JP3412962B2 - Eccentricity measuring method and eccentricity measuring device using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eccentricity measuring method and an eccentricity measuring apparatus using the same, and in particular, the spherical surface of a single lens or the eccentricity of each surface of an optical system composed of a plurality of optical elements is incorporated in a metal object. It is suitable for direct measurement.

[0002]

2. Description of the Related Art Various devices for measuring the eccentricity of lenses have been proposed. As a highly accurate measuring method, there is an axis deviation detecting method utilizing two-beam interference disclosed in Japanese Patent Application Publication No. 51-42495 in 1976.

According to this method, two coherent light fluxes are made incident so as to intersect with each other at the center of curvature of the surface to be measured, and these lights reflected on the surface to be inspected are superposed to generate interference fringes. The phase difference between the two reflected light beams is measured from the fluctuation of the interference fringes generated when the object is rotated, and the axial deviation, that is, the eccentricity of the measured surface is measured from the result.

[0004]

However, if the above-mentioned conventional method is applied to the measurement of the eccentricity of each surface of the lens system composed of a large number of parts, this lens system is used as the reference axis for the eccentricity measurement. Must be rotated around.
Therefore, for example, in a lens system that is not axially symmetric, such as a lens system in which the optical axis is bent by a mirror, or in a lens system in which the size of the lens barrel is extremely large or the structure is complicated, rotate these lens systems. It becomes difficult to measure eccentricity.

Further, since it is necessary to let the measuring light flux enter and exit from one end of the lens system, in a lens system where there is no space for disposing an optical element for entering and exiting the measurement light at one end of the lens system, Since the measuring light cannot enter from the end portion, there is a problem that eccentricity measurement cannot be performed by the above conventional method.

The present invention solves the above-mentioned problems, and the eccentricity of each surface of a lens system composed of a large number of optical elements can be easily and highly accurately measured while the lens system to be measured is stationary. An object of the present invention is to provide a measuring method and an eccentricity measuring device using the measuring method.

[0007]

The eccentricity measuring device of the present invention comprises: (1-1) splitting a light beam from a light source into a first light beam and a second light beam by a splitting means, and the both light fluxes to a condenser lens. , Incident as a light flux parallel to the optical axis, and irradiate both light flux emitted from the condensing lens on the surface to be measured of the optical system to be measured by condensing and intersecting in the vicinity of the apparent curvature center, Both light fluxes reflected from the surface are caused to interfere via the condenser lens and the dividing means, and the interference light is rotated about the optical axis of the condenser lens and the light receiving device. However, it is characterized in that the light is received by the light receiver and the eccentricity information of the surface to be measured is obtained from the signal from the light receiver.

In particular, (1-1-1) a plane mirror is installed in the optical path of the optical system to be measured so as to deflect a light beam overlapping the optical axis of the condenser lens so as to be overlapped with the reference axis of the optical system to be measured. To do. (1-1-2) The condenser lens is a variable focal length lens. (1-1-3) A polarization plane setting means is provided between the light source and the dividing means, and the polarization plane of the light flux from the light source is controlled according to the polarization element existing on the path to the surface to be measured. . (1-1-4) At least one of the two light beams undergoes frequency modulation by the frequency modulation means provided between the splitting means and the condenser lens, and the phase measuring means determines the phase of the beat of the interference light. To detect. It is characterized by such things.

Further, according to the eccentricity measuring method of the present invention, (1-2) the luminous flux from the light source is divided into the first luminous flux and the second luminous flux by the dividing means, and at least one of the two luminous fluxes is divided.
Frequency-modulates one of the light fluxes through a frequency modulation means, makes both light fluxes enter a condenser lens as light fluxes parallel to the optical axis thereof, and emits both light fluxes to the measured surface of the measured optical system. The two light beams reflected from the surface to be measured are condensed and intersected in the vicinity of the apparent center of curvature, and the two light beams are heterodyne-interfered via the condenser lens, the frequency modulation means, and the division means, and Receiving the heterodyne interference light,
The phase of the beat of the interference light is divided by the dividing means, the condenser lens,
The light receiving device is characterized in that the phase measuring means detects it while rotating the light receiving device about the optical axis of the condenser lens, and obtains the eccentricity information of the surface to be measured from the signal from the phase measuring means.

In particular (1-2-1), a plane mirror is installed in the optical path of the optical system to be measured so as to deflect a light beam overlapping the optical axis of the condenser lens so as to overlap with the reference axis of the optical system to be measured. To do. (1-2-2) The condenser lens is a variable focal length lens. (1-2-3) A polarization plane setting means is provided between the light source and the dividing means, and the polarization plane of the light flux from the light source is controlled according to the polarization element existing on the path to the surface to be measured. ing. It is characterized by such things.

Further, the eccentricity measuring apparatus of the present invention is (1-3): the light flux from the light source is split into two light fluxes having different frequencies symmetrically with respect to the optical axis by the interference optical system, and the divided light flux is emitted. After converging on the apparent curvature center of the surface to be measured by using a plane mirror provided in the optical path of the system, the two light beams reflected by the surface to be measured are made incident on the surface to be measured through the plane mirror. The interference optical system is caused to interfere, and the beat signal of the interference light is detected by a light receiver by rotating at least a part of the interference optical system with the optical axis of the interference optical system as a rotation axis, and a signal from the light receiver. Is used to obtain the eccentricity information of the surface to be measured.

In particular, (1-3-1) the interference optical system has a condenser lens with a variable focal length, and the focal length of the condenser lens is changed so that the two light fluxes appear on the surface to be measured. It is characterized in that it is focused on the center of curvature of.

[0013]

Embodiment 1 FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention. In the figure, 1 is a laser as a light source, 2 is a light flux emitted from the laser 1, 3 is a polarization plane setting means, and the direction of the polarization plane of the light flux 2 can be arbitrarily set. A half mirror (splitting means) 5 splits the light flux 2 into two light fluxes 2a and 2b,
Reference numerals 6, 7, and 8 are mirrors that bend the luminous fluxes 2a and 2b that are divided into two.

Reference numeral 9 denotes a variable focal length lens (condensing lens), which adjusts the focal length to intersect the light beams 2a and 2b at the center of curvature of the surface to be measured. The variable focal length lens 9 is a lens whose back focus changes according to the change of the focal length.

Reference numeral 10 is a photodetector (photodetector), which detects the interference light of the returned light beams 2a and 2b. Reference numeral 11 is an acousto-optic element (frequency modulation means) that changes the frequency of the light beam 2a.

The half mirror 5, the mirrors 6, 7, and 8, the variable focal length lens 9, the photodetector 10, the acousto-optic element 11 and the like constitute one element of the interference optical system 4. Interference optical system 4
Splits the light beam 2 into two light beams, emits the light beam toward the center of curvature of the surface to be measured, and causes the returned two light beams to interfere with each other to be guided to the photodetector 10. Note that the interference optical system 4 rotates about the optical axis of the focal length variable lens 9 as a rotation axis during measurement. The optical axis of the variable focal length lens 9 is defined as the optical axis of the interference optical system 4.

Reference numeral 12 is a rotary stage, and the interference optical system 4
To rotate. Reference numeral 13 is a plane mirror, and the interference optical system 4
The two light fluxes 2a and 2b emitted from are guided to the lens system to be measured. Reference numeral 14 is a fine adjustment device for the installation angle of the plane mirror 13.

Reference numeral 15 denotes a lens system to be measured (optical system to be measured),
Reference numeral 16 denotes a measured surface of the measured lens system 15 during measurement.
The single lenses 17 to 22, the mirror 23, the polarization beam splitter 24, and the like are constituent elements of the lens system 15 to be measured. The constituent elements of the measured lens system 15 are arranged along the optical axis (reference axis) O _K of the measured lens system 15.

Reference numeral 28 denotes an acousto-optic element driver, which supplies high-frequency power to the acousto-optic element 11. An amplifier 29 amplifies the output signal of the photodetector 10. Reference numeral 30 denotes a bandpass filter, which passes only a specific frequency component in the output of the amplifier 29. Reference numeral 31 is a frequency divider, which sets the frequency of the output signal of the bandpass filter 30 to 2
Make it one-half. 32 is a phase meter, and the acousto-optic device 28
The phase difference between the high-frequency power supplied to and the output signal of the frequency divider 31 is measured. The bandpass filter 30,
The frequency divider 31, the phase meter 32, etc. constitute one element of the phase measuring means.

A rotary stage driver 33 drives the rotary stage 12 in accordance with a command value. An arithmetic unit 34 measures and displays the eccentricity of the surface 16 to be measured from the command value to the rotary stage driver 33 and the output signal of the phase meter 32.

The operation of this embodiment will be described. The parallel light flux 2 from the linearly polarized laser 1 as the light source is the polarization plane setting means 3
Thus, the light having a desired polarization plane is incident on the interference optical system 4 along the optical axis of the variable focal length lens 9. In the interference optical system 4, the light flux 2 is split by the half mirror 5 into light fluxes 2a and 2b, and then the two light fluxes are converted into a light flux parallel to the optical axis of the focal length variable lens 9 via the mirrors 6, 7 and 8. Then, the light enters the lens 9. At this time, one of the light fluxes 2a passes through the acousto-optic element 11 driven at the frequency f ₁ , so that the frequency changes by f ₁ .

The focal length of the variable focal length lens 9 is adjusted so that the position where the light beams 2a and 2b are condensed and intersects is approximately coincident with the center of curvature of the surface 16 to be measured of the lens to be measured. Since it may not be possible to match the centers of curvature of all the surfaces to be measured with one type of variable focal length lens 9, a plurality of variable focal length lenses with different variable range of focal length are prepared, and the measured object is measured. A variable focal length lens suitable for the radius of curvature of the surface 16 is used.

Since the two light fluxes incident on the variable focal length lens 9 are both parallel to the optical axis of this lens 9, the light emitted from the variable focal length lens 9 is the rotation axis of the interference optical system 4 (= the variable focal length lens). It is rotated about the optical axis 9), is reflected by the plane mirror 13, and is introduced into the lens system 15 to be measured.

The plane mirror 13 is a fine adjustment device 14 for the installation angle.
The installation angle is adjusted so that the rotation axis of the interference optical system 4 and the reference axis are symmetric with respect to the reflection surface of the plane mirror 13 (thus, a ray overlapping the optical axis of the focal length variable lens 9 is reflected. Overlaid on the reference axis). Therefore, when the rotating stage 12 rotates, the light beams 2a and 2b are reflected by the plane mirror 13 and then rotate around the reference axis of the lens system 15 to be measured.

Since the points where the light beams 2a and 2b are condensed and intersect with each other are substantially coincident with the center of curvature of the surface 16 to be measured, some of the light beams 2a and 2b reflected by the surface 16 to be measured follow the path up to that point. Go backwards and return to half mirror 5. At that time, since the light beam 2a passes through the acousto-optic element 11 again, the frequency f ₁
Only changes. On the other hand, since the frequency of the light beam 2b remains unchanged, the light beam 2a and the light beam 2 superposed by the half mirror 5 are
The interference light of b produces a beat of frequency 2f ₁ . The interference light is received by the photodetector 10, and the output signal of the photodetector 10 is amplified by the amplifier 29 so as to be suitable for the signal processing in the subsequent stage.

By observing the output signal of the amplifier 29 and finely adjusting the focal length variable lens 9 along the rotation axis of the rotary stage 12 so that the beat amplitude of the interference light is maximized, the light beams 2a and 2b are condensed. The intersecting point can be made to almost completely coincide with the center of curvature of the measured surface 16. Then, as will be described later, by measuring the phase φ of the beat of the interference light, the amount and direction of eccentricity of the measured surface 16 can be obtained.

A procedure for measuring the phase φ of the beat of the interference light will be described. The output signal of the amplifier 29 is passed through the bandpass filter 30 to remove components other than the frequency 2f ₁ , and the frequency divider 31 halves the frequency of the output signal, that is, the acousto-optic device driver 28.
To the same f ₁ as the output frequency of. Divider 31 at this stage
The phase .phi. Can be obtained by comparing the phase difference between the output of the above-mentioned and the output of the acousto-optic element driver 28 with the phase meter 32.

This embodiment constitutes a so-called heterodyne interferometer, and the phase φ can be measured with high resolution, resulting in highly accurate eccentricity measurement.

Next, the principle of obtaining the eccentricity data of the surface 16 to be measured from the phase φ of the beat of the interference light will be described. FIG. 2 is an explanatory view of the measurement principle, and shows the variable focal length lens 9 to the measured surface 16 on the reference axis O _K.
2A is a side view, and FIG. 2B is a front view of the measured surface 16 viewed from the front.

In the figure, F is the focal point of the variable focal length lens 9, and this position is near the center of curvature C of the surface 16 to be measured on the reference axis O _K. S is a point at which the measured surface 16 intersects with the reference axis O _K, and A and B are points at which the measurement light beams 2a and 2b hit the measured surface 16, respectively. Note that Z along the reference axis O _K
Axis, in the side view Y in the direction orthogonal to the Z axis
XYZ coordinates are set with the axis and the direction perpendicular to the paper surface as the X axis.

As is well known in the heterodyne interferometry, the phase φ of the beat of the interference light is the luminous flux 2 as shown in the following equation.
The difference in optical path length between a and 2b is proportional to ΔL = FB-FA.

Φ = 2πΔL / λ (1) where λ is the wavelength of the light beam 2. Further, the optical path length difference ΔL and the eccentricity of the surface 16 to be measured have the following relationship.

ΔL = 2D · α · cos (θ−ψ) (2) where D is the distance between the two light fluxes 2 a and 2 b on the surface 16 to be measured,
That is, the distance AB. α is the tilt angle, that is, the measured surface 1
6 is an angle formed with the reference axis O _K , which is ∠FSC in the figure. θ is an angle formed by a plane including the center line of the light beam 2a and the center line of the light beam 2b with a reference plane (for example, the YZ plane), and ψ is an eccentric direction, that is, a normal line SC of the measured surface 16 and a reference of the measured lens system 15. A plane including the axis O _K is an angle formed with the reference plane. Assuming that the radius of curvature SC of the surface 16 to be measured is R and the eccentricity FC is h, then h = Rα (3). Therefore, from equations (1), (2), and (3),

[0034]

[Equation 1] Becomes Since the angle θ changes with the rotation of the interference optical system 4, the phase φ changes sinusoidally. Therefore, the phase φ is measured while rotating the interference optical system 4 by the rotary stage 12,
Using the equation (4), the arithmetic unit 34 can determine the magnitude h of the eccentricity and the azimuth ψ of the eccentricity from the rotation angle θ of the interference optical system 4, that is, the rotation angle of the rotary stage 12 and the value of the phase φ. The above is the principle of obtaining the eccentricity data of the measured surface 16 according to the present embodiment.

In FIG. 1, the surface 16 closest to the plane mirror 13 is measured as the surface to be measured, but when the second closest surface is measured next, the eccentricity of the nearest surface 16 is first measured, and then the The variable focal length lens 9 is adjusted so that the two light fluxes 2a and 2b intersect at the apparent curvature center of the second surface, that is, at the image point of the curvature center of the corresponding measured surface viewed from the plane mirror 13 side.

Since the magnitude h of the eccentricity and the azimuth ψ of the eccentricity obtained here are affected by the eccentricity of the front surface, the net eccentricity is calculated by correcting them. Similarly, the eccentricity of the inner surface can be measured in sequence.

When there is a polarizing element such as the polarization beam splitter 24 in the optical path of the two light beams 2a and 2b to the surface to be measured, the polarization plane setting means 3 makes the two light beams 2a and 2b as efficient as possible. If the polarization plane is set so as to reach, it is possible to measure the eccentricity of the plane that cannot be measured depending on the orientation of the polarization element when the polarization state is fixed.

The polarization plane setting means 3 may be, for example, a half-wave plate having a polarizer and a rotation mechanism, and has a structure in which the laser 1 as a light source is linearly polarized and rotated around the light beam 2. May be.

Even if the interference optical system 4 rotates, the laser 1 and the polarization plane setting means 3 remain stationary, so that the luminous fluxes 2a and 2b.
The polarization state of is kept almost constant. At this time, in order to reduce the change in the polarization state set by the polarization plane setting means 3, when the light beams 2, 2a, 2b are reflected by the half mirror 5, the mirrors 6, 7, 8, the incident angle is made as small as possible. Better keep it.

The acousto-optic element 11 is of a type that does not change the polarization state. As described above, of the components of the lens system 15 to be measured, the components to which the two light beams 2a and 2b reach by the plane mirror 13, that is, the single lenses 19 and 2,
The eccentricity of the planes of 0, 21, 22 and the polarization beam splitter 24 can be measured.

FIG. 3 is an explanatory view in the case where the measurement two light fluxes 2a and 2b are introduced by changing the insertion / installation place and the direction of the plane mirror 13 while the lens system 15 to be measured is left as it is. The same elements as those in FIG. 1 are denoted by the same reference numerals.

With the arrangement shown in FIG. 3, it is possible to measure the eccentricity of the surfaces of the single lenses 17, 18 and 19 of the components of the lens system 15 to be measured. By setting the installation location of the plane mirror 13 to the location shown in FIG. 3, both sides of the single lens 19 can be measured for eccentricity in both cases of FIG. 1 and FIG. Therefore, the relative eccentricity between all the parts that can be measured in FIG. 1 and the parts that can be measured in FIG. 3 is obtained by measuring the eccentricity of the single lens 19.

By repeating this method, even if the eccentricity of all parts cannot be measured at one time due to the large number of parts,
Relative eccentricity of all components can be measured by changing the measurement range while interposing components that can be commonly measured in sequence.

FIG. 4 is a schematic view of the essential portions of Embodiment 2 of the present invention. The main difference of this embodiment from the first embodiment is that a second acousto-optic element is provided in the optical path of the light beam 2b. Example 1
Elements that are the same as are given the same reference numerals.

In the figure, reference numeral 35 is a second acousto-optic device,
The frequency of the light beam 2b is changed. A second acousto-optic element driver 36 supplies high frequency power of frequency f2 to the second acousto-optic element 35. Reference numeral 37 is a difference frequency output device, which outputs the difference frequency signal from the high frequency power of the two acousto-optic device drivers 28 and 35.

In this configuration, the light beam 2b has a frequency of 2 when reflected by the surface to be measured and returned to the half mirror 5.
Only f ₂ has changed. Therefore, the interference light of the light beam 2a and the light beam 2b superposed by the half mirror 5 has a frequency of 2 (f ₁
-F ₂ ) beats are generated (when f ₁ > f ₂ ).

Generally, the frequency of the high frequency power for driving the acousto-optic device is several tens of MHz to several hundreds of tens of MHz, so the beat frequency of the interference light is also high in the first embodiment, and the photodetector 1
0, bandpass filter 30, frequency divider 31, phase meter 3
Devices such as 2 will process high frequency signals. On the other hand, in the second embodiment, if the difference between f ₁ and f ₂ is set to several tens of kHz, each of the above devices can handle signals of about 100 kHz, so that the handling is easy and the manufacturing cost is reduced. is there.

[0048]

EFFECTS OF THE INVENTION With the above-described structure, the present invention makes it possible to measure the eccentricity of each surface of a lens system composed of a large number of optical elements easily and with high accuracy while the lens system to be measured is stationary. A method and an eccentricity measuring device using the method are achieved.

In particular, the following effects are excellent. (2-1) The eccentricity can be measured even when it is difficult to rotate the lens system to be measured. (2-2) It is possible to easily measure eccentricity of a surface having different curvature center positions in the lens system to be measured. (2-3) Even when the lens system to be measured includes a polarization element, the polarization plane of the measurement light beam can be appropriately set by using the polarization plane setting means, so that the eccentricity measurement of the surface behind the polarization element is also possible. . (2-4) By using the heterodyne interferometry, highly accurate eccentricity measurement is possible.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

[Figure 2] Illustration of the measurement principle

FIG. 3 is an explanatory diagram for performing eccentricity measurement by changing the insertion location and the orientation of the plane mirror in the first embodiment.

FIG. 4 is a schematic view of the essential portions of Embodiment 2 of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 laser 28 acousto-optic element driver 2 light flux 29 amplifier 3 polarization plane setting means 30 band pass filter 4 interference optical system 31 frequency divider 5 half mirror 32 phase meter 6 to 8 mirror 33 rotary stage driver 9 focal length variable lens 34 arithmetic unit 10 Photodetector 35 Second Acoustooptic Element 11 Acoustooptic Element 36 Second Acoustooptic Element Driver 12 Rotation Stage 37 Difference Frequency Output Device 13 Plane Mirror 14 Installation Angle Fine Adjustment Device 15 Measured Lens System 16 Measured Surface 17 to 22 single lens 23 mirror 24 a polarizing beam splitter O _K reference axis

Claims (11)

(57) [Claims] 1. A light flux from a light source is split into a first light flux and a second light flux by a splitting means, both light fluxes are made incident on a condenser lens as a light flux parallel to its optical axis, and the light flux is emitted from the condenser lens. Both emitted light beams are irradiated onto the surface to be measured of the optical system to be measured by converging and intersecting them in the vicinity of the apparent center of curvature, and both light beams reflected from the surface to be measured are passed through the condenser lens and the dividing means. The interference light, and the interference light is received by the light receiver while rotating the splitting means, the condenser lens, and the light receiver around the optical axis of the condenser lens, and the measured object is measured by a signal from the light receiver. An eccentricity measuring device characterized by obtaining surface eccentricity information. 2. A flat mirror is provided in the optical path of the measured optical system so as to deflect a light beam overlapping the optical axis of the condenser lens so as to overlap the reference axis of the measured optical system. Item 1. An eccentricity measuring device. 3. The eccentricity measuring device according to claim 1, wherein the condenser lens is a variable focal length lens. 4. A polarization plane setting means is provided between the light source and the dividing means, and the polarization plane of the light flux from the light source is controlled according to a polarization element existing in a path to the surface to be measured. The eccentricity measuring device according to claim 1, 2 or 3. 5. At least one of the two light beams undergoes frequency modulation by a frequency modulation means provided between the splitting means and the condenser lens, and the phase measuring means detects the phase of the beat of the interference light. Claim 1 characterized in that
2, 3 or 4 eccentricity measuring device. 6. A light flux from a light source is split into a first light flux and a second light flux by a splitting means, at least one of the two light fluxes is frequency-modulated by a frequency modulating means, and both light fluxes are condensed. Let it enter the lens as a light beam parallel to its optical axis,
Both light fluxes emitted from the condensing lens are irradiated onto the surface to be measured of the optical system to be measured by condensing and intersecting them in the vicinity of the apparent center of curvature, and two light fluxes reflected from the surface to be measured are condensing lens. Heterodyne interference is caused via the frequency modulation means and the dividing means, and a photodetector receives the heterodyne interference light, and the phase of the beat of the interference light is adjusted by the dividing means, the condenser lens, and the photodetector. An eccentricity measuring method characterized in that phase measuring means detects while rotating about an optical axis of an optical lens, and eccentricity information of the surface to be measured is obtained from a signal from the phase measuring means. 7. A flat mirror is provided in the optical path of the optical system to be measured, which deflects a light beam overlapping the optical axis of the condenser lens so as to overlap with a reference axis of the optical system to be measured. Item 6. An eccentricity measuring method. 8. The decentering measuring method according to claim 6, wherein the condenser lens is a variable focal length lens. 9. A polarization plane setting means is provided between the light source and the dividing means, and the polarization plane of the light flux from the light source is controlled according to a polarization element existing in a path to the surface to be measured. The eccentricity measuring method according to claim 6, 7, or 8. 10. A plane mirror provided in the optical path of an optical system to be measured is used in which a light beam from a light source is split into two light beams having different frequencies symmetrically with respect to the optical axis by an interference optical system and emitted. After the light is focused on the apparent center of curvature of the surface to be measured, it is incident on the surface to be measured, and the two light beams reflected by the surface to be measured are caused to interfere with each other by the interference optical system via the plane mirror, and the beat of the interference light is obtained. The signal is detected by a light receiver by rotating at least a part of the interference optical system with the optical axis of the interference optical system as a rotation axis, and the eccentricity information of the measured surface is obtained using the signal from the light receiver. An eccentricity measuring device characterized in that 11. The interference optical system has a condenser lens with a variable focal length, and the focal length of the condenser lens is changed to condense the two light beams at an apparent curvature center of the surface to be measured. The eccentricity measuring device according to claim 10, wherein