KR101139178B1 - Device for measuring the 3d cubic matter using a digital holography - Google Patents

Abstract

PURPOSE: A 3-dimensional measurement apparatus using digital holography is provided to minimize the generation of optical noise and improve the precision of a product by simplifying structure and lowering manufacturing cost. CONSTITUTION: A 3-dimensional measurement apparatus(100) using digital holography comprises a first photographing unit(110), a second photographing unit(120), an optical source(101), a first beam splitter(121), a second beam splitter(122), a first band pass filter(131), a second band pass filter(132), and a controller. The first photographing unit and the second photographing unit obtain one shot digital hologram. The optical source emits the white light including the wavelength components in a range of ultraviolet-visible ray. The first beam splitter reflects composite light including reference light and measurement light toward an object(140). The second beam splitter transmits the composite light through the first photographing unit. The first band pass filter is placed on the optical path between the first photographing unit and the second beam splitter. The second band pass filter is placed on the optical path between the second beam splitter and the second photographing unit.

Description

Device for Measuring the 3D Cubic Matter using a Digital Holography}

The present invention relates to an apparatus capable of three-dimensionally measuring an object by using digital holography, and more particularly, in order to implement digital holography, the structure is simple and easy to align, and the speckle is made using a white light source. It is possible to reduce or eliminate noise completely, and to acquire digital holography images using ONE SHOT using two CCDs, we propose a structure that can be applied to Single Fourier Transform by software. It relates to a three-dimensional measuring device using holography.

In general, the method using digital holography among the optical-based three-dimensional stereoscopic (3D) measurement technology is important because of the ease of high-speed measurement.

1 is a view for explaining the concept of 3D measurement technology using digital holography.

As shown in FIG. 1, the state in which the measurement light reflected from the measurement object, which is a three-dimensional object, is captured by the CCD camera is illustrated, and the imaging object is photographed without using an imaging lens in front of the CCD camera. Because of this, there is a big difference from the conventional 3D measurement method.

That is, the image captured by the CCD camera is an encrypted signal represented by a digital hologram, and the information included in the digital hologram is numerically calculated by calculating the image information on the measurement object through Fresnel transform. You get

Since the 3D measurement method using digital holography does not use an imaging lens, it is also called lensless imaging. Since the 3D information of the measurement object is stored in the digital hologram, the conventional vision optical system is used. In addition to the two-dimensional information has a variety of three-dimensional information can be extracted in recent years has been in the spotlight as a three-dimensional measurement technology.

On-axis method and off-axis method are proposed as three-dimensional measurement technology using digital holography. In the off-axis method, the stereoscopic information can be acquired from a single hologram. The -axis method is widely used.

FIG. 2 is a diagram illustrating a configuration of a stereoscopic measuring apparatus using conventional off-axis digital holography.

In the conventional method using off-axis digital holography, a single hologram obtained from a CCD camera is used to reproduce an image of a measurement object through a Fresnel transform.

In general, a stereoscopic measuring apparatus using digital holography has a limited measurement range according to the wavelength of a laser beam.

For example, when the wavelength of the laser beam is 633 nm, when a sudden height change of 312 nm or more, which is a half wavelength of 633 nm, occurs on the surface of the measurement object, measurement error occurs due to phase ambiguity.

In order to overcome the limitation of the measurement range according to the wavelength of the laser beam, a dual wavelength digital holography technique has been proposed.

3 is a diagram illustrating a configuration of a 3D measuring apparatus using a conventional off-axis dual wavelength digital holography.

As shown in FIG. 3, the 3D measurement apparatus using conventional off-axis dual-wavelength digital holography uses a light source for irradiating laser beams having different wavelengths, and operates two laser beams independently of each other. That is, a method of imaging with a CCD camera with different beam paths of the reference beam is applied. This is a beating effect of the frequency (Beating effect), and the equivalent wavelength can be made much larger than the existing wavelength by using a laser beam of mutually different wavelengths as shown in Equation 1 below.

Here, Λ is the equivalent wavelength, and λ1 and λ2 are the two existing wavelengths, respectively.

For example, when λ 1 is 675 nm and λ 2 is 635 nm, the equivalent wavelength Λ is arithmetically approximately 10 μm, thereby greatly increasing the measurement range.

However, since the conventional 3D measurement apparatus using off-axis dual-wavelength digital holography operates the reference beam independently for two wavelengths, the structure is very complicated in hardware as shown in FIG. 3. have. This causes a large number of components such as a mirror, so that the overall manufacturing cost is high, and the unit of alignment is also a disadvantage.

In addition, the 3D measuring apparatus using the conventional off-axis dual-wavelength digital holography has at least three two-dimensional fast fourier transformations (FFTs) because the holograms for the two wavelengths are picked up and hologramized by one CCD camera. Since only a convolution formulation is performed, the computational speed is high in software.

This is because the Single Fourier Transform method does not apply to a single hologram in common because the magnification reproduced at the same distance varies as the wavelength is changed.

In addition, the device using the conventional dual wavelength off-axis holography has a limitation in that a strong light source is required for reliable data acquisition because the device is large, difficult to align, and a large number of polarizers exist on the optical axis due to the complexity of the structure. Will have

This requires the use of a light source, such as a laser, which causes so-called speckle phenomena due to the very high coherence of the measured object, which causes noise to interfere with three-dimensional shape measurements. This reduces the accuracy of the measurement data.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and its object is to implement a digital holography with a simple structure and easy alignment in hardware, and to reduce or completely eliminate speckle noise using a white light source. It is possible to acquire a digital holography image by ONE SHOT using two CCDs and propose a structure that can be applied to Single Fourier Transform by software to provide a 3D measuring device using digital holography with improved calculation speed. I would like to.

As a specific means for achieving the above object, the present invention, the first imaging unit and the second imaging unit for obtaining the ONE SHOT digital hologram; A light source unit for emitting white light including wavelength components of the ultraviolet-visible light region; A first beam splitter for reflecting the composite light including the reference light and the measurement light of the light source emitted from the light source unit and reflected by the reflection mirror toward the measurement object; A second beam splitter configured to pass the synthesized light reflected from the measurement object and passed through a first beam splitter to the first image pickup side, and to be reflected to the second image pickup side; The first wavelength lambda 1 of the specific wavelength band monochromatic light, which is disposed on the optical path between the first image pickup unit and the second beam splitter, is preset in the synthetic light including the measurement light and the reference light. A first band pass filter configured to pass toward the first image pickup unit; A second band pass filter disposed on an optical path between the second image pickup unit and a second beam splitter, and configured to pass a second wavelength? And a control unit for measuring a surface shape of the measurement object by using two holograms captured by the first imaging unit and the second imaging unit.

The present invention may also include a first image pickup unit and a second image pickup unit for obtaining a one shot digital hologram; A light source unit for emitting white light including wavelength components of the ultraviolet-visible light region; A first beam splitter for dividing the white light emitted from the light source into a reference light and a measurement light to irradiate the reflection mirror and the measurement object side; A second beam that reflects a part of the composite light that is reflected from the measurement object and the reflecting mirror, passes through the first beam splitter, and interferes with the first imager, and reflects the remainder of the synthesized light to the second imager; Splitter; A first wavelength λ1 of a specific wavelength band monochromatic light, which is disposed on an optical path between the first image pickup unit and the second beam splitter, and is set in advance among the synthetic light including the measurement light and the reference light; A first band pass filter configured to pass toward the first image pickup unit; A second band pass filter disposed on an optical path between the second image pickup unit and a second beam splitter to pass a second wavelength? And a control unit for measuring a surface shape of the measurement object by using two holograms captured by the first imaging unit and the second imaging unit.

Preferably, the first bandpass filter and the second bandpass filter have a lambda 1c-λ2c ≥ (Δλ1 + Δλ2) / 2 when the FWHM1 of the first wavelength λ1c is Δλ1 and the FWHM2 of the second wavelength λ2c is Δλ2. Satisfies the conditions.

The first wavelength λ1c is calculated by Equation 2 when the wavelength selective efficiency distribution function of the first band pass filter is f1 (λ), the start wavelength is λ1s, and the ending wavelength is λ1e. The second wavelength λ 2c is calculated by Equation 3 when the wavelength selection efficiency distribution function of the second band pass filter is f 2 (λ), the starting wavelength is λ 2s, and the ending wavelength is λ 2e.

Preferably, the alignment unit further includes an alignment unit to align the first imaging unit with respect to the second imaging unit, wherein the alignment unit includes a translational motion mechanism capable of moving x, y, and z axes and each axis in the α, β, and γ directions. It has a rotary motion mechanism that can rotate it.

The present invention as described above has the following effects.

(1) Compared to the conventional stereoscopic measuring apparatus, the structure can be simplified to reduce manufacturing cost, and the occurrence of optical noise can be minimized to increase the precision of the product.

(2) Speckle noise can be completely removed using white light as a light source.

(3) By changing the hardware structure, the holograms for each wavelength are acquired by two imaging units, that is, CCD cameras, respectively by ONE SHOT, and by applying the Single Fourier Transform method to each hologram, Software can speed up computation.

1 is a schematic diagram illustrating the concept of 3D measurement technology using digital holography.
FIG. 2 is a diagram illustrating a configuration of a stereoscopic measuring apparatus using conventional off-axis digital holography.
3 is a diagram illustrating a configuration of a 3D measuring apparatus using a conventional off-axis dual wavelength digital holography.
4 is an overall configuration diagram showing a stereoscopic measuring apparatus using digital holography according to the first embodiment of the present invention.
5 is a schematic diagram showing a stereoscopic measuring apparatus using digital holography according to the first embodiment of the present invention.
6 is a schematic diagram showing a stereoscopic measuring apparatus using digital holography according to a second embodiment of the present invention.

The objects, features and advantages of the present invention described above will become more apparent from the following detailed description. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIGS. 4 and 5, the stereoscopic measuring apparatus 100 using digital holography according to the first exemplary embodiment of the present invention includes the first and second imaging units 110 and 120, the light source unit 101, and the first and second units. Beam splitters 121 and 122, first and second band pass filters 131 and 132, and a controller.

The light source unit 101 emits white light including wavelength components of the ultraviolet-visible light region toward the reflective mirror 102 disposed to be inclined at a predetermined angle on the optical path.

The white light emitted from the light source unit is light having the same intensity of visible light, and includes all colors of red, orange, yellow, green, blue, indigo, and purple, and the wavelength of the white light is determined. Rather, light with various wavelengths is collected.

 The light emitted from the light source unit 101 passes through the lens system 104 and is converted into an approximate parallel light and is incident to the reflection mirror 102.

The first beam splitter 121 is a means for reflecting the composite light including the reference light and the measurement light of a specific wavelength band included in the light reflected by the reflection mirror 102 toward the measurement object 140.

The composite light reflected by the first beam splitter 121 passes through the objective lens 105 and is irradiated onto the measurement object 140, and then returns to the first beam splitter 121 side.

The second beam splitter 122 is configured to acquire a ONE SHOT digital hologram image from a composite light including measurement light and reference light reflected from the measurement object 140 and passed through the first beam splitter 121. Spectroscopic means for splitting and reflecting the image pickup unit 110 and the second image pickup unit 120, respectively.

The first band pass filter 131 is disposed on an optical path between the first image pickup unit 110 and the second beam splitter 131 so that a band pass filter is specified in the synthesized light. Is a band pass filter member that passes the first wavelength λ1 of the monochromatic light toward the first image pickup unit 110.

The second band pass filter 132 is disposed on an optical path between the second imaging unit 110 and the second beam splitter 131 so that the first band pass filter 131 is formed in the synthesized light. ) Is a band pass filter member for passing the second wavelength [lambda] 2 of monochromatic light passing through a filter having a different band to the second imaging unit 120.

That is, the synthesized light passing through the first beam splitter 121 and incident on the second beam splitter 122 is split into two parts while being output from the second beam splitter 122. The composite light is directed toward the first band pass filter 131 and the reflected synthetic light is directed toward the second band pass filter 132.

The synthetic light directed to the first band pass filter 131 may transmit only light having a wavelength satisfying a condition given by the first band pass filter 131 having the characteristics of the center wavelength, λ 1c and half width, and FWHM1. The synthesized light directed to the second band pass filter 132 is spatially transmitted by transmitting only light having a wavelength satisfying the condition by the second band pass filter 132 having a center wavelength, λ 2c and a half width, and FWHM 2. The composite light can be separated into the first wavelength lambda 1c and the second wavelength lambda 2c, respectively, and directed to the first imaging unit and the second imaging unit.

Subsequently, the light of the first wavelength λ1c separated by the first band pass filter 131 is disposed between the first image pickup unit 110 and the first band pass filter 131. A second hologram image, which is input to the first photographing unit 110 by the unit 133 and acquires a digital hologram image based on light of a first wavelength, is separated by the second band pass filter 132. The light of [lambda] 2c) is inputted to the second imaging unit 120 by the second eyepiece unit 134 disposed between the second imaging unit 120 and the second band pass filter 132, thereby providing the second wavelength. A digital hologram image based on light is obtained.

Meanwhile, the interference lens system 125 is detachably provided between the measurement object 140 and the first beam splitter 121 so that the reference light and the measurement light emitted through the first beam splitter 121 are separated by the interference lens. Can be synthesized.

As shown in FIG. 6, the stereoscopic measuring apparatus 100a using digital holography according to the second embodiment of the present invention includes the first and second imaging units 110 and 120, the light source unit 101, and the first and second beam splitters. Beam splitters 121 and 122, first and second band pass filters 131 and 132, and a controller.

The light source unit 101 emits white light including wavelength components of the ultraviolet-visible light region toward the reflective mirror 102 disposed to be inclined at a predetermined angle on the optical path.

The first beam splitter 121 is disposed between the light source unit 101 and the reflecting mirror 102 and passes through the lens system 104 to convert white light converted into approximate parallel light into two reference wavelengths of a specific wavelength band. It divides into measurement light.

Light passing through the first beam splitter 121 and traveling toward the reflection mirror 102 becomes reference light, and light reflected from the first beam splitter 121 and traveling toward the measurement object 140 becomes measurement light. The measurement light is returned to the first beam splitter 121 after being irradiated to the measurement object 130.

A portion of the measurement light returned to the first beam splitter 121 side is transmitted and irradiated to the second beam splitter 122 side, and a part of the reference light reflected on the reflection mirror 102 is the first beam splitter 121. Is reflected and irradiated to the second beam splitter 122 side.

In this case, the reference light and the measurement light interfere with each other to form one summed light.

The second beam splitter 122 acquires an ONE SHOT digital hologram image from a composite light including measurement light passing through the first beam splitter 121 and reference light reflected by the first beam splitter 121. For this purpose, the first and second imaging units 110 and 120 respectively reflect spectroscopic means.

The first band pass filter 131 is disposed on an optical path between the first image pickup unit 110 and the second beam splitter 131 so that a band pass filter is specified in the synthesized light. Is a band pass filter member that passes the first wavelength λ1 of the monochromatic light toward the first image pickup unit 110.

The second band pass filter 132 is disposed on an optical path between the second imaging unit 110 and the second beam splitter 131 so that the first band pass filter 131 is formed in the synthesized light. ) Is a band pass filter member for passing the second wavelength [lambda] 2 of monochromatic light passing through a filter having a different band to the second imaging unit 120.

That is, the synthesized light passing through the first beam splitter 121 and incident on the second beam splitter 122 is split into two parts while being output from the second beam splitter 122. It is directed toward the two-band pass filter 132, and the reflected synthetic light is directed toward the first band pass filter 131.

The synthetic light directed to the first band pass filter 131 may transmit only light having a wavelength satisfying a condition given by the first band pass filter 131 having the characteristics of the center wavelength, λ 1c and half width, and FWHM1. The synthesized light directed to the second band pass filter 132 is spatially transmitted by transmitting only light having a wavelength satisfying the condition by the second band pass filter 132 having a center wavelength, λ 2c and a half width, and FWHM 2. The composite light can be separated into the first wavelength lambda 1c and the second wavelength lambda 2c, respectively, and directed to the first imaging unit and the second imaging unit.

Subsequently, the light of the first wavelength λ1c separated by the first band pass filter 131 is disposed between the first image pickup unit 110 and the first band pass filter 131. A second hologram image, which is input to the first photographing unit 110 by the unit 133 and acquires a digital hologram image based on light of a first wavelength, is separated by the second band pass filter 132. The light of [lambda] 2c) is inputted to the second imaging unit 120 by the second eyepiece unit 134 disposed between the second imaging unit 120 and the second band pass filter 132, thereby providing the second wavelength. A digital hologram image based on light is obtained.

According to the above configuration, the first image capturing unit 110 captures a digital hologram image of the first wavelength? 1c to obtain a single hologram, and the second image capturing unit 120 has a second wavelength? 2c. Since the digital hologram image for is taken and another hologram is obtained, holograms having different wavelengths are obtained separately.

The first imaging unit 110 and the second imaging unit 120 may be provided in various forms capable of capturing an image. In the present invention, the first imaging unit 110 and the second imaging unit 120 may be provided in the form of a charge-coupled device (CCD) camera. .

The control unit three-dimensionally measures the surface shape of the measurement target by using two holograms having different wavelength bands.

In this case, since the two holograms have the same beam path, that is, the reference light and the measured light travel along the same beam path, the control unit applies a single Fourier transform or a single fast Fourier transform. The surface shape of the measurement object is measured.

In this case, the first imaging unit 110 and the second imaging unit 120 are aligned at the same magnification at the initial setting so that the Single Fourier Transform or the Single Fast Fourier Transform can be applied. do.

That is, the two holograms obtained at the same time extract the real image terms only through the Fast Fourier Transform (FFT) and the intensity and intensity of the real images using the Fresnel Transform or Angular Spectrum Method (ASM). Phase is obtained.

The shape information of the three-dimensional three-dimensional measurement object is calculated by using the phase obtained in the process of restoring each hologram, and the effective wavelength formed by the dual wavelength, λ = λ1cλ2c / | λ1c λ2c | However, the range of three-dimensional solids that can be measured without ambiguity is limited to λ / 4.

In the present invention, two holograms can be obtained at the same time, thereby real-time measurement, and when the light source uses a white light source, the speckle can be eliminated, thereby greatly improving the accuracy of three-dimensional shape measurement.

In addition, a light source such as a tunable laser or a laser diode having different wavelengths may be used in fields where high precision and real time measurement are not required.

Meanwhile, as described above, the difference between the first wavelength λ1c and the second wavelength λ2c may be λ1c−λ2c> = (Δλ1 + Δλ2) / 2 to obtain reliable data.

Accordingly, the first bandpass pallet 131 and the second bandpass filter 132 have a lambda 1c-λ2c ≥ when the FWHM1 of the first wavelength λ1c is Δλ1 and the FWHM2 of the second wavelength λ2c is Δλ2. It is preferable to satisfy the condition of (Δλ 1 + Δλ 2) / 2.

Here, since the first and second band pass filters have a certain wavelength distribution, the center wavelength of the band pass filter is determined by numerical integration after measuring the wavelength distribution function or obtaining the result by theoretical calculation.

In addition, when the first wavelength λ1c is a wavelength selection efficiency distribution function of the first band pass filter 131 as f1 (λ), a starting wavelength is λ1s and a ending wavelength is λ1e, Equation 2 The second wavelength λ2c is calculated by the wavelength selective efficiency distribution function of the second band pass filter 132 is f2 (λ), the starting wavelength is λ2s, the ending wavelength is λ2e Calculated by Equation 3.

Moreover, although this invention demonstrated the application example to the measurement object of macro size, it is a matter of course that it is applicable also to the measurement object of micro size. In this case, the present invention can be applied to a micro-sized measurement object by disposing a microscope object lens in front of the measurement object.

The alignment unit 124 may be further provided to align the second imaging unit 120 with respect to the first imaging unit 110, and the alignment unit 124 may include x, y, and z. It is desirable to have a translational movement mechanism capable of axial movement and a rotational movement mechanism capable of rotating each axis in the α, β, and γ directions.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

101: light source
102: reflection mirror
110: first imaging unit
120: second imaging unit
121: first beam splitter
122: second beam splitter
131: first band pass filter
132: second band pass filter

Claims (5)

A first imaging unit and a second imaging unit for acquiring a one-shot digital hologram;
A light source unit for emitting white light including wavelength components of the ultraviolet-visible light region;
A first beam splitter for reflecting the composite light including the reference light and the measurement light of the light source emitted from the light source unit and reflected by the reflection mirror toward the measurement object;
A second beam splitter configured to pass the synthesized light reflected from the measurement object and passed through a first beam splitter to the first image pickup side, and to be reflected to the second image pickup side;
The first wavelength lambda 1 of the specific wavelength band monochromatic light, which is disposed on the optical path between the first image pickup unit and the second beam splitter, is preset in the synthetic light including the measurement light and the reference light. A first band pass filter configured to pass toward the first image pickup unit;
A second band pass filter disposed on an optical path between the second image pickup unit and a second beam splitter, and configured to pass a second wavelength? And:
And a control unit for measuring the surface shape of the measurement object by using two holograms captured by the first and second imaging units. A first imaging unit and a second imaging unit for acquiring a one-shot digital hologram;
A light source unit for emitting white light including wavelength components of the ultraviolet-visible light region;
A first beam splitter for dividing the white light emitted from the light source into a reference light and a measurement light to irradiate the reflection mirror and the measurement object side;
A second beam that reflects a part of the composite light that is reflected from the measurement object and the reflecting mirror, passes through the first beam splitter, and interferes with the first imager, and reflects the remainder of the synthesized light to the second imager; Splitter;
A first wavelength λ1 of a specific wavelength band monochromatic light, which is disposed on an optical path between the first image pickup unit and the second beam splitter, and is set in advance among the synthetic light including the measurement light and the reference light; A first band pass filter configured to pass toward the first image pickup unit;
A second band pass filter disposed on an optical path between the second image pickup unit and a second beam splitter to pass a second wavelength? 2 of a predetermined wavelength band monochromatic light of the synthesized light to the second image pickup unit; And:
And a control unit for measuring the surface shape of the measurement object by using two holograms captured by the first and second imaging units. The method according to claim 1 or 2,
The first band pass filter and the second band pass filter have a condition of λ 1c -λ 2c ≥ (Δλ 1 + Δλ 2) / 2 when the FWHM 1 of the first wavelength λ 1c is Δλ 1 and the FWHM 2 of the second wavelength λ 2c is Δλ 2. Three-dimensional measuring apparatus using digital holography, characterized in that to satisfy. The method according to claim 1 or 2,
The first wavelength λ1c is a wavelength selection efficiency distribution function of the first band pass filter, f1 (λ), a starting wavelength is λ1s, and an ending wavelength is λ1e.

Calculated by
The second wavelength [lambda] 2c is a wavelength selection efficiency distribution function of the second band pass filter 132 is f2 ([lambda]), a starting wavelength is [lambda] 2s, and an ending wavelength is [lambda] 2e.

3D measurement apparatus using digital holography, characterized in that calculated by.
The method according to claim 1 or 2,
An alignment unit is further included to align the second imaging unit based on the first imaging unit.
And the alignment unit has a translational motion mechanism capable of moving x, y, and z axes and a rotational motion mechanism capable of rotating each axis in the α, β, and γ directions.

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