Patent Application
20250231022
The entire disclosure of Japanese Patent Application No. 2024-003795, filed on Jan. 15, 2024, is incorporated herein by reference in its entirety.
The present disclosure relates to a three-dimensional shape measurement apparatus, a three-dimensional shape measurement method, and a non-transitory computer-readable recording medium.
Conventionally, an apparatus that measures a three-dimensional shape using the principle of the phase shift method (hereinafter referred to as “three-dimensional shape measurement apparatus”) has been developed. For example, a three-dimensional shape measurement apparatus is disclosed in each of Japanese Laid-Open Patent Publication No. 2019-191310, Japanese Laid-Open Patent Publication No. 2018-146521, Japanese Laid-Open Patent Publication No. 2013-88261, and Japanese Laid-Open Patent Publication No. 2016-31284. The three-dimensional shape measurement apparatus using the phase shift method includes a projector that projects a stripe pattern on a measurement target, and a camera that captures an image of the measurement target on which the stripe pattern is projected.
In the case of a three-dimensional shape measurement apparatus using the phase shift method, depending on the cycle of a stripe pattern projected on a measurement target, the contrast of a captured image obtained by capturing an image of the stripe pattern with a camera varies. As the contrast of the captured image decreases, a variation in the height position of a three-dimensional shape to be output increases, resulting in decrease of the measurement accuracy of the three-dimensional shape.
An object of the present disclosure is to improve the measurement accuracy of a three-dimensional shape measured by a three-dimensional shape measurement apparatus using the phase shift method.
To achieve at least one of the abovementioned objects, according to an aspect of the present invention, a three-dimensional shape measurement apparatus reflecting one aspect of the present invention comprises: a projector that includes a projector lens and projects a stripe pattern; a camera that includes a camera lens and captures an image of the stripe pattern projected by the projector to acquire the captured image of the stripe pattern; and a hardware processor. The hardware processor measures a three-dimensional shape of a measurement target based on the captured image. The hardware processor determines a cycle of the stripe pattern to be projected by the projector from a plurality of cycle candidates. The plurality of cycle candidates are set based on a synthetic MTF (Modulation Transfer Function) characteristic generated by combining a first MTF characteristic of the projector lens and a second MTF characteristic of the camera lens.
To achieve at least one of the abovementioned objects, according to an aspect of the present invention, a measurement method for measuring a three-dimensional shape of a measurement target by a three-dimensional shape measurement apparatus, reflecting one aspect of the present invention, comprises: determining a cycle of a stripe pattern to be projected by a projector including a projector lens, from a plurality of cycle candidates; projecting the stripe pattern by the projector; capturing an image of the stripe pattern projected by the projector, by a camera including a camera lens, to acquire the captured image of the stripe pattern; and measuring a three-dimensional shape of the measurement target based on the captured image. The plurality of cycle candidates are set based on a synthetic MTF characteristic generated by combining a first MTF characteristic of the projector lens and a second MTF characteristic of the camera lens.
To achieve at least one of the abovementioned objects, according to an aspect of the present invention, a non-transitory computer-readable recording medium storing a measurement program for causing one or more computers to execute a measurement method for measuring a three-dimensional shape of a measurement target by a three-dimensional shape measurement apparatus, reflecting one aspect of the present invention is provided. The measurement method comprises: determining a cycle of a stripe pattern to be projected by a projector including a projector lens, from a plurality of cycle candidates; projecting the stripe pattern by the projector; capturing an image of the stripe pattern projected by the projector, by a camera including a camera lens, to acquire the captured image of the stripe pattern; and measuring a three-dimensional shape of the measurement target based on the captured image. The plurality of cycle candidates are set based on a synthetic MTF characteristic generated by combining a first MTF characteristic of the projector lens and a second MTF characteristic of the camera lens.
The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention.
Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. In the following description, the same parts and constituent elements are denoted with the same reference signs. Their names and functions are the same. Therefore, a detailed description thereof will not be repeated. Note that the embodiments and modifications described below may be selectively combined as appropriate.
The three-dimensional shape measurement apparatus 100 measures a three-dimensional shape of a measurement target 300 using the principle of the phase shift method. The measurement target 300 includes a tray 302 and a plurality of workpieces 304 placed in bulk on the tray 302. The three-dimensional shape measurement apparatus 100 outputs, to the robot 200, data (hereinafter referred to as “three-dimensional point cloud data”) indicating the measured three-dimensional shape.
Based on the three-dimensional point cloud data received from the three-dimensional shape measurement apparatus 100, the robot 200 determines a workpiece 304 to be grasped and performs a pick-and-place operation for the workpiece 304 to be grasped. Specifically, the robot 200 grasps a workpiece 304 on the tray 302 and places the workpiece 304 on a conveyance belt 500.
Note that the system to which the three-dimensional shape measurement apparatus 100 is applied is not limited to the system 1000 illustrated in
The projector 1 includes a light source 11, a light modulation apparatus 12, and a projection optical system 13. A light flux emitted from the light source 11 is modulated by the light modulation apparatus 12 and is projected on the measurement target 300 via the projection optical system 13.
The light source 11 includes, for example, a light emitting diode (LED), an ultra-high pressure mercury lamp, or a halogen lamp. For example, the light source 11 emits white light. Note that the light source 11 may emit monochromatic light of red, blue, or green.
The light modulation apparatus 12 modulates the light from the light source 11 to generate a projection image. The light modulation apparatus 12 includes an image display element 121. The image display element 121 is, for example, a digital micromirror device (DMD) or a liquid crystal panel. In the present embodiment, the light modulation apparatus 12 is capable of generating a stripe pattern as a projection image. Here, the stripe pattern will be described with reference to
Referring again to
The camera 2 captures an image of a subject and generates image data (hereinafter referred to as “captured image”). By way of example, the camera 2 captures an image of the stripe pattern projected on the measurement target 300 by the projector 1 to acquire the captured image of the stripe pattern. The camera 2 includes a camera sensor 21 and a light-collection optical system 22.
The camera sensor 21 converts, into an electric signal, the intensity of light obtained through the light-collection optical system 22. The camera sensor 21 includes, for example, a charge coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS).
The light-collection optical system 22 is an optical system for collecting light incident from the outside, and typically includes one or more lenses. In the example illustrated in
The cycle L of the stripe pattern in the captured image, that is, the stripe pattern on the camera sensor 21 differs from the cycle L of the stripe pattern on the measurement surface 305.
The distance measurement device 4 is disposed at the same height as that of the projector 1. The distance measurement device 4 measures a distance d1 between the projector 1 and the measurement target 300. Hereinafter, the distance d1 measured by the distance measurement device 4 is referred to as “measurement distance.” The distance measurement device 4 includes, for example, a millimeter-wave sensor or the like that can measure the distance in a short time. However, the distance measurement device 4 is not limited thereto, and may be configured as a known distance measurement sensor.
The distance measurement device 4 may measure, for example, the distance to a partial range 308 that is a part of the measurement target 300. The partial range 308 has a length of, for example, one cycle of the stripe pattern on the measurement surface 305.
A user adjusts the focus of the projector lens 131 and the focus of the camera lens 221 depending on the distances d1 between the projector 1 and the measurement target 300. Note that the projector 1 may include an autofocus mechanism that automatically adjusts the focus of the projector lens 131 on the measurement target 300. Further, the camera 2 may include an autofocus mechanism that automatically adjusts the focus of the camera lens 221 on the measurement target 300.
The computer 3 controls the projector 1, the camera 2, and the distance measurement device 4. The computer 3 includes a processor 31, a memory 32, and a storage 33.
The processor 31 is an example of “hardware processor” in the present disclosure. The processor 31 is constituted, for example, of a central processing unit (CPU), a micro-processing unit (MPU), or the like. The memory 32 is constituted, for example, of a volatile storage device such as a dynamic random access memory (DRAM) or a static random access memory (SRAM). The storage 33 is constituted, for example, of a nonvolatile storage device such as a hard disk drive (HDD), a solid state drive (SSD), or a flash memory.
The storage 33 stores a program 34. The program 34 includes one or more computer-readable instructions for controlling the projector 1, the camera 2, and the distance measurement device 4. The program 34 includes a “measurement program” in the present disclosure. The storage 33 is an example of “non-transitory computer-readable recording medium” in the present disclosure. The processor 31 controls the projector 1, the camera 2, and the distance measurement device 4 by executing the program 34, to thereby implement various types of processing according to the present embodiment.
The program 34 may be incorporated in a part of an appropriate program and provided, rather than provided as a single program. In this case, the processing according to the present embodiment is implemented in cooperation with the appropriate program. Such a program that does not include a part of modules is not deviated from the gist of the three-dimensional shape measurement apparatus 100 according to the present embodiment. Further, part or all of the functions provided by the program 34 may be implemented by dedicated hardware.
The storage 33 further stores a table 35. The table 35 is used for controlling the cycle L of the stripe pattern projected by the projector 1.
The processor 31 measures the three-dimensional shape of the measurement target 300 using the principle of the phase shift method. Specifically, the processor 31 controls the projector 1 to project the stripe pattern while shifting the phase. The processor 31 acquires, from the camera 2, a plurality of captured images corresponding to a plurality of phase shift amounts of the stripe pattern. For example, the processor 31 acquires four captured images for respective phase shift amounts of 0, π/2, π, and 3π/2.
The luminance value of each pixel in the plurality of captured images is expressed by the following formula (1).
Ii=a cos(φ+δi)+b Formula (1)
“Ii” represents the luminance value in an i-th captured image. “a” represents a contrast component. “b” represents an offset component. “δi” represents a phase shift amount corresponding to the i-th captured image. “φ” represents a phase.
In Formula (1), unknowns are “a”, “b”, and “p”. Therefore, the processor 31 can calculate “a”, “b”, and “φ” for each pixel by acquiring at least three captured images.
tan φ=−(I3−I1)/(I2−I0) Formula (2)
The phase φ and the height h of the measurement target 300 in the pixel satisfy the following formula (3).
h=(p/sin α)×(φ+2nπ)/2π Formula (3)
“p” represents a pitch of the stripe pattern. “α” represents a projection angle of the stripe pattern. “n” represents an order. The processor 31 converts the phase φ into the height h in accordance with Formula (3), and generates three-dimensional point cloud data indicating the height h for each pixel.
The luminance value of each pixel indicated by the captured image may include an error due to an influence of noise of the camera 2, a linearity error of the projector 1, or the like. Hereinafter, the error included in the luminance value is referred to as “luminance error.”
Due to the influence of the phase error Δφ, an error is also generated in the height h converted from the phase φ. In the example illustrated in
If the amplitude of the luminance value when the phase shift amount is changed is decreased, the influence of the luminance error becomes relatively large. As a result, the phase error Δφ is increased to result in an increased error included in the height h converted from the phase φ. Hereinafter, the error of the height h is also referred to as “measurement error.”
The amplitude of the luminance value when the phase shift amount is changed is correlated with the contrast of the stripe pattern in the captured image. If the contrast of the stripe pattern in the captured image is decreased, the amplitude of the luminance value when the phase shift amount is changed is decreased. Therefore, if the contrast of the stripe pattern in the captured image is decreased, the error included in the height h converted from the phase φ is increased.
A line 61 represents an MTF characteristic of the lens a. The MTF characteristic of the lens a indicates a correlation between the spatial frequency and the contrast of the image of the stripe pattern formed by the lens a. A line 62 represents an MTF characteristic of a lens b, which is different from the lens a. The MTF characteristic of the lens b indicates a correlation between the spatial frequency and the contrast of the image of the stripe pattern formed by the lens b. A line 63 represents a correlation between the spatial frequency and the accuracy of conversion from a phase φ to a height h.
As illustrated in
In view of the characteristics illustrated in
Therefore, for the three-dimensional shape measurement apparatus 100 according to the present embodiment, cycle candidates of the stripe pattern are set in consideration of the contrast and the accuracy of conversion from the phase φ to the height h.
The distance measurement device 4 measures the distance d1 (i.e., measurement distance) between the projector 1 and the measurement target 300. The determination unit 351 determines, from a plurality of cycle candidates, the cycle L of the stripe pattern projected on the measurement target 300 by the projector 1, based on the measurement distance measured by the distance measurement device 4. The plurality of cycle candidates are included in a table 35 stored in the storage 33.
The light modulation apparatus 12 generates a stripe pattern having the cycle L determined by the determination unit 351. The projection optical system 13 enlarges and projects, on the measurement target 300, the stripe pattern generated by the light modulation apparatus 12.
The camera 2 captures an image of the stripe pattern projected by the projector 1 and acquires the captured image of the stripe pattern. The measurement unit 352 measures the three-dimensional shape of the measurement target 300 based on the captured image using the principle of the phase shift method.
A method of setting the cycle candidate will be described with reference to
In a first step of the method of setting the cycle candidate, an MTF characteristic of the projector lens 131 and an MTF characteristic of the camera lens 221, for the distance d1 between the projector 1 and the measurement target 300 are acquired by an experiment. A line 91a represents the MTF characteristic of the projector lens 131 in the case where the distance d1 between the projector 1 and the measurement target 300 is 200 mm. A line 91b represents the MTF characteristic of the projector lens 131 in the case where the distance d1 between the projector 1 and the measurement target 300 is 300 mm. A line 91c represents the MTF characteristic of the projector lens 131 in the case where the distance d1 between the projector 1 and the measurement target 300 is 500 mm. A line 92a represents the MTF characteristic of the camera lens 221 in the case where the distance d1 between the projector 1 and the measurement target 300 is 200 mm. A line 92b represents the MTF characteristic of the camera lens 221 in the case where the distance d1 between the projector 1 and the measurement target 300 is 300 mm. A line 92c represents the MTF characteristic of the camera lens 221 in the case where the distance d1 between the projector 1 and the measurement target 300 is 500 mm.
The MTF characteristic of the projector lens 131 is an example of “first MTF characteristic” in the present disclosure. The MTF characteristic of the projector lens 131 represents a correlation between the spatial frequency on the image display element 121 (the cycle L of the stripe pattern on the image display element 121) and a first contrast representing the contrast performance of the projector lens 131.
The MTF characteristic of the camera lens 221 is an example of “second MTF characteristic” in the present disclosure. The MTF characteristic of the camera lens 221 represents a correlation between the spatial frequency on the camera sensor 21 (the cycle L of the stripe pattern on the camera sensor 21) and a second contrast representing the contrast performance of the camera lens 221.
The MTF characteristic of the projector lens 131 for a target distance among a plurality of distances between the projector 1 and the measurement target 300, and the MTF characteristic of the camera lens 221 for the target distance are acquired in accordance with a method of acquiring the MTF characteristic described below.
In a first step of the method of acquiring the MTF characteristic, a screen is installed at a position located away from the projector 1 by the target distance, and the projector lens 131 and the camera lens 221 are focused on the surface of the screen.
In a second step of the method of acquiring the MTF characteristic, a plurality of stripe patterns having different cycles L are sequentially projected on the screen by the projector 1.
In a third step of the method of acquiring the MTF characteristic, for each stripe pattern projected on the screen, the contrast in a predetermined region including the position on an optical axis k1 (see
In a fourth step of the method of acquiring the MTF characteristic, the MTF characteristic of the projector lens 131 is generated by associating the spatial frequency of the stripe pattern on the image display element 121 that is projected on the screen, with the contrast of the stripe pattern measured in the third step of the method of acquiring the MTF characteristic.
In a fifth step of the method of acquiring the MTF characteristic, a plurality of test charts are sequentially arranged on the screen and their images are captured by the camera 2. A stripe pattern is drawn on each test chart. The plurality of test charts have different cycles L of the stripe patterns from each other.
In a sixth step of the method of acquiring the MTF characteristic, for each test chart, the contrast on the camera sensor 21 is measured for a predetermined region including the position on an optical axis k2 (see
In a seventh step of the method of acquiring the MTF characteristic, the MTF characteristic of the camera lens 221 is generated by associating the spatial frequency, on the camera sensor 21, of the stripe pattern drawn on the test chart, with the contrast of the test chart measured in the sixth step of the method of acquiring the MTF characteristic.
In this way, the MTF characteristic of the projector lens 131 and the MTF characteristic of the camera lens 221 are acquired for each of a plurality of distances between the projector 1 and the measurement target 300.
In a second step of the method of setting the cycle candidate, a synthetic MTF characteristic for the distance d1 between the projector 1 and the measurement target 300 is generated. A line 93a represents a synthetic MTF characteristic in the case where the distance d1 between the projector 1 and the measurement target 300 is 200 mm. A line 93b represents a synthetic MTF characteristic in the case where the distance d1 between the projector 1 and the measurement target 300 is 300 mm. A line 93c represents a synthetic MTF characteristic in the case where the distance d1 between the projector 1 and the measurement target 300 is 500 mm.
The synthetic MTF characteristic is generated by combining the MTF characteristic of the projector lens 131 and the MTF characteristic of the camera lens 221. The synthetic MTF characteristic represents a correlation between the spatial frequency on the image display element 121 (the cycle L of the stripe pattern on the image display element 121) and a third contrast. The third contrast is expressed by the following Formula (4).
R=Q1/100×Q2/100×100 Formula (4)
“R” represents the third contrast (%) for a first spatial frequency P1 on the image display element 121 indicated by the synthetic MTF characteristic. “Q1” represents a first contrast (%) for the first spatial frequency P1 on the image display element 121 indicated by the MTF characteristic of the projector lens 131. “Q2” represents a second contrast (%) for a second spatial frequency P2 on the camera sensor 21 indicated by the MTF characteristic of the camera lens 221. The first spatial frequency P1 on the image display element 121 and the second spatial frequency P2 on the camera sensor 21 have the same spatial frequency on the measurement surface 305 of the three-dimensional shape measurement apparatus 100.
The first spatial frequency on the image display element 121 and the second spatial frequency on the camera sensor 21 that have the same spatial frequency on the measurement surface 305 are specified by a first conversion process and a second conversion process.
The first conversion process is a process of converting, based on the following three elements e1 to e3, the first spatial frequency on the image display element 121 of the MTF characteristic of the projector lens 131, into the spatial frequency on the measurement surface 305 of the three-dimensional shape measurement apparatus 100.
The second conversion process is a process of converting, based on the following three elements e4 to e6, the second spatial frequency on the camera sensor 21 of the MTF characteristic of the camera lens 221, into the spatial frequency on the measurement surface 305 of the three-dimensional shape measurement apparatus 100.
“Ra” illustrated in
In this way, the synthetic MTF characteristic is generated for each of the plurality of distances between the projector 1 and the measurement target 300.
In a third step of the method of setting the cycle candidate, a cycle candidate is set for each of the plurality of distances between the projector 1 and the measurement target 300. More specifically, in the case where a cycle candidate for a target distance among the plurality of distances between the projector 1 and the measurement target 300 is set, the cycle candidate is set to the shortest cycle in a range of the cycle of the stripe pattern for which the third contrast is equal to or more than a predetermined value, for the synthetic MTF characteristic for the target distance.
In step S1, the processor 31 acquires a measurement distance from the distance measurement device 4. In the next step S2, the processor 31 determines the cycle L of the stripe pattern to be projected by the projector 1, based on the measurement distance.
Step S2 includes steps S21 and S22. In step S21, the processor 31 reads, from the table 35, the cycle candidate associated with the measurement distance. In the next step S22, the processor 31 determines the cycle L of the stripe pattern on the basis of the read cycle candidate.
For example, when a distance that is different from the measurement distance by an extent falling in a predetermined range is included in the table 35, the processor 31 reads the cycle candidate associated with this distance and determines the read cycle candidate as the cycle L of the stripe pattern. When a distance that is different from the measurement distance by an extent falling in the predetermined range is not included in the table 35, the processor 31 reads two cycle candidates associated with two distances different from the measurement distance by a smaller extent, and determines the cycle L of the stripe pattern by an interpolation using the read two cycle candidates.
In the next step S3, the processor 31 instructs the projector 1 to project the stripe pattern having the cycle L determined in step S2 on the measurement target 300. Thus, the projector 1 projects, on the measurement target 300, the stripe pattern in an enlarged form having the cycle L determined in step S2.
In the next step S4, the processor 31 causes the camera 2 to capture an image of the stripe pattern projected on the measurement target 300, and acquires the captured image of the stripe pattern from the camera 2. In the next step S5, the processor 31 identifies the three-dimensional shape of the measurement target 300 based on the captured image, by using the principle of the phase shift method. After step S5, the measurement process ends.
Thus, the three-dimensional shape measurement apparatus 100 according to the present embodiment determines the cycle L of the stripe pattern to be projected by the projector 1, from a plurality of cycle candidates. The plurality of cycle candidates are set on the basis of a synthetic MTF characteristic generated by combining the MTF characteristic of the projector lens 131 and the MTF characteristic of the camera lens 221. Therefore, the three-dimensional shape measurement apparatus 100 according to the present embodiment can improve the measurement accuracy of the three-dimensional shape, relative to the measurement accuracy in the case where the cycle L of the stripe pattern is set by using the MTF characteristic of the projector lens without using the MTF characteristic of the camera lens.
The third contrast for the first spatial frequency on the image display element 121 indicated by the synthetic MTF characteristic is acquired by multiplying the first contrast for the first spatial frequency on the image display element 121 indicated by the MTF characteristic of the projector lens 131 by the second contrast for the second spatial frequency on the camera sensor 21 indicated by the MTF characteristic of the camera lens 221. The first spatial frequency on the image display element 121 and the second spatial frequency on the camera sensor 21 have the same spatial frequency on the measurement surface 305 of the three-dimensional shape measurement apparatus 100. Therefore, an error between the third contrast indicated by the synthetic MTF characteristic and the contrast of the stripe pattern on the camera sensor 21 in the actual measurement process is reduced. Thus, the three-dimensional shape measurement apparatus 100 according to the present embodiment can improve the measurement accuracy of the three-dimensional shape.
Moreover, in the three-dimensional shape measurement apparatus 100 according to the present embodiment, cycle candidates are set for all of a plurality of distances between the projector 1 and the measurement target 300. As described above with reference to
In Modification 1, the table 35 associates each of a plurality of cycle candidates with a combination of the distance between the projector 1 and the measurement target 300, the f-number of the projector lens 131, and the f-number of the camera lens 221.
In Modification 1, in the first step of the method of setting the cycle candidate, the MTF characteristic of the projector lens 131 and the MTF characteristic of the camera lens 221 for the combination of the distance between the projector 1 and the measurement target 300, the f-number of the projector lens 131, and the f- number of the camera lens 221 are acquired by an experiment.
In Modification 1, in the second step of the method of setting the cycle candidate, a synthetic MTF characteristic for the combination of the distance between the projector 1 and the measurement target 300, the f-number of the projector lens 131, and the f-number of the camera lens 221 is generated.
In Modification 1, in the third step of the method of setting the cycle candidate, the cycle candidate is set for each of a plurality of combinations of the distance between the projector 1 and the measurement target 300, the f-number of the projector lens 131, and the f-number of the camera lens 221. More specifically, when the cycle candidate for a target combination among a plurality of combinations of the distance between the projector 1 and the measurement target 300, the f-number of the projector lens 131, and the f-number of the camera lens 221 is set, the cycle candidate is set to the shortest cycle in a range of the cycle of the stripe pattern for which the third contrast is equal to or larger than a predetermined value for the synthetic MTF characteristic for the target combination.
The determination unit 351 determines the cycle L of the stripe pattern to be projected on the measurement target 300 by the projector 1, from a plurality of cycle candidates included in the table 35, based on the combination of the distance between the projector 1 and the measurement target 300, the f-number of the projector lens 131, and the f-number of the camera lens 221. Modification 1 is similar to the above-described embodiment in other respects.
Thus, according to Modification 1, the cycle L of the stripe pattern to be projected on the measurement target 300 by the projector 1 is determined to be a cycle based on the combination of the distance between the projector 1 and the measurement target 300, the f-number of the projector lens 131, and the f-number of the camera lens 221. Thus, according to Modification 1, the measurement accuracy of the three-dimensional shape is improved.
In general, the contrast of an image of a stripe pattern formed by a lens decreases as the distance from the optical axis of the lens increases. In view of this, in Modification 2, the MTF characteristic of the projector lens 131 corresponds to a first position farthest from the optical axis k1 of the projector lens 131, in a measurement region 306 of the three-dimensional shape measurement apparatus 100. Furthermore, in Modification 2, the MTF characteristic of the camera lens 221 corresponds to a second position farthest from the optical axis k2 of the camera lens 221, in the measurement region 306. The measurement region 306 is a region where the projection range of the projector 1 and the image capturing range of the camera 2 overlap each other. In
In Modification 2, the MTF characteristic of the projector lens 131 for a target distance among a plurality of distances between the projector 1 and the measurement target 300 and the MTF characteristic of the camera lens 221 for the target distance are acquired by the following method of acquiring the MTF characteristic.
The method of acquiring the MTF characteristic in Modification 2 differs from the method of acquiring the MTF characteristic in the above embodiment, in terms of the third step and the sixth step. In the steps other than the third step and the sixth step, the method of acquiring the MTF characteristic in Modification 2 is the same as the method of acquiring the MTF characteristic in the above-described embodiment.
In Modification 2, in the third step of the method of acquiring the MTF characteristic, the contrast is measured in a predetermined region including the first position farthest from the optical axis k1 of the projector lens 131, in the measurement region 306, for each stripe pattern projected on the screen. The first position farthest from the optical axis k1 of the projector lens 131 in the measurement region 306 is, for example, the vertex v4 illustrated in
In Modification 2, in the sixth step of the method of acquiring the MTF characteristic, the contrast on the camera sensor 21 is measured, for each test chart, for a predetermined region including the second position farthest from the optical axis k2 of the camera lens 221 in the measurement region 306. The second position farthest from the optical axis k2 of the camera lens 221 in the measurement region 306 is, for example, the vertex v2 illustrated in
Regarding the projector lens 131, the contrast is likely to decrease at the first position in the measurement region 306. Regarding the camera lens 221, the contrast is likely to decrease at the second position in the measurement region 306.
As seen from the above, in Modification 2, the first contrast and the second contrast are different from those of the above embodiment. Modification 2, however, is similar to the above embodiment in other respects.
Therefore, according to Modification 2, the synthetic MTF characteristic is generated by combining the MTF characteristic of the projector lens 131 and the MTF characteristic of the camera lens 221 at positions where the contrast is low in the measurement region 306. Thus, according to Modification 2, the three-dimensional shape measurement apparatus 100 can make the measurement accuracy of the three-dimensional shape equal to or higher than a specified value, at any position in the measurement region 306.
In general, when the distance d1 between the projector 1 and the measurement target 300 changes in a state where the projector lens 131 is focused on the measurement target 300, the contrast of an image of a stripe pattern formed by the projector lens 131 decreases. That is, in a state where the projector lens 131 is focused on a measurement bottom surface 309a of the measurement region 306 of the three-dimensional shape measurement apparatus 100, the contrast of the stripe pattern projected on a measurement top surface 309b of the measurement region 306 of the three-dimensional shape measurement apparatus 100 is lower than the contrast of the stripe pattern projected on the measurement bottom surface 309a.
When the distance between the camera 2 and the measurement target 300 changes in a state where the camera lens 221 is focused on the measurement target 300, the contrast of an image of a stripe pattern formed by the camera lens 221 decreases.
In view of this, in Modification 3, the MTF characteristic of the projector lens 131 corresponds to the measurement top surface 309b of the measurement region 306 in a first state where the projector lens 131 is focused on the measurement bottom surface 309a of the measurement region 306 of the three-dimensional shape measurement apparatus 100. Furthermore, in Modification 3, the MTF characteristic of the camera lens 221 corresponds to the measurement top surface 309b of the measurement region 306 in a second state where the camera lens 221 is focused on the measurement bottom surface 309a of the measurement region 306 of the three-dimensional shape measurement apparatus 100.
In Modification 3, the MTF characteristic of the projector lens 131 for a target distance among a plurality of distances between the projector 1 and the measurement target 300 and the MTF characteristic of the camera lens 221 for the target distance are acquired by the following method of acquiring the MTF characteristic.
In the method of acquiring the MTF characteristic according to Modification 3, step 1A and step 1B described below are added to the method of acquiring the MTF characteristic according to the embodiment described above. Step 1A is performed after the first step of the method of acquiring the MTF characteristic according to the above embodiment.
In step 1A, a height d2 of the measurement region 306 of the three-dimensional shape measurement apparatus 100 is calculated. The height d2 is the distance between the measurement bottom surface 309a and the measurement top surface 309b. After step 1A, step 1B is performed.
In step 1B, the distance between the projector 1 and the screen is reduced by the height d2 calculated in step 1A. After step 1B, the second step to the seventh step of the method of acquiring the MTF characteristic in the above embodiment are performed.
Thus, Modification 3 differs from the above embodiment in terms of the first contrast and the second contrast. Modification 3, however, is similar to the above embodiment in other respects.
Therefore, according to Modification 3, in a state where the projector lens 131 and the camera lens 221 are focused on the measurement bottom surface 309a, the MTF characteristic of the projector lens 131 and the MTF characteristic of the camera lens 221 at the measurement top surface 309b located at the farthest position from the measurement bottom surface 309a in the measurement region 306 are combined to generate the synthetic MTF characteristic. Thus, according to Modification 3, the three-dimensional shape measurement apparatus 100 can make the measurement accuracy of a three-dimensional shape equal to or higher than a specified value, at any position in the measurement region 306.
While the three-dimensional shape measurement apparatus 100 includes the distance measurement device 4 in the above embodiment, it may not include the distance measurement device 4. In the case where the three-dimensional shape measurement apparatus 100 does not include the distance measurement device 4, a user may input a measurement distance to the three-dimensional shape measurement apparatus 100. In the case where the user inputs the measurement distance to the three-dimensional shape measurement apparatus 100, the processor 31 receives the measurement distance from the user in step S1 in
Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2024-003795 | Jan 2024 | JP | national |
