JPH06174430A - Center thickness measuring method and device used for it - Google Patents

Abstract

PURPOSE:To measure the center thickness of a lens with high precision not to injure the lens. CONSTITUTION:The apex of the first plane 40a of a lens 40 to be measured is matched with the convergence point P1 of the measuring light by a condensing lens 51 to set the first state. The optical axis of the measurement light in the first state is matched with the optical axis of the lens 40, the apex of the second plane 40b of the lens 40 is matched with the convergence point P2 of the measuring light by a condensing lens 52 to set the second state. The distance between the convergence points P1, P2 in the first state and the second state or the distance that the lens 40 is moved to set the first state and the second state is measured along the optical axis direction of the measuring light to obtain the center thickness of the lens 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact method for measuring the center thickness of a lens such as an optical lens and a device used therefor.

[0002]

2. Description of the Related Art Generally, the outer diameter of a lens is machined (centering) by rotating the optical axis of the lens (the straight line connecting the spherical centers of the first and second surfaces of the lens) and the centering device. It is performed in a state where the central axis is located on the same straight line. Therefore,
A center thickness measuring device for measuring the center thickness of a lens subjected to such centering (the length by which a straight line connecting the spherical centers of the first surface and the second surface of the lens crosses the lens) is The optical axis of this lens to be measured is aligned with the measuring axis of the measuring apparatus (two coaxially arranged probe axes) by installing the measuring lens) in the measuring apparatus with its outer diameter as a reference. Then, the probe is brought into contact with both sides of the lens to be measured. Then, the displacement of the probe is obtained from the position of the probe obtained by bringing these probes into contact with each other before the lens is installed and the position of the probe at the time of installing the lens (at the time of measurement) by a digital micrometer or the like. The center thickness of the measuring lens was measured.

[0003]

However, since the above-described conventional center thickness measuring device measures by contact between the probe and the lens to be measured, when the lens to be measured is elastically deformed (elastic proximity). The value was measured and measurement error was unavoidable. Further, there is a drawback that the contact portion with the probe may be left as a flaw depending on the glass type (material) of the lens to be measured. Further, when the lens to be measured is installed, since the outer diameter of the lens is used as a reference, there is a problem that an error in installation and an error in centering the lens to be measured appear as an error in measuring the center thickness. It was

The present invention aims to solve such problems.

[0005]

To achieve the above object, according to the present invention, (a) the apex of the first surface of the lens to be measured and the condensing point of the measuring light by the condensing lens are made to coincide with each other. (B) in a state where the optical axis of the measurement light in the first state and the optical axis of the lens under measurement are aligned,
Setting the second state by making the condensing point of the condensing lens of the measuring light coincide with the apex of the second surface of the lens to be measured; and (c) the first state and the second state. Along the optical axis direction of the measurement light, the distance between the condensing points of the respective measurement light in, or the distance moved by the lens to be measured for setting the first state and the second state. A center thickness measuring method for obtaining a center thickness of the lens to be measured by measuring is provided.

For that purpose, the interference lens having the interference fringe measuring means for measuring the interference fringes generated by the interference between the measurement light reflected by the lens under test and the reference light reflected by the reference surface is supported. At the same time, at least one of the supporting means for moving the lens in the optical axis direction of the measuring light and the condensing point of the lens to be measured or the measuring light is “the both measuring light when irradiated to the lens. Optical axis "
The center thickness measuring device is constituted by the moving means for moving the center thickness in the direction (claim 2).

Further, the first optical path, which is the optical path of the first measuring light emitted from one surface side of the lens to be measured, and the other surface side of the lens to be measured are irradiated to the lens. And a second optical path which is an optical path of the second measuring light, and interference caused by the interference of the measuring light traveling in each of the optical paths with the reflected light from the lens to be measured and the reference light reflected from the reference surface. An interference fringe measuring unit for measuring fringes, and an interference unit configured so that the optical axes of the both measurement lights when irradiated to the measured lens are supported together with the measured lens. "Irradiating the lens, at least one of support means for moving the lens in the direction of the" optical axes of the two measuring lights when irradiated to the lens "and at least one of the lens to be measured and the converging point of the measuring light. In the direction of the “optical axis of both measuring light beams” To constitute a center thickness measuring device and moving means for moving (claim 3).

[0008]

The present invention utilizes the image forming action of the collimating lens (condensing lens) on the measurement light side of the optical system that constitutes the interferometer to determine each measurement point on both sides of the lens to be measured. In that state, the center thickness is measured by detecting the interference fringes of the measurement light and the reference light with the optical axis of the measurement light of the interferometer as a reference. Therefore, the center thickness of the lens to be measured can be measured with high accuracy without contact.

The measuring principle of the present invention will be described with reference to FIG. Although FIG. 1 uses a Fizeau interferometer as an interferometer, the principle is exactly the same even if a Twyman-Green interferometer is used. In FIG. 1A, the first measurement light optical path and the second measurement light optical path are arranged so that the optical axes 11 of the measurement lights 12 traveling in the respective optical paths are aligned with each other. Measuring light 12 by means of light collecting means 51 and 52 (in this case also serving as a Fizeau lens) installed at
These condensing means 51, 5 so that the condensing points P of
The two installation positions are set respectively. This sets the zero reference. In practice, two sets of (Fizeau) interferometers may be used, and both interferometers may be arranged so that the optical axes of the measuring light beams in each interferometer may coincide with each other. Alternatively, one may be divided into two, and one may be guided to the first measurement light optical path and the other to the second measurement light optical path.
In the latter case, when measuring the center thickness, it is preferable to provide a switching means for guiding the measuring light to a desired measuring light optical path, and to appropriately switch the measuring light path by this switching means.

In this state, the interference fringes output by the interferometer are mainly "the Fizeau surface (reference surface) 51a of the Fizeau lens (referred to as 51) which is a condensing means installed on one measurement light optical path. It is an interference fringe generated between the "reflected light" and "the light reflected by the Fizeau surface (reference surface) 52a of the Fizeau lens 52 installed on the other measurement light optical path". Since the surface accuracy of the Fizeau surface (reference surface) is normally maintained at a sphericity of RMS 0.02λ (λ = 0.633 μm) or less, the interference state here is a so-called “stripe color” state. .

In FIG. 1 (b), a lens 40 to be measured is arranged between the both condensing means (Fizeau lens), and the apex of the first surface 40a of the lens 40 to be measured is connected to one measuring optical path. The state (cat's eye reflection state) of focusing on the converging point P ₁ of the measuring light 12a which progresses is shown. At this time, the interference fringes obtained by the interferometer were reflected by the measurement light 12a reflected at the apex (cat's-eye reflection) and the Fizeau surface 51a of the Fizeau lens 51 collecting the measurement light prior to the apex reflection. It is formed by interference with the reference light, and they interfere with each other with respect to the optical axis 11 of the measurement light while being shifted by 180 °. Therefore, the passing positions of the optical elements forming the interferometer are different between the forward path and the return path of the measurement light optical path, and the errors of these optical elements are not canceled. Therefore, it is difficult to bring the interference fringes into the “one-color stripe” state as in the zero reference. However, if the aberration of the condenser lens (Fizeau lens) is small, the interference fringes obtained by the interferometer will be in a “straight line” state, so it is easy to grasp the in-focus state of the apex and the measurement light. .

In FIG. 1 (c), the lens 40 to be measured is moved in the direction of the optical axis 11 of the measuring light, and the second surface 40 of this lens is moved.
A state in which the apex of b is focused on the condensing point P ₂ of the measurement light 12b traveling on the other measurement light optical path (cat's eye reflection state)
Indicates. At this time, if the optical axis of the lens 40 to be measured (defined by a straight line passing through the spherical centers of the first and second surfaces) coincides with the optical axis 11 of the measuring light of the interferometer, the lens to be measured 4
The movement amount S of 0 represents the center thickness of the lens 40. Then, at the time of measurement, alignment may be performed so that the optical axis of the lens 40 to be measured and the optical axis 11 of the measurement light in each measurement state ((a) to (c) of FIG. 1) match.

The method of this alignment will be described below. The first alignment method is, as shown in FIG. 2, a method of utilizing the tilt of the measured lens 40. When the lens 40 to be measured is largely inclined (θ) with respect to the optical axis 11 of the measurement light as shown in the figure, the effective measurement range by the interferometer becomes smaller than the effective range of the Fizeau surface 20a, and the A "lack" occurs in the effective range.
Therefore, by adjusting the tilt of the lens under measurement 40 while monitoring the interference fringes so as not to cause this “chipped”, the spherical center of the surface under test of the lens under measurement 40 is adjusted to the optical axis 11 of the measuring light of the interferometer. Can be located on top. When the radius of curvature of the surface to be inspected is large, the correction by the tilt is more sensitive and easier in alignment than the correction by the shift described later. Further, the identification of the “lack” becomes easier as the bf (back focus) of the Fizeau lens (condensing lens) 20 increases.

The second alignment method is to move (shift) the lens 40 to be measured in the direction orthogonal to the optical axis 11 of the measuring light, as shown in FIG. When the lens 40 to be measured is properly aligned (when the optical axis of the lens 40 and the optical axis 11 of the measuring light coincide with each other), the obtained interference fringes are in the “linear” state as described above. When the lens 40 to be measured is leftwardly or rightwardly shifted from this state in the direction orthogonal to the optical axis 11 of the measurement light, the obtained interference fringes are bent. This is due to the focus shift in the focus direction, and if the shift amount is further increased, “interference fringes” will be generated as in the case of tilting. Therefore, by utilizing this change in the state of the stripes, the spherical center of the surface to be measured of the lens to be measured can be positioned on the optical axis of the measurement light of the interferometer. The number of stripes at this time is the Fizeau lens 20.
The larger the NA (numerical aperture) of, the larger. Therefore, the condenser lens (Fizeau lens) 20 having a large NA facilitates alignment.

In the above alignment method, from the viewpoint of alignment sensitivity, b. Of the condensing lens (Fizeau lenses 51 and 52 in FIG. 1) of the interferometer used in terms of the apparatus configuration.
Both f. and NA are preferably large. In any of the alignment methods, a focus shift in the focus direction usually occurs each time the lens to be measured is moved, and therefore correction is needed as appropriate.

Further, by using the focus correction value obtained by "fringe scanning" of the interference fringes in the cat's eye reflection state, higher measurement resolution can be realized with respect to the position of the lens to be measured in the optical axis direction. It will be possible. The calculation of the position in the optical axis direction can be obtained, for example, by directly applying the relational expression between the focus correction value obtained when “fringe scanning” the interference fringes in the spherical core reflection state and the focus shift at that time. That is, when the focus shift is A (μm), the F number of the condenser lens of the interferometer is F, and the focus correction value is H (λ), the focus correction value H is obtained by the following equation.

[0017]

[Equation 1]

[0018]

Embodiment 1 FIG. 4 is a schematic view showing an embodiment of the present invention. The center thickness measuring device used in this embodiment includes an interference means, a supporting means 41 for supporting the lens 40 to be measured, a moving means 42, a moving amount detecting means 43 and a calculating means 44.

The interference means includes a light source (for example, a laser light source) 45 for emitting coherent light, a collimating lens 46,
Beam splitter 47, image pickup means (for example, CCD) 4
8, a movable mirror 49, a deflecting mirror 50, a first Fizeau lens (collimating lens) 51, and a second Fizeau lens 52. The first Fizeau lens 51 and the second Fizeau lens 52 are set to have the same bf (back focus). These first Fizeau lens 51 and second Fizeau lens 5
2 are arranged so as to face each other, and are set so that the optical axes of the measurement light passing through both Fizeau lenses coincide with each other. Then, the first surface 40a of the measured lens 40 and the second surface 40a
To irradiate each of the surfaces 40b of the
And the second measurement light optical path 53b. The measurement light traveling in each measurement light optical path is the light source 4
It can be obtained by distributing the coherent light emitted from the movable mirror 49. The movable mirror 49 is used for the drive unit 4.
9a rotates in the direction of arrow A in the figure. When the movable mirror 49 is at the position shown by the dotted line, the beam splitter 4
The light emitted from 7 is guided to the first measurement light optical path 53a, is bent at a right angle by the deflection mirror 50a, and then enters the first Fizeau lens 51. Further, when the movable mirror 49 is at the position shown by the solid line in the figure, the light emitted from the beam splitter 47 is guided to the first measurement light optical path 53a, and the deflection mirrors 50b and 50c.
After the paths are bent at right angles by the
Is incident on the Fizeau lens 52. In the configuration of FIG. 4, when the measurement light is guided to the first measurement light optical path 53a, the light transmitted through the second Fizeau lens 52 passes through the second measurement light optical path 53b and then the first measurement light optical path 53a. May interfere with the returned measurement light. Therefore, when the measurement light is guided to the first measurement light optical path 53a, the second measurement light optical path 53b is used.
It is preferable to prevent the interference by providing a light shielding plate or the like. In the following description, when the movable mirror 49 is in the position shown by the dotted line in the figure, it is called the "first state", and when it is in the position shown by the solid line, it is called the "second state".

In the interfering means having such a structure, the coherent light (hereinafter referred to as measurement light) emitted from the light source 45 is
After being collimated by the collimating lens 46,
The beam is reflected by the beam splitter 47 and the path can be bent 90 °. The "first state" in which the movable mirror 49 is at the position indicated by the dotted line
Then, the measurement light is guided to the first measurement light optical path 53a,
After the path is bent at a right angle by the deflecting mirror 50a, the light enters the first Fizeau lens 51. The measurement light emitted from the Fizeau surface 51a of the first Fizeau lens 51 is reflected by the measurement surface of the object to be measured (lens to be measured), enters again from the Fizeau surface 51a, and is reflected by the Fizeau surface 51a (reference light). Interfere with. The interference light has its path bent at a right angle by the deflecting mirror 50a, then passes through the beam splitter 47 and enters the image pickup means 48, and the interference fringes are measured by the image pickup means 48. On the other hand, in the “second state” in which the movable mirror 49 is moved to the position indicated by the solid line by the driving unit 49a, the measurement light is emitted from the second measurement light optical path 53b.
Is guided to the second Fizeau lens 52 after being bent at a right angle by the deflection mirrors 50b and 50c. Fizeau surface 52a of the second Fizeau lens 52
From the measurement surface of the object to be measured (lens to be measured), enters again from the Fizeau surface 52a, and interferes with the light (reference light) reflected by the Fizeau surface 52a. The interference light has its paths bent at right angles by the deflecting mirrors 50b and 50c, is reflected by the movable mirror 49, passes through the beam splitter 47, enters the image pickup means 48, and the interference fringes are measured by the image pickup means 48. It

The supporting means 41 includes a focus mechanism for moving the lens 40 to be measured in the optical axis 53c direction (arrow Bz direction in the figure) of the measuring light incident on the Fizeau lenses 51 and 52, and a direction orthogonal thereto (in the figure). A shift mechanism for moving the measured lens 40 in the directions of the arrows Bx and By) and an optical axis 53
and a tilt mechanism that tilts with respect to c (see FIG. 2A) (both not shown). Further, the focus mechanism, the shift mechanism, and the tilt mechanism are configured to be able to operate independently of each other.
Furthermore, when supporting the lens 40 to be measured, the lens 4
0 should be supported so that no distortion occurs.

The moving means 42 is the second Fizeau lens 5
2 and the deflection mirrors 50b and 50c are moved in the optical axis 53c direction (arrow Z direction). When moving, the optical axis of the measurement light incident on the second Fizeau lens 52 and the optical axis of the measurement light incident on the first Fizeau lens 51 are kept in agreement with each other. In this embodiment, the moving means 42 is a moving stage and this moving stage is the optical axis 53.
The second Fizeau lens 52 and the deflecting mirrors 50b, 5b are composed of a driving means for moving in the c direction (arrow X direction).
0c was placed on the moving stage. Then, the second Fizeau lens 52 and the deflection mirrors 50b and 50c installed on the moving stage are collectively moved by the driving means.

The moving amount detecting means 43 detects the moving amount of the moving means 42. The method of detecting the amount of movement is not particularly limited, and means for directly or indirectly measuring the amount of movement of the moving stage may be used.
When using an optical measuring means, as shown in FIG.
It is preferable to match the measurement axis of the measuring means with the optical axis 53c of the measurement light so as to reduce the Abbe's error, because the amount of movement can be detected more accurately.

The calculation means 44 performs correction based on the movement amount of the movement means 42 obtained by the movement amount detection means 43 to calculate the center thickness of the lens 40 to be measured.

The measurement procedure according to this embodiment will be described below. (A) First, with the lens 40 to be measured not mounted on the supporting means 41, the movable mirror 49 is set to the position indicated by the dotted line by the drive unit 49a to be in the "first state". Then, while the measuring light is introduced into the first measuring light optical path 53a by the interference means and the second Fizeau lens 52 is moved by the moving means 42, the interference fringes detected at this time are observed by the imaging means 48. Then, the time when the interference fringes are in the "one-color stripe" state is the time when the converging point of the measurement light by the first Fizeau lens 51 and the converging point of the measurement light by the second Fizeau lens 52 match. See FIG. 5 (a).
It is also possible to set the movable mirror 49 to the position indicated by the solid line by the drive unit 49a to be in the "second state", and similarly, by detecting the interference fringes, the interference fringes become the "one-color stripe" state.

The supporting means 41 is a lens 40 to be measured.
If is not placed, it is configured so as not to obstruct the path of the measurement light. In the present embodiment, the supporting means 41 itself is provided with a mechanism for moving in the lateral direction (By direction) so as to be separated from the optical path of the measuring light, but the lens 40 is laterally (direction orthogonal to the optical axis of the measuring light. ), So that the measurement light is not disturbed. (B) Next, the movable mirror 49 is set to the position shown by the dotted line to be in the “first state”, the moving means 42 is moved away from the first Fizeau lens 51, and the supporting means 41 measures the object to be measured. The lens 40 is located on the optical path of the measurement light. Then, the lens 40 is moved to the B
The interference fringe at this time is detected by the interference means while moving in the z direction. Then, the interference fringe becomes a “straight line” state, and the converging point of the measurement light by the first Fizeau lens 51 coincides with the apex of the one surface (first surface) 40 a of the lens under measurement 40 (cat's eye reflection state ( The movement of the supporting means 41 is stopped at the time when the state shown in FIG. At this time, if the actually measured range detected by the imaging means 48 matches the effective range of the predetermined Fizeau surface 51a, the optical axis of the lens 40 to be measured and the optical axis 53c of the measurement light match. ing.
If not (see FIG. 2B), alignment is performed to match the optical axis of the lens 40 and the optical axis 53c of the measurement light. The alignment method is the measured lens 4
Although the outer diameter of 9 may be used as a reference, in the present embodiment, by tilting and shifting the lens 40 to be measured by the supporting means 41, the actually measured range detected by the imaging means 48 is a predetermined Fizeau surface 51a. Enabled to match the effective range of. (C) When the measurement range and the effective range of the Fizeau surface 51a match, the movable mirror 49 is set to the position shown by the solid line to be in the "second state". Then, the second Fizeau lens 52 is moved by the moving means 42 in the optical axis direction (Bz
The interference fringe at this time is detected by the interference means while moving in the direction). Then, the interference fringe becomes a “straight line” state, and the converging point of the measurement light by the second Fizeau lens 52 coincides with the apex of the other surface (second surface) 40b of the lens 40 to be measured (cat's eye reflection state ( The movement of the moving means 42 is stopped at the time when the state shown in FIG. At this time, if the actually measured range detected by the image pickup means 48 matches the effective range of the predetermined Fizeau surface 52a, the optical axis of the lens 40 to be measured and the optical axis 53c of the measurement light match. ing.
If not (see FIG. 2B), alignment is performed by the same method as the above (B) in order to align the optical axis of the lens 40 with the optical axis 53c of the measurement light. The operations of (b) and (c) are repeated until the alignment is matched in the "first state" and the "second state" by switching the movable mirror 49, and the optical axis of the lens 40 to be measured and the measurement light are measured. The optical axis 53c of the above is substantially matched. (D) When the alignment is completed, the movement amount detection means 43 detects the movement amount of the movement means 42. The amount of movement S of the second Fizeau lens 52 in the optical axis direction (Bz direction) of the measurement light can be known from the amount of movement of the moving means 42. This movement amount S is equal to the center thickness S of the measured lens 40, so the center thickness S can be obtained from the output value of the movement amount detection means 43.

If the focusing error in the cat's eye reflection state is removed as described above, the measurement resolution is improved and the center thickness of the lens to be measured can be obtained more accurately. Therefore, in the present embodiment, the calculation means 44 having a correction calculation function is provided to correct the output value from the movement amount detection means 43 so that the center thickness of the measured lens 40 can be obtained with higher accuracy.

In the calibration method of the correction calculation function here, a reference lens whose center thickness (ST) is measured in advance with high accuracy is prepared, and the center thickness is actually measured with respect to this reference lens. Then, the difference between the output value S ′ from the movement amount detection means 43 obtained by this measurement and the ST is set as an offset value, and the arithmetic means 44 calculates the central thickness from the output value and the offset value. is there.

In addition to the above, as a calibration method, there is a method of performing a correction calculation using the focus correction value H at the time of "fringe scanning" measurement in the cat's eye reflection state. This method is a method of obtaining an offset value by using, for example, an optical component as shown in FIG. This jig 81 has a hole 82 and a λ / 30P-V
Two circular plates 83 each having a high precision plane are brought into optical contact with each other.
The procedure for correction is as follows (i) to (iv). (I) In the same manner as in (a) of the measurement procedure, FIG.
Set the state as shown in. At this time, "first state"
And the interference fringes measured by the interference means in the "second state" are in the "one-color stripe" state, but since the focusing error is included, the "fringe scanning" of the interference fringes is performed and the focus correction value is obtained. Find H _K. In this case, as described above, when the focus shift is A (μm) and the F number of each condenser lens is F, the focus correction value H _K is H _K = A (1−cos (sin ⁻¹ (1/2 /F)))/0.63
Determined by 3. (Ii) Next, as shown in FIG.
On a stage (not shown) having good straightness (may be shared with the supporting means 41) set so as to move in a direction (indicated by an arrow in FIG. 9) orthogonal to the optical axis 53c of the measurement light. The jig / tool 81 is installed. Then, after the jig 81 is aligned by the stage so that the cat's eye reflection state is obtained in the "first state", "fringe scanning" measurement is performed, and the focus correction value _HRL is obtained in the same manner as in (i). (Iii) Further, as shown in FIG. 9B, the jig 81 is moved by the stage so as to be in the cat's eye reflection state in the “second state”. After that, the “fringe scanning” measurement is performed, and the focus correction value H _RU is obtained in the same manner. (Iv) The offset value P is calculated from the obtained focus correction value. Offset value P, P = H _K - can be calculated by (H _RL + H _RU). Then, this offset value P may be offset when measuring the center thickness of the measured lens 40.

When simultaneously confirming whether the moving direction of the jig 81 is orthogonal to the optical axis direction of the measurement light of each interferometer, FIG.
It is preferable to use the jig 85 as shown in (b). This jig / tool 85 is one in which two discs 88 and 89 each having a high precision plane of about λ / 30P-V having two holes 86 and 87 are brought into optical contact with each other with each high precision plane.
The holes of the two discs are contacted so that they partially overlap each other. With this jig 85, the direction of arrow V in the figure and the moving direction of the stage are made to coincide with each other, and the same measurement as described above as shown in FIG. 10 is performed. Then, after confirming the orthogonality, the slide range is reduced and the work of (i) to (iv) is performed.

In the center thickness measuring device used in this embodiment, the measuring light emitted from one light source is moved by the movable mirror 49.
By switching by switching between "first state" and "second state"
However, two sets of interference means may be provided so as to individually measure the interference fringes in each state. Further, the supporting means 41 is convenient for measurement when it is configured to tilt and rotate the lens 40 with at least one apex of the measured lens 40 as a rotation center.

[0032]

Second Embodiment FIG. 6 is a schematic diagram showing a second embodiment of the present invention. In this embodiment, the movement amount detecting means 43 of the first embodiment is used.
Instead of, the reference lens 61 whose center thickness is known (ST) is used, and the center thickness S of the measured lens 40 is comparatively measured. The device used for the measurement may have a configuration in which the movement amount detecting means 43 and the computing means 44 are removed from the configuration of the device shown in FIG. 4 used in the first embodiment. In this embodiment, the difference in center thickness between the reference lens 61 and the lens 40 to be measured is set within a range in which analysis by the "fringe scanning" described in [Operation] is possible. Further, if a true sphere as shown in the figure is used as the reference lens 61, the alignment becomes easy.

The measurement procedure according to this embodiment will be described below. (A) First, the movable mirror 49 is set to the position shown by the dotted line to be in the "first state", and the reference lens 61 mounted on the supporting means 41 is positioned on the optical path of the measurement light. Then, while moving the reference lens 61 in the Bz direction by the support means 41, the interference fringes at this time are detected by the interference means. Then, when the interference fringe becomes a “straight line” state and the converging point of the measurement light by the first Fizeau lens 51 coincides with the apex of the reference lens 61 and becomes a cat's eye reflection state (see FIG. 6A). The movement of the support means 41 is stopped by. Further, so that the actually measured range detected by the image pickup means 48 matches the effective range of the predetermined Fizeau surface 51a (so that the optical axis of the reference lens 61 and the optical axis 53c of the measurement light match). Perform alignment. The alignment is performed in Example 1.
The same method as described in (b) of was used. (B) Next, the movable mirror 49 is set to the position shown by the solid line to be in the "second state". Then, the second Fizeau lens 52 is moved by the moving means 42 in the optical axis direction (Bz
The interference fringe at this time is detected by the interference means while moving in the direction). Then, the movement of the moving means 42 is stopped when the interference fringes become a “straight line” state and the converging point of the measurement light by the second Fizeau lens 52 is in the cat's eye reflection state in which it coincides with the apex of the reference lens 61. . Further, so that the actually measured range detected by the imaging means 48 matches the effective range of the predetermined Fizeau surface 51a (so that the optical axis of the reference lens 61 and the optical axis 53c of the measurement light match). Perform alignment. The alignment is performed in Example 1.
The same method as described in (b) of was used. (C) In each of the “first state” and the “second state”, “stripe scanning” is performed to obtain the focus correction values H _RL and H _RU . (D) Next, the reference lens 61 is removed from the supporting means 41 without moving the Fizeau lenses 51 and 52, and the lens 40 to be measured is placed instead. Then, the alignment is performed as described above. (E) Further, in each of the “first state” and the “second state”, by performing “fringe scanning”,
The respective focus correction values H _WL and H _WU are obtained. (F) Then, calculation means (not shown) (calculation means 4 in FIG. 4)
4 may be used), and the center thickness S of the lens 40 to be measured is calculated from the following equation.

[0034]

[Equation 2]

In this embodiment, it is not necessary to calibrate the error due to the focus correction value described in the first embodiment, and the measurement work is simplified. Further, since the moving amount detecting means is not required, there is an advantage that the structure of the device is simplified. Furthermore, when performing measurements on multiple lots of the same shape, it is sufficient to select one master as a reference lens and measure the center thickness of the master lens with high accuracy with another measuring device, which improves efficiency. .

[0036]

Third Embodiment FIG. 11 is a schematic configuration diagram of a measuring apparatus used in the third embodiment of the present invention. Note that, in FIG. 11, components having the same functions as those in FIG. 4 are denoted by the same reference numerals, and the description thereof will be appropriately omitted. In this embodiment, the center thickness S of the lens 40 to be measured is comparatively measured by using the reference lens 61 whose center thickness is known (denoted as ST).

The measurement procedure according to this embodiment will be described below.
It (A) First, by the support means 41,
The mounted reference lens 61 is located on the optical path of the measurement light.
To do so. Then, the reference lens 6 is supported by the supporting means 41.
1 while moving 1 in the direction of the optical axis 53c of the measurement light,
The interference fringes at this time are measured by the image pickup means 48 by the means.
It And when this interference fringe becomes a "straight line" state
The movement of the support means 41 is stopped to stop the first Fizeau lens 51.
The measurement light of the reference lens 61 enters the condensing point of the measurement light by
Match the apex of the surface 61a on the side opposite to the shooting side,
7 (a)) The cat's eye reflection state is set. further,
In this state, the actual measurement detected by the image pickup means 48
The range matches the effective range of the predetermined Fizeau surface 51a.
Sea urchin (the optical axis of the reference lens 61 and the optical axis 53c of the measuring light are
Align (to match). alignment
Is effective due to the influence of the spherical aberration of the reference lens 61 itself.
On the other hand, since concentric interference fringes appear, the concentricity is used as a reference.
Went as. Depending on the shape of the lens,
The diameter of the lens may be
May be used as a reference. Then, in this state, "striped scan"
Take a measurement. (B) Next, the supporting means 41 is moved in the direction of the optical axis 53c of the measurement light.
Move the other surface of the reference lens 61 (incident of measurement light).
The converging point of the measurement light is made to coincide with the apex of the side surface 61b.
(See FIG. 7B). Then, as in the first and second embodiments,
The reference lens 61 with respect to the surface 61b.
After that, a “fringe scan” measurement is performed. In addition, the reference
The position of the lens 61 and (a) the cat's eye reflection state
The amount of movement I of the lens 61 from the position of the lens 61_RThe amount moved
It is measured using the detection means 91. (C) Both sides of the reference lens 61 measured in (a) and (b)
Focus correction value H for 61a and 61b_R,and
Movement amount I of the reference lens 61 measured in (b)_RFrom
“(Offset amount for error) = I_R+ H_R-ST "
Ask for. (E) Remove the reference lens 61 from the support means 41,
The lens 40 to be measured is placed on. And procedure (a) ~
Perform the same measurement as in (c), and_W(Movement amount) and H _W(F
Calculate the focus correction value). And using these values
Then, the center thickness S of the lens 40 to be measured is calculated by the following equation "center thickness S = I_W+ H_W− (Offset for error
Amount) ”.

In this embodiment, for example, the lens 40 under test is measured.
It is possible to measure the center thickness of the lens 40 even when the measurement light can be incident from only one direction, such as when the lens is attached to a polishing dish. Note that FIG.
Although spherical aberration occurs during alignment in the state shown in (a), since this aberration is an axially symmetric aberration, the alignment method described in the action (FIG. 2) can be applied as it is.

Further, the effective measurement area when performing the fringe scanning measurement may be limited by a mask, and alignment in the focus direction may be performed with the mask as a reference. FIG. 12 is a schematic diagram for explaining a modified example of this embodiment. Further, FIG. 13 is an enlarged view of the vicinity of the measured lens 40 in the state of FIG. A concave lens is used as the lens 40 to be measured here.

The actual center thickness of the measured lens 40 is T, the refractive index of the measured lens 40 is n, and the radius of curvature of the measured lens 40 on the side facing the Fizeau surface 51a of the condenser lens (Fizeau lens) 51 is Let R. t is the lens 40 to be measured when setting the first state (FIG. 12A) and the second state (FIG. 12B) obtained by the same method as in this embodiment.
Represents a distance moved, and α is a value obtained from NA of the condenser lens 51 at an angle obtained by sin ⁻¹ (NA).

In FIG. 13, the following equation is obtained from the law of refraction. sin (α + γ) = n sin ξ Also, the following equation holds. (R / sin α) = (R + t) / sin (α + γ) Furthermore, since (R + t) / sin (α + γ) = s / sinγ, and (T−t) / sin (α + γ−ξ) = s / sinβ are established, The following formula is obtained.

[0042]

[Equation 3]

Formula (R / sin α) = ((T−t) / sin (α + γ−ξ)) × (sin β / sin γ) Here, β + γ = ξ is established, and when this is substituted into the formula, the following formula is established. To do.

[0044]

[Equation 4]

Formula (R / sin α) = ((T−t) / sin (α + γ−ξ)) × (sin (ξ−γ) / s inγ) When the above formula is modified, sin (α + γ) = ((R + t )
/ R) x sin α is obtained. Since α is known, γ can be obtained from this. Then, by substituting this value of γ into the equation, ξ can be obtained. Further, by substituting the value of ξ into the equation, the central thickness T of the lens 40 to be measured can be obtained.

That is, the above "I _W + H _W " can be converted into the central thickness T, and the reference lens can be eliminated.

[0047]

As described above, according to the present invention, the center thickness of a lens can be measured with high accuracy without contact. Therefore, the lens is not scratched. It is also possible to measure the center thickness of a lens that has not been centered. The present invention is not limited to the case where both surfaces of the lens to be measured are formed into curved surfaces, and can be applied to a lens in which one surface is formed into a flat shape.

[Brief description of drawings]

FIG. 1 is a principle diagram showing the principle of the present invention.

FIG. 2 is a principle diagram according to the present invention (during tilt alignment).

FIG. 3 is a principle diagram according to the present invention (during shift alignment).

FIG. 4 is a schematic configuration diagram showing an example of a center thickness measuring device of the present invention.

FIG. 5 is a schematic view showing a first embodiment of the present invention.

FIG. 6 is a schematic view showing a second embodiment of the present invention.

FIG. 7 is a schematic view showing a third embodiment of the present invention.

FIG. 8 is a schematic view of a calibration jig used for measuring the center thickness.

FIG. 9 is an explanatory diagram showing a method of using a jig for calibration.

FIG. 10 is an explanatory diagram showing a method of using a jig for calibration.

FIG. 11 is a schematic configuration diagram of a center thickness measuring device used in Example 3.

FIG. 12 is a schematic diagram for explaining a modification of the third embodiment.

FIG. 13 is a schematic diagram for explaining a modification of the third embodiment.

[Explanation of symbols for main parts]

 40 Measured Lens 41 Supporting Means 42 Moving Means 43 Moving Amount Measuring Means 44 Computing Means 45 Light Source 48 Imaging Means 49 Movable Mirrors 50 Deflection Mirrors 51 First Fizeau Lens 52 Second Fizeau Lens 61 Reference Lens 91 Moving Amount Detecting Means

Claims (4)

[Claims] 1. (a) The first state is set by matching the apex of the first surface of the lens to be measured with the condensing point of the condensing lens of the measurement light, and (b) the first state. In the state where the optical axis of the measuring light and the optical axis of the lens to be measured are aligned with each other, the converging point of the condensing lens of the measuring light is aligned with the apex of the second surface of the lens to be measured. Setting a second state, and (c) setting a distance between condensing points of the respective measurement lights in the first state and the second state, or setting the first state and the second state The center thickness of the measured lens is obtained by measuring the distance traveled by the measured lens along the optical axis direction of the measurement light in order to obtain the center thickness of the measured lens. 2. An interference means having an interference fringe measuring means for measuring an interference fringe generated by interference between the measurement light reflected by the lens under measurement and the reference light reflected by the reference surface, and supporting the lens under measurement, Supporting means for moving the lens in the optical axis direction of the measuring light, and at least one of the lens to be measured or the condensing point of the measuring light,
A center thickness measuring device comprising a moving means for moving in a direction of "the optical axes of the two measuring lights when irradiated to the lens". 3. A first optical path, which is an optical path of a first measurement light with which the lens to be measured is irradiated from one surface side of the lens,
A second optical path, which is an optical path of the second measurement light emitted from the other surface side of the lens to be measured, and reflected light of the measurement light traveling in each of the optical paths on the lens to be measured. And an interference fringe measuring means for measuring an interference fringe generated by interference with the reference light reflected by the reference surface, so that the optical axes of the both measuring lights when irradiated to the lens to be measured coincide with each other. Interfering means configured, supporting means for supporting the lens to be measured, and moving the lens in the "optical axis of the both measuring beams when the lens is irradiated", and the lens to be measured or the measurement A center thickness measuring device comprising a moving means for moving at least one of the light converging points in the direction of "the optical axes of the two measuring lights when the lens is irradiated". 4. The center according to claim 2, further comprising a movement amount detection unit that detects a movement amount of the lens to be measured or a focal point of the measurement light by the movement unit. Thickness measuring device.