JPH04240534A - Measuring method and measuring apparatus of aspheric surface - Google Patents

Abstract

PURPOSE:To measure a deep aspheric surface without contacting the same in a short time by arranging a recorded hologram at a specific position, passing the light from a member to be inspected and a reference light able to interfere with the light through the hologram, and forming interference fringes at an observation surface. CONSTITUTION:Parallel luminous fluxes are allowed to pass through a half mirror 51 and a condensing lens 53 to be reflected on an aspheric surface 57 of an aspheric lens prototype 55 manufactured as designed. The reflecting light is moved backward to the mirror 51 and reflected towards a photosensitive material 59. On the other hand, as a reference light enters from above, the luminous flux reflected by the aspheric surface interferes with the reference light and the interference fringes are recorded to the photosensitive material 59 as a hologram 23. The interference fringes are formed on the observation surface by the reflecting light passing through the hologram 23 from the lens to be inspected and the reference light if the hologram 23 is placed at the recording surface and the aspheric lens to be inspected is placed at the position of the prototype 55. It is made clear how much the aspheric surface of the lens shifts from the design by observing the interference fringes.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aspherical surface measuring method and a measuring device for measuring the shape of an aspherical surface using holographic technology.

0002

BACKGROUND OF THE INVENTION In recent years, aspheric lenses have been increasingly used in optical devices, such as camera lenses. In particular, advances in technology regarding optical plastic materials have made it possible to produce aspherical lenses relatively easily and at low cost, so plastic aspherical lenses have come into widespread use. Furthermore, at the final stage of the manufacturing process, aspherical lenses are inspected and measured to see if the aspherical surface is formed as designed. Here, in the measurement method for measuring the aspherical shape of an aspherical lens, ■ it is non-contact, and ■ the surface (
It is possible to measure two-dimensional (two-dimensional) information, ■ deep aspherical (
It is possible to measure aspherical surfaces with a large amount of aspherical surface, ■
Conditions such as not being affected by aberrations of the measurement optical system are particularly important. However, it is more difficult to measure the optical characteristics of an aspherical lens than that of a spherical lens, and there has been no suitable measuring method that satisfies all of the above conditions.

0003

OBJECTS OF THE INVENTION The present invention provides a method and apparatus for measuring an aspheric surface, which can be carried out in a short time without contact, can measure a deep aspheric surface, and is not affected by aberrations of the measurement optical system. The purpose is to

0004

SUMMARY OF THE INVENTION In order to achieve this object, the present invention superimposes the light from the aspheric surface of a prototype having an aspheric surface of a designed shape, which is placed at a test position, on a reference light, and places it at a specific position. A hologram is formed by recording on a photosensitive material, and the recorded hologram is placed at the specific position, and a member to be tested is placed at the test position, and the light from the member to be tested and the light are The present invention is characterized in that the reference light coherent with the hologram is transmitted through the hologram to form interference fringes on the observation surface. Further, in the present invention, it is preferable that the test position and the recording surface are conjugate, and the test position and the observation surface are conjugate.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on embodiments shown in the accompanying drawings. FIG. 1 is a configuration diagram showing the main parts of an optical system of an embodiment of an aspheric lens measuring device used in the measurement method of the present invention, and FIG. 2 is an optical system for recording a hologram used in the measurement method of the present invention. FIG. First, recording of a hologram used in this measurement method will be explained with reference to FIG.

[0006] A parallel light beam is transmitted through a half mirror 51 and a condensing lens 53, and an aspherical prototype manufactured according to the design value is placed at a test position behind the focal point of the condensing lens 53. It is reflected by the aspherical surface 57 of 55. Then, the light reflected from this aspherical surface 57 is made to travel backwards to the half mirror 51, and the half mirror 51 moves the light to a specific position (recording surface).
The light is reflected toward a high-resolution photosensitive material 59 placed on the surface. Note that the above-mentioned test position and the above-mentioned recording surface are conjugate due to the condensing lens 53.

On the other hand, a reference beam that is coherent with the parallel light beam and is emitted from the same light source as the parallel light beam is made to enter the high-resolution photosensitive material 59 from an oblique direction. Therefore, the parallel light beam reflected by the aspherical surface 57 interferes with the reference light, and this interference pattern is recorded on the high-resolution photosensitive material 59. When this high-resolution photosensitive material 59 is developed, it becomes a hologram 23.

[0008] As the aspherical prototype 55, it is not necessary to use plastic, for example, a metal member may be used. The aspheric surface 57 of the aspheric prototype 55 is precisely formed using an ultra-precision processing machine to have the same curved shape as the aspheric surface of the aspheric lens to be measured. Then, the processed aspherical surface 57 may be precisely measured separately to confirm that it is manufactured according to the designed value.

Furthermore, if this hologram 23 is placed on the recording surface (replacing the photosensitive material 59) and a test aspheric lens is placed in place of the aspheric prototype 55 at the position of the aspheric prototype 55,
Interference fringes are formed on the observation surface by the reflected light from the aspherical lens and the reference light that have passed through the hologram 23. By observing these interference fringes, it can be determined how much the aspheric surface of the aspheric lens deviates from the designed value.

Next, a method of measuring the aspherical lens 21 having the same design value as the aspherical surface 57 will be explained with reference to FIG.

A laser beam emitted from the laser oscillator 11 is converted into a large diameter parallel beam by an objective lens 13 and a collimating lens 15. This parallel light beam passes through the second half mirror 33 and the first half mirror 17, is focused by the condenser lens 19, is reflected by the aspheric surface 22 of the test aspheric lens 21 placed at the test position, and passes through the optical path. The light travels backwards, passes through the condensing lens 19, and is reflected by the first half mirror 17 in a substantially perpendicular direction. The light then passes through the hologram 23 placed on the recording surface, and is imaged by the imaging lens 25 onto the photosensitive surface (observation surface) of the CCD camera 27 . Note that this hologram 23 is recorded on a high-resolution photosensitive material placed on the recording surface by placing an aspheric prototype 55 at the test position before placing the aspheric lens 21 at the test position. It is.

On the other hand, the parallel light beam transmitted through the second half mirror 33 is reflected by the first half mirror 17 in the opposite direction to the CCD camera 27, and is further reflected toward the hologram 23 by the first mirror 29 and the second mirror 31. irradiated. The irradiated light is then diffracted by the hologram 23, goes in the same direction as the reflected light from the aspherical lens 21, and is imaged by the imaging lens 25 on the CCD camera 27. The parallel light beam reflected by the first and second mirrors 29 and 31 becomes the reference light. Interference fringes caused by the test light reflected by the aspherical lens 21 and the reflected light reflected by the first and second mirrors 29 and 31 are imaged by the CCD camera 27. These interference fringes are obtained as a difference from the aspherical shape of the aspherical prototype 55, that is, a difference from the designed shape. Therefore, by reproducing, observing and measuring the interference fringes captured by the CCD camera 27 on the TV monitor 41, the processing accuracy and condition of the aspherical lens 21 can be known. In addition, the interference fringes observed here are
Since the aberrations caused by the first half mirror 17 are the same during recording of the flat prototype and during inspection of the lens to be tested, they cancel each other out, and no measurement error occurs.

The aspherical surface 22 (test surface) and the hologram 2
3 (recording surface) are arranged conjugately, and the hologram 23
(recording surface) and a CCD camera 27 (observation surface) are arranged in a conjugate relationship. By arranging the condenser lens 19, the imaging lens 25, the first half mirror 17, and the first and second mirrors 29 and 31 in such a conjugate relationship, the effects of aberrations, axis misalignments, etc. of the optical system can be reduced. I no longer receive it. Furthermore, even if the incident angle of the reference light is changed when measuring the lens to be tested, it is possible to form wide interference fringes that are easy to measure without being affected by aberrations.

Furthermore, this embodiment also makes it possible to measure spherical lenses. In other words, a part of the parallel light beam emitted from the collimating lens 15 is reflected by the second half mirror 33 in a substantially perpendicular direction, further reflected by the third mirror 35 that produces the second reference light beam, and travels backward along the optical path. Second
It passes through the half mirror 33 and is captured by the imaging lens 37.
An image is formed on the D camera 39. By displaying the interference fringes captured by the CCD camera 39 on the TV monitor 42, the state of the spherical lens can be measured.

Although not shown, the aspherical lens 21 is movable in the optical axis direction, and the radius of curvature ( It is also possible to measure the focal length (focal length).

On the other hand, a part of the reflected light from the aspherical lens 21 passes through the converging lens 19 and the first half mirror 17 and travels back along the optical path as a parallel light beam to the second half mirror 33. 33 toward the imaging lens 37, and an image is formed on the CCD camera 39. Therefore, the light reflected by the third mirror 35 and the light reflected by the aspherical lens 21 interfere, forming annular interference fringes. By observing these interference fringes, it is possible to check the alignment state of the lens.

The interference fringes of the aspherical prototype and the aspherical lens measured by the above measuring device are shown in FIGS. 3 to 5.

FIG. 3A shows the interference observed by a hologram recorded by an aspherical prototype having an accurately formed aspherical surface A (aspherical amount approximately 700 (λ), λ=0.6328μ). FIGS. 3B and 3C show the interference fringes of individual resin lenses A that were actually produced with the aspherical surface A as the design value, as observed by the measuring device described above.

FIG. 4A is a hologram recorded with an aspherical prototype having an accurately formed aspherical surface B (aspherical amount approximately 1000 (λ), λ=0.6328μ), and FIG. 4B
is the appearance of interference fringes of an actually manufactured resin lens B with the aspherical surface B as the design value, observed using this hologram. From FIG. 4B, it can be seen that this resin lens B has air bubbles in the portion indicated by the reference numeral 61.

FIG. 5A shows a hologram recorded with an aspherical prototype having an accurately formed aspherical surface C (aspherical amount approximately 400(λ), λ=0.6328μ), and FIG. 5B shows this hologram. This is the appearance of interference fringes of a resin lens C formed by glass molding that was actually manufactured using an aspherical surface C as a design value. Observing FIG. 5B, it can be seen that the interference fringes are disturbed near both the upper and lower ends. It can be assumed that this is caused by, for example, fluctuations in the feed of the cutting tool on the lathe when forming the mold for the lens.

As described above, according to this embodiment, it is possible to measure a deep aspherical surface, and moreover, two-dimensional information (planar information) can be obtained instantaneously. Since the reflected light from the aspherical prototype surface and the reflected light from the test surface pass through almost the same optical path in the measurement optical system, they are not affected by aberrations in the optical system along the way. Furthermore, since the test surface, the hologram, and the observation surface are provided conjugately, the coordinates of the test surface and the coordinates of the observation surface have a one-to-one correspondence, and alignment is extremely easy.

Furthermore, according to this embodiment, it is only necessary to precisely prepare one prototype for one type of lens.
It is simple and low cost. Furthermore, measurement can be easily performed by simply replacing the hologram, so even if a large number of different types of aspherical lenses are produced in small quantities, each can be easily measured.

Although the present invention has been described above based on the embodiments shown in the accompanying drawings, the present embodiments are not limited thereto. For example, although the present embodiment uses reflected light from the surface to be inspected, light that passes through the surface to be inspected may also be used. Furthermore, a monitor optical system for focus adjustment may be provided.

[0024]

[Effects of the Invention] As described above, the present invention creates a hologram formed by superimposing light from a prototype having an aspheric surface of a designed shape and a reference light and recording it on a photosensitive material placed at a specific position. The hologram is placed at the specific position, the member to be tested is placed at the test position, and the light from the member to be tested and the reference light are transmitted through the hologram to form interference fringes on the observation surface. Measurement of spherical lenses is also possible.

Furthermore, since the reflected light from the aspherical standard surface and the reflected light from the test surface pass through almost the same optical path of the measurement optical system,
It is not affected by aberrations in the optical system along the way. Furthermore, if the test surface, the hologram, and the observation surface are provided conjugately, the coordinates of the test surface and the coordinates of the observation surface will have a one-to-one correspondence, making alignment very easy.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a main part of an optical system of an embodiment of an aspherical surface measuring apparatus according to the present invention.

FIG. 2 is a configuration diagram showing the main parts of an optical system for recording a hologram used in the aspheric surface measuring device of the present invention.

3A, 3B, and 3C are interference fringes of an aspherical prototype having an aspherical surface A, a resin lens, and another resin lens measured by the measuring device of this example.

4A and 4B are interference fringes of a resin lens, an aspheric prototype having an aspheric surface B, measured by the measuring device of this example.

5A and 5B are interference fringes of a resin lens, an aspherical prototype having an aspherical surface C, measured by the measuring device of this example.

[Explanation of symbols]

11 Laser oscillator 13 Objective lens 15 Collimating lens 17 First half mirror 19 Condensing lens 21 Test lens (aspherical lens) 23 Hologram 25 Imaging lens 27 CCD camera 29 First mirror 31 Second mirror 33 Second half mirror 35 Third mirror 37 CCD camera 41 TV monitor 42 TV monitor 51 Half mirror 53 Condensing lens 55 Aspheric prototype 59 High resolution photosensitive material

Claims (7)

[Claims] Claim 1: Superimposing light from an aspherical surface of a prototype having an aspherical surface of a designed shape placed at a test position and a reference light,
A hologram is formed by recording on a photosensitive material placed at a specific position, the recorded hologram is placed at the specific position, a member to be tested is placed at the test position, and light from the member to be tested and A method for measuring an aspheric surface, comprising transmitting the reference light coherent with the reference light through the hologram to form interference fringes on an observation surface. 2. A method for measuring an aspheric surface according to claim 1, wherein the test position and the hologram at the specific position are conjugate, and the test position and the observation surface are conjugate. . 3. A method for measuring an aspherical surface according to claim 1, wherein the light from the surface to be measured of the member to be measured is light reflected by the surface to be measured. 4. A method for measuring an aspherical surface according to claim 1, wherein the light from the surface to be measured of the member to be measured is light that has passed through the surface to be measured. 5. The aspheric surface measuring method according to claim 1, wherein the interference fringes are imaged by a CCD camera disposed on the observation surface. 6. A hologram forming optical system that forms interference fringes on a certain recording surface by light from a surface to be measured placed at a test position and a reference beam that is coherent with the light, and A hologram placed on the recording surface, in which interference fringes caused by light from the aspherical surface of the prototype having an aspherical surface of a designed shape and the reference beam are recorded in advance on the recording surface, and a hologram transmitted through the hologram. An aspheric surface measuring device comprising: an observation optical system for observing interference fringes formed by the light from the test member placed at the test position and the reference light. 7. The measuring device according to claim 6 further comprises:
An aspherical surface characterized by comprising a monitor optical system that irradiates the test position and forms interference fringes by superimposing the light before the test position is irradiated and the light from the test position. measuring device.