JP2002081923A - Method and device for measuring three-dimensional shape of object by projecting moire fringe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-dimensional shape measuring method and device capable of improving a lattice-pattern-projecting-type three-dimensional shape measuring method and measuring not only the three-dimensional shape of a hard object but also that of a soft object such as a living body by projecting moire fringes obtained by overlaying two lattices one on top of the other and obtaining a projection pattern with high sinusoidal properties. SOLUTION: The plurality of lattices GA and GB are overlaid one on top of the other at appropriate distances from an object to be measured A to make the relative angle θ between the lattices variable, and the lattices are arranged in such a way as to be simultaneously or relatively moved. The relative angle and relative distance between the lattices are adjusted according to the three- dimensional shape of the object to be measured A. A light source C is applied from behind the lattices GA and GB to project moire fringes by each lattice to the surface of the object to be measured via a projecting lens. The image of a fringe pattern formed on the surface of the object is picked up to obtain image pickup data, and arithmetic processing is performed on the image pickup data to obtain the three-dimensional shape of the object.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for projecting moire fringes on the surface of a three-dimensional object to obtain a projection pattern having a high sineness, thereby enabling the three-dimensional shape of not only a hard object but also a soft object such as a living body. The present invention relates to a three-dimensional shape measurement method capable of measurement and an apparatus therefor.

[0002]

2. Description of the Related Art As a method of measuring the three-dimensional shape of an object, there is a stylus type measuring method. In this method, not only long measurement time is required to obtain three-dimensional information of the whole shape, but also Since it is not suitable for shape measurement of an object having a flexible surface, there is a method using an interferometer as a non-contact type measurement method. The method using this interferometer can perform extremely high-sensitivity measurement, but is not suitable for general use because the measurement range is narrow and the apparatus itself must be expensive.

Therefore, a three-dimensional measuring method using moire topography (hereinafter, referred to as moiré method) has been developed. This moiré method has a solid grid type and a grid projection type, and both can capture the moire contours to be displayed on the target with a camera or a television camera, etc., so that the three-dimensional shape can be intuitively grasped. It is widely used in various fields, particularly in biological fields.

However, in practice, (a) it is difficult to judge surface irregularities from one Moire photograph, and (b) the measurement sensitivity is rather low, so it is not suitable for high-sensitivity three-dimensional measurement. At present, the interval between moiré fringe contour lines is limited to about 10 μm), (c) Since the visibility of the moiré fringes is not uniform for each fringe, it is pointed out that it is difficult to treat the moiré image as a target of image processing, and the like. ing.

[0005] A conventional grid pattern projection type three-dimensional shape measuring method, which has been developed from the moire topography method, is as follows.
As shown in Fig. 6, a projection grid is arranged, this grid is projected on the object to be measured by a lens, and the grid lines deformed according to the shape of the object are captured and analyzed by a CCD camera, and the three-dimensional shape of the object is obtained. Trying to get When the phase shift method is used for this analysis, it is necessary that the intensity distribution of the projected pattern is sinusoidal.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, the present invention improves a three-dimensional shape measuring method of a grid pattern projection type and projects moire fringes obtained by superimposing two grids. It is an object of the present invention to provide a three-dimensional shape measuring method and a device capable of measuring not only a hard object but also a three-dimensional shape of a soft object such as a living body by obtaining a projection pattern having a high sineness. It is.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to provide a measuring method according to the present invention, wherein a plurality of gratings are overlapped at an appropriate distance from an object to be measured and the relative angle of each grating is set. Variable, and each grid is arranged so as to be able to move simultaneously or relative to each other, adjust the relative angle and relative distance of each grid corresponding to the three-dimensional shape of the measurement object, and light source from behind the grid The moiré fringes by the respective gratings are projected onto the surface of the measurement object via a projection lens, and the image data obtained by imaging the fringe pattern formed on the surface of the object is arithmetically processed to process the image data of the object. It is characterized by obtaining a three-dimensional shape.

Further, the configuration of the measuring apparatus of the present invention for executing the above method comprises a plurality of gratings for forming moiré fringes having a sinusoidal intensity distribution by being closely adhered or superposed with an appropriate gap therebetween. Means for simultaneously or relatively linearly moving the grating, means for relatively rotating the superimposed grating, and moire fringes formed by the superimposed grating on the surface of the object to be measured. A lens system for projecting, an imaging device for photographing a stripe pattern formed on the surface of the object to form input data of an image measurement device, and calculating a three-dimensional shape of the object from the stripe pattern data of the measurement device And an arithmetic processing unit.

The inventor of the present invention has described a method for measuring the three-dimensional shape of not only a hard object but also a soft object such as a living body.
Earlier, we invented a three-dimensional shape measurement method using a moire topography, which has been already patented (No. 2887517).
No.), but as a result of repeated research on a more sensitive three-dimensional shape measurement method, high-sensitivity measurement is possible by improving the pattern projection type three-dimensional shape measurement method using the moiré phenomenon. Thus, the present invention has been accomplished.

That is, in the conventional grating projection type three-dimensional shape measuring method, as described above, small gratings G1 and G2 are arranged for projection and observation, respectively, and the grating GI is set to the object to be measured by the lens L1. Is projected onto the grid G2 through the lens L2, and the grid lines deformed according to the shape of the object are imaged on the grid G2, and the fringe contour lines are generated at a predetermined distance from the reference plane. When the phase shift method is used as the method, the sineness of the projected grid pattern is important because the measurement accuracy is affected by the intensity distribution of the projected grid pattern.

In the present invention, in order to obtain the sineness of the projection pattern, for example, two gratings are superposed and arranged, and they are simultaneously or relatively linearly moved with respect to the object to be measured. By moving the two gratings relative to each other separately from the movement, 1) a high sine pattern can be obtained, 2) the pitch of the pattern to be projected can be arbitrarily changed, 3) the direction of the pattern to be projected The inventor has learned that it is possible to project an optimal grid pattern corresponding to the three-dimensional shape of the object to be measured without changing the grid to be used, so that the present invention is completed.

[0012]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram for explaining one embodiment of the measurement method of the present invention, FIG. 2 is a diagram showing a light intensity distribution of transmitted light of a grating when one grating is used, and FIG. FIG. 4 is a diagram showing a light intensity distribution of transmitted light of a grating when used, FIG. 4 is a side view of an example of a moiré pattern projection unit, and FIG. 5 is a front view showing an example of a grating holder and a grating.

In FIG. 1, GA and GB are two binary lattices (hereinafter simply referred to as lattices), and D is two lattices GA and GB.
, Θ is the angle formed by the two gratings GA and GB, A is the target object to be measured, B is the CCD camera which is an imaging device, L
1 is a projection lens arranged between the grating GB and the measurement object A, L
Reference numeral 2 denotes a photographing lens disposed between the object A and an imaging device B including a CCD camera or the like. When light is emitted from a light source C disposed behind the lattice GA toward the lattice GA, two lattices GA and GB are provided. Is projected on the object A through the lens L1, and a deformed lattice image generated at that time is captured from another direction by the CCD camera used as an example of the imaging device B through the photographing lens L2.

The image data picked up by the CCD camera is input to an image measurement device P and processed into measurement data. The arithmetic processing device R calculates the three-dimensional shape of the object from a stripe pattern formed on the surface of the object. Is calculated, the three-dimensional shape of the object A can be measured. In the above example, two gratings are used, but the present invention is not limited to this, and may be used more.

In the present invention, a moiré fringe to be projected is produced by superimposing the above two gratings GA and GB. The two grating lines are given by the following equation. x = b · p (1) y = x · cotθ− (aq / sinθ) (2) where θ is the angle between the two grids, a and b are the pitches of the grid, p and q are the orders, The moire fringes obtained at this time are given by the following equation. y = x · cotψ− (Nd / sinψ) (3) d = ab / √ (a ² + b ² -2ab · cos θ) (4) sinψ = b · sin θ / √ (a ² + b ² -2ab · cos θ) ( 5) Here, ψ is the angle of the moire fringe, d is the pitch, and N is the order.

In general, the light intensity distribution of the moire fringes has a shape in which the light intensity distribution of the two original gratings is correlated.
When two moiré fringes are created by closely contacting two binary gratings, the light intensity distribution of the moiré fringes is a triangular wave because of the superposition of two rectangular waves, but the distance D between the two gratings is D.
By separating them, a light intensity distribution with high sineness can be obtained on the projection plane. This is because the light intensity distribution of the transmitted light of the grating GA on the light source side is changed from a rectangular wave to a sine wave by separating by a distance D in FIG. 1, and the sine wave light intensity distribution and the light intensity distribution of the binary grating are overlapped. This is because moire fringes obtained by the combination are projected.

Normally, the light intensity distribution of the transmitted light of the binary grating changes as the rectangular wave shape is distorted as the distance from the grating is increased.
As shown in (1), high sineness cannot be obtained.

Therefore, in the present invention, as shown in FIG. 3, by using two gratings, moire fringes having a light intensity distribution obtained by correlation of the light intensity distributions of two binary gratings are projected. Thus, a projection pattern having high sineness can be obtained as compared with the method of projecting one binary pattern.

In the case of the binary grating, since the light intensity distribution is rectangular, it contains many high-frequency components in addition to the frequency of the grating pitch, and this high-frequency component causes an error in the phase analysis. In the case of the moiré fringes by the lattice, it can be confirmed that the high frequency component is small and the sineness is high as compared with the projection pattern of one binary lattice.

When such a measurement is performed, the measurement can be performed with high accuracy when the grid pitch to be projected is small. However, in the case of an object having a large step, phase connection cannot be performed correctly. When the pitch is large, the accuracy is reduced, but measurement at a large step is possible. In the present invention, since the number of grids is two (two in the embodiment) and these are relatively rotated or relatively moved, the pitch size and direction can be arbitrarily changed without replacing the grids. It is also possible to measure highly undulated shapes with high accuracy. Conventionally, when a pattern is projected parallel to a step, accurate measurement cannot be performed. However, in the present invention, such a problem can be avoided because the projected pattern can be arbitrarily tilted.

Next, a description will be given of an example of the structure of a moiré pattern projection unit using two gratings GA and GB. 5 and 6, reference numeral 1 denotes a base, and 2 denotes a support for supporting the holder 3 of the grid GA on the light source C side. In the illustrated example, the grid GA is moved in the right and left directions and in a direction perpendicular to the plane of the drawing. And a Z stage 22 for moving the light source in the vertical direction. With this configuration, the light source-side grating GA is supported by the other grating GA so as to be relatively movable. 4 is a column supporting the holder 5 of the grid GB on the projection lens side in a fixed position,
Reference numeral 6 denotes a support for supporting the projection lens L1.

With the above configuration, the distance between the two gratings GA and GB and the pitch of the gratings can be changed by moving the XY stage 21. Also, lattice holder 3
And 5 support the gratings GA and GB via the bearings 7 so that their relative rotation allows the gratings to be rotated to any angle, and the rotation produces moiré fringes in any pattern. You can do it.

[0023]

As described above, the present invention relates to a pattern projection method, which is one of the methods for measuring the three-dimensional shape of an object in a non-contact manner. The relative angle of each grid is variable, and each grid is arranged so as to be able to move simultaneously or relatively, and the relative angle and relative distance of each grid are adjusted according to the three-dimensional shape of the object to be measured. The imaging data obtained by irradiating a light source from behind the grid, projecting Moire fringes by the respective grids onto the surface of the measurement object via a projection lens, and imaging a fringe pattern formed on the surface of the object. Is calculated to obtain the three-dimensional shape of the target object, it is possible to project a high sinusoidal moiré fringe pattern, and, without replacing the grid used, of the object to be measured Depending on the shape, Since it projects a grid pattern with a suitable pitch and direction, it is possible to measure three-dimensional shape with high precision regardless of what 如 the properties of the measuring object.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating one embodiment of the measurement method of the present invention.

FIG. 2 is a diagram showing a light intensity distribution of transmitted light of a grating when one grating is used.

FIG. 3 is a diagram showing a light intensity distribution of transmitted light of a grating when two gratings are used.

FIG. 4 is a side view of an example of a moiré pattern projection unit.

FIG. 5 is a front view showing an example of a grid holder and a grid.

FIG. 6 is a view for explaining a conventional method for measuring a three-dimensional shape of a projection object using a lattice pattern.

[Explanation of symbols]

 GA Light source side grating GB Lens side grating D Grating gap θ Grating angle A Object to be measured L1 Lens arranged between object and grating GB L2 Lens arranged between object and imaging device C Light source B Imaging device PC Image measurement device R Arithmetic processing unit 1 Base 2 Light source side lattice support 21 XY stage 22 Z stage 3 Light source side lattice holder 4 Support 5 Projection side lattice holder 6 Projection lens support

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[Procedure amendment]

[Submission date] September 14, 2000
4)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

FIG. 3

FIG. 4

FIG. 5

FIG. 6

Claims (2)

[Claims] 1. A tertiary measurement method for measuring an object by superposing a plurality of gratings at appropriate distances from the object to be measured, changing the relative angle of each of the gratings, and arranging each of the gratings simultaneously or relatively movable. Adjusting the relative angle and the relative distance of each of the gratings corresponding to the original shape, projecting the moiré fringes by the respective gratings onto the surface of the measurement object through a projection lens by applying a light source from behind the gratings, A method for measuring the three-dimensional shape of an object by projecting moiré fringes, wherein the image data obtained by imaging a stripe pattern formed on the surface of the object is subjected to arithmetic processing to determine the three-dimensional shape of the object. 2. A plurality of gratings for forming Moiré fringes having a sinusoidal intensity distribution by closely contacting or superimposing with an appropriate gap therebetween, and means for simultaneously or relatively linearly moving the gratings; Means for relatively rotating the superimposed grating, a lens system for projecting the moiré fringes formed by the superimposed grating onto the surface of the object to be measured, and a lens system formed on the surface of the object. A moiré fringe projection comprising: an imaging device that captures a fringe pattern to form input data of an image measuring device; and an arithmetic processing device that calculates a three-dimensional shape of the object from the fringe pattern data of the measuring device. 3D shape measuring device for objects.