JPH1047920A - Calibration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a calibration method wherein higher precision can be attained by removing errors to be caused by binarizing process. SOLUTION: A distance image at each moving point when a measurement plate 1, as a calibration object, is moved by yaw rotation, pitch rotation and back and forth movement against a 3-dimension visual sensor 4, is obtained with the 3-dimension visual sensor 4, and the obtained distance image is processed for the providing 3-dimension coordinate value of each pixel for each distance image, so that a calibration value is obtained from the obtained 3-dimension coordinate value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a calibration method in a three-dimensional measuring device required for measuring a three-dimensional position of an object to be measured by an imaging means such as a camera.

[0002]

2. Description of the Related Art Conventionally, a method shown in FIG. 19 has been known as a calibration method in a three-dimensional measuring apparatus of this kind (for example, see Japanese Patent Application Laid-Open No. 5-248819). This method uses a measurement plate 52 on which a grid line 51 (or a number of points) indicating coordinates is engraved as a calibration target, and moves the measurement plate 52 back and forth by a control device 53 while using a three-dimensional visual sensor 54. Grid lines 51
Is recognized and processed by the computer 55 to obtain calibration data. In this case, when recognizing the grid line 51, an image processing method called a binarization process is used.

[0003]

However, in the conventional calibration method described above, the grid lines 5
When extracting 1 by image processing, the grid lines 51 are blurred due to the light environment and cannot be extracted neatly, or the center of the grid lines 51 cannot be extracted and a biased line is extracted. There is a problem in that accurate coordinate cannot be performed due to the deviation of the given coordinate value from the correct position.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a calibration method capable of removing errors due to a binarization process and achieving high accuracy. Is what you do.

[0005]

In order to achieve the above-mentioned object, a calibration method according to the present invention is directed to a method of irradiating a surface of an object to be measured with light by a light projecting means and imaging a reflected light thereof. Means for measuring the position of the object to be measured based on the principle of triangulation from the information of the reflected light to be imaged. On the other hand, a distance image at each moving point when the yaw rotation, the pitch rotation, and the forward / backward movement are performed is captured by the imaging unit, and the captured distance image is processed, and the three-dimensional image of each pixel for each distance image is processed. A coordinate value is obtained, and a calibration value is obtained from the obtained three-dimensional coordinate value.

In the calibration method of the present invention, for example, a calibration object such as a measurement plate is yaw-rotated, pitch-rotated or moved back and forth by a fixed amount with respect to an image pickup means such as a camera at each moving point. A distance image is obtained by the imaging means. Then, by processing the acquired distance image, a three-dimensional coordinate value of each pixel for each distance image is obtained, and a calibration value is obtained from the obtained three-dimensional coordinate value.

According to the present invention, a correspondence table (look-up table) between 256-step distance information replaced with light / dark information of each pixel by rotating and moving the calibration object back and forth and a three-dimensional coordinate value is created. Therefore, it is possible to eliminate the occurrence of an error due to the binarization processing as in the conventional extraction of the grid lines by image processing, and it is possible to realize highly accurate calibration.

In the present invention, when processing a distance image picked up by the image pickup means, a median value around a specific pixel for one image is set as a distance image of that pixel, and the distance image obtained in this way is set. Is preferably set a plurality of times at each position, and the median values of the plurality of times are set as correction values of the distance image of the pixel. By doing so, even if the pixel value of the acquired image is distorted due to irregular reflection on the surface of the calibration target, noise can be removed and the acquired image can be smoothed.
Calibration with higher accuracy can be performed.

[0009]

Next, a specific embodiment of the calibration method according to the present invention will be described with reference to the drawings.

FIG. 1 shows a system configuration diagram of a three-dimensional measuring apparatus according to one embodiment of the present invention. The three-dimensional measuring apparatus according to the present embodiment includes a measuring plate 1 as a calibration target constituted by a plain plate, a measuring plate moving device 2 for moving the measuring plate 1 to a desired position, and a measuring plate moving device. 2, a three-dimensional visual sensor 4 provided to face the measuring plate 1, and a control device for controlling the measuring plate control device 3 according to the moving position of the measuring plate 1. A computer 5 for storing and processing the distance image acquired by the three-dimensional visual sensor 4;

The measuring plate moving device 2 includes a linear motion slider 2
a, and a gonio rotating device 2c provided on the linear motion slider 2a via a rotary table 2b, whereby the measuring plate 1 is rotated in yaw with respect to the three-dimensional visual sensor 4 (rotation about a vertical rotation axis). , Pitch rotation (rotation about a horizontal rotation axis) and forward / backward movement. The three-dimensional visual sensor 4 includes a laser irradiator that irradiates the surface of the measurement plate 1 with laser light (coded pattern light), and a CCD as an imaging unit that captures light reflected from the surface of the measurement plate 1. A camera is provided, and an image obtained by the CCD camera is sent to the computer 5. Thus, the distance image at each moving point is acquired by the three-dimensional vision sensor 4 while moving the measuring plate 1 by a fixed amount based on the control signal from the computer 5.

The three-dimensional visual sensor 4 converts the distance between the three-dimensional visual sensor 4 and the measuring plate 1 into bright and dark information such that the near area is bright and the far area is dark, and is output. Then, what three-dimensional coordinates actually correspond to the value indicating the brightness is taught by performing the calibration.

Next, the calibration method according to the present embodiment will be described with reference to FIGS.
The description will be made according to the flowchart shown in FIG.

First, a flow for creating an X-direction lookup table for storing X-direction position data will be described with reference to FIGS.

S1: All axes of the movement axis of the measurement plate 1 with respect to the three-dimensional visual sensor 4, in other words, a vertical rotation axis (Y axis),
Each axis of the horizontal rotation axis (X axis) and the longitudinal movement axis (Z axis) is moved to the origin as a measurement reference. S2: In order to acquire distance image data in the X direction, FIG.
As shown in FIG. 5A, the measuring plate 1 is set at an angle of + 30 ° around the vertical rotation axis, that is, at an angle of + 30 ° vertically with respect to the three-dimensional visual sensor 4.

S3 to S5: CCD of three-dimensional visual sensor 4
The distance image data of the measuring plate 1 is acquired by a camera, and the acquired image is corrected by a median filter (smoothing filter) in order to remove noise due to reflection on the surface of the measuring plate 1 or the like. Note that this median filter determines the density value of a pixel to be measured in a region near the pixel (for example, 3 ×
It is replaced by the median value (median value) of 3). This process is repeated until the image at each position is acquired three times.

S6 to S7: When three distance images are obtained at each position, the values of the same pixels are compared to obtain the median value (median value), and this median value is set as the final distance image. I do. Thereafter, the obtained distance image is written to a distance image file in a storage device in the computer 5.

S8-S9: Distance image data is obtained in the same manner as described above by shifting the front and rear position of the measurement plate 1 backward by a fixed pitch (for example, 0.1 mm), and this data is obtained for the entire distance image file ( 1500 times) The distance image file xp0. ckd to xp14
99. Write to ckd. Thus, for example,
All the distance image data at the time of the normal rotation of the X axis in the measurement range of 125 mm is acquired.

S10 to S11: Next, as shown in FIG. 15 (b), the measuring plate 1 is set vertically at an angle of -30.degree. 1 is returned to the origin position in the front-back direction.

S12 to S18: The same processing as in the above S3 to S9 is performed to acquire all the distance image data at the time of the negative rotation of the X axis in the measurement range of, for example, 75 mm to 125 mm. Of the distance image file xn0. kmt to xn1499. Write to kmt.

S19: Initial settings are made to create a lookup table in the X direction. In this initial setting, lut indicating the X coordinate of the lookup table is used.
_- (during forward rotation of the X-axis) x and lut - sets the indeterminate value w _(when the negative rotation of the X axis). S20 to S22: Distance image file xp0.x during normal rotation of the X-axis created as described above. kmt to xp14
99. Read kmt.

S23 to S26: There is a gap in the distance image data obtained depending on how the measuring plate 1 is installed, and the data becomes noise, so a process for eliminating this noise is performed. That is, first, the distance image i × j
(I; 256 pixels, j; 242 pixels) are compared with the previous image data for each pixel, and for example, the image data xp10.
kmt and the value of the image data xp. The value of the pixel of the same n rows and m columns of kmt is compared, and if the pixel is within 50 mm from the head and the difference between the values of the preceding and following pixels is 128 or more, the data is invalidated to invalidate this data. Lut _- x [m] of pixel position
The values of [n] [0] to lut _- x [m] [n] [255] are set to undefined values. S27 to S28: When the value of the pixel value lut _- x is an indefinite value, the moving distance when the file read in lut _- x of the pixel is captured is set. Here, the file xpa. The α part of kmt indicates the order of the file,
When the file number α is multiplied by 0.1, the movement amount is obtained (α × 0.1 mm). As a result, the position of the first appearing code value of each pixel is stored in lut _- x.

S29: The processing of S23 to S28 is performed for all pixels of i; 256 pixels, j; 242 pixels. S30: All distance image files xp0. kmt to xp
1499. It is confirmed whether or not processing has been performed for kmt.

S31 to S41: Distance image file xn0. kmt to xn1499. kmt, the distance image file xp at the time of the normal rotation of the X axis described above.
0. kmt to xp1499. kmt (S2
0 to S28) to perform lut ₋
Set the read pixel position in w.

S42 to S49: Value of each pixel
(Z; 0 to 255) for the first time during the forward rotation of the X-axis.
The relative distance in the Z-axis direction from the initial position is ip = lut_-x
[I] [j] [z] and initial position at the time of negative rotation of the X-axis
Relative distance in the Z-axis direction from the position in = lut_-w [j]
[I] [z] is the position where the specified pixel value is first found.
Set to ip and in. And these
When ip and in are not indefinite values,
The X coordinate for the pixel value at the position is calculated. X = (ip−in) / (2 × tan θ) θ: tilt angle of measurement plate 1 As shown in FIG.
p-in) is the image position during X-axis positive rotation and X-axis negative rotation
It represents the difference from the image position at the time of turning. Therefore, the measurement
X of point A representing the same pixel value during forward rotation and negative rotation of plate 1
The coordinates are represented by an equation. Note that the X coordinate of this point A is
The above-mentioned memory lut to save memory _-x [i]
[J] is stored in [z]. On the other hand, ip or in
Is an indefinite value, the memory lut_-x [j] [i]
Set an undefined value to [z].

S50: The above-described processing of S42 to S49 is performed for all pixels of i; 256 pixels, j; 242 pixels, and the lookup table in the X direction is completed, and the flow ends.

Next, a Y-direction look-up table for storing the Y-direction position data is created according to each of the steps T1 to T44 shown in FIGS.

As shown in FIGS. 17 (a) and 17 (b), the flow for creating the lookup table in the Y direction is such that the measuring plate 1 is set horizontally at an angle of ± 20 ° (step T2). , T10) to obtain distance image data in the Y direction and store the distance image data in the distance image file yp0. kmt to yp1499. kmt and y
n0. kmt to yn1499. Except for writing to kmt, it is the same as the processing in each step of S1 to S50 shown in FIGS. Therefore, description of the details of this flow will be omitted.

Subsequently, Z for storing position data in the Z direction
A flow for creating a direction lookup table will be described with reference to FIGS.

U1: All axes of the movement axis of the measuring plate 1 with respect to the three-dimensional visual sensor 4, in other words, the vertical rotation axis (Y axis),
Each axis of the horizontal rotation axis (X axis) and the longitudinal movement axis (Z axis) is moved to the origin as a measurement reference.

U2 to U4: CCD of three-dimensional visual sensor 4
The distance image data of the measurement plate 1 is acquired by a camera, and the acquired image is corrected by a median filter (smoothing filter). Then, this processing is performed by dividing the image at each position by 3
Repeated times until it is obtained.

U5 to U6: When three distance images are obtained at each position, the values of the same pixels are compared to determine the median value (median value), and this median value is set as the final distance image. I do. Thereafter, the obtained distance image is written to a distance image file in a storage device in the computer 5.

U7 to U8: The distance image data is obtained in the same manner as described above by shifting the front and rear positions of the measuring plate 1 backward by a fixed pitch (for example, 0.1 mm), and this data is obtained for the entire distance image file ( 1000 times). Repeatedly, the distance image file z0. kmt to z999. Write to kmt. In this way, for example, all the distance image data on the Z axis in the measurement range of 100 mm to 200 mm is acquired.

U9: Initial settings are made to create a Z-direction lookup table. In this initial setting, lut showing the Z coordinate of the look-up table _-
Set an undefined value to z. U10 to U11: Pixel positions z0... Of the Z-axis distance image file created as described above. Read kmt.

U12 to U15: A process for eliminating noise from the distance image data obtained in the same manner as steps S23 to S26 in FIGS. That is, first, each pixel of i and j (i; 256 pixels, j; 242 pixels) is compared with the immediately preceding image data, and the pixel is 5 pixels from the top.
If the distance is within 0 mm and the difference between the preceding and following pixels is 128 or more, the l
Set the value of ut _- z to an undefined value. U16 to U17: When the value of the pixel value lut _- z is an indefinite value, the moving distance when the file read in the lut _- z of the pixel is captured is set. As a result, the position of the first appearing code value of each pixel is stored in lut _- z.

U18: The processing of U11 to U17 is performed for all pixels of i; 256 pixels, j; 242 pixels. U19: All distance image files z0. kmt to z99
9. It is confirmed whether or not processing has been performed for kmt.

U20 to U25: For the value (Z; 0 to 255) of each pixel, the position where the designated pixel value is first found is i = lut _- z [j] [i] [z].
Set to. When this i is not an indefinite value, the value of i is stored in lut _- z [j] [i] [z] to calculate the Z coordinate for the pixel value at that position.
On the other hand, when i is an indefinite value, it is confirmed whether or not it is all pixel values, and the process returns to step U22.

U26: The above processing of U22 to U25 is performed for all pixels of i; 256 pixels, j; 242 pixels, and the lookup table in the Z direction is completed to terminate the flow.

According to this embodiment, a correspondence table (look-up table) between the brightness information of each pixel and the three-dimensional coordinate value is created using a plain plate, so that a conventional grid line is extracted by image processing. The accuracy can be significantly improved as compared with the case of performing the above.

In this embodiment, when the distance image is processed, the correction is performed using the median value. However, the correction may be performed using an average value instead of the median value. Further, it is also possible to perform a combination of the correction based on the median value and the correction based on the average value, such that the first correction is performed using the median value and the second correction is performed using the average value.

In this embodiment, the case where a three-dimensional image is obtained by irradiating the coded pattern light to the measuring plate has been described. However, the present invention is applicable to a case where a three-dimensional image is obtained by two cameras. Needless to say, it can be applied.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a three-dimensional measuring apparatus according to one embodiment of the present invention.

FIG. 2 is a flowchart for creating a lookup table in the X direction.

FIG. 3 is a flowchart for creating an X-direction lookup table;

FIG. 4 is a flowchart for creating an X-direction lookup table;

FIG. 5 is a flowchart for creating an X-direction lookup table;

FIG. 6 is a flowchart for creating a lookup table in the X direction.

FIG. 7 is a flowchart for creating a lookup table in the Y direction.

FIG. 8 is a flowchart for creating a lookup table in the Y direction.

FIG. 9 is a flowchart for creating a lookup table in the Y direction.

FIG. 10 is a flowchart for creating a lookup table in the Y direction.

FIG. 11 is a flowchart for creating a lookup table in the Y direction.

FIG. 12 is a flowchart for creating a Z-direction lookup table;

FIG. 13 is a flowchart for creating a lookup table in the Z direction.

FIG. 14 is a flowchart for creating a lookup table in the Z direction.

FIG. 15 is an explanatory diagram of a movement state of a measurement plate for acquiring a distance image in the X direction.

FIG. 6 is an explanatory diagram of a calculation method of distance image data in the X direction.

FIG. 17 is an explanatory diagram of a movement state of a measurement plate for acquiring a distance image in the Y direction.

FIG. 18 is an explanatory diagram of a movement state of a measurement plate for acquiring a distance image in the Z direction.

FIG. 19 is an explanatory diagram of a conventional calibration method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measuring plate 2 Measuring plate moving device 2a Linear motion slider 2b Rotary table 2c Goniometer rotating device 3 Measuring plate control device 4 3D vision sensor 5 Computer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor: Shozo Hirose 8-2-12 Nanko-Higashi, Suminoe-ku, Osaka-shi Inside Ogis Soken Co., Ltd. 12 Ogis Research Institute, Inc. (72) Inventor Kosuke Sato 8916-5 Takayamacho, Ikoma City, Nara Prefecture University Housing A 503 (72) Inventor Takayuki Kataoka 3-1-1 Ueno, Hirakata City, Osaka Komatsu Manufacturing Co., Ltd. Inside the Technical Research Institute

Claims (2)

[Claims] 1. A light projecting unit irradiates a surface of an object with light, an image of a reflected light thereof is taken by an image pickup unit, and information of the object to be measured is obtained based on information of the imaged reflected light based on a principle of triangulation. A calibration method in a three-dimensional measuring device for measuring a position, wherein a distance image at each moving point when a calibration object is yaw-rotated, pitch-rotated and moved back and forth with respect to the imaging means is obtained by the imaging means. And processing the captured distance image to obtain a three-dimensional coordinate value of each pixel for each of the distance images, and obtaining a calibration value from the obtained three-dimensional coordinate value. . 2. When processing a distance image picked up by the image pickup means, a median value around a specific pixel for one image is set as a distance image of the pixel, and the distance image obtained in this way is stored in each position. 2. The calibration method according to claim 1, wherein the median value is set a plurality of times, and the plurality of median values are set as correction values of the distance image of the pixel.