JPH0140921B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a displacement meter such as a linear meter or a rotation angle meter using holography.

For example, in machine tools, etc., a tool rest or the like moves linearly along a guide, and the linearity of this movement is an important factor in determining the quality of machining accuracy. Therefore, in such machine tools, it is necessary to inspect the lateral runout (two components of displacement in a plane perpendicular to the direction of motion) and rotational displacement of the tool rest, etc. during assembly and precision inspection.
There are also attempts to improve machining accuracy by constantly detecting lateral vibration and rotational displacement of parts such as the tool rest during machining and controlling the movement linearly. To detect displacement, a displacement meter such as a linear meter or rotation angle meter is used. Among such displacement meters, auto-collimators have traditionally been used as optical displacement meters, but auto-collimators are obtained by superimposing the reflected light image and the original image, and the reflector is If it is tilted by θ, then if the focal length of the objective lens is f, then
It is given by 2fθ. In addition, reading accuracy is determined by the F value of the lens, and the focal length is long.
Moreover, since it is difficult to obtain a lens with a small F value, there is a limit to the measurement accuracy.

On the other hand, recently, holographic technology has been applied to interferometric measurements, and the properties of the resulting interference fringes are being clarified, so it is being considered to apply holographic interferometry to displacement meters. In this case, in order to implement a hologram as a displacement meter, real-time interference must be performed, but until now holographic interferometry has mainly been performed using double Research has been carried out using exposure methods. In addition, with displacement meters that apply conventional holographic interferometry, there are issues that need to be resolved regarding the accuracy of the displacement meter, the effects of air fluctuations and external vibrations, and the measurable range of the moving distance along the optical axis of the movable body. It remained. In order to solve some of these problems, the inventor of this invention has developed a new displacement meter using holography, which can easily implement real-time interference, reduce the effects of air fluctuations and external vibrations, and Made high-precision measurement possible (Patent Application No. 39476/1983;
(See No. 168996, etc.)

Among these newly developed displacement meters, one example of a linear meter is briefly explained as shown in Figure 1.
The laser light emitting device 2, which is a constituent element of the optical element group 10 located on a fixed body, is caused to emit light, and the beam splitter 3 splits the light into light _F1 and light _F2 , and the light _F2 is positioned on the moving body. The object light is reproduced from the hologram 4 (reproduced object light), and the diffuser plate 5 is illuminated with light F ₁ to cause this object light to interfere with the aforementioned reproduced object light. Interference fringes produced by this interference are observably projected onto the screen 6. By observing these interference fringes, one or two components of the displacement of the moving body within a plane perpendicular to the optical axis of the object light can be detected simultaneously.

Also, to briefly explain an example of a rotation angle meter,
As shown in FIG. 2, a laser emitting device 2, which is a component of an optical element group 10 located on a fixed body, emits light, and a beam splitter 3 separates light _F1 and light _F2.
The light F ₂ is irradiated onto the hologram 4 located on the fixed body through the reflective element 17 on the moving body, and the object light is reproduced from the hologram 4 (regenerated object light) _. The diffuser plate 5 is illuminated, and the object light from the diffuser plate 5 is irradiated onto the hologram 4 via the reflection element 17, and this object light and the above-mentioned reproduced object light are caused to interfere with each other. The interference fringes caused by this interference are observably projected onto the screen 6, and by observing these interference fringes, the rotational displacement of the moving body around the y-axis (the axis perpendicular to the plane of the paper) can be detected. I can do it.

However, the optical element group 10 used here has the function of generating object light and reference light, but it also includes a laser emitting device 2, a microscope objective lens 7, a pinhole 8, a mirror 9, and a collimator. a lens 11, a diffuser plate 5 made of ground glass, etc.;
collimator lens 12, beam splitter 3,
It includes a mirror 13, a microscope objective lens 14, a pinhole 15, a beam splitter 16, etc.
The large number of components makes the device complex and makes correct setting of each component quite difficult.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a hologram displacement meter that can reduce the number of constituent elements of an optical element group, simplify the configuration, and facilitate its setting. This is the purpose.

Corresponding to this purpose, the holographic displacement meter of the present invention is a displacement meter that detects the displacement of a moving body that causes a displacement to be detected with respect to a fixed body, and which is optically at infinity or equivalent to infinity. A first hologram recording an object beam and a reference beam of an object located at a distance, and a second hologram recording interference fringes formed by the object beam and the reference beam at a reference position of the object are fixed. a reflective element is installed on the other of the fixed body or the movable body, and light from a light source located at a fixed position is reflected by the reflective element after being incident on the first hologram. The hologram is characterized in that it is configured such that it is incident on the second hologram.

The details of this invention will be explained below with reference to the drawings showing one embodiment.

FIG. 3 shows an embodiment in which the present invention is applied to a rotation angle meter. In FIG. 3, 1 is a rotation angle meter. The rotary angle meter 1 consists of a component indicated by block A and a component indicated by block B. The components included in block A are attached to a moving object such as a tool rest whose rotation is to be detected, and the components included in block B are attached to a fixed part such as a foundation.

A component included in block A is a reflective element 17, which is mounted on a moving body. The moving body is originally configured to be able to move along a linear movement path 18 in the optical axis direction.

On the other hand, the components included in block B include a light source 19, a microscope objective lens 14, a pinhole 15, a collimator lens 12, and a hologram 2.
0, a hologram 4, a collimator lens 23, and a screen 6. The hologram 20 has the function of generating object light and reference light.

On the other hand, the reflective element 17 consists of two mirrors 21 and 22.
It is equipped with The mirrors 21 and 22 are positioned so that their reflective surfaces are parallel and facing each other, and are positioned midway on the optical path from the hologram 20 to the hologram 4. The mirrors 21 and 22 form a predetermined angle with respect to the optical axis of the light beam from the hologram 20 (in this embodiment, 45 degrees with respect to the optical axis). The beam then changes its optical path and enters the mirror 22, and is further reflected by the mirror 22 to change its optical path and irradiates the hologram 4.

Hologram 4 and hologram 20 were created as follows. That is, a rotary angle meter 1 shown in FIG. 3 is prepared in which the hologram reproducing optical element group 20 is replaced with the fourth optical element group 20'. The optical element group 20' functions as an optical element that generates an object beam and a reference beam, and is similar to the optical element group 10 shown in FIGS. 1 and 2.
is the same as That is, the optical element group 20'
are a diffuser plate 5 such as ground glass, a beam splitter 16, a collimator lens 12, a beam splitter 3, a mirror 13, a microscope objective lens 14,
It includes a pinhole 15, a laser emitting device 2, a microscope objective lens 7, a pinhole 8, a mirror 9, and a collimator lens 11. The optical element group 20' shown in FIG. 4 is incorporated in place of the hologram reproducing optical element group 20 in FIG.
The configuration shown in the figure is adopted.

When creating the hologram 4, the following procedure is performed in the configuration shown in FIG. First, the photosensitive material 4' is placed at the position of the hologram 4, and then the laser emitting device 2 is activated to emit light. Laser emitting device 2
The beam splitter 3 splits the light into two parts, and one of the lights F ₁ is spread by the microscope objective lens 7 and the collimator lens 11 , converted into a parallel light beam, illuminates the diffuser plate 5 made of ground glass, and the collimator lens 1
2 is used as an object beam after passing through, and the photosensitive material 4' located at the position of the hologram 4 is exposed. The other light _F2 is the microscope objective lens 14 and the collimator lens 1.
2 to make it a parallel beam of light and use it as a reference beam. In this way, the object light from the diffuser plate 5 is recorded as a hologram on the photosensitive material 4' placed at the position of the hologram 4 using a plane wave reference beam, and the hologram 4 is completed by photographic processing. On the other hand, in order to create the hologram 20, a photosensitive material 20'' is placed on the optical path exit side of the optical element group 20', and the photosensitive material 20'' is exposed and photographically processed in the same manner as in the case of creating the hologram 4. . As a result, a hologram 20 is obtained in which the object light and reference light of an object (diffusion plate 5) located at an optically infinite distance or at a distance equivalent to infinity are recorded.

The holograms 4 and 20 obtained in this way are set on a fixed body to form a rotary angle meter 1 as shown in FIG.
is completed. The rotation angle meter 1 shown in FIG. 3,
As is clear from a comparison with the rotation angle meter 1' shown in FIG. 2, the rotation angle meter 1 replaces the optical element group 10 in the rotation angle meter 1' in FIG. 2 with a hologram reproduction optical element group 20. and since the hologram 20 records the object light and reference light emitted by the optical element group 20',
When the hologram 20 is irradiated with a parallel light beam from the light source 19, it is equivalent to the optical element group 10 in the function of generating an object beam and a reference beam, and therefore the rotation shown in FIGS. 2 and 3 Angle meter 1,
1' performs the same optical function.

Measurement of the rotational displacement of a moving body using the rotational angle meter 1 constructed in this way is performed as follows. First, light from the light source 19 is converted into a parallel beam by the microscope objective lens 14, pinhole 15, and collimator lens 12, and the hologram 20 is illuminated with this light.
By this illumination, the object light and reference light of an object (diffusion plate 5) located at an optically infinite distance or at a distance equivalent to infinity, which were previously recorded in the hologram 20, are reproduced. Both the object beam and the reference beam enter the hologram 4 on the fixed body, and the reference beam reproduces the object beam recorded on the hologram 4 to generate a reproduced object beam. interfere with light. Interference fringes produced by this interference are observably projected onto the screen 6. By analyzing these interference fringes, the rotational displacement of the moving body can be determined. The method of analyzing interference fringes is described in the above-mentioned patent application.
It is the same as that described in the specification of No. 55-168996.

Next, the present invention can also be applied to a linear meter that detects linear displacement. An example of this is the specification of Japanese Patent Application No. 178615-1978 "Hologram Linemeter Equipped with Reflective Element" and the linemeter 2 shown in Figure 3 of the drawing.
The optical element 32 of 1 is connected to the hologram 20 and the light source 19
This can be achieved immediately by replacing it with .

That is, FIGS. 6 and 7 show an embodiment in which the present invention is applied to a line meter.

In FIGS. 6 and 7, 1b is a linear meter. The straight line gauge 1b consists of a component indicated by block A and a component indicated by block B. The components included in block A are attached to a moving body such as a tool post whose lateral displacement is to be detected, and the components included in block B are attached to a fixed part such as a foundation.

Components included in block A include a hologram 4, a collimator lens 23, and a screen 6. These holograms 4, collimator lens 23, and screen 6 are arranged along the optical axis and mounted on a moving body. . Further, in the block A, a hologram reproducing optical element group 20 is mounted on a moving body. A mobile object is originally
It is configured to be able to move along a linear movement path in the optical axis direction.

On the other hand, block B includes a reflective element 33 and a reflective element 34 as constituent members.
The reflective element 33 has mirrors 45, 46 located in orthogonal planes, and the reflective element 34 has mirrors 47, 48 located in orthogonal planes, each mirror 45, 46, 47, 48 having a It forms an angle of 45° to the optical path. However, the reflective elements 33, 3
4 can also each be replaced with a prism.
A pair of reflective elements 33 and 34 are arranged at fixed positions along the linear movement path and face each other with block A positioned between them. The reflective element 33 is arranged so as to change the direction of the optical path of the light from the optical element 32 by 180 degrees within the xz plane, and the reflective element 34
The optical path of the light from the hologram 4 is changed by 180° within the yz plane, and the hologram 4 is arranged so as to be incident on the hologram 4.

The hologram reproducing optical element group 20 includes a light source 19, a microscope objective lens 14, a pinhole 15, a collimator lens 12, and a hologram 20, as shown in FIG.

Hologram 4 and hologram 20 are created as follows.

First, when creating the hologram 4, in the configuration in which the optical element group 20' shown in FIG. 9 is incorporated in place of the hologram reproduction optical element group 20 in FIGS. 6 and 7, the following procedure is performed. . First, the photosensitive material 4' is placed at the position of the hologram 4, and then the laser emitting device 2 is activated to emit light. The light from the laser emitting device 2 is split into two by a beam splitter 3,
One light F ₁ is expanded by the microscope objective lens 7 and the collimator lens 11, converted into a parallel light beam, illuminates the diffuser plate 5 made of ground glass, and the collimator lens 12
After passing through, the light is used as object light to expose the photosensitive material 4' located at the position of the hologram 4. The other light F ₂ is made into a parallel light beam by the microscope objective lens 14 and the collimator lens 12, and is used as a reference light. The photosensitive material 4' placed at the position of the hologram 4 in this way
The object light from the diffuser plate 5 is recorded as a hologram using a plane wave reference beam, and photographically processed to create a hologram 4.
is completed.

On the other hand, to create the hologram 20, place the photosensitive material 20'' on the optical path exit side of the optical element group 20', and use the photosensitive material 20'' as in the case of creating the hologram 4.
The image is exposed and completed through photo processing. As a result, a hologram 20 is obtained in which the object light and reference light of an object (diffusion plate 5) located at an optically infinite distance or at a distance equivalent to infinity are recorded.

The hologram 4 thus obtained is set on a fixed body, and the hologram 20 is set in the hologram reproducing optical element group 20 to complete the straight line gauge 1b shown in FIG.

Measurement of the displacement of the moving body using the linear meter 1b configured in this way is performed as follows. First, light source 1
The light from 9 is made into a parallel light beam by a microscope objective lens 14, a pinhole 15, and a collimator lens 12, and the hologram 20 is illuminated with this light. By this illumination, the object light and reference light of an object (diffusion plate 5) located at an optically infinite distance or at a distance equivalent to infinity, which were previously recorded in the hologram 20, are reproduced. Both the object beam and the reference beam enter the hologram 4 on the fixed body, and the reference beam reproduces the object beam recorded on the hologram 4 to generate a reproduced object beam. interfere with light. Interference fringes produced by this interference are observably projected onto the screen 6. By analyzing this interference pattern, the lateral displacement of the moving object can be determined.

Next, an embodiment will be described in which the above-described interference fringe analysis method is applied to a line meter.

(1) If the moving body whose movement direction is coincident with or parallel to the optical axis is laterally displaced, the hologram will be laterally displaced, and the wavefront of the reproduced object light will be displaced laterally. In this way, in the case of lateral displacement, interference fringes occur on a straight line and are localized on the screen. From the analysis of interference fringes by holography so far, it can be seen that the direction perpendicular to the line direction of the interference fringes is the direction of displacement of the movable body.

FIG. 10 shows three typical interference patterns and displacement directions, and in this way displacement in a two-dimensional plane perpendicular to the optical axis can be measured.

(2) Determining whether the direction of displacement of the movable body is positive or negative: Through the above operations, it is possible to determine whether the movable body has been displaced in the left/right direction or in the vertical direction, but next, it is possible to determine whether the direction of displacement is positive or negative. Let's talk about. Now, the hologram 4 is moved, for example, to the right, and interference fringes are generated on the screen 6. At this time, when the movable body is displaced to the right, the number of interference fringes increases, and when the movable body is displaced to the left, the number decreases. In this way, by increasing or decreasing the number of interference fringes, it is possible to determine whether the direction is positive or negative.

(3) Accuracy: Let's find an ideal case with no air fluctuations or external vibrations. Now, if the amount of lateral displacement of the moving body 8 is Δx, Δy in a plane perpendicular to the optical axis, and the coordinates on the screen 6 are ζ, η, then the locus of the maximum intensity of the interference fringe is Δx・η+Δy・ζ=nλf( However, n=
0, ±1, ±2, . . . , f is the focal length of the focusing lens 7). For simplicity, if only lateral displacement occurs, Δy=0 and Δx
= nλ·f/η, if n interference fringes occur in the field of view, Δx = nλF (where F is the F number of the lens). Now, if the amount of movement required for one interference fringe to increase in the field of view is Δx _l , then Δx _l = λF,
When λ=0.633 μm and F=15, λx _l ≈9.5 μm. If the increase in interference fringes can be read down to 1/10 fringe, lateral movement up to about 1 μm can be detected.

As is clear from the above description, according to the present invention, the optical element group for generating the reference light and object light in a conventional hologram linear meter can be configured with a light source and one hologram. It is possible to obtain a displacement meter such as a linear meter, rotation angle meter, etc., which has a small number of elements, has a simple structure, and is easy to handle.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing an example of a conventional hologram linear meter, FIG. 2 is a configuration explanatory diagram showing an example of a conventional hologram rotation angle meter, and FIG. 3 is a hologram rotation angle diagram according to an embodiment of the present invention. FIG. 4 is a configuration explanatory diagram showing the optical element group,
FIG. 5 is an explanatory diagram of the configuration of the hologram rotation meter in FIG. 3 in which the light source and hologram are replaced with a group of optical elements, and FIG. 6 is a plan configuration diagram showing the configuration of a hologram linear meter according to another embodiment of the present invention. 7 is a perspective structural explanatory diagram showing the configuration of the hologram linear meter shown in FIG. 6, FIG. 8 is a structural explanatory diagram showing the hologram reproducing optical element group, and FIG. 9 is a structural explanatory diagram showing the optical element group. , and FIG. 10 are explanatory diagrams showing interference fringes. 1...Hologram rotation angle meter, 4...Hologram,
19... Light source, 20... Hologram, 20'... Optical element group, 20... Hologram reproducing optical element group.

Claims (1)

[Claims] 1 A displacement meter that detects the displacement of a moving body that causes a displacement to be detected with respect to a fixed body, and records the object light and reference light of an object located at an optically infinite distance or at a distance equivalent to infinity. and a second hologram recording interference fringes formed by the object beam and the reference beam at the reference position of the object are installed on one of the fixed body or the movable body, and a reflective element is installed on one of the fixed body or the movable body. installed on the other of the fixed body or the movable body, and configured such that light from a light source located at a fixed position is incident on the first hologram, reflected by the reflective element, and incident on the second hologram. A hologram displacement meter characterized by: