JP6611872B2 - Measuring device - Google Patents

Description

  The present invention relates to a measuring apparatus that measures the shape of a test object.

  With the recent development of robot technology, robots are taking on complicated processes such as assembly of industrial products. In order to realize assembly by a robot, it is required to measure a relative position and orientation between an end effect such as a robot hand and a gripping target component. As a method for measuring the position and orientation of the target component, Patent Literature 1 can be cited. The method described in Patent Document 1 is performed by fitting a model such as CAD using both edge information obtained from a grayscale image and a distance image obtained from a three-dimensional measurement method such as a pattern projection method. Measure the position and orientation of parts.

  In order to obtain a grayscale image and a distance image from a single image sensor, it is necessary to acquire each image with a time shift, or to acquire each image separately from one captured image. In order to adapt to the high-speed assembly process, it is necessary to measure the position and orientation of the target part while the robot moves. Therefore, when images are acquired while being shifted in time, positional deviation occurs between the images. In addition, if each image is to be obtained separately from one captured image, the pattern light for the distance image is superimposed on the edge of the target component, and an erroneous detection of the edge occurs in the grayscale image. Attitude measurement accuracy is reduced.

  Therefore, in Patent Document 2, the object to be examined is simultaneously illuminated by illumination for grayscale images having different wavelengths and illumination for distance images for projecting pattern light. In the method described in Patent Document 2, the light reflected by the test object is collected via an imaging lens and separated into two wavelengths by a wavelength division element such as a dichroic prism, and then the same is obtained using two sensors. A gray image and a distance image of the time are acquired.

Japanese Patent No. 5393318 Japanese Patent No. 5122729 Japanese Patent No. 2517062

  In the method disclosed in Patent Document 2, a light beam is separated by a reflection surface of a dichroic prism, and a distance image and a grayscale image are acquired. When a reflective surface is used as in Patent Document 2, when the dichroic prism is deformed or its position and orientation are changed due to vibration, a change in the attitude of the device or a change in ambient temperature, the displacement of the reflected light is compared with the transmitted light. And then grows. In particular, when a distance image is acquired by the principle of triangulation such as a pattern projection method, the measurement error amount accompanying the amount of displacement of the light beam is amplified by the configuration condition of the convergence angle.

  Therefore, an object of the present invention is to provide a measuring apparatus that improves the decrease in accuracy caused by the wavelength division element.

One aspect of the present invention relates to a measurement device, and the measurement device includes a first illumination unit that illuminates an object with pattern light having a first wavelength, and the object with light having a second wavelength different from the first wavelength. A second illuminator that illuminates the light, and transmits light of the first wavelength among light from the object illuminated by the first illuminator and the second illuminator, and reflects light of the second wavelength A wavelength separation element that forms a first image on the first imaging element by the light of the first wavelength that has passed through the wavelength separation element without being reflected by the wavelength separation element once, and the wavelength separation element; An optical system that forms a second image on the second image sensor with the light having the second wavelength reflected by the light source, and the first image sensor without using information on an image formed by the light reflected by the wavelength separation element. Process the information of the first image formed on A processing unit which obtains information indicating a three-dimensional shape of the object, also acquires information indicating an edge of the object by processing the information of the second image formed on the second image pickup element by a, Have

  According to the present invention, it is possible to provide a measuring apparatus that improves a decrease in accuracy caused by a wavelength division element.

The figure which shows the measuring device of 1st Embodiment. The figure which shows the sensitivity which the light ray by the position and orientation of a dichroic prism changes. The figure which showed the measurement error ratio of the distance image by a convergence angle, and a grayscale image. The figure which shows the dot pattern light in 1st Embodiment. The figure which shows the measuring device of 2nd Embodiment. The figure which shows the modification of the imaging part of 2nd Embodiment. The figure which shows the sensitivity which the light ray by the position and orientation of a dichroic prism changes.

[First Embodiment]
A measuring apparatus according to a first embodiment for measuring the shape of a test object will be described with reference to FIG. The measurement apparatus of the present embodiment includes a first illumination unit 1 for a distance image (first image) indicating a three-dimensional shape of a test object, and a second for a grayscale image (second image) indicating the contour of the test object. An illumination unit 2, an imaging unit 3, and a processing unit 4 are included. The 1st illumination part 1 illuminates the to-be-tested object 5 with the pattern light (1st light) of a 1st wavelength. At the same time, the second illumination unit 2 illuminates the test object 5 with the second light having the second wavelength different from the first wavelength.

  First, distance image measurement will be described. The distance image is acquired by a pattern projection method based on the principle of triangulation, and the three-dimensional shape information of the test object 5 is generated as point cloud data. In the present embodiment, the first illumination unit 1 for distance images includes a light source 6, a pattern light generation unit 7, and a projection lens 8. The pattern light generator 7 generates pattern light used for acquiring a distance image from the first light having the first wavelength emitted from the light source 6. The projection lens 8 enlarges the pattern light and illuminates the test object 5 with the enlarged pattern light. Reflected light and scattered light from the test object 5 are received by the first imaging element 11 via the dichroic prism 10 which is a wavelength division element by the imaging lens 9 in the imaging unit 3, and the pattern light component (first A first image of the test object 5 by the light component of the wavelength is formed. The first image sensor 11 is, for example, a CCD or a CMOS camera. The processing unit 4 detects the peak coordinates of the pattern light from the data of the first image by the pattern light formed by the first image sensor 11, and acquires (calculates) the distance image based on the principle of triangulation. In the present embodiment, it is assumed that the moving test object 5 is measured, and the distance is calculated from the data of the first image of the single pattern light. For example, as described in Patent Document 3, the pattern light generation unit 7 generates dot pattern light encoded by dots. The dot pattern light is illustrated in FIG. The processing unit 4 detects the position of the dot from the image obtained by illuminating the test object 5 with the dot pattern light, and associates the projection pattern with the captured image based on the positional relationship. A distance image is acquired from one image.

  Next, measurement of a grayscale image will be described. The grayscale image is a grayscale image (second image) formed by the second image sensor 12 and having a monochrome light and shade and having a second wavelength light component. The processing unit 4 detects an edge corresponding to the contour or ridge line of the test object 5 from the data of the grayscale image, and uses the edge as a feature of the image to measure the position and orientation of the test object 5. In the present embodiment, in the measurement of the grayscale image, the test object 5 is uniformly illuminated with the second light having the second wavelength by the second illumination unit 2 such as ring illumination. Reflected light and scattered light from the test object 5 are imaged by the imaging lens 9 via the dichroic prism 10 and imaged. The processing unit 4 detects an edge corresponding to the contour or ridge line of the test object 5 from the captured second image data. As a method for detecting an edge, there are the Canny method and various other methods, and any method may be used in the present embodiment. The processing unit 4 calculates the position and orientation of the test object 5 by performing model fitting using CAD data of the test object 5 input in advance, a distance image, and a grayscale image. In the present embodiment, the imaging lens 9 and the dichroic prism 10 that is a wavelength division element constitute an imaging optical system.

  The point of the first embodiment is that the dichroic prism 10 that separates the first light and the second light having different wavelengths as transmitted light and reflected light is used as the wavelength division element, and the measurement error due to the change in the position and orientation of the prism 10 and deformation. It is to suppress the influence of. The dichroic prism 10 is deformed or changes its position and orientation due to vibration, a change in posture of the measuring device, a change in ambient temperature, and the like. In that case, the amount of displacement of the reflected light beam on the surface of the second image sensor 12 is larger than the amount of displacement of the transmitted light beam on the surface of the first image sensor 11. For example, FIG. 2 shows displacement amounts of transmitted light and reflected light on the surface of the first image sensor 11 and the second image sensor 12 due to a change in the position and orientation of a dichroic prism 10 having a dimension of 17 mm. In the transmitted light, there is no displacement of the light with respect to the position shift of the dichroic prism 10, and the displacement of the light occurs only when the attitude around the axis perpendicular to the optical axis of the imaging optical system is changed. On the other hand, in the reflected light beam, the displacement of the light beam occurs due to the change in the position and posture on the reflection surface of the dichroic prism 10, and the displacement amount of the reflected light beam is several times larger than the displacement amount of the transmitted light beam. Yes.

The method for obtaining a distance image in this embodiment is a pattern projection method based on the principle of triangulation. A measurement error ΔZ when a deviation occurs in the peak coordinates of the pattern light intensity detected in this method is expressed by the following equation 1. Here, δXC is the displacement amount [pixel] of the peak coordinate of the pattern light intensity in the coordinate system on the first image sensor surface, θ is the convergence angle, and the optical axis of the first illumination unit 1 for the distance image and the imaging optical system The angle formed by the optical axis.
ΔZ = δXc × (pixel size of the first image sensor on the object plane) / tan θ (1)
On the other hand, the measurement error ΔP (x, y) with respect to the edge position coordinates detected in the grayscale image is expressed by the following equation 2. Here, δPC (xC, yC) is the displacement [pixel] of the position of edge detection in the coordinate system on the second image sensor surface.
ΔP (x, y) = δPC (xC, yC) × (pixel size of the second image sensor on the object plane) (2)
As shown in Equation 2, the edge position measurement error is obtained by simply multiplying the amount of displacement in the coordinate system on the second image sensor surface by the pixel size of the image sensor on the object surface. FIG. 3 shows a change in the ratio of the sensitivity of the measurement error to the amount of displacement of the light beam on the first and second imaging element surfaces in the distance image and the grayscale image by the convergence angle θ using Expression 1 and Expression 2. For example, it is assumed that the baseline length, which is the distance between the principal points of the first illumination unit 1 and the imaging unit 3, is 50 mm, and the working distance to the test object 5 is 200 mm. In this case, the convergence angle is about 11 °, and the amount of error with respect to the same amount of light displacement is four times larger in the distance image.

  In the distance image measurement by the pattern projection method, it is necessary to secure the measurement range by reducing the NA of the projection lens 8 and taking the depth of field. In order to perform highly accurate measurement under such conditions, a high-luminance LED light source can be used as the light source 6. As the LED light source, three primary colors of red, green, and blue are available, but the wavelength with the highest luminance is blue (450 to 470 nm). Therefore, a blue LED is used as the light source for the distance image, and the dichroic prism 10 has an optical characteristic of transmitting blue wavelength light. By doing so, the accuracy can be ensured not only in the change in the position and orientation of the prism 10 but also in a state where a sufficient exposure time cannot be secured, such as measurement of the moving object 5 to be measured.

  FIG. 7 shows the relationship between the sensitivity of measurement error due to the position and orientation of the prism 10 and the convergence angle. In FIG. 7, the solid line indicates the relationship when the distance image measurement is performed with the light transmitted through the prism 10 and the grayscale image measurement is performed with the light reflected by the prism 10. A dotted line indicates a relationship when distance image measurement is performed with light reflected by the prism 10 and grayscale image measurement is performed with light transmitted through the prism 10. In the present embodiment, the sensitivity of the measurement error to the light beam displacement of the distance image is higher than that of the grayscale image under the condition that the convergence angle is small. However, accuracy can be ensured by acquiring a distance image from the transmission direction of the dichroic prism 10 in which the amount of displacement of the light beam is small. On the other hand, when the gray image is acquired from the reflection direction of the dichroic prism 10, the amount of displacement of the light beam in the reflection direction for the gray image becomes large. However, under the condition where the convergence angle is small, the sensitivity of the measurement error to the light beam displacement of the grayscale image is low, so that the measurement accuracy of the grayscale image can be ensured.

  In the present embodiment, the convergence angle is set to an angle smaller than 39 ° based on FIG. 7, and the first imaging element 11 receives the first light transmitted through the dichroic prism 10 and is reflected by the dichroic prism 10. Is received. By doing so, it is possible to ensure the same level of measurement accuracy for both the distance image and the measurement result of the grayscale image, and the measurement accuracy of the measurement apparatus can be ensured. In this embodiment, the wavelength division element divides the light incident thereon into transmitted light and reflected light. However, the wavelength division element, for example, the light that has entered the light without being reflected by the wavelength division element even once, the light that has been reflected without transmission by the wavelength division element, and the wavelength separation element There is one that divides the light into the light that has been transmitted and reflected. In such a case, the first imaging element 11 receives light that has been transmitted without being reflected once by the wavelength division element 10, and receives light that has been reflected at least once by the wavelength division element.

[Second Embodiment]
A measuring apparatus according to the second embodiment will be described with reference to FIG. The measurement apparatus according to the second embodiment includes a first illumination unit 1 for a distance image, a second illumination unit 2 for a grayscale image, an imaging unit 3, and a processing unit 4. Descriptions of parts common to the first embodiment are omitted.

  The measurement apparatus of the second embodiment includes a parallel plate dichroic mirror 13 as a wavelength division element. In contrast to the prism-shaped wavelength division element of the first embodiment, in the second embodiment, by using a parallel plate type wavelength division element, the rigidity of the wavelength division element itself decreases and the displacement of the reflected light beam increases. When the parallel plate type dichroic mirror 13 is used, since the distance in the medium through which the transmitted light passes is shortened, the displacement of the transmitted light becomes small. Therefore, the second embodiment is particularly effective under the condition that the convergence angle is small and the sensitivity of the error of the distance image to the displacement of the light beam is high. Further, the second embodiment has an advantage that it is less expensive than the prism type.

  As described above, it has been described that the displacement of the light beam on the imaging element surface contributes to the measurement accuracy. However, in reality, it is necessary to assume that the first image sensor 11 is displaced with respect to the light beam even if the light beam is not displaced. As a countermeasure against this, as shown in FIG. 6, a holding unit 14 that holds the first image sensor 11 fixed to the imaging optical system is used. Since the rigidity between the imaging lens 9 and the first imaging element 11 can be increased as compared with the case where the first imaging element 11 and the imaging lens 9 are independently held in the housing 15, the relative position of the first imaging element 11 can be increased. The displacement becomes smaller.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  1: 1st illumination part. 2: 2nd illumination part. 3: An imaging unit. 4: Processing unit. 9: Imaging lens. 10: Dichroic prism (wavelength division element). 11: First image sensor. 12: Second image sensor. 13: Dichroic mirror.

Claims (16)

A first illuminating unit that illuminates an object with patterned light of a first wavelength;
A second illumination unit that illuminates the object with light of a second wavelength different from the first wavelength;
A wavelength separation element that transmits light of the first wavelength and reflects light of the second wavelength among light from the object illuminated by the first illumination unit and the second illumination unit; Light of the second wavelength reflected by the wavelength separation element while forming a first image on the first imaging element by the light of the first wavelength that has passed through the wavelength separation element without being reflected once by the separation element An optical system for forming a second image on the second image sensor,
Information indicating the three-dimensional shape of the object is obtained by processing the information of the first image formed on the first imaging element without using the information of the image formed by the light reflected by the wavelength separation element. And a processing unit that acquires information indicating an edge of the object by processing information of the second image formed on the second imaging element. The information indicating the edge of the object, the measurement device according to claim 1, characterized in that includes information indicating the contour or edge line of the object. The wavelength separation device, the measurement device according to claim 1 or 2, characterized in that a dichroic prism. The wavelength separation device, the measurement device according to claim 1 or 2, characterized in that a dichroic mirror in the parallel plate type. The said 1st illumination part forms the pattern light of the said 1st wavelength using the light from blue LED, The said wavelength separation element permeate | transmits the light of the wavelength of 450-470 nm, It is characterized by the above-mentioned. 5. The measuring device according to any one of items 4 to 4 . Measurement apparatus according to any one of claims 1 to 5, characterized in that it comprises a holding portion for holding said first imaging device and the second imaging element fixed to the optical system. The pattern light measuring device according to any one of claims 1, characterized in that the light of the dot pattern 6. The second illumination unit, the measurement device according to any one of claims 1 to 7, characterized in that to uniformly illuminate the object with light of the second wavelength. Wherein the processing unit, information indicating the three-dimensional shape of the object, and by processing information that indicates the edge of the object, any of claims 1 to 8, characterized in that to determine the position and orientation of the object The measuring device according to claim 1. The processing unit processes the information of the first image and the information of the second image obtained when the object is simultaneously illuminated by the first illumination unit and the second illumination unit. measurement apparatus according to any one of claims 1 and obtains the information indicating the information with the edges of the object showing the shape 9. The processing unit indicates the three-dimensional shape of the object by processing the information of the first image and the information of the second image obtained when the relative position of the object and the measuring device is changing. information and measuring apparatus according to any one of claims 1 to 10, characterized in that acquires information indicating an edge of the object. The processing unit obtains information indicating the position and orientation of the object by model-fitting an image indicating a three-dimensional shape of the object and an image indicating an edge of the object with CAD data of the object. The measuring device according to any one of claims 1 to 11 . An acquisition method for acquiring information indicating a three-dimensional shape of an object and information indicating an edge of the object,
Irradiating the object with a first wavelength pattern light and a second wavelength light different from the first wavelength;
A first image formed by the pattern light having the first wavelength that has not been reflected once after being reflected by the object, and a second image formed by the light having the second wavelength reflected after being reflected by the object. And a process of acquiring
Without using the information of the image formed by the light reflected after being reflected by the object, obtains the information indicating the three-dimensional shape of the object based on the first image, also based on the second image And acquiring information indicating the edge of the object. An acquisition method for acquiring information on the position and orientation of an object,
Irradiating the object with a first wavelength pattern light and a second wavelength light different from the first wavelength;
A first image formed by the pattern light having the first wavelength that has not been reflected once after being reflected by the object, and a second image formed by the light having the second wavelength reflected after being reflected by the object. And a process of acquiring
Without using the information of the image formed by the light reflected after being reflected by the object, obtains the information indicating the three-dimensional shape of the object based on the first image, also based on the second image Obtaining information indicating the edge of the object,
And acquiring information on the position and orientation of the object by processing information indicating the three-dimensional shape of the object and information indicating the edge of the object. In the step of acquiring the information indicating the three-dimensional shape of the object and the information indicating the edge of the object, a relative position between the measurement apparatus that acquires the first image and the second image and the object is changed. based on the first image and the second image obtained when according to claim 13 or 14, characterized in that acquires the information indicating the information with the edges of the object showing a three-dimensional shape of the object Acquisition method. The irradiating step irradiates the object with the first wavelength pattern light and the second wavelength light simultaneously,
In the step of acquiring the information indicating the three-dimensional shape of the object and the information indicating the edge of the object, the object is obtained when the pattern light of the first wavelength and the light of the second wavelength are simultaneously irradiated on the object. based on the first image and the second image according to any one of claims 13 to 15, characterized in that acquires the information indicating the information with the edges of the object showing a three-dimensional shape of the object Acquisition method.

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