JP2020085704A - Multiaxis laser interference length measurer - Google Patents

Abstract

To obtain a high-accuracy multiaxis laser interference length measurer with which alignment work is simple.SOLUTION: Provided is a multiaxis laser interference length measurer, comprising: a polarization beam splitter 21 for splitting the laser beam emitted from a light source 1 into a standard measurement beam 61 and a reference measurement beam 60; a half-mirror 41 for branching the split reference measurement beam 60 into a first reference measurement beam 62, a second reference measurement beam 63, ..., an n-th reference measurement beam; n+1 retroreflectors 51, 52, 53, ..., each reflecting the reference measurement beam 61 and the n reference measurement beams 62, 63, ..., and attached to a measurement unit and an interferometer, etc.; and n optical receivers 11, 12, ..., for photoelectrically converting respective interference signals obtained by branching the reference measurement beam 61 after reflection into n pieces and merging these with the n reference measurement beams 62, 63, ..., respectively.SELECTED DRAWING: Figure 1

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-axis laser interferometric length measuring device, and more particularly to a laser length measuring device for performing accuracy inspection on a plurality of axes of an NC machine tool or the like.

Conventionally, laser interferometers have been widely used for measuring the amount of movement and position control of an ultra-precision stage by taking advantage of the features of ultra-high accuracy, non-contact measurement, and ease of installation. The range of application is ultra-precision machine tools, aspherical surface shape measuring instruments, ultra-precision measuring instruments such as ultra-high-precision three-dimensional measuring instruments, electron beam/laser beam drawing devices, steppers, bonders, IC handlers, etc. It covers semiconductor manufacturing equipment.

The laser interferometer is equipped with a laser light transmitter and a receiver for interference light, and is installed between a plane mirror that reflects the laser light emitted from the light transmitter, a reflection target such as a retroreflector, and the like. And a polarization beam splitter which is an interferometer as a basic configuration. For example, when measuring the moving distance of the NC machine tool, the reflection target is fixedly mounted on a moving table, a spindle or the like.

The operation direction of the NC machine tool is, for example, three-axis directions of x, y, and z. The laser head that serves as a light-transmitting part is fixed in each of the axial directions, and the main axis position is aligned with the optical axis of the laser head. The interferometer is fixedly disposed on the moving table, and the reflection target is fixedly disposed on the moving table as an extension of the interferometer. That is, a preparatory work called alignment is required. This alignment work takes time and becomes more difficult as the number of measurement axes increases. In addition, when measuring the angle and length of a certain axis, not only the preparation time but also replacement time for each measurement item and measurement error due to displacement of the mounting position due to equipment replacement may occur.

In addition, the optical fiber coupling type laser interferometer is a laser light source and an interferometer coupled by an optical fiber, and the interferometer can be freely attached to a place to be measured without worrying about the optical path of the laser. .. Even if the measuring axis is oblique or the space inside the machine is narrow, the measurement can be easily performed. Furthermore, in addition to the ease of setting, it is suitable for reducing the number of man-hours required for machine tool precision inspection.

The compact configuration of the multi-axis interferometer has a small number of beam optical paths, thereby making it a compact one for the multi-axis interferometer. Patent Document 1 describes that a common measurement optical path and a common reference optical path are used for the reflection of 1 and the light is divided into a plurality of individual beams corresponding to the respective measurement axes.

In order to reduce the alignment work between the light source and the interferometer, the spectroscopic mechanism part of the multi-axis interferometer and the optical fiber for guiding the laser light from the light source part to the spectroscopic mechanism part are provided, and the emission direction of the multi-axis interferometer is switched. Japanese Patent Application Laid-Open Publication No. 2004-242242 discloses that the length is measured.

JP, 2004-239905, A Japanese Patent Laid-Open No. 9-196623

Since the one described in Patent Document 1 uses a plane mirror, if the mirror surface of the plane mirror is not arranged exactly facing the optical axis of the interferometer, the reflected light is likely to shift and the length measurement is performed. It is difficult to adjust the mounting because it causes the amount of light received by the optical system to become insufficient. Further, since the measuring light is a double-pass type length measuring device in which the measuring light reciprocates twice between the interferometer and the measured portion, it is easily affected by atmospheric turbulence, and high precision is required for alignment work.

Further, even if the alignment work is performed very strictly, if the moving body that is the object to be measured makes an angular motion such as pitching or yawing, the alignment is deviated and the light receiving sensitivity is lowered due to insufficient light receiving amount.

The one described in Patent Document 2 is, as a spectroscopic mechanism portion of a multi-axis interferometer, splits an incident laser beam and emits it in each axial direction, and at the same time, an interfering beam of measuring light and reference light is transmitted. It requires a multi-axis interferometer with a built-in meter body and its switching mechanism. The multi-axis interferometer is large in size because it has a polarization beam splitter, a pentaprism, and a switching mechanism. And, it is difficult to adapt to a narrow space such as found in a semiconductor manufacturing facility. Fabricating such large optical quality components can be costly and difficult.

The object of the present invention is to solve the above-mentioned problems of the conventional technology and to save the installation space, thereby making it possible to use various sizes for each model, machine tools in the moving direction, etc. The objective is to obtain a highly accurate multi-axis laser interferometer with easy alignment work.

The present invention that achieves the above object obtains an interference signal by branching laser light emitted from a light source by an optical system and reflecting each of them with a reflection target to join them, and photoelectrically converting the interference signal to obtain an optical path difference. In the multi-axis laser interferometer for calculating, the optical system is a polarization beam splitter that splits the laser light emitted from the light source into standard measurement light and reference measurement light, and the branched reference measurement light A half mirror that splits the first, second,..., Nth reference measurement light beams, and n+1 reflection mirrors that are attached to the measurement unit of the movable table and that reflect the standard measurement light beam and the n reference measurement light beams, respectively. Retroreflector, and n photodetectors for photoelectrically converting each of the interference signals obtained by branching the reflected reference measurement light into n pieces and merging with the n reference measurement lights, respectively. , Are provided.

In addition, in the above-mentioned thing, it is desirable to provide n polarization beam splitters for respectively joining the reference measurement light after reflection and the reference measurement light after reflection into n pieces.

Further, the polarization beam splitter has a first polarization beam splitter that splits the laser light emitted from the light source into the standard measurement light and the reference measurement light, and the half mirror divides the reference measurement light into the first measurement light and the reference measurement light. It has a first half mirror (41) that splits into one reference measurement light and a second reference measurement light, and the retroreflector is attached to the measurement section of the movable table as the reflection target and reflects the reference measurement light. A first retro-reflector (51), a second retro-reflector (52) attached to the measuring section of the movable table as the reflection target and reflecting the first reference measurement light, and a measurement of the movable table as the reflection target. A third retro-reflector (53) attached to the part and reflecting the second reference measurement light, wherein the half mirror splits the reference measurement light reflected by the first retro-reflector (51). And a second half mirror (42), and one of the reference measurement light beams branched by the second half mirror (42) and the second retroreflector (52) in the first polarization beam splitter. The reflected first reference measurement light enters, and the polarization beam splitter reflects the other of the reference measurement light branched by the second half mirror (42) and the third retroreflector (53). A first light receiving device that has a second polarization beam splitter on which a second reference measurement light beam is incident, and photoelectrically converts an interference signal between the first reference measurement light beam and the reference measurement light beam obtained by the first polarization beam splitter. And a second light receiving unit that photoelectrically converts an interference signal between the second reference measurement light and the reference measurement light obtained by the second polarization beam splitter.

Further, it is desirable that the first reference measurement light reflected by the retro-reflector (52) be bent by a mirror (31) and enter the first polarization beam splitter.

Further, it is preferable that the second reference measurement light be bent by the mirrors (32, 33) and reflected by the retroreflector (53).

Further, in the above, the optical system includes a first polarization beam splitter (21) that splits the laser light emitted from the light source into the standard measurement light and the reference measurement light, and the reference measurement light into a first polarization beam splitter (21). A half mirror (41, 44) that splits into one reference measurement light, a second reference measurement light, and a third reference measurement light, and a retroreflector attached to the measurement unit of the movable table as the reflection target and reflecting the reference measurement light. A reflector (51), a retroreflector (52) attached to the measuring section of the movable table as the reflection target, and reflecting the first reference measurement light, and a retroreflector attached to the measuring section of the movable table as the reflection target; A retro-reflector (53) that reflects the second reference measurement light, a retro-reflector (54) that is attached to the measurement unit of the movable table as the reflection target and that reflects the third reference measurement light, and the retro-reflector ( 51) half mirrors (42, 43) for branching the reference measurement light, and the first reference measurement light reflected by the branched reference measurement light and the retroreflector (52). One polarization beam splitter (21), a second polarization beam splitter into which the split reference measurement light and the second reference measurement light reflected by the retroreflector (53) are incident, and the split reference measurement light And a third polarization beam splitter on which the third reference measurement light reflected by the retroreflector (54) is incident, and the first reference measurement light and the reference measurement obtained by the first polarization beam splitter (21). A first light receiving section for photoelectrically converting an interference signal with light; and a second light receiving section for photoelectrically converting an interference signal between the second reference measurement light and the standard measurement light obtained by the second polarization beam splitter. A third light receiving unit for photoelectrically converting an interference signal between the third reference measurement light and the standard measurement light obtained by the third polarization beam splitter.

Further, the reference measurement light reflected by the retro-reflector (51) is branched by the half mirrors (42, 43), and the first polarization beam splitter (21), the second polarization beam splitter (22), It is desirable that the light is incident on the third polarization beam splitter (23).

Further, the reference measurement light is split into the first reference measurement light by the half mirror (41) and is split into the third reference measurement light and the second reference measurement light by a half mirror (44), The second reference measurement light is preferably bent by the mirrors (32, 33) and reflected by the retroreflector (53).
Further, the reference measurement light is branched by the half mirror (44) into the third reference measurement light and the second reference measurement light, and the third reference measurement light is reflected by the retroreflector (54). Is desirable.

According to the present invention, in the multi-axis laser interferometer, the laser light emitted from the light source is split into the standard measurement light and the reference measurement light by the polarization beam splitter. Then, the branched reference measurement light is branched into the first, second,..., Nth reference measurement lights, the standard measurement light and the n reference measurement lights are respectively reflected by the n+1 retroreflectors, and the reference light after the reflection is reflected. The measurement light is branched into n pieces, which are respectively merged with the n reference measurement lights, and the interference signal is photoelectrically converted by the n light receivers. Therefore, according to this configuration, it is possible to simultaneously measure n axes with one light source and one unit, and one reference measurement light as an axis. Therefore, there is no variation in the position and angle of the measurement axis in the alignment adjustment that accompanies the setup change required when each of the n measurements is performed. Moreover, it is basically unnecessary to change the equipment, which reduces the man-hours required for the work.

In addition, the installation space is saved, and it can be used universally for machine tools of various sizes and movement directions depending on the model, and can be easily installed and adjusted, making it stable and less susceptible to atmospheric turbulence. It is possible to perform the measurement.

FIG. 3 is a schematic diagram of an optical system that measures two axes according to an embodiment of the present invention. FIG. 3 is a perspective view showing the arrangement of a reflection target and a laser interferometer when measuring yawing and pitching according to an embodiment of the present invention. The perspective view which shows the arrangement|positioning of the reflection target and laser interferometer in the case of measuring the yawing and pitching by the conventional single function laser interferometer. The top view explaining the influence of the error by a measurement axis (movement axis of movable table 40) and a measurement position (laser optical axis). The side view explaining the influence of the error by a measurement axis (movement axis of movable table 40) and a measurement position (laser optical axis). The schematic diagram of the optical system which measures 3 axes which concerns on other embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an optical system 20 for measuring two axes according to the first embodiment of the present invention. As an example of measuring the accuracy of a moving table of a machine tool or the like, FIG. 2 shows an arrangement of a reflection target and a laser interferometer for measuring yawing and pitching by the multi-axis laser interferometer of the first embodiment. It is a perspective view showing. FIG. 3 is a perspective view similarly showing the arrangement by the conventional single-function laser interferometer.

In the single-function laser interferometer, as shown in FIG. 3, the retroreflectors 71, 72, 81, and 82, which are reflection targets, are fixed to the movable table 40 by a magnetic stand or the like so that they will serve as a reference during measurement. To do. The polarization beam splitters 70 and 80, which are interferometers, are fixed to stages (not shown) whose positions can be adjusted so that the retroreflectors 71, 72, 81, and 82 are positioned on the extension of the optical axis of the laser light source. Adjust, ie align, place and fix.

The retro-reflectors 71 and 72 measure yawing of the movable table 40 (rotation in the horizontal plane about the vertical axis: arrow Y direction in the figure), and the distance from the polarization beam splitter 70 to the retro-reflectors 71 and 72. The angle of yawing is detected by measuring Similarly, the retro-reflectors 81 and 82 measure the pitching of the movable table 40 (rotation about the left and right axes: arrow P direction in the figure), and measure the distance from the polarization beam splitter 80 to the retro-reflectors 81 and 82. By measuring, the pitching angle is detected.

Reference numeral 73 is a light source to which an optical fiber for entering laser light is connected to the optical system of the polarization beam splitter 70, and 74 is a light receiving portion to which an optical fiber for receiving light is connected. Similarly, reference numeral 83 is a light source to which an optical fiber for injecting laser light is connected to the optical system of the polarization beam splitter 80, and 84 is a light receiving portion to which an optical fiber for receiving light is connected. In the length measuring device using the conventional single-function laser interference length measuring device shown in FIG. 3, the light sources 73 and 83 are independently required.

Further, since the retro-reflectors 71, 72 and the retro-reflectors 81, 82 must be installed at a distance, it is necessary not only to adjust the respective optical axes but also to prevent the optical axes from being displaced from each other. Also, the error due to the measurement position in the angle (yawing/pitching) measurement can be said to be a small value because it changes almost uniformly when the measurement object is a rigid body, but when measuring the length at the same time, the error due to the optical axis position Cause

FIG. 2, which is the first embodiment, shows the arrangement of the reflection target and the optical system 20 when yawing and pitching are measured by a multi-axis laser interferometer as compared with the conventional example of FIG. The optical system 20 has the three axes coupled together. Retroreflectors 51, 52, and 53, which are reflection targets, are integrated with the movable table 40 so as to be arranged close to each other, and serve as a reference during measurement, so that they are fixed by a magnetic stand or the like so as not to move. The optical system 20, which is an interferometer, is fixed to a stage (not shown) whose position is adjustable, and the light of each laser light source (standard measurement light 61, first reference measurement light 62, second reference measurement light 63) is emitted. Adjustment, that is, alignment work is performed so that the retroreflectors 52, 51, 53 are positioned on the extension of the shaft, and the retroreflectors are arranged and fixed.

The retro-reflectors 51, 52 measure yawing of the movable table 40 (rotation in a horizontal plane about the vertical axis: arrow Y direction in the figure). The distance difference from the optical system 20 to the retro-reflectors 51, 52 is measured. The angle of yawing is detected by measuring The pitching of the movable table 40 (rotation about the left and right axes: the direction of arrow P in the figure) is measured by the retroreflectors 52 and 53, and the distance difference from the optical system 20 to the retroreflectors 52 and 53 is measured. , The pitching angle is detected.

Reference numeral 1 is a light source to which an optical fiber for entering laser light into the optical system 20 is connected, 11 and 12 are light receiving portions to which an optical fiber for receiving light is connected, 11 is a first light receiving portion, and 12 is a second light receiving portion. It is a light receiving part. Unlike the length measuring device using the conventional single-function laser interference length measuring device of FIG. 3, only one light source 1 is required. Further, the retro-reflectors 51, 52 and 53 are integrated.

Therefore, the retro-reflectors 51, 52, and 53 are installed close to each other, and it is sufficient to adjust the combined optical axis in the yawing and pitching measurements. That is, the position adjustment of the optical system 20 and the alignment work may be performed. Further, even when the length is measured at the same time, the error factor due to the optical axis position can be reduced.

In the laser interferometer, the environment has a great influence, and it is important to minimize the environmental error. Environmental factors include mechanical vibration of the measurement target and air turbulence. For the mechanical vibration to be measured, it is necessary to sufficiently fix the optical system 20 and the retroreflectors 51, 52, 53.

In the case of insufficient fixation, this vibration may be amplified and the measurement accuracy deteriorates. When fixing the retro-reflectors 51, 52, 53, if the distance from the fixed position is long, vibration is amplified, so it is necessary to fix the retro-reflectors as short as possible. Since the retro-reflectors 51, 52, and 53 are installed close to each other, and the optical axis can be adjusted only once, the multi-axis laser interferometer length measuring device shown in FIG. The error factor can be reduced compared to the one.

When a local temperature difference occurs in the air of the measurement environment, air turbulence occurs, and the air turbulence locally changes the wavelength of the laser light propagating in the air, which causes turbulence in the measurement data, It deteriorates repeatability.

As a method of reducing the local temperature difference, it is preferable to stir the air over the measurement path by a device such that the fluctuation of the air does not affect the measurement optical path, for example, with a large fan. In addition, optical components may cause abnormality in the optical system such as lens mold and coating abnormality due to dew condensation, and it is important to control temperature and humidity.

FIG. 1 is a schematic diagram showing details of an optical system 20 of a multi-axis laser interferometer for measuring two axes. The basic principle follows the Michelson interferometer. The Michelson interferometer splits a beam into two paths by using a laser beam having a known wavelength, and reflects the beams at respective reflecting targets to join them again. Then, an interference signal that produces interference fringes is created, the interference signal is photoelectrically converted, the optical path difference is calculated from the number of interference fringes, and the moving distance of the reflection target is calculated.

The basic configuration is as follows. (1) The laser beam output from the light source is split into standard measurement light and reference measurement light by a polarization beam splitter or the like. (2) The branched reference measurement light is branched into first, second,..., Nth reference measurement light by a half mirror or the like. (3) The standard measurement light and the n reference measurement lights are reflected by the retroreflectors which are n+1 reflection targets attached to the measurement unit such as the movable table. (4) The standard measurement light after reflection is branched into n pieces, interferes with each reference measurement light, and each interference signal is photoelectrically converted by n light receivers.

The number of measurements is equal to the n-th order of the reference measurement light, and one retro-reflector is required for each reference measurement light. Further, n polarization beam splitters are provided and merged in order to cause the reference measurement light after reflection branched into n pieces and the reference measurement light of n pieces to interfere with each other. With this configuration, one light source, one unit, and n reference axes can be simultaneously measured for n axes.

Therefore, there is no variation in the position and angle of the measurement axis in the alignment adjustment that accompanies the setup change required when each of the n measurements is performed. Moreover, it is basically unnecessary to change the equipment, which reduces the man-hours required for the work.

Reference numeral 1 denotes a light source, which uses laser light that emits laser light having a predetermined wavelength. The laser light emitted from the light source 1 is split into the standard measurement light 61 and the reference measurement light 60 by the first polarization beam splitter 21. After that, the reference measurement light 61 is reflected by the retro-reflector 51, which is a reflection target, and is branched by the half mirror 42. Then, one of the reference measurement lights 61 passes through the half mirror 42 and enters the first polarization beam splitter 21, and the other one is reflected by the half mirror 42 and is reflected by the half mirror 42, and the second polarization beam splitter 22 disposed at the subsequent stage of the half mirror 42. Incident on.

The reference measurement light 60 split by the first polarization beam splitter 21 is split by the half mirror 41 into a first reference measurement light 62 and a second reference measurement light 63. The first reference measurement light 62 is further bent by the mirror 31 and reflected by the retro-reflector 52 which is a reflection target fixed to the object to be measured. Further, it is bent by the mirror 31 and is incident on the first polarization beam splitter 21.

The first reference measurement light 62 interferes with the standard measurement light 61 at the first polarization beam splitter 21, and enters the first light receiving unit 11. The second reference measurement light 63 is bent by the mirrors 32 and 33, reflected by the retro-reflector 53, and enters the second polarization beam splitter 22. Then, the reference measurement light 61 interferes with the second polarization beam splitter 22, and enters the second light receiving unit 12.

The interference fringes, which are the light and shade of the light that interferes in the first polarization beam splitter 21 and the second polarization beam splitter 22, are the reference measurement light 61 and the first reference measurement light 62, and the reference measurement light 61 and the second reference measurement light 63. It represents the phase difference of the optical path length. One interference fringe corresponds to the phase difference of the wavelength of the light source. Since the wavelength of the light source is 632.8 nm in the case of He-Ne laser, the interferometer of the reciprocal optical path has a very small fringe 1 phase of 0.3 μm, which causes a slight displacement or change of the retroreflectors 51, 52, 53. It becomes possible to measure.

As described above, the laser light output from the light source 1 is split into the standard measurement light 61 and the reference measurement light 60 by the first polarization beam splitter 21. The branched reference measurement light 60 is split into a first reference measurement light 62 and a second reference measurement light 63 by the half mirror 41. The three retro-reflectors 51, 52, 53 attached to the measurement unit reflect the standard measurement light 61 and the two reference measurement lights, that is, the first reference measurement light 62 and the second reference measurement light 63, respectively. The standard measurement light 61 after reflection is split into two beams, interferes with each reference measurement beam, and the interference signal is observed by the two light receivers, the first light receiving unit 11, and the second light receiving unit 12.

4 and 5 show the influence of an error due to the measurement axis (moving axis of the movable table 40) and the measurement position (laser optical axis) as a case of measuring with a laser interferometer as shown in FIG. 4 is a top view and FIG. 5 is a side view. It can be said that the error due to the measurement position in the angle (yawing/pitching) measurement is a value that can be ignored because the measurement object changes almost uniformly when it is a rigid body. However, in the case of measuring the length, an error due to the position causes an Abbe error.

The laser interferometer measures the yawing and pitching angles by measuring the distance to the retroreflector, which is the reflection target, so the measurement axis and laser optical axis are arranged on the same straight line according to the Abbe principle. This is preferable as a design principle.

FIG. 4 shows the case of yawing measurement, and the distance and inclination between the laser optical axis which is the reference measurement light 61 and the measurement axis cause Abbe error. FIG. 5 shows the case of the pitching measurement, and the distance and the inclination between the laser optical axis which is the second reference measurement light 63 and the measurement axis cause an error. However, according to the present embodiment, since it is sufficient to adjust the optical axes of multiple axes at once, it is possible to reduce the error factor as compared with the conventional method in which the optical axes are individually adjusted.

FIG. 6 is a schematic diagram showing details of the optical system 20 for measuring three axes according to the second embodiment. Reference numeral 1 denotes a light source, which uses laser light that emits laser light having a predetermined wavelength. The light emitted from the light source 1 is split into the standard measurement light 61 and the reference measurement light 60 by the first polarization beam splitter 21. After that, the reference measurement light 61 is reflected by the retro-reflector 51, which is a reflection target, and is branched by the half mirrors 42 and 43 to form the first polarization beam splitter 21, the second polarization beam splitter 22, and the third polarization beam splitter 23. Incident on.

The reference measurement light 60 branched by the first polarization beam splitter 21 is branched by the half mirrors 41 and 44 into a first reference measurement light 62, a second reference measurement light 63, and a third reference measurement light 64. The reference measurement light 60 is branched by the half mirror 41 into the first reference measurement light 62, and is branched by the half mirror 44 into the second reference measurement light 63 and the third reference measurement light 64. The first reference measurement light 62 is further bent by the mirror 31 and reflected by the retro-reflector 52 which is a reflection target fixed to the object to be measured. Further, it is bent by the mirror 31 and is incident on the first polarization beam splitter 21.

The first reference measurement light 62 interferes with the standard measurement light 61 at the first polarization beam splitter 21, and enters the first light receiving unit 11. The second reference measurement light 63 is bent by the mirrors 32 and 33, reflected by the retro-reflector 53, and enters the second polarization beam splitter 22. Then, the reference measurement light 61 interferes with the second polarization beam splitter 22, and enters the second light receiving unit 12.

The third reference measurement light 64 is reflected by the retroreflector 54 and enters the third polarization beam splitter 23. The standard measurement light 61 and the third reference measurement light 64 interfere with each other at the third polarization beam splitter 23 and enter the third light receiving unit 13. The interference fringes, which are the light and shade of the light interfered by the first polarization beam splitter 21, the second polarization beam splitter 22, and the third polarization beam splitter 23, are the standard measurement light 61, the first reference measurement light 62, and the standard measurement light 61. The phase difference between the optical path lengths of the second reference measurement light 63, the standard measurement light 61, and the third reference measurement light 64 is shown. Therefore, it becomes possible to measure minute displacements and changes of the retroreflectors 51, 52, 53, 54.

As described above, the laser light output from the light source 1 is split into the standard measurement light 61 and the reference measurement light 60 by the first polarization beam splitter 21. The split reference measurement light 60 is split by the half mirrors 41 and 44 into a first reference measurement light 62, a second reference measurement light 63, and a third reference measurement light 64. The three reference retroreflectors 51, 52, 53 attached to the measurement section and the retroreflector 54 fixed to the interferometer section are used as the reference measurement light 61 and the first reference measurement light 62 and the second reference measurement light 62 as the three reference measurement lights. The measurement light 63 and the third reference measurement light 64 are reflected respectively. The standard measurement light 61 after reflection is branched into three and interferes with each reference measurement light, and the interference signal is received by the three light receivers, that is, the first light receiving unit 11, the second light receiving unit 12, and the third light receiving unit 13. Observe.

According to the second embodiment, the angle and the length can be easily measured at the same time. In the measurement of the angle alone, the mechanical error in the movement of the measured object becomes the measurement position error as it is, whereas the interferometer capable of acquiring the angle and the length at the same time can manage the measurement point in the submicron unit.

Further, according to this configuration, one light source, one unit, and three measurements can be performed simultaneously with one reference measurement light as an axis. Therefore, the variation in the position and angle of the measurement axis in the alignment adjustment, which is required when the three measurements are performed, does not occur.

As described above, in the multi-axis laser interferometer, the laser beam emitted from the light source is split into the standard measurement light and the reference measurement light by the polarization beam splitter. Further, the branched reference measurement light is branched into the first, second,..., Nth reference measurement light. The standard measurement light and the n reference measurement lights are reflected by the n+1 retroreflectors, respectively, and the reflected reference measurement light is branched into n pieces, which are combined with the n reference measurement lights to generate an interference signal n. Photoelectric conversion is performed with each light receiver.

Therefore, it is possible to simultaneously measure n axes with one light source and one unit of an optical system and one reference measurement light as an axis. Therefore, equipment that can measure a plurality of items is used, and the mounting (measurement) position shift due to the setup change is eliminated, and the measurement time can be reduced. In addition, the installation space can be saved, the installation can be adjusted easily, and stable measurements that are less likely to be affected by atmospheric turbulence can be performed, thus increasing versatility.

The posture change (yawing, pitching) accompanying the movement of the stage can be measured as the angle from the change in the optical path length to each retroreflector with a resolution of 0.05 seconds and an accuracy of about ±0.2%. Further, it can be applied to a system for measuring the angular position of the index table of the machine tool in a short time, and the error when mounting the system can be corrected.

Therefore, since the setting can be completed without precise adjustment, the measurement is completed in about 1/3 the time of the conventional method. Further, not only the positioning accuracy but also the behavior analysis of the stage and the spindle required for the machine tool and the dynamic behavior analysis can be supported.

1, 73, 83... Light source, 20... Optical system, 40... Movable table, 70, 80... Polarization beam splitter, 74, 84... Light receiving section 11... First light receiving section, 12... Second light receiving section, 13... Third Light receiving section 21... First polarization beam splitter 22... Second polarization beam splitter 23... Third polarization beam splitter 31, 32, 33... Mirrors 41, 42, 43, 44... Half mirrors 51, 52, 53, 54, 71, 72, 81, 82... Retroreflector 60... Reference measurement light, 61... Standard measurement light 62... First reference measurement light, 63... Second reference measurement light, 64... Third reference measurement light

Claims (9)

Multi-axis laser interferometry for calculating the optical path difference by opto-electrically converting the interference signals by splitting the laser light emitted from the light source by an optical system, reflecting each with a reflection target and merging In the vessel
The optical system is
A polarization beam splitter that splits the laser light emitted from the light source into standard measurement light and reference measurement light,
A half mirror for branching the branched reference measurement light into first, second,..., Nth reference measurement light,
N+1 retro-reflectors attached to the measurement unit of the movable table as the reflection target and reflecting the standard measurement light and the n reference measurement lights, respectively.
The reference measurement light after reflection is branched into n pieces, and n photoreceivers for photoelectrically converting the respective interference signals obtained by merging with the n reference measurement lights, respectively.
A multi-axis laser interferometer, which is characterized by comprising: 2. The multi-axis laser according to claim 1, further comprising n polarization beam splitters for respectively joining the reference measurement light after reflection and the reference measurement light after reflection split into n pieces. Interferometer. The polarization beam splitter has a first polarization beam splitter that splits the laser light emitted from the light source into the standard measurement light and the reference measurement light,
The half mirror has a first half mirror (41) that splits the reference measurement light into a first reference measurement light and a second reference measurement light,
The retro-reflector is
A first retro-reflector (51) attached to the measuring section of the movable table as the reflection target and reflecting the reference measurement light;
A second retro-reflector (52) attached to the measuring section of the movable table as the reflection target and reflecting the first reference measurement light;
A third retro-reflector (53) that is attached to the measurement unit of the movable table as the reflection target and reflects the second reference measurement light;
The half mirror includes a second half mirror (42) that branches the reference measurement light reflected by the first retroreflector (51),
One of the standard measurement light beams split by the second half mirror (42) and the first reference measurement light beam reflected by the second retroreflector (52) are incident on the first polarization beam splitter.
The polarization beam splitter is a second polarized light on which the other of the standard measurement light split by the second half mirror (42) and the second reference measurement light reflected by the third retroreflector (53) are incident. Has a beam splitter,
A first light receiving unit that photoelectrically converts an interference signal between the first reference measurement light and the standard measurement light obtained by the first polarization beam splitter;
A second light receiving unit that photoelectrically converts an interference signal between the second reference measurement light and the standard measurement light obtained by the second polarization beam splitter;
The multi-axis laser interferometer according to claim 1 or 2, further comprising: The multiple reference light according to claim 3, wherein the first reference measurement light reflected by the second retroreflector (52) is bent by a first mirror (31) and enters the first polarization beam splitter. Axis laser interferometer. The second reference measurement light is bent by a second mirror (32) and a third mirror (33) and is reflected by the third retroreflector (53). Multi-axis laser interferometer. The optical system is
A first polarization beam splitter that splits the laser light emitted from the light source into the standard measurement light and the reference measurement light;
A half mirror (41, 44) for branching the reference measurement light into a first reference measurement light, a second reference measurement light and a third reference measurement light;
A retro-reflector (51) attached to the measuring section of the movable table as the reflection target and reflecting the reference measurement light;
A retro-reflector (52) attached to the measurement unit of the movable table as the reflection target and reflecting the first reference measurement light;
A retro-reflector (53), which is attached to the measurement unit of the movable table as the reflection target and reflects the second reference measurement light;
A retroreflector (54) for reflecting the third reference measurement light;
Half mirrors (42, 43) for branching the reference measurement light reflected by the retroreflector (51);
A first polarization beam splitter into which the split reference measurement light and the first reference measurement light reflected by the retroreflector (52) are incident;
A second polarization beam splitter into which the split reference measurement light and the second reference measurement light reflected by the retroreflector (53) are incident;
A third polarization beam splitter into which the split reference measurement light and the third reference measurement light reflected by the retroreflector (54) are incident,
A first light receiving unit that photoelectrically converts an interference signal between the first reference measurement light and the standard measurement light obtained by the first polarization beam splitter;
A second light receiving unit that photoelectrically converts an interference signal between the second reference measurement light and the standard measurement light obtained by the second polarization beam splitter;
A third light receiving section for photoelectrically converting an interference signal between the third reference measurement light and the standard measurement light obtained by the third polarization beam splitter;
The multi-axis laser interferometer according to claim 1 or 2, further comprising: The reference measurement light reflected by the retro-reflector (51) is branched by the half mirrors (42, 43), and the first polarization beam splitter, the second polarization beam splitter, and the third polarization beam splitter (23). ) Is incident on the multi-axis laser interferometer. The first reference measurement light is branched by the half mirror (41), and the reference measurement light is branched by the half mirror (44) into the third reference measurement light and the second reference measurement light. The multi-axis laser interferometer according to claim 6 or 7, wherein the reference measurement light is bent by mirrors (32, 33) and reflected by the retroreflector (53). The reference measurement light is split into the third reference measurement light and the second reference measurement light by the half mirror (44), and the third reference measurement light is reflected by the retroreflector (54). The multi-axis laser interferometer according to any one of claims 6 to 8.