JP2001264031A - Shape-measuring method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shape-measuring method and a shape-measuring device, capable of measuring the shape of an object with high accuracy irrespective of the size. SOLUTION: A plurality of referential planes R0 to RN-1 are set at prescribed intervals in the direction normal to the planes. The object 3 to be measured is disposed between two end-positioned planes R0 and RN-1 of the plurality of planes, Then, in order to find the coordinates of a point S on a surface of the object 3, the planes R0 to RN-1 are used to find points P0, P1 and points C0, C1, at which a sight line Lc of a camera and a light beam Lp from a projector, both passing through the point S, cross the planes R0 to RN-1, respectively, and the z-coordinates thereof are used to select two reference planes Ri and Ri+1 closest to the point S, These planes Ri and Ri+1 are used to measure the shape of the object 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring a shape, and more particularly to a method and an apparatus for non-contact shape measurement in the field of factory line inspection and human body shape measurement. The present invention relates to a shape measuring method and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, as a method of measuring the three-dimensional shape of an object in a non-contact manner, a predetermined grid is projected on the object, and an image obtained by photographing the grid from different angles is analyzed. A grid projection method for obtaining a dimensional shape is used. This grid projection method specifically includes (1)
Projecting a predetermined grid on the object, (2) capturing the projected grid to obtain a grid image, and (3) analyzing the grid image and calculating a grid phase value;
(4) calculating three-dimensional coordinates from the lattice phase value.

The accuracy in the above steps (1) and (2) is determined by the performance of a projector or a CCD camera used for projection and photographing. In order to improve the accuracy in the step (3), a Fourier transform phase shift method is preferably used. In this method, the influence of noise can be almost ignored, and the grid image can be analyzed with extremely high accuracy.

In order to improve the accuracy in the step (4), in the calculation of three-dimensional coordinates, in the grid image analysis, the lens center position of a CCD camera as an image pickup device or a projector as a light irradiation device is used. It is required to accurately determine optical system parameters such as the direction of the optical axis and the direction of the optical axis. In order to respond to this requirement, the present inventors use a reference plate on which a two-dimensional lattice as a reference surface is drawn, and use the phase distribution obtained by analyzing a lattice image of the reference plate to obtain the optical system. It has been found that parameters can be obtained with high accuracy. This measurement method has been patented by the present inventors (Japanese Patent No. 291).
3021).

FIG. 1 is a conceptual diagram for explaining a measuring method by the present inventors. First, two reference planes R ₀ and R ₁ on which a two-dimensional grid is drawn are prepared. Next, the lattice images of these reference planes are photographed by the CCD camera 1. These lattice images are subjected to a Fourier transform in an arithmetic processor (not shown) to be converted into a predetermined phase distribution.
Since the coordinate position at each grid point of the two-dimensional grid drawn on the reference plane is known, if the phase value of the two-dimensional grid corresponding to each pixel of the CCD camera is known, the reference position captured by that pixel is determined. The coordinates of the point on the surface will be obtained. The coordinate positions on the reference planes R ₀ and R ₁ are stored as phase data in the arithmetic processing unit.

A two-dimensional grid is projected from the projector 2 onto the reference planes R ₀ and R ₁ , and the two-dimensional grid image is
Photographed by the D camera 1. These grid images are also subjected to a Fourier transform in an arithmetic processor (not shown) to be converted into a predetermined phase distribution. From this phase distribution, each projection line of the two-dimensional grating projected from the projector is
It is possible to determine which pixel of the camera is photographed. Since the coordinates on the reference planes R ₀ and R ₁ corresponding to each pixel of the CCD camera are already known, the coordinates of the point where each projection line from the projector is projected on the reference planes R ₀ and R ₁ are obtained. be able to. Reference planes R ₀ and R
The coordinate position of the two-dimensional grid projected from the projector on ₁ is also stored as phase data in the processor. Note that the positions of the CCD camera 1 and the projector 2 are not moved in the state where they are initially installed, both when photographing the reference plane and when measuring the shape of the object.

To measure the shape of an object, an object 3 is placed between reference planes R ₀ and R ₁ , and this object 3 is
Project a dimensional grid. At this time, the positions of the CCD camera 1 and the projector 2 are not moved while being initially installed as described above. When shooting an object 3 from the projector 2 two-dimensional grating is projected by the CCD camera 1, S point light L _P is projected exists on the line of sight L _C of the CCD camera 3, corresponding to the line of sight L _C Photographed in pixels. As described in the above description, the coordinates of the points C ₀ and C ₁ on the reference planes R ₀ and R ₁ photographed on the pixel are obtained from the phase data accumulated in the arithmetic processing unit. to become, so that the obtained accurately as a straight line of sight L _C passes through the point C ₀ and C _1.

Further, the light beam L_PHas the phase projected on the object
Can be obtained from the captured grid image
You. As described in the above description, the ray L_PIs the reference plane R₀Passing
And R₁Point P which intersects with₀And P₁The coordinates of
Obtained from the phase data stored in the processor
That is, the ray L_PIs the point P₀And P₁As a straight line passing through
Will be obtained with high accuracy. Therefore, a point on the object
S is line of sight L_CAnd ray L _PCan be obtained as the intersection of
You. By performing the same operation at each point on the object surface
Thus, the shape of the object can be measured.

[0009]

However, even in the above-described method, it is not possible to obtain an accurate optical parameter depending on the size of the object to be measured and the like. In some cases, measurement could not be performed accurately without contact.

An object of the present invention is to provide a novel shape measuring method which does not have the above-mentioned problem, and a shape measuring apparatus which can be suitably used for this method.

[0011]

According to the shape measuring method of the present invention, a plurality of different reference planes are set, and a measurement sample is arranged between these reference planes. Further, the light emitted from the light irradiation device and the line of sight of the imaging device intersect on the surface of the measurement sample, and the coordinate values on the plurality of reference planes corresponding to the position of the light irradiation device, and The arithmetic processing is performed on each coordinate value on the plurality of reference planes corresponding to the position of the apparatus. And, the plurality of reference planes are at least 3 in a normal direction of the reference plane.
And the shape of the measurement sample is measured by two of the plurality of reference planes arranged close to the measurement sample.

The present inventors have made intensive studies to find out why the shape of an object cannot be measured accurately depending on the size of the object in the shape measuring method using the reference plane as described above. . As a result, it has been found that the more the object to be measured is placed away from the reference plane, the larger the shape error of the object becomes. That is,
If a reference plane is set for a certain object and an attempt is made to measure the shape of an object smaller than the object using the reference plane, the object is necessarily arranged at a distance from the reference plane. Become. Therefore, it has been found that an error increases in the shape measurement of the small object.

Therefore, the present inventors have tried to set a reference plane at any time according to the size of an object to be measured. However, in such a method, it takes a long time to perform a Fourier transform to the phase data of the coordinate position accompanying the setting of the reference plane, and this causes a new problem that a long time is required for the measurement. Had caused it. Therefore, the present inventors have conducted intensive studies to find a new shape measurement method.

As a result, in the above-described measurement method by the present inventors, three or more reference planes are set in advance in place of the two reference planes conventionally used, and the position where the object to be measured is placed is set. The present inventors have conceived of selecting the closest reference plane and performing the shape measurement of the object by using the reference plane. The present invention has been made as a result of finding the above-described cause and searching for a new shape measuring method based on the cause.

Therefore, according to the present invention, even when the size of an object changes, the shape of the object is measured using the reference plane closest to the object so as to adapt to the size. Can be. For this reason, the measurement accuracy of the object shape can be dramatically improved.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments of the present invention. 2 and 3 are conceptual diagrams for explaining the shape measuring method of the present invention. Note that FIG.
1 and 3 are denoted by the same reference numerals.

First, as shown in FIG. 2, reference planes R _{0 to} R _N-1 (a natural number of N ≧ 3) on which a two-dimensional grid is drawn are
These are set at predetermined intervals in the normal direction of the reference plane. In the drawings, the normal direction is Z for convenience.
There is a direction. Then, the coordinate position _Z 0 of the Z direction coordinate axis with respect to the respective reference plane _R 0 _{~R N-1 ~Z N-
1} is stored in a predetermined processor (not shown).

As a reference object, a reference plate of a two-dimensional lattice is used.
Used. Reference plane is reference plane R₀~ R _N-1Sequentially in position
Install and draw at each position as described above.
From the two-dimensional grating phase distribution and the projector
Fourier transform the phase distribution of the projected two-dimensional grating
And the phase data in the arithmetic processor, respectively.
It accumulates in the form of data. That is, by this operation, the reference plane R
₀~ R_N-1Each line of sight of the CCD camera at the position
All the coordinates that pass and the coordinates that each projection line of the projector passes
Will be required. After this operation is completed,
Is removed.

Thereafter, the object 3 to be measured is placed between the reference planes R ₀ and R _{N- 1} located farthest from each other. Then, the similarly, the light beam L _P emitted from the line of sight L _C and the projector 2 of the CCD camera 1 crosses the surface of the object 3. This intersection is defined as S ′. The position of the intersection S ′ is determined by the CCD camera 1 and the projector 2 according to the above-described conventional measurement method by the present inventors.
Can be determined from the coordinate positions P ₀ and C ₀ on the reference planes R ₀ and R _N-1 corresponding to the position of, and _PN-1 and C _{N -1} . That is, it is possible to know the 'coordinate position Z _S in the Z direction coordinate of _the' intersection S from these coordinate positions.

Next, the arithmetic processing unit is provided with a Z for each reference plane.
Since the directional coordinate position is stored, two reference planes R _i and R _{i + 1} at the Z _i coordinate position and the Z _{i + 1} coordinate position closest to the coordinate position Z _{S ′} are selected. Thereafter, in the same manner as in the conventional method, the arithmetic processing unit of the coordinate positions P _i and C _{i of} the reference planes R _{i and} R _{i + 1} , and P _{i + 1} and C _{i + 1} corresponding to the positions of the CCD camera 1 and the projector 2. The coordinates of the point S on the surface of the object 3 are obtained from the calculation according to, and the shape of the object 3 is measured by this.

FIG. 4 shows that, according to the invention, a size of 15
It is a figure which shows the measurement error at the time of performing shape measurement of the flat object of 0x150 mm. As is clear from the figure, this measurement is performed in the normal direction (Z direction) of the reference plane.
This shows a result when five reference planes R _{0 to} R ₅ are arranged at equal intervals of 20 mm, and the object is arranged at a predetermined position in the Z direction. FIG. 5 shows the reference plane R
₀ and using only R _5, is a diagram illustrating a measurement error when performing a shape measurement of an object in the same manner as described above.

As is apparent from FIGS. 4 and 5, the reference plane R
In the case _{where 0} and using only R ₅ represents increasing distance from the reference plane R ₀ and R _5, i.e., as the said object from these reference surfaces are spaced apart, can be seen the measurement error increases. Contrary to this, in the measuring method of the present invention using the reference plane R ₀ to R _5, the reference plane R ₀ and R
It was found that the measurement error between _{5 and 5} was almost constant. Then, the measurement error is seen to decrease below approximately about 1/3 the conventional measuring method using a reference plane R ₀ and R _5. That is, according to the shape measuring method of the present invention, it is understood that the shape of the object can be accurately measured regardless of the size of the object by using the reference plane closest to the object to be measured.

FIG. 6 is a diagram showing an example of a measuring apparatus which can be suitably used for carrying out the shape measuring method of the present invention. The shape measuring device shown in FIG. 6 includes a CCD camera 1 as an imaging device, a projector 2 as a light irradiation device, a liquid crystal display 4 as an image display device,
The moving stage 5 is a moving means for supporting the liquid crystal display 4.

The CCD camera 1 and the projector 2 are arranged in parallel with each other as shown in FIGS. The moving stage 5 can continuously move the liquid crystal display 4 toward the CCD camera 1 and the projector 2. On the liquid crystal display 4, a predetermined two-dimensional lattice is projected on the screen in response to a signal from the arithmetic processing unit 6, and the liquid crystal display screen itself is set to form a reference plane. Have been. All operations such as the positions of the CCD camera 1, the projector 2, the liquid crystal display 4, and the moving stage 5 and the irradiation intensity are performed by the arithmetic processing unit 6.

The shape measurement using the shape measuring device shown in FIG. 6 is performed as follows. First, the liquid crystal display 4 is directed to the CCD camera 1 and the projector 2 by the moving stage 5 for a predetermined distance (N-1: N).
≧ 3) Move. Then, in each moving stage, the two-dimensional lattice image displayed on the screen of the liquid crystal display 4 is photographed by the CCD camera 1. As a result, N reference planes are substantially set.

Thereafter, the object to be measured is arranged between the reference planes located at the both ends, and the shape of the object is measured according to the above-described shape measuring method of the present invention.

In the shape measuring apparatus according to the present invention, the reference plane is constituted by a two-dimensional grid displayed on the screen of the liquid crystal display, and the liquid crystal display is configured to be moved by a predetermined distance several steps. Therefore, a plurality of reference planes separated by a predetermined distance can be set only by a single liquid crystal display, thereby simplifying the device configuration.

As described above, the present invention has been described in detail based on the embodiments of the present invention with reference to specific examples. However, the present invention is not limited to the above contents, and is not limited to the scope of the present invention. All modifications and changes are possible. For example, in the above-described measuring method and measuring device, a CCD is used as an imaging device, a light irradiation device, and an image display device.
Although the case where a camera, a projector, and a liquid crystal display are used is shown, a known image pickup device, projection device, display device, or the like can be used instead.

[0029]

As described above, according to the shape measuring method and the shape measuring apparatus of the present invention, it can be understood that an arbitrary large object shape can be measured with high accuracy.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram for explaining a conventional shape measurement method.

FIG. 2 is a conceptual diagram illustrating a shape measuring method according to the present invention.

FIG. 3 is a conceptual diagram for explaining a shape measuring method according to the present invention.

FIG. 4 is a graph showing a measurement error when an object shape is measured by the shape measurement method of the present invention.

FIG. 5 is a graph showing a measurement error when an object shape is measured by a conventional shape measurement method.

FIG. 6 is a diagram showing an example of the shape measuring device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 CCD camera 2 Projector 3 Shape measuring object 4 Liquid crystal display 5 Moving stage 6 Arithmetic processor _R0- RN _-1 reference plane

Claims (8)

[Claims] 1. A plurality of different reference planes are set, a measurement sample is arranged between the reference planes, and a light beam L _P emitted from a light irradiation device on the surface of the measurement sample is set.
And crossed the line of sight L _C of the imaging device, each of the coordinate values of the plurality of reference surfaces corresponding to the position of the light irradiation device, each of the coordinates in the plurality of reference surfaces corresponding to the position of the imaging device A method for calculating the shape of the measurement sample by calculating the value and the shape of the measurement sample, wherein the plurality of reference planes are arranged in parallel at least three in the normal direction of the reference plane, A shape measuring method, characterized in that measurement is performed using two of the plurality of reference planes arranged close to the measurement sample. 2. The method according to claim 1, wherein the reference plane is a plane drawn on a reference plate.
The shape measuring method according to claim 1, wherein the shape measuring method comprises a three-dimensional lattice. 3. The reference plate comprises an image display device,
3. The shape measuring method according to claim 2, wherein the two-dimensional grid includes an image displayed on the image display device. 4. The method according to claim 1, wherein the arithmetic processing is performed based on a phase distribution created by capturing an image of each of the plurality of reference planes by the imaging device and performing a Fourier transform on the image. The shape measuring method according to claim 1. 5. A light irradiation device, an imaging device, an image display device, and moving means for supporting the image display device,
The light irradiation device and the imaging device are arranged so as to be parallel to each other and to face the image display device, and the moving unit continuously moves the image processing device toward the light irradiation device and the imaging device. A shape measuring device characterized by moving. 6. The shape measuring device according to claim 5, wherein the image display device is a liquid crystal display. 7. The shape measuring device according to claim 5, wherein the light irradiation unit is a projector. 8. The shape measuring apparatus according to claim 5, wherein said imaging device is a CCD camera.