Dual-camera three-dimensional topography measurement apparatus and method based on digital micromirror device

Abstract

The application discloses a kind of three-dimensional topography measuring device and method based on digital micromirror device's dual camera, and it belongs to the field of stereo vision imaging.The three-dimensional topography measuring device based on digital micromirror device's dual camera includes parallel light source, first digital micromirror device, projection system, objective, second digital micromirror device, first relay lens, second relay lens, first CCD camera and second CCD camera.The three-dimensional topography measuring method based on digital micromirror device's dual camera includes image acquisition and phase calculation, through time sequence difference and dual camera difference, the topography measurement of measured target is realized, and common-mode noise is eliminated, and measurement precision is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of based on digital micromirror device Dual-camera three-dimensional topography measurement device and method, belong to stereo vision imaging field. BACKGROUND

[0002] Light projection technology is loaded with depth information by projecting phase-shifted fringe, and then the sequence fringe image is dephased and the three-dimensional image of the target object is calculated using triangulation method, which can obtain full-field high-precision point cloud data in a short time, and has been widely used in three-dimensional topography measurement and additive manufacturing field in recent years. However, due to the influence of ambient light and the limitation of optical system, common-mode noise will be introduced into the fringe grating and the imaging system of the projection system, which will affect the measurement accuracy, and in severe cases, it will cause the measurement to be impossible, such as lens glare. SUMMARY

[0003] In view of the above prior art, the present application provides a kind of based on digital micromirror device Dual-camera three-dimensional topography measurement device and method to solve the above problems.

[0004] The technical scheme of the three-dimensional topography measurement device based on the digital micromirror device of the present application is as follows: the device comprises a parallel light source, a first digital micromirror device, a projection system, an objective lens, a second digital micromirror device, a first relay lens, a second relay lens, a first CCD camera and a second CCD camera; the parallel light source provides uniform monochromatic light to the first digital micromirror device; the first digital micromirror device modulates the parallel light into cosine grating fringe with opposite amplitude; the projection system projects time-sequenced phase-shifted sinusoidal grating fringe onto the measured target, loading the depth information of the measured target; the objective lens images the fringe image carrying the depth information of the measured target onto the second digital micromirror device; the second digital micromirror device modulates the image carrying the measured surface profile information twice and reflects it alternately to the two CCD cameras; the first relay lens images the reflecting surface of the second digital micromirror device to the photosensitive surface of the first CCD camera; the second relay lens images the reflecting surface of the second digital micromirror device to the photosensitive surface of the second CCD camera; the first CCD camera and the second CCD camera complete the photosensitive imaging alternately.

[0005] The first CCD camera and the second CCD camera, the first relay lens and the second relay lens are symmetrically installed, forming a dual-camera structure.

[0006] The three-dimensional topography measurement method based on the digital micromirror device of the present application is based on the above-mentioned three-dimensional topography measurement device based on the digital micromirror device, and the steps are as follows:

[0007] Step one, image acquisition:

[0008] Fine-tune the position of the second DMD relative to the first and second CCD cameras so that the pixels of both CCD cameras are aligned with the micromirrors of the second DMD, i.e. each CCD camera pixel corresponds to the same micromirror of the second DMD.

[0009] The two-dimensional micromirror array of the first DMD is controlled to flip in a cosine- varying arrangement in the x-axis direction, with the cosine amplitude of the point (x, y) at T1 being b1(x, y) and the cosine amplitude of the point (x, y) at T2 being 1-b1(x, y); the flipping state of the two-dimensional micromirror array of the second DMD is controlled so that the modulation amplitude of the point (x, y) relative to the left first CCD camera is b2(x, y) and the modulation amplitude of the point (x, y) relative to the left second CCD camera is 1-b2(x, y); the first and second CCD cameras are exposed to imaging at T1 and T2, respectively, to record four images and

[0010] Suppose the reflectivity distribution of the measured target is r(x, y), the basic light intensity distribution is a(x, y), the common-mode noise introduced when the measured target is projected with a fringe is Δ p (x, y), the common-mode noise directly entering the objective lens without the measured target is Δ e (x, y), and the common-mode noise of the imaging system is Δ s (x, y), then the four images recorded by the first and second CCD cameras are expressed as:

[0011]

[0012] Step two, phase calculation: the three types of common-mode noise Δ p (x, y), Δ e (x, y), and Δ s (x, y) are all after the modulation of the first DMD, so the time-difference denoising of the images at T1 and T2 can be performed:

[0013]

[0014] Without considering the modulation processing of the second DMD, the denoising formula can be further simplified as:

[0015]

[0016] When only considering the common-mode noise Δ s (x, y) or Δ p (x, y) ≈ 0, Δ e (x, y) ≈ 0, the influence of the b1 amplitude distribution is excluded:

[0017]

[0018] Carrying out dual-camera differential denoising:

[0019]

[0020] Adding step phase 2π / N to formula (3) and formula (5), N is the number of phase shift steps, then the image light intensity distribution function of the k step is respectively:

[0021]

[0022] At this time, the truncated phase formula is expressed as:

[0023]

[0024] Subsequently, phase unwrapping and depth coordinate mapping are carried out, and the three-dimensional topography measurement based on the digital micromirror device dual camera can be completed, and the common mode noise is removed. The phase unwrapping and depth coordinate mapping in the method of the application are common methods in phase profilometry, and those skilled in the art can easily realize them, and therefore will not be described here.

[0025] Compared with the prior art, the beneficial effects of the application are:

[0026] The three-dimensional topography measurement device and method based on the digital micromirror device dual camera provided by the application realize common mode noise elimination in phase shift profilometry through time sequence difference and dual camera structure difference. Compared with the prior art, the three-dimensional topography measurement device based on the digital micromirror device dual camera provided by the application uses a digital micromirror device to modulate imaging light, and dual cameras are used for synchronous imaging, which can effectively eliminate common mode noise in the imaging system. The three-dimensional topography measurement method based on the digital micromirror device dual camera provided by the application uses amplitude complementary time sequence projection stripes to carry out time sequence difference to eliminate common mode noise, and improve measurement accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The three-dimensional topography measurement device based on the digital micromirror device dual camera provided by the application is shown in the structural diagram;

[0028] Figure 2 The amplitude modulation principle diagram of the three-dimensional topography measurement method based on the digital micromirror device dual camera provided by the application is shown in the structural diagram;

[0029] In the figure: 1-parallel light source, 2-first digital micromirror device, 3-projection system, 4-objective lens, 5-second digital micromirror device, 6-first relay lens, 7-second relay lens, 8-first CCD camera, 9-second CCD camera, 10-measured target. DETAILED DESCRIPTION

[0030] The present invention will now be described in further detail with reference to specific embodiments.

[0031] like Figure 1 As shown, the present invention discloses a three-dimensional topography measurement device based on a dual-camera system using digital micromirror devices, comprising a parallel light source 1, a first digital micromirror device 2, a projection system 3, an objective lens 4, a second digital micromirror device 5, a first relay lens 6, a second relay lens 7, a first CCD camera 8, and a second CCD camera 9. The parallel light source 1 provides uniform monochromatic light to the first digital micromirror device 2. The first digital micromirror device 2 modulates the parallel light into cosine grating fringes with opposite amplitudes. The projection system 3 projects the time-phase-shifted sinusoidal grating fringes onto the target 10, loading the target 10. 0 Depth information; the objective lens 4 images a striped image carrying the depth information of the target 10 onto the second digital micromirror device 5; the second digital micromirror device 5 modulates the image carrying the contour information of the surface being measured and alternately reflects it to two CCD cameras; the first relay lens 6 images the reflective surface of the second digital micromirror device 5 onto the photosensitive surface of the first CCD camera 8; the second relay lens 7 images the reflective surface of the second digital micromirror device 5 onto the photosensitive surface of the second CCD camera 9; the first CCD camera 8 and the second CCD camera 9 alternately complete photosensitive imaging.

[0032] The first CCD camera 8 and the second CCD camera 9, the first relay lens 6 and the second relay lens 7 are symmetrically installed to form a dual-camera structure.

[0033] The present invention proposes a three-dimensional topography measurement method based on a dual-camera system using a digital micromirror device. This method utilizes the aforementioned three-dimensional topography measurement device based on a dual-camera system using a digital micromirror device and follows these steps:

[0034] Step 1: Image Acquisition

[0035] The position of the second digital micromirror device 5 relative to the first CCD camera 8 and the second CCD camera 9 is finely adjusted so that the pixels of the two CCD cameras are registered with the micromirror elements of the second digital micromirror device 5, that is, each CCD camera pixel corresponds to the same micromirror element of the second digital micromirror device 5.

[0036] like Figure 2As shown, the two-dimensional micro-mirror array of the first digital micro-mirror device 2 is controlled to flip states in a cosine-variation arrangement in the x-axis direction, the cosine amplitude of the point (x, y) at T1 is b1(x, y), and the cosine amplitude of the point (x, y) at T2 is 1-b1(x, y); the flipping state of the two-dimensional micro-mirror array of the second digital micro-mirror device 5 is controlled to have a modulation amplitude of b2(x, y) relative to the point (x, y) of the left first CCD camera 8 and a modulation amplitude of 1-b2(x, y) relative to the point (x, y) of the left second CCD camera 9; the first CCD camera 8 and the second CCD camera 9 are exposed to imaging at T1 and T2, and four images are recorded respectively and

[0037] Suppose the reflectivity distribution of the measured target 10 is r(x, y), the basic light intensity distribution is a(x, y), the common-mode noise introduced when the measured target 10 is projected with a stripe is Δ p (x, y), the common-mode noise directly entering the objective lens 4 without the measured target 10 is Δ e (x, y), and the common-mode noise of the imaging system is Δ s (x, y), then the four images recorded by the first CCD camera 8 and the second CCD camera 9 are expressed as:

[0038]

[0039] Step two, phase calculation: the three types of common-mode noise Δ p (x, y), Δ e (x, y), and Δ s (x, y) are all after the modulation of the first digital micro-mirror device 2, so the time sequence difference denoising of the images at T1 and T2 can be performed:

[0040]

[0041] Without considering the modulation processing of the second digital micro-mirror device 5, the denoising formula can be further simplified as:

[0042]

[0043] When only considering the common-mode noise Δ s (x, y) or Δ p (x, y) ≈ 0, Δ e (x, y) ≈ 0, the influence of the b1 amplitude distribution is excluded:

[0044]

[0045] Double-camera difference denoising is performed:

[0046]

[0047] Add step phase 2π / N to formula (3) and formula (5), N is the number of phase shift steps, then the image light intensity distribution function of the k step is respectively:

[0048]

[0049] At this time, the truncated phase formula is expressed as:

[0050]

[0051] Subsequently, phase unwrapping and depth coordinate mapping are carried out, so that the three-dimensional topography measurement based on the digital micro-mirror device dual-camera is completed, and the common-mode noise is removed. The phase unwrapping and depth coordinate mapping in the method of the application are common methods in phase profilometry, and can be easily realized by those skilled in the art, and will not be described here.

[0052] Embodiment:

[0053] The application will be further described in detail by examples as follows:

[0054] The resolution of the first CCD camera 8 and the second CCD camera 9 is selected as 1920x1080, that is, the two-dimensional pixel array of the CCD is 1920x1080, the sensor size is 1 / 2 inch, and the two-dimensional micro-mirror element array of the first digital micro-mirror device 2 and the second digital micro-mirror device 5 is 1920x1080.

[0055] The position of the second digital micro-mirror device 5 relative to the first CCD camera 8 and the second CCD camera 9 is finely adjusted, so that the pixels of the two CCD cameras are aligned with the micro-mirror elements of the second digital micro-mirror device 5, that is, each CCD camera pixel corresponds to the same micro-mirror element of the second digital micro-mirror device 5.

[0056] The two-dimensional micro-mirror element array of the first digital micro-mirror device 2 is controlled to flip in a cosine variation arrangement mode in the x-axis direction to compensate for the uneven light distribution of the projection system and improve the contrast of the projected fringe, the cosine amplitude of the point (x, y) at T1 is set as b1(x, y), b1(x, y) is the uneven light distribution compensation value of the projection system, and the cosine amplitude of the point (x, y) at T2 is 1-b1(x, y); the flipping state of the two-dimensional micro-mirror element array of the second digital micro-mirror device 5 is controlled to avoid imaging oversaturation, so that the modulation amplitude of the point (x, y) relative to the left first CCD camera 8 is b2(x, y), b2(x, y) is the light-on and light-off duty cycle value of the micro-mirror element, and the modulation amplitude of the point (x, y) relative to the left second CCD camera 9 is 1-b2(x, y); the first CCD camera 8 and the second CCD camera 9 are exposed and imaged at T1 and T2, and four image information is recorded respectively and

[0057] Let the reflectivity distribution of the measured object 10 be r(x, y), the base light intensity distribution be a(x, y), and the common-mode noise introduced when the measured object 10 is projected with a fringe be Δ p (x, y), the common-mode noise not directly entering the objective 4 through the measured object 10 be Δ e (x, y), and the common-mode noise of the imaging system be Δ s (x, y).

[0058] Embodiment One:

[0059] The three types of common-mode noise Δ p (x, y), Δ e (x, y), and Δ s (x, y) are all after the modulation of the first digital micromirror device 2, so time-difference denoising of the T1 and T2 period images can be performed:

[0060]

[0061] Taking the four-step phase shift method as an example, a step phase of π / 2 is added to formula (3), so the sequence image light intensity distribution function is:

[0062]

[0063] Truncated phase:

[0064] φ(x, y) = arctan[(F1 2 -F1 4 ) / (F1 1 -F1 3 )] (9)

[0065] Embodiment Two:

[0066] When only the common-mode noise Δ s (x, y) or Δ p (x, y) of the imaging system is considered, Δ e (x, y) ≈ 0, the influence of the b1 amplitude distribution is excluded, and double-camera difference denoising can be performed:

[0067]

[0068] Taking the four-step phase shift method as an example, a step phase of π / 2 is added to formula (5), so the sequence image light intensity distribution function is:

[0069]

[0070] Truncated phase:

[0071]

[0072] Subsequently, phase unwrapping and depth coordinate mapping are performed, and the three-dimensional profile measurement based on the digital micro-mirror device dual-camera is completed, and the common-mode noise is removed. The phase unwrapping and depth coordinate mapping in the method of the present application are common methods in phase profilometry, and can be easily realized by those skilled in the art, and thus will not be described herein.

[0073] Although the present application is described above in combination with the drawings, the present application is not limited to the specific embodiments described above, and the specific embodiments described above are merely illustrative but not restrictive, and many modifications can be made by those skilled in the art without departing from the spirit of the present application under the inspiration of the present application, and these all belong to the protection of the present application.

Claims

1. A digital micromirror device-based dual-camera three-dimensional topography measuring apparatus, characterized by, It comprises a parallel light source (1), a first digital micromirror device (2), a projection system (3), an objective lens (4), a second digital micromirror device (5), a first relay lens (6), a second relay lens (7), a first CCD camera (8) and a second CCD camera (9). The parallel light source (1) provides uniform monochromatic light to the first digital micromirror device (2); the first digital micromirror device (2) modulates the parallel light into cosine grating fringes with opposite amplitudes; the projection system (3) projects the time-sequenced phase-shifted sinusoidal grating fringes onto the measured target (10) to load the depth information of the measured target (10); the objective lens (4) images the fringe image loaded with the depth information of the measured target (10) onto the second digital micromirror device (5); the second digital micromirror device (5) twice modulates the image loaded with the measured surface profile information and alternately reflects it to the two CCD cameras; the first relay lens (6) images the reflecting surface of the second digital micromirror device (5) onto the photosensitive surface of the first CCD camera (8); the second relay lens (7) images the reflecting surface of the second digital micromirror device (5) onto the photosensitive surface of the second CCD camera (9); the first CCD camera (8) and the second CCD camera (9) alternately complete photosensitive imaging; the common-mode noise elimination in phase-shifted profile measurement is realized through time-sequenced difference and double-camera structure difference. The first CCD camera (8) and the second CCD camera (9), the first relay lens (6) and the second relay lens (7) are symmetrically installed to form a double-camera structure.

2. A two-camera three-dimensional topography measurement method based on digital micro-mirror device, characterized in that, The projection measurement is performed by using the double-camera three-dimensional profile measurement device based on the digital micromirror device in claim 1, which comprises the following steps: Step one, image acquisition: The position of the second digital micromirror device (5) is finely adjusted relative to the positions of the first CCD camera (8) and the second CCD camera (9), so that the image elements of the two CCD cameras are matched with the micromirror elements of the second digital micromirror device (5), that is, each CCD camera image element corresponds to the same micromirror element of the second digital micromirror device (5); The two-dimensional micro-mirror element array of the first digital micro-mirror device (2) is controlled to flip the state in a cosine-variation arrangement in the x-axis direction, the cosine amplitude of the point (x, y) at T1 time point is b1(x, y), and the cosine amplitude of the point (x, y) at T2 time point is 1-b1(x, y); the flipping state of the two-dimensional micro-mirror element array of the second digital micro-mirror device (5) is controlled so that the modulation amplitude of the point (x, y) relative to the left first CCD camera (8) is b2(x, y), and the modulation amplitude of the point (x, y) relative to the right second CCD camera (9) is 1-b2(x, y); the first CCD camera (8) and the second CCD camera (9) are exposed and imaged at T1 and T2 time periods, and four image information is recorded respectively and Let the reflectivity distribution of the measured object (10) be r(x, y), the base light intensity distribution be a(x, y), the common mode noise introduced when the measured object (10) is projected with a stripe be Δ p (x, y), the common mode noise directly entering the objective lens (4) without passing through the measured object (10) be Δ e (x, y), the common mode noise of the imaging system be Δ s (x, y), then the four images recorded by the first CCD camera (8) and the second CCD camera (9) are expressed as: Step two, phase calculation: the three types of common-mode noise Δ p (x,y), Δ e (x,y), Δ s (x,y) are all modulated by the first digital micromirror device (2), so that the time sequence difference denoising of T1 and T2 period images can be carried out: Without considering the modulation processing of the second digital micromirror device (5), the denoising formula can be further simplified as: When considering only the imaging system common mode noise Δ s (x,y) of the imaging system, Δ p (x,y) ≈ 0, Δ e (x,y) ≈ 0, the influence of the b1 amplitude distribution is excluded: Double-camera differential denoising is performed: The stepping phase 2π / N is added to formula (3) and formula (5), and N is the phase shift step number, so that the image light intensity distribution functions of the kth step are respectively: At this time, the truncated phase formula is expressed as: Subsequently, phase unwrapping and depth coordinate mapping are performed, so that the double-camera three-dimensional profile measurement based on the digital micromirror device can be completed, and the common-mode noise can be removed.

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