CN102261896A - Method and system for measuring three-dimensional shape of object based on phase measurement - Google Patents

Abstract

The invention relates to a method and a system for measuring the three-dimensional shape of an object based on phase measurement. The method comprises the following steps of: generating a high-precision digital phase shift grating image by using computer programming; projecting the grating image with phase shift on the surface of an object to be tested by a digital light processing (DLP) projector; sequentially acquiring a moire fringe image modulated by the surface of the object to be tested by using a charge coupled device (CCD) camera; processing the acquired image by using an image acquisition card; transmitting the image to a computer to calculate the phase of each pixel of the moire fringe image; calculating three-dimensional point cloud data of the surface of the object to be tested according to a mapping relation between the phase and the height; and transmitting the three-dimensional point cloud data to three-dimensional reconstruction software for processing to obtain the three-dimensional shape of the object. The method has the advantages of high measurement accuracy, simplicity and convenience for operation, high speed, high reliability and the like, and has high actual application value.

Description

A kind of object dimensional topography measurement method and system based on phase measurement

Technical field:

The invention belongs to the three-dimensional measurement field, be specifically related to a kind of object dimensional topography measurement method and system based on phase measurement.

Technical background:

Present many industrial circles need the inspected object three-dimensional appearance, comprising production quality control, detection and reverse-engineering field.Most systems all adopts binocular grating measuring method to measure at present, its principle of work is: based on optical triangulation shape principle, utilize white visible light transmissive physical grating that one group of grating fringe is projected to body surface, because optical interference takes place in grating fringe on curved surface, utilize two digital cameras that it is filmed again, through graphical analysis, calculate, the last 3D cloud data that just can obtain object, utilize the gray-scale value of different images to come in the patent " a kind of based on two-dimensional encoded 3 D measuring method; application number: 200710052728.9 " of Central China University of Science and Technology's application to encoding through the project objects under the structured light irradiation, image division is become the block of a plurality of big or small non-overlapping copies, process decoding and phase calculation obtain the coded message and the phase information of each spatial point, obtain the coordinate of measurement space point.Though this method precision is higher, make the physical grating more complicated, and measuring speed is slow.This method is the use physical grating, precision and grating manufacture process requirement to projection arrangement inner control system are very high, the phase shift step pitch unanimity of projected image can be accurately controlled in requirement, and these 3 have just determined that the cost of total system is very expensive, and very high in the follow-up maintenance expense.Along with some research institution of the development of technology proposes to utilize the digit optical projector equipment to come the alternative physical grating, digital projection equipment can utilize computer programming method, produce high precision phase-shifted grating image easily, cost can reduce greatly like this, utilize computing machine to produce uniform grid line in the patent " frequency conversion shadow casting raster line three-dimensional shape measuring apparatus and measuring method thereof; application number: 200710045595.2 " of 11 research institutes of China Shipbuilding Industry Corporation the 7th application, external projector of while, grating projectin is arrived the testee surface, replaced the physics projection gate, the density uniformity of grating like this, the striped rectilinearity is guaranteed, but in subsequent processes, adopt the level line that calculates Moire fringe to obtain the three-dimensional appearance of object, because it is lower that the Moire fringe level line calculates object dimensional pattern precision, this kind method is fit to the lower occasion of measuring accuracy.

Summary of the invention:

The object of the present invention is to provide a kind of three-dimensional body topography measurement method and system based on phase measurement, its technical scheme is: at first place object under test, during measurement, utilize computer programming to produce high-precision digital phase-shifting technique raster image, and raster image is projected the object under test surface by DLP projector, because the program that configures in advance, the DLP projector that links to each other with computing machine will produce the four amplitude grating images that phase shift is θ, ccd video camera also will successively obtain corresponding four width of cloth Moire fringe images with phase shift θ simultaneously, after handling the picture signal that captures, image pick-up card sends into the phase place of each pixel of COMPUTER CALCULATION Moire fringe image again, calculate the three dimensional point cloud on testee surface at last according to the phase place and the mapping relations of height, the three dimensional point cloud that obtains is sent into the three-dimensional appearance that the three-dimensional reconstruction software processes can obtain object.

The present invention also provides a kind of system that is used to implement above-mentioned measuring method, and it is to be made of DLP projector, ccd video camera, image pick-up card, computing machine.

Beneficial effect of the present invention: the complicacy that the first has avoided using the sum of errors in the coding and decoding process that the three-dimensional appearance of Methods for Coding Measuring Object brings to handle; It two is to have avoided the use physical grating to produce Moire fringe, has greatly reduced precision and grating manufacture process requirement to projection arrangement inner control system, effectively reduces cost; It three is relative heights of calculating each pixel by the phase place of calculating each pixel of Moire fringe image, its have the measuring accuracy height, simple to operation, speed fast, the advantage of high reliability.

Description of drawings:

To the detailed description of the invention, wherein Fig. 1 is the structure diagram of measuring system below in conjunction with drawings and Examples, 1. computing machines among Fig. 1,2. object under test, 3.DLP projector, 4.CCD video camera, 5. image pick-up card.

Fig. 2 is the algorithm flow chart of the three-dimensional body topography measurement method of phase measurement.

Specific embodiments:

As shown in Figure 1, at first place object under test (2) and make its normal and DLP projector (3) angle at 45, its normal becomes 0 ° of angle with ccd video camera (4) simultaneously, when beginning to measure, utilize computing machine (1) programming to produce high-precision digital phase-shifting technique raster image, and raster image is projected object under test (2) surface by DLP projector (3), catch the Moire fringe image of modulating through object under test (2) this moment by ccd video camera (4), because the program that configures in advance, the DLP projector (3) that links to each other with computing machine (1) will produce the four amplitude grating images that phase shift is θ, ccd video camera (4) also will successively obtain corresponding four width of cloth Moire fringe images with phase shift θ simultaneously, after handling the picture signal that captures, image pick-up card (5) sends into the phase place that computing machine (1) calculates each pixel of Moire fringe image again, the specific algorithm flow process as shown in Figure 2, computing machine is at first selected the pixel of testee, calculate the light intensity value of the selected phase pixel of every amplitude phase diagram then, calculate the phase value of each pixel again according to light intensity value, calculate the three dimensional point cloud of each pixel at last according to phase value, concrete steps are as follows: the phase shift between every width of cloth Moire fringe image of known DLP projector (3) projection is θ, θ can be a unknown constant, so following relation is arranged between the light intensity value of each pixel and the phase shift theta:

I ₁＝I ₀+Acos(φ+θ)

I ₂＝I ₀+Acos(φ+2θ)

I ₃＝I ₀+Acos(φ+3θ)

I ₄＝I ₀+Acos(φ+4θ)

I wherein ₀Be the background light intensity value of every width of cloth Moire fringe image, A is the amplitude of every width of cloth Moire fringe image, I ₀With A be constant but according to the Strength Changes of illumination, θ can be obtained by following formula:

$\mathrm{\θ}={\cos }^{-1}\left(\frac{(I_1-I_4)-(I_2-I_3)}{2(I_2-I_3)}\right)$

And then the phase of each pixel as can be known, as shown in the formula:

$\mathrm{\&phi;}={\tan }^{-1}\left[\left(\frac{(I_1-I_4)-(I_2-I_3)}{({\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="HSA00000476084300011.png"\; state="\{\{state\}\}">I</figure-callout>}}_2+I_3)-(I_1+I_4)}\right)\tan \mathrm{\&theta;}\right]$

Phase value substitution following formula with each pixel:

Z(x，y)＝W*(N+φ(x，y)/2π)

Can obtain the three dimensional point cloud of each pixel.

The three dimensional point cloud that finally obtains is sent into the three-dimensional appearance that the three-dimensional reconstruction software processes can obtain object.

The above is preferred embodiment of the present invention, is not to be used for limiting practical range of the present invention, and all equivalences of being done according to claim scope of the present invention change and modify, and all belong in protection scope of the present invention.

Claims (2)

1. object dimensional topography measurement method based on phase measurement, it is characterized in that: at first place object under test, during measurement, utilize computer programming to produce high-precision digital phase-shifting technique raster image, and raster image is projected the object under test surface by DLP projector, because the program that configures in advance, the DLP projector that links to each other with computing machine will produce the four amplitude grating images that phase shift is θ, ccd video camera also will successively obtain corresponding four width of cloth Moire fringe images with phase shift θ simultaneously, after handling the picture signal that captures, image pick-up card sends into the phase place of each pixel of COMPUTER CALCULATION Moire fringe image again, calculate the three dimensional point cloud on testee surface at last according to the phase place and the mapping relations of height, the three dimensional point cloud that obtains is sent into the three-dimensional appearance that the three-dimensional reconstruction software processes can obtain object.

2. object dimensional topography measurement system based on phase measurement, it is characterized in that: by computing machine (1), object under test (2), DLP projector (3), ccd video camera (4), image pick-up card (5) constitutes, at first place object under test (2) and make its normal and DLP projector (3) angle at 45, its normal becomes 0 ° of angle with ccd video camera (4) simultaneously, when beginning to measure, utilize computing machine (1) programming to produce high-precision digital phase-shifting technique raster image, and raster image is projected object under test (2) surface by DLP projector (3), catch the Moire fringe image of modulating through object under test (2) this moment by ccd video camera (4), because the program that configures in advance, the DLP projector (3) that links to each other with computing machine (1) will produce the four amplitude grating images that phase shift is θ, ccd video camera (4) also will successively obtain corresponding four width of cloth Moire fringe images with phase shift θ simultaneously, after handling the picture signal that captures, image pick-up card (5) sends into the phase place that computing machine (1) calculates each pixel of Moire fringe image again, calculate the three dimensional point cloud on testee surface at last according to the phase place and the mapping relations of height, the three dimensional point cloud that obtains is sent into the three-dimensional appearance that the three-dimensional reconstruction software processes can obtain object.

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