DE2514671A1 - GRID FOR PROJECTING A LIGHT PATTERN ON A REFERENCE PLANE AND METHOD FOR CREATING SUCH A GRID - Google Patents

Description

25H671

ZS-PA 74 12045 9546-75 Dr.v.B / S

from 04/04/1974

öompagnie .ülectro-Mecanique, 12 Rue Portalis, Paris 8e,

France

Grid for projecting a light pattern onto a reference plane and method for producing such a grid

The present invention relates to a grid with parallel lines for projecting a light pattern onto a reference plane via an optical system, creating a Network of parallel, equidistant strips of light is created on the reference plane, which is a certain distance from the optical system and with its optical axis forms an angle different from 90. The invention relates to also to a method for producing such a grid and a device for carrying out this method.

The grid according to the present invention is particularly suitable for the visualization of contour lines of an in the reference plane located object with the help of the moire effect.

It is known to create contour lines of a three-dimensional object using the moiré effect with white light

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to make visible. This is the case with these procedures Moiré from the superposition of the grid pattern and its shadow on the three-dimensional object to be analyzed. This procedure can be carried out well in real time has the disadvantage, however, that grids of the size of the object to be analyzed are required, which limits the scope restricts.

Also the projection of incoherent streaks of light a three-dimensional object to be analyzed has already been used to generate a moire on the object. There are two options for displaying such moiré patterns. One consists in illuminating the object with two patterns of light in such a way that the object is divided into two identical light strip fields are located, which are angularly offset from one another. A second procedure is the object is illuminated by a grid and at a different angle by a lens and another grid or looking at a mask. In this second method, the moire effect is created by multiplying the light intensities and not by a superposition as in the first mentioned i'alle, so that there is a better contrast. This method, which is known in principle, has already been used in various ways in particular for the analysis of deformations of objects and in projectors for modified profiles. So far is known, this technique for the formation of a moiré pattern to make contour lines visible on three-dimensional Items have not yet been used. You can also use the previously used to display iloire patterns Grids do not receive contour lines because they do not allow a periodic light pattern with an oblique To project the angle of incidence onto a reference plane, so that in this creates a distribution of parallel, equidistant strips.

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The object of the invention is primarily to provide a new one Specify card file with parallel lines, e.g. for projection a light pattern through an optical system on a reference plane, so that a grid of parallel, equidistant strips results on this plane, if these are present Plane is at a certain distance from the optical system and at a certain angle other than 90 ° forms the optical axis of the optical system.

The present invention is intended to provide a manufacturing method for such a grid and a device for implementing this method are specified.

The grid according to the present invention is characterized in that it contains strips or lines, which have an aperiodic distribution with a pseudoperiod P given by the following recursion formula:

fptgoC '(2d _? -f) VU (^ - 1) ² tg ² 0C «P ₌ * - - ¹ -

[(cL ₂ -f) tgOC «+ npj [(d ₂ -f) tgoC ¹ + (n + 1) pl

Herein mean:

η a whole positive or negative number (the value η = 0 corresponds to the line adjacent to the optical axis,

f is the focal length of the optical system,

ρ is the period of the equidistant stripes on the reference plane ,

dp is the distance of the reference plane from the optical system and OC ^{1 is} the angle between the reference plane and the optical axis.

By arranging the grid according to the invention in a plane which is the optical conjugate of the reference plane

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with respect to the optical system (the conjugate plane also forms an angle other than 90 ° with the optical axis of the system) and using a projection system, it is possible through the grid and the optical System to project a periodic light pattern onto a reference plane in such a way that there is a grid of parallel, equidistant Forms stripes on the reference plane. If now a three-dimensional object is placed in the reference plane is and this object through a second optical system, the axis of which is perpendicular to the reference plane, and through If a second grid is viewed, lines or moiré stripes appear on the object, which are nothing else as contour lines of the object with respect to the reference plane.

The manufacturing method according to the invention is characterized in that a photograph or an image of the desired, Grating arranged in the reference plane with the same optical system that is used to project the light pattern is used on the reference plane The optical system and the reference plane are arranged in the same way when recording as when projecting the Light pattern and in a plane which is optically conjugate with respect to the optical system to the reference plane, is a photographic plate or film to be developed after shooting.

The negative image obtained in this way can now be used directly as a grid according to the invention. Of the Raster consists of a transparent sheet, e.g. a photographic film, on which opaque strips or lines are shown. A variant consists in using the film negative obtained in this way, e.g. by means of a photo-etching process a series of lines that alternately absorb and reflect light to form an opaque plate, so that you get a partially reflective and partially

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non-reflective grid. In the first case is the projection system used with the Easter of the invention arranged for projecting a light pattern onto the reference plane so that the light emerging from it passes through the grid falls, while in the second lalle the projection system so is arranged that the exiting light beam is reflected by the grid.

Further details are given below with reference explained in more detail on the drawings; show it:

Figure 1 is a graph showing the in the Manufacture of the grid according to the invention can be seen parameters to be taken into account;

FIG. 2 shows a plan view of part of a razor according to an exemplary embodiment of the invention;

FIG. 3 schematically shows an optical system for production of a grid according to the invention. After a few changes, the same optical system can be used to make contour lines visible of a three-dimensional object can be used.

In Figure 1, a grid T is shown according to an embodiment of the invention, which is arranged by way of a light beam of a projection device (not shown) and allows a periodic light pattern on a reference _{plane through an optical system, which consists for example of a converging lens L 1} Project Pr with an oblique incidence (angle i fi 0). More precisely, with the present grid · T, a pattern or grating 1 can be formed on the reference plane P, which is located at a certain distance dp from the optical system L ₁ and forms a predetermined angle oc ¹ with the optical axis of the system L ₁ parallel, equidistant strips, the periodicity of which is denoted by "p" in FIG. 2, are generated. In order to obtain strips with exactly the same (constant) width (periodicity) in the reference plane P,

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it is not sufficient to have a periodic grid in the plane P _T , which is optically conjugate with respect to the optical system L- to the plane P, forms an angle oC with the optical axis, and is at a distance d. from the optical system L ₁ (measured along the optical axis) is to be arranged, wherein

d ₁ tgoC = d ₂ tgoCi (1)

^ ♦ 4 - i U)

(f = focal length of the optical system L ₁ ). If one were to use a customary periodic grid instead of the grid T _r , then one would get P in the reference plane. aperiodic stripes. This is due to the fact that the magnification of the optical system is not the same for all points of the grid and the conjugate of the reference plane P, because the reference plane and the grid run obliquely to the optical axis, and the magnification is a puncture of the distance of this plane and the Raster from the optical system.

To create a grid pattern with even stripes in the To obtain reference plane P, the lines of the grid T must therefore be arranged aperiodically. Figure 2 shows enlarged a section of a grid T according to an embodiment of the invention.

Using known formulas of geometric optics, it can be shown that the strips or lines 2 of the grid T are arranged aperiodically with a pseudoperiod P.

^r η

according to the appeal s ion _formula:;

fptgoC «. (2d "-f). V Λ + (ψ ² - - D ² tg ² oc '

ρ ₌ L i (3)

ⁿ Qd ₂ -f) tgoc ¹ + np "J £ (d ₂ -f) tgoc + (n + 1)]

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in which η is a whole positive or negative number (the value η = 0 corresponds to the _{line lying next to the optical axis of the lens L 1} with the focal length f) and the parameters p, or ¹ and dr, those given above and from FIG. 1 have obvious meanings.

As can be seen from Figure 2, the lines 2 of the grid T have different widths depending on the parameters listed above and the width of the stripes 1 of the stripe pattern desired in the reference plane P. So far if it is only about the representation of contour lines of a three-dimensional object, the width is the Penalties 1 not critical, it is sufficient if the strips 1 run parallel to each other and all have the same width, are arranged periodically, i.e. have a period ρ, and that they are sufficiently rich in contrast. Among the in figure The geometrical relationships shown, in which the width of the strips 1 is practically equal to p / 2, is the width of the lines 2 of the grid T as a first approximation by the same formula as that for the pseudoperiod P given by the Parameter ρ is replaced by p / 2.

In order to now produce a grid according to the invention Tr for given geometric conditions, it would be possible to calculate the various values of the pseudoperiod P and the line widths using the formula (3) given above and then to manufacture the mask or the grid Tr. Another extremely simple method of manufacture such a grid is based on the principle of optical inversion. For making a grid according to the invention you only need to arrange a grid or grid with a periodic line structure or an image of the in the plane P to generate the desired periodic stripe grating or raster and of the desired grating or its image with

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Using the optical system L ₁ and a photographic plate or film Ph (Fig. 3) to take a photograph. The reference plane P, the optical system Ii- and the plate Ph are geometrically arranged in the same way as the plane P, the optical system Iu and the rasber Tr when a light pattern is projected and contrasting stripes are formed in the reference plane P. In other words, the reference plane P and the photographic plate Ph are arranged at a distance dp and d., Respectively, from the optical system L ₁ and form the angles οζ 'and QC with the optical axis of this system. Once the image of the desired gate has been recorded on the plate Ph, the latter only needs to be developed, and the negative obtained in this way with a transparent base and a certain number of opaque lines or strips corresponds to the structure described with reference to FIGS so that it can be used directly as a grid to form a grid with periodic stripes or lines in a reference plane P.

When creating a photographic image of the desired Stripe grating on the plate pH can indeed be a grating with periodically arranged lines in the reference plane P. arrange, but it is more convenient not to arrange this periodic grid yourself in the reference plane P, but only to map it in this. As FIG. 3 shows, one can get an image of a periodic lattice in the reference plane Generate P by another optical system, for example, from a converging lens Lp, a grid or a mask M with a grid of parallel and equidistant lines and a lighting device consisting of a light source S and a condenser L. From Figure 3 it can also be seen that the optical axis of the from the light source S, the condenser L ", the mask M and the optical system Lp existing arrangement perpendicular to the Reference plane P is and this plane is in the same point as

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the optical axis of the optical system L ₁ intersects. The mask M is located in a plane which is _{optically conjugate with respect to the optical system L 2} to the reference plane P, and the capacitor L ₃ images the source S in the plane of the converging lens Lp.

With the arrangement described with reference to FIG. 3, as mentioned, a haster according to the invention can be produced in a very simple manner. With a slight modification, the same arrangement can also be used to make the contour lines of a three-dimensional object visible. A first possibility is to look at the contour lines of a three-dimensional object located in the reference plane P with the aid of the arrangement shown in FIG the mask M and the optical system L _{2 is} illuminated with a periodic light pattern. If a three-dimensional object illuminated in this way is now _{viewed through the optical system L 1} and the Rsdber Tr, then contour lines appear on this object. However, since the direction of observation runs obliquely to the reference _{plane P r} , which also represents the reference plane for the contour lines, the arrangement shown in FIG. 3 is of little practical interest, since the contour lines obtained in this way are difficult to evaluate. For practical reasons, the direction of observation of the contour lines should be perpendicular to the reference plane. In order to achieve this, the arrangement shown in FIG. 3 can be modified as follows: The lighting system SL. Is detachably mounted on the arrangement so that it can be replaced by a viewing device, for example a ground glass, an eyepiece, a Yidikon tube connected to a television receiver or any other equivalent viewing device. The photographic plate Ph can also be detachably arranged and developed by the

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and negatively serving as Easter Tr, and you can attach your own lighting system to the arrangement for illuminating the Eeferens plane P by the Easter Tr and the optical system I ₁ . This latter lighting system can be the dismantled lighting system SL previously arranged behind the mask M. With these changes, the arrangement shown in FIG. 3 can be used to illuminate an object located in the reference plane P with a periodic light pattern and, through the optical system I «and the mask M, the contour lines that appear on the three-dimensional object, to observe.

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Claims (6)

25U671 Claims ί 1./Raster with parallel stripes, especially for projection of a light pattern through an optical system onto a reference plane in order to move onto the reference plane, which is located in a predetermined distance from the optical system and with its optical axis one of 90 different Forms an angle, a grid of parallel and equidistant To produce stripes, characterized in that that the lines of the grid are aperiodic with a pseudoperiod P, according to the recursion formula f ρ tgoc · (2d ₉ -f) V 1 + w -ι tgOC «+ np 2 [(d ₂ -f) tgOCt ₊ ( _{n + 1} ) _p are arranged in v / elcher η a whole negative or positive number (the value η = 0 corresponds to the strip adjacent to the optical axis), f is the focal length of the optical system, ρ is the period of the equidistant stripes in the reference plane, dp is the distance of the reference plane from the optical system and OC 'that formed by the reference plane and the optical axis Angle. 2. Grid according to claim 1, characterized in that that it consists of a transparent support on which opaque strips are formed. 3. Grid according to claim 1, characterized in that euaus an opaque Carrier on which a series of alternately light absorbing and reflecting strips are arranged. 509843/0808 25U671 4. Method of making a grid according to a of claims 1 to 3, characterized in that that a photographic image of a stripe pattern located in the reference plane or of an image the same by the same optical system that is also used to project the light pattern onto the reference plane, is formed, wherein the optical system and the reference plane are arranged as in the projection and a photographic Plate or egg is placed in a plane which is the optical conjugate of the reference plane with respect to of the optical system and that the photographic plate is then developed. 5. Apparatus for carrying out the method according to claim 4 »characterized by an illumination system with mainly a light source (S) and a condenser (L ~), a mask (M) arranged in the path of the light beam generated by the illumination system and having a grid of parallel and equidistant stripes, and an optical system (Lp) for imaging the mask on a reference plane (P), the mask (M) and the reference plane (P) being in conjugate planes perpendicular to the optical axis of the optical system, further by another Optical system (L ₁ ), the axis of which forms a certain angle (OC ') with the reference plane different from 90 °, and which is arranged at a certain distance from the reference plane; and a detachable photographic plate (Ph) arranged in a plane which is the optical conjugate of the reference plane with respect to the latter optical system (L ..). 6. Use of a grid according to claim 1 for visualizing the contour lines of a located in the reference plane three-dimensional object using the moire effect. 509843/0808