Three-dimensional shape measurement method

Abstract

To provide a three-dimensional shape measurement method capable of performing high-speed three-dimensional shape measurement using a phase shift method by referring to a phase-coordinate table for each pixel.SOLUTION: A three-dimensional shape measurement method uses a three-dimensional measuring device 1 having a projection section 2, and a photographing section 3 having a predetermined number of pixels for obtaining a photographed image by photographing an article M and a support 4, derives a phase value for each pixel by using a phase shift method and creates a phase-coordinate table in which the phase value and a z-axis coordinate value are correlated in a relation of one to one in each position in a z-axis direction in calibration, and calibrates a camera parameter of a pin hole camera model, derives a phase value for each pixel by using a phase shift method from a photographed image in three-dimensional shape measurement, derives a z-axis coordinate value corresponding to the phase value by referring to the phase-coordinate table, and calculates x-axis and y-axis coordinate values corresponding to the z-axis coordinate value for each pixel by the pin hole camera model with a calibrated camera parameter, thus measuring a three-dimensional shape of the measurement article.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a three-dimensional shape measurement method using a phase shift method. [Background technology]

[0002] A three-dimensional shape measurement method using a phase shift method is known as a method for measuring the three-dimensional shape of an object without contact. In this three-dimensional shape measurement method, a sinusoidally varying stripe pattern is projected onto the surface of the object by a projection unit and then photographed by an imaging unit. The phase of the stripe pattern is sequentially shifted by a predetermined angle (e.g., π / 2 or 2π / 3) to obtain a set of photographed images (e.g., four or three). The set of photographed images is then processed to derive a phase value for each pixel and derive the three-dimensional coordinate values ​​corresponding to the phase value, thereby measuring the three-dimensional shape of the object.

[0003] Among such three-dimensional shape measurement methods, as disclosed in Patent Documents 1 and 2, there is known a method that enables high-precision, high-speed measurement during three-dimensional shape measurement by creating a phase-coordinate table indicating three-dimensional coordinate values ​​corresponding to phase values ​​for each pixel of a captured image during calibration, and then determining the phase value for each pixel using a phase shift method or the like during three-dimensional shape measurement and then referencing the phase-coordinate table to determine the three-dimensional coordinate value. This phase-coordinate table is created by gradually moving a reference plate, on which a two-dimensional pattern such as a two-dimensional grid on which the x-axis and y-axis coordinate values ​​of any location can be identified, in the z-axis direction (the normal direction of the reference plate), determining the x-axis and y-axis coordinate values ​​for each pixel of the captured image at each position in the z-axis direction, and then further determining the phase value using a phase shift method or the like, thereby establishing a one-to-one correspondence between the phase value and the three-dimensional coordinate values ​​(x-axis, y-axis, and z-axis coordinate values) for each pixel.

[0004] Known projection units include those that use a projector as described in Patent Document 1, and those that use a grid-pattern plate (stripe pattern forming optical element) that forms a grid pattern (stripe pattern) by passing light from a plurality of light sources arranged in a row as described in Patent Document 2. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-281491 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-242178 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, a phase-coordinate table, which associates phase values ​​with three-dimensional coordinate values ​​(x-axis, y-axis, and z-axis coordinate values) for each pixel on a one-to-one basis, can have a large number of pixels depending on the size of the object to be measured and the required accuracy, resulting in an enormous amount of data. On the other hand, if the amount of data in the phase-coordinate table becomes enormous, it takes a long time to refer to the phase-coordinate table when determining the three-dimensional coordinate values ​​of a product (measurement object) placed on an inspection line and measuring its three-dimensional shape (during three-dimensional shape measurement), which can impair high-speed inspection.

[0007] The present invention has been made in view of the above circumstances, and its object is to provide a three-dimensional shape measurement method that is capable of performing high-speed three-dimensional shape measurement using the phase shift method by referencing a phase-coordinate table for each pixel, even if the number of pixels in a captured image is large. [Means for solving the problem]

[0008] In order to achieve the above object, a three-dimensional shape measurement method according to claim 1 uses a three-dimensional measurement device comprising: a projection unit that projects a stripe pattern, the phase of which is sequentially shifted by a predetermined angle, onto an object; an imaging unit that has a predetermined number of pixels and images the object to obtain a captured image; and a support to which the projection unit and the imaging unit are fixed; and during calibration, a calibration object is used that can be switched between a surface on which a two-dimensional pattern, on which x-axis and y-axis coordinate values ​​of any location can be specified, and a plain surface; the support or the calibration object is moved to a plurality of positions in a predetermined z-axis direction, and at each position, a phase value for each pixel is derived from a set of captured images in which each of the stripe patterns is projected onto the plain surface of the calibration object using a phase shift method, and a phase-coordinate table in which the phase values ​​and z-axis coordinate values ​​correspond one-to-one; and the two-dimensional pattern of the calibration object is captured at a plurality of positions. and calibrating the camera parameters by performing an iterative method using the camera parameters of the pinhole camera model as variables so as to reduce errors between the X-axis and Y-axis coordinate values ​​of the plurality of coordinate value extraction points and the X-axis and Y-axis coordinate values ​​calculated using a pinhole camera model. When measuring the three-dimensional shape, a measurement object is used as the object, the position of the support in the z-axis direction is fixed, and a phase value for each pixel is derived using a phase shift method from a set of the measurement object onto which each of the stripe patterns is projected. The z-axis coordinate value corresponding to this phase value is derived by referring to the phase-coordinate table. Finally, the x-axis and y-axis coordinate values ​​corresponding to the z-axis coordinate value for each pixel are calculated using the pinhole camera model with the calibrated camera parameters, thereby measuring the three-dimensional shape of the measurement object.

[0009] The three-dimensional shape measurement method described in claim 2 is the three-dimensional shape measurement method described in claim 1, wherein the projection unit has a plurality of light sources arranged in a row, each of which has its lighting and light radiation intensity controlled, and a stripe pattern forming optical element that passes the light from the light sources in a stripe pattern, and the plurality of light sources are each turned on sequentially to project a stripe pattern onto the object, the phase of which is sequentially shifted by a predetermined angle, and during the calibration and the three-dimensional shape measurement, the z-axis direction is approximately vertical.

[0010] The three-dimensional shape measurement method described in claim 3 is the three-dimensional shape measurement method described in claim 1 or 2, wherein the calibration item is a flat plate that can be slid to switch between a surface on which the two-dimensional pattern is displayed and a plain surface, or a flat plate that can be switched between a surface on which a two-dimensional pattern whose x-axis and y-axis coordinate values ​​of any location are identified and a plain surface, or a flat plate that has a surface on which a two-dimensional pattern whose x-axis and y-axis coordinate values ​​of any location are identified and a plain surface on both sides.

[0011] A three-dimensional shape measuring method according to claim 4 is the three-dimensional shape measuring method according to claim 2, wherein the calibration object is placed on an object inspection line, and the measurement object is placed on the object inspection line. [Effects of the Invention]

[0012] According to the three-dimensional shape measurement method of the present invention, even if the number of pixels in a captured image is large, high-speed three-dimensional shape measurement using the phase shift method is possible by referring to a phase-coordinate table for each pixel during three-dimensional shape measurement. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a front view showing, in a reduced scale, an outline of a three-dimensional shape measuring device used in a three-dimensional shape measuring method according to an embodiment of the present invention when measuring a three-dimensional shape. [Figure 2] FIG. 2 is a front view showing a projection unit, an imaging unit, and a support body of the three-dimensional shape measuring device. [Figure 3]10A and 10B show the components constituting the projection unit in the three-dimensional shape measurement device, where FIG. 10A is a bottom view of a plurality of light sources, and FIG. 10B is a bottom view of the projection unit case that houses a plurality of light sources and a stripe pattern forming optical element. [Figure 4] 3 is a circuit diagram of a plurality of light sources of a projection unit in the three-dimensional shape measurement device of the same. FIG. [Figure 5] These are front cross-sectional views of the stripe pattern forming optical element in the same three-dimensional shape measurement device, cut horizontally near the vertical center, where (a) is an example in which multiple passing portions are formed in a regular stripe pattern, and (b) is an example in which multiple cylindrical lenses are formed in a regular pattern. [Figure 6] FIG. 2 is a waveform diagram showing, in a simplified form, the timing of projection and photography of the three-dimensional shape measuring device of the same. [Figure 7] FIG. 2 is a block diagram illustrating a three-dimensional shape measurement processing unit of the three-dimensional shape measurement device implemented by a computer. [Figure 8] 1 is a front view showing, in a reduced scale, an outline of the three-dimensional shape measuring device used in the three-dimensional shape measuring method during calibration. FIG. [Figure 9] 10 is a photograph of a captured image of a surface on which a two-dimensional pattern of a calibration object is displayed in the three-dimensional shape measuring device of the same. [Figure 10] 10 is a photograph of a set of images taken of a plain surface of a calibration object in the three-dimensional shape measurement device. [Figure 11] 10 is a photograph of a set of images of an object to be measured by the three-dimensional shape measuring device. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the present invention will be described below. As shown in Figures 1 and 2, a three-dimensional shape measuring device 1 used in a three-dimensional shape measuring method according to an embodiment of the present invention includes a projection unit 2, an imaging unit 3, and a support 4. Furthermore, as shown in Figure 1, the three-dimensional shape measuring device 1 includes a projection control unit 5 and a three-dimensional shape measurement processing unit 6.

[0015] The projection unit 2 projects stripe patterns P1, P2, P3, and P4, each having a phase sequentially shifted by a predetermined angle, onto the article M. The stripe patterns P1, P2, P3, and P4 emitted from the projection unit 2 have light radiation intensities that vary sinusoidally. The predetermined angle of the phase shift is π / 2 in this embodiment, but it can also be 2π / 3, for example.

[0016] Although a projector can be used as the projection unit 2, in this embodiment, the projection unit 2 has a plurality of (specifically, four) light sources 21A, 21B, 21C, and 21D and a stripe pattern forming optical element 22. Unless otherwise specified, the projection unit 2 is assumed to have a plurality of light sources 21A, 21B, 21C, and 21D and a stripe pattern forming optical element 22. The plurality of light sources 21A, 21B, 21C, and 21D and the stripe pattern forming optical element 22 can be housed in a projection unit case 23. The number of light sources depends on the predetermined angle of the phase shift described above, and in this embodiment, the predetermined angle of the phase shift is π / 2, so the number is four. If the predetermined angle of the phase shift is 2π / 3, the number of light sources is three.

[0017] The plurality of light sources 21A, 21B, 21C, and 21D are arranged in a row (in a row in the horizontal direction). Each of the plurality of light sources 21A, 21B, 21C, and 21D can be configured with a plurality of (six in this embodiment) light-emitting elements 210 arranged in a row in the vertical direction, as shown in Fig. 3(a). The plurality of light-emitting elements 210 are connected in parallel, in series, or in a combination thereof in terms of a circuit. For example, as shown in Fig. 4, all of the light sources 21A, 21B, 21C, and 21D can be connected in series.

[0018] 4, reference numeral 211 denotes a current limiting resistor. Reference numerals 21Aa, 21Ba, 21Ca, and 21Da denote current inflow terminals, and reference numerals 21Ab, 21Bb, 21Cb, and 21Db denote current outflow terminals. It is also possible to combine multiple current inflow terminals 21Aa, 21Ba, 21Ca, and 21Da and multiple current outflow terminals 21Ab, 21Bb, 21Cb, and 21Db into a single common terminal.

[0019] The stripe pattern forming optical element 22 passes light from the multiple light sources 21A, 21B, 21C, and 21D in a stripe pattern. As shown in FIGS. 3(b) and 5(a), the stripe pattern forming optical element 22 has multiple passing portions 22a formed in a regular stripe pattern (grid pattern). The multiple passing portions 22a pass light from the multiple light sources 21A, 21B, 21C, and 21D. The areas other than the multiple passing portions 22a are blocking portions 22b that do not pass light. In this embodiment, the stripe pattern forming optical element 22 is disposed close to and behind the front surface of the projection unit case 23, and an opening 23a is formed in the front surface of the projection unit case 23. The light that passes through the multiple passing portions 22a of the stripe pattern forming optical element 22 is emitted to the outside of the projection unit 2 through the opening 23a. In addition, in FIG. 3(b) and FIG. 5(a), the shielded portion 22b of the stripe pattern forming optical element 22 is painted black to make it easier to understand.

[0020] The stripe pattern forming optical element 22 may have a plurality of passing portions 22a arranged in a regular stripe pattern, or may have a plurality of cylindrical lenses 22c arranged in a regular pattern, as shown in FIG. 5(b). Each of the plurality of cylindrical lenses 22c is a convex lens that refracts and focuses light and radiates it to the outside. As a result, light that passes through this stripe pattern forming optical element 22 forms a stripe pattern. In a stripe pattern forming optical element 22 having such cylindrical lenses 22c formed therein, all light passes through, thereby increasing the amount of light emitted.

[0021] The projection unit 2 sequentially lights up a plurality of light sources 21A, 21B, 21C, and 21D, thereby projecting stripe patterns P1, P2, P3, and P4, the phases of which are sequentially shifted by a predetermined angle, onto the object M. Because the operation of this projection unit 2 simply involves sequentially lighting up a plurality of light sources 21A, 21B, 21C, and 21D, it is possible to quickly project the phase-shifted stripe patterns and to reduce the size and weight of the projection unit 2.

[0022] The photographing unit 3 has a predetermined number of pixels and photographs the item M.

[0023] The support 4 is a member to which the projection unit 2 and the imaging unit 3 are fixed and which supports them. The shape of the support 4 is not particularly limited, and for example, a plate material large enough to support the projection unit 2 and the imaging unit 3 can be used. During calibration, which will be described later, the support 4 can freely move in the z-axis direction relative to the article M (i.e., the article placement member 4C on which the article M is placed). For example, the support 4 can be fixed to a slider member 4A, and the slider member 4A can freely move electrically or manually in the z-axis direction of a linear guide member 4B extending in the z-axis direction, and can be fixed at any position.

[0024] Here, if the projection unit 2 uses multiple light sources 21A, 21B, 21C, and 21D and the stripe pattern forming optical element 22 as described above, it can be made smaller and lighter, and this smaller size and lighter weight allows the projection unit 2 to be supported on a support 4 together with the imaging unit 3, with the z-axis direction being the approximately vertical direction (height direction), and the support 4 can be easily moved in the z-axis direction relative to the article M. This makes it possible, as will be described later, to make the article placement member 4C on which the calibration article M1 is placed as the article M during calibration the same as the article inspection line L on which the measurement article M2 is placed as the article M during three-dimensional shape measurement. In this case, naturally, the article inspection line L as the article placement member 4C is stationary during calibration.

[0025] Note that even when the projection unit 2 uses a projector, or when the projection unit 2 uses multiple light sources 21A, 21B, 21C, and 21D and the stripe pattern forming optical element 22, if the size or weight is not sufficient to move the projection unit 2 and the image capture unit 3 relative to the object M (calibration object M1) along the z-axis direction, which is approximately vertical, during calibration, the following can be done. That is, the z-axis direction can be set to a direction other than the approximately vertical direction (for example, approximately horizontal), and the projection unit 2 and the image capture unit 3 can be supported by a support 4, and the support 4 can be moved along the z-axis direction relative to the object M. Alternatively, instead of moving the support 4, the object M (calibration object M1) (more specifically, for example, an object placement member 4C on which the calibration object M1 is placed) can be moved along the z-axis direction, with the z-axis direction being approximately vertical or a direction other than the approximately vertical direction (for example, approximately horizontal), and the position from the moved position to the support 4 can be treated as the same as the position to which the support 4 has moved.

[0026] The projection control unit 5 controls the projection and light radiation intensity of the projection unit 2. When a plurality of light sources 21A, 21B, 21C, and 21D are used, the projection control unit 5 controls the lighting and light radiation intensity of each of the light sources.

[0027] In detail, as shown in FIG. 6, during a projection period Ta synchronized with a trigger signal TR, a current I A , I B , I C , I D (See FIG. 4) is supplied to emit light. The projection period Ta has a preset length. The current can be a PWM pulse current, a constant current, or a constant voltage current. For example, in the case of a PWM pulse current, the PWM period Tb has a preset length. The PWM pulse width Tc A , Tc B , Tc C , Tc Dcan be controlled for each of the light sources 21A, 21B, 21C, and 21D, and by widening the width, the light radiation intensity increases, and by narrowing the width, the light radiation intensity decreases, thereby making it possible to adjust the light radiation intensity of the plurality of light sources 21A, 21B, 21C, and 21D. The projection period Ta is synchronized with the exposure period Td (signal EX in FIG. 6 indicates the timing of exposure) in the photographing unit 3. Also, in FIG. 6, the above-mentioned period Tb and pulse width Tc A , Tc B , Tc C , Tc D is shown enlarged for ease of understanding.

[0028] The three-dimensional shape measurement processing unit 6 performs image processing on the captured image obtained by the imaging unit 3 .

[0029] Specifically, the 3D shape measurement processing unit 6 can be realized by a computer including a CPU 6a, an auxiliary storage device 6b such as a hard disk or nonvolatile memory, a main memory (work memory) 6c, and an input / output interface 6d (input / output terminals are omitted in FIG. 7), as shown in FIG. 7. A calibration image processing program 6ba for performing image processing during calibration and a 3D shape measurement image processing program 6bb for performing image processing during 3D shape measurement are stored in the auxiliary storage device 6b, and can be transferred to the main memory 6c and executed when each program is executed. In addition, a storage area 6bc for a phase-coordinate table (described later) and a storage area 6bd for camera parameters can be provided in the auxiliary storage device 6b.

[0030] Next, we will explain the calibration of the three-dimensional shape measuring device 1 in the three-dimensional shape measuring method according to the embodiment of the present invention. Here, the calibration of the three-dimensional shape measuring device 1 refers to creating a phase-coordinate table to be referenced when deriving the z-axis coordinate value (the z-axis coordinate value among the three-dimensional coordinate values ​​(x-axis, y-axis, and z-axis coordinate values) of the article M (measurement article M2)) corresponding to a pixel from a phase value θ obtained for each pixel of a captured image using a phase shift method during three-dimensional shape measurement, which will be described later, and calibrating the camera parameters to be used when deriving the x-axis and y-axis coordinate values ​​from the derived z-axis coordinate value.

[0031] During calibration, calibration object M1 is used as object M, as shown in Figure 8. Calibration object M1 is a flat plate that can be switched between a surface M1a on which a two-dimensional pattern is displayed, allowing the x-axis and y-axis coordinate values ​​of any location to be identified, and a plain surface M1b (no pattern is displayed), relative to the imaging unit 3. The two-dimensional pattern can be a regular pattern such as a checkered pattern (two colors of squares of a fixed size arranged alternately in a two-dimensional pattern), a dot pattern (dots arranged in a two-dimensional pattern at a fixed pitch), or a two-dimensional grid pattern (multiple parallel lines arranged at regular intervals in the x-axis and y-axis directions).

[0032] It is preferable that the calibration article M1 be a flat plate having a surface M1a on which a two-dimensional pattern is drawn and a plain surface M1b on the other, which can be manually turned over. In this way, the thickness of the flat plate is necessarily constant between the surface M1a on which the two-dimensional pattern is drawn and the plain surface M1b, and the surface M1a on which the two-dimensional pattern is drawn and the plain surface M1b can be easily and precisely flattened. Furthermore, the two-dimensional pattern can be easily and clearly drawn. In this way, high-precision calibration is possible.

[0033] Furthermore, the calibration object M1 can be composed of two components: a flat plate with a surface M1a on which a two-dimensional pattern is drawn and a flat plate with a plain surface M1b, and these can be manually switched between them. Alternatively, a flat plate can be used that has a portion with a surface M1a on which a two-dimensional pattern is drawn and a portion with a plain surface M1b on the same plane, and these portions can be switched by sliding electrically or manually. In this way, the thickness of the flat plate can be easily and precisely kept constant between the surface M1a on which the two-dimensional pattern is drawn and the plain surface M1b, and the surface M1a on which the two-dimensional pattern is drawn and the plain surface M1b can be easily and precisely flattened. Furthermore, the two-dimensional pattern can be easily and clearly drawn. In this way, high-precision calibration is possible.

[0034] It is also possible to use a liquid crystal display device that can display a two-dimensional pattern on the surface M1a and that can prevent any pattern from being displayed on the surface M1b.

[0035] The support 4 (or the calibration object M1) is moved to a plurality of positions in a predetermined z-axis direction in order from an initial position (z=0). For example, the initial position may be the position where the support 4 is furthest from the calibration object M1, and then the z-axis direction value may increase as the support 4 approaches the calibration object M1.

[0036] The phase-coordinate table is created as follows.

[0037] At a plurality of positions in the z-axis direction including the initial position (for example, positions every 1 mm), the projection unit 2 sequentially projects sinusoidally varying stripe patterns P1, P2, P3, and P4 onto the plain surface M1b of the calibration object M1, and the images are captured by the capture unit 3 to obtain a set of captured images. In this embodiment, there are four captured images. If there are three light sources, there will be three captured images. In this set of captured images, as shown in Figures 10(a) to (d), each of the stripe patterns P1, P2, P3, and P4 is regular and without distortion.

[0038] Then, the 3D shape measurement processing unit 6 applies the phase shift method to the set of captured images to derive the phase value θ for each pixel. Since the phase shift method is a well-known method, a detailed description will be omitted, but for example, in the case where there are four light sources, if I1, I2, I3, and I4 are the luminance values ​​of the stripe patterns P1, P2, P3, and P4, respectively, the phase value θ for each pixel can be derived using the following equation. tanθ=(I4-I2) / (I1-I3)

[0039] In this way, a phase-coordinate table can be created in which the phase value θ and the z-axis coordinate value are associated one-to-one for each pixel for a predetermined number of z-axis coordinate values. The phase-coordinate table can be stored in the auxiliary storage device 6b of the 3D shape measurement processing unit 6.

[0040] Next, we will explain the calibration of camera parameters. Camera parameters are variables that represent the mathematical relationship between the position (actual position) (three-dimensional coordinate values) of the item M and its position on the captured image (two-dimensional coordinate values). The mathematical relationship depends on the camera model used. Among these, the pinhole camera model is known as a typical camera model.

[0041] Specifically, the camera parameters can be calibrated, for example, as follows.

[0042] By capturing images of the surface M1a of the calibration object M1, on which the two-dimensional pattern is displayed, at a plurality of positions using the image capture unit 3, data on the X-axis and Y-axis coordinate values ​​on the captured image corresponding to the actual x-axis and y-axis coordinate values ​​of the calibration object M1 at a plurality of points (coordinate value extraction points) is extracted for the purpose of calibrating the camera parameters. At this time, the projection unit 2 is not operated. Note that the actual x-axis and y-axis coordinate values ​​of the calibration object M1 at the coordinate value extraction points are known. In this embodiment, the plurality of positions (the plurality of positions captured by the image capture unit 3) are a plurality of positions in different z-axis directions. The plurality of positions in the z-axis direction can include an initial position, and do not need to coincide with the plurality of positions in the z-axis direction when creating the phase-coordinate table; for example, positions every 5 mm can be used.

[0043] The coordinate value extraction points can be, for example, corners of a rectangle if the two-dimensional pattern of the calibration object M1 photographed by the photographing unit 3 is a checkered pattern as shown in Figure 9(a), centers of dots if the two-dimensional pattern is a dot pattern as shown in Figure 9(b), or intersections of parallel lines if the two-dimensional grid pattern is as shown in Figure 9(c). Note that although detailed methods for determining the X-axis and Y-axis coordinate values ​​of the coordinate value extraction points on the photographed image are not the gist of this application and will not be described here, they can be obtained with sub-pixel accuracy by gradient processing of pixel values. The X-axis and Y-axis coordinate values ​​of multiple coordinate value extraction points on the photographed image can be numbered for multiple positions in different z-axis directions (i.e., z-axis coordinate values) and temporarily stored in the auxiliary storage device 6b or main memory 6c.

[0044] In the pinhole camera model, the relationship between the X-axis and Y-axis coordinate values ​​on the captured image and the actual x-axis, y-axis, and z-axis coordinate values ​​of the calibration object M1 is expressed by the following equation (1) using the projection matrix P and the function g X , g Y This can be expressed by the following equations (2(1)) and (2(2)) using TIFF2025127416000002.tif30170TIFF2025127416000003.tif21170In equation (1), P is a 3x4 matrix, and s is a coefficient determined so that the third component on the left side becomes 1. The function g in equations (2(1)) and (2(2)) X , g Y is a function that represents the distortion of the lens.

[0045] If P=AB, equation (1) can be expressed as the following equation (3). In equation (3), A is a matrix of internal camera parameters that represent the optical center and focal length of the imaging unit 3, and B is a matrix of external camera parameters that represent the positional relationship, including translation and rotation, between the object M and the imaging unit 3. A is a 3x4 matrix, and B is a 4x4 matrix.

[0046] For example, B can be expressed by the following equation (4). In equation (4) TIFF2025127416000005.tif30170, a 11 , a 12 , a 13 , a 21 , a 22 , a 23 , a 31 , a 32 , a 33 is an extrinsic camera parameter that represents the rotational positional relationship, and a 14 , a 24 , a 34 is a matrix of external camera parameters that represents the positional relationship of translation.

[0047] The function g in equations (2(1)) and (2(2)) X , g Y is a nonlinear function. The function g X , g Y is not particularly limited, but for example, when only the radial distortion of the lens is taken into consideration, it can be given as a simple function by the following equations (5(1)) and (5(2)). TIFF2025127416000006.tif30170 where κ is the camera parameter for the distortion coefficient.

[0048] The calibration of camera parameters in the pinhole camera model can be performed by performing an iterative method with the camera parameters as variables, so as to reduce the error (root mean square (RMS) value) between the X-axis and Y-axis coordinate values ​​on the captured image (specifically, the z-axis coordinate values ​​that are numbered and temporarily saved) and the X-axis and Y-axis coordinate values ​​on the captured image calculated using the pinhole camera model (specifically, equations (1), (2(1)), and (2(2))) at multiple coordinate value extraction points. In this case, if the magnitude of change in all camera parameters during the iteration falls below the specified accuracy value, the iteration can be terminated as convergence has occurred.

[0049] The camera parameters calibrated in this way can be stored in the auxiliary storage device 6b.

[0050] In addition to the above, various other methods are possible for calibrating the camera parameters, such as a method of obtaining the camera parameters by capturing images at multiple positions including rotation and translation (a method known as Zhang's method).In this case, as with the above, the camera parameters can be calibrated by extracting the X-axis and Y-axis coordinate values ​​of multiple coordinate value extraction points on the captured image of the surface on which the two-dimensional pattern of calibration object M1 is displayed at multiple positions, and performing an iterative method with the camera parameters of the pinhole camera model as variables so as to reduce the error between the X-axis and Y-axis coordinate values ​​of the multiple coordinate value extraction points and the X-axis and Y-axis coordinate values ​​calculated by the pinhole camera model.

[0051] Next, three-dimensional shape measurement in a three-dimensional shape measuring method according to an embodiment of the present invention will be described.

[0052] When measuring a three-dimensional shape, a measurement object M2 is used as the object M (see Figure 1). When measuring a three-dimensional shape, a calibrated three-dimensional shape measuring device 1 is placed on an object inspection line L and inspects the measurement objects M2 that flow one after another on the object inspection line L. The support 4 has a fixed position in the z-axis direction (for example, fixed at a position z = 0). Typically, the object inspection line L is a belt conveyor, and the z-axis direction is set to the approximately vertical direction (height direction), allowing the measurement objects M2 that are placed on the object inspection line L and flow one after another to be inspected. Note that the phase-coordinate table and camera parameters are usually transferred from the auxiliary storage device 6b to the main memory 6c when the three-dimensional shape measurement starts.

[0053] Then, just as with the plain surface M1b of calibration object M1 during calibration, sinusoidally varying stripe patterns P1, P2, P3, and P4 are projected sequentially by projection unit 2 onto measurement object M2, which are then photographed by photographing unit 3 to obtain a set of photographed images. In this set of photographed images, as shown in Figures 11(a) to 11(d), each of the stripe patterns P1, P2, P3, and P4 is distorted in accordance with the three-dimensional shape of measurement object M2 (a gable shape in Figures 11(a) to 11(d)).

[0054] The three-dimensional shape measurement processing unit 6 then applies the phase shift method to derive a phase value θ for each pixel from a set of captured images, in the same manner as for the plain surface M1b of the calibration object M1 during calibration. Then, the z-axis coordinate value corresponding to the phase value θ is derived by referring to the phase-coordinate table. In this case, the z-axis coordinate value corresponding to the phase value θ may be a value obtained by interpolating between z-axis coordinate values ​​corresponding to large and small phase values ​​close to the phase value θ in the phase-coordinate table, or may simply be the z-axis coordinate value corresponding to the phase value closest to the phase value θ in the phase-coordinate table.

[0055] Then, the x-axis and y-axis coordinate values ​​corresponding to the z-axis coordinate value are calculated for each pixel using a pinhole camera model with calibrated camera parameters, thereby enabling measurement of the three-dimensional shape of the measurement object M2.

[0056] The x-axis and y-axis coordinate values ​​can be calculated as follows.

[0057] For example, the above equations (5(1)) and (5(2)) can be transformed into the following equations (5(1)') and (5(2)') using an inverse function. TIFF2025127416000007.tif30170In this way, equations (2(1)) and (2(2)) are functions g X -1 , g Y -1 can be transformed into the following equations (2(1)') and (2(2)'). TIFF2025127416000008.tif21170

[0058] The above equation (3) can be expressed as the following equation (3') for a specific z-axis coordinate value z0. In equation (3'), B' is a 4x3 matrix. B' can be expressed as the following equation (4') by modifying equation (4) above. TIFF2025127416000010.tif30170

[0059] Therefore, if P'=AB', the above equation (1) can be expressed as the following equation (1') for a specific z-axis coordinate value z0. In the TIFF2025127416000011.tif30170(1´) formula, P´ is a 3x3 square matrix. P´ is the inverse matrix P´ -1 Since there is a possibility that TIFF2025127416000012.tif30170

[0060] Therefore, by using equations (2(1)') and (2(2)') (for example, equations (5(1)) and (5(2))) and equation (1''), the x-axis and y-axis coordinate values ​​for each pixel can be calculated quickly.

[0061] As described above, according to the 3D shape measurement method of the present invention, during 3D shape measurement, the z-axis coordinate value corresponding to each pixel in the captured image is derived from the phase value θ obtained for that pixel using the phase shift method. Then, the x-axis and y-axis coordinate values ​​corresponding to the z-axis coordinate value are calculated for each pixel using a pinhole camera model with calibrated camera parameters. In this case, compared to a method in which the x-axis and y-axis coordinate values ​​corresponding to the z-axis coordinate value for each pixel are stored and referenced, the total time required to access the main memory 6c can be shortened, thereby reducing the total time required to calculate the x-axis and y-axis coordinate values. Therefore, high-speed 3D shape measurement is possible even when the number of pixels in the captured image is large.

[0062] Furthermore, it is possible to reduce the area of ​​the auxiliary storage device 6b and the main memory 6c used for three-dimensional shape measurement.

[0063] Although the three-dimensional shape measurement method according to the embodiment of the present invention has been described above, the present invention is not limited to the embodiment described above, and various design modifications are possible within the scope of the claims. For example, it is also possible to provide two projection units 2 so that stripe patterns P1, P2, P3, and P4 are projected onto the article M from different directions, and to fix the two projection units 2 to the support body 4. [Explanation of symbols]

[0064] 1. 3D shape measurement device 2 Projection section 21A, 21B, 21C, 21D light source 21Aa, 21Ba, 21Ca, 21Da current inflow terminal 21Ab, 21Bb, 21Cb, 21Db Current drain terminal 210 Light-emitting element 211 Resistance 22 Stripe pattern forming optical element 22a Passing section 22b Shield part 22c cylindrical lens 23 Projection unit case 23a Projection unit case opening 3. Filming Department 4 Support 4A Slider material 4B Linear guide member 4C Item placement components 5 Projection control unit 6 3D shape measurement processing section 6a CPU 6b Auxiliary storage 6ba Calibration Image Processing Program 6bb 3D shape measurement image processing program 6bc Storage of the phase-coordinate table 6bd Camera parameter storage area 6c main memory 6d Input / Output Interface EX Signal indicating exposure timing I A , I B , I C , I D Current flowing through the light source L Item Inspection Line M Goods M1 Calibration article M1a Surface on which a 2D pattern is displayed M1b plain surface M2 measurement article P1, P2, P3, P4 stripe patterns Ta projection period Tb PWM period Tc A , Tc B , Tc C , Tc D PWM pulse width Td exposure period TR trigger signal

Claims

1. a projection unit that projects a stripe pattern onto an article, the phase of which is sequentially shifted by a predetermined angle; an imaging unit having a predetermined number of pixels for imaging the article to obtain a captured image; a support to which the projection unit and the imaging unit are fixed; Using a three-dimensional measurement device equipped with When calibrating, a calibration article that can be switched between a surface on which a two-dimensional pattern on which x-axis and y-axis coordinate values ​​of any location can be specified and a plain surface; At each of the positions to which the support or the calibration article is moved in a predetermined z-axis direction, a phase value for each pixel is derived from a set of captured images in which each of the stripe patterns is projected onto the plain surface of the calibration article using a phase shift method, and a phase-coordinate table is created in which the phase values ​​correspond one-to-one to z-axis coordinate values; extracting X-axis and Y-axis coordinate values ​​of a plurality of coordinate value extraction points on a photographed image of the surface of the calibration object on which the two-dimensional pattern is displayed, at a plurality of positions; calibrating the camera parameters by performing an iterative method using the camera parameters of the pinhole camera model as variables so as to reduce errors between the X-axis and Y-axis coordinate values ​​of the plurality of coordinate value extraction points and the X-axis and Y-axis coordinate values ​​calculated by the pinhole camera model; When measuring 3D shapes, Using a measurement article as the article, A three-dimensional shape measurement method for measuring the three-dimensional shape of a measurement object by fixing the position of the support in the z-axis direction, deriving a phase value for each pixel using a phase shift method from a set of captured images of the measurement object onto which each of the stripe patterns is projected, deriving a z-axis coordinate value corresponding to that phase value by referring to the phase-coordinate table, and calculating x-axis and y-axis coordinate values ​​corresponding to the z-axis coordinate value for each pixel using the pinhole camera model of the calibrated camera parameters.

2. 2. The three-dimensional shape measurement method according to claim 1, the projection unit has a plurality of light sources arranged in a row, each of which has its lighting and light radiation intensity controlled, and a stripe pattern forming optical element that passes light from the light sources in a stripe pattern, and projects stripe patterns onto the article, the phases of which are sequentially shifted by a predetermined angle by sequentially lighting up each of the plurality of light sources; The three-dimensional shape measurement method, wherein the z-axis direction is set to be a substantially vertical direction during the calibration and the three-dimensional shape measurement.

3. 3. The three-dimensional shape measurement method according to claim 1, A three-dimensional shape measurement method in which the calibration item is a flat plate that can be slid to switch between a surface on which the two-dimensional pattern is displayed and a plain surface, or an item that can be switched between a flat plate with a surface on which a two-dimensional pattern whose x-axis and y-axis coordinate values ​​of any location are displayed and a plain surface, or a flat plate that has a surface on which a two-dimensional pattern whose x-axis and y-axis coordinate values ​​of any location are displayed and a plain surface on both sides.

4. 3. The three-dimensional shape measurement method according to claim 2, A three-dimensional shape measurement method, wherein the calibration object is placed on an object inspection line, and the measurement object is placed on the object inspection line.

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