JP3512092B2 - Calibration device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a calibration apparatus and a hologram capable of automating camera calibration. [0002] Conventionally, an image picked up by a camera is processed,
When measuring the position of an object, camera calibration (calibration of the relative positional relationship between the world coordinate system, the camera coordinate system, and the screen coordinate system) must be performed. If this calibration is not performed, it is not possible to know exactly where the object position on the screen captured by the camera corresponds in the world coordinate system (absolute coordinate system), so the position of the object must be measured accurately. Can not. Therefore, performing camera calibration with high accuracy is indispensable for performing position measurement of an object with high accuracy. In addition, the calibration may come after a certain period of time has elapsed due to a change in the position of the camera with time or a positional shift of the optical system and the image pickup device inside the camera. Therefore, it is necessary to perform calibration periodically. In particular, when measuring the position of a component with an image for automatic assembly in a factory, an automated calibration system is necessary to perform calibration periodically. In the conventional camera calibration, a plurality of points in a three-dimensional space whose positions in a world coordinate system (absolute coordinate system) are known are imaged by the camera, and the calibration parameters of the camera are obtained by calculation. Like that. In general, prepare a calibration plate depicting a lattice pattern, checkerboard pattern, black circles, etc., use intersections or black circles of the lattice or checkerboard pattern as points in the binary space, and further go directly to this plate. By moving in the direction, a plurality of three-dimensionally distributed points are obtained. Therefore, in order to automate the calibration, a device that automatically moves the calibration plate is required. [0005] However, the above-mentioned conventional calibration method has the following problems. (1) Since it is necessary to automatically and accurately move the calibration plate, a driving unit for moving the calibration plate and a control unit for controlling the driving unit are required.
The calibration device becomes large-scale. (2) Since there is a mechanically movable part, an error occurs in the position of the calibration plate due to gear backlash or the like, and it is difficult to perform highly accurate camera calibration. (3) A plurality of images must be taken by moving the calibration plate and subjected to image processing, which takes time and labor. SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to eliminate a movable portion, thereby enabling a highly accurate calibration with a simple configuration. It is to provide an application device. [0007] To solve the above-mentioned problems,
In order to achieve the object, a calibration device according to the present invention is a calibration device for presenting three-dimensional position information to an imaging camera in order to perform calibration of the imaging camera , wherein the light of the imaging camera is axis
A plurality of sheets at predetermined intervals in each direction and parallel to each other
Liquid crystal that is arranged and can display a predetermined pattern in each
Panel and the plurality of liquid crystal panels alternately with the predetermined pattern.
And a drive device for displaying a pattern of the turn . Since the calibration device according to the present invention is configured as described above, the calibration device remains fixed to the camera. In this state, three-dimensional position information can be input to the camera at one time, so there is no need for a moving mechanism for moving the calibration plate as in the past, and the camera can be calibrated with high accuracy using a simple configuration. Can be performed. Also, since only one image is required for camera calibration, the processing can be speeded up. Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. (First Embodiment) FIGS. 1 to 3 show a calibration apparatus according to a first embodiment. In FIG.
The calibration device 12 displays a pattern on the surface of a quadrangular pyramid, and uses a dot (black circle) as the pattern, for example, as illustrated. FIG. 2 shows another example of the calibration device, in which a pattern of dots (black circles) is displayed on the surface of a cone as shown. FIG. 3 shows still another example of the calibration device, which is configured by displaying a dot pattern on the surface of a pyramid-shaped block. The calibration device having the above configuration is used as follows. First, one image is captured by a camera installed above the calibration device 12. Next, 2
A dot pattern is extracted from the input image by using a value conversion process or the like. The extracted dot pattern has an elliptical shape, for example, in the calibration device shown in FIGS. 1 and 2 because the dot is on a slope. The center of gravity of this dot pattern is obtained. Since the center of the dot pattern coincides with the center of gravity, the center of gravity of the binarized dot pattern is set as the center position of the dot. Next, the center position of the pattern on the screen and the actual calibration device 3
Associate the dimensional center position. Then, the camera parameters are calculated from the position information by a known method. As described above, if the calibration apparatus shown in FIGS. 1 to 3 is used, three-dimensional position information can be input to the camera at one time with one calibration apparatus, and the movable part can be eliminated. Therefore, the configuration of the camera calibration device can be simplified, and highly accurate calibration can be performed.
Further, since only one input image is required, the speed of the calibration process can be increased. (Second Embodiment) Next, FIG. 4 is a diagram showing a calibration apparatus according to a second embodiment. In FIG. 4, the calibration device 1
Reference numeral 4 denotes a structure in which colored yarns are stretched in a lattice and three-dimensionally. The color yarns are stretched, for example, in three layers, and the colors of the yarns in each layer are different colors. Thereby, the intersection of the color yarns of one layer indicates a two-dimensional position, and the position of the intersection of the yarns in the depth direction can be known from the difference in the color of the yarn of each layer. That is, the three-dimensional position can be captured on one screen of the camera. The calibration device configured as described above is used as follows. First, one image is captured by a camera installed above the calibration device 14. Next, the intersection of the warp and the weft in the same layer is extracted from the input image. At this time, yarns in the same layer are extracted using the color information of the yarns. Next, the position of the intersection of the yarn in the image is associated with the position of the intersection in the world coordinate system (absolute coordinate system).
Then, the camera parameters are calculated from the position information by a known method. As described above, if the calibration device shown in FIG. 4 is used, three-dimensional position information can be input to the camera at one time with one calibration device, and the movable part can be eliminated. In addition, the configuration of the camera calibration device can be simplified, and highly accurate calibration can be performed. Also,
Since only one input image is required, the speed of the calibration process can be increased. In addition, since the three-dimensional arrangement state of the intersections of the yarns can be known by using the colored yarns, it is easy to associate the positions of the intersections on the screen with the three-dimensional positions on the world coordinate system. Can be. (Third Embodiment) FIG. 5 is a diagram showing a configuration of a calibration device according to a third embodiment. In FIG. 5, the calibration device 1
Reference numeral 6 denotes a hologram plate on which a three-dimensional pattern is recorded. A first light source 18 that emits a laser beam as reference light A is provided diagonally forward of the hologram plate 16.
A second light source 20 that emits laser light as reference light B is arranged. When the hologram plate 16 is irradiated with the reference light A, the camera 10 using an imaging device such as a CCD
An image A formed by the reference light A is captured. Also,
When the hologram plate 16 is irradiated with the reference light B, the camera 1
At 0, an image B formed by the reference light B is captured. The image A and the image B are formed at different positions from the camera 10 as shown in the figure. The image A is, for example, one in which square dots are arranged in a grid, and the image B is, for example, one in which triangular dots are arranged in a lattice. However, the image A and the image B are not limited to these quadrangular or triangular patterns, and any pattern may be used as long as the central position thereof is determined. The calibration device configured as described above is used as follows. First, the hologram plate 16 is moved to the world coordinate system (X
-YZ coordinate system).
Next, the camera 10 and the light sources 18 and 20 are fixed at unknown positions. However, the light sources 18 and 20 may be fixed within a certain error (within a range where an image appears by the reference light). Next, the camera 10 captures a three-dimensional image (ie, image A and image B) using the reference light from the light sources 18 and 20. From the captured three-dimensional image and the known position of the hologram plate 16 on the world coordinate system, the internal parameters of the camera 10 (focal length, CCD cell size, etc.), external parameters (mounting position, etc.), And light source 18,
Calibrate 20 mounting errors. Note that the method of the camera calibration process may use a conventionally used method. Further, the mounting error of the light sources 18 and 20 can be calculated backward from the image distortion. In the above description, the case where two images are stored in the hologram plate is described. However, the present invention is not limited to this, and three or more images are stored in the hologram plate and three or more images are stored. The hologram plate may be irradiated with a laser beam by the light source of (1). If three or more images are used for camera calibration in this way, the accuracy of the calibration will be further improved. Next, FIG. 6 is a diagram showing a case where the calibration apparatus using the hologram plate as described above is applied to an actual production line. As shown in FIG. 6, when a part of the equipment or a movable part is present in the range where the position of the work is actually measured, it is difficult to set a calibration reference. Therefore, a hologram plate for calibration is installed in a surplus space of the equipment, and a reference image is projected on an actual measurement range. FIG. 7 is a diagram showing another example in which a calibration device using a hologram plate is applied to an actual production line. As shown in FIG. 7, a half mirror is provided between the work and the camera, and a hologram plate is provided in a range reflected by the half mirror. Even if you do this,
As in the case of FIG. 6, it is possible to arrange the calibration device at a position that does not interfere with a part of the equipment or the movable part. Further, according to the configuration of FIG. 7, by projecting the reference image onto the measurement range during the operation of the manufacturing line, the calibration can be performed even during the operation of the line. As a result, maintenance-free operation of the work position measurement system is realized. As described above, in the third embodiment, images spaced apart by a predetermined distance in the axial direction of the camera are stored in the hologram plate, and the hologram plate receives reference light from a plurality of light sources. By irradiating, a three-dimensional image can be easily input to the camera, and calibration of the camera can be performed using only one image. (Fourth Embodiment) FIGS. 8 and 9 are diagrams showing a configuration of a calibration device according to a fourth embodiment. In FIG. 8, reference numeral 22 denotes an apparatus for presenting a calibration pattern.
The camera 28 is composed of a plurality of liquid crystal panels that are fixed at a predetermined distance from each other in the optical axis direction of the camera 28 and that are accurately fixed in parallel with each other. 24 is each liquid crystal panel 22
A driving device for driving the liquid crystal panel 26 receives position data indicating an image pattern from the control device 40 that controls the entire calibration device, and alternately drives the liquid crystal panel 22 to display the pattern at that position. Is a drive control device. Reference numeral 28 denotes a camera to be calibrated, 3
0 is a control device for controlling the camera 28, 32 is an A / D converter for converting an analog output signal from the camera 28 into a digital signal, 34 is an image data holding device for storing digital image data, and 36 is an image data holding device. An output device for extracting a feature and outputting the position of the feature on the screen, 38
An arithmetic unit that calculates camera parameters from position data in the world coordinate system of the feature received from the control device 40 and position data in the screen of the feature received from the output device 36. In the above-described calibration apparatus, as described above, the n liquid crystal panels are accurately set so as to be parallel to each other. A liquid crystal panel that can change the amount of light transmitted through the liquid crystal layer from 0% to 100% is used. As shown in FIG. 9, the liquid crystal panels are denoted by LC1, LC2,..., LCn in order from the camera side. now,
LCD panels LC1, LC2,..., LCi-1 (i = 2, 3,
When the pattern is displayed by setting the transmittance of the light of..., N) to 100% and the transmittance of LCi to 0%, the pattern displayed on the LCi is imaged by the camera 28 installed in front of the liquid crystal panel. be able to. The driving control device 26 controls the liquid crystal panel driving device 24 so that the liquid crystal panel LCi
An arbitrary pattern can be displayed at (i = 1, 2,..., N). That is, when the pattern shape and the presentation position data are given to the drive control device 26, the specified pattern can be displayed at the commanded position. Only one pattern is displayed, and the state is
, The position of the pattern in the world coordinate system and the position in the screen coordinate system are easily associated with each other. FIG. 10 shows a coordinate system. In FIG. 10, the world coordinate system O (X, Y,
The origin O of Z) is located at the upper left of the liquid crystal panel LC1, the X axis is directed rightward in the horizontal direction as viewed from the camera, the Y axis is directed downward in the vertical direction, and the Z axis is directed from the front to the back as viewed from the camera. Panel coordinate system O 'of liquid crystal panel LCi (Xi', Yi ')
Is located at the upper left of the liquid crystal panel LCi, and Xi '
The axis and the Yi 'axis are parallel to the X and Y axes, respectively. At this time, the position of the origin Oi 'in the world coordinate system is (0, 0, di
(Where di = 0). The origin of the camera coordinate system o (x, y, z) is at the focal point of the camera, the x-axis is vertically upward, the y-axis is rightward in the horizontal direction, and the z-axis is along the optical axis. The imaging plane of the camera is assumed to be perpendicular to the z-axis at the position of z = f, and the origin o 'of the screen coordinate system o' (p, q) is at the position of (0, 0, f). The axes are parallel to the x-axis and the y-axis, respectively. The operation of the calibration device configured as described above will be described with reference to the flowchart shown in FIG. First, an arbitrary liquid crystal panel CLi (i = 1,
, N), only one pattern Sij is displayed at the position of (Pij, Qij) (step S2). At this time, the pattern S
When the position of ij is represented in the world coordinate system, (Pij, Qij, di)
It becomes. For example, if a circle is used as the pattern, the position of the pattern is represented by the center of the circle. Next, an image is captured by the camera 28 (step S4). After the image signal captured by the camera 28 is converted from an analog signal to a digital signal by the A / D converter 32 (step S6), the image is stored in the image data holding device 34 (step S8). The pattern is extracted from the image by the output device 36, and the position (pij, qij) of the pattern Sij on the screen is obtained (step S1).
0). When a circle is used as a pattern, the circle is extracted by a binarization process or the like, and the position of the center of gravity of the extracted circle is determined as the position of the pattern. Then, for j = 1 to k, that is, for each of the plurality of liquid crystal panels, a series of processes for obtaining the position of the center of gravity of the pattern from the display of the pattern is repeated (step S12). The k sets of Sij (P
ij, Qij, di) and sij (pij, qij) are calculated by the arithmetic unit 38.
To calculate camera parameters (step S1).
4). The calculation of the camera parameters is performed by a known method. As described above, according to the calibration device of the fourth embodiment, the control device controls the input of an image from the camera and the calibration pattern presenting device (liquid crystal panel) to thereby control the camera. Calibration can be performed automatically. By controlling the calibration pattern presenting apparatus and displaying the pattern on an arbitrary liquid crystal panel, a function equivalent to moving a conventional calibration plate can be obtained. Since there is no mechanical movable part, a highly accurate camera configuration can be realized. Further, by controlling the pattern to be displayed, it is possible to easily associate the position on the screen with the position in the three-dimensional space. The present invention can be applied to a modification or modification of the above embodiment without departing from the spirit thereof. As described above, according to the calibration apparatus and the hologram of the present invention, three-dimensional position information can be provided to the camera at one time while the calibration apparatus is fixed to the camera. Since the input can be performed, the camera can be calibrated with high accuracy with a simple configuration without requiring a moving mechanism for moving the calibration plate as in the related art. Further, since only one image is required for the camera calibration, the processing can be speeded up. [0050]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a calibration device according to a first embodiment. FIG. 2 is a diagram illustrating a calibration device according to a first embodiment. FIG. 3 is a diagram illustrating a calibration device according to a first embodiment. FIG. 4 is a diagram illustrating a calibration device according to a second embodiment. FIG. 5 is a diagram illustrating a configuration of a calibration device according to a third embodiment. FIG. 6 is a diagram showing a case where a calibration device using a hologram plate is applied to an actual production line. FIG. 7 is a diagram showing another example in which a calibration device using a hologram plate is applied to an actual production line. FIG. 8 is a diagram illustrating a configuration of a calibration device according to a fourth embodiment. FIG. 9 is a diagram illustrating a configuration of a calibration device according to a fourth embodiment. FIG. 10 is a diagram showing a coordinate system. FIG. 11 is a flowchart showing the operation of the calibration device. [Description of Signs] 10 Cameras 12, 14 Calibration device 16 Hologram plate 18, 20 Light source 22 Presentation device 24 Drive device 26 Drive control device 28 Camera 30 Camera control device 32 A / D converter 34 Image data holding device 36 Output device 38 arithmetic unit 40 control unit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-311485 (JP, A) JP-A-64-1078 (JP, A) JP-A-7-35644 (JP, A) JP-A-1- 44805 (JP, A) (58) Fields studied (Int. Cl. ⁷ , DB name) G01B 11/00-11/30

Claims (1)

(57) Claims 1. A calibration device for presenting three-dimensional position information to an imaging camera in order to perform calibration of the imaging camera , wherein the optical axis of the imaging camera is provided. 且 apart respectively predetermined intervals in the direction
A plurality of liquid crystal panels arranged in parallel with each other and each capable of displaying a predetermined pattern pattern; and a driving device for alternately displaying the predetermined pattern pattern on the plurality of liquid crystal panels. Calibration device.