KR20100011192A - Moire measurement device using digital micromirror device - Google Patents

Abstract

PURPOSE: A moire measurement device using DMD is provided to measure the moire image without a mechanical error and to increase the phase transition speed. CONSTITUTION: A moire measurement device using DMD comprises a first DMD(Digital Micromirror Device, 131), a second DMD(132), a first light projecting part(141), a second light projecting part(151), a grid image photo diode(180), and an image processing part. The DMD produces the grid image controlling the radiated light. The DVD produces and emits the phase-shifted first and second grid image. The second light projecting part blocks the projecting of the grid image while the first light projecting part is projecting the grid image. The first projecting part blocks the projecting of the grid image while the second light projecting part is projecting the grid image.

Description

Moire measurement device using digital micromirror device

The present invention relates to an image measuring apparatus based on moiré phenomena, and more particularly, to a moire image measuring apparatus using DMD.

A number of three-dimensional shape measuring methods capable of measuring the height of the conventional observation object have been proposed. Proposed prior art includes optical triangulation, optical profilometry, confocal microscopy, non-contact measurement using moire patterns, and the like. These techniques have been widely used because of the advantage of not damaging the object.

The shape measurement method using the moire pattern of the three-dimensional shape measurement method measures the information on the height of the object surface by measuring and analyzing the interference fringe overlapping two or more periodic patterns having a certain shape on the surface of the object to be measured To acquire.

In general, the three-dimensional shape measurement method using a moire pattern is divided into a shadow moire (projection moire) method.

The shadow moire is a method of measuring a shape of a subject by using a moire pattern generated from a shadow of a grid pattern appearing on a surface of a subject without using a lens, and the shaw moire is a subject. There was a technique of obtaining a moire pattern by scanning a grid pattern by using a white light or monochromatic light projector, and by superimposing a grid with the same pitch as one grid by scanning a grid image transformed according to the shape of an object.

However, the three-dimensional shape measurement apparatus using the above-mentioned shadow moiré has a simple advantage of the installation, but there is a problem that is applied only when the grid and the subject can be sufficiently close because the shadow of the grid should be used.

In addition, the above-described projection moiré is preferred because the size of the target object is not limited by the size of the lattice, and there is no restriction to place it close to the object when measuring a minute object having a small height difference, but the projection moiré method is Since the grid pattern is projected on the subject by tilting it at a predetermined angle, the shadow is generated on the opposite side of the projected object by the height of the tilted angle. Projection of the grid pattern on both sides was used.

In the related art, a three-dimensional shape was measured using a grid image in which a phase shift was performed by using a mechanical device such as an actuator.

However, when performing the phase shift in a mechanical manner, there is a limit in obtaining precise results due to the position error value, the phase shift speed is slow, and there is a complicated problem of adjusting the spacing of the grid image.

The present invention has been proposed to solve the above problems, and an object of the present invention is to propose a moiré image measuring apparatus for performing phase shift in a precise manner.

A further object of the present invention is to propose a moiré image measuring apparatus which is simple in operation and has a small amount of control.

According to the present invention, an image measuring apparatus using moiré includes: a first DMD (Digital Micromirror Device) for generating a phase shifted first grating image by controlling light emitted from a first light source and emitting the first grating image; A second DMD for controlling a light emitted from a second light source to generate a phase shifted second grating image, and emitting the second grating image; A first light projector projecting the first grating image in a first direction on a measurement object; A second light projector projecting the second grating image in a second direction on the measurement object; A lattice image receiving unit receiving a lattice image reflected from the measurement object; And while the first DMD projects the grid image onto the measurement object, the second DMD blocks the projection of the grid image onto the measurement object, and conversely, while the second DMD projects the grid image onto the measurement object. The first DMD blocks the projection of the grid image to the measurement object.

Preferably, the image processor superimposes a first measurement image calculated through an image on which the first grating image is reflected and a second measurement image calculated through an image on which the second grating image is reflected.

The device according to the present invention can quickly perform the phase shift of the grid image, and can easily measure the height of the workpiece by controlling the interval of the grid image, etc., and accurate moiré image measurement without mechanical error .

Specific features, operations, and effects of the present invention will be further embodied by one embodiment of the present invention described below.

1 is an example of a moiré image measuring apparatus according to an exemplary embodiment. As shown, a digital micromirror device (DMD) is provided to generate a grid image.

The DMD is a device in which hundreds of thousands of fine mirrors are integrated into a semiconductor chip by using a MEMS (Micro Electro Mechanical System) technology, and performs various operations such as light modulation. When light emitted through a light source is input to the DMD, the DMD may emit a grid image by using light from the light source. 2 to 5 illustrate an example in which a DMD generates a grating image according to a phase shift (PSI) method. To reflect / reflect the light of the light source, as shown in the drawing, a grid image is generated by selectively turning on / off pixels of a DMD having a number of 1024 * 768 pixels, and a projection lens provided inside or outside the DMD. Can be projected onto the measurement object, etc. Since each of the grating images shown in FIGS. 2 to 5 has a phase difference of λ / 4 from each other, after sequentially projecting four grating images as shown in FIGS. 2 to 5, the sequentially projected grating images are reflected. The 3D image may be obtained by processing the result according to a conventional phase shifting technique (PSI).

Since the apparatus of FIG. 1 generates a grid image by using a DMD, it is possible to perform phase shift of the grid image faster than the conventional technique of generating the grid image by a mechanical method, and the grid image through simple software control. Pitch can be easily controlled, and accurate grid image can be generated without mechanical error.

When measuring a measurement object on a specific field of view, as shown in FIGS. 2 to 5, the grid image having a constant pitch is sequentially projected. Since the spacing of the grid images is related to the resolution, first create a grid image with a relatively small spacing for precise measurement, and if the measurement range of the height of the measurement object cannot be measured with the spacing of the existing grid image, the grid image It is desirable to increase the interval of.

1 includes at least two DMDs 131 and 132, and each of the DMDs 131 and 132 receives light through the lights 111 and 112 and the lenses 121 and 122. The illustrated first DMD 131 receives light from the first light 111 to generate a phase shifted first grating image, and the second DMD 132 receives light from the second light 112 to phase Generate a transitioned second grating image.

The first grating image and the second grating image are transferred to the first light projecting unit 141 and the second light projecting unit 151, respectively. Each light projector projects the first and second grating images onto the measurement object 160 using optical means such as a projection lens. In the example of FIG. 1, the first light projector 141 projects the grating image in the first direction through the lens, and the second light projector 142 projects the grating image in the second direction through the lens. do.

In the example of FIG. 1, the measurement object 160 may be observed in different directions through the light projectors 141 and 151. Therefore, it is possible to solve a problem such as a shadow generated when the measurement object 160 is observed in one direction.

By operation of the DMDs 131 and 132, four grid images are generated while the first DMD 131 projects the first grid image (for example, when four grid images are sequentially projected). While projecting through a first DMD 131, the second DMD 132 blocks the projection of the grid image, and while the second DMD 132 projects the grid image, the first DMD 131. ) Blocks the projection of the grid image. That is, the measurement object 160 is observed only in one direction for an arbitrary moment.

The grating image reflected from the measurement object 160 is received by the grating image receiving unit 180 that can be implemented by a camera through the imaging lens 170. As described above, the result of reflecting the grid image projected by the first DMD 131 and the result of reflecting the grid image projected by the second DMD 132 are separately received. Each result received separately is image processed by an image processor (not shown).

The image processing unit obtains a three-dimensional image (first measurement image) of observing the measurement object 160 in the first direction by using the reflection result of the grid image projected by the first DMD 131, and the second DMD 132. ) To obtain a three-dimensional image (second measurement image) of observing the measurement object 160 in the second direction, and to superimpose both results to obtain a final three-dimensional image of the measurement object 160.

The method of obtaining a 3D image using the reflected grid image may be according to a conventional phase shifting technique (PSI). For example, as illustrated in FIGS. 2 to 4, when sequentially projecting four grid images at quarter intervals, light intensities I ₁ , I ₂ , I ₃ , and I ₄ corresponding to each of the four grid images. Can be obtained. In this case, the phase phi at a specific position (x, y) is determined as follows.

That is, the four light intensities are converted to the phase at the corresponding position, and when the phase value at the corresponding position is known, the height of the corresponding measurement position may be calculated using the reference wavelength.

The image processor may correct the error occurrence part by overlapping the result of the reflection of the second grating image on the portion where the error occurs on the result of the reflection of the first grating image.

6 to 8 are views illustrating a concept of a technique for measuring a point where a measurement error occurs in the image processor.

As shown in FIG. 6, when acquiring a phase using a plurality of sinusoidal waves, phases of more than '-PI / 2' and less than 'PI / 2' form one period, and the period is repeated through the measurement area. Appears.

In the case of FIG. 6, since specific phase values are fixed in an area of more than '-PI / 2' and less than 'PI / 2', only the amount of change in one period can be determined, and thus, a phase extension technique of sequentially connecting each period This applies.

7 is an example of a case where a phase extension technique is applied. As shown, the phase at point 701 belonging to the region where the period is Nth is determined to be the value of (PI * N) added to the original phase A1. In addition, the phase at point 702 belonging to the Nth region is determined by a value obtained by adding (PI * N) to the original phase A2. In the same way, the phase at point 703 (original phase is B1) is B1 + (PI * (N + 1)), and the phase at point 704 (original phase is B2) is determined as B2 + (PI * (N + 1)). do.

When the phase extension technique described above is applied, the phase of the received grating image should be measured in such a way that it continuously increases in one direction. However, when the shadow region is generated by the shape of the measurement object 160 as shown in FIG. Since it does not increase continuously, you can see that an error has occurred. For example, the illustrated point S1 or point S2 does not measure the phase larger than the point S0, so it can be seen that an error has occurred at that point.

As described above, a point where an error occurs can be superimposed with the result obtained by reflecting the grid image reflected from another direction to obtain a measurement result without a shadow area. In addition to the phase extension technique described above, a conventionally proposed grating image overlap matching technique may be additionally applied to obtain more accurate measurement results.

9 is a view showing still another example according to the present invention. As shown, the example of FIG. 9 includes a first DMD 911, a first projection lens 921, a first mirror 931, a second mirror 932, a second DMD 912, and a second projection. A lens 922, a third mirror 933, a fourth mirror 934, an imaging lens 970, and a camera 980 are included.

In FIG. 9, unlike the example of FIG. 1 described above, the first grating image generated from the first DMD 911 is transferred to the object 960 through the first mirror 931 and the second mirror 932. The second grating image generated from the second DMD 912 is projected onto the observation object 960 through the third mirror 933 and the fourth mirror 934. Since the rest of the configuration corresponds to the example of FIG. 1, a detailed description thereof will be omitted. 9 has an advantage that the moiré image measuring apparatus can be implemented through an optical means having a simple structure such as a mirror.

This embodiment generates a grid image using a DMD, unlike a moiré image measuring device that generates a grid image by a conventional mechanical technique. Since the DMD is controlled by software or the like, there is an advantage in that the grid spacing and the like can be freely changed without a mechanical change.

The above-described embodiment is for convenience of description of the present invention, and the present invention is not limited to the specific numerical values, symbols, and the like used in the above-described embodiment.

Preferred embodiments of the present invention described above are disclosed for purposes of illustration, and those skilled in the art having various ordinary knowledge of the present invention may make various modifications, changes, and additions within the spirit and scope of the present invention. And additions are within the scope of the following claims.

The present invention relates to a moiré image measuring apparatus that is attracting attention in the field of fine processing / measurement and its industrial applicability will be recognized.

1 is an example of a moiré image measuring apparatus according to an exemplary embodiment.

2 to 5 illustrate an example in which a DMD generates a grid image according to a phase shift method.

6 to 8 are views illustrating a concept of a technique for measuring a point where a measurement error occurs in the image processor.

9 is a view showing still another example according to the present invention.

Claims (5)

In the image measuring apparatus using moiré A first DMD (Digital Micromirror Device) for generating a phase shifted first grating image by controlling light emitted from a first light source, and emitting the first grating image; A second DMD for controlling a light emitted from a second light source to generate a phase shifted second grating image, and emitting the second grating image; A first light projector projecting the first grating image in a first direction on a measurement object; A second light projector projecting the second grating image in a second direction on the measurement object; A grid image receiver for receiving a grid image reflected from the measurement object; And Including an image processor for performing an image processing on the received grid image, The second DMD blocks the projection of the grid image onto the measurement object while the first DMD projects the grid image onto the measurement object, and conversely, while the second DMD projects the grid image onto the measurement object. Moiré image measuring device using a DMD, characterized in that the first DMD blocks the projection of the grid image to the measurement object The method of claim 1, The DMD is a moiré image measuring apparatus using a DMD, characterized in that to control the plurality of fine mirrors to emit a grid image subjected to the phase shift The method of claim 1, The image processing unit uses a DMD to superimpose a first measurement image calculated through an image on which the first grid image is reflected and a second measurement image calculated through an image on which the second grid image is reflected. Moire image measuring device The method of claim 3, The image processor is a moiré image measuring apparatus using a DMD, characterized in that for estimating the error occurrence point in the first grid image using the phase of the image reflected the first grid image The method of claim 4, wherein An error occurrence point in the first grating image is corrected by using an image in which the second grating image is reflected.

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