference plane>
The aspherical lens 1 to be measured has a front surface (first surface) 1a and a back surface (second surface) 1b and is formed in an aspheric shape. The aspherical lens 1 is held by a lens holder 2 made of a metal having a constant thickness and a low coefficient of thermal expansion. The lens holder 2 is further positioned by a reference pin 21 fixed to a jig such as a scanner. A holding hole 3 is formed at the center of the lens holder 2. The holding hole 3 is formed with a recess 4 corresponding to the diameter of the aspheric lens 1 and is fixed by a ring cap 5 with the periphery of the aspheric lens 1 placed on the bottom thereof.

  As shown in FIGS. 2 and 3, pinholes 6 as “common reference points” are formed at three positions of the lens holder 2 so as to pass through the lens holder 2 from the front surface 1 a to the back surface 1 b, and thus the common reference surface Sc. Is stipulated. The pinhole 6 can be easily formed, and the three-dimensional position can be easily detected by image processing. That is, each pinhole is fixed to each other and formed in the lens holder, and the light transmitted through the pinhole 6 is detected by the two-dimensional imaging device via the optical system, and each pinhole is detected from the acquired two-dimensional image. 6 is detected in the horizontal plane direction. Also, the vertical position of each pinhole can be detected from the focal position of the objective optical system. As a result, the three-dimensional position of the pinhole 6 can be measured. The size of each pinhole is, for example, about 10 μm in diameter and length. With the above method, the first reference coordinates can be defined on the three-dimensional space from the position of each pinhole. Since the aspherical lens as the lens to be measured is fixed to the lens holder, the position of the aspherical lens is fixed to the common reference point 6. Therefore, the measurement result of the three-dimensional measurement of the aspheric lens surface described later can be described by the first reference coordinates. Further, the lens holder is turned over to measure the three-dimensional position of each pinhole in the same manner to define the second reference coordinate, and the result of the three-dimensional measurement of the surface of the opposite surface of the aspherical lens is expressed by the second reference coordinate. Can be described.

  In this case, the same pinhole can be used for both position detection on the first surface (front surface) and the second surface (back surface). Accordingly, since the second reference coordinates corresponding to the first reference coordinates are coordinates relating to the same point, the three-dimensional measurement data on both surfaces of the aspheric lens is described by the same three-dimensional coordinate system (X, Y, Z). It becomes possible to do. In addition, you may use the laser probe method mentioned later for the position detection of a perpendicular direction.

<Three-dimensional measurement of lens surface by laser probe method>
The lens holder 2 is set on the scan stage 7 that moves precisely in the XY directions with the front surface 1a or the back surface 1b facing up. The semiconductor laser beam L from the laser irradiation device 8 is irradiated to the front surface 1a and the back surface 1b of the aspherical lens 1 held by the lens holder 2 through an autofocus optical system.

  Specifically, the semiconductor laser beam L from the laser-irradiating device 8 is reflected through the mirror 9 and irradiated onto the aspherical lens 1, for example, the surface 1 a through the objective lens 10. The laser beam L applied to the aspherical lens 1 is a beam that does not substantially spread only on the optical axis L. The laser beam L passes through a position away from the optical axis L0 of the objective lens 10 in a plane parallel to the ZY plane, and enters the aspherical lens obliquely (non-parallel to the optical axis L0). The laser beam L intersects with the optical axis L0 of the objective lens in the focal plane of the objective lens 10 in the absence of an obstacle. Accordingly, since the laser beam L is irradiated obliquely to one point on the surface 1a of the aspherical lens 1, triangulation is possible if the position of that point in the XY plane (horizontal plane in the figure) can be detected. The position in the Z direction (height in the figure) can be measured by the principle of. That is, if one point (reflection point) on the surface of the object to be measured irradiated with the laser beam L is at the focal position of the objective lens 10, the one point is on the optical axis L0 of the objective lens and is shifted from the focal position. If there is, the position of one point is shifted in the Y direction accordingly. Therefore, the deviation of the surface of the object to be measured from the focal position can be detected by converting the surface position in the Z direction into the position of the reflection point in the Y direction. Such a laser beam L is a so-called “laser probe”.

  The laser beam L irradiated to one point of the aspherical lens 1 is scattered and reflected there, and a part of the component L ′ passes through the objective lens 10 again and is reflected by the two mirrors 9 and 11 to form an imaging lens. 12 to the optical position detection device 13. The optical position detector 13 includes a photodetector that detects the position of the optical center of gravity, and the position of the center 13 s of the photodetector corresponds to the focal plane position of the objective lens 10. The scattered / reflected component L 'is a light beam that normally spreads, but is represented by reflected light in the figure.

  The objective lens 10, the imaging lens 12, the optical position detection device 13, the servo mechanism 14, and the like constitute an autofocus optical system. That is, when the reflected light L ′ from the surface of the aspherical lens deviates from the center 13s of the optical position detection device 13, the servo mechanism 14 moves the objective lens 10 in the focus direction (Z direction) in order to correct the deviation. The autofocus is realized by feedback control so that it is moved to. As a result, the height dimension of the front surface 1a or the back surface 1b of the aspherical lens 1 can be measured from the amount of movement of the objective lens 10 in the optical axis direction (Z axis).

  By scanning the scan stage 7 in the X direction and the Y direction with respect to the laser beam L or the objective lens 10, the laser beam L is irradiated and reflected on the surface 1a including the apex Pa of the aspherical lens 1 in the YZ plane. Is done.

  The mirror 9 is a half mirror, and an entire image of the lens holder 2 can be taken by a two-dimensional imaging device (CCD camera) 16 through the mirror 9 and the imaging lens 15. An image processing unit 17 and a monitor 18 are connected to the two-dimensional imaging device 16. The image processing unit 17 is also connected to the servo mechanism 14, and recognizes the three pinholes 6 set in the lens holder 2 from the image on the surface of the lens holder 2, and measures the three-dimensional position thereof. be able to.

  Next, an actual measurement procedure will be described with reference to FIGS. First, with the surface 1a of the aspheric lens 1 facing upward, the lens holder 2 is set on the scan stage 7, and the scan stage 7 is scanned in the X direction to include the apex Pa of the surface 1a of the aspheric lens 1 The cross-sectional shape on the X axis is measured (the cross-sectional shape can be measured with an accuracy of micrometer or less). The cross-sectional shape measurement by scanning in the X direction is repeated with a predetermined pitch movement in the Y direction.

  Next, in the same manner, the scanning in the Y direction is repeated while moving the scanning stage 7 by a predetermined pitch in the X direction, and the one-dimensional sectional shape on the Y axis including the vertex Pa of the surface 1a of the aspherical lens 1 is measured. To do. This is equivalent to the scanning measurement by the laser probe L relative to the aspherical lens to be measured as shown in FIG.

  Finally, the three-dimensional positions of the three pinholes 6 in the lens holder 2 are calculated by the image processing unit 17 from the image obtained by the CCD camera 16 and the amount of movement of the objective lens 10 in the focusing direction. Ask.

  Next, with the lens holder 2 turned upside down and with the back surface 1b of the aspheric lens 1 facing up, the X axis and Y axis including the apex Pb of the back surface 1b of the aspheric lens 1 are the same as described above. Measure the cross-sectional shape. Further, the three-dimensional positions of the three pinholes 6 with the lens holder 2 on the back side are obtained by calculation by the image processing unit 17 from the images obtained by the CCD camera 16 in the same manner.

<Aspherical fitting>
The shape measurement data of the front surface 1a and the back surface 1b of the aspheric lens 1 obtained as described above is obtained by inverting the Z-axis coordinate system in the XY coordinate system determined based on the three-dimensional position of the pinhole 6. It can be handled as data in the same coordinate system.

Therefore, in the common XY coordinate system, the measured aspheric shape is fitted to a complete aspheric shape obtained by a calculation formula. The aspheric shape is generally represented by the following aspheric expression.

  Here, C is a curvature of C = 1 / R where R is a radius of curvature, k is a conic constant, and Ai is an aspherical coefficient (i = 1, 2,...).

  If the design value of the lens to be measured is known, the surface shape can be measured, and the vertex position and the inclination of the optical axis can be obtained by fitting the above equation using the least square method or the like. In the fitting, a point where the error curve is symmetric with respect to the Z axis is searched.

  First, when the surface shape is measured by scanning in the y direction in FIG. 7A, the surface shape for the cross sections S2 and S3 that generally do not pass through the apex of the aspheric surface is obtained. Since it is a cross-section of the surface shape targeted for the axis, as shown in FIG. 7B, a common symmetry axis Ls also exists in the cross-sections S2 and S3, and a plane perpendicular to the y-axis and passing through the symmetry axis Ls passes through the optical axis Sa. . Therefore, a cross-sectional shape in the x-axis direction passing through the apex Pa can be obtained by scanning in the x-direction along a plane including the optical axis Sa and the symmetry axis Ls that are aspherical symmetry axes. The cross-sectional shape in the y-axis direction can be obtained in the same manner. The same applies to the cross-sectional shape measurement of the back surface (second surface) 1b.

  By the above operation, the angle deviation (θx, θy) between the optical axes Sa and Sb and the position deviation (D) between the vertices Pa and Pb from the vertices Pa and Pb and the optical axes Sa and Sb at the best fitting. Can be obtained quantitatively with an accuracy of micrometer or less. Note that the inclination of the optical axis Sb in FIG. 8 is exaggerated. Actually, it is so small that it cannot be illustrated.

  According to the present embodiment, the amount of eccentricity related to the obtained angular deviation (θx, θy) or positional deviation (D) is fed back to the design of the mold for manufacturing the aspherical lens 1, and more complete. A mold capable of forming such an aspheric lens 1 can be manufactured.

Example 2
In the optical axis eccentricity measuring apparatus according to the second embodiment of the present invention, the shape measuring instrument using the laser probe method and the operation thereof are the same as those in the first embodiment, so the description of common parts is omitted.

  The lens holder 22 according to the present embodiment has four common reference points as shown in FIG. 9, and is arranged so that the reference points 6b and 6d are orthogonal to the arrangement direction of the two reference points 6a and 6c.

  From the three-dimensional position measurement of the reference points 6b and 6d, the x axis passing through these two points is defined, and from the three-dimensional position measurement of the reference points 6a and 6c, the y axis passing through these two points and orthogonal to the x axis is defined. A position is described by an orthogonal coordinate system (x, y, z) by defining a z-axis orthogonal to. A virtual plane defined by the x axis and the y axis is the common reference plane Sc. By setting the orthogonal coordinate system with such a common reference point 6, the position can be described in the same reference coordinate system even if the lens and the lens holder are turned over. For example, when the lens and the lens holder are turned around the x axis, the positions of the reference points 6b and 6d are not changed, and the positions of the reference points 6a and 6c are completely exchanged, so that the positions can be easily associated.

<Detection of vertex position>
In this embodiment, the amount of eccentricity is estimated based on the apex position of the aspherical lens. In an aspheric lens, there is only one vertex that is an axis target, so that the vertex position can be specified, and the position of the optical axis can be specified from the vertex position. Also, due to recent improvements in mold processing technology, the deviation of the angle of the optical axis on both sides of the aspherical lens is often improved to the extent that it does not interfere with the eccentricity measurement. Since the amount of eccentricity can be calculated based on each vertex position, more rapid measurement is possible.

  In FIG. 10, a temporary center point P 'is set in the vicinity of the actual vertex P0, and one-dimensional shape measurement (cross-sectional shape measurement) is performed in the x-axis direction and the y-axis direction, respectively. Assuming that the coordinate system obtained by projecting the temporary center point P ′ onto the common reference plane is (x ′, y ′), as shown in FIG. 11, x ′ = Δx in the cross-sectional shape in the x-axis direction and y-axis direction An apparent vertex is found at the position of y ′ = Δy in the cross-sectional shape. Therefore, the position (Δx, Δy) of the vertex projected from the vertex position on each axis to the reference plane is specified. If the temporary center point P ′ is far from the actual vertex, the above operation is repeated to converge to the actual vertex and measure the vertex position with higher accuracy.

  By performing the above operation on both the first surface and the second surface of the aspherical lens, the amount of eccentricity can be calculated from the deviation of the apex position in the reference surface.

<Modified Example>
When the aspherical part and the flange part of the aspherical lens are processed simultaneously, these boundary lines are concentric with the optical axis of the aspherical lens. Therefore, by detecting the boundary line between the aspheric surface portion and the flange portion on both surfaces of the aspheric lens, the center position of the concentric circle in the reference surface can be obtained as the projected position of the vertex.
As shown in FIG. 12, a temporary center point is set in the vicinity of the center of the actual concentric circle C0, and a two-dimensional image in a region e1 including a point separated from the temporary center point by a designed radius is acquired, and the image The edge position 31 in the concentric circle is detected from the luminance change (spatial differentiation) and the position is read. In the other regions e2 and e3, the coordinates of the center C0 of the concentric circle can be obtained by performing edge detection in the same manner. Edge detection is performed in three or more areas.
Since the coordinates of the center C0 correspond to the vertex position of the aspheric lens, the eccentricity can be calculated from the deviation of the vertex position within the common reference plane by performing the above operation on both surfaces of the aspheric lens.

Advantageous Effects of Invention According to the first technical aspect of the present invention, the relative eccentricity between the front and back surfaces of an aspheric lens can be quantitatively determined with an accuracy smaller than a micrometer. As a result, the obtained eccentricity can be fed back to the design of the mold for manufacturing the aspherical lens, and a mold capable of forming a more complete aspherical lens can be manufactured.

  According to the second technical aspect of the present invention, the relative eccentricity between the front and back surfaces of the aspherical lens is determined by quickly detecting the apex of the surface shape. Therefore, it is possible to promptly feed back to the mold design for manufacturing the aspherical lens.

Industrial Applicability In the above embodiments, the pinhole 6 is taken as an example as a common reference point, but is not limited thereto. Moreover, although the example which measures the three-dimensional position of the pinhole 6 by image processing was shown, you may detect using the laser probe for measuring the aspherical lens 1.

(US designation)
This application relates to the designation of the United States, and the benefit of priority under Japanese Patent Application No. 119 (a) for Japanese Patent Application No. 2005-228760 (filed on Aug. 5, 2005) filed on Aug. 5, 2005. Is used to cite the disclosure.

Claims (6)

A method for measuring the amount of eccentricity of the optical axis on both front and back surfaces of an aspheric lens
Positioning an aspherical lens having a first surface and a second surface on a holder having three or more reference points fixed to each other;
Measuring a one-dimensional surface shape of the first surface at a predetermined pitch in each of the first direction and the second direction of the holder with respect to the first surface;
Measuring the first position of the reference point on the first surface side at the position of the holder when measuring the one-dimensional surface shape of the first surface;
Measuring the one-dimensional surface shape of the second surface at a predetermined pitch in each of the first direction and the second direction of the holder with respect to the second surface;
Measuring the second position of the reference point on the second surface side at the position of the holder when measuring the one-dimensional surface shape of the second surface;
Based on the measured first position and second position, the surface shape of the first surface of the aspheric lens and the surface shape of the second surface of the aspheric lens are described in the same three-dimensional coordinate system. And
Fitting the surface shape of the first surface and the surface shape of the second surface with a predetermined surface shape, and calculating the amount of eccentricity of the optical axis from the vertex position and the inclination of the optical axis at the best fitting. See
Measuring the first position and the second position of the reference point;
Illumination light transmitted through the pinhole at each reference point is imaged through an optical system from a third direction (Z-axis) orthogonal to the first direction and the second direction, and the first direction and the first direction Measuring the position of the pinhole in two directions;
Measuring wherein the containing Mukoto and measuring the position of the third direction of the reference point based on the position of the focus about the pin hole of the optical system. Measuring the one-dimensional surface shape of the first surface includes
Measuring a one-dimensional surface shape of the first surface in the first direction to detect a first vertex position;
Measuring a one-dimensional surface shape of the first surface in the second direction within a virtual plane passing through the first vertex position to detect a second vertex position;
The measurement method according to claim 1, further comprising: determining a measurement position based on the first vertex position and the second vertex position.   The measuring method according to claim 1, wherein each of the reference points is a pinhole formed in the holder, and penetrates the holder from the first surface side to the second surface side. A method for measuring the amount of eccentricity of the optical axis on both front and back surfaces of an aspheric lens
Providing a holder having a first reference point (6b), a second reference point (6d), a third reference point (6a), and a fourth reference point (6c) fixed to each other; The first reference point and the second reference point are arranged along a first direction (x-axis), and the third reference point and the fourth reference point are a second direction (y-axis) orthogonal to the first direction. And those arranged along
Fixing an aspherical lens having a first surface (1a) and a second surface (1b) to the holder;
Detecting a first position of each reference point on the first surface side, and setting common reference coordinates based on the first direction and the second direction;
Detecting the first vertex position of the first surface and describing it by the common reference coordinates;
Inverting the holder;
Detecting a second position of each reference point on the second surface side and associating it with the common reference coordinates;
Detecting and describing the second vertex position of the second surface in association with the common reference coordinates;
Calculating an amount of eccentricity from the first vertex position and the second vertex position,
Measuring the first position and the second position of the reference point;
Illumination light transmitted through the pinholes at the respective reference points is imaged via an optical system from a third direction orthogonal to the first direction and the second direction, and the illumination light is transmitted in the first direction and the second direction. Measuring the position of the pinhole;
Measuring wherein the containing Mukoto and measuring the position of the third direction of the reference point based on the position of the focus about the pin hole of the optical system. Detecting the first vertex position includes
Measuring a one-dimensional surface shape of the first surface in the first direction to detect a first symmetrical center position;
Measuring a one-dimensional surface shape of the first surface in the second direction to detect a second symmetrical center position;
The measurement method according to claim 4, further comprising: calculating the first vertex position from the first symmetry center position and the second symmetry center position. When the boundary with the flange portion of the aspheric lens is formed concentrically with respect to the optical axis,
5. The measurement method according to claim 4, wherein detecting the first vertex position detects the concentric boundary, and obtains the first vertex position from a center position of the concentric circle. 6.

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