RU2583852C2 - Graph-projection moire method of measurement - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement of deformations. In graphic-projection method of measuring objects on surface of analysed object projector projected raster with given in installed on computer software parameters. Then it is scanned image of photographic camera, images obtained so is introduced into computer, in which previously laid "imaginary" raster. "Imaginary" raster is obtained by means of typographic raster and photographic camera or projector, photographic camera and flat surface or mathematical model in laboratory conditions, "imaginary" raster image obtained by scanning a photographic camera, have different contrast and colour.

EFFECT: technical result is high accuracy of measuring deformation.

2 cl, 5 dwg

Description

The invention relates to the field of measurements and can be used for measurements of various objects.

There is a method of measuring geometric imperfections of objects manually, which consists in using various measuring devices and devices for measuring objects (Kuzyakov, O.N., Kucheryuk, V.I. Methods and means of measuring surface topology, displacements, and deformations. Tyumen: Tsogu, 2002. - 172 s). The known method has been widely used in flaw detection due to the fact that it allows you to accurately determine the location and size of the defects. The main disadvantages of this method are its complexity, large losses of time and significant cash costs when examining large objects.

Known shadow moiré method for measuring the shape and displacement of the surface of the object (Theokaris P. Moiré strip in the study of deformations. - M .: Mir, 1972. - 336 S.), which consists in the use of a camera, projector and reference raster made of glass for measurements or transparent plastic mounted near the surface of the subject, at some distance from the camera and projector. The projector is installed at an angle to the reference raster, the camera is installed perpendicular to the reference raster, while the optical axes of the camera and the projector intersect at one point on the surface of the reference raster. When a projector projects a light beam onto a reference raster, a moire pattern appears on the surface of the object, which can be observed on the camera.

The advantages of this method are high sensitivity and ease of implementation. The disadvantages of this method is the need to move the reference raster, limiting the surface area of the study and limiting its use in the presence of protruding parts of the surface of the investigated object.

Known projection moire method (Novitsky VV New research on the method of moire // Calculation of spatial structures. - M: Stroyizdat, issue 11, 1967.), which consists in using the projector and matte plate on which the reference raster is applied . Using a projector, object rasters shot on camera film are projected onto a matte plate. Rotation of object rasters is carried out together with the projector using rotary devices. Moire stripes are formed due to the rotation of the projected object raster at an angle of 3-10 ° relative to the initial position.

The known method is not widespread due to low sensitivity and the need for control rasters.

Known electronic projection moire method for measuring the shape and displacements of the surface of the object (RU 2065570 C1, IPC6 G01N 21/00, publ. 08.20.96), which consists in using for measuring the camera, projector and computer with a software package that provides the addition of a model of a reference raster - an “imaginary” raster defined by the formula, and an object raster obtained from the camera. Thus, the known method simulates a shadow moire method.

The advantage of this method is the possibility of non-contact study of surfaces of significant sizes with protruding parts and having an elevated temperature.

The disadvantages of this method is the accumulation of errors during line-by-line scanning of an object raster and the complexity of its processing.

The known method is the closest to the claimed technical solution and adopted as a prototype.

The task to which the proposed technical solution is directed is to expand the technical capabilities of the graphical projection moire method of measurement.

The technical result of the application of the proposed technical solution is to increase the accuracy of determining the topology of the surface of objects, improve the quality of recognition, increase the accuracy of measurements.

The specified technical result is achieved by the fact that a camera and a projector are used to implement the method, the optical system is controlled by a computer, the projector is installed at an angle to the surface of the object being studied, and the camera is perpendicular to the surface of the object being studied. The computer contains an image of an “imaginary” raster obtained in advance in laboratory conditions at a certain distance. An "imaginary" raster can be obtained in the laboratory using a typographic raster, using a projector, or specified as a mathematical model. A reference raster is set in the computer, the parameters of which depend on the distance to the object under study. Using the projector, the reference raster is projected onto the object under study. Then the camera scans the object raster, and in digital format, the image is transmitted to the computer via a communication line. In the computer, in the installed software, the “imaginary” raster and the object raster are added together and a moire pattern is obtained. Further, in the software installed on the computer, the centers of the moire bands on the surface of the object under study, the distances from the centers of the moire bands to the plane of the "imaginary" raster, the distance from the centers of the moire bands to the optical system and the magnitude of the deformations are calculated according to the given formulas.

In the claimed technical solution, an “imaginary” raster is obtained using a typographic raster and a camera, using a projector, a camera and a flat surface, or as a mathematical model, to improve the quality of moire pattern patterns, an “imaginary” raster and an object raster of different contrast and color are used.

The principle of implementation of the graphical projection moire measurement method is shown in FIG. 1, in FIG. 2 and 3, which shows the process of obtaining the "imaginary" raster, in FIG. 4 shows a diagram for calculating the distance from an optical system including a projector and a camera to the surface of an object being examined; FIG. 5 shows a block diagram of an algorithm for a graph projection moire measurement method.

To improve the quality of the patterns of moire stripes, in contrast to the known method adopted for the prototype, an “imaginary” raster 3 and an object raster 9 of different contrast and color can be used, at the intersection of the lines of which a more contrasting pattern of moire stripes is formed, which improves the quality of recognition.

For the implementation of the graphical projection moire method of measurement, a camera 1 and a projector 2 are required, which are installed on one rotary platform. Adjustment of the optical axes of the projector and the photo-recording device, as well as the rotation of the platform is carried out remotely by stepper motors. This allows you to explore the initial imperfections of cylindrical surfaces (tanks). (Kucheryuk V.I., Yakubovsky Yu.E. Determination of the initial death of shells by the shadow moire method // Factory Laboratory, M .: 1983, No. 2, p. 77-80). The optical system is controlled by computer 5 (Fig. 1). The projector 2 is installed at an angle to the surface of the investigated object 4, and the camera 1 is perpendicular to the surface of the studied object 4.

Computer 5 contains an image of an “imaginary” raster 3 obtained in advance in laboratory conditions at a distance d (Fig. 2, 3). An “imaginary” raster 3 for distance d can be obtained:

- using a printing raster 10 and a camera 1 (Fig. 2);

- using a projector 2, a camera 1 and a flat surface 11 (Fig. 3);

- as a mathematical model.

An “imaginary” raster 3 for distance d using a printing raster 10 and camera 1 can be obtained as follows (Fig. 2). A flat typographic raster 10 with a stripe pitch a is placed at a distance d from the camera 1, which is perpendicular to the typographic raster 10. Using the camera 1, the object raster is scanned and transmitted digitally via communication line 6 to computer 5. In computer 5, installed software, the image is processed and an “imaginary” raster 3 is obtained for a distance d.

 An “imaginary” raster 3 for a distance d can be defined as a mathematical model. In this case, the object raster obtained by examining the object is also translated into a mathematical model, and the reference and object raster are added using the well-known formulas for determining the stripe pitch.

The study of object 4 using a graphical projection moire method of measurement is as follows (Fig. 1).

In computer 5, in the installed software, a reference raster with a step of bands a is set, the parameters of which depend on the distance to the object under study 4.

Using a projector 2, a reference raster is projected onto the surface of an object 4.

Then, the camera 1 scans the object raster 9 and in digital format via a communication line 6, the image is transmitted to the computer 5.

In computer 5, in the installed software, the “imaginary” raster 3 is added for distance d and the object raster 9, receiving and processing the moire pattern. In this case, the condition must be met

a _p = a _f

where a _p is the stripe pitch of the projector 2 at a given distance d, a _f is the stripe pitch of the camera 1 at a given distance d.

When applying an “imaginary” raster 3 and an object raster 9 of different contrast and color, after processing, the intersection of the dark lines of the “imaginary” raster 3 and the object raster 9 form a contrasting picture of moire stripes.

Next, in the software package installed on the computer 5, the centers of the moire fringes on the surface of the object 4, the distances h from the centers of the moire fringes to the plane of the “imaginary” raster 3, and the distances D from the centers of the moire fringes to the optical system including the camera 1 are calculated according to the given formulas projector 2 and strain values (FIG. 5).

The distance D from the centers of the moire bands to the optical system, including a camera 1 and a projector 2, is determined by the formula

D = d + h,

where d is the distance from the optical system to the plane of the "imaginary" raster 3, h is the distance from the centers of the moire bands to the plane of the "imaginary" raster 3.

The distance h from the centers of the moire bands to the plane of the "imaginary" raster 3 is determined by the formula

, $$h=\frac{na}{\tan \alpha }$$

,

where a is the stripe pitch of the “imaginary” raster 3, n is the strip order, α is the angle of incidence of the projector's rays.

The stripe pitch of the “imaginary” raster 3 is determined by the formula

a = ma _em ,

where m is the scale of the "imaginary" raster 3, and _em is the step of the strips of the "imaginary" raster 3, determined by direct measurements upon receipt of the "imaginary" raster 3 for the distance d in laboratory conditions.

The scale of the imaginary raster 3 is determined by the formula (Fig. 5)

, $$m=\frac{d_{\mathrm{uh}m}}{d_{\partial }}$$

,

where d _em is the distance to the "imaginary" raster 3, d _∂ is the distance to the specified "imaginary" raster 12.

Given the angle of incidence of the rays for each point, the angle of incidence of the rays of the projector is determined by the formula

, $$\arccos \alpha =\frac{d\cos {\alpha }_{\upsilon }}{\sqrt{{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="00000007.png,00000010.png"\; state="\{\{state\}\}">d</figure-callout>}}^2+x^2+{\mathrm{<figure-callout\; id="2"\; label="y"\; filenames="00000007.png,00000010.png"\; state="\{\{state\}\}">y</figure-callout>}}^2+2dx\sin {\alpha }_{\upsilon }}}$$

,

where d is the distance from the focus of the camera to the center of the light spot on the surface of the object, α _υ is the angle between the central beam and the normal to the surface of the object, x, y are the coordinates of the point on the surface of the object.

Claims (2)

1. A graphic projection method for measuring objects, characterized in that a raster is projected onto the surface of the object to be studied by the projector with parameters specified in the software installed on the computer, the image is scanned by the camera, images obtained in this way are entered into the computer in which it is preliminarily stored "Imaginary" raster, characterized in that the "imaginary" raster is obtained using a printing raster and a camera or projector, a camera and a flat surface or mathematical models in the laboratory, while the "imaginary" raster and image obtained by scanning with a camera have different contrast and color, and when obtaining a picture of moire stripes, the condition must be met
a _p = a _f
where a _p is the stripe pitch of the projector at a given distance, and _f is the stripe pitch of the camera at a given distance. 2. The method according to p. 1, characterized in that the distance from the centers of the moire bands to the plane of the "imaginary" raster is determined by the formula

,
where a is the stripe pitch of the “imaginary” raster, n is the strip order, α is the angle of incidence of the projector's rays, calculated by the formula
α = ma _em ,
where m is the scale of the "imaginary" raster, and _em is the step of the strips of the "imaginary" raster, determined by direct measurements upon receipt of the "imaginary" raster in laboratory conditions, while m is calculated by the formula

,
where d _em is the distance to the "imaginary" raster, d _∂ is the distance to the specified "imaginary" raster.

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