KR100997948B1 - a system for simultaneous measurement of linear and angilar displacement - Google Patents

Abstract

According to the present invention, a means for changing the light incident and reflected by a stage mirror is composed of a quarter-wave plate, so that displacement and incidence at the same time are prevented from decreasing the intensity of the light to reduce the contrast. It relates to a measuring device.

The device for simultaneously measuring displacement and inclination of the present invention reflects some of the light irradiated by the light source, partially transmits the light splitter, and makes the light passed through the light splitter into a collimated beam. Reflected by a lens, a polarization splitter that passes P-polarized light and reflects S-polarized light among the light passing through the lens, a stage mirror that reflects the light that has passed through the polarizer and sends it back to the polarizer, A quarter-wave plate that changes the polarization direction of the linearly polarized light and sends it to the reference mirror, a linear polarizer that transmits only one side of the P-polarized light and the S-polarized light transmitted through the polarization splitter toward the photodetector, and is reflected on the stage mirror. A device for simultaneously measuring displacement and deflection angle, comprising a photodetector for detecting returning light, the polarizing splitter and a stage mirror It is characterized in that it is configured to install a quarter-wave plate for changing the polarization direction of the light passing through the polarization splitter.

Interferometer, Autocollimator, 1/4 Wavelength Plate

Description

A system for simultaneous measurement of linear and angilar displacement

The present invention relates to a device for measuring displacement and deflection at the same time by combining a laser interferometer for measuring a distance and an autocollimator for measuring an angle so that the distance and the angle can be measured with one device.

In particular, the present invention relates to a device for measuring displacement and incidence at the same time by configuring a means for changing light incident and reflected by a stage mirror into a quarter-wave plate to reduce the intensity of the light to prevent the contrast from falling.

In general, precision measuring instruments and processing equipment are equipped with a stage for moving the measuring instrument or the processing machine to a desired position. When the stage is driven, the stage has a linear motion in the direction of the drive shaft and a rotation angle (yaw or pitch in two directions perpendicular to the drive shaft). ) Movement occurs.

Since the performance of these stages is determined by how accurate linear movement is performed without rotation, the position change (displacement) of the feed shaft and the angle change (declination) of the two axes can be measured for accurate driving or performance improvement of the feeder. Means are required.

An interferometer is used as a means for measuring such a displacement, and an autocollimator is used as a means for measuring an incidence.

However, the above-mentioned interferometer cannot measure the change of angle, and the auto-collimator cannot measure the displacement, so the laser interferometer and the auto-collimator must be used together to measure both the displacement and the change of angle. In the case of measuring the angular change and the measurement axis of the two physical quantities are different from each other, there is an abbe error (abbe error), there is a limitation of the measurement performance. In addition, there was a drawback that the cost of measuring displacement and angle change was increased because a separate additional device was needed to measure change and angle change simultaneously with two different equipment.

There is a patent application No. 10-0608892 (method and apparatus for simultaneously measuring displacement and angular change) which has been developed and registered by some of the applicants to improve this disadvantage.

This displacement and deflection measuring apparatus is constructed by combining an auto collimator and an interferometer as shown in FIG.

That is, the light source 51 for irradiating light, the light splitter 53 for reflecting part of the light irradiated by the light source, and transmitting part of the light source, and the light emitted from the light source are collimated beams. A main lens 54, a polarization splitter 55 for passing P-polarized light and reflecting S-polarized light, and a linear polarizer 56 for polarizing only linearly polarized light in a specific direction of light passing through the polarizer ), A stage mirror 57 that reflects the light passing through the linear polarizer 56 and sends it back to the linear polarizer, and a quarter wave plate 58 that converts the linear polarized light into circular polarized light once transmitted, and 1 A reference mirror 59 for reflecting light transmitted through the / 4 wavelength plate, a linear polarizer 60 for polarizing only one side of the P-polarized light and the S-polarized light transmitted through the polarization splitter toward the photodetector 61; Including a photo detector 62 for detecting the light reflected back to the stage mirror Castle and,

A signal processing circuit (not shown) connected to the photodetector 61 and the phase difference between the light reflected by the reference mirror 59 and the light reflected by the stage mirror 57 in the computer are analyzed and compared to the stage mirror 57, that is, the stage. The position of the light incident on the photodetector 62 by a computer and a signal processing circuit (not shown) connected to the photodetector 62 are calculated by calculating the front and rear movement distances of the measuring instrument of the precision measuring instrument or the processing machine of the processing instrument moved by the position. It is possible to calculate the angle change in two directions of the stage mirror 57, that is, the measuring device of the precision measuring device or the processing machine of the processing device moved by the stage.

In the conventional arrangement for measuring the displacement and the angle change at the same time, the linear polarizer 56 is placed at 45 ° so that the light passes through the linear polarizer 56 having the horizontal P-polarized component at 45 °. In addition, there is a disadvantage that the loss to be reduced is not inevitable, and as a result, the intensity of light reflected from the reference mirror 59 and incident on the photodetector 61 and the photodetector reflected from the stage mirror 57 attached to the stage are reflected. A large difference occurs in the intensity of light incident on 61, resulting in a drop in contrast of the interference signal.

In addition, due to the loss of light generated through the linear polarizer, there was a disadvantage that the light intensity for measuring the inclination is also relatively weak.

The present invention was developed to solve the problems of the prior art as described above, by using a 1/4 wavelength plate installed at a particular angle as a rotation means of linearly polarized light, the light generated in the process of rotating the polarization in the existing invention It is an object of the present invention to provide a device for measuring displacement and inclination at the same time, which can completely eliminate the loss and increase the intensity of light for measuring the angle, thereby measuring more accurate displacement and inclination information.

In particular, by using a quarter wave plate placed at 22.5 ° with respect to the horizontal direction as the means for rotating the linearly polarized light, when the horizontal P-polarized light passes through the quarter wave plate, the polarization state is changed to an ellipse, After the reflection, once again passing through the quarter-wave plate, it is converted into linearly polarized light rotated 45 ° in the incident direction, and has both P-polarized light and S-polarized light, and the displacement to maintain the intensity of the incident light. It is an object of the present invention to provide a device for simultaneously measuring the and angle of incidence.

In order to achieve the above object, a device for measuring displacement and inclination at the same time includes a light splitter that reflects some of the light irradiated by a light source, and transmits a part of the light, and a collimated beam of light passing through the light splitter. And a polarization splitter that passes P-polarized light and reflects S-polarized light, a stage mirror that reflects the light that has passed through the polarizer and sends it back to the polarizer, and a polarizer splitter. The polarization direction of the linearly polarized light is changed to 45 ° with respect to the horizontal direction to be sent to the reference mirror, and only one polarization of the P-polarized light and the S-polarized light transmitted through the polarization splitter is transmitted to the photodetector side. In the device for simultaneously measuring the displacement and the angle of deflection comprising a linear polarizer and a photodetector for detecting the light reflected back to the stage mirror In addition, between the polarization splitter and the stage mirror is characterized in that the 1/4 wavelength plate for changing the polarization direction of the light passing through the polarization splitter is installed by 45 ° to the horizontal direction.

According to the present invention, a quarter wave plate is used as a means for changing the incident or reflected light into the stage mirror, so that when the horizontal P-polarized light passes through the quarter wave plate, the polarization state is changed to an ellipse, and the stage mirror After reflecting in, once again passing through the quarter-wave plate, it changes into linearly polarized light rotated 45 ° in the incident direction, not only having both P- and S-polarized components, but also maintaining the intensity of the incident light. It is possible to count the intensity of light detected by the photodetectors, which has the effect of measuring a more accurate displacement and deflection.

Hereinafter, an apparatus for simultaneously measuring displacement and inclination according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a configuration diagram of a device for simultaneously measuring displacement and angular change, FIG. 2 is a diagram comparing the intensity of light for displacement measurement with the conventional art, and FIG. 3 is a diagram comparing the sharpness of the interference signal with the conventional art. 4 is a chart comparing the intensity of light for angular measurement with a conventional one, and FIG. 5 is a chart comparing the loss of light with a conventional one.

A feature of the device for simultaneously measuring displacement and deflection angle according to the present invention is provided with a quarter wave plate 50 as a means for changing the light incident on or reflected from the stage mirror 60. .

That is, the apparatus for measuring displacement and incidence at the same time according to the present invention collimated the light passing through the light splitter 20 and the light splitter 20 to reflect some of the light irradiated by the light source 10, and partially transmitted Through a lens 30 to make a beam (collimated beam), a polarization splitter 40 to pass the P-polarized light of the light passed through the lens 30 and reflects the S-polarized light, and a polarization splitter 40 The stage mirror 60 reflects the light and sends it back to the polarization splitter 40 and the quarter wave plate 70 which changes the polarization direction of the linearly polarized light by the polarization splitter 40 and sends it to the reference mirror 80. And a linear polarizer 90 which transmits only one side polarization of the light P-polarized light and the S-polarized light transmitted through the polarization splitter 40 toward the photodetector 2, and detects the light reflected by the stage mirror and returned. In the device for simultaneously measuring the displacement and the angle of variation comprising a photodetector (1), Between the polarization splitter 40 and the stage mirror 60, a quarter wave plate 50 for changing the polarization direction of the light passing through the polarization splitter 40 is further provided.

The components constituting the device for measuring the displacement and inclination of the present invention configured as described above are the same as those of the device for simultaneously measuring the displacement and the inclination of the prior art, and a detailed description thereof will be omitted.

Only the quarter wave plate 50 which is the subject of this invention is demonstrated in detail.

The quarter-wave plate 50 serves to change the P-polarized light of the light passing through the polarization splitter 40 as described above, and the horizontal direction is the polarization direction of the light passing through the polarization splitter 40. It is set at 22.5 ° relative to.

The quarter-wave plate 50 placed at 22.5 ° does not cause light loss in the course of rotating the polarization so that light passing therethrough is transmitted to each of the photodetectors 1 and 2 to have sufficient intensity to measure displacement and variation. Becomes

When the horizontal P-polarized light passes through the quarter wave plate 50, the polarization state is changed to an ellipse, and the quarter wave plate 50 is once again reflected by the stage mirror 60. When passed, the light is changed to linearly polarized light rotated by 45 ° with respect to the direction of incidence, thereby having both P-polarized light and S-polarized light, and maintaining the intensity of incident light.

In addition, the intensity of light for measuring the angle is also stronger than the conventional method.

Table 1 shows the light intensity of each part when using a conventional measuring device and the present invention at the same time the displacement and deflection angle.

Conventional and one embodiment are compared under the same conditions as a whole, and the second embodiment is when the overall conditions are the same as the conventional and the first embodiment, but the polarization direction of the light incident on the polarization splitter 40 is 35.26 ° with respect to the horizontal direction. .

In Table 1, A is the intensity of light incident on the polarization splitter,

B is the intensity of light incident on the linear polarizer 90 after passing through the polarization splitter after being reflected by the reference mirror 80,

C is the intensity of light reflected by the stage mirror 60 and then reflected by the polarization splitter and incident on the linear polarizer 90,

D is a light reflected by the stage mirror 60, then transmitted through the polarization splitter, and reflected by the light splitter 20 for angle measurement, and then incident to the photodetector 1.

As can be seen in Table 1, in the second embodiment, when the incident light is incident by making the polarization direction of the incident light 35.26 ° with respect to the horizontal, the light is reflected by 1/3 in the polarization splitter 40 and 2/3 Is transmitted, and the intensity of the two lights used for distance measurement is the same, and the sharpness of the interference signal becomes 1, which is the maximum value, which is an optimal condition for distance measurement.

In Table 1, the sharpness means the sharpness of the interference fringe, and the closer to 1, the sharper the signal. The sharpness increases as the size of B and C is the same, so when decorating the interferometer it is best to make the intensity of the interfering light the same. The method of calculating the sharpness V is made by the following equation.

Where V is the sharpness and B and C are as described above.

Comparison of the intensity of light for displacement measurement, the intensity of interference signals, the intensity of light for angular measurement, and the loss of light according to the first and second embodiments of the present invention are shown in a diagram in FIGS. 2 to 5.

As can be seen from each diagram, it can be seen that the device for simultaneously measuring displacement and inclination according to the present invention is superior in intensity and clarity of light than the device for simultaneously measuring displacement and inclination.

That is, the apparatus for measuring the displacement and the angle of incidence of the present invention is a means for changing the polarization state of the light incident on or reflected from the stage mirror 60 to 12.5 placed in the horizontal direction 1 / By providing a four-wave plate 50 can be seen that completely eliminated the loss of light,

By reducing the loss of light as described above, the intensity of light reaching each photodetector 1 or 2 is sufficient, so that displacement and angular measurement can be facilitated.

The operation or principle of the displacement and deflection measurement apparatus of the present invention configured as described above can be easily understood from the prior art, and a detailed description thereof will be omitted.

1 is a configuration diagram of a device for measuring displacement and angle change simultaneously;

2 is a chart comparing the intensity of light for displacement measurement with the prior art,

3 is a diagram comparing the sharpness of the interference signal with the prior art,

4 is a chart comparing the intensity of light for angular measurement with the prior art,

5 is a diagram comparing the loss of light with the prior art,

6 is a block diagram showing an example of a conventional apparatus for simultaneously measuring displacement and inclination.

Claims (2)

A light splitter 20 which reflects some of the light irradiated by the light source 10 and transmits a part thereof, a lens 30 which makes the light passing through the light splitter into a collimated beam; Polarizer splitter 40 which passes P-polarized light and reflects S-polarized light among the light passing through the lens 30, and a stage mirror which reflects the light passed through the polarizer splitter 40 and sends it back to the polarizer splitter 40. (60), the quarter wave plate (70) to be transmitted to the reference mirror (80) by changing the polarization direction of the linearly polarized light reflected by the polarization splitter (40), and P- passing through the polarization splitter (40). A linear polarizer 90 for transmitting only one side of the polarized light and the S-polarized light to the photodetector 2 side, and a photodetector 1 for detecting the light reflected by the stage mirror and return, simultaneously In the measuring device, Between the polarization splitter 40 and the stage mirror 60, a quarter wave plate 50 for changing the polarization direction of the light passing through the polarization splitter 40 is further installed. Device for simultaneous measurement. The method of claim 1, And the quarter-wave plate (50) is placed at 22.5 ° with respect to the horizontal direction, which is the polarization direction of light passing through the polarization splitter (40).

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