JPH11118422A - Dimension measuring device using moire fringe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine the moving direction of a grid easily with the simple structure and high speed when measuring a dimension using moire fringes formed by the grid having two different grid pitches and to realize a highly accurate dimension measuring device by improving detecting accuracy of the grid position. SOLUTION: Moire fringes are generated by a moving grid 11 and a fixed grid 13 with different grid pitches, and a moving direction determining grid 12 is provided with the grid pitch equal to the moving grid 11 and a different intensity distribution. When the moving direction determining grid 12 is moving, a light having passed through it is received by a light receiver with a single light receiving face, and the moving direction and the number of moving grids are detected from change in the light intensity. When the moving grid 11 is stopped, the moire fringes formed by permeation through the moving grid 11 and the fixed grid 13 are detected by a line sensor, and a moving distance less than the grid pitch of the moving grid 11 is detected from the movement of the moire fringes at a reference position. A dimension is measured from the above detected number of movement of the grids and the moving distance less than the grid pitch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dimension measuring apparatus to which moire interferometry is applied, and more particularly to a configuration of a dimension measuring apparatus using moire fringes generated when two gratings having different grating pitches are superposed.

[0002]

2. Description of the Related Art In a production line that requires fine processing, there is a need to measure the size, shape, and the like of a workpiece (work) on the spot with accuracy in a submicron range. As a small and simple dimension measuring device, a device using an optical scale (linear encoder) is widely used. This uses an optical scale in which a grid pattern consisting of black and white binary intensity is formed on a glass substrate.When the optical scale attached to the stylus moves, the light intensity reflected by the grating or transmitted through the grating This is a device that measures the change and detects the moving distance of the grating to measure the dimensions. The measurement resolution of the optical scale method is one pitch length of the grating and one resolution of the grating.
It is determined by the number of divisions when the pitch is finely divided to detect the grid position. Normally one pitch length of the grating is 10μ
If it is about m, and it is divided into 10 and detected, the measurement resolution is 1 μm.

[0003] As an example other than the optical scale method, there has been proposed an apparatus for detecting moire fringes generated when two lattices each having a large number of the above-mentioned black and white lattices are superposed. FIG. 5 shows the principle of a conventional general moiré interferometry. FIG.
The gratings 51 and 52 shown in (a) and (b) have the same grating width and grating pitch. Note that the two gratings 51 and 52
, The width of the white pattern is equal to the width of the black pattern. The grating 51 shows a state where it is installed in the horizontal direction, and the grating 52 shows a state where it is installed at an angle θ from the horizontal direction. The moiré fringes 53 shown in FIG.
Are generated when they are superimposed, and the intensity distribution is determined by the product of the light transmission intensities of the two gratings. When the inclination angle θ of the grating 52 is small, the moire fringes have a shape in which a wide black pattern is periodically formed in a substantially vertical direction, and a rhombic white pattern is generated therebetween. The pitch w of the wide black pattern in the vertical direction is w = P / θ. Here, P is the length of one period of the grating. The pitch w changes in accordance with the inclination angle θ of the grating 52. The larger the θ, the shorter the pitch w, and the shorter the width of the black pattern having a wide moire fringe.

When the grating 52 is fixed while keeping the inclination angle θ of the grating 52 constant, and the grating 51 is moved in the horizontal direction,
Moiré fringes are perpendicular to the direction of grid movement (vertical direction in the figure)
Go to At this time, if the grating is moved by one pitch P, the moire fringes move by one pitch w. That is,
The movement of the lattice is detected to be enlarged, and the magnification is 1 / θ. For example, when θ is 5 degrees, the movement of one pitch of the grating is enlarged to about 11 times. For example, one of the grid
When the pitch is 10 μm, one cycle of the moire fringes is approximately 11
0 μm. Therefore, if the movement of the moire fringes is detected with an accuracy of 1 μm, the movement of the grating 51 by about 0.1 μm can be detected. As described above, if the moiré fringes are used, it is possible to detect a minute movement of the lattice by enlarging it into a large movement of the moiré fringes,
The feature is that high-resolution dimension measurement can be performed.

FIG. 6 shows a configuration example of a conventional dimension measuring apparatus using moiré fringes. Light emitted from a light source 60 such as a halogen lamp irradiates a moving grating 62 via a collimating lens 61. The moving grid 62 is composed of the grid 51 shown in FIG. 5A, and is attached to a stylus, not shown, and moves according to the movement of the stylus. The fixed grid 63 is composed of the grid 52 shown in FIG. 5B, and is fixedly installed near the moving grid 62. At this time, the moving grating 62 and the fixed grating 63 have the same grating pitch, and the fixed grating 63 is installed at an angle θ from the horizontal direction. Moving grating 62 and fixed grating 6
The light that has passed through both 3 forms moire fringes behind the fixed grating 63, and the moire fringes are detected by the light receiver 65 via the condenser lens 64.

The light receiver 65 for detecting moire fringes has a plurality of light receiving surfaces, and each outputs a light intensity signal detected on each light receiving surface. For example, when the light receiver 65 is composed of two light receiving surfaces, the center distance between the light receiving surfaces is separated by a distance corresponding to １ ／ of the moire fringe pitch w, and the light intensity of the moire fringes is individually detected. It outputs two light intensity signals. As another method, a method is also used in which four light receivers are provided at respective positions obtained by dividing the pitch of the moiré fringe into four, and four light intensity signals are output. The signal processor 66 converts the plurality of light intensity signals output from the
The movement is detected to measure the size. In order to measure the dimensions, it is necessary to detect the moving direction of the moving grid 62 and the number of moving grids, and to detect the position where the moving grid 62 has stopped at the start and end of the measurement. The detection of the grating moving direction is determined based on the lead / lag of the mutual phase of the plurality of light intensity signals. In the detection of the grating position, it is determined which phase state of the light intensity signal in which the grating 62 is stopped in one cycle of the moire fringes.

[0007]

When one optical scale is used, the number of divisions of one pitch width of the grating in the detection of the grating position is about 10, so that one pitch of the grating is 10 μm.
In the case of m, the resolution is 1 μm. For this reason, there is a problem in accuracy that submicron measurement accuracy cannot be obtained. In the case of the conventional moiré fringe method, a plurality of light receivers are required to detect the moving direction of the moving grating, and the position of each light receiving surface is set to a specific position within one cycle of the moiré fringe. Needed. Therefore, there is an adjustment problem that the position adjustment of the light receiver becomes complicated. Further, there is another problem in the circuit configuration that when determining the moving direction from the plurality of obtained light intensity signals, the signal processing circuit for determining the lead / lag of the phases of the signals becomes complicated.

In the formation of moire fringes, it is necessary to incline one of the fixed gratings by an angle θ.
There is also a problem that adjustment is difficult. When the angle θ is a small value of several degrees, a slight shift in the mounting angle causes a large variation in the pitch of the moire fringes. For this reason, the conversion factor when converting the pitch of the moiré fringes into a dimension changes, which causes a problem that an error occurs in the dimension measurement. Furthermore, there is a problem that the detection accuracy of the grid position when the moving grid is stopped is low. A wide black pattern of moiré fringes and a narrow black and white rhombus pattern between them can be obtained by converting the rhombic pattern portion into a wide white pattern by image processing, which is approximately square wave at a pitch w. It can be considered that the intensity pattern changes. Therefore, if the light intensity is detected by a photodetector having two or four light-receiving surfaces, the phase detection of the square wave, that is, the detection accuracy of the lattice position is reduced, and the dimension measurement accuracy is poor.

The main cause of the above problems is that the grating pitch of the moving grating and that of the fixed grating are equal. Since the grating pitches are equal, it is necessary to tilt one of the gratings to generate moiré fringes, and the generated moiré fringes have an intensity distribution symmetrical in the pitch direction. For this purpose, a plurality of light intensity signals are detected using a light receiving device having a plurality of light receiving surfaces to determine a moving direction or to detect a grating stop position. The present invention solves the above-described problems by newly adopting a third grating having a special intensity distribution together with two gratings having different grating pitches, and realizes a highly accurate dimension measuring device having a simple configuration. The purpose is to:

[0010]

In order to solve the above-mentioned problems, a dimension measuring apparatus according to the present invention has the following arrangement. A moving grating having a first grating pitch that moves together with the stylus; and a fixed grating having a second grating pitch different from the first grating pitch, wherein the fixed grating is fixed near the moving grating. A size measuring device that uses a moiré fringe for illuminating the moving grating and the fixed grating with light from a light source and detecting a generated moiré fringe to measure a dimension, wherein the moving grating and the first grating are arranged. A moving optical scale having the same pitch as the moving grating and having a different intensity distribution from the moving grating, and a moving optical scale irradiated with light from a light source, and the moving optical scale is moving. A first light receiver for detecting light transmitted through the movement direction determination grating, and a movement for detecting a movement direction of the movement direction determination grating from a first light intensity signal detected by the first light receiver. A direction determining unit, A moving grating counting unit for detecting the number of pulses of the first light intensity signal generated by the movement of the moving direction determination grating, and a light transmitted through the moving grating and the fixed grating when the moving optical scale is stopped. A second light receiver for detecting a moiré fringe to be formed, and a preset position of the moiré fringe before and after the movement of the moving grating is detected from a second light intensity signal detected by the second light receiver. A moiré fringe position detecting section, grid moving distance information corresponding to the number of moving grids of the moving direction determination grid detected by the moving grid counting section, and a grid before and after movement of the moving grid detected by the moiré fringe position detecting section. And a dimension calculation unit for calculating a dimension value to be measured from the position information of the moving direction determination grating and the movement of the moire fringes caused by the change in the light intensity and the movement of the moire fringes caused by the movement of the movement grating. And measuring a.

In the moving direction determination grating having the above structure, the ratio of the width of a black pattern having a low light transmittance to the width of a white pattern having a high light transmittance constituting the grating is set to at least three types. The black pattern width is sequentially changed in the same direction from a wide width to a narrow width in accordance with the ratio, and the change in the pattern width is periodically repeated as one unit, which is asymmetric with respect to the direction in which the lattice is formed. The intensity pattern is used. Further, the first light receiver has a single light receiving surface, and the light receiving surface detects light intensity from a grating portion having a width approximately half the first grating pitch of the moving direction determination grating. And outputs the single first light intensity signal by detecting the light intensity from the movement direction determination grating transmitted through the slit. Further, the second light receiver is a line sensor having a plurality of light receiving surfaces divided into a large number, and is configured to detect the intensity distribution of the moire fringes and output a second light intensity signal.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a configuration of an apparatus for measuring a size from moiré fringes generated when two gratings having different grating pitches are superimposed. In a grid composed of linear black-and-white patterns (light and dark patterns) at equal intervals (white pattern width and black pattern width are equal), two grids with different grid pitches are superimposed while being held parallel to each other. The moiré fringe that occurs sometimes has a cycle corresponding to the difference between the two grating pitches, and has a characteristic that the smaller the pitch difference between the two gratings, the longer the cycle of the moiré fringe. The intensity of the moiré fringes is the product of the light transmission intensities of the two gratings, and a black pattern and a white pattern appear alternately, and the pattern width of the black pattern and the white pattern repeatedly increases and decreases periodically. As a whole, the intensity distribution is such that the width of the black pattern is widened, and the width of the white pattern is small near the wide black pattern.

If one of the gratings is fixed and the other is moved, the moire fringes move in the moving direction of the grating.
At this time, if the grating moves by one pitch, the length of one period of the moire fringes moves. When the pitch difference between the two gratings is small, one cycle of the moiré fringes is about several tens times the grating pitch, so that a minute movement of the moving grating can be detected by being enlarged to several tens times. That is, moire fringes formed by gratings having different grating pitches have an effect of enlarging the movement of the grating, and when applied to dimension measurement, measurement sensitivity and resolution are improved. At this time, since the two gratings may be installed in parallel, there is an advantage that adjustment of the positional relationship when setting both of them is simplified.

Each grating for generating the above-described moiré fringes has a symmetrical intensity distribution in the direction in which the grating is formed. Therefore, detecting the moving direction of the grid from such a grid pattern has the same disadvantage as the conventional example.
Also, detecting the moving direction of the grating from the moiré fringes complicates the signal processing and causes inconvenience. Therefore, a dedicated grating for determining the moving direction, which has a different shape from the grating for generating moiré fringes, is newly provided. The moving direction determination grating has the same pitch as the grating pitch of the moving grating for generating moiré fringes, and the width of the black pattern portion in one pitch is changed to at least three or more types. Since the lattice pitch is constant, the width of the white pattern portion changes in a similar manner. At this time, the black pattern width is sequentially changed from a wide width to a narrow width, for example, in a direction in which the width becomes narrower, and the pattern is periodically repeated. That is, the moving direction determination grid has an intensity distribution that is asymmetric in the direction in which the grid is formed.

A moving grating and a moving direction judging grating, which are one of the gratings for generating moiré fringes, are formed at separate positions on a moving optical scale that moves together with a stylus, and both are illuminated with light from a light source. At this time, the light transmitted through the moving grating and the light transmitted through the moving direction determination grating are detected by separate light receivers provided at different positions, and another signal processing is performed. While the moving optical scale is moving, the light intensity signal from the moving direction determination grid is detected, and the moving direction is determined and the number of moved grids is measured. At this time, the light transmitted through the moving grating is not measured. When the moving optical scale is stopped,
Moire fringes formed by the moving grid and the other grid (fixed grid) fixed are detected, and grid position information when the moving grid is stopped is measured. As described above, different signal processing is performed by changing the measurement mode during the movement and the stop of the grating.

When the moving optical scale moves together with the stylus, the light intensity transmitted through the moving direction determination grating changes in signal width at which the light intensity becomes low according to the width of the black pattern. The direction in which the signal width changes, for example, the signal width is large →
The direction of movement of the movable optical scale can be determined by detecting the direction of change from small to small to large. This can be achieved by making the intensity distribution of the moving direction determination grid asymmetric. Further, when the moving direction determination grating is moving, the number of pulses of the light intensity signal is measured simultaneously by using a circuit for generating one pulse from the light intensity signal every time the grating moves by one pitch, and Detect number N. By detecting the number of moving grids, a moving distance of N times one pitch of the moving grid is measured.

Since only one light intensity signal needs to be detected, the light intensity is detected by a light receiver having a single light receiving surface and a single light intensity signal is output. In the light intensity detection by the light receiver, it is necessary to select and detect only the transmitted light intensity from a width of about half of one pitch of the moving direction determination grating. Therefore, a slit corresponding to the above width is attached to the light receiving surface of the light receiver, and the light intensity is detected through the slit.

When the moving optical scale is stopped, the stop position of the moving grating is detected by measuring the intensity pattern of the moire fringes. This detection is performed twice, at the start of measurement and at the end of measurement. The intensity distribution of the moiré fringes is a pattern in which the width of the black pattern repeats periodically increasing and decreasing, and the moiré fringes enlarged to a certain magnification are detected by a light receiver such as a line sensor having a multi-divided light receiving surface. Since the position of the moiré fringes shifts according to the lattice position of the moving lattice with respect to the fixed lattice, the stop position of the lattice can be detected from the change in the moiré fringe position. Therefore, a specific position of the moiré fringe, for example, a position where the pattern width of a white pattern near a wide black pattern is minimized is set as a reference position, and how much the reference position changes before and after movement is detected. . The detection of this position is the detection of one pitch width or less of the moving grating. The resolution of the dimension measurement is determined by the position detection sensitivity. Therefore, the dimension is measured from the grid position information before and after the start of the measurement and the distance information based on the number of grid movements detected while the grid is moving.

[0019]

FIG. 1 shows an example of a grid pattern used in a dimension measuring apparatus according to the present invention. FIG. 1A shows a moving optical scale 10.
Moving grid 11 (lower side) and moving direction determination grid 1
In the example of the 2 (upper) grating pattern, both are formed at different positions on the same moving optical scale 10. The moving grating 11 has a first grating pitch and is a grating for generating moiré fringes. The moving direction determination grating 12 has the same grating pitch as the first grating pitch, has a different intensity distribution from the grating pattern of the moving grating 11, and moves with the determination of the moving direction when the moving optical scale 10 moves with the stylus. This is a grid for detecting the number of grids. Moving grid 11 is grid 1
A pitch width P _1, equal the width of a black pattern portions and white pattern portion constituting the grid, in the direction in which the grating is formed is a symmetrical intensity distribution.

The moving direction determination grid 12 changes the ratio of the width of the black pattern portion to the width of the white pattern portion to at least three types, and sequentially changes the width of the black pattern from a wide width to a narrow width according to the ratio. Shape. In the example shown in the figure, the black pattern width is 75%, 50%, and 25% of one grid pitch.
These three types of patterns are periodically repeated to form a lattice. Since the lattice pitch is constant, the width of the white pattern portion also changes periodically from a narrow width to a wide width. Therefore, the pattern has an intensity distribution that is asymmetric in the direction in which the grating is formed. By making the intensity distribution asymmetric, it is easy to determine a moving direction described later.

FIG. 1B shows a grid pattern of a fixed grid 13 which is the other grid for generating moire fringes.
Similar to the moving grating 11, the fixed grating 13 has the same width of the black pattern portion and the white pattern portion, and has a symmetric intensity distribution in the direction in which the grating is formed. The fixed grid 13 is a moving grid 11
A second grating pitch P ₂ which is different from the. When the moving grating 11 and the fixed grating 13 are installed in parallel with each other, Moire fringes are generated by light transmitted through both. At this time,
The distance L between the moving grating 11 and the fixed grating 13 is set to satisfy the Fourier image condition. When the pitch of the moving grating 11 is d and the wavelength of the illumination light is λ, the distance L where L = nd ² / λ is the Fourier image condition. Here, n is an order such as an integer 1 or 2. d = 20 μm, λ =
L in the case of 0.5 μm is 0.8 mm (n = 1);
6 mm (n = 2). That is, the position where the intensity distribution of the light transmitted through the moving grating 11 is proportional to the original light transmission intensity distribution of the moving grating 11 is L. Therefore, the fixed grid 13
Is placed at a position L behind the moving grid 11, moire fringes with good contrast can be created.

FIG. 2 shows an example of moire fringes. The moire fringe pattern 20 has a period corresponding to the difference between the grating pitches of the moving grating 11 and the fixed grating 13. The relationship between the two pitches P ₁ and P ₂ is represented by P ₁ = P ₂ (1 + ε). Here, ε is a minute value smaller than 1, and corresponds to a pitch ratio. The length of one cycle of the moiré fringes generated at this time is ~ P ₁ / ε, and the cycle of the moiré fringes is expanded to 1 / ε of the original grating pitch. Therefore, when the difference between the two grating pitches is small, the period of the moire fringes is long, and when the difference in pitch is large, the period of the moire fringes is short. The example in FIG. 2 shows the case where ε = 0.1 and shows two periods of the moiré fringe. One period of the moiré fringe corresponds to the distance between points 21 and 22. Moiré fringes are formed in the direction in which the lattice pattern is formed, and have a shape in which black patterns and white patterns appear alternately, and their pattern widths change periodically.

The characteristic feature of the moire fringes is that the black pattern area 2 having a width wider than the width of the original black lattice pattern.
With the appearance of 3, a white pattern 24 having a small width is generated near the black pattern. In the moiré fringe position measurement described later, the white pattern 24 having the minimum width is used as a moiré fringe reference position, and the reference position is detected. When the moving grating 11 moves, the positional relationship with the fixed grating 13 changes, and the moire fringes move in the left-right direction in the figure. If the moving grating 11 moves by one pitch, the length of one cycle of the moire fringes shifts, and P
Move by ₁ / ε. That is, when ε = 0.1, the minute movement of the moving grating 11 is magnified ten times. For example, one pitch length of two lattice patterns is 20 μm, 22
At μm, one cycle of the moiré fringes is up to 200 μm, and if the grating moves 20 μm, the moiré fringes move up to 200 μm. Therefore, if the movement of the moiré fringes is detected by 1 μm, the movement of the grating by 0.1 μm can be detected.

FIG. 3 is a block diagram showing the configuration of a dimension measuring apparatus using moire fringes according to the present invention. The illumination light source 30 includes a light emitting diode or the like, and illuminates the movable optical scale 10 via a collimating lens 31. The moving optical scale 10 has the moving grating 11 and the moving direction judging grating 12 shown in FIG. 1A formed at different positions, and moves in accordance with the movement of the stylus, not shown. The light transmitted through the moving grating 11 enters the fixed grating 13. Note that the fixed grating 13 is fixedly installed at a position behind the moving grating 11 where the Fourier image condition is satisfied. Moving direction determination grid 12
Is not incident on the fixed grating 13 but directly
Is detected by the photodetector 32. Moving grating 11 and fixed grating 13
Is detected by the second light receiver 33. When the movable optical scale 10 is moving, the first optical receiver 32
Detects the transmitted light and outputs a first light intensity signal 320. When the moving optical scale 10 is stopped, the second
The second light intensity signal 330 representing the intensity pattern is output by detecting the moiré fringes by the light receiver 33.

While the moving optical scale 10 is moving, the moving direction is detected by the moving direction judging section 34. The light intensity transmitted through the moving direction determination grating 12 changes according to the light transmission intensity distribution of the grating. The moving direction determination grid 12 is shown in FIG.
Has an asymmetrical intensity distribution as shown in (1), the first light intensity signal 320 changes asymmetrically according to the movement of the grating. The moving direction is determined from the direction in which the asymmetry of the signal appears. While the moving optical scale 10 is moving, the moving grid counting unit 35 further counts the moving grid number N of the moving direction determination grid 12, and outputs the count number N with a signal 350. With this N, the moving distance NP _1, which is an integral multiple of the length of one pitch of the moving direction determination grid 12 as a unit, is obtained.

Since the determination of the moving direction and the counting of the number of moving grids can be performed with only one light intensity signal 320, the first light receiver 32 may have a single light receiving surface. In general, since the illumination light source 30 has a spread and the first light receiver 32 has a large area, the light transmitted through the moving direction determination grating 12 and received includes the light transmission intensity from many gratings. Have been. Therefore, in order to selectively detect only the light transmission intensity from one specific grating immediately before the light receiver 32, a slit is attached to the light receiving surface, and the light intensity is detected through the slit. The slit width at this time is set to a width that can detect the light intensity from a width of about half the grating pitch of the movement direction determination grating 12. As described above, the masking effect of the slit is used to detect the light intensity from the grating that is not the measurement target, thereby improving the accuracy of determining the moving direction and counting the number of moving gratings.

FIG. 4 shows an example of a light intensity signal detected when the movement direction judging grid 12 moves in order to explain the above-mentioned operation. A waveform 41 is a light intensity signal detected by the first light receiver 32. The region 42 with low light intensity is due to light transmitted through the black pattern portion. The region 43 with high light intensity is due to the light transmitted through the white pattern portion. In the waveform 41, the width of the region where the light intensity is low changes in the right direction, that is, in the direction of large → middle → small → large → middle →. In this case, it is determined that the movement direction determination grid 12 is moving to the left. Conversely, if it moves to the right, it changes in the direction of large → small → middle → large → small →. The direction of movement is determined from the manner of this change. A waveform 44 in FIG. 4 is a waveform obtained by a circuit that generates a pulse when the light intensity signal changes from the H level to the L level, and counts the number of moving grids of the moving direction determination grid 12. Since the distance La between the measurement start position 45 and the first pulse 46 and the distance Lb between the measurement end position 47 and the last pulse 48 are both distances equal to or less than one pitch width of the grating, La , Lb
Is detected from moiré fringes described later.

Next, referring to FIG.
The measurement operation when is stopped will be described. In dimension measurement, the pattern pitch of the moving grating 11 is a reference scale for measurement. In order to measure the dimension with high accuracy, it is necessary to finely divide the interval between the reference graduations and detect the stop position of the grating with a position detection accuracy equal to or less than the width of the grating pitch. The overall measurement accuracy is determined by the division accuracy. The moiré fringe position detection unit 36 performs the measurement twice at the start of measurement and at the end of measurement.
The grid position when the moving grid 11 is stopped is detected from the moire fringes. When the moving grating 11 moves within a distance of one pitch, the moire fringes shift by a length within one cycle, and the position of the moire fringes changes. Therefore, a reference position of the moiré fringe is set, and how the reference position has changed is measured, thereby detecting a movement of the moving grating 11 of less than one pitch. As the reference position of the moire fringes, the position of the white pattern 24 having the minimum width between the wide black patterns shown in FIG. 2 is employed.

The second light receiver 33 is composed of a multi-divided light receiving surface such as a line sensor, and detects moire fringes enlarged at a fixed magnification. When the grating pitch between the moving grating 11 and the fixed grating 13 for generating moiré fringes is 20 μm and 22 μm, one cycle of the moiré fringes immediately after the fixed grating 13 is ２０20.
0 μm. The moiré fringes are enlarged to a magnification corresponding to the width of the detection surface of the line sensor by placing a lens between the fixed grating 13 and the second light receiver 33, and the intensity distribution of the moiré fringes is measured. The reference position of the stripe is detected. At this time, the pixel position at the center of the line sensor is used as a detection reference point, and the grid stop position is detected from the number of pixels having a difference from the reference position of the moiré fringe. The grid position information detected at the start of the measurement is output as a signal 360, and the grid position information detected at the end of the measurement is output as a signal 365. Regarding the measurement resolution, for example, when one line sensor has 512 pixels and one cycle of the moire fringes is detected with an accuracy of one pixel, the grid position can be detected with a resolution of 20/512 ≒ 0.04 μm.

The dimension calculating section 37 includes a moving grid counting section 3
5 and the grid position information signal 3 output from the moiré fringe position detector 36.
The dimensions to be measured are calculated from 60 and 365. The grid position information detected by the moiré fringe position detection unit 36 is not a detection of the absolute position of the grid position but a detection of a relative position. Therefore, using a sample whose dimensions are known in advance, the correlation between the lattice position information detected by the signals 360 and 365 and the actual dimensions is measured to calculate the conversion factor, and the actual dimension value is calculated using the conversion factor. Is calculated. With the above-described configuration, it is possible to realize a dimension measuring device having a submicron accuracy with a simple configuration.

[0031]

As described above, the dimension measuring apparatus using the moiré fringes according to the present invention comprises a moving grating and a fixed grating having different grating pitches, and a moving direction judging grating having the same grating pitch as the moving grating and having a different intensity distribution. This is a configuration using the three gratings. Since the moving direction determination grating has an asymmetric intensity distribution in the direction in which the grating is formed, the change in the light intensity signal is asymmetric and the moving direction can be directly determined. Therefore, the light intensity can be detected by a light receiver having a single light receiving surface, and only one light intensity signal needs to be output. As a result, the configurations of the light receiver and the determination circuit for determining the moving direction can be simplified, and the adjustment of the light receiver position setting can be simplified.

In the present invention, the measurement mode is changed while the grating is moving and stopped. While the grating is moving, only the light intensity from the first light receiver is detected. Because this detection is fast,
The movement of the grating can be sufficiently followed even at a high speed, and a high-speed measurement can be performed, thereby improving the reliability of the measurement. While the grating is stopped, the second light receiver measures moire fringes. If this measurement is performed with a line sensor, one cycle of moiré fringes can be divided into about 500, so that the grating position can be detected with a resolution of about 1/500 of one pitch of the grating, and dimension measurement with submicron accuracy is possible. is there. Further, since the measurement of the moiré fringes only needs to be performed twice before and after the start of the measurement, the measurement can be speeded up as a whole.

The above moire fringes can be obtained by installing two gratings having slightly different grating pitches in parallel with each other. Therefore, unlike the conventional moire fringe creation, it is not necessary to set one of the gratings at a slight angle of several degrees, so that the grating setting can be simplified.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a light transmission intensity pattern of a grating according to the present invention.

FIG. 2 is a diagram showing a pattern of moire fringes obtained by a grating according to the present invention.

FIG. 3 is a block diagram showing a configuration of a dimension measuring device using moire fringes according to the present invention.

FIG. 4 is a diagram illustrating the intensity of a sine wave.

FIG. 5 is a diagram illustrating the generation of moire fringes in the related art.

FIG. 6 is a diagram showing a configuration of a conventional dimension measuring device using moiré fringes.

[Explanation of symbols]

 Reference Signs List 10 moving optical scale 11 moving grating 12 moving direction judging grating 13 fixed grating 20 moiré fringe 32 first light receiver 33 second light receiver 34 moving direction judging unit 35 moving grating counting unit 36 moiré fringe position detecting unit 37 dimension calculating unit

Claims (4)

[Claims] 1. A moving grating having a first grating pitch that moves with a stylus and a second grating different from the first grating pitch.
Having a fixed grating having a grating pitch, illuminating the fixed grating with the fixed grating in the vicinity of the moving grating, illuminating the moving grating and the fixed grating with light from a light source, and detecting the generated moiré fringes. A size measuring apparatus using a moiré fringe for measuring a size, wherein the moving grating and a moving direction determination grating having the same pitch as the first grating pitch and having a different intensity distribution from the moving grating. A moving optical scale configured to be irradiated with light from a light source, a first light receiving device for detecting light transmitted through the moving direction determination grating when the moving optical scale is moving, and a first light receiving device A moving direction determining unit that detects a moving direction of the moving direction determining grid from the first light intensity signal detected by the detector;
A moving grating counting unit that detects the number of pulses of the first light intensity signal generated by the movement of the moving direction determination grating; and light transmitted through the moving grating and the fixed grating when the moving optical scale is stopped. A second light receiver for detecting moiré fringes formed by the following method, and a predetermined position of the moiré fringes before and after the movement of the moving grating from the second light intensity signal detected by the second light receiver. A moiré fringe position detecting unit to detect, grid moving distance information corresponding to a moving grid number of the moving direction determination grid detected by the moving grid counting unit, and before and after the movement of the moving grid detected by the moiré fringe position detecting unit. A dimension calculation unit that calculates a dimension value to be measured from the position information of the grating, and a change in light intensity and a movement of the moiré fringes caused by the movement of the movement direction determination grating and the movement grating. Dimension measuring apparatus using the moiré fringes and measuring the Luo dimensions. 2. The moving direction determination grid according to claim 1, wherein a ratio of a width of a black pattern having a low light transmittance to a width of a white pattern having a high light transmittance constituting the grid is at least three.
In addition to setting the type ratio, the black pattern width is sequentially changed from the wide width to the narrow width in the same direction according to the ratio, and the change in the pattern width is periodically repeated as one unit, and the lattice is formed. A dimension measuring apparatus using moiré fringes, wherein the intensity pattern is an asymmetrical intensity pattern with respect to the direction in which is formed. 3. The first light receiving device according to claim 1, wherein the first light receiving device has a single light receiving surface, and the light receiving surface is a first light receiving surface of the moving direction determination grating.
A slit for detecting the light intensity from a grating portion having a width approximately half the grating pitch of the grating, and detecting the light intensity from the moving direction determination grating transmitted through the slit to obtain a single first A dimension measuring apparatus using moire fringes, wherein the dimension measuring apparatus is configured to output a light intensity signal. 4. The line receiver according to claim 1, wherein the second light receiver is a line sensor having a plurality of light-receiving surfaces divided into multiple parts.
A dimension measuring apparatus using moiré fringes, wherein the apparatus is configured to detect an intensity distribution of moiré fringes and output a second light intensity signal.