JPH05264238A - Method and device for measuring surface of rotation - Google Patents

Abstract

PURPOSE:To provide a method and a device capable of sampling data from images of interference fringes of always almost same size in measuring a surface of rotation by means of scanning along an axis of rotation, regardless of changes in the radius of curvature of a cross section to be measured due to scanning of the surface for measurement. CONSTITUTION:Coherent light is applied to a surface 7a for measurement and a reference plane 6a, and interference fringes are formed as to one cross section to be measured of the surface for measurement and are focused on a sensor 10. The surface for measurement is scanned parallel to an axis of rotation by a supporting block 13, and the images of the interference fringes are successively focosed on the sensor and are stored on interference fringe image data storage means 14. A lateral magnification computation means 15 computes the radius (r) of curvature of each cross section to be measured according to the designed value of the form of the surface for measurement, and calculates the lateral magnification (m) of each of the images of the interference fringes according to the radii, and a correction arithmetic means 16 multiplies the lateral magnification (m) by data about the interference fringes, and the data are stored on corrected data storage means 17 as data about the images of the interference fringes f the same size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for measuring the surface shape and surface accuracy of a rotating surface such as a toroidal surface, and in particular, forming an interference fringe on one measurement cross section of the rotating surface as a surface to be inspected. Scan the rotating surface along the rotation axis to form interference fringes one after another, and correct the size of each interference fringe when connecting the interference fringes and measuring the surface accuracy and surface shape of the entire rotating surface. It is about technology.

[0002]

2. Description of the Related Art Toroidal surfaces differ in the radius of curvature of main diameter lines that are orthogonal to each other at their vertices. One of these main diameter lines is a busbar (hereinafter referred to as "G main diameter line") It is formed by rotating along the other main diameter line (hereinafter referred to as "R main diameter line"). Alternatively, it can be said that the G main diameter line (bus line) is formed by rotating around the rotation axis, and in the present specification, the toroidal surface is mainly treated as one form of the rotation surface.

As a technique for measuring the surface accuracy of the toroidal surface with high accuracy below the wavelength, the applicant of the present application has filed Japanese Patent Application No.
No. 126659 proposes a method for measuring a toroidal surface of a donut type or a normal type (hereinafter referred to as “NTS”). The toroidal surface here is treated as a surface formed by rotating one G main diameter line along the other R main diameter line.

Japanese Patent Application No. 3-050 of the earlier application filed by the same applicant
No. 104 proposes a method for measuring a barrel-shaped toroidal surface (hereinafter referred to as "BTS") or a saddle-shaped toroidal surface (hereinafter referred to as "KTS") having a long G main diameter line and a short R main diameter line. , It can be said that the toroidal surface is treated as a rotating surface. This will be described below with reference to FIGS. 5 (a) and 5 (b).

In the figure, reference numeral 1 denotes a light source, which is a gas laser or semiconductor laser having high coherence. 2a,
2b is a beam expander for expanding a narrow light beam from the light source 1 to an appropriate size. 3 is a spatial filter, which cuts off unnecessary light such as ghost light and reflected light. An optical isolator 4 is a beam splitter 4a, λ /
It has four plates 4b and a reflecting surface 4c.

The light beams expanded by the beam expanders 2a and 2b pass through the objective lens 6 and reach the toroidal surface 7a as the surface to be examined of the subject 7. This toroidal surface 7a
Is, as described above, the R main radial lines AB and G which are orthogonal to each other at the vertex.
It is formed by rotating the R main radial line of the main radial line CD around the rotary shaft 12.

The final surface of the objective lens 6 is a reference surface 6a as a semi-transparent mirror, and the center of curvature thereof coincides with the rotation axis 12 described above. Further, the reference surface 6a or the toroidal surface 7a is arranged so as to be slightly shiftable and / or tiltable in the xz section. Then, a part of the light incident on the objective lens 6 is reflected by the reference surface 6a, and the rest is transmitted to irradiate the toroidal surface 7a, and is reflected from here.

Reference numeral 13 denotes a support base for fixing the subject 7, which is driven by a linear motor, a linear air slider or the like (not shown) and can scan the toroidal surface 7a in parallel with the rotary shaft 12.

The coherent light reflected by the reference surface 6a and the toroidal surface 7a is returned along the optical path and is superimposed, and the reference surface 6a.
6 and the toroidal surface 7a interfere with each other on one measurement section parallel to the R main diameter line which can be regarded as substantially parallel, and the focusing lens 9 forms an interference fringe image 11 on the area sensor 10 as shown in FIG. ..

When the support base 13 is scanned along the rotary shaft 12, the measurement cross sections move to form interference fringe images one after another,
By connecting these, the surface shape and surface accuracy of the entire toroidal surface 7a can be measured. Further, the above-mentioned device is not limited to the BTS, and can measure all the rotating surfaces such as all toroidal surfaces and cylindrical surfaces. In this case, it should be noted that even if the rotation axis is a three-dimensionally curved rotation surface, the support base may scan in accordance with the bending of the rotation axis, and thus it is applicable.

FIG. 7 shows a state in which the BTS plane is measured.
Reference numeral 7a in the figure is a BTS (barrel-shaped toroidal surface) as a surface to be inspected. O indicates the center of curvature of the G main diameter line AB (bus line). One reference surface 6a ₁ is located at the center of the surface 7a to be inspected, and the other reference surface 6a ₂ is in a state of being moved downward from the center of the surface 7a to be inspected by scanning. During this time, the coherent light irradiates the reference surface 6a and the test surface 7a so that the coherent light is always focused on the rotating shaft 12. Also, the subject 7
The width l (Fig. 7 (b)) is constant in the direction of the rotating shaft 12.

When the reference surface comes to the position of 6a ₁ , as shown in FIG.
The reference wave reflected at the center of the reference surface 6a ₁ and the test wave reflected from the measurement cross section 7a _{1 at} the center of the test surface 7a are overlapped as shown by an arrow to form an interference fringe. The length of the interference fringe at that time is wo as shown in FIG.
When the reference surface 6a moves to the position of 6a ₂ by scanning, the reference wave and the test wave incident and reflected at a right angle on both the reference surface 6a ₂ and the test surface 7a interfere with each other.
₂ is Δh shifted on the rotation axis 12, and the interference fringe image is the rotation axis 6a.
_An image is deviated from the optical axis of ₂ by Δh '. Further, since the measurement cross section 7a ₂ approaches the rotation axis 12, the length of the interference fringe is w.
And becomes longer than wo.

FIG. 8 shows the interference fringes imaged on the area sensor 10. For the reason described in FIG. 7, the length of the interference fringe image becomes as short as wo at the central portion where the R main radius line is present. It becomes longer as it goes away from the R main radius line, and Δh 'from the center
Deviated. Therefore, when the interference fringes are processed by FFT or the like to calculate the surface accuracy and the surface shape, the data lengths are different, which makes the processing difficult.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve this problem, and when measuring a rotating surface, the radius of curvature of the measured cross section changes with the scanning of the surface to be inspected. It is an object of the present invention to provide a method and an apparatus capable of obtaining data from interference fringes having almost the same size.

[0015]

In order to achieve the above object, the measuring method of the present invention uses coherent light from the same light source,
Irradiate the rotating surface as the surface to be inspected and the reference surface to be the reference,
A step of superposing the reference wave and the test wave reflected from both surfaces to form an interference fringe for one measurement cross section of the surface to be inspected, and forming the interference fringe on the sensor to store the data of the interference fringe image. A step of scanning the surface to be inspected in parallel with the rotation axis of the rotating surface to continuously form the interference fringes on each measurement section, and a radius of curvature r of each measurement section from a design value of the shape of the surface to be inspected.
And a measurement section length 1 to calculate the lateral magnification m of the interference fringe image at each measurement section, and the lateral magnification m is multiplied to the stored data of each interference fringe image to perform scanning. And a step of correcting the size of the resulting interference fringe image.

The lateral magnification may be determined by measuring the size of the interference fringe image on each measurement cross section. Alternatively, the radius of curvature ro of the reference measurement section is measured by the spherometer method with reference to an arbitrary measurement section of the surface to be inspected.
Then, the generatrix of the test surface is obtained by counting the number of fringes of the interference fringe image flowing on the sensor in accordance with the scanning in the rotation axis direction, and from the curvature radius ro of these reference measurement cross sections and the bus bar of the test surface. A method of obtaining the lateral magnification m by obtaining the shape of the surface to be inspected may be used.

[0017]

The coherent light is applied to the rotating surface and the reference surface to form interference fringes on one measurement cross section of the surface to be inspected and form an image on the sensor. The surface to be inspected is scanned in parallel with the rotation axis, the interference fringe images are continuously formed on the sensor, and the data of each interference fringe image is extracted and stored.

On the other hand, the radius of curvature r ₀ is determined with reference to an arbitrary measurement section, and the radius of curvature r is determined for each measurement section. From these, the lateral magnification m of the interference fringe image of each measurement section with respect to the reference interference fringe image. To calculate. This lateral magnification m
Is multiplied by the interference fringe data, the size of the interference fringe image in each measurement cross section can be corrected and always treated as an interference fringe image of approximately the same size as the interference fringe image of the reference measurement cross section.

The radius of curvature of the measured cross section can be obtained from the design value of the surface to be inspected if the shape is known. When the shape of the surface to be inspected is unknown, the length of the interference fringe image of each measurement section is measured, and the lateral magnification m is calculated for each measurement section.
You can also ask. As another method, the radius of curvature r of the reference measurement section is measured by the spherometer method.
o is obtained, the bus bar is obtained by counting the flow of the fringe pattern of the interference fringe image formed on the sensor based on the scanning, the shape of the test surface is known from these, and any measurement can be performed from the shape of the test surface. The radius of curvature r and the lateral magnification m of the cross section can also be obtained.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a rotating surface measuring apparatus according to the present invention. The part surrounded by the dotted line in FIG.
The same interference optical system as that shown in FIG. Inside, only the reference surface 6a, the surface 7a to be inspected, the area sensor 10 and the support base 13 are shown, and the others are omitted.

The test wave from the test surface 7a and the reference wave from the reference surface 6a are superimposed, and an interference fringe image for one measurement cross section of the test surface is formed on the area sensor 10. Various sensors can be used as the area sensor, and the output of the area sensor 10 is temporarily stored as the interference fringe data storage means 1.
4 RAM, floppy disk or the like. The surface 7a to be inspected is scanned by the support base 13 along the rotation axis, and the scanning movement amount can be known by a linear encoder provided on the support base 13.

Reference numeral 15 is a lateral magnification calculating means for calculating the lateral magnification m for an arbitrary measurement section from the design value of the shape of the surface to be inspected. That is, if the shape of the surface to be inspected is known, the radius of curvature r in an arbitrary measurement cross section can be calculated from the scanning amount from the linear encoder and the equation of the generatrix of the rotating surface. The change in the size (length) can be predicted in advance from the value of r, the width of the surface to be inspected, the constant of the interference optical system, and the like. For example, when the surface to be inspected 7a is BTS,

R = ro + R−√ {R ² − (h + Δh) ² } (1) where, ro: short radius of curvature in the central portion (reference measurement section) of the BTS r: short measurement section at an arbitrary scanning amount Hand radius of curvature R: Longitudinal radius of curvature in the central portion of BTS (reference measurement section) (curvature radius of G main diameter line or generatrix) h: Scan movement amount from the reference measurement section Δh: Measurement section position correction amount (Fig. 7 ( On the other hand, the size w of the interference fringe image after passing through the reference lens again is: w = (r / l) × f (2) where f: focal length of the reference lens 6 l: subject 7 width (FIG. 7 (b)) At this time, the lateral magnification m of the interference fringe image formed on the area sensor 10 for each measurement cross section can be obtained by the following equation. m = (wo / w) × mo (3) where mo: lateral magnification of the interference optical system wo: size of the interference fringe image in the reference measurement section

That is, w for an arbitrary measurement cross section can be obtained from the equations (1) and (2), and the length of the interference fringe image 11 formed on the area sensor 10 can be predicted. Thus, the lateral magnification m at that time can be calculated.

Therefore, in the correction calculation means 16, the lateral magnification calculation means 1 is added to the interference fringe data in the interference fringe data storage means 14.
If the lateral magnification m from 5 is multiplied, the size w of the interference fringe image corresponding to an arbitrary scanning movement amount h can be treated as a constant value. The corrected interference fringe data thus obtained is stored in the corrected data storage means 17. The correction data storage means 17, like the interference fringe data storage means 14, is composed of a RAM, a floppy disk, or the like. The corrected interference fringe data is input to the surface accuracy calculation means 18, and here, the above-mentioned Japanese Patent Application No. 3-05010.
Processed by the FFT calculation method described in No. 4,
The surface accuracy and surface shape of the surface to be inspected are displayed on the output unit 19 such as a display.

In the above embodiment, the reference measurement cross section is the central portion of the BTS, but there is no inevitable reason for determining the reference measurement cross section here, so any reference measurement cross section is used as the reference. be able to.

FIG. 2 is a block diagram showing a second embodiment of the present invention. While the first embodiment is applied to a known object shape, this embodiment is applicable to an unknown rotating surface. Interference fringe data storage means 14
The process up to the step of storing the interference fringe data is the same as in the embodiment of FIG. However, in this embodiment, the lateral magnification calculation means 15 calculates the lateral magnification m from the value of w of each interference fringe image stored in the interference fringe data storage means 14 regardless of the design value. At this time, the reference measurement cross section may be set at an arbitrary position and the value of wo may be determined.

3 and 4 show a third embodiment of the present invention. Also in this embodiment, the interference fringe data storage means 14
The process up to the step of storing the interference fringe data is the same as in the embodiment of FIG. However, in the interference optical system of this embodiment,
Further, there is a second support 13 'so that the surface 7a to be detected can be moved in the optical axis direction. This second support 1
3'is basically the same as the support table 13 except that the scanning directions are orthogonal to each other, and is preferably formed integrally with the support table 13. However, the interference optical system from the light source 1 to the reference surface 6a may of course be moved. Then, the short-side curvature radius ro of the reference measurement cross section is obtained in advance by the spherometer method.

The spherometer system is as shown in FIG.
First, the center of curvature of the reference surface 6a and the center of curvature of the surface to be inspected are
Match and generate interference fringes, and reduce the number of fringes as much as possible.
6a ₃Position, the center of curvature of the reference surface 6a, and the surface 7a to be tested.
Cat's eye interference fringes are formed by matching with the surface of 6
a_FourPosition and the amount of movement on the optical axis between them is calculated.
This is a method of setting the radius of curvature ro of the reference measurement cross section. Transfer above
The amount of movement is determined by the linear axis in the optical axis direction provided on the support base 13 '.
Read by the encoder and calculate the surface shape as the value of ro
It is input to the means 20.

On the other hand, the generatrix, that is, the radius of curvature R in the longitudinal direction is obtained by the following method. As the surface to be inspected 7a is scanned by the support base 13 along the rotation axis 12, the distance between the reference surface 6a and the surface to be inspected 7a changes, but this change is due to the stripes in the interference fringe image on the area sensor 10. Observed as a pattern flow. Therefore, if one point is set on the interference fringe image and the number of fringes passing through this point is counted, the displacement amount of the surface to be inspected 7a in the optical axis direction can be known. Since the flow of stripes can be grasped as a change in the output of the element of the area sensor that constitutes the above point, it may be counted by the counting means 21 such as a pulse counter.

The number of stripes counted by the counting means 21 determines the coordinates of one measurement section in the optical axis direction, and the support 13
The signal of the scanning movement amount from the linear encoder is input to the bus bar computing means 22. Of the above, the number of stripes determines the coordinates of one measurement cross section in the optical axis direction, and the signal from the linear encoder determines the coordinates in the direction perpendicular to the optical axis. Therefore, the busbar computing means 22 uses the least squares method. By applying
It is possible to calculate the radius of curvature R in the longitudinal direction along the rotation axis of the surface to be inspected 7a or the equation of the generatrix of the rotation surface.

The R signal from the busbar calculating means 22 and the ro signal from the second supporting base 13 'are input to the surface shape calculating means 20, where the surface shape of the surface 7a to be tested is determined. Become. Once the surface shape is determined, the lateral magnification m is calculated by the lateral magnification calculation means 15 in the same flow as in the embodiment of FIG. 1 and converted into an interference fringe image of substantially the same size to determine the surface accuracy and surface shape. You can ask.

[0033]

As described above, according to the present invention, in the measurement of the surface shape and surface accuracy of the rotating surface, it is almost the same even though the radius of curvature of the measurement cross section changes with the scanning of the surface to be inspected. Data can be obtained from the interference fringes of a size.
Further, according to the invention of claim 1, it is suitable for measurement of a test surface whose design shape is known, and according to the inventions of claims 2 and 3, it is possible to measure a rotating surface of unknown shape.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a rotating surface measuring apparatus according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a third embodiment of the present invention.

FIG. 4 is a diagram illustrating a method of obtaining a radius of curvature of a measurement cross section by a spherometer method.

FIG. 5 is a diagram showing an apparatus for measuring a toroidal surface of a BTS in the example of the prior application, (a) is a yz plane view, and (b) is an xz plane view.

6 is a diagram showing an interference fringe image formed on an area sensor by the apparatus of FIG.

FIG. 7 is a diagram showing a state in which the positional relationship between the surface to be inspected and the reference surface is changed by scanning in the rotation axis direction, (a) is a yz plane view,
(b) is an xz view.

FIG. 8 is a diagram showing a state in which the size (length) of an interference fringe image changes with scanning.

[Description of Reference Signs] 1 light source 6a reference surface 7a surface to be measured (rotating surface or BTS) 9 focusing optical system 12 rotating shaft 13 support base 13 'second support base 14 interference fringe data storage means 15 lateral magnification calculation means 16 correction calculation Means 17 Correction data storage means 20 Surface shape calculation means 21 Counting means 22 Busbar calculation means

Claims (6)

[Claims] 1. Coherent light from the same light source is applied to a rotating surface as a surface to be inspected and a reference surface as a reference, and the reference wave and the wave to be inspected reflected from both surfaces are superposed. A step of forming interference fringes on one measurement cross section of the surface; a step of forming the interference fringes on a sensor and storing data of the interference fringe image; and a surface to be inspected is scanned in parallel with the rotation axis of the rotating surface. And continuously forming the interference fringes for each measurement cross section, and calculating the radius of curvature r of each measurement cross section from the design value of the surface shape to be measured, and obtaining the lateral magnification m of the interference fringe image in each measurement cross section. And a step of correcting the size of the interference fringe image generated during scanning by multiplying the stored data of each interference fringe image by the lateral magnification m. Method. 2. Coherent light from the same light source is applied to a rotating surface as a surface to be inspected and a reference surface serving as a reference, and the reference wave and the wave to be inspected reflected from both surfaces are superposed. A step of forming interference fringes on one measurement cross section of the surface; a step of forming the interference fringes on a sensor and storing data of the interference fringe image; and a surface to be inspected is scanned in parallel with the rotation axis of the rotating surface. And continuously forming the interference fringes on each measurement cross section, measuring the size of the interference fringe image on each measurement cross section, and obtaining the lateral magnification m of the interference fringe image on each measurement cross section. And a step of correcting the change in the size of the interference fringe image that occurs during scanning by multiplying the data of each of the interference fringe images by the lateral magnification m. 3. Coherent light from the same light source is applied to a rotating surface as a surface to be inspected and a reference surface as a reference, and the reference wave and the wave to be inspected reflected from both surfaces are superposed. Forming an interference fringe for one measurement cross section of the surface, determining a radius of curvature ro of the reference measurement cross section by a spherometer method using an arbitrary measurement cross section of the surface to be measured as a reference, and forming the interference fringe on the sensor And storing the data of the interference fringe image; a step of scanning the surface to be inspected in parallel with the rotation axis of the rotation surface to continuously form the interference fringes on each measurement section; A step of obtaining a generatrix of the surface to be inspected by counting the number of fringes of the interference fringe image flowing on the sensor with scanning, and a shape of the surface to be inspected from the radius of curvature ro of the reference measurement cross section and the generatrix of the surface to be inspected. Based on the required process and the shape of the surface to be inspected, Of the interference fringe image corresponding to the surface,
The step of obtaining the lateral magnification m of the reference measurement cross section with respect to the interference fringe image, and the change in the size of the interference fringe image generated during scanning by multiplying the stored lateral fringe m by the stored data of the respective interference fringe images. A method of measuring a rotating surface, which comprises the step of: 4. Coherent light from the same light source is applied to a rotating surface as a surface to be inspected and a reference surface as a reference, and the reference wave and the wave to be inspected reflected from both surfaces are superposed. A device for forming interference fringes on one measurement cross section of a surface, a support for scanning the surface to be inspected along the rotation axis of the rotating surface, a sensor for imaging the interference fringes, and an interference fringe imaged on the sensor Interference fringe data storage means for storing image data, lateral magnification calculation means for knowing the radius of curvature r in each measurement section of the surface to be measured from the design value of the surface to be measured, and calculating the lateral magnification m in each measurement section. A measuring device for a rotating surface, comprising: a correction calculation means for correcting the interference fringe data by multiplying the lateral magnification m by the interference fringe image data. 5. Coherent light from the same light source is applied to a rotating surface as a surface to be inspected and a reference surface serving as a reference, and the reference wave and the wave to be inspected reflected from both surfaces are superposed. A device for forming interference fringes on one measurement cross section of a surface, a support for scanning the surface to be inspected along the rotation axis of the rotating surface, a sensor for imaging the interference fringes, and an interference fringe imaged on the sensor Interference fringe data storage means for storing image data; lateral magnification calculation means for calculating a lateral magnification m of each interference fringe from the interference fringe data; and lateral magnification m for multiplying the interference fringe image data by A measuring device for a rotating surface, comprising: a correction calculation means for correcting interference fringe data. 6. A coherent light beam from the same light source is applied to a rotating surface as a surface to be inspected and a reference surface as a reference, and the reference wave and the wave to be inspected reflected from both surfaces are superposed. A device for forming interference fringes on one measurement cross section of a surface, a sensor for imaging the interference fringes, a support for scanning the surface to be inspected along a rotation axis, and a relative surface between the surface to be inspected and the reference surface. Second support table that can measure the amount of movement while giving various movements, a means for counting the number of fringes of the interference fringe image flowing on the sensor along with the scanning along the rotation axis, the output of the counting means and the support table. A busbar calculating means for calculating a busbar of the surface to be inspected from the scanning amount of the object, a radius of curvature ro of the reference measurement surface obtained by the spherometer method by the second support, and a shape of the entire surface to be inspected from the busbar by the busbar calculating device. And a surface shape calculation means for calculating It is comprised of lateral magnification calculating means for calculating the lateral magnification m of each measurement section from the output of the stage, and correction computing means for multiplying the lateral magnification m with the data of the interference fringe image to correct the interference fringe data. Measuring device for rotating surface.