JPH0140284B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a linemeter 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, etc., it is necessary to inspect the lateral runout (one-component or two-component displacement in a plane perpendicular to the direction of movement) of the tool rest, etc. during assembly and precision inspection. There has also been an attempt to improve machining accuracy by constantly detecting the lateral vibration of a tool post or the like during machining and controlling the movement linearly.

In such cases, a line meter is used, and optical line meters such as auto collimators and laser line meters (touring lasers) are conventionally used to detect rotation or displacement of one component. However, all of them were insufficient for the above purpose due to lack of accuracy.

On the other hand, recently, holographic technology has been applied to interferometric measurements, and the nature of the resulting interference fringes has been clarified.
It is being considered to apply holographic interferometry, which can measure lateral displacement within a dimensional plane, to a linear meter.
In this case, in order to implement a hologram as a linear meter, real-time interference must be performed, but until now, holographic interferometry has been mainly used as a secondary method because experiments using real-time interferometry are quite difficult. Research has been carried out using the heavy exposure method. In addition, with linemeters that apply conventional holographic interferometry, there are issues that need to be resolved regarding the accuracy of the linemeter, the effects of air fluctuations and external vibrations, and the measurable range of the moving distance along the optical axis of the movable object. It remained. To solve some of these problems, the inventors of this invention have developed a new linemeter using holography, which allows easy implementation of real-time interferometry,
This made it possible to eliminate the effects of air fluctuations and external vibrations, and to perform highly accurate measurements (see Japanese Patent Application No. 55-39476).

To briefly explain this newly developed linemeter, as shown in Fig. 1, the laser emitting device 2 included in the B block located on the fixed body emits light.
The beam splitter 3 splits the beam into light _F1 and light _F2 , and irradiates the light _F2 onto the hologram 4 included in the A block located on the moving object, and reproduces the object beam from the hologram 4 (regenerated object beam). ), and the diffuser plate 5 is illuminated with the light _F1 , the object light from the diffuser plate 5 is irradiated onto the hologram 4, and this object light is caused 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 movable body in a plane perpendicular to the optical axis of the object light can be detected. However, the accuracy of this hologram linemeter is related to the change in the number of interference fringes per unit of lateral displacement of the movable body, and it is desirable to increase the change in the number of interference fringes.

This invention was made in view of the above-mentioned circumstances, and allows for easy real-time interference, reduces the effects of air fluctuations and external vibrations, and enables especially highly accurate displacement measurement. The purpose of this invention is to provide a linear meter that can

Corresponding to this purpose, the high-sensitivity linear meter of the present invention includes an optical element capable of emitting object light and reference light;
A hologram formed by the object beam and the reference beam at a reference position where the amount of movement of the movable body is zero is disposed on the movable body that can move along a linear movement path on the fixed body. , one or more reflecting devices are provided on a fixed body in the middle of the optical path between the optical element and the hologram and reverse the direction of the optical path so that the incident optical path and the reflected optical path are parallel; The object light and the reference light from the element are reflected by the reflection device, reversed, and then incident on the hologram, and are configured to be incident on the hologram as the movable body is displaced in a plane perpendicular to the linear movement path. The apparatus is configured to generate equi-inclined interference fringes that include information on the direction and amount of relative deviation between the wavefront of the reconstructed image from the hologram and the wavefront of the object light from the optical element as the inclination angle and interval of the fringes. It is characterized by

Hereinafter, details of the present invention will be explained with reference to the drawings showing one embodiment.

In FIGS. 2 and 3, 21 is a line gauge. The straight line gauge 21 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 movable body 22 such as a tool rest 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 23, a condensing lens 24, and a screen 25.
There are these holograms 23, condensing lenses 2
4 and the screen 25 are arranged along the optical axis,
It is attached on the movable body 22. Further, in the block A, an optical element 32 is mounted on the movable body 22. The movable body 22 is originally configured to be movable in the optical axis direction. Note that the optical element 32 functions as an optical element that generates object light and reference light.

On the other hand, block B includes a prism 33 and a prism 34 as constituent members.
However, each of the prisms 33 and 34 can be replaced with two plane mirrors. The prism 33 is arranged to change the optical path direction of the light from the optical element 32 by 180 degrees in the xz plane, and the prism 34 changes the optical path of the light from the prism 33 by 180 degrees in the yz plane to create a hologram. 23.

As shown in FIG. 4, the optical elements 32 include a laser emitting device 26, a microscope objective lens 27, a pinhole 28, a mirror 29, a collimator lens 31,
Diffusion plate 36 such as ground glass, beam splitter 37, collimator lens 38, beam splitter 39, mirror 41, microscope objective lens 42,
It includes a pinhole 43.

The hologram 23 is created as follows. First, place the photosensitive material 23' at the position of the hologram 23,
Next, the laser light emitting device 26 is caused to emit light. The light from the laser emitting device 26 is transferred to the beam splitter 39
split the light into two, and send one light _F1 to the microscope objective lens 2.
7 and a collimator lens 31, the beam is expanded into a parallel light beam that illuminates a diffuser plate 36 made of frosted glass, and after passing through a collimator lens 38, is used as object light to expose a photosensitive material 23' at the position of the hologram 23. The other light F ₂ is the microscope objective lens 42
The collimator lens 28 converts the light into a parallel beam of light, which is used as a reference light. In this way, a diffuser plate 36 is placed on the photosensitive material 23' placed at the position of the hologram 23.
The object light from the hologram 23 is recorded as a hologram using a plane wave reference light, and photographically processed to complete the hologram 23.

The hologram 23 thus obtained is set on the movable body 22 to complete the straight line gauge 21 shown in FIGS. 2 and 3.

Measurement of the lateral displacement of the movable body 22 using the linear meter 21 configured as described above is performed as follows. First, the laser light emitting device 26 is caused to emit light again to generate an object light and a reference light from the diffuser plate 36. Both the object light and the reference light enter the hologram 23 on the movable body 22, and the reference light reproduces the object light recorded on the hologram 23 to generate a reproduced object light. Interfering with object light in real time. Interference fringes produced by this interference are observably projected onto a screen 25 placed at the focal plane of the lens 24.

If the movable body 22, whose movement direction is coincident with or parallel to the optical axis, is displaced laterally, the hologram 23 is displaced laterally, which causes the wavefront of the reproduced object light to be displaced laterally. In the case of lateral displacement as described above, linear interference fringes are formed that are localized on the screen 25. From previous analyzes of interference fringes by holography, it has been found that the direction of displacement of the movable body is perpendicular to the line direction of the interference fringes. The method for analyzing interference fringes was published in patent application No. 1 in 1982.
It is the same as shown in No. 39476. However,
It is particularly important to note here that in the linear meter of the present invention, as the optical path is changed by 180° by the prisms 33 and 34, the amount of lateral movement of the movable body is doubled. The point is that it is amplified, thereby doubling the accuracy. That is, when considering the lateral movement of the movable body in the xz plane, as shown in the plan view in FIG. Since point b is reached, if point a and point b correspond to each other, then even if the movable body is lateral displaced by Δx, points a and b will be displaced by Δx and will reach points a' and b', respectively. However, after the light emitted from point a' changes its optical path by 180° due to reflection at prism 33, it changes to hologram 2.
It reaches a position shifted by 2·Δx from point b' on 3. This also applies to lateral movement in the yz plane.

In this way, when the lateral movement of the movable body is Δx, the amount of displacement in the hologram 23 is 2・Δx, and the lateral movement is doubled, and for the same amount of displacement, the above-mentioned The number of equi-inclination angle interference fringes is doubled compared to the case of the developed hologram linemeter. In other words, if the fringe spacing of equi-inclined interference fringes is Δξ, the amount of movement of the movable body is Δx, the wavelength of light is λ, and the focal length of the lens is f, then in the case of the above-mentioned hologram linemeter, Δξ=λf/Δx... ...(1), but in the case of this invention, Δξ=λf/2Δx ...(2) Therefore, in the hologram linemeter mentioned above, one equi-inclined interference fringe is formed in the field of view of the screen. If this occurs, two lines will be generated in the case of the present invention, and the accuracy will be doubled.

Example (i) Theoretical value Δx=100μm=0.1mm, λ=0.63×10 ^-3 mm, f
= 360 mm, then from equation (2) Δξ = 0.63 × 10 ^-3 × 360 / 2 × 0.1 = 1.134 The fringe spacing of equi-inclined interference fringes Δξ = 1.134 mm.

(ii) Experimental value It can be seen from Figure 6 that when the movable body moves by 100 μm = 0.1 mm, 8.85 equal-angle interference fringes are generated per 1 cm. Therefore, the fringe spacing Δξ of the equi-inclined interference fringes is Δξ=10 mm/8.85=1.13 mm.

Therefore, the experimental value and the theoretical value almost agree.

As is clear from the above description, the present invention provides a linear meter that can easily perform real-time interference, reduce the effects of air fluctuations and external vibrations, and enables highly accurate displacement measurement. be able to.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing a conventional holographic line meter, FIG. 2 is a perspective explanatory diagram showing the configuration of a line meter according to an embodiment of the present invention, and FIG. 3 is a configuration of the line meter shown in FIG. 2. FIG. 4 is an explanatory plan view showing the configuration of the optical element, FIG. 5 is an explanatory view showing a part of the optical path, and FIG. 6 is a graph showing the relationship between the number of interference fringes and the amount of displacement. 21... Line meter, 23... Hologram, 32...
...Optical element, 33... Prism, 34... Prism.

Claims (1)

[Claims] 1. An optical element capable of emitting object light and reference light;
A hologram formed by the object beam and the reference beam at a reference position where the amount of movement of the movable body is zero is disposed on the movable body that can move along a linear movement path on the fixed body. , one or more reflecting devices are provided on a fixed body in the middle of the optical path between the optical element and the hologram and reverse the direction of the optical path so that the incident optical path and the reflected optical path are parallel; The object light and the reference light from the element are reflected by the reflection device, reversed, and then incident on the hologram, and are configured to be incident on the hologram as the movable body is displaced in a plane perpendicular to the linear movement path. The apparatus is configured to generate equi-inclined interference fringes that include information on the direction and amount of relative deviation between the wavefront of the reconstructed image from the hologram and the wavefront of the object light from the optical element as the inclination angle and interval of the fringes. A high-sensitivity linear meter featuring