KR20000075148A - moire image capturing apparatus and method - Google Patents

Abstract

PURPOSE: An apparatus and a method for obtaining a moire pattern are provided to simplify the structure by removing a reference grating and accordingly omit the necessity to remove images of the reference grating except the moire pattern having shape information. CONSTITUTION: An apparatus for obtaining a moire pattern includes a light source(1) mounted with a first distance from a reference surface(S) to lay an object(7) on, a projecting grating(3) disposed between the reference surface and the light source, an imaging lens(9) mounted at a position with a predetermined distance from an optical axis(A1) of a projecting optical system formed by the light source and the projecting grating for passing though light beams reflected against the object, and a light receiving part(11) disposed at one side of the imaging lens for receiving the light beams passing through the imaging lens, wherein the optical axis of the projecting system formed by the light source and the projecting grating is parallel to an optical axis(A2) of an imaging optical system formed by the imaging lens and the light receiving part and perpendicular to the reference surface, and the distance from the reference surface to the light source is equal to the distance to the imaging lens.

Description

Moire image capturing apparatus and method

The present invention relates to a moiré pattern acquisition apparatus and method.

In general, there are two techniques for measuring the three-dimensional shape of the free-form surface shape. The method of measuring the entire curved shape by measuring a single point on the curved surface by using a three-dimensional measuring instrument has been widely used for a long time. However, this method has a disadvantage of excessive measurement time, and in recent years, many non-contact measuring methods, such as the moiré method, have been used. Have.

In the moiré method, in order to obtain a moire fringe having three-dimensional shape information of the measurement object, a straight line of uniform intervals must be formed on the measurement object, and it must be precisely transferred. In the conventional method for this purpose, the linear glass lattice in which a straight line of regular intervals is engraved in chrome on one surface of the glass is projected onto the measurement object using a projection optical system. In addition, in order to transfer the linear stripes formed on the measurement object at regular intervals, a linear glass grid transfer field device is used.

When a straight glass grid as shown in Fig. 1A is projected onto the measurement object, stripes are formed on the measurement object as shown in Fig. 1B, and the stripes are bent according to the height of the measurement object. When the measurement object having the streaks shown in FIG. 1B is overlapped with the linear glass grid shown in FIG. 1A, an image as shown in FIG. 1C can be obtained. In Figure 1c, the shape of the wave pattern can be seen, which is called a "moire pattern". Since the moiré pattern is a contour line formed according to the height of the measurement object, the moire pattern is analyzed to measure the shape of the measurement object.

As a device for realizing such a moiré method, a phase shifting moiré meter which is widely used now is shown in FIG. 2. In FIG. 2, a white light source, a condenser, a projection grating, and a projection lens project a grating onto an object to form a deformed stripe, and thus, FIG. To get the same result. The grating actuator is a device for transferring the projection gratings at equal intervals of about 3 to 5 steps. The same reference grating, relay lens, and imaging lens that are identical to the projection grating are used to form an image as shown in FIG. 1C in a CCD camera.

By the way, in the image (FIG. 1C) obtained by the conventional moire method measuring device configured as described above, the moire pattern indicating the height information of the measurement object and the pattern of the reference grating placed in front of the CCD camera are simultaneously displayed.

Therefore, there is a problem that a separate means for removing the image of the reference lattice is required and the structure becomes complicated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a moiré pattern acquisition apparatus and method that can simply obtain a moire pattern without using a reference grid.

1a to 1c is a view showing a process of obtaining a conventional moire pattern,

2 is a schematic diagram showing the structure of a conventional moiré measuring device;

3 is a schematic configuration diagram showing a moire fringe obtaining apparatus according to the present invention;

4 is an explanatory diagram for explaining a moire pattern acquisition method according to the present invention;

5 is a real picture of the device used in the experiment of the moire pattern acquisition device according to the present invention,

6A is a photograph of a grid pattern image projected on a reference plane captured by a CCD camera by the experimental apparatus of FIG. 5;

FIG. 6B is a photograph showing an image in which a projection lattice is projected onto a measurement object having a lip-shaped gypsum shape by the experimental apparatus of FIG.

7A is a diagram showing the phase of each point of the reference plane;

7B is a diagram showing the phase of each point of the workpiece;

Figure 7c is a diagram showing the moiré phase.

<Explanation of symbols for the main parts of the drawings>

One ; Light source 3: projection grid

5: projection grid feed means 7: measured object

9: imaging lens 11: light receiving part

A1, A2: optical axis

The moiré pattern obtaining apparatus according to the present invention includes a light source installed at a position spaced apart by a first interval from a reference plane on which a measurement object is placed, a projection grid disposed between the reference plane and the light source, and light reflected from a measurement object placed on the reference plane. And an imaging lens installed at a position spaced apart from the optical axis of the projection optical system formed by the light source and the projection grid so as to pass therethrough, and a light receiving unit disposed at one side of the imaging lens to receive the light passing through the imaging lens. The optical axis of the projection optical system formed by the light source and the projection lattice, and the optical axis of the imaging optical system formed by the imaging lens and the light receiving unit are parallel to each other and perpendicular to the reference plane, and the distance from the reference plane to the light source and at the reference plane The distance to the imaging lens is the same.

The method of acquiring the moire pattern according to the present invention is to make the optical axis of the projection optical system in which the light source and the projection lattice are aligned perpendicular to the reference plane, and the optical axis of the imaging optical system formed by aligning the imaging lens and the light receiving unit in a direction perpendicular to the reference plane. And equalizing the distance from the reference plane to the light source and the distance from the reference plane to the imaging lens, and by installing a measurement object on the reference plane, the light from the light source passes through the projection grid and is reflected from the measurement object. And moiré pattern is obtained from the difference between the reference plane phase and the measurement object phase by reaching the light receiving unit through the imaging lens.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail, referring an accompanying drawing.

As shown in FIG. 3, a light source 1 for generating light is provided at a position spaced apart from the reference plane S on which the measurement object 7 is placed by the first interval L _L , and the reference plane S is provided. Between the light source 1 and the light source 1 is provided a projection grid 3 is engraved with a grid pattern, the light source 1 and the projection grid so that the light reflected from the measurement object 7 placed on the reference plane (S) passes through An imaging lens 9 is provided at a position spaced a predetermined distance from the optical axis A1 of the projection optical system formed by (7), and a light receiving portion is formed at one side of the imaging lens so that light passing through the imaging lens 9 is received. 11) is installed.

The projection grid transfer means 5 is coupled to the projection grid 3 so as to transfer the projection grid 3.

The optical axis A1 of the projection optical system formed by the light source 1 and the projection grid 3 and the optical axis A2 of the imaging optical system formed by the imaging lens 9 and the light receiving unit 11 are parallel to each other. The distance from S) to the light source 1 and the distance from the reference plane S to the imaging lens 9 are equal, and the optical axis A1 of the projection optical system and the optical axis A2 of the imaging optical system are on the reference plane. It is vertical.

The light source 1 is preferably made of a laser diode or a halogen light source called a semiconductor laser, which is compact, lightweight and inexpensive.

The light receiver 11 is a two-dimensional image sensor, preferably a CCD (charge coupled device) camera.

The projection lens 3 and the imaging lens 9 are known lenses.

In this structure, the light emitted from the light source 1 passes through the projection grid 3 and is reflected by the measurement object 7, and then reaches the light receiving part 11 through the imaging lens 9. The image is formed, and eventually a moire pattern is obtained. In this case, in order to implement an algorithm such as 3, 4, 5 buckets or n buckets, the projection grids are transferred at equal intervals using the projection grid transfer means 5.

Hereinafter, a method of forming a moire pattern according to the present invention will be described in detail with reference to FIG. 4.

First, a process of obtaining the deformed grid pattern will be described.

The optical axis of the CCD camera is perpendicular to the reference plane, and the optical axis of the light source perpendicular to the projection grid is also perpendicular to the reference plane. The distance between the image plane of the CCD camera and the imaging lens along the optical axis of the camera is f _C , the distance from the imaging lens to the reference plane is L _C , and between the point light source and the projection grid along the optical axis of the light source. The distance is referred to as f _L , the distance from the point light source to the reference plane is referred to as L _L , and any point on the image plane of the CCD camera and any point on the projection grid is at a distance x _i and x _g perpendicular to the respective optical axis. Indicates.

The light incident from the point light source at a point x _g on the projection lattice is incident on a point (x _o , h (x _o )) on the object after passing through the projection lattice. The reflected light passes through the center of the imaging lens and reaches the position x _i on the image plane of the CCD camera.

At this time, the light transmittance T (x _g ) of the projection lattice is expressed as follows when the grating pitch is g.

Where Δ is the initial position of the projection grid.

When the brightness of light incident at a point x _g of the projection grating is I _L (x _g ), the brightness I _p (of light incident through the projection grating at the point of measurement object (x _o , h (x _o )) x _o , h (x _o )) looks like this:

Using the following geometric relationship

x _g is represented as:

I _p (x _o , h (x _o )) appears as

When the reflectance of one point (x _o , h (x _o )) of the object to be measured is R (x _o , h (x _o )), the brightness of light I (I) incident on a point x _i on the image plane of the CCD camera x _i )

Using the following geometric relationship

I (x _i ) appears as

If L _L = L _C = L, f _L = f _c = f, equation (8) is as follows.

Because of, Say,

The grid pattern deformed by Equation (10) can be represented.

Looking at equation (10), it can be seen that the deformed grid pattern includes the height information hi of the object.

In the existing moiré method, the reference grid is installed in front of the light receiving unit, and the moiré phase related only to the height information of the object is as follows. Is seeking.

Next, a process of obtaining a moire fringe using only the deformed lattice without using a reference lattice will be described.

In the general case of external illumination other than a point light source, the brightness I _ij of the deformed lattice for Δ = Δ _j is as follows.

Here, M _i is the brightness of the background and N _i corresponds to the contrast of the deformed grid.

With shape information Is the measurable phase And the integer n are expressed as

when h _i is 0, i.e., the reference phase obtained using the image of the reference plane

The phase of the workpiece height h _i , i.e., the phase of the workpiece, with the workpiece placed on the reference plane. Can be obtained. Where is defined as the difference between the two phases Is the moiré phase of equation (11) Corresponds to

It can be seen that the moiré pattern (phase) can be obtained without using the reference grid by the above method.

5 shows an experimental setup used in the experiments of the present invention. In this case, human lip gypsum was used as the measurement object.

The camera used SONY XC-75 monochrome CCD camera and the lens used SPACECOM TV zoom lens S6X11. The projection grid used a binary grating having a pitch g of 0.92 mm. The frame grabber uses a monochrome frame grabber DT3155 with a resolution of 640x480 from DATA TRANSLATION.

FIG. 6A shows a grid pattern image projected on a reference plane by a CCD camera, and FIG. 6B shows an image on which a projection grid is projected onto a lip plaster which is a measurement target.

Each phase was calculated using the following four bucket algorithm.

7A shows the phase of the reference plane 8b shows the workpiece phase Indicates. Figure 7c is a moiré pattern (phase) calculated as the difference between the reference phase and the measured phase Indicates. As can be seen from the result of FIG. 7C, only the pattern of contour lines according to the height of the measurement object (height from the reference plane) appears in the moire pattern obtained by the present invention, and the image of the reference grid as shown in FIG. It can be seen that it does not appear.

According to the apparatus and method for acquiring a moire pattern according to the present invention, the structure is simplified by eliminating the reference grid, and it is not necessary to remove an image other than the moire pattern having the shape information, that is, the image of the reference grid. Therefore, the price is low and the structure is simple.

Claims (2)

A light source installed at a position spaced apart from the reference plane on which the workpiece is placed by the first interval, A projection grid disposed between the reference plane and the light source; An imaging lens installed at a position spaced a predetermined distance from an optical axis of the projection optical system formed by the light source and the projection grid so that light reflected from the measurement object placed on the reference plane passes; A light receiving part disposed on one side of the imaging lens to receive the light passing through the imaging lens; The optical axis of the projection optical system formed by the light source and the projection lattice, and the optical axis of the imaging optical system formed by the imaging lens and the light receiving unit are parallel to each other and perpendicular to the reference plane. Moiré pattern acquisition device, characterized in that the distance from the reference plane to the light source and the distance from the reference plane to the imaging lens is the same. The optical axis of the projection optical system in which the light source and the projection lattice are aligned perpendicular to the reference plane, and the optical axis of the imaging optical system formed by aligning the imaging lens and the light receiving unit perpendicular to the reference plane, The distance from the reference plane to the light source is equal to the distance from the reference plane to the imaging lens, By installing the measurement object on the reference plane, The light from the light source passes through the projection lattice and is reflected from the measurement object, and then reaches the light receiving portion through the imaging lens to obtain a moire pattern from the difference between the reference plane phase and the measurement object phase. How to get a pattern.