JPH06273129A - Method and apparatus for measuring rotary surface - Google Patents

Abstract

PURPOSE:To provide a method and an apparatus whereby an image of interference fringes can be formed at all times on a line sensor when a to-be-inspected surface is scanned along a rotary shaft used to form a rotary surface to measure the rotary surface utilizing the interference. CONSTITUTION:A coherent light from the same light source 1 is cast to a reference surface 6a and a to-be-inspected surface 7a which is a rotary surface. A reference wave and a to-be-inspected wave reflected at both surfaces are overlapped, whereby an image of interference fringes is formed on an area sensor 10 and a line sensor 10' via an image forming lens 9 and a beam splitter 15. When the to-be-inspected surface 7a is scanned along a rotary shaft 12, the image of interference fringes is moved. The moving amount is measured by the area sensor 10, corresponding to which the beam splitter 15 is moved in a y-axis or z-axis direction so that the image of interference fringes is superposed on the line sensor 10' at all times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates a reference surface and a reference surface composed of a rotating surface with coherent light so that a reflected reference wave and a test wave are superposed and interfered with each other to form an image of an interference fringe. The present invention relates to a technique for forming an image on a sensor to measure a surface shape and a surface accuracy, and more particularly to a technique for following movement of an interference fringe image in an image forming surface in accordance with scanning of a surface to be inspected.

[0002]

2. Description of the Related Art As a technique for forming interference fringes using a coherent light such as a laser beam and measuring the surface shape and surface accuracy of a toroidal surface with high accuracy below a wavelength, the applicant of the present invention has
In Japanese Patent Application Laid-Open No. 4-269609 of the prior application, FIGS. 10 (a) and 10 (b)
We have proposed a toroidal surface measuring device shown in.

In FIG. 1, reference numeral 1 denotes a light source, which is a gas laser or semiconductor laser having high coherence. 2,5
Is a beam expander for expanding a narrow luminous flux from the light source 1 to an appropriate size. A spatial filter 3 cuts unnecessary light such as ghost light and reflected light. Four
Is an optical isolator, a beam splitter 4a, a λ / 4 plate 4
b and the reflecting surface 4c.

The light flux expanded by the beam expanders 2 and 5 passes through the objective lens 6 and reaches the surface 7a to be inspected of the subject 7. The surface 7a to be inspected is a barrel-shaped toroidal surface, which is formed by rotating around the rotary shaft 12 with one main radial line AB among the main radial lines having different radii of curvature orthogonal to each other at the apex as a generatrix. It is a rotating surface.

The final surface of the objective lens 6 is a reference surface 6a as a semi-transparent mirror, and the center of curvature thereof is the rotation axis 12.
It is placed in a position that matches the top. Also, this reference surface 6a
Alternatively, the toroidal surface 7a is arranged such that it can be slightly shifted and / or tilted to form interference fringes.

[0006] Reference numeral 8 is a translation table for fixing the subject 7
The surface 7a to be inspected is scanned along the rotary shaft 12 by a DC servo motor, a stepping motor or the like (not shown).

The coherent light emitted from the light source 1 is reflected by the reference surface 6
a and the surface to be inspected 7a are reflected to become a reference wave and an inspected wave,
The optical path that came is returned and superimposed, and the reflecting surface 4 of the optical isolator 4
After being reflected by c, the image forming lens 9 forms a slit-shaped interference fringe image 11 on the sensor 10 as shown in FIG.

FIG. 12 is a diagram showing the relationship among the surface 7a to be tested, the reference surface 6a and the rotary shaft 12. Although the reference surface 6a moves with respect to the surface 7a to be detected by the movement of the translation table 8, the moving state is illustrated at three positions. In this movement, the center of curvature O ″ of the reference surface 6a always overlaps the rotation axis 12, and the coherent light emitted from the objective lens 6 is set so as to be focused on the point O ″ on this rotation axis. . The point O'indicates the center of curvature of the surface 7a to be tested.

When the reference surface 6a shifts up or down from the center line 14 of the test surface, the reference light and the test wave overlap and interfere with each other. . Further, the length of the interference fringe image 11 also changes with the change in the radius of curvature of the measurement cross section. That is, when the reference surface 6a scans the surface 7a to be inspected, the interference fringe image 11 moves within a range indicated by a virtual line 11 'in the image plane 13 as shown in FIG.

Therefore, the surface to be inspected 7 is scanned by the translation table 8.
By forming an interference fringe image for each measurement cross section of a and connecting the interference fringe images, the surface accuracy of the entire rotating surface can be measured. In that case, it is convenient to dispose an area sensor on the image plane 13. The above-mentioned device can measure various toroidal surfaces such as a toroidal surface and various types of rotating surfaces including spherical surfaces.

When the translation table 8 is scanned along the rotary shaft 12, the distance between each measurement section and the reference plane changes, as can be seen from FIG. When the change in the distance is observed with an interference fringe image, the interference fringes appear to flow in the x-axis direction in FIG. Therefore, if a fixed observation point is set in the interference fringe image and the number of fringes passing through the observation point is counted,
The change in the distance between the measurement section and the reference plane can be measured from the wavelength of the coherent light. That is, the shape of the generatrix AB of the rotating surface, that is, the surface shape can be known. In this case, the sensor 1
A line sensor of 0 is easier to count. Regarding this measurement, the applicant of the present application has filed a prior application, Japanese Patent Application No. 4-3.
No. 47001.

[0012]

However, when measuring the above-mentioned rotating surface, especially when measuring the surface shape by the line sensor, the interference fringe image moves in the image forming plane as described with reference to FIG. Therefore, it is necessary to make the line sensor follow the position of the interference fringe image. The present invention has responded to this request, and an object of the present invention is to provide a method and apparatus capable of always forming an interference fringe image on a line sensor in measuring a rotating surface.

[0013]

To achieve the above object, the measuring method of the present invention irradiates coherent light from the same light source onto a reference surface and a surface to be inspected, which is a rotating surface, and from both surfaces. An image of interference fringes is formed on the sensor by superimposing the reflected reference wave and the test wave, and the test surface is scanned along the rotation axis used to create the rotation surface and the interference fringes are continuously formed. In a method of measuring a rotating surface for forming an image, a reflection optical system is provided in a light beam for forming the interference fringe, and the reflection optical system and / or the sensor is moved to always form the interference fringe image on the sensor. It is characterized by the configuration.

Alternatively, the reflection optical system splits the light beam forming the interference fringe into two, one of the light beams forms an image of the interference fringe on the area sensor, and the other light beam forms the interference fringe on the line sensor. It is characterized in that an image is formed and the reflection optical system and / or the line sensor is moved to always form an interference fringe image on the line sensor.

Next, the device of the present invention irradiates the coherent light from the same light source onto the surface to be inspected and the reference surface as a reference, and superimposes the reference wave and the wave to be inspected reflected from both surfaces. A device for forming an interference fringe image, a sensor provided at an image forming position of the interference fringe image, a translation stage for scanning the surface to be inspected along the rotation axis used for its creation, and an optical path for forming the interference fringe. The reflection optical system and / or the sensor so that the interference fringe image is always formed on the sensor by following the movement of the interference fringe image accompanying the scanning of the translation table and the reflection optical system. It is characterized by a configuration including a tracking device for driving the.

Alternatively, the coherent light from the same light source is applied to the test surface and the reference surface as a reference, and the reference wave and the test wave reflected from both surfaces are superposed and interfered with each other. A variable-magnification optical system that forms an interference fringe image from the reference wave and the test wave, a sensor provided at the position where the interference fringe image is formed, and the surface to be inspected is scanned along the rotation axis used to create it. The translation stage and the sensor are moved in response to the scaling signal from the scaling optical system, and the interference fringe image is always formed on the sensor regardless of the movement of the interference fringe image accompanying the scanning of the translation stage. The sensor moving device is provided.

[0017]

The coherent light emitted from the light source is applied to the test surface and the reference surface to form a slit-shaped interference fringe image on a part of the test surface. When the surface to be inspected is scanned by the translation table,
Slit-shaped interference fringe images are formed one after another, but these images move within the image formation plane due to scanning, and come off the sensor. Therefore, if a reflection optical system is provided in the image forming optical path and the interference fringe image is formed at a position away from the sensor, the reflection optical system and / or the sensor is moved so that the interference fringe image and the sensor coincide with each other. To follow.

A beam splitter is used as the reflection optical system, an area sensor is placed in one optical path, and a line sensor is placed in the other optical path. Along with the above scanning, the reflection optical system is moved so that the interference fringes are imaged on the line sensor.

Since the movement amount of the interference fringe image can be known from the position of the interference fringe image formed on the area sensor, the follow-up device of the reflection optical system and / or the line sensor is automatically controlled by this movement amount. be able to.

If the imaging lens is a variable power optical system, the size of the interference fringe image can be changed. When the interference fringe image becomes large, scanning may cause the interference fringe image to protrude from the area sensor. In that case, the area sensor is moved so that an interference fringe image is always formed on the area sensor.
This makes it possible to measure the surface shape and surface accuracy of various rotary bodies.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the configuration of the measuring apparatus according to the present invention, but most of it is the same as the conventional apparatus described in FIG. Therefore, the configuration will be described below focusing on the difference. Note that an interferometer of a type different from the illustrated interferometer may be used.

The apparatus of the present invention is provided with a beam splitter 15 as a reflection optical system in the parallel light flux emitted from the imaging lens 9. As the beam splitter 15, a half mirror or a half prism can be used. The beam splitter 15 divides the luminous flux from the imaging lens 9 into two.
The image is divided into two parts, one of which is emitted to the area sensor 10 and the other of which is emitted to the line sensor 10 'to form an interference fringe image on each sensor. For area sensors and line sensors,
A CCD, a photodiode array or the like can be used. The surface accuracy information is obtained from the intensity signal of the interference fringe image formed on the area sensor 10, and the surface shape information is obtained from the intensity signal of the line sensor 10 '.

The beam splitter 15 is fixed on a tracking device 16, and the tracking device 16 can be moved in the y-axis direction (or z-axis direction) by a stepping motor or the like not shown.

The interference fringe image formed on the area sensor 10 is
Although it moves in the image plane as the translation table 8 scans, the movement amount calculating means 17 can calculate the movement amount, and a signal corresponding to the movement amount is sent to the tracking device 16.

FIG. 2A shows the beam splitter 15
It is a figure explaining a mode that an interference fringe image is followed. Incident ray
Is the beam splitter 1 that initially enters from I and is shown by the solid line.
P in 5₁And P₂It is divided into For scanning the translation table 8
Therefore, the incident light beam moves to I ′ and the beam splitter 1
If 5 stays in the position of the solid line, this time P₁'When
P ₂’ P₂To P₂Move to ′
There is no problem because it is a movement within the sensor 10, but P₁From
P₁When moving to ', the line sensor 10' will be disengaged.
It becomes impossible to count the interference fringes.

Therefore, the moving amount calculating device 17 shown in FIG. 1 measures the distance d between P ₂ and P ₂ ′, and accordingly, the moving table 16 or the beam splitter 15 is moved in the y-axis direction orthogonal to the optical axis. Move by e and overlap P ₁ ′ with P ₁ . Note that FIG.
As shown in (b), the beam splitter 15 is moved to the optical axis (z
It may be configured to move by e'in the (axis) direction.

FIG. 3 is a diagram showing the configuration of the second embodiment of the present invention. In this embodiment, the beam splitter 15 as a reflection optical system is arranged at a position where the light beam emitted from the optical isolator 4 is focused. In addition, the tracking device 18
Is a turntable, and the rotation thereof follows the movement of the interference fringes.

The operation will be described with reference to FIG. The incident ray is
Initially incident from the direction of I. The beam splitter 15 is initially located at the position shown by the solid line and splits the incident light beam into P ₁ and P ₂ . When the incident light beam is moved from the direction I'by scanning the translation table 8, it is divided into P ₁ 'and P ₂ '. Therefore, the moving distance d of the interference fringe image is obtained by the area sensor 10. Since the distance from the beam splitter 15 to the area sensor 10 is constant, P ₁ and P ₁ 'from the value of the d
Then, the angle θ required to overlap with each other is calculated, and the rotary table 18 is rotated to the position indicated by the imaginary line.

In FIG. 5, the half mirror of the beam splitter 15 is masked 15b except inside the small circle 15a at the center. By focusing the light flux within the small circle 15a, stray light can be eliminated and a clear interference fringe image can be obtained.

FIG. 6 is a diagram showing another embodiment of the present invention. A variable magnification lens such as a variable focus lens or a zoom lens is used as the imaging lens 9'in this figure, and the size of the interference fringe image can be freely changed. A beam splitter 15 is placed as a reflection optical system in the parallel light flux emitted from the imaging lens 9 '. The beam splitter 15 in this embodiment is fixed.

The beam splitter 15 splits the light beam coming from the imaging lens 9'into the line sensor 10 'and the mirror 19. The light flux reflected by the mirror 19 reaches the sensor 10 and forms an interference fringe image.

The line sensor 10 'is fixed on the tracking device 20 and moves back and forth in the y-axis direction. This movement is performed by a DC servo motor, a stepping motor, or the like (not shown) similar to the translation table 8. The area sensor 10 is a moving device 2
1 and moves back and forth in the y-axis direction together with the moving device 21,
The distance from the imaging lens 9 to the area sensor 10 is changed.

In the movement amount calculation device 17, the area sensor 10
The movement amount is calculated from the position of the interference fringe image formed above, and the tracking device 20 is driven based on the calculated movement amount. Reference numeral 22 denotes a sensor control device, which receives a signal corresponding to the zoom magnification from the imaging lens 9 and drives the moving device 21 to form an interference fringe image so as not to protrude from the area sensor 10.

The operation of the apparatus shown in FIG. 6 will be described with reference to FIGS. 7 to 9. First, the locus 11 'of the interference fringe image 11 formed when the translation table 8 scans the entire surface to be inspected is shown in FIG.
As shown in (b), the area sensor 10 does not have to be moved when the area sensor 10 is represented by a virtual line.

On the other hand, in the line sensor 10 ', the movement amount calculation device 17 calculates the movement amount of the interference fringe image, and the tracking device 20 follows the interference fringe image accordingly. This embodiment is different from the above-described embodiments in that the line sensor 10 'is moved without moving the beam splitter 15 as the reflection optical system.

Next, the loci of the interference fringe images are shown in FIGS. 8 (a) and 8 (b).
Even if it is represented by an imaginary line that fits within the area sensor 10 as shown in FIG. 3, if the length d ₀ of the interference fringe image at the center is short, the interval between the fringes becomes small and the distinction between bright and dark is made. It becomes difficult to do.

Therefore, the image forming lens 9'enlarges the interference fringe image as shown in FIG. 9 (a). By doing so, the contrast of the interference fringes becomes clear, and the surface shape and surface accuracy can be easily measured.

However, if the interference fringe image is enlarged, when the surface to be inspected is scanned, the interference fringe image will protrude from the area sensor 10 as shown in FIG. 9B. Therefore, the sensor control device 22 receives a signal according to the magnification from the imaging lens 9 ', drives the moving device 21 according to the protruding length shown in FIG. 9 (b), and moves the area sensor 10 forward and backward in the arrow direction. Let By doing so, it becomes possible to measure a rotating surface having a shape that is conventionally difficult to measure.

The variable power optical system 9'in this embodiment is used.
It will be apparent from the above description that can also be used in the embodiment shown in FIG.

[0040]

As described above, according to the present invention,
In the measurement of the rotating surface, the interference fringe image can be always formed on the line sensor, even though the interference fringe image moves due to the scanning of the rotating surface. The device can be made compact by adopting a method of moving the reflection optical system. Further, if the imaging lens is a zoom lens or a variable focus lens and the area sensor is movable, it is possible to measure various rotating surfaces.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an apparatus of the present invention.

FIG. 2 is a diagram illustrating a tracking principle by a reflective optical system,
(a) is for moving the reflective optical system in the y-axis direction, (b) is for z
The case of moving in the axial direction is shown.

FIG. 3 is a diagram showing a configuration of an embodiment in which a reflective optical system is rotated to follow.

FIG. 4 is a diagram illustrating the following principle of FIG. 3;

FIG. 5 is a diagram showing a state in which the reflective surface of the reflective optical system is masked.

FIG. 6 is a diagram showing the configuration of another embodiment of the present invention.

7A and 7B are diagrams for explaining the operation of FIG. 6, where the size of an interference fringe image is just right, FIG. 7A is a diagram showing a relationship between a line sensor and a locus of interference fringes, and FIG. It is a figure which shows the relationship between an area sensor and the locus | trajectory of an interference fringe.

FIG. 8 is an example when the size of an interference fringe image is too small,
(a) is a diagram showing the relationship between the line sensor and the locus of interference fringes,
(b) is a diagram showing a relationship between an area sensor and a locus of interference fringes.

FIG. 9 is an example showing a state in which the size of an interference fringe image is enlarged,
(a) is a diagram showing the relationship between the line sensor and the locus of interference fringes,
(b) is a diagram showing a state in which the area sensor moves to form an interference fringe image.

FIG. 10 is a diagram showing a configuration of a conventional measuring device for a rotating surface,
(a) is a yz plane view, (b) is an xz plane view.

FIG. 11 is a diagram showing a state in which an interference fringe image is formed on the area sensor.

FIG. 12 is a diagram illustrating a state in which an interference fringe image moves with respect to a reference surface as a rotating surface is scanned.

FIG. 13 is a diagram showing a state in which an interference fringe image moves in the image plane along with the scanning shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 6a reference surface 7a test surface 9, 9'imaging lens 10 area sensor 10 'line sensor 11 interference fringe image 12 rotating shaft 15 reflection optical system (beam splitter) 16, 18, 20 tracking device 17 movement amount calculating device 21 moving device 22 sensor control device

Claims (11)

[Claims] 1. Coherent light from the same light source is applied to a reference surface and a surface to be inspected consisting of a rotating surface, and the reference wave and the wave to be detected reflected from both surfaces are superimposed to form an interference fringe on the sensor. An optical path for forming the interference fringes in a method of measuring a rotating surface, which forms an image and scans the surface to be inspected along the rotation axis used to create the rotating surface to continuously form the interference fringe image. A method of measuring a rotating surface, characterized in that a reflection optical system is provided inside, and the reflection optical system and / or the sensor is moved to constantly form the interference fringe image on the sensor. 2. The reflection optical system splits a light beam forming the interference fringe into two, one light beam forms an interference fringe image on an area sensor, and the other light beam forms an interference fringe on a line sensor. 2. The method for measuring a rotating surface according to claim 1, wherein an image is formed, and the reflection optics and / or the line sensor is moved so that an interference fringe image is always formed on the line sensor. 3. The reflection optical system is placed in a parallel light flux forming the interference fringes, and the reflection optical system linearly moves so that the one interference fringe image is always formed on a line sensor. The method for measuring a rotating surface according to claim 2, wherein 4. The reflection optical system is placed at a focal point of a light flux forming the interference fringes, and the reflection optical system is rotated to constantly form the one interference fringe image on the line sensor. The method for measuring a surface of revolution according to claim 2, characterized in that. 5. The area sensor measures the amount of movement of the interference fringe image, and the reflection optical system and / or the line sensor is moved in accordance with the amount of movement so that the other interference fringe image is always on the line sensor. 3. Forming an image.
The method of measuring the surface of revolution described. 6. Coherent light from the same light source is applied to a reference surface and a surface to be inspected, which is a rotating surface, and the reference wave and the wave to be detected reflected from both surfaces are superimposed on the surface to be inspected on the sensor. In the measuring method of the rotating surface for forming an image of the interference fringes on one measurement cross section, and moving the surface to be tested along the rotation axis used to create the rotating surface to continuously form the interference fringe image. An area sensor is used as the sensor, and the length of the interference fringe image is scaled to a desired size to form an image on the area sensor,
A method for measuring a rotating surface, characterized in that when the surface to be inspected is moved along the rotation axis, the interference fringe image moves and the portion that extends beyond the area sensor is moved to follow the area sensor. 7. An apparatus for irradiating a coherent light beam from the same light source on a test surface and a reference surface as a reference, and superimposing a reference wave and a test wave reflected from both surfaces to form an interference fringe image. , A sensor provided at the image forming position of the interference fringe image, a translation stage for scanning the surface to be inspected along the rotation axis used for its creation, and a reflection optics provided in the optical path for forming the interference fringe image. A system and a tracking device that drives the reflection optical system and / or the sensor so that the interference fringe image is always formed on the sensor by following the movement of the interference fringe image accompanying the scanning of the translation table. A measuring device for a rotating surface, characterized by: 8. The reflection optical system is a beam splitter that divides a light beam forming the interference fringe into two beams, and the sensor connects a line sensor arranged on an image plane of one optical path and the other optical path. An area sensor disposed on the image plane, and a follow-up device for driving the reflection optical system and / or the line sensor so that one interference fringe image is always formed on the line sensor. The device for measuring a rotating surface according to claim 7. 9. An apparatus for calculating the movement amount of the interference fringe image from the position of the interference fringe image formed on the area sensor, wherein the tracking device outputs the movement amount of the interference fringe image output from the movement amount calculation apparatus. The rotating surface measuring device according to claim 8, wherein the rotating surface measuring device is driven in response to the signal. 10. A device for irradiating a coherent light beam from the same light source on a test surface and a reference surface as a reference, and superimposing and interfering a reference wave and a test wave reflected from these both surfaces with each other. A variable-magnification optical system that forms an interference fringe image from the reference wave and the test wave, a sensor that is provided at the position where the interference fringe image is formed, and the surface to be inspected is scanned along the rotation axis used to create it. The translation stage and the sensor are moved in response to the scaling signal from the scaling optical system, and the interference fringe image is always formed on the sensor regardless of the movement of the interference fringe image accompanying the scanning of the translation stage. A measuring device for a rotating surface, characterized by being provided with a sensor moving device for moving the sensor. 11. The sensor is an area sensor, and a sensor control device for calculating a movement amount of the area sensor from a magnification signal of the magnification changing optical system is provided, and the sensor movement device is driven by the sensor control device. The measuring device for the rotating surface according to claim 10.