JP7558726B2 - Measurement program and measuring device - Google Patents

Description

Embodiments of the present invention relate to a measurement program and a measurement device.

Various techniques have been developed to measure the two-dimensional distribution of the amount of light deflection caused by the refractive index distribution and refractive index gradient inside an optically transparent object such as a lens on a specified projection surface of the object.

JP 2012-117999 A

It would be desirable for the above-mentioned technology to be able to measure not only the two-dimensional distribution of the amount of deflection of light generated in the measurement object, but also the three-dimensional distribution of features related to the amount of deflection (e.g., features that cause the deflection) within the measurement object.

The measurement program according to the embodiment is a measurement program that causes a computer to execute the following operations: acquiring an image from an imaging device that shows a background image through an optically transparent measurement target; measuring a two-dimensional distribution of the amount of deflection of light generated in the measurement target on a projection plane of the measurement target that intersects with the optical axis of the imaging device based on a comparison between the acquired image and a predetermined reference image; acquiring the symmetry of the shape of the measurement target; and measuring a three-dimensional distribution of features related to the amount of deflection inside the measurement target based on the two-dimensional distribution and the symmetry.

FIG. 1 is an exemplary schematic diagram showing an overall configuration of a measurement system according to an embodiment. FIG. 2 is an illustrative schematic diagram showing an example of a captured image obtained when positioning a measurement target according to the embodiment. FIG. 3 is an exemplary schematic block diagram showing the functions of the measurement device according to the embodiment. FIG. 4 is an exemplary schematic flowchart showing a series of processes executed by the measurement device according to the embodiment. FIG. 5 is an exemplary schematic block diagram showing a hardware configuration of the measurement device according to the embodiment. FIG. 6 is an exemplary schematic diagram showing a measurement target according to a modified example.

Embodiments and variants of the present disclosure will be described below with reference to the drawings. The configurations of the embodiments and variants described below, as well as the actions and effects brought about by said configurations, are merely examples and are not limited to the contents described below.

<Embodiment>
FIG. 1 is an exemplary schematic diagram showing an overall configuration of a measurement system according to an embodiment.

The measurement system according to the embodiment is based on the configuration described below and performs a method known as the Schlieren method or background-type Schlieren method to measure the three-dimensional distribution of features related to the refractive index distribution and the deflection of light caused by the refractive index gradient of an optically transparent object such as a lens.

The following mainly describes a configuration for measuring the three-dimensional distribution of the refractive index, which is one of the above-mentioned features, but according to the technology of the embodiment, it is also possible to measure the three-dimensional distribution of other physical quantities related to the refractive index, such as density, temperature, stress, concentration, or sound pressure. Note that while a quantitative evaluation of density, temperature, stress, concentration, or sound pressure cannot be performed unless the refractive index is specified, a qualitative evaluation of density, temperature, stress, concentration, or sound pressure can be performed without specifying the refractive index.

As shown in FIG. 1, the measurement system according to the embodiment includes a measurement object 10, an imaging device 21, a background image 22, an illumination device 23, a symmetry detection device 24, a reference surface 25, a stage 26, a lens effect suppression structure 27, and a measurement device 30.

In the example shown in FIG. 1, for ease of explanation, the X-axis, Y-axis, Z-axis, θ-direction, φ-direction, and ψ-direction are defined. The X-axis is defined to be along the optical axis Ax11 of the imaging device 21 in the horizontal plane, and the Y-axis is defined to be perpendicular to the X-axis in the horizontal plane. The Z-axis is defined to be along the vertical direction perpendicular to the X-axis and Y-axis. The θ-direction, φ-direction, and ψ-direction are defined as rotation directions around the Z-axis, X-axis, and Y-axis, respectively.

The measurement object 10 is configured as a lens in which a cylindrical portion 11 and a hemispherical portion 12 are integrated. More specifically, the measurement object 10 is configured to be axially symmetrical around an axis of symmetry Ax20 extending in the Z direction. Note that the measurement object 10 shown in FIG. 1 is merely an example. Therefore, the technology of the embodiment can be applied to measurement objects having shapes different from the measurement object 10 shown in FIG. 1. In the example shown in FIG. 1, the measurement object 10 is disposed at a position where the optical axis Ax11 of the imaging device 21 intersects with the axis Ax12 extending along the Y axis at the position of X=0. In general, the refractive index inside an optical component such as a lens is non-uniform due to the influence of molding conditions, etc. Ideally, it is considered that an axially symmetric refractive index distribution occurs inside a lens having an axially symmetric shape.

The imaging device 21 is, for example, a digital camera that captures a background image 22 through the measurement object 10 and a lens effect suppression structure 27 described below. Note that the magnification of the captured image obtained by imaging the imaging device 21, taking into account the optical distance inside the measurement object 10 and the lens effect suppression structure 27, is assumed to be known.

The background image 22 is, for example, a random dot pattern printed on a film. The background image 22 is set parallel to the Y-Z plane, and the X coordinate is known. Details will be described later, but in the embodiment, the two-dimensional distribution of the deflection amount of light generated in the measurement object 10 on the projection plane as a plane parallel to the cross section along the Y-Z plane is measured based on the displacement amount of the dots calculated by comparing the captured image obtained by the imaging device 21 in a state in which the measurement object 10 and the lens effect suppression structure 27 are interposed between the imaging device 21 and the background image 22 with a predetermined reference image corresponding to the captured image obtained by the imaging device 21 in a state in which the measurement object 10 and the lens effect suppression structure 27 are not interposed between the imaging device 21 and the background image 22. Alternatively, a two-dimensional distribution of the amount of light deflection occurring in the measurement target 10 on a projection plane as a plane parallel to a cross section along the Y-Z plane may be measured based on the displacement of dots calculated by comparing an image captured by the imaging device 21 in a state where the measurement target 10 and the lens effect suppression structure 27 are interposed between the imaging device 21 and the background image 22 with a predetermined reference image corresponding to an image captured by the imaging device 21 in a state where the measurement target 10 is not interposed between the imaging device 21 and the background image 22. Such a method for measuring the two-dimensional distribution of the refractive index of the measurement target 10 may be called the Schlieren method or the background type Schlieren method. In the Schlieren method or the background type Schlieren method, the method of selecting the reference image and the captured image to be compared with the reference image may vary depending on the purpose of the measurement.

The lighting device 23 is a light source such as a red LED that emits monochromatic red light. Note that the light source used as the lighting device 23 in the embodiment may be a light source other than a red LED, such as an infrared LED that emits infrared light, as long as it takes into account the wavelength dependency of the refractive index, which is a physical property of the measurement object 10, and emits light of a wavelength that has a narrow range of refractive index in the measurement object 10 corresponding to the wavelength spectrum width of the light source. Depending on the required measurement accuracy, general light sources such as sunlight, white light, or various types of lighting may also be used.

The symmetry detection device 24 detects the symmetry of the measurement object 10. For example, in the example shown in FIG. 1, the symmetry detection device 24 outputs laser light in a direction along the Z axis to the reference plane 25 via the measurement object 10, and detects the arrival position of the laser light on the reference plane 25 to detect whether the position of the symmetry axis Ax20 of the measurement object 10 coincides with the optical axis of the laser light.

More specifically, in the example shown in FIG. 1, the reference surface 25 is provided with a reference position P25 that the laser light from the symmetry detection device 24 reaches when it travels straight on the surface and inside the measurement object 10 without deflection. When the laser light passes through the symmetry axis of the measurement object 10, the laser light passes through an axis that has no refractive index gradient due to axial symmetry, so ideally the laser light is not deflected. In other words, when the laser light from the symmetry detection device 24 reaches the reference position P25, it can be said that the symmetry axis Ax20 of the measurement object 10 coincides with the optical axis of the laser light. Therefore, the symmetry detection device 24 detects the position of the symmetry axis of the measurement object 10 based on whether the laser light reaches the reference position P25 or not.

The method of detecting symmetry is not limited to the above method. For example, the symmetry detection device 24 may be configured as a laser interferometer or a laser microscope that measures the surface shape of the measurement target 10. In this case, if the surface shape of the measurement target 10 is axially symmetric about the Z axis, the symmetry detection device 24 can use a known method such as combinatorial Hough transformation to detect whether the symmetry axis coincides with the Z axis using the measured surface shape. In addition, if the surface shape of the measurement target 10 is uniform in the X axis direction and has a symmetry plane parallel to the X-Z plane or the Y-Z plane, the symmetry detection device 24 can detect the symmetry plane using a known method such as combinatorial Hough transformation and detect whether the symmetry plane coincides with the X-Z plane or the Y-Z plane.

The detection results of the symmetry detection device 24 can be displayed in real time on the display 32 via the measurement device 30. In addition, the symmetry detection device 24 can also acquire and refer to shape data of the measurement object 10 for use in predicting the position of the axis of symmetry when detecting symmetry. The symmetry detection device 24 may also detect the symmetry of the measurement object 10 using an image captured by the imaging device 21. In this case, since there is no need to use laser light for detecting symmetry, there is no need to provide a reference surface 25, and there is no need to position the measurement object 10 between the symmetry detection device 24 and the reference surface 25.

The stage 26 supports the measurement object 10 in a desired position and orientation. The stage 26 fixes the measurement object 10 in a position and orientation suitable for imaging by the imaging device 21, for example, so that the refractive index of the measurement object 10 in the measurement system is properly measured. Note that the position and orientation of the measurement object 10 may be changed automatically in response to the drive of a six-axis actuator (not shown) or a required number of axes, or may be changed manually in response to human operation. The position and orientation of the measurement object 10 may also be changed taking into account the detection results of the symmetry detection device 24.

In light of the above, when the measurement target 10 is positioned by the stage 26, the way in which the measurement target 10 is captured in the image obtained by the imaging device 21 changes as shown in the following Figure 2.

Figure 2 is an illustrative and schematic diagram showing an example of an image obtained when positioning the measurement target 10 according to an embodiment.

In the example shown in FIG. 2, image IM201 shows an image obtained before the positioning of the measurement object 10 is completed. In this image IM201, the measurement object 10 is captured in a position shifted from the center. Then, when the positioning of the measurement object 10 is completed, an image such as image IM202 in which the measurement object 10 is captured near the center is obtained. At this time, an arrow A201 indicating the axial direction as the orientation of the symmetry axis Ax20 and an arrow A202 indicating the radial direction relative to the axial direction can be displayed on the image IM202 as the detection results of the symmetry detection device 24.

Returning to FIG. 1, the lens effect suppression structure 27 is a structure that suppresses the lens effect caused by the surface shape of the measurement object 10. The lens effect suppression structure 27 is not a necessary structure for measuring the refractive index of the measurement object 10, but is an effective structure when it is difficult to capture the background image 22 from the imaging device 21. For example, the lens effect suppression structure 27 is realized as a lens having a surface shape with the opposite concave and convex shapes to the measurement object 10. The lens effect suppression structure 27 may also be realized by immersing the measurement object 10 in a liquid such as a glycerin aqueous solution or silicone oil having a refractive index approximately equal to that of the measurement object 10.

The measuring device 30 measures the refractive index as a feature related to the deflection of light occurring in the measurement object 10, based on the captured image obtained by the imaging device 21 and the symmetry detected by the symmetry detection device 24. The measuring device 30 is configured as an information processing device such as a PC that can accept input from a keyboard 31 and output images to a display 32.

Here, various methods have been considered for measuring the two-dimensional distribution of the deflection amount on a predetermined projection plane onto which the measurement object 10 is projected, such as the above-mentioned Schlieren method and background-type Schlieren method. However, it would be desirable to be able to measure not only the two-dimensional distribution of the refractive index on the projection plane, but also the three-dimensional distribution inside the measurement object 10.

Therefore, the measurement device 30 according to the embodiment measures the three-dimensional distribution of refractive index inside the measurement object 10 based on the functions described below.

Figure 3 is an exemplary schematic block diagram showing the functions of the measurement device 30 according to an embodiment.

As shown in FIG. 3, the measuring device 30 according to the embodiment includes an image acquisition unit 301, a first measurement unit 302, a symmetry acquisition unit 303, and a second measurement unit 304.

The image acquisition unit 301 acquires an image from the imaging device 21, which shows the measurement target 10 and a background image through the lens effect suppression structure 27. The first measurement unit 302 then measures the two-dimensional distribution of the amount of deflection of light occurring inside the measurement target 10 on a projection plane along the Y-Z plane intersecting with the optical axis Ax11 of the imaging device 21, based on a comparison between the image acquired by the image acquisition unit 301 and the reference image described above.

Then, the symmetry acquisition unit 303 acquires the symmetry of the measurement target 10 as the detection result of the symmetry detection device 24. The second measurement unit 304 then measures the three-dimensional distribution of the refractive index inside the measurement target 10 based on the two-dimensional distribution of the deflection amount measured by the first measurement unit 302 and the symmetry acquired by the symmetry acquisition unit 303.

For example, the three-dimensional distribution of the refractive index of the axially symmetric measurement target 10 can be obtained by mathematically reconstructing the two-dimensional distribution of the deflection amount of the light beam measured as a two-dimensional distribution of the displacement amount of the dot pattern. For example, a non-patent document (Ohno, H. and Toya, K., "Localized gradient-index field reconstruction using background-oriented schlieren," Applied Optics, Vol. 58, Issue 28, (2019), pp.7795-7804) shows a method of reconstructing an axially symmetric refractive index distribution from the displacement amount of the dot pattern by using the scalar potential of the deflection angle.

The contents of the above non-patent literature are briefly explained below.

First, the coordinates in the yz plane are expressed as (ξ _y , ξ _z ), and the vector u is defined as the following equation (10).

The deviation of the refractive index field in the measurement medium is denoted as Δn(r,z), and the standard refractive index of the measurement medium is denoted as n _0. The distances from the imaging lens to the background and the image plane are denoted as l _o and l _i, respectively, and the distance from the origin O to the background is denoted as l _m . The light ray originating from the background with the dot pattern passes through the medium and the imaging lens and reaches the image plane.

Here, the image position when the light ray is not deflected is represented by Q, and the image position when the light ray is deflected by the refractive index field is represented by Q'. The refractive index of the surroundings is represented by _nb .

The deflection angle vector ε can be expressed as the following equation (20) using the image positions Q' and Q.

In the above equation (20), l* is the effective distance from the origin O to the background. Taking into account the refractive index of the medium, l* can be written as the following equation (21). In the following equation (21), d is the thickness of the measurement medium.

In addition, in the above formula (20), M ₀ * is the effective magnification of the background. Taking into account the refractive index of the medium, M ₀ * can be written as the following formula (22).

Furthermore, in the above equation (20), Q'-Q represents the displacement of the background dot pattern. Since it can be assumed that the deflection occurs at ξ on the plane x=0, ξ can be written as the following equation (23) using Q'.

In the above formula (23), M _m * is the effective magnification of the internal plane of the medium at x = 0. Taking into account the refractive index of the medium, M _m * can be written as the following formula (24).

Based on the above, the refractive index field representing the axially symmetric refractive index distribution can be derived from the displacement of the dot pattern as shown in the following equation (25).

The above equation (25) expresses the refractive index field as an integral of the dot pattern displacement. This shows that an axisymmetric three-dimensional refractive index field can be reconstructed by measuring the displacement of the dot pattern.

In this way, by utilizing the technology described in the above non-patent document, it is possible to mathematically determine the refractive index field inside the axially symmetric measurement object 10, i.e., the three-dimensional distribution of refractive index, based on the displacement of the dots.

Whether the refractive index of the axially symmetric measurement object 10 is truly symmetric about the axis of symmetry Ax can be checked by comparing the measurement results of multiple three-dimensional distributions under multiple conditions in which the measurement object 10 has different orientations about the axis of symmetry Ax. In this case, the second measurement unit 304 can determine the symmetry of the measurement object 10 about the axis of symmetry Ax based on the consistency of multiple three-dimensional distributions measured under multiple conditions in which the measurement object 10 has different orientations about the axis of symmetry Ax.

Based on the above configuration, the measurement device 30 according to the embodiment executes a series of processes as shown in the following FIG. 4 in order to measure the three-dimensional distribution of the refractive index of the measurement object 10. The series of processes shown in FIG. 4 starts after the positioning of the measurement object 10 on the stage 26 is completed.

Figure 4 is an exemplary schematic flowchart showing a series of processes executed by the measurement device 30 according to an embodiment.

As shown in FIG. 4, in this embodiment, first, in S501, the image acquisition unit 301 of the measurement device 30 acquires an image from the imaging device 21, which includes the measurement target 10 and the background image 22 through the lens effect suppression structure 27.

Then, in S502, the first measurement unit 302 of the measurement device 30 measures the two-dimensional distribution of the amount of light deflection generated in the measurement object 10 as a feature related to the refractive index, projected onto a cross section intersecting the optical axis Ax11 of the imaging device 21, based on a comparison between the captured image acquired in S501 and a predetermined reference image.

Then, in S503, the symmetry acquisition unit 303 of the measurement device 30 acquires the symmetry of the measurement object 10 detected by the symmetry detection device 24.

Then, in S504, the second measurement unit 304 of the measurement device 30 measures the three-dimensional distribution of the refractive index inside the measurement target 10 based on the two-dimensional distribution measured in S502 and the symmetry acquired in S503. Then, the process ends.

Finally, the hardware configuration of the measurement device 30 according to the embodiment will be described. The measurement device 30 according to the embodiment has a hardware configuration as shown in the following FIG. 5.

Figure 5 is an exemplary schematic block diagram showing the hardware configuration of the measurement device 30 according to an embodiment.

As shown in FIG. 5, the measurement device 30 includes a processor 601, a memory 602, a storage 603, an input interface (input I/F) 604, and an output interface (output I/F) 605. These pieces of hardware are connected to a bus 606.

The processor 601 is configured, for example, as a CPU (Central Processing Unit) and provides overall control over the operation of each part of the measuring device 30.

Memory 602 includes, for example, ROM (Read Only Memory) and RAM (Random Access Memory), and provides volatile or non-volatile storage of various data such as programs executed by processor 601, and a working area for processor 601 to execute programs.

Storage 603 includes, for example, a hard disk drive (HDD) or a solid state drive (SSD), and stores various types of data in a non-volatile manner.

The input interface 604 controls the input of data to the measuring device 30 via the keyboard 31. The output interface 605 controls the output of data from the measuring device 30 via the display 32.

In an embodiment, each function shown in FIG. 3 possessed by the measuring device 30 is realized by cooperation between hardware and software as a result of the processor 601 executing a measurement program stored in the memory 602 or the storage 603. However, in an embodiment, at least some of the functions shown in FIG. 3 may be realized as dedicated hardware (circuitry).

The measurement program according to the embodiment does not necessarily have to be stored in advance in the memory 602 or the storage 503. For example, the measurement program may be provided as a computer program product recorded in an installable or executable format on a computer-readable recording medium such as various magnetic disks or optical disks.

The measurement program according to the embodiment may be provided or distributed via a network such as the Internet. In other words, the measurement program may be provided in a state where it is stored on a computer connected to a network such as the Internet, and is available for download via the network.

As described above, the measurement device 30 according to the embodiment includes an image acquisition unit 301, a first measurement unit 302, a symmetry acquisition unit 303, and a second measurement unit 304. The image acquisition unit 301 acquires an image from the imaging device 21, in which a background image 22 is captured through an optically transparent measurement target 10. The first measurement unit 302 measures a two-dimensional distribution of the amount of light deflection generated as a feature related to the refractive index of the measurement target on a projection plane along the Y-Z plane intersecting with the optical axis Ax11 of the imaging device 21, based on a comparison between the captured image and a predetermined reference image. The symmetry acquisition unit 303 acquires the symmetry of the shape of the measurement target 10. The second measurement unit 304 measures a three-dimensional distribution of the refractive index inside the measurement target 10 based on the two-dimensional distribution measured by the first measurement unit and the symmetry acquired by the symmetry acquisition unit 303.

With the above configuration, it is possible to measure the three-dimensional distribution of the refractive index inside the measurement object 10 based on the two-dimensional distribution of the deflection amount measured by the first measurement unit and the symmetry acquired by the symmetry acquisition unit 303.

<Modification>
In the above-described embodiment, an axially symmetric measurement target 10 in which symmetry of the refractive index around the symmetry axis Ax can be expected is exemplified, but for symmetry other than axial symmetry, some symmetry of the refractive index can be expected depending on the symmetry. Therefore, the technology of the embodiment can be applied to a measurement target having symmetry other than axial symmetry. As an example of a measurement target having symmetry other than axial symmetry, for example, a measurement target 700 as shown in the following FIG. 6 can be considered.

Figure 6 is an exemplary schematic diagram showing a measurement target 700 according to a modified example.

The measurement object 700 shown in FIG. 6 has a semi-cylindrical shape extending along the X-axis. The internal refractive index of this measurement object 700 is expected to be uniform in the direction along the X-axis. In other words, the two-dimensional distribution of the refractive index of any cross section of the measurement object 700, including cross section P700 along the Y-Z plane perpendicular to the X-axis, is expected to be approximately equal.

Therefore, in the example shown in FIG. 6, first, the two-dimensional distribution of the deflection amount on the projection surface along the Y-Z plane perpendicular to the X-axis is measured by the Schlieren method or the background-type Schlieren method. Then, taking into account the uniformity of the refractive index in the direction along the X-axis described above, the three-dimensional distribution of the refractive index inside the measurement object 700 is measured.

Although the above describes the embodiments and modifications of the present invention, the above-mentioned embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. The above-mentioned novel embodiments and modifications can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. The above-mentioned embodiments and modifications are included within the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

10, 700 Measurement object 21 Imaging device 30 Measurement device 301 Image acquisition section 302 First measurement section 303 Symmetry acquisition section 304 Second measurement section

Claims (6)

Acquiring an image from an imaging device, the image including a background image through an optically transparent measurement target;
measuring a two-dimensional distribution of a deflection amount of light generated at the measurement object on a projection plane of the measurement object intersecting with an optical axis of the imaging device based on a comparison between the captured image and a predetermined reference image;
acquiring information on the position of a symmetry axis of the measurement object as information on the symmetry of the shape of the measurement object from a symmetry detection device;
moving a stage supporting the measurement object so that the axis of symmetry is located at a center of the captured image;
displaying the axis of symmetry detected by the symmetry detection device on a display;
Measuring a three-dimensional distribution of a feature related to the amount of deflection within the measurement object based on the two-dimensional distribution and the symmetry; and
A measurement program for causing a computer to execute the above. The characteristics include a refractive index.
The measurement program according to claim 1 . The captured image includes the measurement object and the background image via a lens effect suppression structure that cancels the lens effect of the measurement object.
The measurement program according to claim 1 or 2. The captured image shows the background image through the measurement object when red monochromatic light is irradiated.
The measurement program according to any one of claims 1 to 3. When the symmetry is axial symmetry around an axis of symmetry extending in a direction intersecting with an optical axis of the imaging device, determining uniformity around the axis of symmetry of the measurement object based on consistency of the three-dimensional distribution measured under each of a plurality of conditions in which the posture of the measurement object around the axis of symmetry is different;
The measurement program according to any one of claims 1 to 4, further causing the computer to execute the following: an image acquisition unit that acquires an image including a background image through an optically transparent measurement target from an imaging device;
a first measurement unit that measures a two-dimensional distribution of a deflection amount of light generated at the measurement object on a projection plane of the measurement object that intersects with an optical axis of the imaging device based on a comparison between the captured image and a predetermined reference image;
a symmetry acquisition unit that acquires information on the position of a symmetry axis of the measurement object from a symmetry detection device as information on the symmetry of the shape of the measurement object;
an actuator that moves a stage supporting the measurement object so that the axis of symmetry is located at the center of the captured image;
a display control unit that displays the axis of symmetry detected by the symmetry detection device on a display;
a second measurement unit that measures a three-dimensional distribution of a feature related to the amount of deflection inside the measurement object based on the two-dimensional distribution and the symmetry;
A measuring device comprising:

Images