KR20100041024A - Apparatus for six-degree-of-freedom displacement measurement using a two-dimensional grating - Google Patents

Abstract

PURPOSE: An apparatus for six-degree-of-freedom displacement measurement using a two-dimensional grating is provided, which uses the light coming from the same light source. CONSTITUTION: An apparatus for six-degree-of-freedom displacement measurement using a two-dimensional grating comprises a light source(12), a diffraction grating(11), a Z-axis displacement measuring unit, an X-axis displacement measuring unit, and a Y-axis displacement measuring unit. The light source has a monochromatic laser beam. The diffraction grating is attached to the surface of the measurement object. The diffraction grating generates a plurality of diffraction beams. The Z-axis displacement measuring unit measures the Z-axis axial displacement of the diffraction grating. The X-axis displacement measuring unit measures the X-axis axial displacement of the diffraction grating. The Y-axis displacement measuring unit measures the Y-axis axial displacement of the diffraction grating.

Description

Apparatus for six-degree-of-freedom displacement measurement using a two-dimensional grating}

The present invention relates to a six degree of freedom displacement measuring apparatus, and more particularly, to a six degree of freedom displacement measuring apparatus capable of measuring six degrees of freedom including a three axis rotation angle by extending a three axis displacement measuring method using a two-dimensional diffraction grating. It is about.

Usually, a precision measuring instrument and a processing apparatus are attached with a stage for moving a measuring instrument or a processing machine to a desired position. When this stage is driven, the stage generates parasitic motion (two-axis linear motion and three-axis rotational motion) together with the linear motion in the drive shaft direction. Therefore, the performance of the precision stage is determined by evaluating and reducing these parasitic motions to ensure accurate linear motion.

Therefore, in order to accurately drive or improve the performance of the feeder, a device capable of measuring the position change (displacement) and multi-axis parasitic motion of the feed shaft is required. Conventional measuring methods cannot measure the driving displacement and parasitic motion in the 5-axis direction at the same time. Therefore, various types of measuring instruments have to be used, which reduces the measurement accuracy and increases the difficulty of the measurement.

6 is an exemplary diagram of a Michelson interferometer for measuring displacement.

First, P-polarized light out of the light source 101 is reflected by a polarizing beam splitter 102 to pass through a quarter wave plate 105 and then the reference The incident light is incident on the mirror 106 and the S-polarized light is incident on a stage mirror 104 that passes through the polarization splitter 102 and the quarter wave plate 103 and then moves with the stage.

At this time, the P-polarized light, which is linear polarized light that was incident on the reference mirror 106 by the quarter wave plate 105 as circular polarized light, passes through the quarter wave plate 105 again. After deforming to the S-polarized component that is vertically redirected, it is transmitted through the polarization splitter 102 and is incident on the linear polarizer 107.

This S-polarized light is transformed into linearly polarized light having both S-polarized light and P-polarized light by the linear polarizer 107 having a polarization direction of 45 ° to the photodiode 108 as a reference light for distance measurement. Incident.

In addition, the S-polarized light, which is circularly polarized light incident on the stage mirror 104 by the quarter wave plate 103, is reflected and transmitted vertically while passing through the quarter wave plate 103. After being converted into components, it is reflected by polarization splitter 102.

This P-polarized light is transformed into a linearly polarized light having both an S-polarized component and a P-polarized component while passing through the linear polarizer 107 having a 45 ° polarization direction, and is incident on the photodetector 108 as light for distance measurement. do.

Accordingly, a signal process circuit (not shown) connected to the photo detector 108 and a computer compare and analyze the phase difference between the light reflected by the reference mirror 106 and the light reflected by the stage mirror 104. The front and rear movement distances of the measuring device of the precision measuring device or the processing device of the processing device which are moved by the mirror 104, that is, the stage, can be calculated.

Since the laser interferometer measures displacement based on the wavelength of light, the laser interferometer can accurately measure down to the nanometer level, but cannot measure the angular change. In some cases, the structure of the laser interferometer may be changed to measure the displacement and the angle change in one direction at the same time, but the displacement and the angle in both directions may not be measured at the same time.

7 is a principle diagram of an autocollimator for measuring precise angle changes.

First, some of the light emitted from the light source 201 through the pin hole 202 passes through the light splitter 203 and becomes a collimated beam through the lens 204 to form the stage mirror 205. Is incident on and the remaining portion is reflected (not shown) by the light splitter 203.

Some of the light that has been incident on the stage mirror 205 is reflected by the light splitter 203 and is incident on the position sensitive detector 206, and the other part passes through the light splitter 203 to emit light. Incident (not shown) to 201 is made.

At this time, the light incident on the position detection detector 206 is collected by a lens 204 to one point so as to accurately determine the incident position.

Accordingly, a signal processing circuit and a computer (not shown) connected to the position detection detector 206 analyze the position of the light incident on the position detection detector 206 to detect the position of the stage mirror 205, that is, the precision measuring device that is moved by the stage. The angle change in two directions of the measuring machine or the processing machine can be calculated.

The auto collimator is a device that accurately measures small angle changes, and can measure angle changes in two directions (yaw and pitch), but cannot measure distance. Therefore, a laser interferometer and an autocollimator must be used together to measure both displacement and angle change.

However, in case of measuring displacement and angular change with two different devices, the measurement axes of the two physical quantities are different from each other, resulting in an Abbe error, thereby limiting the measurement performance.

In addition, the measurement of displacement and angle change with two different equipment requires a separate additional device, which increases the cost of measuring displacement and angle change.

The present invention has been made in view of the above, by extracting one more diffraction beam for rotation angle measurement from the diffraction beam from one light source using a light splitter instead of a mirror in the conventional three-axis displacement measurement, The purpose of the present invention is to provide a six degree of freedom displacement measuring device capable of simultaneously measuring the three-axis displacement and the change in the rotation angle in three directions of a diffraction grating attached to a stage for moving a measuring device or a processing machine in a precision measuring device or a processing device. have.

The above object is a light source having a single wavelength laser beam; A diffraction grating attached to a surface of a workpiece and generating a plurality of diffraction beams incident from the light source; Z-axis displacement measuring means for measuring the Z-axis displacement of the diffraction grating; X-axis displacement measuring means for measuring the X-axis displacement of the diffraction grating; Y-axis displacement measuring means for measuring the Y-axis displacement of the diffraction grating; It is achieved by a six degree of freedom displacement measuring device characterized in that it comprises a three-axis rotation angle measuring means for measuring the X, Y, Z axis rotation angle of the diffraction grating.

Preferably, the Z-axis displacement measuring means is disposed between the light source and the diffraction grating, the Z-axis splitter for reflecting some of the light emitted from the light source and transmits the remaining portion; A polarization splitter that reflects a part of the light transmitted from the light splitter and transmits a part of the light; A reference beam photodetector and a Z-axis photodetector for detecting the phase difference of the beam reflected by the Z-axis optical splitter and the polarization splitter, and measuring the displacement in the Z-axis direction through the phase difference detected by the photodetector .

The X-axis displacement measuring means includes a mirror disposed in the path of the X-axis diffraction beam reflected by the diffraction grating to reflect the diffraction beam; An X-axis polarization splitter that reflects a portion of the diffracted beam reflected by the mirror and transmits the remaining portion; And first and second photodetectors for detecting a phase difference between the diffracted beam and the transmitted beam reflected through the X-axis polarization splitter, and measuring displacement in the X-axis direction through the phase difference detected by the photodetector.

The Y-axis displacement measuring means includes a Y-axis splitter disposed in a path of the Y-axis diffraction beam reflected by the diffraction grating to reflect a portion of the diffraction beam; A Y-axis polarization splitter that reflects a portion of the diffracted beam reflected by the Y-axis splitter and transmits the remaining portion; And a third and fourth photodetectors for detecting a phase difference between the diffracted beam and the transmitted beam reflected through the Y-axis polarization splitter, and measuring displacement in the Y-axis direction through the phase difference detected by the photodetector.

The three-axis rotation angle measuring means includes a position detection detector for detecting a position change of the diffraction beam transmitted through the Y-axis optical splitter, and a lens installed to transmit the diffraction beam between the Y-axis optical splitter and the position detection detector. Then, the rotation angle of the three axes is calculated by the position change detected by the position detection detector.

Accordingly, according to the six-degree-of-freedom displacement measuring apparatus according to the present invention, by configuring a single complex measuring device having all of the existing grating interferometer, laser interferometer, auto collimator function, the measuring device of the precision measuring device that is moved by the stage It is possible to simultaneously measure the three-axis movement displacement and the three-axis rotation angle of the measurement object such as the processing machine of the processing equipment.

In addition, it is possible to measure distance and angle change at the same time with a single device, which not only shortens the measurement time but also reduces the cost because there is no need to purchase equipment for displacement measurement and angle measurement.

In addition, since the light from the same light source is used, the three-axis linear displacement and the three-axis angle change can be simultaneously measured without an error of ABE.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a conceptual view illustrating a concept of a 6 degree of freedom displacement measuring apparatus according to an embodiment of the present invention, FIG. 2 is a plan view of FIG. 1, and FIG. 3 is a view of the 6 degree of freedom displacement measuring apparatus of FIG. 1. 4 is a configuration diagram showing a side in the X-axis direction, FIG. 4 is a configuration diagram showing a side in the Y-axis direction in the 6 degrees of freedom displacement measuring apparatus of FIG. 1, and FIG. 5 is a 3 axis in the 6 degrees of freedom displacement measuring apparatus of FIG. 1. This is a conceptual diagram illustrating a method of measuring a rotation angle, and shows a change in sensing position of a diffraction beam on a position detector according to each axial rotational displacement.

In the precision measuring device or processing device according to the present invention, six degrees of freedom of the precision measuring device or processing device (measurement 10), that is, X axis, Y axis, Z axis displacement, and X axis, Y axis, Z axis rotation angle A diffraction grating 11 is attached for measurement.

The diffraction grating 11 has a concave-convex shape in a two-dimensional plane in the X-axis and Y-axis directions, and protrudes in a rectangular or sinusoidal shape of a periodic shape when viewed from above. At this time, the interval of the diffraction grating 11 is determined so that the angle of the diffraction beam generated by the vertically incident laser beam is easy to construct the measurement system.

The light source 12 emits light having the same wavelength, phase, and propagation direction, and uses a laser beam that emits monochromatic light having a very high intensity and transmitted without spreading far.

The light source 12 is incident on the plane of the diffraction grating 11 in the vertical direction and four diffraction beams -1x, + 1x, -1y, and + 1y which are reflected on the plane of the diffraction grating are obtained.

First, a light splitter 13 (BS, beam splitter) and a polarizer splitter 14 (PBS) in the Z-axis direction between the light source 12 and the diffraction grating 11 to obtain a displacement in the Z-axis direction. ), A reference beam photodetector 18, and a Z-axis photodetector 19.

The light splitter 13 divides the light from the light source 12 into two, reflects some of the light from the light source 12, and transmits the other part.

Some of the light emitted from the light source 12 is reflected by the light splitter 13, passes through the 45 ° polarization filter 17 and then enters the reference beam photodetector 18, and a part of the light emitted from the light source 12. After passing through the light splitter 13, the light splitter 13 is reflected by the polarization splitter 14 to pass through the half wave plate 15.

Some of the light emitted from the light source 12 passes through the light splitter 13, the polarizer splitter 14, and the half wave plate 15 and then enters the diffraction grating 11.

The zero-order diffracted beam reflected by the diffraction grating 10 is transmitted through the half wave plate 15 and then reflected by the polarization splitter 14 to pass through the 45 ° polarization filter 17 and then Z-direction. It enters into the photodetector 19.

Therefore, the signal processing circuit connected to the reference beam photodetector 18 and the Z-axis photodetector 19 and the phase difference between the light reflected by the optical splitter 13 and the computer reflected by the optical splitter 13 By comparing and analyzing the Z-axis displacement of the workpiece 10 can be calculated.

Next, the X and Y axis displacements are measured. The mirror 20 and the polarization splitter 21 are further configured to measure the X-axis displacement.

The light emitted from the light source 12 passes through the light splitter 13 and the polarization splitter 14 and is then reflected by the diffraction grating 11 to obtain diffraction beams of -1x and + 1x. The -1x and + 1x diffraction beams are reflected by the mirror 20 and split into two lights through the X-axis polarization splitter 21.

Some of the -1x diffracted beams reflected by the mirror 20 are reflected by the polarization splitter 21 and then incident to the first optical detector 22 in the X-axis direction, and the light transmitted through the polarization splitter 21 is X Incident on the axial second photodetector 23.

In addition, part of the + 1x diffracted beam reflected from the mirror 20 is reflected by the polarization splitter 21 and is incident to the second optical detector 23 in the X-axis direction, and the light transmitted through the polarization splitter 21 is It enters into the X-axis direction first photodetector 22.

Accordingly, the signal processing circuit and the computer connected to the first and second photodetectors 22 and 23 in the X-axis direction, the light reflected by the polarization splitter 21 and the light transmitted through the polarization splitter 21 By comparing the phase difference, the X-axis displacement of the workpiece 10 may be calculated.

A light splitter 26 and a polarizer splitter 21 are further configured to measure the Y-axis displacement.

Here, the purpose of using the optical splitter 26 without using the mirror 20 is to extend the three-axis displacement to measure the three-axis rotation angle at the same optical axis (light source 12). This is because, if the mirror 20 is used, since the diffraction beam is changed only by changing the path, the diffraction beam for measuring the rotation angle cannot be obtained in the present invention with one optical axis.

The light emitted from the light source 12 passes through the light splitter 26 and the polarization splitter 21 and is reflected by the diffraction grating 11 to obtain a diffraction beam of -1y and + 1y. The -1y and + 1y diffraction beams are reflected by the light splitter 26 and split into two lights through the Y-axis polarization splitter 21.

Some of the -1y diffraction beams reflected by the optical splitter 26 are reflected by the polarization splitter 21 and then incident to the third optical detector 24 in the Y-axis direction, and the light transmitted through the polarizer splitter 21 It enters into the Y-axis fourth photodetector 25.

In addition, some of the + 1y diffracted beams reflected by the optical splitter 26 are reflected by the polarization splitter 21 and are incident to the fourth optical detector 25 in the Y-axis direction, and transmitted through the polarization splitter 21. Is incident on the Y-axis direction third photodetector 24.

Accordingly, the signal processing circuit and the computer connected to the third and fourth photodetectors 24 and 25 in the Y-axis direction and the light transmitted by the polarizer splitter 21 and the light transmitted through the polarizer splitter 21 are used. The phase difference may be compared and analyzed to calculate the Y-axis displacement of the workpiece 10.

Meanwhile, the rotation angles (θx, θy, θx) of the X-axis, Y-axis, and Z-axis of the measurement object 10 are measured using the Y-axis diffraction beam transmitted through the Y-axis light splitter 26. The position detection detector 28 detects the position change of the diffraction beam using the diffraction beam in the Y axis direction, and then converts the position change of the diffraction beam into an angle as follows.

Here, dX ₊₁ , dX _-1 , dY ₊₁ , dY _-1 are the amount of change in the X and Y axis directions of the diffraction beam measured by the position detector 28, and f is between the lens 27 and the photodiode. The values of dX _{+ 1} , dX _-1 , dY ₊₁ , and dY _-1 are separate values from the 3-axis displacement measurement.

The principle of measuring the three-axis rotation angle is the same as that of an autocollimator. That is, the diffracted beam reflected from the diffraction grating 11 and transmitted through the light splitter 26 is incident to the position detector 28, and the light incident on the position detector 28 is a lens so as to accurately determine the incident position. By 27, the light is collected at one point.

Therefore, a signal processing circuit and a computer (not shown) connected to the position detection detector 28 can analyze the position of the light incident on the position detection detector to calculate the angular change in the three axis directions of the moved object 10. have.

According to this method, the principle of measuring the three-axis displacement using four diffraction beams obtained by injecting the light source 12 into the diffraction grating 11 is similar to the conventional three-axis displacement measurement, the mirror 20 Instead, by extracting one more diffraction beam through the optical splitter 26 and measuring the three-axis rotation angle, the three-axis displacement measurement can be extended to measure the three-axis rotation angle simultaneously on the same optical axis.

While the invention has been shown and described with respect to certain preferred embodiments thereof, the invention is not limited to these embodiments, and has been claimed by those of ordinary skill in the art to which the invention pertains. It includes all the various forms of embodiments that can be carried out without departing from the spirit.

1 is a conceptual diagram for explaining the concept of a six degree of freedom displacement measuring apparatus according to an embodiment of the present invention,

2 is a plan view of FIG.

3 is a configuration diagram showing the side of the X-axis direction in the 6 degree of freedom displacement measurement device of FIG.

4 is a configuration diagram showing the side in the Y-axis direction in the six degree of freedom displacement measurement device of FIG.

5 is a conceptual diagram for explaining a three-axis rotation angle measuring method in the six degree of freedom displacement measuring apparatus of FIG.

6 is an exemplary diagram of a Michelson interferometer for measuring displacement;

7 is a principle diagram of an autocollimator for measuring precise angle changes.

<Description of the symbols for the main parts of the drawings>

10: measuring object 11: diffraction grating

12 light source 13 Z-axis light splitter

14 Z-axis polarization splitter 15 Half-wave plate

16,20 mirror 17 polarization filter

18: reference beam photodetector 19: Z-axis photodetector

21: X-axis, Y-axis polarization splitter 22: First photodetector

23: second photodetector 24: third photodetector

25: fourth photodetector 26: Y-axis light splitter

27: lens 28: position detection detector

Claims (5)

A light source having a single wavelength laser beam; A diffraction grating attached to a surface of a workpiece and generating a plurality of diffraction beams incident from the light source; Z-axis displacement measuring means for measuring the Z-axis displacement of the diffraction grating; X-axis displacement measuring means for measuring the X-axis displacement of the diffraction grating; Y-axis displacement measuring means for measuring the Y-axis displacement of the diffraction grating; And 6-axis displacement angle measuring means for measuring the X, Y, Z axis rotation angle of the diffraction grating. The method according to claim 1, The Z-axis displacement measuring means is disposed between the light source and the diffraction grating, the Z-axis splitter for reflecting a portion of the light emitted from the light source and transmits the remaining portion; A polarization splitter that reflects a part of the light transmitted from the light splitter and transmits a part of the light; A reference beam photodetector and a Z-axis photodetector for detecting the phase difference of the beam reflected by the Z-axis optical splitter and the polarization splitter, and measuring the displacement in the Z-axis direction through the phase difference detected by the photodetector 6 degrees of freedom displacement measuring device. The method according to claim 2, The X-axis displacement measuring means includes a mirror disposed in the path of the X-axis diffraction beam reflected by the diffraction grating to reflect the diffraction beam; An X-axis polarization splitter that reflects a portion of the diffracted beam reflected by the mirror and transmits the remaining portion; A first and second photodetectors for detecting a phase difference between the diffracted beam and the transmitted beam reflected through the X-axis polarization splitter, and measuring displacement in the X-axis direction through the phase difference detected by the photodetector. 6 degrees of freedom displacement measuring device. The method according to claim 3, The Y-axis displacement measuring means includes a Y-axis splitter disposed in a path of the Y-axis diffraction beam reflected by the diffraction grating to reflect a portion of the diffraction beam; A Y-axis polarization splitter that reflects a portion of the diffracted beam reflected by the Y-axis splitter and transmits the remaining portion; And a third and fourth photodetectors for detecting a phase difference between the diffracted beam and the transmitted beam reflected through the Y-axis polarization splitter, and measuring displacement in the Y-axis direction through the phase difference detected by the photodetector. 6 degrees of freedom displacement measuring device. The method according to claim 4, The three-axis rotation angle measuring means includes a position detection detector for detecting a position change of the diffraction beam transmitted through the Y-axis optical splitter, and a lens installed to transmit the diffraction beam between the Y-axis optical splitter and the position detection detector. And calculating a rotation angle of three axes by the position change detected by the position detection detector.

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