Calibration jig and calibration method

Abstract

To provide a calibration jig and a method for calibration which can accurately calibrate the relative position of a light source and a camera.SOLUTION: A calibration jig 10 is for calibrating the relative position of a slit light source 2 and a camera 3a, and includes: a frame 11; at least three markers 12 supported by the frame 11 at different positions, the camera 3a being capable of imaging the markers 12; and inclination detection means supported by the frame 11, the inclination detection means detecting the inclination of a flat surface formed by a beam of light when the slit light source 2 emits a slit-like beam of light which forms a flat surface in the air.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a calibration jig and a calibration method. [Background technology]

[0002] The light-section method is known as a method for measuring the shape of a measurement object. In shape measurement using the light-section method, it is necessary to calibrate the relative positions of a light source and a camera and unify the coordinate system of the light source and the coordinate system of the camera. A known method for calibrating the relative positions is to use a calibration jig that is installed on the measurement object, as disclosed in Patent Document 1, for example. Patent Document 1 discloses a calibration process that uses a calibration jig that has multiple reference surfaces that are parallel to each other and have known height differences. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-177596 Summary of the Invention [Problem to be solved by the invention]

[0004] In the calibration process of Patent Document 1, since the camera position is calibrated using a calibration jig and then the light source position is calibrated using information about the camera position, there is a problem that a calibration error in the camera position propagates to the calibration of the light source position, making it difficult to calibrate the relative position between the light source and the camera with high accuracy.In particular, for a large or long measurement target, since the calibration jig is imaged with a camera placed far from the calibration jig, the calibration accuracy of the camera position inevitably decreases, and therefore the calibration accuracy of the light source position also decreases.

[0005] The present invention has been made based on the above background, and has an object to provide a calibration jig and a calibration method that are capable of calibrating the relative position between a light source and a camera with high precision. [Means for solving the problem]

[0006] In order to achieve the above object, a calibration jig according to a first aspect of the present invention comprises: A calibration jig for calibrating the relative position between a slit light source and a camera, The frame and Three or more markers that are supported on the frame at different positions and can be photographed by the camera; an inclination detection means supported by the frame, for detecting an inclination of a plane formed by a slit-shaped light beam emitted from the slit light source and forming a plane in space; Equipped with 、 The inclination of the plane formed by the light beam is specified by a rotation angle of the plane formed by the light beam around an axis of the emission direction of the light beam and a rotation angle of the plane formed by the light beam around an axis of the width direction of the light beam. do.

[0007] In order to achieve the above object, a calibration jig according to a second aspect of the present invention comprises: A calibration jig for calibrating the relative position between a slit light source and a camera, The frame and Three or more markers that are supported on the frame at different positions and can be photographed by the camera; an inclination detection means supported by the frame, for detecting an inclination of a plane formed by a slit-shaped light beam emitted from the slit light source and forming a plane in space; Equipped with The tilt detection means a beam splitter that splits the slit-shaped light beam emitted from the slit light source into a transmitted light beam and a reflected light beam; the beam splitter Reflection a first detecting means for receiving the slit-shaped light beam emitted from the light source and detecting a rotation angle of the light beam around an axis of the light beam emission direction on the plane formed by the light beam; the beam splitter Through and receiving the slit-shaped light beam, and forming a Ta a second detecting means for detecting a rotation angle of the light beam on the plane about an axis in the width direction; Equipped with R .

[0008] The first detecting means is the beam splitter Reflection a first lens that forms an image of the slit-shaped light beam that has been focused by the first lens; and an image pickup element that captures an image of the light beam that has been focused by the first lens, The second detecting means is the beam splitter Through The imaging device may further include a second lens that focuses the slit-shaped light beam, and a position detection element that detects the irradiation position of the light beam focused by the second lens.

[0009] the frame includes a base member and a pair of holding members extending upward from the base member and sandwiching the tilt detection means to hold the tilt detection means therebetween; The marker may be supported on at least one of the holding members.

[0010] In order to achieve the above object, the present invention 3 The calibration method according to the above aspect is A calibration method for calibrating a relative position between a light source and a camera using the calibration jig, comprising: placing the calibration fixture in the focal plane of the camera; calibrating the position and tilt of the camera by photographing the marker with the camera; and, A slit-shaped light beam is irradiated from the slit light source to the tilt detection means, calibrating the tilt of the plane formed by the light beam; removing the calibration fixture from the focal plane of the camera; Includes. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a calibration jig and a calibration method that are capable of calibrating the relative position between a light source and a camera with high precision. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a front view showing a configuration of a shape measurement system according to an embodiment of the present invention. [Figure 2] 1 is a diagram showing an example of an image of a timber captured by a camera according to an embodiment of the present invention; [Figure 3]1A and 1B are a front view and a plan view, respectively, showing the configuration of a calibration jig according to an embodiment of the present invention. [Figure 4] 3A and 3B are diagrams illustrating propagation paths of laser beams in a calibration jig according to an embodiment of the present invention. [Figure 5] 5A to 5C are diagrams for explaining the principle of detecting the rotation angle of the laser plane around the Y axis by the calibration jig according to the embodiment of the present invention. [Figure 6] 1A and 1B are diagrams illustrating the principle of detecting the rotation angle of the laser plane around the X-axis using a calibration jig according to an embodiment of the present invention. [Figure 7] 1 is a diagram illustrating a relationship between a reference coordinate system and a camera coordinate system according to an embodiment of the present invention. [Figure 8] FIG. 1A is a block diagram showing the hardware configuration of a processing unit according to an embodiment of the present invention, and FIG. 1B is a diagram showing an example of a data table of a parameter storage unit according to an embodiment of the present invention. [Figure 9] 10 is a flowchart showing the flow of a calibration process according to an embodiment of the present invention. [Figure 10] 10 is a flowchart showing the flow of a camera calibration process according to an embodiment of the present invention. [Figure 11] 10 is a flowchart showing the flow of a light source calibration process according to an embodiment of the present invention. [Figure 12] FIG. 10 is a diagram showing the configuration of a calibration jig according to a modified example of the present invention. [Figure 13] FIG. 10 is a front view showing the configuration of a shape measurement system according to a modified example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] A calibration jig and a calibration method according to an embodiment of the present invention will be described in detail below with reference to the drawings. In the drawings, the same or equivalent parts are designated by the same reference numerals.

[0014] A calibration jig is a jig used to calibrate the relative position between a light source that emits a light beam toward a measurement object and a camera that captures the measurement object illuminated by the light beam. The light source and camera are used to measure the position and shape of the measurement object using the principle of triangulation. Below, we will explain an example of calibrating the relative position between the light source and camera in the shape measurement system shown in Figure 1.

[0015] 1 is a front view showing the configuration of a shape measurement system 1 according to an embodiment. The shape measurement system 1 is a system that measures the shape of a square timber based on an image of the square timber being measured. The shape measurement system 1 includes a slit light source 2 that draws a light-section line on the measurement target surface of the square timber by irradiating the measurement target surface of the square timber with a spatially planar slit-shaped laser beam, an imaging unit 3 that images the measurement target surface of the square timber on which the light-section line has been drawn by the slit light source 2, and a processing unit 100 that calculates data indicating the shape of the measurement target surface of the square timber based on the image captured by the imaging unit 3.

[0016] Hereinafter, a Cartesian coordinate system (reference coordinate system) is used in which the horizontal direction in which the slit light source 2 and the imaging unit 3 are arranged side by side is the Z-axis direction, the direction perpendicular to the Z-axis direction extending on the horizontal plane is the X-axis direction, and the direction perpendicular to the X-axis and Z-axis directions (up and down direction) is the Y-axis direction.

[0017] The slit light source 2 is installed above the timber and draws a light-section line extending in the X-axis direction (width direction of the timber) on the measurement surface of the timber. This light-section line is drawn on the measurement surface of the timber while the laser beam is being irradiated and disappears when the laser beam irradiation is stopped. The position and orientation of the slit light source 2 are fixed by a support means (not shown).

[0018] The imaging unit 3 is installed so that its optical axis is tilted with respect to the laser beam from the slit light source 2, and captures an image of the entire timber from one of the ends facing each other in the longitudinal direction of the timber so as to include the light section line as shown in Figure 2, and transmits data of the captured image showing the light section line to the processing unit 100. The imaging unit 3 includes, for example, a camera 3a and a lens 3b that is disposed at the tip side of the camera 3a and focuses the incident image on the camera 3a. The position and orientation of the imaging unit 3 are also fixed by a support means (not shown) in the same way as the slit light source 2.

[0019] The processing unit 100 is, for example, a general-purpose computer, and is communicatively connected to both the slit light source 2 and the imaging unit 3. The processing unit 100 extracts a profile of the measurement target surface of the square timber based on the positions of pixels that indicate the light-section line in the image captured by the imaging unit 3, and calculates shape data that indicates the shape of the measurement target surface of the square timber.

[0020] Specifically, the processing unit 100 calculates the three-dimensional coordinate values ​​(Xc, Yc, Zc) of the light-section line in the camera coordinate system from the two-dimensional coordinate values ​​(u, v) of the light-section line in the image captured by the camera 3a. The camera coordinate system is an orthogonal coordinate system set with respect to the camera 3a and consisting of the Xc-axis, Yc-axis, and Zc-axis, which are orthogonal to each other. Next, the three-dimensional coordinate values ​​(Xc, Yc, Zc) in the camera coordinate system are converted into three-dimensional coordinate values ​​(X, Y, Z) in the reference coordinate system. Next, the surface shape of the measurement target surface of the square timber is calculated based on the three-dimensional coordinate values ​​(X, Y, Z) of the light-section line in the reference coordinate system.

[0021] Furthermore, the processing unit 100 identifies the relative positions (rotation and translation) of the slit light source 2 and the imaging unit 3 based on measurement data acquired from a calibration jig 10 (described later) and image data captured by the camera 3a. The configuration of the shape measurement system 1 has been described above.

[0022] Next, the configuration of a calibration jig 10 according to an embodiment will be described with reference to Figs. 3 to 6. The calibration jig 10 is installed on the focal plane of the camera 3a of the shape measurement system 1 and is used to calibrate the relative position between the slit light source 2 and the camera 3a. The focal plane of the camera 3a is the plane on which the camera 3a is focused. The size and weight of the calibration jig 10 are preferably small enough to be carried by a single operator. The calibration jig 10 can independently calibrate the inclination of the laser beam from the slit light source 2 and the position and inclination of the camera 3a, and for this purpose has the following configuration.

[0023] 3(a) and 3(b) are a front view and a plan view, respectively, showing the configuration of a calibration jig 10 according to an embodiment. In FIG. 3(a), a portion of a frame 11 is omitted for ease of understanding. The calibration jig 10 includes the frame 11, three markers 12 supported by the frame 11 and capable of being photographed by the camera 3a of the imaging unit 3, and a tilt detection means 13 supported by the frame 11, which detects a laser beam emitted from the slit light source 2 and measures the tilt of the laser plane in a reference coordinate system. The relative positions of the markers 12 and the tilt detection means 13 have been calibrated in advance, and the relative positions of the markers 12 are also known.

[0024] The laser plane is a plane formed by a spatially flat slit-shaped laser beam emitted from the slit light source 2. Hereinafter, the direction in which the laser beam is emitted may be referred to as the emission direction of the laser plane, and the direction extending on the laser plane and perpendicular to the emission direction of the laser plane may be referred to as the width direction of the laser beam.

[0025] The frame 11 includes a base member 11a, a support column 11b that extends vertically from the base member 11a and supports one marker 12 at its tip, and a pair of holding members 11c that extend vertically from the base member 11a and support the two markers 12 while sandwiching and holding the tilt detection means 13. The base member 11a and the holding members 11c are, for example, rectangular plate-like members, and the two markers 12 are each supported by two adjacent vertices at the upper end of one of the holding members 11c.

[0026] The tilt detection means 13 is disposed between the pair of holding members 11c and is supported by the holding members 11c via connecting members 11d fixed to the inside of each holding member 11c. Each part of the frame 11 is preferably made of, for example, a low thermal expansion material to suppress changes in the position and tilt of the markers 12 and the tilt detection means 13 in a high-temperature environment.

[0027] The markers 12 are configured to be photographable by the camera 3a and are used to calculate the position and tilt of the camera 3a. Each marker 12 has the same shape, e.g., a sphere. Each marker 12 may be a self-luminous type so that it can be photographed by the camera 3a even in a dark space.

[0028] The tilt detection means 13 includes a beam splitter 13a that splits the laser beam from the slit light source 2 into a transmitted beam and a reflected beam, and a beam splitter 13b that splits the laser beam from the slit light source 2 into two beams. Reflection an imaging lens 13b (first lens) that receives the laser beam formed by the imaging lens 13b; an image pickup element 13c that detects the laser beam formed by the imaging lens 13b; and a beam splitter 13a. Through The laser beam is focused by the imaging lens 13d (second lens) and the position detecting element 13e detects the position where the laser beam focused by the imaging lens 13d is irradiated.

[0029] The imaging lens 13b and the imaging element 13c are connected to the beam splitter 13a. Reflection The imaging lens 13d and the position detecting element 13e are an example of a first detecting means that receives the slit-shaped laser beam and detects the rotation angle of the laser beam around the axis of the emission direction (Y-axis direction) of the laser beam on the laser plane. Through This is an example of a second detecting means that receives a slit-shaped laser beam and detects the angle of rotation around an axis in the width direction (X-axis direction) of the laser beam on the laser plane.

[0030] The image sensor 13c and the position detecting element 13e are communicatively connected to the processing unit 100 via a wired or wireless communication circuit, and transmit data relating to the image captured by the image sensor 13c and data relating to the irradiation position detected by the position detecting element 13e to the processing unit 100 via the communication line. Upon acquiring the data from the image sensor 13c and the position detecting element 13e, the processing unit 100 executes processing, which will be described later, and calculates the tilt of a laser plane constituted by the slit-shaped laser beam emitted from the slit light source 2 and forming a spatial plane.

[0031] At the time of performing the calibration work, the calibration jig 10 is placed at a specified position on the focal plane of the shape measurement system 1 so that the direction in which the imaging element 13c and the position detection element 13e extend opposite to each other coincides with the direction in which the light cutting line extends (the X-axis direction of the reference coordinate system), and so that the direction in which the position detection element 13e extends coincides with the Z-axis direction of the reference coordinate system.

[0032] Fig. 4 is a diagram showing the propagation path of a laser beam in the calibration jig 10 according to the embodiment. In Fig. 4, the configurations of the frame 11 and the markers 12 are simplified to make it easier to understand the arrangement of the tilt detection means 13. It is also assumed that the calibration jig 10 is placed in the above-mentioned orientation at a specified position on the focal plane.

[0033] The imaging element 13c is positioned so as to capture the entire light-section line when the slit-shaped laser beam focused by the imaging lens 13b is irradiated. On the other hand, the imaging lens 13d is positioned at a position where the transmitted light from the beam splitter 13a is incident. The position detecting element 13e is formed in an elongated shape and is positioned so that when the slit-shaped laser beam focused by the imaging lens 13d is irradiated, the light-section line drawn by the slit-shaped laser beam extends in the width direction of the position detecting element 13e. Therefore, the tilt of the laser plane is expressed by the rotation angle θ around the Y-axis and the rotation angle φ around the X-axis. The procedure for calculating both is explained below.

[0034] FIG. 5 is a diagram illustrating the principle of detecting the rotation angle θ of the laser plane around the Y-axis by the calibration jig 10 according to the embodiment. FIG. 5 illustrates the image sensor 13c observed from the direction of irradiation of the laser beam. Hereinafter, it is assumed that the origin O of the reference coordinate system (the coordinate system of the calibration jig) is set to the image sensor 13c of the calibration jig 10 when the calibration jig 10 and the slit light source 2 are positioned so that the rotation angles θ and φ to be measured are close to zero. Specifically, the origin O of the reference coordinate system is set to the center point of the light section line formed on the image sensor 13c when the laser plane is positioned on the XY plane. At this time, the light section line extends in the Z-axis direction, and the rotation angle θ=0°.

[0035] The slit-shaped laser beam irradiated onto the image sensor 13c of the tilt detection means 13 travels in a straight line from the slit light source 2. Therefore, when the laser plane rotates around the X-axis of the reference coordinate system, the light-section line irradiated onto the image sensor 13c also rotates by the same angle. Therefore, the rotation angle θ around the Y-axis is the tilt of the light-section line with respect to the Z-axis. Furthermore, the distance l is the length of the line segment extending from the origin O in the Z-axis direction to reach the light-section line. The translation vector calculated from the marker 12 plus the distance l within the calibration jig 10 corresponds to the distance from the origin O to the light-section line.

[0036] 6(a) and 6(b) are diagrams illustrating the principle of detecting the rotation angle φ of the laser plane around the X-axis by the calibration jig 10 according to the embodiment. Fig. 6(a) shows the propagation path of the laser beam observed from the side, and Fig. 6(b) shows the position sensitive element 13e observed from the irradiation direction of the laser beam.

[0037] The imaging position (light-section line) of the laser beam on the light-receiving surface of the position-sensitive detector 13e changes depending on the incident angle α of the laser beam relative to the imaging lens 13d. If the imaging position at the incident angle α = 0° is the center line, the distance from the center line to the imaging position in the Z-axis direction is expressed as r, and f' is the focal length of the imaging lens 13d, then the distance r = f' * sin α. Therefore, when the incident angle α is small, it is roughly proportional to the incident angle α. Because the incident angle α is equal to the rotation angle φ around the X-axis, the rotation angle φ can be derived from the imaging position of the position-sensitive detector 13e.

[0038] Calibration jig 10 has the above-described configuration, and therefore can calibrate the position and tilt of camera 3a by using camera 3a to photograph three markers 12, and can derive rotation angles θ and φ that indicate the tilt of the laser beam from slit light source 2 by detecting the laser beam from slit light source 2 with tilt detection means 13. Therefore, the accuracy of calibration of the position and tilt of camera 3a and the accuracy of calibration of the tilt of the laser beam from slit light source 2 do not affect each other. The above is the configuration of the calibration jig 10 according to the embodiment.

[0039] Various parameters set in the calibration of the relative positions of the slit light source 2 and the camera 3a will be explained below with reference to Fig. 7. To explain the parameters set in the calibration of the relative positions, it is necessary to understand the perspective projection equation and the laser plane equation. The above equations will be explained below.

[0040] If the Xc and Yc axes of the camera coordinate system are each parallel to the plane of the image captured by the camera 3a, and the Zc axis of the camera coordinate system is parallel to the optical axis of the camera 3a, the perspective projection equation that converts two-dimensional coordinate values ​​(u, v) on the plane of the captured image into three-dimensional coordinate values ​​(Xc, Yc, Zc) in the camera coordinate system is expressed by the following equation (1). f is the focal length of the camera 3a, and (u0, v0) are the coordinate values ​​of the image center c on the image plane. The image center c is the intersection of the optical axis of the camera 3a and the image plane.

[0041]

number

[0042] The focal length f and the coordinate values ​​u0 and v0 of the image center c are parameters set in calibrating the relative positions of the slit light source 2 and the camera 3a. These parameters are all internal parameters of the camera 3a and can be derived, for example, using Zhang's method, in which a reference plane on which a specific pattern is printed is observed from multiple viewpoints.

[0043] Next, the equation of the laser plane in the camera coordinate system is expressed by the following equation (2), where a, b, c, and d are all coefficients. aXc+bYc+cZc+d=0 …(2)

[0044] The two-dimensional coordinate values ​​(u, v) of the light-section line on the captured image can be obtained by image processing, and the internal parameters of the camera and the coefficients a, b, c, and d of the laser plane can be obtained in advance through calibration. Therefore, by solving the four equations obtained from equations (1) and (2), the three-dimensional coordinate values ​​(Xc, Yc, Zc) of the light-section line in the camera coordinate system can be obtained.

[0045] To derive the coefficients a, b, c, and d of the plane equation, we need to calculate the relative position between the reference coordinate system and the camera coordinate system, calculate the plane equation that shows the laser plane in the reference coordinate system, and move the laser plane expressed in the reference coordinate system by the amount of the relative position between the reference coordinate system and the camera coordinate system. The specific procedure for this will be explained below.

[0046] First, calculate the relative position between the reference coordinate system and the camera coordinate system. The relationship between the camera coordinate system and the reference coordinate system is expressed by the following equation (3). R is a rotation matrix, R = (r1, r2, r3). ​​r1, r2, and r3 are unit vectors that indicate the directions of the Xc, Yc, and Zc axes of the camera coordinate system as seen from the reference coordinate system. t is a translation vector that starts at the origin of the reference coordinate system and ends at the origin O of the camera coordinate system.

[0047]

number

[0048] The rotation matrix R and the translation vector t indicate the position and tilt of the camera coordinate system in the reference coordinate system, and are both external parameters of the camera 3a. The rotation matrix R and the translation vector t are calculated by capturing images of three markers 12, which are provided on the calibration jig 10 and whose relative positions are known, with the camera 3a, and solving a PnP (Perspective n Point) problem in the captured image.

[0049] Next, calculate the plane equation that represents the laser plane in the reference coordinate system. The equation of the laser plane in the reference coordinate system is expressed by the following equation (4), where a', b', c', and d' are all coefficients. a'X+b'Y+c'Z+d'=0 …(4)

[0050] Furthermore, the rotation angles θ and φ of the laser plane around the Y-axis and X-axis in the reference coordinate system, and the distance L from the origin O to the light-section line are expressed by the following equations (5) to (7) using coefficients a', b', c', and d'. The distance L from the origin O to the light-section line can be derived by adding the distance l within the calibration jig 10 to the translation vector obtained from the marker 12. tanθ=-a' / c' …(5) tanφ=-b' / c' …(6) L=-d' / c' …(7)

[0051] Using equations (5) to (7), equation (4) can be transformed into equation (8) below. Xtanθ+Ytanφ-Z+L=0 …(8)

[0052] The rotation angles θ and φ of the reference coordinate system and the distance L from the origin O to the light-section line are all external parameters of the camera 3a, and as described above, are derived by detecting the laser beam from the slit light source 2 with the tilt detection means 13 of the calibration jig 10 and performing calculations based on the detection results. By substituting the values ​​of the rotation angles θ and φ of the laser plane obtained from the calibration jig 10 and the distance L from the origin O to the light-section line into equations (5) to (8) and solving the simultaneous equations, the coefficients a', b', c', and d' are obtained.

[0053] Next, the laser plane expressed in the reference coordinate system is moved by the amount of the relative position between the reference coordinate system and the camera coordinate system. Specifically, the coefficients a', b', c', and d' are converted to coefficients a, b, c, and d using the following equation (9). (abcd)=(a'b'c'd')(R,t) …(9) The above is the procedure for deriving the coefficients a, b, c, and d of the laser equation in the reference coordinate system.

[0054] The rotation angles θc and φc of the laser plane around the Yc axis and the Xc axis in the camera coordinate system, and the distance Lc from the origin O to the light-section line are parameters required for calibrating the relative positions of the slit light source 2 and the camera 3a, and are calculated based on the coefficients a, b, c, and d derived using the calibration jig 10. The rotation angles θc and φc of the laser plane around the Yc axis and the Xc axis in the camera coordinate system, and the distance Lc from the origin O to the light-section line are calculated by substituting the coefficients a, b, c, and d into the following equations (10) to (12). tanθc=-a / c …(10) tanφc=-b / c …(11) Lc=-d / c …(12) The above are the various parameters that are set when calibrating the relative positions of the slit light source 2 and the camera 3a.

[0055] 8(a) is a block diagram showing the hardware configuration of a processing unit 100 according to an embodiment. The processing unit 100 includes an operation unit 110, a display unit 120, a communication unit 130, a storage unit 140, and a control unit 150. The components of the processing unit 100 are connected to each other via an internal bus (not shown).

[0056] The operation unit 110 receives instructions from the user and supplies an operation signal corresponding to the received operation to the control unit 150. The operation unit 110 includes, for example, a mouse and a keyboard.

[0057] The display unit 120 displays various images to the user based on data relating to the shape of the measurement target surface of the square timber supplied from the control unit 150.

[0058] The communication unit 130 is an interface that can be connected to a communication network such as the Internet.

[0059] The storage unit 140 includes, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, and a hard disk. The storage unit 140 stores programs executed by the control unit 150 and various data. The storage unit 140 also temporarily stores various types of information and functions as a work memory for the control unit 150 to execute processes. The storage unit 140 also includes a coordinate value storage unit 141, an arithmetic expression storage unit 142, and a parameter storage unit 143.

[0060] The coordinate value storage unit 141 stores coordinate values ​​that serve as references for the tilt of the laser plane and the position and tilt of the camera 3a. For example, the coordinate value storage unit 141 stores two-dimensional coordinate values ​​(u', v') of each pixel at which a light-section line is depicted on the image sensor 13c when the rotation angle θ=0° when the calibration jig 10 is installed at a specified position on the focal plane, position data of the center line at which the light-section line is detected by the position detection element 13e when the rotation angle φ=0°, and three-dimensional coordinate values ​​(X1, Y1, Z1), (X2, Y2, Z2), and (X3, Y3, Z3) that indicate the positions of the three markers 12 in the reference coordinate system.

[0061] The calculation formula storage unit 142 stores formulas (1) to (12) required for calculating various parameters, and also stores a calculation formula that indicates the correspondence relationship between the distance r between the center line and the light cutting line and the rotation angle φ.

[0062] 8(b) shows an example of a data table of the parameter storage unit 143 according to the embodiment. The parameter storage unit 143 stores various parameters obtained by a calibration process described later. For example, the parameter storage unit 143 stores the focal length f, which is an internal parameter of the camera 3a, and the coefficients a, b, c, and d of the plane equation, which are external parameters.

[0063] The control unit 150 includes a processor and controls each part of the processing unit 100. The processor is, for example, a CPU (Central Processing Unit). The control unit 150 executes the programs stored in the storage unit 140 to perform the calibration process of Fig. 9, the camera calibration process of Fig. 10, and the light source calibration process of Fig. 11. Functionally, the control unit 150 includes an acquisition unit 151, a calculation unit 152, and an output unit 153.

[0064] The acquisition unit 151 acquires image data including the marker 12 photographed by the camera 3a, image data including the light-section line photographed by the imaging element 13c, and position data of the light-section line detected by the position detection element 13e, and stores them in the storage unit 140. Furthermore, acquisition of data by the acquisition unit 151 includes reading out each of the various image data and position data stored in the storage unit 140.

[0065] The calculation unit 152 calculates a rotation matrix R and a translation vector t by solving the PnP problem in the image including the marker 12 acquired by the acquisition unit 151. Furthermore, the calculation unit 152 refers to the coordinate value storage unit 141 and the calculation formula storage unit 142 to calculate a rotation angle θ and a distance L of the laser plane from the image of the image sensor 13c acquired by the acquisition unit 151, and calculates a rotation angle φ of the laser plane from the position data of the light-section line on the position detection element 13e acquired by the acquisition unit 151. Then, the calculation unit 152 refers to the calculation formula storage unit 142 to calculate coefficients a, b, c, and d of the laser plane equation from the rotation matrix R and the translation vector t, as well as the rotation angles θ and φ and the distance L.

[0066] The output unit 153 outputs to the outside the various parameters calculated by the calculation unit 152. The output unit 153 causes the parameter storage unit 143 to store the various parameters calculated by the calculation unit 152, for example. The above is the configuration of the processing unit 100.

[0067] (Calibration process) The flow of the calibration process executed by the processing unit 100 according to the embodiment will be described with reference to Fig. 9. The calibration process starts when an instruction from the user is received.

[0068] Before the processing unit 100 performs the calibration process, the calibration jig 10 is placed on the focal plane of the shape measurement system 1. As shown in Fig. 4, the calibration jig 10 is placed on the focal plane of the shape measurement system 1 so that the horizontal direction in which the imaging element 13c and the position detection element 13e extend opposite to each other coincides with the X-axis direction, and so that the direction in which the position detection element 13e extends coincides with the Z-axis direction of the reference coordinate system.

[0069] When the control unit 150 receives an instruction from the user, it executes a camera calibration process to calibrate the position and tilt of the camera 3a (step S1). Hereinafter, the flow of the camera calibration process executed by the control unit 150 will be described with reference to FIG.

[0070] (Camera calibration process) First, the control unit 150 causes the camera 3a to capture an image of the area including the three markers 12 of the calibration jig 10 (step S11).

[0071] Next, the calculation unit 152 calculates a rotation matrix R and a translation vector t based on the image captured in step S11 (step S12), and returns the process. Specifically, the image captured in step S11 is input into the processing unit 100, and the rotation matrix R and the translation vector t are calculated by solving the PnP problem for the captured image including the three markers 12 captured by the camera 3a. The above is the flow of the camera calibration process.

[0072] 9, the control unit 150 executes a light source calibration process to calibrate the tilt of the slit light source 2 (step S2). Hereinafter, the flow of the light source calibration process executed by the control unit 150 will be described with reference to FIG.

[0073] (Light source calibration process) First, the control unit 150 causes the slit light source 2 to irradiate the calibration jig 10 with a slit-shaped laser beam (step S21).

[0074] Next, the calculation unit 152 calculates the rotation angle θ around the Y axis and the distance L from the origin O to the light cutting line based on the inclination of the slit-shaped laser beam irradiated onto the image pickup element 13c of the calibration jig 10 (step S22). Specifically, the slit-shaped laser beam emitted in step S21 is imaged by the image pickup element 13c, the imaged image is captured, and the rotation angle θ and the distance L are calculated by referring to the coordinate value storage unit 141.

[0075] Next, the calculation unit 152 calculates the rotation angle φ around the X axis based on the detection position of the laser beam detected by the position detection element 13e of the calibration jig 10 (step S23), and returns the process. Specifically, the calculation unit 152 causes the position detection element 13e to detect the irradiation position of the slit-shaped laser beam emitted in step S21, takes in the detected position information, and calculates the rotation angle φ by referring to the calculation formula stored in the calculation formula storage unit 142. The above is the flow of the light source calibration process.

[0076] 9, the calculation unit 152 calculates the coefficients a, b, c, and d of the plane equation based on the rotation matrix R and translation vector t obtained in the processing of step S1 and the rotation angles θ, φ, and distance L obtained in the processing of step S2 (step S3). Specifically, the calculation unit 152 applies the rotation angles θ, φ, and distance L obtained in the processing of step S2 to equations (5) to (8) to calculate the coefficients a', b', c', and d'. Next, the calculation unit 152 applies the rotation matrix R and translation vector t obtained in the processing of step S1 and the coefficients a', b', c', and d' to equation (9) to calculate the coefficients a, b, c, and d.

[0077] Next, the output unit 153 stores the coefficients a, b, c, and d calculated in the process of step S3 in the parameter storage unit 143 (step S4), and ends the process. The above is the flow of the calibration process.

[0078] After the calibration process is completed, the user removes the calibration jig 10 from the focal plane of the camera 3a. A separate calibration process is performed on the internal parameters of the camera 3a. This completes preparations for measuring the shape of the timber. The user activates the shape measurement system 1 at the desired timing and performs shape measurement of the timber. Specifically, the processing unit 100 captures an image of the measurement target surface of the timber with the camera 3a while irradiating the measurement target surface with a slit-shaped light beam from the slit light source 2, thereby acquiring a captured image including a light-section line. Next, the processing unit 100 converts the multiple two-dimensional coordinate points (u, v) that constitute the light-section line on the captured image into three-dimensional coordinate values ​​(Xc, Yc, Zc) in the camera coordinate system using Equation (1), and then converts the three-dimensional coordinate values ​​(Xc, Yc, Zc) in the camera coordinate system into three-dimensional coordinate values ​​(X, Y, Z) in the reference coordinate system using Equation (3).

[0079] As described above, the shape measurement system 1 according to the embodiment includes a frame 11, three or more markers 12 supported by the frame 11 at different positions and capable of being photographed by the camera 3a, and a tilt detection unit 13 supported by the frame 11, which detects the tilt of a plane formed by a slit-shaped light beam that forms a plane in space when the slit light source 2 emits the light beam. Therefore, the tilt of the laser-irradiated surface can be measured independently of the position and tilt of the camera 3a, and the relative positions of the slit light source 2 and the camera 3a can be calibrated with high accuracy. Furthermore, since a decrease in calibration accuracy can be prevented even when the slit light source 2 and the camera 3a are separated from each other, high-accuracy shape measurement can be achieved even for large or long measurement targets.

[0080] The present invention is not limited to the above-described embodiment, and the following modifications are possible.

[0081] (Variation) In the above embodiment, the slit light source 2 emits a laser beam, but the present invention is not limited to this. As long as the imaging unit 3 can capture an image of a light section line, the beam emitted from the slit light source 2 may be something other than a laser beam. Furthermore, unless the shape of the measurement object is to be measured, a light source other than the slit light source 2 that emits a laser beam spread in a plane may be used. For example, a section line may be drawn on the surface of the measurement object by scanning a laser beam from the laser light source in the X-axis direction.

[0082] In the above embodiment, the tilt of the laser plane is measured in a reference coordinate system, but the present invention is not limited to this. For example, the tilt of the laser plane may be measured in a camera coordinate system and the coordinates may be converted on the image.

[0083] In the above embodiment, the frame 11 of the calibration jig 10 includes the base member 11a, the support 11b, the holding member 11c, and the connecting member 11d, but the present invention is not limited to this. The shape and structure of the frame 11 may be any as long as it can fix the positions of the markers 12 and the tilt detection means 13.

[0084] In the above embodiment, three markers 12 are provided on the calibration jig 10, but the present invention is not limited to this. To calculate the position and tilt of the camera 3a in the reference coordinate system, it is sufficient that three or more markers 12 are present on the calibration jig 10. For example, six markers 12 may be used to simplify the calculation for calculating the position and tilt of the camera 3a in the reference coordinate system.

[0085] 12, a cubic frame is created with twelve rod-shaped members constituting each side, and four markers 12 are placed at the four vertices of the top surface of the frame, one marker 12 is placed at the midpoint of one side extending in the vertical direction, and the remaining markers 12 are placed on the side surface including the side on which marker 12 is placed, at the midpoint between the marker 12 placed at the midpoint of that side and the marker 12 on a vertex not located on that side. The remaining marker 12 can be supported by another rod-shaped member connecting the marker 12 placed at the midpoint of that side and the marker 12 on a vertex not located on that side.

[0086] In the above embodiment, there is one slit light source 2 and one camera 3a, but the present invention is not limited to this. For example, as shown in FIG. 13 , an illumination unit 2A may be provided that includes multiple slit light sources 2 spaced apart in the Z-axis direction, and the relative positions of each slit light source 2 and the camera 3a may be sequentially determined to unify the coordinate system of each slit light source and the camera coordinate system. Alternatively, multiple cameras 3a may be provided in the imaging unit 3, and the coordinate system of the slit light source and the coordinate system of the multiple cameras may be unified. In this case, the calibration jig 10 may be arranged so that all markers 12 are visible to the respective cameras 3a, and the markers 12 may be photographed by each camera 3a, thereby unifying the coordinates.

[0087] In the above embodiment, the arithmetic expression indicating the correspondence relationship between the distance r between the center line and the light-section line and the rotation angle φ is stored in the arithmetic expression storage unit 142. However, the present invention is not limited to this. For example, a data table storing the correspondence relationship between the distance r between the center line indicating the imaging position of the position detection element 13e and the light-section line and the rotation angle φ may be stored in the storage unit 140.

[0088] In the above embodiment, various data are stored in the storage unit 140 of the processing unit 100, but the present invention is not limited to this. For example, all or part of the various data may be stored in an external control device or computer via a communication network.

[0089] In the above embodiment, the processing units 100 each operate based on a program stored in the storage unit 140, but the present invention is not limited to this. For example, the functional configuration realized by the program may be realized by hardware.

[0090] In the above embodiment, the processing unit 100 is, for example, a general-purpose computer, but the present invention is not limited to this. For example, the processing unit 100 may be realized by a computer provided on a cloud.

[0091] In the above embodiment, the processing performed by processing unit 100 was realized by an apparatus having the above-mentioned physical configuration executing a program stored in memory unit 140, but the present invention may also be realized as a program or as a storage medium on which the program is recorded.

[0092] In addition, a program for executing the above-mentioned processing operations may be stored and distributed on a non-transitory computer-readable recording medium such as a flexible disk, a CD-ROM (Compact Disk Read-Only Memory), a DVD (Digital Versatile Disk), or an MO (Magneto-Optical Disk), and the program may be installed on a computer to configure an apparatus that executes the above-mentioned processing operations.

[0093] In the above embodiment, a square timber is used as the measurement object, but the present invention is not limited to this. For example, the shape of a round timber may be measured. Furthermore, the measurement object is not limited to wood, and the shape of a steel material may be measured, for example.

[0094] The above-described embodiments are merely examples, and the present invention is not limited to these. Various embodiments are possible within the scope of the invention as set forth in the claims. The components described in each embodiment and modification can be freely combined. Furthermore, inventions equivalent to the inventions set forth in the claims are also included in the present invention. [Explanation of symbols]

[0095] 1. Shape measurement system 2 slit light source 2A Lighting Unit 3 Imaging unit 3a Camera 3b lens 10 Calibration fixture 11 frames 11a Base member 11b Post 11c Holding member 11d Connecting member 12 markers 13 Tilt detection means 13a Beam splitter 13b Imaging lens 13c image sensor 13d imaging lens 13e Position detection element 100 processing units 110 Operation section 120 Display section 130 Communications Department 140 Storage section 141 Coordinate value storage unit 142 Arithmetic expression storage section 143 Parameter storage unit 150 control section 151 Acquisition Department 152 Arithmetic section 153 Output section

Claims

1. A calibration jig for calibrating the relative position between a slit light source and a camera, The frame and three or more markers that are supported on the frame at different positions and that can be photographed by the camera; an inclination detection means supported by the frame, for detecting an inclination of a plane formed by a slit-shaped light beam emitted from the slit light source and forming a plane in space; Equipped with the tilt of the plane formed by the light beam is specified by a rotation angle of the plane formed by the light beam around an axis of the emission direction of the light beam and a rotation angle of the plane formed by the light beam around an axis of the width direction of the light beam. Calibration fixture.

2. A calibration jig for calibrating the relative position between a slit light source and a camera, comprising: The frame and three or more markers that are supported on the frame at different positions and that can be photographed by the camera; an inclination detection means supported by the frame, for detecting an inclination of a plane formed by a slit-shaped light beam emitted from the slit light source and forming a plane in space; Equipped with The tilt detection means a beam splitter that splits the slit-shaped light beam emitted from the slit light source into a transmitted light beam and a reflected light beam; a first detection means for receiving the slit-shaped light beam reflected by the beam splitter and detecting a rotation angle of the light beam about an axis of the emission direction on the plane formed by the light beam; a second detection means for receiving the slit-shaped light beam transmitted through the beam splitter and detecting a rotation angle of the light beam about an axis in the width direction on the plane formed by the light beam; A calibration fixture comprising:

3. the first detecting means includes a first lens that forms an image of the slit-shaped light beam reflected by the beam splitter, and an image pickup element that captures an image of the light beam formed by the first lens; the second detecting means includes a second lens that forms an image of the slit-shaped light beam that has passed through the beam splitter, and a position detecting element that detects the irradiation position of the light beam that has been formed into an image by the second lens. The calibration jig according to claim 2 .

4. the frame includes a base member and a pair of holding members extending upward from the base member and sandwiching the tilt detection means to hold the tilt detection means therebetween; The marker is supported on at least one of the holding members. The calibration jig according to any one of claims 1 to 3.

5. A calibration method for calibrating a relative position between a light source and a camera using the calibration jig according to any one of claims 1 to 4, comprising: placing the calibration fixture in the focal plane of the camera; calibrating the position and tilt of the camera by photographing the marker with the camera; a step of irradiating a slit-shaped light beam from the slit light source onto the tilt detection means, thereby calibrating the tilt of the plane formed by the light beam; removing the calibration fixture from the focal plane of the camera; A calibration method including:

Images