High speed phase shift profilometry for three-dimensional measurement of moving objects

Abstract

The application discloses high-speed phase shift profilometry for three-dimensional measurement of a moving target, first sets two phase shift fringe images with periods T1 and T2 (T1 < T2) as the GB layer of a blank RGB color image, then projects the color image through a DLP projector, collects the modulated color image of the measured target surface through a camera, and finally calculates the unwrapped phase of the measured target surface profile. The high-speed phase shift profilometry provided by the application can obtain the unwrapped phase of the detected target only through a single image, greatly improves the practicability of the phase shift profilometry, and solves the problem of three-dimensional appearance measurement of a fast moving target.

Description

Technical Field

[0001] The present invention belongs to the technical field of three-dimensional measurement, and specifically relates to a high-speed phase-shifting profilometry for three-dimensional measurement of moving targets. Background Art

[0002] With the continuous maturity of research on three-dimensional reconstruction technology, it has been widely applied in machine vision, reverse mechanical design, industrial detection and other aspects. Among numerous three-dimensional reconstruction technologies, fringe projection profilometry has become a research hotspot due to its characteristics of high precision, low cost and non-contact property. This method requires a digital projector to project multiple fringe images onto the surface of the target to be measured, which are captured by an industrial camera and then transmitted to a computer, and a phase extraction algorithm is used to obtain the unwrapped phase containing the height information of the target to be measured. A general phase extraction algorithm is divided into two parts: first, the wrapped phase needs to be calculated by a phase-shifting method, and then the wrapped phase is unwrapped to obtain the unwrapped phase. However, no matter the most commonly used N-step phase-shifting method, the multi-frequency heterodyne phase unwrapping method or the complementary Gray code phase unwrapping method, a large number of images are required to be projected in principle, which greatly reduces the efficiency of fringe projection profilometry and makes it inapplicable to three-dimensional measurement of the surface topography of moving targets. For traditional color fringe images, the images in the GB layers are susceptible to interference from the image in the R layer. Summary of the Invention

[0003] The objective of the present invention is to provide a high-speed phase-shifting profilometry for three-dimensional measurement of moving targets, so as to solve the problems that the existing fringe projection profilometry requires projecting a large number of images, which greatly affects the efficiency of fringe projection profilometry and makes it unable to be used for three-dimensional measurement of the surface topography of moving targets, and that the images in the GB layers of traditional color fringe images are susceptible to interference from the image in the R layer.

[0004] To achieve the above objective, the technical solution adopted by the present invention is: the high-speed phase-shifting profilometry for three-dimensional measurement of moving targets, wherein two phase-shifting fringe images with periods of T1 and T2 (T1<T2) are first set to the G and B layers of a blank RGB color image, then the color image is projected by a DLP projector, the modulated color image on the surface of the measured target is collected by a camera, and finally the unwrapped phase of the surface profile of the measured target is obtained through calculation.

[0005] As a preferred technical solution of the present invention, obtaining the unwrapped phase of the surface profile of the measured target through calculation is specifically implemented according to the following steps:

[0006] Step 1: performing layer separation processing on the collected modulated color image to obtain the modulated phase-shifting fringe image of the green layer and the modulated phase-shifting fringe image of the blue layer, which are denoted as I1 and I2 respectively;

[0007] Step 2: Eliminate the influence of background light on I1 and I2 through parameter compensation. The results after elimination are denoted as I1′ and I2′, respectively.

[0008] Step 3: Using formulas (1) and (2), obtain the mixed phase-shifted fringe image, denoted as follows: Where: x is the x-coordinate of the image, w, It is a constant value;

[0009]

[0010]

[0011] Step 4: First, Perform a Fast Fourier Transform (FFT), and then filter the result, denoted as .

[0012] Step 5: [Regarding...] Performing an inverse fast Fourier transform yields the truncated phase at the corresponding frequency, denoted as .

[0013] Step 6: [The sentence is incomplete and requires more context to be translated accurately.] Substituting this into the multi-frequency heterodyne phase expansion method, we obtain the expanded phase of the detected target, denoted as ψ.

[0014] As a preferred technical solution of the present invention, in step 6, the... Substituting into the multi-frequency heterodyne phase expansion method, the expanded phase of the detected target is obtained by calculating using formulas (3) to (8), denoted as ψ:

[0015]

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[0018]

[0019]

[0020]

[0021] As a preferred embodiment of the present invention, the camera is an industrial camera.

[0022] As a preferred embodiment of the present invention, the industrial camera is a high-speed industrial camera.

[0023] The beneficial effects of the present invention are: the high-speed phase-shift profilometry for three-dimensional measurement of moving objects of the present invention is a high-speed phase-shift profilometry based on a single color fringe image containing only GB layers. Only a single projected fringe image is required to obtain the unwrapped phase of the outer contour of the detected object, which greatly improves the detection efficiency and can be used for three-dimensional topography measurement of fast-moving objects. Brief Description of the Drawings

[0024] Figure 1 is an effect diagram of the high-speed phase-shift profilometry for three-dimensional measurement of moving objects according to the present invention. Detailed Description of the Embodiments

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] The present invention is further described below through examples, which are not limited to the following embodiments.

[0027] Embodiment 1

[0028] In the high-speed phase-shift profilometry for three-dimensional measurement of moving objects of the present invention, two phase-shift fringe images with periods of T1 and T2 (T1<T2) are first set to the GB layers of a blank RGB color image, then the color image is projected by a DLP projector, the modulated color image on the surface of the measured object is collected by a camera, and finally the unwrapped phase of the surface contour of the measured object is obtained through calculation.

[0029] As shown in Figure 1 , it is the unwrapped phase diagram of the high-speed phase-shift profilometry for three-dimensional measurement of moving objects provided by the present invention. It can be seen from the unwrapped phase diagram that the unwrapped phase of the surface contour of the measured product is obtained. By adopting the high-speed phase-shift profilometry provided by the present invention, the unwrapped phase of the detected object can be obtained with only a single image, which improves the detection efficiency, greatly enhances the practicability of phase-shift profilometry, and solves the problem of three-dimensional topography measurement of fast-moving objects.

[0030] Embodiment 2

[0031] The difference from Embodiment 1 is that in this embodiment, for the high-speed phase-shift profilometry for three-dimensional measurement of moving objects of the present invention, obtaining the unwrapped phase of the surface contour of the measured object through calculation is specifically implemented according to the following steps:

[0032] Step 1: Perform layer separation processing on the collected modulated color image to obtain the green layer modulated phase-shift fringe image and the blue layer modulated phase-shift fringe image, which are denoted as I1 and I2 respectively;

[0033] Step 2: Eliminate the influence of background light on I1 and I2 through parameter compensation. The results after elimination are denoted as I1′ and I2′, respectively.

[0034] Step 3: Using formulas (1) and (2), obtain the mixed phase-shifted fringe image, denoted as follows: Where: x is the x-coordinate of the image, w, It is a constant value;

[0035]

[0036]

[0037] Step 4: First, Perform a Fast Fourier Transform (FFT), and then filter the result, denoted as .

[0038] Step 5: [Regarding...] Performing an inverse fast Fourier transform yields the truncated phase at the corresponding frequency, denoted as .

[0039] Step 6: [The sentence is incomplete and requires more context to be translated accurately.] Substituting into the multi-frequency heterodyne phase expansion method, the expanded phase of the target is obtained by formulas (3) to (8), and denoted as ψ.

[0040]

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[0045]

[0046] This invention proposes a high-speed phase-shift profilometry for 3D measurement of moving targets. Compared to complementary Gray code phase profilometry, which requires N+M and 3N images respectively to obtain the unfolded phase of the target (N is the number of phase-shift steps, and M is the number of Gray code images), the method proposed in this invention can obtain the unfolded phase of the surface profile of the product under test under the premise of projecting a single image, thus improving the detection efficiency.

[0047] Example 3

[0048] Unlike Embodiment 1, in this embodiment, the high-speed phase-shift profilometry for three-dimensional measurement of moving targets of the present invention uses a high-speed industrial camera, which can ensure the clarity and accuracy of the acquired images, so as to obtain more accurate data through calculation.

[0049] The foregoing description illustrates and describes several preferred embodiments of the invention. However, as previously stated, it should be understood that the invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the invention should be within the protection scope of the appended claims.

Claims

1. A high-speed phase-shifting profilometry technique for three-dimensional measurement of moving targets, characterized in that: First, the two periods are respectively , The phase-shifted fringe image is set as the GB layer of a blank RGB color image. Then, the color image is projected using a DLP projector. Next, a camera acquires the modulated color image of the target surface. Finally, the unfolded phase of the target surface contour is calculated. ; The unfolded phase of the surface profile of the target object is obtained by calculation, specifically by following these steps: Step 1: The acquired modulated color image is processed into layers to obtain a green layer modulated phase-shifting fringe image and a blue layer modulated phase-shifting fringe image, denoted as follows: , ; Step 2: Eliminate background light pairs through parameter compensation , The effects of elimination are denoted as follows: , ; Step 3: Using formulas (1) and (2), obtain the mixed phase-shifted fringe image, denoted as follows: , ,in: The x-coordinate of the image. , It is a constant value; (1) (2) Step 4: First, , Perform a Fast Fourier Transform, and then filter the result, denoted as . , ; Step 5: [Regarding...] , Performing an inverse fast Fourier transform yields the truncated phase at the corresponding frequency, denoted as . , ; Step 6: Put , Substituting into the multi-frequency heterodyne phase expansion method, the expanded phase of the detected target is obtained, denoted as... ; In step 6, , Substituting into the multi-frequency heterodyne phase expansion method, the expanded phase of the detected target is obtained by calculating using formulas (3) to (8), denoted as... : (3) (4) (5) (6) (7) (8)。 2. The high-speed phase-shifting profilometry for three-dimensional measurement of moving targets according to claim 1, characterized in that, The camera in question is an industrial camera.

3. The high-speed phase-shifting profilometry for three-dimensional measurement of moving targets according to claim 2, characterized in that, The industrial camera mentioned is a high-speed industrial camera.

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