JP2001255118A - Target for measuring center position and center position measuring apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the center position of a target at a higher accuracy, without being affected by quantum errors regardless of longer distance to an image pickup plane from the target. SOLUTION: An optical system 12 admits image pickup light from a target 11 into a CCD image sensor 13. The CCD image sensor 13 generates an image pickup signal, based on the incident image pickup light to be supplied to an arithmetic circuit 15 through an A/D converter 14. The arithmetic circuit 15 performs a selective arithmetic processing, based on the image pickup signal near the edge of a concentric circle of the target 11 to calculate the center position of the target 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a target for central position measurement, an apparatus and method for central position measurement,
The present invention relates to a center position measuring target, a center position measuring apparatus, and a method suitable for use in detecting a center position of a target and measuring a three-dimensional position by triangulation.

[0002]

2. Description of the Related Art
In order to measure the position of the object to be measured, it has been proposed that a target is attached to the object to be measured, an image of the target is taken, and a predetermined image processing is performed on an imaged output to measure the center position of the target. I have. For example, JP-A-9-18
No. 9513 discloses a marker center-of-gravity measuring method and apparatus for making a target rhombic and measuring the center position of the target.

However, in this technique, when an image is taken by an imaging apparatus, the center position of a target is measured on the premise that the long axis or the short axis of the diamond coincides with the X axis or the Y axis of the pixel. Therefore, when the target is attached to a moving object in a three-dimensional space, there is a problem that the center position of the target cannot be measured at all.

Further, Japanese Patent Application Laid-Open No. 7-237094 discloses a method of detecting the center position of a target mark by image processing. In this technique, the center position is detected using concentric target marks.
However, this technique does not suggest the distance from the camera to the target mark. Therefore, when the distance from the camera to the target mark changes significantly, the center position of the target mark may not be detected.

Further, in the above technique, no consideration is given to a quantization error in the case of using an imaging device, and it is impossible to measure the center position of a target at a sub-pixel level.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has a target and a center for measuring a center position which can measure the center position of the target with high accuracy regardless of the target position. It is an object to provide a position measuring device and method.

[0007]

According to a first aspect of the present invention, there is provided a target for measuring a center position used in a center position measuring device for measuring a center position by capturing an image. And a plurality of edges in one direction.

The target has a pattern,
The pattern emits light with high luminance by the illumination light. Therefore, an image can be easily taken. The target further has a plurality of edges in one direction. The edge refers to a portion where the portion of the pattern that emits high luminance changes, for example, a boundary between high luminance and low luminance. Therefore, the target has an edge that is a boundary in a high-luminance pattern in one direction. By imaging this, it is possible to obtain an imaging signal capable of easily detecting the boundary of the high-luminance portion. Since there are a plurality of these boundaries, for example, the center position can be easily obtained from the two boundaries. The one direction refers to one direction such as a horizontal direction and a vertical direction, and may be any angle. The direction is not limited to one direction, and may be two or more directions. If a plurality of directions are applied, the center position can be obtained for each direction.

[0009] The plurality of edges may be configured to be concentrically distributed as in the second aspect of the present invention.
By distributing concentrically, the center position of one circle matches the center position of another circle, and it is possible to always find the same center position regardless of the size of the applied circle. it can. Further, it is possible to detect an edge in any direction on the concentric circle.

Further, as in the invention according to claim 3, the apparatus may further comprise light emission control means for controlling light emission luminance of the pattern.

According to a fourth aspect of the present invention, there is provided a center position measuring apparatus according to any one of the first to third aspects, wherein the target for center position measurement and the target for center position measurement are imaged. An imaging unit for generating a signal, and a measuring unit for measuring the center position of the target from the vicinity of the edge of the target for center position measurement based on the imaging signal generated by the imaging unit are provided.

[0012] The imaging means captures an image of the target for center position measurement, thereby obtaining imaging signals corresponding to a plurality of edges in at least one direction. The measuring means measures the center position of the target from the image signal. That is, the edge itself or a position near the edge can be specified by imaging. Therefore, from the positions of the plurality of edges, the center position thereof can be measured.

The positional relationship between the target and the imaging means is not always constant. In the present invention, since the target has a plurality of edges in at least one direction, even if the optical magnification changes due to the positional relationship between the target and the imaging unit approaching or separating, any one of the plurality of edges may be used. And the center position can be easily measured. In this case, if a target having a plurality of edges distributed on concentric circles is used, not only the positional relationship but also the directionality can be considered, and the center position can be easily measured regardless of the rotation of the target or the measuring direction of the measuring means. it can.

[0014] The imaging means may further include an aperture control means for controlling the aperture of the incident light. Thus, even if the distance to the target for measuring the center position is long, the depth of field can be increased by narrowing the incident light. As a result, a good image can be captured in a wide range.

[0015] The imaging means may further include an exposure control means for controlling an exposure amount. Thereby, even when the exposure amount becomes small,
Exposure can be increased. For example, a sufficient exposure amount can be obtained by lengthening the exposure time.

According to a seventh aspect of the present invention, there is provided the center position measuring method, wherein the target for center position measurement according to any one of the first to third aspects is imaged to generate an image signal, and the generated image signal is generated. The center position of the target is measured from the vicinity of the edge of the center position measurement target based on the imaging signal.

[0017] The center position measuring method may further include:
As in the invention described above, the stop of the incident light may be further controlled during the imaging.

The method for measuring the center position may be as follows.
As in the invention described above, the exposure amount of incident light may be further controlled during the imaging.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. The present invention can be applied to, for example, the center position measuring device 1 having the configuration shown in FIG.

The center position measuring device 1 includes an optical system 12 for adjusting the aperture and the focus of the imaging light from the target 11;
A CCD image sensor 13 for generating an image signal, an A / D converter 14 for digitizing the image signal, and an arithmetic circuit 15 for calculating the center position of a concentric circle of the target 11
And an exposure control circuit 16 for controlling the exposure time of the CCD image sensor 13 and a CPU 17 for controlling each circuit.

The target 11 has a black and white concentric pattern as shown in FIG. Target 11
Specifically, as shown in FIG. 2B, a light source 111 that emits, for example, 4 w light, and a glass 112 on which a concentric pattern is drawn are provided. Note that the light emission luminance of the light source 111 can be controlled by a light emission control circuit (not shown). The light emitted from the light source 111 passes through the glass 112 except for the portion where the concentric pattern is drawn, and goes to the outside. Therefore, the portion where the concentric circle on the glass 112 is drawn becomes the light shielding portion 113, and the other portion becomes the transmission portion 114. The glass 112 having the concentric pattern can be manufactured by using a pattern transfer technique of a semiconductor manufacturing process.

The method of manufacturing the target 11 utilizing the semiconductor manufacturing process draws a metal concentric pattern on a glass substrate by applying a mask transfer technique of the semiconductor process. Quartz glass, BK-5 or B
As a metal such as K-7, aluminum or the like can be deposited. According to this manufacturing method, it is easy to draw and manufacture a highly accurate mask pattern by an established technique, and it is possible to easily duplicate many patterns having the same accuracy as this.

Further, the metal pattern made of, for example, aluminum formed by vapor deposition has a very small thickness (several microns). Therefore, when the target is imaged from the image pickup device, there is almost no influence of the visibility of the edge due to the positional relationship. Further, since a metal deposition part such as aluminum hardly transmits light, the brightness contrast with the glass part can be clarified by the transmitted illumination, and it is optimal as an edge. Also,
In order to prevent reflection of light from the outside to the metal deposition portion, a surface treatment such as an alumite treatment may be applied to the metal deposition portion such as aluminum. Thereby, unnecessary reflection of light can be prevented.

The luminance distribution of the target 11 is shown in FIG.
As shown in FIG. Generally, as shown in FIG. 4, it is considered that the accuracy of detection of the center by the center of gravity calculation is higher when the target has a normal luminance distribution than when the target has a uniform luminance distribution. However, in practice, it is very difficult to produce a target exhibiting such a luminance distribution, and even if such a target is produced, the influence of the quantization error of the luminance at the time of imaging will be entirely within the circle. Occurs over. Therefore, target 11
Is so that the quantization error of luminance can be ignored.
It has a uniform luminance distribution.

The target 11 is thus a light source 111
, The brightness of the concentric pattern can be increased. Furthermore, by making the pattern of the target 11 circular, even if the target 11 rotates around the center of the circle as a rotation axis, the rotation direction component can be canceled.

The optical system 12 includes a target 11 having high brightness.
An iris function is provided for adjusting the aperture of the imaging light to be large or small in order to image the image with appropriate brightness. Further, the optical system 12 fixes the positions of a plurality of lenses (not shown). Therefore, the imaging light incident on the CCD image sensor 13 is out of focus. Thereby, when an image based on the imaging signal is obtained, the optical system 12 gradually changes the luminance value from 255 to 0 (or vice versa) so that the edge of the concentric circle of the target 11 is not sharpened. I have.

The CCD image sensor 13 includes an optical system 12
An imaging signal is generated based on imaging light incident through the A / D converter, and the imaging signal is supplied to the A / D converter.
The A / D converter 14 digitizes the image pickup signal and supplies it to the arithmetic circuit 15.

The arithmetic circuit 15 calculates the center position of the concentric circle based on the imaging signal from the A / D converter 14.
Specifically, first, an image based on the imaging signal is binarized. The threshold value for binarization is preferably high because the target 11 is performing transmitted illumination, and is preferably a value that detects only transmitted light. For example, in the case of 256 gradations, about 200 is preferable.

The arithmetic circuit 15 detects the target 1 from the imaging surface.
In accordance with the distance to 1, the configuration of the concentric pattern, that is, the number of shades of the concentric circle is recognized. The number of shades of this concentric circle may be set by, for example, the CPU 17.
It may be set automatically according to the distance from the imaging surface to the target 11. Then, the arithmetic circuit 15 counts the number of times that the shading changes from the center, and obtains the center radius of the target concentric circle. Then, returning to the grayscale image, the center of gravity is calculated at a point within a range of ± Δ (Δ is, for example, 距離 of the distance from the target concentric circle to the inner concentric circle) in the radial direction from the target concentric circle, Calculate the center of the circle. Here, the peripheral portion of the circumferential coordinates refers to a portion where the edge gradually changes, as described above. The center of gravity (Ci, Cj) is calculated according to the following equation when the luminance value is V.

Ci = Σ (V × coordinate value i) / ΣV Cj = Σ (V × coordinate value j) / ΣV

The exposure control circuit 16 controls the exposure time of the CCD image sensor 13. The exposure control circuit 16 controls, for example, to increase the exposure time when the optical system 12 is narrowing down the imaging light, and to control to shorten the exposure time when the optical system 12 is not narrowing down the imaging light. .

The CPU 17 controls the optical system 12, the arithmetic circuit 15, and the exposure control circuit 1 based on the operation of an operation unit (not shown).
6 is controlled.

The center position measuring device 1 can increase the distance from the imaging surface to the target 11 (hereinafter, referred to as “imaging distance”) by increasing the depth of field. At this time, the size of the target that can be imaged also changes.

Here, the size of the concentric circle of the target 11 needs to be determined in consideration of the influence of the quantization error.
As will be described in detail later, by verifying the measurement accuracy by simulation, under a predetermined condition, when the angle of view is 50 mm, 3
A center detection accuracy of about μm can be obtained. Within the imaging distance (10
If the target accuracy at 0 mm to 1000 mm) is 10 μm, the angle of view is 150 mm at the maximum. Since the angle of view increases in proportion to the imaging distance, for example, as shown in FIG.
It was set to 50 mm. Note that the angle of view 150 mm is a pixel resolution of 0.3 m when the number of vertical and horizontal pixels is 500 pixels.
m / pixel. To obtain this condition, the size of the CCD image sensor 13 is 1/3 inch and the lens f =
25 mm and an extension ring of 1 mm were employed.

Therefore, the target 11 is 150 m
What is necessary is just to provide a concentric pattern with a diameter smaller than m.
However, if the size of the concentric circle is almost the same as the screen or the size is about 10 pixels, the center position cannot be detected with the required accuracy. Therefore, the required size of the concentric circle is set to 150 to 300 pixels. This is about one-third of the number of pixels in the vertical direction of the CCD image sensor 13.
3 to 2/3.

The number of concentric circles of the target 11 and the size of its diameter are determined as follows. Here, the angle of view is set to 150 mm when the imaging distance is 1000 mm, and the relationship between the imaging distance and the angle of view is shown in FIG. A horizontal line segment indicates a range in which the target 11 occupying 150 to 300 pixels in the angle of view has a diameter on the scale of the vertical axis. For example, the line segment AA ′ has a diameter of 30 mm.
Indicates a circle. This circle occupies 300 pixels in the angle of view when the imaging distance is 350 mm, and occupies 150 pixels in the angle of view when the imaging distance is 750 mm. The line segment BB 'is
Shows a circle with a diameter of about 60 mm. This circle has an imaging distance of 750
mm, occupy 300 pixels in the angle of view, and the imaging distance is 1
In the case of 000 mm, about 180 pixels are occupied in the angle of view, so that an imaging distance of up to 1000 mm can be covered. Based on this concept, 100mm to 100mm
Up to 0 mm, the number of pixels in the angle of view is 150 to 300
Determine the number and diameter of the concentric circles so that For example,
Four concentric patterns with diameters of 7 mm, 14 mm, 28 mm and 56 mm can be determined.

Then, the center position measuring device 1 having such a configuration captures an image of the target 11 while changing the depth of field as follows.

For example, when the imaging distance is 100 mm, the optical system 12 enlarges the aperture of the imaging light without changing the focal position of the imaging light. The arithmetic circuit 15 calculates the center position (center coordinates) of the target 11 based on the imaging signals from the CCD image sensor 13 and the A / D converter 14.

When the distance is 100 mm, the arithmetic circuit 15 selects the inner concentric circle from the concentric circle pattern of the target 11. Specifically, the arithmetic circuit 15 binarizes the image based on the imaging signal from the A / D converter 14, counts the number of times the density of the target 11 changes, and recognizes the concentric circle to be selected. The arithmetic circuit 15 calculates the center coordinates from the vicinity of the edge of the concentric circle by calculating the center of gravity.

Therefore, the center position measuring device 1 can measure the center coordinates of the concentric circle drawn on the target 11 with high accuracy.

For example, when the imaging distance is 1000 mm, the optical system 12 reduces the aperture of the imaging light from the target 11 to increase the depth of field. The exposure control circuit 16 controls the CCD image sensor 13 so as to adjust the exposure time to obtain a predetermined exposure amount.

The CCD image sensor 13 includes an optical system 12
An imaging signal is generated based on imaging light incident through the A / D converter and supplied to the arithmetic circuit 15 via the A / D converter. The arithmetic circuit 15 includes a CCD image sensor 13, A
The center coordinates of the target 11 are calculated based on the imaging signal from the / D converter 14.

When the distance is 1000 mm, the arithmetic circuit 15 selects an outer concentric circle from the concentric circle pattern of the target 11. Specifically, the arithmetic circuit 15 binarizes the image based on the imaging signal from the A / D converter 14,
Then, the number of times the density of the target 11 changes is counted, and the concentric circle to be selected is recognized. The arithmetic circuit 15 calculates the center coordinates from the vicinity of the edge of the concentric circle by calculating the center of gravity.

As described above, even when the distance from the imaging surface to the target 11 is long, the center position measuring apparatus 1 can increase the depth of field by reducing the iris diaphragm. As a result, the measurable three-dimensional range of the target 11 can be expanded.

At this time, since the center position measuring device 1 adjusts the exposure time so as to obtain a predetermined exposure amount, the luminance of the target 11 is increased as in the case where the distance from the imaging surface to the target 11 is short. Thus, the quantization error can be reduced, and the center-of-gravity calculation processing can be performed accurately. Note that a predetermined exposure amount may be obtained by controlling the emission luminance of the target 11.

The center position measuring device 1 can measure the center position of the target 11 by generating an image signal from out-of-focus image light, so that it is not necessary to perform zooming control and correction of the lens center axis. Can be.

The center position measuring device 1 uses the target 11 on which the concentric circle pattern is drawn even if the image resolution changes due to the increase of the imaging distance, and the optimum position corresponding to the distance is obtained. Since the concentric circle is selected and the center-of-gravity calculation process is performed, the center coordinates of the concentric circle can be measured with the same high accuracy as when the imaging distance is short.

Further, since the center position measuring device 1 performs the center-of-gravity calculation using only the gray value at the edge of the concentric circle of the target 11 in order to reduce the influence of the quantization error, it is binarized. The center position can be measured more accurately than using a target that draws a circle or a normalized circle.

Further, since the concentric pattern is drawn on the target 11, the center position measuring device 1 changes the center of gravity calculation processing for finding the center of the concentric circle regardless of whether the imaging distance is short or long. There is also an advantage that it can be processed with the same algorithm since there is no such algorithm.

The present invention is not limited to the above-described embodiment. For example, concentric circles drawn on the target 11 may be single instead of plural. The target 11 is preferably of a transmission type, but may be of a recursive type, or of a reflection type if sufficient luminance can be obtained.

Although the concentric circle pattern of the target 11 is black and white, other colors may be used as long as the concentric circle pattern has a high luminance. Furthermore, even if the concentric circle pattern is not drawn on the target 11,
If a point-symmetric pattern such as a square, a regular hexagon, or a regular octagon is drawn, it can be applied.

Further, in the above-described embodiment, the case where a continuous circular pattern is used has been described as an example. However, a chord shape using a part of a circular shape may be used. this is,
This is effective when the measurement direction is within a certain range. Further, rectangular minute patterns or minute circles may be arranged concentrically or arcuately.

[0053]

According to the target for center position measurement according to the present invention, by providing a pattern which emits light with high luminance by illumination light and a plurality of edges in one direction, quantization at the time of center position measurement is achieved. The influence of the error is reduced, and the center position of the target can be measured with high accuracy from the positional relationship between the plurality of edges.

According to the apparatus and method for measuring the center position according to the present invention, an imaging signal is generated from incident light from the target for center position measurement, and the vicinity of the edge of the target for center position measurement is generated based on the imaging signal. By measuring the center position of the pattern from, the center position of the target can be measured with high accuracy without changing the conditions of the optical system regardless of the distance from the imaging surface to the target.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a center position measuring device to which the present invention is applied.

FIG. 2A is a front view of a target used in the center position measuring device, and FIG.

FIG. 3 is a diagram showing a target having a uniform luminance distribution.

FIG. 4 is a diagram showing a target whose luminance distribution is normalized.

FIG. 5 is a diagram illustrating a relationship between an angle of view and an imaging distance when an imaging distance is set to 1000 mm and an angle of view is set to 150 mm.

FIG. 6 is a diagram showing the number of pixels in a diagram showing the relationship between the angle of view and the imaging distance when the imaging distance is set to 1000 mm and the angle of view is set to 150 mm.

[Explanation of symbols]

 Reference Signs List 1 center position measuring device 11 target 12 optical system 13 CCD image sensor 15 arithmetic circuit 16 exposure control circuit

Continuing from the front page (72) Inventor Hiroshi Ito 41 No. 41, Chukumi Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture F-term (reference) 2F065 AA17 BB01 CC00 FF01 FF04 JJ03 JJ26 LL30 LL50 NN02 NN12 QQ03 QQ04 QQ31 UU09 5L096 AA11 FA04 FA06 FA60 FA62 FA69 JA18

Claims (9)

[Claims] 1. A center position measuring target used in a center position measuring device for measuring a center position by capturing an image, comprising: a pattern that emits light with high brightness by illuminating light; and a plurality of edges in one direction. A target for center position measurement, characterized in that: 2. The center position measuring target according to claim 1, wherein the plurality of edges are concentrically distributed. 3. The target for center position measurement according to claim 1, further comprising light emission control means for controlling light emission luminance of said pattern. 4. The target for center position measurement according to claim 1, an imaging unit for generating an image signal by imaging the target for center position measurement, and the imaging unit Measuring means for measuring the center position of the target from the vicinity of the edge of the target for center position measurement based on the imaging signal generated in step (a). 5. The center position measuring device according to claim 4, wherein said image pickup means further comprises a stop control means for controlling a stop of incident light. 6. The center position measuring device according to claim 4, wherein said image pickup means further comprises an exposure control means for controlling an exposure amount. 7. An image pickup signal is generated by imaging the target for center position measurement according to any one of claims 1 to 3, and an image pickup signal is generated based on the generated image pickup signal. A center position measuring method for measuring the center position of the target from the vicinity of the edge of the target. 8. The center position measuring method according to claim 7, further comprising controlling the stop of the incident light during the imaging. 9. The center position measuring method according to claim 7, wherein an exposure amount of incident light is further controlled during the image pickup.