Measuring system of three-dimensional shape of strong reflecting surface based on high dynamic strip projector

A measurement system and three-dimensional topography technology, applied in measurement devices, instruments, optical devices, etc., can solve the problem of inability to effectively measure measurement accuracy, and achieve high measurement accuracy and adaptability to overcome the influence of background light on measurement. Effect

Active Publication Date: 2013-02-20
BEIHANG UNIV
4 Cites 34 Cited by

AI-Extracted Technical Summary

Problems solved by technology

[0005] The purpose of the present invention is to provide a three-dimensional topography measurement system for strongly reflective surfaces based on a high dynamic stripe projector, so as to solve the problem that the existing non-contact optical ...
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Method used

[0026] The high dynamic stripe projector adopts digital projection technology and FPGA-based high-speed DMD control circuit, which can realize high-speed projection up to 700Hz frame frequency. The relationship between them is that FPGA acts as the main control terminal, on the one hand, it sends image data to DMD for projection, on the other hand, it coordinates with it to control the working state of the LED light source, and at the same time generates a trigger control signal to control the camera to shoot synchronously; it has input and output The synchronous trigger module can realize the accurate coordination between the projector and the receiving periph...
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Abstract

The invention relates to a measuring system of a three-dimensional shape of a strong reflecting surface based on a high dynamic strip projector. The measuring system comprises a computer, the high dynamic strip projector and an image acquisition unit. Projection control information is sent to the high dynamic strip projector by the system through the computer, strip images in different light intensities and gray levels are controlled to be projected, meanwhile, control information is sent to the image acquisition unit by the computer, and the image acquisition unit is controlled to carry out photographing in different time periods of exposure; collected image information is transmitted to the computer by the image acquisition unit, the image is processed by the computer, and three-dimensional information of a to-be-detected object is acquired by image fusion, dephasing, phase unwrapping and stereo matching. According to the measuring system of the three-dimensional shape of the strong reflecting surface based on the high dynamic strip projector, saturation and/or excessive darkness of a collected strip image caused by the strong reflecting surface can be overcome, high-precision non-contact optical measurement of the three-dimensional shapes of the strong reflecting surfaces of metals and the like can be realized, and the measuring system of the three-dimensional shape of the strong reflecting surface based on the high dynamic strip projector can be applied to high-precision non-contact optical measurement of the three-dimensional shapes of the strong reflecting surfaces and mirror-similar surfaces of various metals.

Application Domain

Using optical means

Technology Topic

Three dimensional shapeOptical measurements +10

Image

  • Measuring system of three-dimensional shape of strong reflecting surface based on high dynamic strip projector
  • Measuring system of three-dimensional shape of strong reflecting surface based on high dynamic strip projector
  • Measuring system of three-dimensional shape of strong reflecting surface based on high dynamic strip projector

Examples

  • Experimental program(1)

Example Embodiment

[0015] see figure 1 , The present invention is a high-dynamic fringe projector-based three-dimensional topography measurement system of a strong reflective surface, which includes a computer, a high-dynamic fringe projector and an image acquisition unit. This system sends projection control information to the high dynamic stripe projector through the computer to control it to project fringe images with different brightness and different gray levels. At the same time, the computer sends control information to the image acquisition unit to control the image acquisition unit to shoot under different exposure times. Among them, the high dynamic fringe projector and the image acquisition unit are connected through a synchronization trigger signal to ensure real-time synchronization of the projected image and the captured image; after the shooting is completed, the image acquisition unit transmits the collected image information to the computer, and the computer processes the image. The three-dimensional information of the object to be measured is obtained through multi-brightness image fusion, dephase, phase expansion, and stereo matching.
[0016] The computer part is the control center of the entire measurement system.
[0017] In the computer part, the projection parameters are preset according to prior information such as the surface reflectance of the object to be measured and the ambient light intensity. The projection parameters include the specific projected image, the sequence of the projected images, and the brightness information corresponding to the projected image. The computer will project the parameters And the information is written into the high dynamic stripe projector through the standard USB port, waiting to be projected.
[0018] The prior information in the computer part is obtained through pre-projection before the measurement starts. Under different exposure times, first use the high dynamic stripe projector to shoot the workpiece under the background light. The computer extracts the surface reflection of the object, the ambient light intensity and other information according to the captured image, and the computer saves this information. During the formal measurement, based on this information, projected images with different characteristics that need to be projected are generated.
[0019] The computer part is connected with the image acquisition unit, before the projection starts, the acquisition control information is sent to the image acquisition unit, and the image acquisition unit is controlled to collect under different exposure times. After the image acquisition is completed, the image acquisition unit transmits the acquired image information to the computer, and the computer performs image processing and calculation.
[0020] The acquisition control information described in the computer part includes the exposure mode, exposure time, aperture size, trigger mode, etc. of the image acquisition unit.
[0021] The computer part combines the obtained multiple fringe images with different brightness and different exposure time to obtain a complete phase shift map of the strong reflective surface. Then the phase shift map is dephased, phase expanded and stereo matched, and finally the strong The complete three-dimensional topography information of the reflective surface.
[0022] The image fusion described in the computer section refers to the modulation brightness value of the image by comparing different brightness and different exposure time to obtain the modulation brightness value of the image, recording the phase shift diagram corresponding to the maximum value of the modulation brightness for each point, and finally extracting each point, The points merge into a new phase shift map. For the new phase shift diagram, the modulation brightness value of each point is the maximum, and the phase shift diagram at each point also corresponds to the same exposure time and brightness value.
[0023] The phase solution described in the computer part generally adopts the phase shift method. The light intensity function of each image can be expressed as: gi(x,y)=a(x,y)+r(x,y)cos[Φ(x,y)+i*2π/N], which is solved by the least square method The phase Φ(x,y) has the following expression: Φ ( x , y ) = - arctan ( X i = 0 N - 1 g i ( x , y ) sin 2 πi N X i = 0 N - 1 g i ( x , y ) cos 2 πi N ) , Among them, when N=4, it is the famous four-step phase shift method.
[0024] The phase expansion described in the computer part generally adopts the heterodyne multi-frequency phase expansion method. The heterodyne multi-frequency phase expansion method generally projects two sets of frequencies as f 1 ,f 2 Sine grating, the phase principal values ​​calculated by the two sets of gratings are Φ 1 (x,y) and Φ 2 (x,y). According to the heterodyne principle, for frequency f b =f 1 -f 2 Sine grating, the phase dominant value at point (x,y) is Φ b (x,y)=Φ 1 (x,y)-Φ 2 (x,y), assuming φ 1 (x,y) is the pair Φ 1 (x,y) The result of phase unwrapping, then: φ 1 ( x , y ) = f 1 f 1 - f 2 Φ b ( x , y ) .
[0025] According to the stereo matching described in the computer part, the three-dimensional coordinates of a point in space are obtained after obtaining the image coordinates of the left and right cameras and the internal and external parameters of the camera. S L u L v L 1 = A L [ R L | T L ] X W Y W Z W 1 S R u R v R 1 = A R [ R R | T R ] X R Y R Z R 1 You can get it. The computer is DELL's Optiplex series 980.
[0026] High dynamic fringe projector, using digital projection technology and FPGA-based high-speed DMD control circuit, can achieve high-speed projection up to 700Hz frame rate. The relationship between this is that FPGA acts as the main control terminal, on the one hand it sends image data to the DMD for projection, on the other hand it controls the working state of the LED light source in coordination with it, and at the same time generates a trigger control signal to control the camera to synchronize shooting; it has input and output The synchronous trigger module can realize the accurate coordination of the projector and the receiving peripheral device, and ensure the accurate collection of the projected image by the receiving device. The lighting part uses multiple LED chips, and the brightness and light-emitting time of each LED chip can be modulated as required, which greatly expands the dynamic range of the projector's brightness. The high-dynamic fringe projector is connected to the two high-speed network port cameras in the image acquisition unit through two identical synchronization trigger signal interfaces to ensure that the image acquisition unit can accurately synchronize images in real time when the high-dynamic fringe projector projects images at high speed Collection.
[0027] The image acquisition unit consists of two high-speed network port cameras with external synchronization trigger interfaces on the left and right. Generally, CCD cameras are selected for image shooting. The high-speed network port camera is piA640-210gm from Basler, Germany.
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Description & Claims & Application Information

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High measurement accuracyFast measurementGray levelStereo matchingMetalImage acquisitionLight intensityLightness
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