JP2016128785A - Shape measurement device and shape measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and a method for proposing that can the shape of a measurement target object rapidly and precisely and in a wide measurement range.SOLUTION: The shape measurement device includes: a lattice pattern projecting unit 11 having a plurality of light sources 11a emitting projection light for projecting a lattice pattern with a predetermined shape to a measurement target object O and a lattice substrate 11b forming a lattice pattern by making the projection light passing through the lattice substrate; an imaging unit 12 imaging the measurement target object O, on which the lattice pattern has been projected; and an analyzing unit 13 obtaining the shape of the measurement target object O by conducting phase analysis on the image taken of the measurement target object O, the light sources 11a being arranged in various different locations separated from the lattice substrate 11b by different distances, respectively, and the locations having at least one of the light sources.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a shape measuring apparatus and a shape measuring method, and more particularly to an apparatus and a method capable of measuring the shape of a measurement target object at high speed and with high accuracy and in a wide measurement range.

  Non-contact measurement technology for 3D object shapes is becoming more important regardless of commercial or industrial fields, and there is a need for highly accurate and compact shape measurement devices that can be incorporated into existing devices. Yes. In the medical field and apparel industry, three-dimensional shape measurement of the human body requires not only accuracy and convenience, but also high speed that can ignore body shake and a wide measurement range that can measure the entire body.

  One method for measuring the three-dimensional shape of a three-dimensional object is a lattice projection method. This grid projection method is a method of determining the shape of a measurement target object by projecting a grid pattern onto the measurement target object, photographing the projected grid pattern, and performing phase analysis. Both the spatial resolution and accuracy are Known as a good technique. (For example, refer to Patent Document 1).

  As a technique for expanding the measurement range in such a grating projection method, Patent Document 2 describes a technique in which phase analysis is performed using two types of grating substrates having different pitches, and phase connection is performed on the obtained phase distribution. ing.

  Non-Patent Document 1 describes a technique in which a liquid crystal panel is used as a grating substrate, phase analysis is performed by changing the pitch of a grating displayed on the panel, and phase connection is performed on the obtained phase distribution. ing.

Japanese Patent No. 2913021 JP 2002-90126 A

Satoshi Kakuuchi, Koichi Iwata, Shinichi Saito, Satoshi Sakamoto, “Three-dimensional shape measurement by 2-pitch grid projection”, Journal of Precision Engineering, 1992, Vol. 58, No. 5, p. 877-882

  However, in the technique described in Patent Document 2, since a process of replacing a lattice substrate having a different lattice pitch is performed, it takes a lot of time to move the lattice substrate. In addition, since the displacement occurs every time the lattice substrate is replaced, the measurement accuracy decreases.

  Further, in the method using a liquid crystal panel as a lattice substrate described in Non-Patent Document 1, since the pitch of the lattice to be displayed is switched by an electric signal, no error due to misalignment occurs. However, since the liquid crystal panel has a slow response speed for displaying a grid, it cannot perform shape measurement at high speed.

  Therefore, an object of the present invention is to propose an apparatus and method that can measure the shape of a measurement target object at high speed and high accuracy, and in a wide measurement range.

  As a result of intensive studies on how to solve the above problems, the present inventors have configured a grid pattern projection unit that projects a grid pattern on a measurement target object so as to include a plurality of light sources and a grid substrate, and It has been found that it is extremely effective to arrange at least one light source at each of a plurality of positions having different distances from the lattice substrate, and the present invention has been completed.

That is, the gist of the present invention is as follows.
(1) An apparatus for measuring the shape of a measurement target object, wherein a plurality of light sources for emitting projection light for projecting a lattice pattern of a predetermined shape on the measurement target object and the projection light are passed through A lattice pattern projection unit having a lattice substrate for forming the lattice pattern, a photographing unit for photographing the measurement target object onto which the lattice pattern is projected, and a phase analysis for the photographed image of the measurement target object And an analysis unit that obtains the shape of the measurement target object by performing processing, wherein the plurality of light sources are disposed at each of a plurality of positions at different distances from the lattice substrate. Shape measuring device.

(2) The shape measuring apparatus according to (1), wherein three or more light sources are arranged at each of the plurality of positions.

(3) The shape measuring apparatus according to (1) or (2), wherein wavelengths of light emitted from the plurality of light sources are different for each of the plurality of positions.

(4) The shape measuring apparatus according to any one of (1) to (3), wherein the light source is a linear light source.

(5) Measurement using the shape measuring apparatus described in (1) to (4) above, wherein the lattice pattern is projected by turning on the light source at each of a plurality of positions having different distances from the lattice substrate. The target object is photographed, and then a phase analysis process is performed on the photographed image of the measurement target object to obtain a phase distribution, and the shape of the measurement target object is determined based on the phase distribution obtained for each of the plurality of positions. A shape measuring method characterized in that

  According to the present invention, in the lattice pattern projection unit having a plurality of light sources and a lattice substrate, since the plurality of light sources are arranged at each of a plurality of positions at different distances from the lattice substrate, the measurement target It is possible to measure the shape of an object at high speed and high accuracy, and in a wide measurement range.

It is a figure which shows the shape measuring apparatus which concerns on this invention. It is a figure which shows the range which can be measured about the case where the pitch of a projection grating | lattice is one. It is a figure which shows an example of the lattice pattern projection part which has a linear light source. It is a figure which shows the lattice pattern projected from a lattice pattern projection part, when the light source arrange | positioned at (a) lower stage and (b) upper stage is lighted. It is a figure which shows an example of the lattice pattern projection part which has three linear light sources in each of an upper stage and a lower stage. It is a figure which shows (a) luminance distribution and (b) phase distribution of a lattice pattern. It is a figure which shows the relationship between a phase shift amount and a brightness | luminance. It is a figure which shows the relationship between the lighting position of the light source and the projected lattice pattern with respect to (a) when the light source A is turned on and (b) when the light source B is turned on. It is a figure which shows a mode that a camera image | photographs a lattice pattern with respect to (a) when the light source A is turned on, and (b) when the light source B is turned on. It is a figure which shows a mode that a table is produced based on the total space table formation method with respect to (a) when the light source A is turned on, and (b) when the light source B is turned on. It is a figure which shows the correspondence table of the phase value with respect to (a) when the light source A is turned on, and (b) when the light source B is turned on. It is a figure which shows the correspondence table of the phase value and coordinate with respect to (a) x coordinate and (b) y coordinate. It is a figure which shows a mode that a camera image | photographs the measurement target object by which the lattice pattern was projected with respect to (a) when the light source A was turned on, and (b) when the light source B was turned on. It is a figure which shows the principle which calculates | requires z coordinate of the point on a measurement target object using the table with respect to (a) when the light source A is turned on, and (b) when the light source B is turned on. It is a figure which shows the shape measuring apparatus produced as an Example. It is a side view of the shape measuring apparatus produced as an Example. It is a figure which shows the mode of a calibration. It is a figure which shows the table obtained by calibration with respect to the case where the light source A is turned on. It is a figure which shows the table obtained by calibration with respect to the case where the light source B is turned on. It is a figure which shows the dimension of a measurement object. It is a figure which shows the positional relationship of a shape measuring device and a measurement object. It is a figure which shows the image of the measurement target object in which the lattice pattern was projected with respect to the case where the light source A was turned on. It is a figure which shows the image of the measurement target object by which the lattice pattern with respect to the case where the light source B was turned on was projected. It is a figure which shows the phase distribution of the grating | lattice pattern with respect to the case where the light source A is lighted. It is a figure which shows the phase distribution of the grating | lattice pattern with respect to the case where the light source B is lighted. It is a figure which shows the candidate value of z coordinate with respect to the case where the light source A is turned on. It is a figure which shows the candidate value of z coordinate with respect to the case where the light source B is lighted.

(Shape measuring device)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a shape measuring apparatus according to the present invention. The shape measuring apparatus 1 in this figure includes a plurality of light sources 11a that emit projection light for projecting a grating pattern of a predetermined shape onto a measurement target object O, and a grating that forms the grating pattern by passing the projection light. A lattice pattern projection unit 11 having a substrate 11b, a photographing unit 12 that photographs a measurement target object O onto which the lattice pattern is projected, and a phase analysis process on the photographed measurement target object O to perform measurement. And an analysis unit 13 for obtaining the shape of the object O. Here, it is important that at least one of the plurality of light sources 11a is arranged at each of a plurality of positions having different distances from the lattice substrate 11b.

  As described above, in the techniques described in Patent Document 2 and Non-Patent Document 1, the measurable range can be expanded, but there is a problem in that the speed and accuracy of shape measurement are sacrificed. It was. In this regard, in the present invention, at least one of the plurality of light sources 11a is arranged at each of a plurality of positions having different distances from the lattice substrate 11b, and is projected onto the measurement target object O by switching the light source to be lit. The pitch of the grid to be played can be changed instantaneously. In addition, since the lattice substrate 11b is not moved, an error due to positional deviation does not occur, and the shape of the measurement target object O can be measured with high accuracy.

Further, as shown in FIG. 2, if the pitch of the projected grating of one range in which the phase is changed by one period (e.g., the range indicated by D ₁ in FIG. 2) is fundamental measurable range . When the regions D ₂ and D ₃ are set as the measurement range, or when the regions D _{1 to} D ₃ are set as the measurement range, points having the same phase value as the region D ₁ exist in the region D ₂ and the region D ₃ . For this reason, it is not possible to distinguish which region the point is from only the phase value. When it is possible to distinguish which region is a point, the measurement range can be expanded. In this regard, in the present invention, as will be described later, even when the range in which the phase changes for a plurality of periods is set as the measurement range, it is possible to distinguish which region the point is, so that the measurement range can be expanded. It can be done. Hereinafter, each configuration of the shape measuring apparatus 1 will be described.

  The plurality of light sources 11 a emit projection light for projecting a lattice pattern having a predetermined shape onto the measurement target object O. As this light source 11a, a point light source or a linear light source can be used. Among them, it is preferable to use a linear light source because the S / N ratio can be increased by increasing the light amount of the light source and the measurement accuracy can be improved. When a linear light source is used as the light source, the linear light source may be configured by arranging point light sources on a straight line. When using a linear light source as a light source, it arrange | positions so that the extension direction may become parallel to the lattice line of the lattice board | substrate 11b.

  FIG. 3 shows an example of a lattice pattern projection unit 11 having a linear light source, where (a) shows a side view and (b) shows a perspective view. The lattice pattern projection unit 11 shown in FIG. 3 has a configuration in which a light source substrate 11c having a light source 11a is disposed on the surface of a stepped member 11d on the lattice substrate 11b side.

  FIG. 4A shows a lattice pattern projected from the lattice pattern projection unit 11 when only the light source 11a arranged at the lower stage of the member 11d is turned on and the light source 11a arranged at the upper stage is not turned on. Yes. On the other hand, FIG. 4B shows a grid pattern projected from the grid pattern projection unit 11 when only the light source 11a arranged in the upper stage of the member 11d is turned on and the light source 11a arranged in the lower stage is not lit. Show.

  As is clear from FIGS. 4A and 4B, in the configuration shown in FIG. 3, the distance between the light source 11a and the lattice substrate 11b is the same as that in the case of the light source 11a arranged on the upper stage of the member 11d. Is bigger. Therefore, the pitch p of the lattice pattern formed when the upper light source 11a is turned on is smaller than when the light source 11a arranged at the lower stage is turned on.

  As described above, the pitch p of the lattice pattern projected onto the measurement target object O differs depending on whether the light source 11a arranged on the upper stage of the member 11d is turned on or the light source 11b arranged on the lower stage is turned on. The pitch p of the lattice pattern can be changed by simply switching the light source 11a to be lit from the upper stage (lower stage) to the lower stage (upper stage). Therefore, the grid pitch p can be changed at high speed and without error due to misalignment. it can.

  Note that the grid pattern projection unit 11 illustrated in FIG. 3 is merely an example, and at least one light source 11a is disposed at each of a plurality of positions at different distances from the grid substrate 11b, and is projected onto the measurement target object O. Any change can be made as long as the pitch p can be changed. For example, in FIG. 3, the member 11d has a two-stage structure, but can have a structure of three or more stages. In FIG. 2, the member 11d is composed of separate members for the upper stage and the lower stage. However, these members may be integrally formed. Furthermore, the light source 11a may be directly disposed on the surface of the member 11d on the lattice substrate 11b side without being disposed on the light source substrate 11c.

  In FIG. 3, one light source 11a is arranged at each of the upper and lower stages, that is, at a plurality of positions at different distances from the lattice substrate 11b. However, as shown in FIG. It is preferable to arrange three or more light sources 11a. Thereby, phase analysis can be performed at high speed using a phase shift method described later. When three or more light sources 11a are arranged on each stage, the light sources are arranged so that the extending directions of the light sources are parallel to each other. Moreover, it is preferable to make the number of the light sources 11a arrange | positioned in each position the same.

  Further, as shown in FIG. 5 (b), a plurality of light sources 11a are attached to a single panel, and the panel is inclined with respect to the lattice substrate, whereby a plurality of light sources 11a and the lattice substrate 11b are arranged. The distances may be different from each other. In the case of FIG. 5B, a grid with a small pitch is projected when the A set of light sources is used, and a grid with a large pitch can be projected when the B set is used. Even in the same set, the distance from the lattice substrate is different and the projected pitch is different, but in a range where the difference is small, it can be used practically without any problem.

  In the case of the light source 11a shown in FIG. 5B, the light sources 11a that are simultaneously turned on in the panel are considered as one set, and the average value of the distances from the lattice substrate 11b of the light sources 11a included in each set is determined as the lattice substrate. Consider the distance of the light source 11a from 11b.

  Furthermore, it is preferable that the wavelength (namely, color) of the light emitted from the plurality of light sources 11a is different for each of a plurality of positions having different distances from the lattice substrate 1b. That is, in the configuration shown in FIG. 3, it is preferable to change the color of the projection light emitted from the light source 11a between the upper stage and the lower stage. As a result, the grid patterns of different colors projected on the measurement target object O are photographed while the light sources 11a arranged at different distances from the grid substrate 1b are simultaneously turned on, and the phase analysis is performed for each color. Since the phase value can be obtained, the time for measuring the shape of the measurement target object O can be shortened.

  The wavelength of light emitted from the plurality of light sources 11a is changed for each of a plurality of positions having different distances from the lattice substrate 1b, and three or more light sources 11a are arranged at each of a plurality of positions having different distances from the lattice substrate 11b. In this case, for example, the number of the light sources 11a arranged at the respective positions is made the same, and the light sources 11a are simultaneously turned on one by one at each position to project a lattice pattern of a different color on the measurement target object O. What is necessary is just to take an image.

  The lattice substrate 11b is a substrate for projecting a predetermined lattice pattern onto the measurement target object O through the projection light emitted from the plurality of light sources 11a. For example, the lattice substrate 11b may be formed by depositing chromium on a glass substrate and drawing lattice stripes called Ronchi ruling.

  When the light source 11a is a linear light source, the positional relationship between the plurality of light sources 11a and the lattice substrate 11b is such that the extending direction of the linear light source of each light source 11a is parallel to the lattice lines of the lattice substrate 11b. Deploy.

  The photographing unit 12 photographs the measurement target object O on which the lattice pattern is projected by the lattice pattern projection unit 11. For example, a CCD camera or a CMOS camera can be used as the photographing unit 12. The captured image of the measurement target object O is output to the analysis unit 13.

  The analysis unit 13 performs a phase analysis process on the captured image of the measurement target object O to obtain the shape of the measurement target object O. Further, the analysis unit 5 generates a light emission control signal for controlling the lattice pattern projection unit 11 so that only one of the light sources 11a emits projection light, and transmits the light emission control signal to the lattice pattern projection unit 11. An imaging control signal for controlling the imaging unit 12 to generate an image of the measurement target object O onto which the pattern is projected is generated and transmitted to the imaging unit 12. As the analysis unit 13, for example, a personal computer (PC) can be used.

  By performing a phase analysis process on the image of the measurement target object O photographed by the photographing unit 12, a phase value can be obtained for each pixel. In the present invention, the specific method for performing the phase analysis processing is not particularly limited. For example, it can be obtained using a Fourier transform method, a spatial fringe analysis method, a weighted phase analysis method, or the like. Further, when three or more light sources are arranged at each of a plurality of positions having different distances from the lattice substrate 11b, the phase value can be obtained at high speed using the phase shift method. Here, a method of obtaining the phase value for each pixel using the phase shift method will be described.

FIG. 6 is a diagram illustrating the relationship between the luminance distribution and the phase distribution of the lattice pattern projected onto the measurement target object O. FIG. 6A shows the luminance distribution of the lattice pattern, and FIG. 6B shows the phase distribution of the lattice pattern. FIG. 7 is a diagram showing the relationship between the phase shift amount and the luminance. In general, the luminance values I (x, y) of the lattice pattern and the interference fringes are distributed in a cosine wave shape in the space (x, y) as shown in FIG. When this is expressed by an equation, the equation (1) is obtained.
Here, the point (x, y) is one point in the captured image, a (x, y) and b (x, y) represent the luminance amplitude and the background luminance, respectively, and θ (x, y) ) Represents the phase value of the grating. In the case of an image in which a lattice is photographed (hereinafter referred to as “lattice image”), the phase can be expressed as an entire real number, but can also be viewed as a repetition of 2π period from 0 to 2π. FIG. 6B represents the distribution of θ (x, y) as a repetition from 0 to 2π.

  The phase shift method is a technique for obtaining a phase distribution from a plurality of obtained images by photographing a plurality of lattice images while changing the phase of the lattice by one period. In all the pixels, the luminance changes by one period, so that the phase value can be obtained independently from the luminance change for each pixel without using the information on the luminance change of the surrounding pixels. Therefore, this is an effective method for measuring the shape of an object having a step or a discontinuous portion. Here, the case of obtaining the phase value from the four luminance values phase-shifted by π / 2, which is most commonly used (that is, when the number of phase shifts is four) is used as an example. The principle will be described.

When the phase shift amount α is added to the expression of the luminance distribution of the lattice pattern shown in Expression (1), the following Expression (2) is obtained.

FIG. 7 shows the relationship between the phase shift amount α and the luminance change at the point (pixel) having the initial phase θ. The initial phase means the phase of the grating when the phase shift amount is zero. Assuming that the luminance when the phase shift amount changes from 0 to π / 2, respectively, is I ₀ , I ₁ , I _2, and I ₃ , these can be expressed as in equations (3) to (6), respectively. . In the following formula, the notation of (x, y) is omitted.

From these equations, the following equations (7) and (8) are obtained.
Furthermore, the following equation (9) is derived from the equations (7) and (8), and the phase value θ for a certain pixel (x, y) can be obtained from this relational equation. That is, if the luminance values I ₀ , I ₁ , I _2, and I ₃ when the phase shift amounts are 0, π / 2, π, and 3π / 2 are obtained, the phase value θ for this pixel can be obtained.

Here, by increasing the number of phase shifts (that is, the number of steps from 0 to 2π), it is possible to reduce the influence of random noise of the camera. When the number of phase shifts is N and the luminance when the phase shift amount is 2πk / N is I _k , the following equation (10) is derived, and tan θ, that is, the phase value θ can be obtained from this relational expression.
Thus, the phase value θ for each pixel on the image can be obtained by the phase shift method.

  The shape of the measurement target object O can be obtained by obtaining the spatial coordinates (x, y, z) of the point on the surface of the measurement target object O from the phase value obtained for each pixel as described above. it can. FIG. 8 shows a state in which lattice patterns with different pitches are projected by using two light sources A and B arranged at two positions with different distances from the projection lattice panel as the lattice substrate 11b. Here, the light source 11a disposed at the position A is referred to as a light source A, and the light source 11a disposed at the position B is referred to as a light source B. In addition, it is assumed that the light source B is installed closer to the projection grid panel than the light source A. Furthermore, the solid line coming out of each light source 11a represents the center of the bright line of the projection grating. If the phase is defined by regarding the change in brightness of the projection grating as a cosine wave, this solid line represents the position where the phase of the projection grating is zero. Since the light source B is closer to the lattice substrate 11b, the pitch of the projected lattice pattern is larger when the light source B is turned on than when the light source A is turned on.

When the distance between the light source and the projection grid panel is a, the distance between the projection grid panel and the measurement target object O is b, and the grid pitch on the projection grid panel is p ₀ , the projection is projected onto the measurement target object O. The pitch p of the grating is given by
From this equation (11), it can be seen that the pitch of the projection grating can be increased by reducing the distance a between the light source 11a and the grating substrate 11b. As shown in FIG. 8, the distance between the light source A and the projection grating panel is a _A , the distance between the light source B and the projection grating panel is a _B, and the distance between the projection grating panel and z = z ₀ is When the distance is b and the pitch of the grating in the projection grating panel is p ₀ , the pitch of the grating projected at the position z = z ₀ is p _A and the p _B.

  FIG. 9 shows a state where a camera as the photographing unit 12 is installed at a position different from the light source 11a. When attention is paid to a certain pixel in an image photographed by the camera, the pixel is photographed on the solid line L in the figure. The solid line L is a straight line that obliquely crosses the projected lattice pattern. On the straight line L, the phase gradually changes as the z coordinate increases.

Therefore, as shown in FIG. 10, a reference plane (reference flat plate) is prepared and installed in the field of view of the camera so as to be perpendicular to the z-axis. The phase value of the projection grating is acquired while the reference plane is translated N times in order from z = z ₀ to z = z _N−1 . The acquired phase values are recorded as a table of z coordinates with respect to the phase values as shown in FIG. This is called calibration. At this time, every time the phase changes by one period, it is recorded as a separate table. In FIG. 11, when the light source A is turned on, the tables A _{z, 1} , A _{z, 2} , A _{z, 3} , A _{z, 4 are obtained} , and when the light source B is turned on, the table B _{z, 1} , B _{z, 2} and B _{z, 3} . According to such a procedure, a table is created for each pixel when the light source A is turned on and when the light source B is turned on.

At this time, in the position between the positions z _i where the reference plane is moved, by performing an interpolation process from the z coordinate of the nearby reference plane and the phase value at that time, not only the position of the reference plane, Table elements can be obtained at all positions from z = z ₀ to z = z _N−1 including the position between the reference planes. In this way, not only the position of the black point shown in FIG. 11 but also a table of z coordinates for the phase θ is created more finely.

Note that a straight line L can be obtained by attaching a pattern capable of reading the x-coordinate and y-coordinate, such as a two-dimensional lattice, to the surface of the reference surface used at this time, or by displaying the pattern on the surface of the reference surface. The x and y coordinates at the upper point can be read. As described above, since the correspondence between the phase and the z coordinate has already been obtained, an x coordinate table for the phase value and a y coordinate table for the phase value can be easily created on the basis thereof. be able to. FIGS. 12A and 12B show examples of correspondence tables (when the light source A is turned on) of the phase value and the x coordinate and the phase value and the y coordinate created as described above, respectively. Also in this case, similarly to the z coordinate table, every time the phase changes by one period, it is recorded as another table. 12 (a) and 12 (b), the table A _{x, 1} , A _{x, 2} , A _{x, 3} , A _{x, 4} is obtained in the case of the x coordinate, and the table A _{y, 1} , in the case of the y coordinate. A _{y, 2} , A _{y, 3} , A _{y, 4} .

Next, the measurement target object O is set in a region from z ₀ to z _N−1 . FIG. 13 shows a state in which a grid is projected onto an object. A point on the object photographed by the line of sight L photographed by the pixel of interest of the camera is defined as a point P. The z coordinate of the point P at this time is z _p. The phases of the points P obtained when the light sources A and B are turned on are θ _A and θ _B , respectively.

FIG. 14 shows a table of z coordinates for the phase values created by the above method. When the light source A is turned on, the values of the z coordinate with respect to the phase θ _A are z _A1 , z _A2 , z from the tables A _{z, 1} , A _{z, 2} , A _{z, 3} , A _{z, 4} , respectively. _A3, the z _A4. Similarly, when the light source B is turned on, the value of the z coordinate with respect to the phase θ _B becomes z _B1 , z _B2 , and z _B3 from the tables B _{z, 1} , B _{z, 2} , and B _{z, 3} , respectively. . Thus, for each of the cases where the light source A and the light source B are turned on, as many z-coordinate candidate values as the number of tables are obtained.

A distance d _nm between the obtained candidate values of a plurality of z coordinates is obtained as follows.
Here, n and m indicate table numbers (subscripted portions of A _{z, n} , B _{z, m} ) when the light source A and the light source B are turned on, respectively.

Regardless of whether the light source A or the light source B is turned on, the point P is the same position on the measurement target object O, and therefore the z coordinate of the point P is the same. Therefore, by searching for a combination of n and m where the distance d _nm between candidate values is 0, the z coordinate of the point P can be found from among a plurality of candidate values of the z coordinate. However, since the obtained phase value varies somewhat due to the influence of random noise or the like of the camera, it generally does not match. Therefore, it is effective to search for a combination of n and m when the distance d _nm between candidate values is not zero but when it is the smallest. Note that the range that can be measured by this method is a range in which one candidate point is determined.

In this way, the respective candidates z _An and z _Bm when the light source A and the light source B are turned on are obtained. One of these, or an average value thereof, or a weighted average value using the intensity of the projection grating at the point P, the amplitude at the time of phase shift, or the like is taken as the measurement result of the z coordinate of the point P. For example, in the example shown in FIG. 14, since d ₃₂ is the smallest, the candidates for the z coordinate of the point P are z _A3 and z _B2 , respectively. Therefore, for example, the z coordinate of the point P can be obtained as the average value z = ((z _A3 + z _B2 ) / 2). Noise can be reduced by calculating an average value or a weighted average value.

When obtaining the x coordinate and y coordinate of the point P, it can be easily obtained by referring to the tables A _{x, n} and A _{y, n} using the value of n obtained when obtaining the z coordinate. . For example, in FIGS. 11A and 11B, x _A3 and y _A3 are the x and y coordinates of the point P. Also in the x coordinate and the y coordinate, by creating a table for the light source B, an average value and a weighted average value can be calculated, and noise can be reduced as in the case of the z coordinate.

  By performing the above processing for each pixel photographed by the camera, the shape can be obtained by obtaining the coordinate distribution of the entire surface of the measurement target object O.

  The above description for determining the coordinates has been made for the case where the light source is arranged at two positions with different distances from the lattice substrate, but the light source is arranged at three or more positions with different distances from the lattice substrate. The case can be similarly performed. Specifically, a correspondence table between phase values and coordinates is created for each light source, coordinate candidate values corresponding to the obtained phase values are obtained for each light source, and the difference between the candidate values is minimized. What is necessary is just to make it the coordinate which should find the average coordinate and should obtain | require the average value of a candidate value, for example.

(Shape measurement method)
Next, the shape measuring method according to the present invention will be described. The shape measuring method according to the present invention uses the shape measuring apparatus 1 according to the present invention described above, and measures the projection of the lattice pattern by turning on the light source 11a for each of a plurality of positions at different distances from the lattice substrate 11b. The target object O is photographed, and then the phase analysis process is performed on the photographed image of the measurement target object O to obtain a phase distribution, and the shape of the measurement target object is determined based on the phase distribution obtained for each of a plurality of positions. Ask. As a result, the shape of the measurement target object can be measured with high speed and high accuracy and in a wide measurement range.

<Shape measuring device>
Examples of the present invention will be described below.
A shape measuring apparatus according to the present invention as shown in FIG. 15 was produced. This apparatus includes a light source using a linear LED device and a lattice pattern projection unit composed of a projection lattice panel as a lattice substrate, and an imaging unit composed of a CMOS camera. Although not shown in the figure, a PC as an analysis unit is also provided. A side view of the lattice pattern projection unit is shown in FIG. The linear LED device has five linear LEDs arranged at intervals of 0.42 mm, and is configured to light any one column. Thereby, five phase shifts are possible.

  The light source has the five linear LEDs arranged at positions A and B at different distances from the projection grid panel, and can light each linear LED independently. The projection grid panel is obtained by attaching a metal film having a grid pattern on a glass flat plate. The CMOS camera is arranged so that its optical axis is inclined by 15 degrees with respect to the normal direction of the projection grating panel. In addition, the direction of the grid lines coincides with the extending direction of each linear LED. The distances from the projection grid panel to the light sources A and B were 20 mm and 17 mm, respectively. Thereby, the lattice pitch projected on the measurement target object is larger when the light source B is turned on than when the light source A is turned on.

<Calibration>
FIG. 17 shows the state of calibration. The reference plane is mounted on the stage so that its normal line is oriented in the z direction and translated in the z-axis direction. The position of the reference plane was moved by 0.2 mm from z ₀ = ₀ mm to z _N-1 = 70 mm by the stage.

  At each position, using the light source A and the light source B, the five linear LEDs were sequentially turned on to shift the phase of the projection grating, and the phase value on the reference plane at each position was obtained. At that time, in order to reduce the influence of random noise of the camera, nine images were taken at the same lighting position and averaged to generate one average image. Using the generated average image, the phase shift method is calculated to calculate the phase value for each pixel of the captured image. This process was performed for light source A and light source B, respectively.

FIG. 18 and FIG. 19 show the relationship between the phase value and the z coordinate at one pixel at the center of the image thus obtained. At this time, starting from z = 0 mm, recording was performed as a separate table every time the phase changed by 2π. FIG. 18 is for the case where the light source A is turned on, and the tables A _{z, 1} , A _{z, 2} , A _{z, 3} . . . It becomes like _{Az, 15} . On the other hand, FIG. 19 is for the case where the light source B is turned on, and the tables B _{z, 1} , B _{z, 2} , B _{z, 3} . . . B _{z, 13} According to such a procedure, a table was created for each pixel when the light source A was turned on and when the light source B was turned on. At that time, in the position between the reference planes, by performing an interpolation process from the z coordinate of the neighboring reference plane and the phase value at that time, not only the positions of the black spots shown in FIGS. 18 and 19 but also the positions between the black spots. A table of z coordinates with respect to the phase value θ was created in detail.

  FIG. 20 shows the dimensions of the measurement target object. FIG. 21 shows the positional relationship between the shape measuring apparatus and the measurement target object. In such a positional relationship, images of the measurement target object onto which the lattice pattern is projected when one of the light source A and the light source B is turned on are shown in FIGS. 22 and 23, respectively. 24 and 25 show phase distributions of the measurement target object onto which the lattice pattern is projected when one of the light source A and the light source B is turned on.

The phase values θ _A and θ _{B at} the center point (pixel) of the images obtained in FIG. 24 and FIG. 25 obtained by the phase shift method were 5.75 radians and 4.31 radians, respectively. From the relationship between the phase value and the z coordinate shown in FIGS. 18 and 19, a plurality of candidate values of the z coordinate for the phase value are obtained as shown in FIGS. 26 and 27, respectively. The obtained candidate values are shown in Table 1 and Table 2, respectively. The smallest distance d _nm between the plurality of z coordinate candidate values obtained in this way is when n = 8 and m = 7, in which case z _A8 = 47.51 and z _B7 = 47.52. These average values are 47.515 mm, and this average value can be used as the z coordinate of the point on the measurement corresponding object corresponding to the center point of the image. Further, by using the tables A _{x, 8} and A _{y, 8} concerning the x coordinate and y coordinate of n = 8, the x coordinate and the y coordinate of the point on the measurement corresponding object can also be obtained.

  The above process was performed on all the pixels, and the shape of the measurement target object shown in FIG. 20 was measured.

DESCRIPTION OF SYMBOLS 1 Shape measuring apparatus 11 Lattice pattern projection part 11a Light source 11b Lattice board | substrate 11c Light source board | substrate 11d Member 12 Imaging | photography part 13 Analysis part

Claims (5)

An apparatus for measuring the shape of an object to be measured,
A lattice pattern projection unit having a plurality of light sources that emit projection light for projecting a lattice pattern of a predetermined shape onto the measurement target object, and a lattice substrate that passes the projection light and forms the lattice pattern When,
An imaging unit that images the measurement target object onto which the lattice pattern is projected;
An analysis unit for obtaining a shape of the measurement target object by performing a phase analysis process on the captured image of the measurement target object;
With
At least one of the plurality of light sources is disposed at each of a plurality of positions having different distances from the lattice substrate.   The shape measuring apparatus according to claim 1, wherein three or more light sources are arranged at each of the plurality of positions.   The shape measuring apparatus according to claim 1, wherein wavelengths of light emitted from the plurality of light sources are different for each of the plurality of positions.   The shape measuring apparatus according to claim 1, wherein the light source is a linear light source.   Using the shape measuring device according to claim 1 to 4, for each of a plurality of positions having different distances from the lattice substrate, shoot the measurement target object on which the lattice pattern is projected by turning on the light source, Next, a phase analysis process is performed on the captured image of the measurement target object to obtain a phase distribution, and a shape of the measurement target object is obtained based on the phase distribution obtained for each of the plurality of positions. Shape measurement method to do.