JPH09126712A - Laser length measuring machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the alignment work and to provide a length measuring device in which no shifting of alignment occurs by constituting a reflection target of a corner prism and providing a small corner prism for receiving a reflected light and reflecting an incident light on the same optical path in the vicinity of an interference gauge. SOLUTION: A corner prism 18 is provided on the lower side of the 1/4λ plate 16 of the prism part of a polarizing beam splitter 12, a corner prism 4 is provided in the upper part of a traveling object 3 and small corner prism 20 is provided on the upper front face of a housing. A reference light is reflected by the polarizing beam splitter 12, reflected by the prism 18 after passing through the 1/4λ plate 16, passed through 1/4λ plate 16 again and made incident on the polarizing beam splitter 12. A measuring light is made incident on the prism 4 after passing through the 1/4λplate 16. A reflected light from the prism 4 is reflected by the prism 20 and made incident again on the polarizing beam splitter 12 after being sent on the same optical path. The measuring light is made to interfere with the reference light and received by a length measuring optical system 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser length measuring machine capable of further improving measurement accuracy by double-passing laser light.

[0002]

2. Description of the Related Art A laser length measuring machine is used for precise measurement of a moving length of a precision XY table. A general configuration of this type of laser length measuring machine is shown in FIG. The laser length-measuring machine shown in FIG. 1 includes a laser head 1, an interferometer 2 (specifically, a polarization beam splitter), and a reflection target 4 (specifically, a reflection target 4 installed on a moving body 3 which is an object to be measured. Is a corner prism), a length measuring optical system 5 and a reference light prism 6.

In this length measuring machine, the laser beam emitted from the laser head 1 is incident on a polarization beam splitter 2, and is split into reflected light and transmitted light by the polarized beam splitter 2, and the transmitted light is measured light. As corner prism 4
And the reflected light illuminates the prism 6 as reference light. The reflected light from the corner prism 4 and the prism 6 is incident on the polarization beam splitter 2 again,
The polarized beam splitter 2 interferes with each other, and the interference light enters the length measurement optical system 5.

The length-measuring optical system 5 which has received the interference light calculates the distance L from the interferometer 2 to the corner prism 4 by detecting and counting interference fringes. The resolution of the length measuring machine having such a configuration is usually about 0.01 μm, and highly accurate measurement can be performed. On the other hand, as a method for further improving this resolution, there is a double-pass method using a plane mirror. FIG.
Shows the measurement system by the double pass method. In the interferometer in the figure, in addition to the configuration of FIG. 4, a prism 6 is arranged below the polarization beam splitter 2 and a 1/4 λ plate 7 is arranged in front of the polarization beam splitter 2. Further, at the measurement position of the moving body 3, instead of the corner prism 4, a plane mirror 8 is arranged so as to face it.

In this structure, the reference beam of the laser beam is the same as that of the length measuring machine, which is the polarization beam splitter 2.
It is reflected inside and returns to the polarization beam splitter 2. On the other hand, the measurement light transmitted through the polarization beam splitter 2 is
Circularly polarized light passes through the 1/4 λ plate 7 to illuminate the plane mirror 8. The reflected light from the play mirror 8 passes through the quarter-wave plate 7 again and enters the polarization beam splitter 2.

Since the incident light is linearly polarized light inclined by 90 ° like the reference light, it is reflected in the polarization beam splitter 2 and enters the prism 6 on the lower side. This incident light is reflected by the prism 6 and again enters the polarization beam splitter 2, and the reflected light after being reflected in the polarization beam splitter 2 passes through the 1/4 λ plate 7 and becomes parallel to the measurement light. The plane mirror 8 is illuminated.

The reflected light from the plane mirror 8 passes through the same optical path as the reflected light and again passes through the 1/4 λ plate 7 to become linearly polarized light inclined by 90 ° and returns to the polarization beam splitter 2. Therefore, this time, the light passes through the polarization beam splitter 2, and is combined with the reference light at this portion to cause interference. In this configuration, the optical path length of the measuring light is twice as long as that in the case of a single path, so that the length of the same measuring distance L is actually measured, and therefore the resolution is It is improved to about 0.005 μm as compared with the case of a single pass, and the length measurement accuracy can be further increased, which is suitable for ultra-precision measurement.

However, in this configuration, since the plane mirror 8 is used as the reflection target,
The following drawbacks have been pointed out.

[0009]

That is, when the plane mirror 8 is used, as shown in FIG. 6, the plane surface of the plane mirror 8 is arranged so as to directly face the optical axis of the interferometer 2. If not, the reflected light is likely to be displaced, which causes a shortage of the amount of light received by the length measurement optical system. For this reason, in this type of double-pass type length measuring machine, high precision is required for alignment work, which takes time and effort.

Further, even if the alignment work is performed very strictly, if the moving body as the object to be measured makes angular movements such as pitching and yawing, the alignment is deviated, and the light receiving sensitivity is lowered due to insufficient light receiving amount. was there. This invention solves the above drawbacks,
The purpose is that the alignment work is easy,
An object of the present invention is to provide a laser length measuring machine having no misalignment.

[0011]

In order to achieve the above object, the invention according to claim 1 of the present invention irradiates a pair of reflective targets with laser light emitted from a laser head through an interferometer. In the laser length measuring machine for causing reflected light from these reflective targets to interfere with each other in the interferometer, and performing distance measurement based on the obtained interference light, at least one of the reflective targets is configured with a corner prism, A small corner prism that receives the reflected light of the corner prism and reflects the incident light on the same optical path as the reflected light is provided near the interferometer. According to the configuration of claim 1, since the optical path length is doubled and the corner prism can be used as the reflection target, the alignment work can be simplified and the amount of light received by the pitching, yawing, etc. of the moving body can be simplified. Can be prevented from decreasing. Further, in the invention of claim 2, the reflection target is composed of a corner prism arranged coaxially in the vertical direction, the corner prism is provided on a measurement object such as a moving body, and each of these corners is provided. A pair of small corner prisms are provided which receive the reflected light from the prisms and reflect the incident light on the same optical path as each reflected light. According to this configuration, the pitching, yawing, and other angles of the measuring object can be measured with extremely high accuracy.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment of a laser length measuring machine according to the present invention. In the following description, the same or corresponding parts as in the related art will be denoted by the same reference numerals, and different parts will be denoted by different reference numerals.

Interferometer 10 in the length measuring machine shown in FIG.
Is a polarizing beam splitter 12 in which a triangular prism portion 12a and a parallelogram prism portion 12b are integrated in a housing, and is arranged on the front surface of the prism portion 12b and the bottom surface of the prism portion 12a of the polarizing beam splitter 12, respectively. Pair of 1/4 λ plates 16a and 16b
Corner prism 18 arranged below the 4λ plate 16b
(Reflective target) and a small corner prism 20 arranged on the front surface of the upper part of the housing.

1 / 4λ provided on the prism portion 12b side
The front surface of the plate 16a faces a corner prism 4 which is a reflection target fixedly arranged on the upper part of the moving body 3, and the small corner prism 20 faces the reflection optical axis of the corner prism 4 coaxially. Further, it is installed in the vicinity of the prism portion 12b in the interferometer 10. The small-sized corner prism 20 receives the reflected light from the corner prism 4 and reflects the light incident on the same optical path as the reflected light.

In the above structure, the reference light of the laser light emitted from the laser head 1 is reflected to the lower side by the polarization beam splitter 12, and the 1/4 λ plate 16
Circularly polarized light by passing through the corner prism 18
The light is reflected by, and again passes through the quarter-wave plate 16 and enters the polarization beam splitter 12. The reference light incident on such an optical path is rotated 90 ° from the original polarization angle by passing through the 1/4 λ plate 16 twice, so that when it is incident on the polarization beam splitter 12, this time from bottom to top. It passes through and is reflected by the prism portion 12b by 90 °, and the length measurement optical system 5
Incident on.

Further, the measurement light passing through the polarization beam splitter 12 passes through the 1/4 λ plate 16 to become circularly polarized light and enters the corner prism 4. The reflected light of the measurement light that has entered the corner prism 4 side shifts upward and enters the small-sized corner prism 20 substantially at the center thereof. The reflected light from the small-sized corner prism 20 passes through the same optical path as the reflected light and enters the corner prism 4 again, and the reflected light from the corner prism 4 follows the same optical path as the measurement light and again becomes 1 / 4λ. The light enters the polarization beam splitter 12 via the plate 16.

As a result, the measuring light is emitted from the quarter-wave plate 16
Will be passed twice, and 90 ° with respect to the original polarization angle.
Polarized beam splitter 1
The reflected light is reflected inside 2 and interferes with the reference light combined in this portion, and these interference lights are received by the length measuring optical system 5. According to the length measuring machine configured in this way,
Since the optical path length of the measuring light is twice as long as that in the case of a single path, it means that a length twice as long as the same measuring distance L is substantially measured, and its resolution is when the plane mirror is used. Similarly, the thickness is about 0.005 μm. In addition to this, as shown in FIG. 2, even if the corner prism 4 is slightly tilted, its incident light and reflected light axes are immovable, so that the length measuring optical system 5 can receive light with a sufficient amount of light. .

Therefore, the alignment work is simplified by this, the light quantity does not change due to the pitching and yawing of the moving body 3, the sensitivity can be kept constant, and stable measurement can be performed. FIG.
The other Example of the length measuring machine concerning this invention is shown. The length measuring machine shown in the figure is a case where the present invention is applied to an angle optical measuring system, and only the characteristic points will be described below. In the embodiment shown in the figure, the polarization beam splitter 3
0 has a pair of parallelogram-shaped prism portions 32 arranged so that one side thereof is closely attached in the vertical direction.

On the exit surface side of each prism 32, ¼λ
Plates 16c and 16d are arranged, and each ¼ λ plate 1
A pair of corner prisms 4a and 4b provided on the moving body 3 side are arranged to face 6c and 16d. Further, on the front side of the polarization beam splitter 30, a pair of small-sized corner prisms 20a, 20b are arranged so as to be close to the front side of the polarization beam splitter 30 and reflect the incident light from each corner prism 4 on the same optical path.

In the length measuring machine configured as described above,
For example, as shown in FIG. 4, when the corner prism 4 is arranged coaxially in the vertical direction and installed on the moving body 3, the transmitted light and the reflected light separated by the polarization beam splitter 30 are respectively reflected by the corner prisms 4a, 4a. 4b and the small corner prisms 20a, 20b and back and forth between the corner prisms 4a, 4b and the ¼ λ plates 16c, 16d, and then enter the polarization beam splitter 32 and enter the polarization beam splitter. 32 interferes with each other and is received by the length measurement optical system 5.

At this time, the vertical corner prism 4
If there is an angular shift between a and 4b, the interference state of the interference light received by the length measuring optics 5 changes, so the flatness of the moving body 3 can be measured by detecting this change. In this case, the resolution of the conventional single pass is 0.06 seconds (angle), but in the length measuring machine of the present embodiment, the substantial length measurement distance is doubled, so the resolution is half that of 0. It can be improved by 0.03 seconds.

[0022]

As described in detail in the above embodiments, in the laser length measuring machine according to the present invention, the optical path length is doubled and a corner prism is used as the reflecting target. And simplification of alignment work,
There is an advantage that the received light amount can be prevented from decreasing due to the pitching and yawing of the moving body, and the measurement can always be performed with a constant sensitivity.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an optical system showing an embodiment of a laser length measuring machine according to the present invention.

FIG. 2 is an explanatory diagram showing the relationship between the inclination of a corner prism and the light receiving and reflecting optical axes.

FIG. 3 is an explanatory view of a main part of an optical system showing another embodiment when the present invention is applied to an angle optical system.

FIG. 4 is an explanatory diagram of an optical system of a conventional single-pass length measuring machine.

FIG. 5 is an explanatory diagram of an optical system of a conventional double-pass type length measuring machine.

FIG. 6 is an explanatory diagram showing the influence of the light receiving and reflecting optical axes due to the inclination of the plane mirror.

[Explanation of symbols]

 1 Laser Head 3 Moving Object 4 Corner Prism 5 Length Measuring Optical System 10 Interferometer 12 Polarizing Beam Splitter 20 Small Corner Prism

Claims (2)

[Claims] 1. A laser beam emitted from a laser head is applied to a pair of reflective targets through an interferometer, and the reflected lights from these reflective targets are caused to interfere with each other by the interferometer. In a laser length-measuring device that measures distances based on light, at least one of the reflection targets is composed of a corner prism, and the reflection light of the corner prism is received in the vicinity of the interferometer and is on the same optical path as this reflection light. A laser length measuring machine characterized in that a small corner prism for reflecting incident light is provided on the. 2. The reflection target is composed of corner prisms arranged coaxially in the vertical direction, and the corner prisms are provided on an object to be measured such as a moving body, and reflected light from each of the corner prisms is provided. 2. The laser length measuring machine according to claim 1, further comprising a pair of small corner prisms for reflecting the incident light on the same optical path as the reflected light.