JP2021139678A - Diffraction grating pitch deviation measuring device - Google Patents

Abstract

To precisely detect a grating pitch deviation without being affected by deformation of a scale caused by attachment, for example, even when the scale is being equipped in a displacement detection target object.SOLUTION: A light irradiation unit 30 outputs a light to a diffraction grating pattern 3. A light reception unit 10 receives a 0-order light D0 from the diffraction grating pattern 3. A light reception unit 20 receives a +1-order DP1 as a diffraction light. An operation unit 40 calculates a change in the angle of the 0-order light D0 and the +1-order light DP1, and calculates a lattice pitch deviation on the basis of the difference between the angular change.SELECTED DRAWING: Figure 1

Description

The present invention relates to a diffraction grating pitch deviation measuring device.

In industrial machines, so-called positioning operations are performed to accurately stop an object at a target position for purposes such as machining and measurement, and a positioning mechanism such as a precision linear slider is used for this purpose. ing. In particular, in a positioning mechanism that requires high-resolution and high-precision positioning in units of sub-micrometers, a displacement sensor that can detect the amount of movement of the slide table with high resolution and high accuracy is used, and the slide table is based on the output. Full closed loop control to control the position is required.

As the displacement sensor for this fully closed loop control, an optical linear encoder and a laser interference displacement meter are mainly used. In particular, from the viewpoint of ease of sensor installation and cost, the number of cases in which an optical linear encoder is applied has increased in recent years. In a linear encoder, for example, a scale having a fine pattern for position detection is mounted on the table side of the slide table, and this fine pattern is detected by an optical reading head fixedly installed on the base side of the slide table. Measure the amount of movement of the table. As the fine pattern, a so-called absolute pattern that enables absolute position detection on a scale and a so-called incremental pattern consisting of a grid-like pattern that realizes high-resolution position detection over nanometers are used. In particular, an optical interference type linear encoder that detects scale displacement by generating interference fringes from diffracted light generated by this lattice pattern can detect displacement finer than nanometers (Non-Patent Documents). 1). On the other hand, in this optical interference method, displacement is detected using the grid pattern engraved on the scale as a scale, so that the fluctuation of the grid pattern interval (grid pitch), that is, the grid pitch deviation is directly used for the displacement detection accuracy. There is a principle feature of influencing. Therefore, in order to guarantee the accuracy of the linear encoder, it is necessary to measure and evaluate the lattice pitch deviation of this grid-like scale with high accuracy.

As a method for measuring the lattice pitch deviation of the scale with high accuracy, there is a method using a length-measuring atomic force microscope. With this method, not only the lattice pitch deviation but also the profile of each lattice pattern on the scale can be measured with a resolution of sub-nanometer units, but the measurement range is limited to about several mm, as described above. There is a drawback that it is difficult to apply the optical linear encoder to the deviation measurement of the lattice pitch over the entire scale (Non-Patent Document 2).

Further, a method using a comparator for a linear scale, which is an optical measurement method, is also used as a method for measuring the lattice pitch of the scale with high accuracy. In this method, it is possible to measure and evaluate the deviation of the grid pitch over the entire length of the scale by combining the edge detection of the grid pattern with the focused light and the high-precision laser interferometer. On the other hand, when the lattice pitch becomes narrow, the influence of light diffraction appears, so that edge detection is difficult with a lattice having a lattice pitch of about 8 micrometers or less. Moreover, since the edge detection accuracy depends on the stability of the laser interferometer, its resolution remains at the sub-nanometer (Non-Patent Document 3).

On the other hand, as a method for quickly measuring the lattice pitch deviation over the entire length of the scale with high accuracy, the diffraction angle of the diffracted light obtained when the laser beam is incident on the diffraction grating of the scale is detected, and the diffraction angle is used as the basis. A method of measuring and evaluating the grating pitch is known. For example, a method has been proposed in which a scale is placed on a rotary table having a highly accurate angle detection mechanism and the lattice pitch is detected by detecting the diffraction angle (retrow angle) (Non-Patent Document 4). Using this method, the grid pitch deviation is measured by scanning the scale with respect to the incident laser light (laser beam) and detecting the grid pitch based on the diffraction angle over the entire length of the scale while changing the laser light incident position. Can be evaluated. The effect of rotational motion error during scale scanning can be suppressed by using a high-precision sliding mechanism such as an air bearing slide, and the rotational motion error of the slide can be monitored using, for example, an optical autocollimator. By doing so, the effect can be canceled (Non-Patent Document 5). In addition, the wave surface when the scale to be evaluated is placed at the 0th and ± 1st retrow angles using a Fizeau interferometer is detected and calculated to cancel the influence of the flatness error of the scale. A method for collectively detecting the lattice pitch deviation has also been proposed (Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-160742 Japanese Patent No. 52320099

Kowei, "Latest Encoder Technology and Prospects", Journal of Precision Engineering, Vol.82, No.9 (2016), pp.773-777 Satoshi Gonta, "SI-Traceable AFM and Nanometrology", Surface Science, Vol.27, No.11 (2006), pp.662-668 M. Sawabe, F. Maeda, Y. Yamaryo, T. Simomura, Y. Saruki, T. Kubo, H. Sakai, S. Aoyagi, "A new vacuum interferometric comparator for calibrating the fine linear encoders and scales", Precision Engineering , No.28 (2004), pp.320-328 S. Gonda, et al., “Proc. Euspen (Proceedings of European Society for Precision Engineering and Nanotechnology)”, Vol. 1 (2006) 454. Wei Gao, “Precision Nanometrology”, Springer, London (2010)

By using the methods described in Patent Document 1 and Non-Patent Document 4, the lattice pitch deviation of the scale to be measured can be measured. However, it is difficult in principle to remove the influence of the flatness error of the scale by the method described in Non-Patent Document 4. Further, in the method described in Patent Document 1, the flatness error of the scale can be evaluated at the same time when the lattice pitch deviation is measured and evaluated, but the measurable range is limited by the measurement range of the Fizeau interferometer and the dimension of the total length of the scale. Depending on the scale, it may be difficult to measure and evaluate the lattice pitch deviation over the entire length of the scale. Further, in these methods, a high-precision measuring machine such as a Fizeau interferometer or a rotary table having a high-precision angle detection mechanism is indispensable. Therefore, for example, it is not possible to measure and evaluate the grid pitch deviation of the scale while it is mounted on the linear slider of a machine tool installed at a machining site. In an actual scale usage environment, environmental disturbances such as temperature fluctuations and scale deformation due to mounting on equipment are unavoidable, so it can be carried out in a scale usage environment and is affected by the flatness error of the scale. It is desired to establish a method for detecting the grid pitch deviation of the scale with high accuracy.

The present invention has been made in view of the above circumstances, and even when the scale is mounted on the displacement detection object, the deviation of the lattice pitch is highly accurate without being affected by the scale deformation due to the mounting or the like. It is an object of the present invention to provide a device capable of detecting.

The lattice pitch deviation measuring device according to the first aspect of the present invention receives the first diffracted light of the light irradiation unit that irradiates the light and the diffracted light from the diffractive lattice irradiated with the light. The light receiving unit of the above, the second light receiving unit that receives the second diffracted light having a diffraction order different from that of the first diffracted light among the diffracted light from the diffractive lattice irradiated with the light, and the first light receiving unit. The first angular variation of the first diffracted light is calculated from the variation of the incident position of the diffracted light, and the second angular variation of the second diffracted light is calculated from the variation of the incident position of the second diffracted light. It is characterized by having a calculation unit that calculates and calculates the deviation of the lattice pitch of the diffraction grid based on the difference between the first angle variation and the second angle variation. As a result, even when the scale is mounted on the displacement detection object, the deviation of the grid pitch can be detected with high accuracy without being affected by the scale deformation due to the mounting or the like.

In the lattice pitch deviation measuring device according to the second aspect of the present invention, in the above-mentioned lattice pitch deviation measuring device, the first diffracted light is 0th-order diffracted light or reflected light, and the second diffracted light is It is desirable that the light is +1st-order diffracted light or -1st-order diffracted light. As a result, the 0th-order diffracted light or the reflected light and the + 1st-order diffracted light or the -1st-order diffracted light are received, and the angular deviation of the + 1st-order diffracted light or the -1st-order diffracted light is detected to obtain a deviation of the lattice pitch with high accuracy. Can be detected.

In the lattice pitch deviation measuring device according to the third aspect of the present invention, in the above lattice pitch deviation measuring device, the first diffracted light is +1st order diffracted light, and the second diffracted light is -1 next time. It is desirable to be characterized by being diffracted. As a result, the deviation of the lattice pitch can be detected with high accuracy by receiving the +1st-order diffracted light and the -1st-order diffracted light and detecting the angular deviation of the + 1st-order diffracted light and the -1st-order diffracted light.

The grating pitch deviation measuring device according to the fourth aspect of the present invention is the above-mentioned grating pitch deviation measuring device, in which the calculation unit is based on the sum of the first angle variation and the second angle variation. , It is desirable to calculate the straightness error of the diffraction grating. Thereby, the straightness error of the diffraction grating can be calculated by using the detection result.

In the lattice pitch deviation measuring device according to the fifth aspect of the present invention, in the above-mentioned lattice pitch deviation measuring device, the reference plane between the diffraction grating and the first light receiving portion is the reference plane of the diffraction grating. A first diffraction grating arranged parallel to and at the same pitch as the average lattice pitch of the diffraction grating so as to be in the arrangement direction of the grating of the diffraction grating, and the diffraction grating and the second light receiving portion. Between the second diffraction gratings arranged at the same pitch as the average lattice pitch of the diffraction gratings so that the reference plane is parallel to the reference plane of the diffraction gratings and is in the arrangement direction of the gratings of the diffraction gratings. The first light-receiving part is arranged so that the central axis is perpendicular to the reference plane of the first diffraction grating, and the second light-receiving part has a central axis of the second. It is desirable that the diffraction grating is arranged so as to be perpendicular to the reference plane. As a result, even when the wavelength of the light output by the light irradiation unit deviates, the deviation of the lattice pitch can be detected while suppressing the influence of the wavelength deviation.

In the lattice pitch deviation measuring device according to the sixth aspect of the present invention, in the lattice pitch deviation measuring device, the calculation unit acquires the intensity of the light applied to the diffraction grating from the light irradiation unit. , The intensity of the first and second diffracted light received by the first and second light receiving units is calculated, respectively, and the intensity of the light applied to the diffraction grating and the first and second diffractions are calculated. It is desirable to calculate the diffraction efficiency of the first and second diffracted light from the light intensity. As a result, the diffraction efficiency can also be calculated using the detection result.

The grid pitch deviation measuring device according to the seventh aspect of the present invention is the above-mentioned grid pitch deviation measuring device, in which the first and second light receiving units are incident on the incident diffracted light in a direction intersecting the incident direction. It is desirable that it is configured so that the fluctuation of the position can be detected. As a result, it is possible to detect an angular deviation of the light incident on the light receiving portion.

The lattice pitch deviation measuring device according to the eighth aspect of the present invention is the lattice pitch deviation measuring device, wherein the first and second light receiving units are in the direction intersecting the incident direction of the incident diffracted light. It is desirable to have a plurality of arranged light receiving elements. As a result, it is possible to detect an angular deviation of the light incident on the light receiving portion.

The lattice pitch deviation measuring device according to the ninth aspect of the present invention is characterized in that, in the above-mentioned lattice pitch deviation measuring device, the light output by the light irradiation unit is light obtained by collimating laser light. Is desirable. As a result, the deviation of the lattice pitch can be detected with high accuracy.

According to the present invention, it is possible to provide an apparatus capable of detecting the deviation of the lattice pitch with high accuracy without being affected by the scale deformation due to the attachment or the like even when the scale is mounted on the displacement detection object.

The above and other objects, features, and advantages of the present invention will be more fully understood from the following detailed description and accompanying drawings. The accompanying drawings are provided for illustration purposes only and are not intended to limit the invention.

It is a figure which shows typically the structure of the lattice pitch deviation measuring apparatus which concerns on Embodiment 1. FIG. It is a figure which shows the more detailed structure of the lattice pitch deviation measuring apparatus which concerns on Embodiment 1. FIG. It is a figure which shows typically the structure when the lattice pitch deviation measuring apparatus which concerns on Embodiment 1 is seen from the plus direction of the Y axis. It is a figure which shows typically the structure of the photoelectric sensor. It is a figure which plotted the lattice pitch deviation according to the change of the incident light in the measurement range (slide distance) of 400 micrometers. It is a figure which shows an example of the result of calculating the fluctuation of the lattice pitch deviation by expanding the measurement range of the scale to 80 mm. It is a figure which shows the result of having calculated the scale surface inclination variation accompanying the flatness error of a scale. It is a figure which shows typically the structure of the lattice pitch deviation measuring apparatus which concerns on Embodiment 2. FIG. It is a figure which shows typically the structure of the lattice pitch deviation measuring apparatus which concerns on embodiment when viewed from the plus direction of the Y axis. It is a figure which shows typically the structure when the lattice pitch deviation measuring apparatus which concerns on Embodiment 3 is seen from the plus direction of the Y axis. It is a figure which shows the optical path of the diffracted light when the wavelength of the incident light fluctuates. It is a figure which shows the optical path of the diffracted light when the wavelength of the incident light fluctuates, and the lattice pitch deviation exists. It is a figure which shows typically the structure of the arithmetic unit which concerns on Embodiment 4. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same elements are designated by the same reference numerals, and duplicate explanations are omitted as necessary.

<Embodiment 1>
The lattice pitch deviation measuring device according to the first embodiment will be described with reference to FIGS. 1 to 4. FIG. 1 is a diagram schematically showing the configuration of the lattice pitch deviation measuring device 100 according to the first embodiment. The grating pitch deviation measuring device 100 is a device for measuring the grating pitch deviation of the diffraction grating pattern 3 provided on the scale 2 mounted on the linear slide 1 which is the object to be measured, and the light receiving units 10 and 20 and the light irradiation. It has a unit 30 and a calculation unit 40. FIG. 2 shows a more detailed configuration of the lattice pitch deviation measuring device 100 according to the first embodiment.

The light irradiation unit 30 includes a laser light source 31, a laser driver 32, a collimated light generation mechanism 33, and a collimated light propagation direction adjusting mechanism 34. The laser light source 31 is a light source that outputs a laser beam L1 having a predetermined wavelength, and is configured as, for example, a semiconductor laser module. The laser driver 32 is configured to drive the laser light source 31. The collimated light generation mechanism 33 converts the laser light L1 output from the laser light source 31 into the collimated light L2. The collimated light propagation direction adjusting mechanism 34 adjusts the propagation direction of the collimated light L2. In this example, the direction parallel to the reference plane RP (XY plane) of the diffraction grating pattern 3 provided on the scale 2. The propagation direction of the collimated light L2 propagating in the (X direction in this example) is changed to a direction (Z direction) perpendicular to the reference plane (XY plane) of the diffraction grating pattern 3. In this configuration, the diffraction grating pattern 3 is formed so that its reference plane RP is parallel to the reference plane (XY plane) of the scale 2.

In this configuration, the collimating light propagation direction adjusting mechanism 34 includes a polarizing beam splitter 34A and a quarter wave plate 34B. The polarization beam splitter 34A reflects a predetermined polarization component (for example, p-polarized light) of the collimated light L2 propagating along the X direction from the collimated light generation mechanism 33, and transmits other polarization components (for example, s-polarized light). Constructed as a thing. The polarized component reflected in the collimated light L2 passes through the 1/4 wave plate 34B and then propagates along the direction (Z direction) perpendicular to the reference plane (XY plane) of the diffraction grating pattern 3. , The incident light L3 is incident on the diffraction grating pattern 3.

The incident light L3 is diffracted by the diffraction grating pattern 3 to generate the next diffracted light. In this configuration, the lattice pitch deviation is measured using the 0th-order light D0 and the + 1st-order light DP1. Since the 0th-order light D0 propagates in the direction opposite to the propagation direction of the incident light L3, it is incident on the collimated light propagation direction adjusting mechanism 34. Therefore, the 0th-order light D0 enters the polarizing beam splitter 34A after passing through the 1/4 wave plate 34B. That is, since the 0th-order light D0 passes through the 1/4 wave plate 34B twice before reaching the polarizing beam splitter 34A, the 0th-order light D0 has a polarization plane of 90 ° as compared with the collimated light L2. It is rotating (for example, p-polarized light → s-polarized light). Therefore, the 0th-order light D0 passes through the polarizing beam splitter 34A.

The 0th-order light D0 transmitted through the collimating light propagation direction adjusting mechanism 34 is incident on the light receiving unit 10, and the + 1st-order light DP1 is incident on the light receiving unit 20.

The light receiving unit 10 is configured to convert the incident 0th-order light D0 into an electric signal, and includes a condenser lens 11, a photoelectric sensor 12, a current-voltage (IV) conversion unit 13, and an analog-digital (A / D). It has a converter 14. The 0th-order light D0 incident on the condenser lens 11 is condensed by the condenser lens 11 and incident on the photoelectric sensor 12. The photoelectric sensor 12 converts the incident 0th-order light D0 into a current signal IS1. The photoelectric sensor 12 has a configuration in which a plurality of photodiodes are arranged in a plane orthogonal to or substantially orthogonal to the optical axis of the 0th order light D0 incident on the ZX plane. The photoelectric sensor 12 is arranged at a position where the central axis passing through the center of the light receiving surface of the photoelectric sensor 12 and parallel to the normal of the light receiving surface is perpendicular to the reference plane RP of the diffraction grating pattern 3. As a result, a current signal can be obtained for each photodiode, so that the incident position of light in the ZX plane can be detected by observing the current signal. Here, for simplification, a plurality of current signals from a plurality of photodiodes are collectively referred to as a current signal IS1. The current-voltage conversion unit 13 converts the current signal IS1 into the voltage signal VS1. The analog-digital converter 14 converts the voltage signal VS1 which is an analog signal into the digital voltage signal S1.

The light receiving unit 20 has the same configuration as the light receiving unit 10, and is configured to convert the incident + 1st order light DP1 into an electric signal, and includes a condenser lens 21, a photoelectric sensor 22, and a current voltage (IV). ) It has a conversion unit 23 and an analog-to-digital (A / D) converter 24. The +1st order light DP1 incident on the condenser lens 21 is condensed by the condenser lens 21 and incident on the photoelectric sensor 22. The photoelectric sensor 22 converts the incident + 1st order optical DP1 into a current signal IS2. The photoelectric sensor 22 has a configuration in which a plurality of photodiodes are arranged in a direction orthogonal to or substantially orthogonal to the optical axis of the incident light in the ZX plane. The photoelectric sensor 22 passes through the center of the light receiving surface of the photoelectric sensor 22, and the central axis parallel to the normal of the light receiving surface is a diffraction grating with respect to the central axis of the photoelectric sensor 22 (that is, the propagation direction of the incident light L3). The pattern 3 is arranged at a position forming the same angle as the diffraction angle α of the +1st order light DP1 when the grating pitch of the pattern 3 is equal to the average grating pitch gm and the local tilt angle β (x) of the scale 2 is zero. As a result, a current signal can be obtained for each photodiode, so that the incident position of light in the ZX plane can be detected by observing the current signal. Here, for simplification, a plurality of current signals from a plurality of photodiodes are collectively referred to as a current signal IS2. The current-voltage conversion unit 23 converts the current signal IS2 into the voltage signal VS2. The analog-digital converter 24 converts the voltage signal VS2, which is an analog signal, into the digital voltage signal S2.

The calculation unit 40 calculates the lattice pitch deviation of the diffraction grating pattern 3 based on the digital voltage signal S1 from the light receiving unit 10 and the digital voltage signal S2 from the light receiving unit 20. Hereinafter, the principle of calculating the lattice pitch deviation of the diffraction grating pattern 3 will be described.

The calculation unit 40 includes angle fluctuation calculation units 41 and 42 and a grid pitch deviation calculation unit 43. The angle fluctuation calculation unit 41 calculates the angle fluctuation information Δθ0 (x) of the 0th-order light D0 received by the light receiving unit 10 based on the digital voltage signal S1 from the light receiving unit 10. The angle fluctuation calculation unit 42 calculates the angle fluctuation information Δθ1 (x) of the +1st order light DP1 received by the light receiving unit 20 based on the digital voltage signal S2 from the light receiving unit 20. The grating pitch deviation calculation unit 43 of the diffraction grating pattern 3 at the incident position x of the incident light L3 is based on the angle fluctuation information Δθ0 (x) of the 0th-order light D0 and the angle fluctuation information Δθ1 (x) of the + 1st-order light DP1. Calculate the grating pitch deviation Δg. The details of the calculation in the angle fluctuation calculation units 41 and 42 and the calculation in the grid pitch deviation calculation unit 43 will be described later.

FIG. 3 is a diagram schematically showing a configuration when the lattice pitch deviation measuring device 100 according to the first embodiment is viewed from the positive direction of the Y axis. In FIG. 3, it is assumed that the incident light L3 is irradiated at the position x of the diffraction grating pattern 3. Here, for simplification of the description, it is assumed that the incident light L3 is incident perpendicular to the reference plane RP (that is, the XY plane) of the diffraction grating pattern 3.

First, the 0th order light D0 will be examined. In the present embodiment, the light receiving unit 10 is arranged at a position where the central axis is perpendicular to the reference plane RP of the diffraction grating pattern 3. Therefore, when the grating pitch g (x) is equal to the average grating pitch gm of the diffraction grating pattern 3 and the local tilt angle β (x) of the scale 2 is zero, the 0th order light D0 is the reference position of the photoelectric sensor 12. That is, it is incident on the central position in the ZX plane of the photodiode array.

FIG. 4 is a diagram schematically showing an example of the configuration of the photoelectric sensor 12. In the photoelectric sensor 12, a plurality of photodiodes PD are arranged in the arrangement direction AF parallel to the ZX plane on the reference plane of the substrate 12A facing the scale 2. In the photoelectric sensor 12, the central axis 12B passing through the center of the array of the plurality of photodiodes PD is arranged along the normal line of the reference plane RP of the diffraction grating pattern 3, so that the arrangement direction AF is the X direction. When there is no lattice pitch deviation in the diffraction grating pattern 3, the 0th-order light D0 is incident along the path of the light LA along the central axis 12B shown in FIG. In this case, the 0th-order light D0 is incident on the photodiode in the center of the photodiode array. On the other hand, when the diffraction grating pattern 3 has a lattice pitch deviation, the incident angle of the 0th-order light D0 fluctuates, so that the 0th-order light D0 is incident along the path of the light LB shown in FIG. 4, for example. In this case, as the incident angle increases, the 0th-order light D0 is incident on the photodiode PD away from the center of the photodiode array.

The configuration of the photoelectric sensor 22 is the same as that of the photoelectric sensor 12. That is, in the photoelectric sensor 22, the central axis 12B passing through the center of the array of the plurality of photodiodes PD is diffracted in the direction in which the +1st order light DP1 is diffracted when there is no lattice pitch deviation and local inclination angle of the diffraction grating pattern 3. Arranged along. When there is no lattice pitch deviation in the diffraction grating pattern 3, the +1st order light DP1 is incident along the path of the light LA along the central axis 12B shown in FIG. In this case, the +1st order light DP1 is incident on the photodiode in the center of the photodiode array. On the other hand, when the diffraction grating pattern 3 has a lattice pitch deviation, the incident angle of the +1st order light DP1 fluctuates, so that the +1st order light DP1 is incident along the path of the optical LB shown in FIG. 4, for example. In this case, as the incident angle increases, the +1st order light DP1 is incident on the photodiode PD away from the center of the photodiode array.

The configurations of the photoelectric sensors 12 and 22 are not limited to the above configurations, and may be any other configuration as long as the incident position of light in the ZX plane can be detected. For example, the photoelectric sensor is a position detection element (PSD: Position Sensitive Device) using the surface resistance of a photodiode, an image sensor such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal-Oxide-Semiconductor), or an incident light. An angle sensor (for example, Patent Document 2) that utilizes the fact that the area of the spot applied to one photodiode changes according to the movement of the spot may be used.

つまり、０次光Ｄ０の角度ずれは、回折格子パターン３の格子ピッチ偏差による影響を受けず、かつスケール２の局所的傾斜角β（ｘ）の影響（正反射の反射角は、反射面における傾斜角の２倍となる）のみを受けることが理解できる。 Next, the calculation of the angular variation of the diffracted light will be described. In this case, the angle fluctuation information Δθ0 (x) indicating the deviation of the 0th-order light D0 from the reference position at the position x on the scale 2 can be obtained by the following equation.

That is, the angle deviation of the 0th-order light D0 is not affected by the lattice pitch deviation of the diffraction grating pattern 3, and is also affected by the local tilt angle β (x) of the scale 2 (the reflection angle of specular reflection is on the reflection surface. It can be understood that only (twice the tilt angle) is received.

Next, the +1st order light is examined. In the present embodiment, in the light receiving unit 20, the central axis of the light receiving unit 20 has an average lattice pitch gm of the diffraction grating pattern 3 with respect to the central axis of the light receiving unit 10 (that is, the incident light L3 propagation direction). It is arranged at a position equal to the diffraction angle α of the +1st order light DP1 when the local tilt angle β (x) of the scale 2 is zero. That is, in this case, the + 1st order optical DP1 is incident on the reference position of the photoelectric sensor 22, that is, the central position in the ZX plane of the photodiode array.

In this configuration, the angle θ1 (x) formed by the +1st order light DP1 with respect to the incident light L3 at the position x on the scale 2 is the actual lattice pitch g (x) of the diffraction grating pattern 3 and the wavelength of the incident light L3. The sum of the + 1st order optical diffraction angle α1 (x) determined by the diffraction grating equation with λ as a variable and the local tilt angle β (x) at the position x of the scale 2 can be obtained by the following equation.

つまり、＋１次光ＤＰ１の角度ズレは、０次光Ｄ０の角度ズレとは異なり、回折格子パターン３の格子ピッチ偏差及び局所的傾斜角β（ｘ）の両方の影響を受けることが理解できる。 In this case, the angle fluctuation information Δθ1 (x) indicating the deviation of the +1st order light DP1 at the position x on the scale 2 from the reference position can be obtained by the following equation.

That is, it can be understood that the angle deviation of the +1st order light DP1 is affected by both the lattice pitch deviation of the diffraction grating pattern 3 and the local inclination angle β (x), unlike the angle deviation of the 0th order light D0.

From the above, it is possible to calculate the angle deviation due to the lattice pitch deviation using the equations [1] and [3] as shown in the following equations.

By modifying the equation [4], the lattice pitch deviation Δg can be obtained. In deriving the equation [4], since the angular deviation of the +1st order light DP1 is extremely small, the approximation of arcsin (λ / g) ≈λ / g is used.

Since the wavelength λ of the incident light L3 is known as a design value of the optical system and Δθ1 (x) and Δθ0 (x) can be measured by this configuration, the lattice pitch deviation Δg = g (x) according to the equation [5]. It is possible to calculate −gm.

Further, the calculation unit 40 can calculate the local inclination angle β (x) of the diffraction grating pattern 3 by using the equation [1] as shown in the following equation.

It is possible to calculate the straightness error of the diffraction grating pattern 3 by performing the integration calculation based on the local inclination angle β (x) of the obtained diffraction grating pattern 3.

Actually, the angle fluctuation information Δθ0 (x) of the 0th-order light D0 obtained by constructing the optical system used in the lattice pitch deviation measuring device 100 according to the present embodiment and sliding the linear slide 1 in the X-axis direction, and FIG. 5 shows an example of the result of measuring the angle fluctuation information Δθ1 (x) of the +1st order optical DP1 and calculating the lattice pitch deviation Δg. FIG. 5 is a plot of the grid pitch deviation according to the change of the incident light L3 in the measurement range (slide distance) of 400 micrometers. Even when the scale 2 was slid in the opposite direction, similar results were obtained in the same measurement range, confirming that the measurement was repeatable.

Further, FIG. 6 shows an example of the result of calculating the fluctuation of the lattice pitch deviation Δg by expanding the measurement range of the scale to 80 mm. In this measurement as well, even when the scale 2 was slid in the opposite direction, similar results were obtained in the same measurement range, confirming that the measurement is repeatable.

From the above, by observing two diffracted lights of different orders generated by the light irradiating one part of the diffraction grating, the lattice pitch of the diffraction grating pattern is not affected by the local tilt angle β of the scale. The deviation can be measured.

Further, as described with reference to FIGS. 5 and 6, according to this configuration, it is possible to continuously measure the lattice pitch deviation while moving the scale to be measured, and it is possible to continuously measure the lattice pitch of the scale. The uniformity can be evaluated.

Further, based on the angle variation information of the +1st order light DP1 and the angle variation information of the 0th order light D0 obtained at the time of measuring the lattice pitch deviation variation shown in FIG. 6, the scale surface associated with the flatness error of the scale 2 The result of calculating the inclination fluctuation is shown in FIG. As shown in FIG. 7, according to this configuration, it can be understood that it is effective for the measurement of the lattice pitch deviation fluctuation in the state where the flatness error exists in the scale.

<Embodiment 2>
The lattice pitch deviation measuring device 200 according to the second embodiment will be described. In the first embodiment, the grid pitch deviation was calculated using the 0th-order light D0 and the + 1st-order light DP1, whereas in the second embodiment, the grid was calculated using the + 1st-order light DP1 and the -1st-order light DM1. A configuration for calculating the pitch deviation will be described. FIG. 8 is a diagram schematically showing the configuration of the lattice pitch deviation measuring device 200 according to the second embodiment. FIG. 9 is a diagram schematically showing a configuration of the lattice pitch deviation measuring device 200 according to the embodiment when viewed from the Y-axis plus direction.

In the grid pitch deviation measuring device 200, the light receiving unit 10 is arranged so as to receive the -1st order light DM1 as compared with the grid pitch deviation measuring device 100. Specifically, in the photoelectric sensor 12, the central axis passing through the center of the light receiving surface of the photoelectric sensor 12 and parallel to the normal of the light receiving surface is the reference plane RP of the diffraction grating pattern 3 (that is, the propagation direction of the incident light L3). ), The grating pitch of the diffraction grating pattern 3 is equal to the average grating pitch gm, and the local tilt angle β (x) of the scale 2 is zero, which is the same angle as the diffraction angle of the -1st order light DM1. It is placed in a position. In other words, the light receiving unit 10 and the light receiving unit 20 are arranged line-symmetrically about the normal line of the reference plane RP of the diffraction grating pattern 3 passing through the incident position x of the incident light L3.

Next, the angle fluctuation information of the angular fluctuation information ΔθP1 (x) of the +1st order light DP1 and the angle fluctuation information ΔθM1 (x) of the -1st order light DM1 will be described.

Since the light receiving unit 20 is the same as in the first embodiment for the +1st order light DP1, the angle θ1 (x) formed by the +1st order light DP1 with respect to the incident light L3 can be obtained by the following equation.

In this case, the angle fluctuation information ΔθP1 (x) indicating the deviation of the +1st order light DP1 at the position x on the scale 2 from the reference position can be obtained by the following equation.

For the -1st order light DM1, the diffraction angle is the sign of the +1st order light diffraction angle α1 (x) minus the sign, so that the deviation from the reference position of the -1st order light DM1 at the position x on the scale 2 The angle fluctuation information ΔθM1 (x) shown can be obtained by the following equation.

In this case, the angle fluctuation information ΔθM1 (x) indicating the deviation of the -1st order light DM1 from the reference position at the position x on the scale 2 can be obtained by the following equation.

From the above, it is possible to calculate the angle deviation due to the lattice pitch deviation using the equations [8] and [10] as shown in the following equations.

However, in this configuration, the angular variation of the +1st order optical DP1 and the angular variation of the -1st order optical DP1 due to the lattice pitch deviation are added. Therefore, ΔθP1 (x) −ΔθM1 (x) in the equation [11] is twice the value of Δθ1 (x) −Δθ0 (x) in the equation [4]. Therefore, from the equation [10], the lattice pitch deviation Δg can be obtained by the following equation. In deriving the equation [11], since the angular deviation between the +1st order light DP1 and the -1st order light DP1 is extremely small, the approximation of arcsin (λ / g) ≈λ / g is used.

Further, the calculation unit 40 uses the equations [8] and [10] to detect the angle of the 0th order light D0 as shown in the following equation, but the local tilt angle β of the diffraction grating pattern 3 ( It is possible to calculate x).

It is possible to calculate the straightness error of the diffraction grating pattern 3 by performing the integration calculation based on the local inclination angle β (x) of the obtained diffraction grating pattern 3.

As described above, according to this configuration, it is possible to measure the lattice pitch deviation of the scale 2 as in the first embodiment even when ± primary light is used.

<Embodiment 3>
The lattice pitch deviation measuring device 300 according to the third embodiment will be described. In the first and second embodiments, it was assumed that only the lattice pitch deviation fluctuates, but in reality, it is also conceivable that the wavelength of the incident light L2 fluctuates due to the stability of the laser light source 31 and the like. sell. Therefore, in the present embodiment, the lattice pitch deviation measuring device 300 having resistance to the wavelength fluctuation of the incident light L2 will be described. FIG. 10 is a diagram schematically showing a configuration when the lattice pitch deviation measuring device 300 according to the third embodiment is viewed from the Y-axis plus direction. The lattice pitch deviation measuring device 300 has a configuration in which the diffraction gratings GR1 and GR2 are added to the lattice pitch deviation measuring device 200 according to the second embodiment.

The diffraction grating GR1 is arranged so that its reference plane RP is parallel to the reference plane of the scale 2. Further, the light receiving unit 10 is arranged so that the central axis is along the normal line of the reference plane of the scale 2. The diffraction grating GR2 is also arranged so that its reference plane RP is parallel to the reference plane of the scale 2. Further, the light receiving unit 20 is arranged so that the central axis is along the normal line of the reference plane of the diffraction grating pattern 3. The diffraction gratings GR1 and GR2 are transmission type diffraction gratings formed in the horizontal direction at the same lattice pitch as the average lattice pitch gm of the diffraction grating pattern 3.

Next, the function of the diffraction grating GR1 will be described. First, it is assumed that the wavelength of the incident light L2 fluctuates by Δλ in a state where the diffraction grating pattern 3 has no lattice pitch deviation and the lattice pitch of the diffraction grating pattern 3 is an average lattice pitch gm. The angle θM1 (x) formed by the + 1st order light DP1 at this time with respect to the incident light L2, that is, the normal of the scale 2 satisfies the following equation, considering that the diffraction grating pattern is a reflection type.

As a result, sinθM1 (x) is expressed by the following equation.

After that, when the +1st order light DP1 is incident on the diffraction grating GR1, it is diffracted again. At this time, the angle formed by the normal of the diffraction grating GR1 and the optical axis of the diffracted + 1st order light DP1 is defined as γ. Considering that the diffraction grating GR1 is a transmission type, the angle γ satisfies the following equation.

As a result, sinγ is represented by the following equation.

Therefore, the diffraction angle γ becomes 0. FIG. 11 shows an optical path of diffracted light when the wavelength of the incident light fluctuates. The +1st order light DP1 propagates in parallel with the normal of the light receiving surface of the photoelectric sensor 12 and is incident on the condenser lens 11. The condenser lens 11 collects the incident light propagating in the same direction so as to be focused on the same focal point. That is, even if the wavelength of the incident light deviates and the angle θM1 (x) fluctuates, the angle of incidence on the condenser lens 11 is corrected by the diffraction grating GR1. As a result, even when the wavelength of the incident light L2 fluctuates, the +1st order light DP1 is always focused at the same position on the photodiode array, so that the influence on the lattice pitch deviation measurement can be prevented.

Next, it is assumed that both the wavelength deviation and the lattice pitch deviation occur. At this time, the angle θM1 (x) formed by the + 1st order light DP1 with respect to the incident light L2, that is, the normal of the scale 2 satisfies the following equation, considering that the diffraction grating pattern 3 is a reflection type.

As a result, sinθM1 (x) is expressed by the following equation.

After that, when the +1st order light DP1 is incident on the diffraction grating GR1, it is diffracted again. At this time, the angle formed by the normal of the diffraction grating GR1 and the diffracted + 1st order light DP1 is defined as γ. Considering that the diffraction grating GR1 is a transmission type, the angle γ satisfies the following equation.

As a result, sinγ is represented by the following equation.

FIG. 12 shows an optical path of diffracted light when the wavelength of the incident light fluctuates and a lattice pitch deviation exists. Considering that Δg is an extremely small value and that the denominator of the formula [21] is squared, it is compared with the influence of the wavelength shift in the configurations of the first and second embodiments represented by the formula [15]. It can be understood that the fluctuation of the incident angle of the diffracted light can be suppressed.

Regarding the diffraction grating GR2 and the light receiving unit 20, the influence of wavelength deviation can be reduced by the same principle as that of the diffraction grating GR1 and the light receiving unit 10.

<Embodiment 4>
The lattice pitch deviation measuring apparatus according to the fourth embodiment will be described. The deviation measuring device 400 according to the fourth embodiment has a configuration in which the calculation unit 40 of the lattice pitch deviation measuring device 200 according to the second embodiment is replaced with the calculation unit 60. FIG. 13 is a diagram schematically showing the configuration of the calculation unit 60 according to the fourth embodiment.

The calculation unit 60 has a configuration in which the light intensity calculation units 61 and 62 and the diffraction efficiency calculation unit 63 are added to the calculation unit 40.

The light intensity calculation unit 61 calculates the light intensity PW1 of the diffracted light received by the photoelectric sensor 12 based on the digital voltage signal S1. The light intensity calculation unit 62 calculates the light intensity PW2 of the diffracted light received by the photoelectric sensor 22 based on the digital voltage signal S2.

The diffraction efficiency calculation unit 63 receives a signal indicating the light intensity PW0 of the laser light L1 or the collimated light L2 monitored by the light irradiation unit 30 from the light irradiation unit 30. The diffraction efficiency calculation unit 63 calculates the diffraction efficiency of the diffracted light received by the photoelectric sensor 12 and the photoelectric sensor 22 by dividing the light intensity PW0 by the light intensities PW1 and PW2.

When the losses of the laser light L1, the collimated light L2, and the received diffracted light are known in advance, the diffraction efficiency calculation unit 63 may calculate the diffraction efficiency after correcting these losses.

As described above, according to this configuration, it is possible to measure not only the lattice pitch deviation but also the diffraction efficiency. Thereby, the lattice pitch deviation and the diffraction efficiency can be measured in parallel.

<Other embodiments>
The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit. For example, the light receiving unit 10 may receive the reflected light from the diffraction grating pattern 3 instead of the 0th-order diffracted light. In this case, the lattice pitch deviation can be calculated by the same process as when receiving the 0th-order diffracted light.

Although the third embodiment has been described as a modification of the second embodiment, the present invention is not limited to this, and the lattice pitch deviation measuring device 100 according to the first embodiment may be configured by adding either the diffraction grating GR1 or the GR2. .. In this case, even if the diffraction grating is added only to the light receiving unit 20 that receives the + 1st-order diffracted light, the influence of the wavelength fluctuation of the incident light can be prevented.

Although the fourth embodiment has been described as a modification of the second embodiment, the present invention is not limited to this, and the lattice pitch deviation measuring device 100 according to the first embodiment may be configured by introducing the calculation unit 60. In this case, it is possible to calculate the diffraction efficiency of the 0th-order light and the + 1st-order light.

1 Linear slide 2 Scale 3 Diffraction grid pattern 10, 20 Light receiving part 11, 21 Condensing lens 12, 22 Photoelectric sensor 12A Substrate 12B Central axis 13, 23 Current-voltage conversion part 14, 24 A / D converter 30 Light irradiation part 31 Laser light source 32 Laser driver 33 Collimated light generation mechanism 34 Collimated light propagation direction adjustment mechanism 34A Polarized beam splitter 34B Wavelength plate 40, 60 Calculation unit 41, 42 Angle fluctuation calculation unit 43 Grid pitch deviation calculation unit GR1, GR2 Diffraction grid 61, 62 Light intensity calculation unit 63 Diffraction efficiency calculation unit 100, 200, 300, 400 Lattice pitch deviation measuring device D0 0th order light DM1 -1st order light DP1 + 1st order light IS1, IS2 Current signal L1 Laser light L2 Collimated light, Incident light L3 Incident Optical PD photodiodes PW0 to PW2 Optical intensity RP reference plane S1, S2 Digital voltage signal VS1, VS2 Voltage signal Δθ0, Δθ1, ΔθM1, ΔθP1 Angle fluctuation information

Claims (8)

A light irradiation part that irradiates light and
Of the diffracted light from the diffraction grating irradiated with the light, the first light receiving portion that receives the first diffracted light and
Of the diffracted light from the diffraction grating irradiated with the light, a second light receiving portion that receives the second diffracted light having a diffraction order different from that of the first diffracted light, and
The first angular variation of the first diffracted light is calculated from the variation of the incident position of the first diffracted light, and the second angular variation of the second diffracted light is calculated from the variation of the incident position of the second diffracted light. An arithmetic unit that calculates the angle variation and calculates the deviation of the lattice pitch of the diffraction grating based on the difference between the first angle variation and the second angle variation.
A diffraction grating pitch deviation measuring device comprising. The first diffracted light is 0th-order diffracted light or reflected light.
The diffraction grating pitch deviation measuring apparatus according to claim 1, wherein the second diffracted light is +1st-order diffracted light or -1st-order diffracted light. The first diffracted light is +1st order diffracted light.
The diffraction grating pitch deviation measuring device according to claim 1, wherein the second diffracted light is a first-order diffracted light. Any one of claims 1 to 3, wherein the calculation unit calculates the straightness error of the diffraction grating based on the sum of the first angle variation and the second angle variation. The diffraction grating pitch deviation measuring device according to the section. Between the diffraction grating and the first light receiving portion, the average lattice pitch of the diffraction grating is set so that the reference plane is parallel to the reference plane of the diffraction grating and is in the arrangement direction of the grating of the diffraction grating. With the first diffraction grating arranged at the same pitch,
Between the diffraction grating and the second light receiving portion, the average lattice pitch of the diffraction grating is set so that the reference plane is parallel to the reference plane of the diffraction grating and is in the arrangement direction of the grating of the diffraction grating. Further equipped with a second diffraction grating arranged at the same pitch,
The first light receiving portion is arranged so that the central axis is perpendicular to the reference plane of the first diffraction grating.
The diffraction grating according to any one of claims 1 to 4, wherein the second light receiving portion is arranged so that the central axis is perpendicular to the reference plane of the second diffraction grating. Pitch deviation measuring device. The calculation unit
The intensity of the light applied to the diffraction grating is obtained from the light irradiation unit, and the intensity of the light is obtained.
The intensities of the first and second diffracted light received by the first and second light receiving units were calculated, respectively.
A claim characterized in that the diffraction efficiency of the first and second diffracted light is calculated from the intensity of the light applied to the diffraction grating and the intensity of the first and second diffracted light, respectively. Item 6. The diffraction grating pitch deviation measuring apparatus according to any one of Items 1 to 5. Any one of claims 1 to 6, wherein the first and second light receiving units are configured to be capable of detecting fluctuations in the incident position of the incident diffracted light in a direction intersecting the incident direction. The diffraction grating pitch deviation measuring apparatus according to the above. The diffraction grating pitch deviation measuring apparatus according to any one of claims 1 to 7, wherein the light output by the light irradiation unit is light obtained by collimating laser light.

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