Method for determining the refractive power of a transparent object, and corresponding device

Abstract

A method for determining a refractive power of a large-surface-area transparent object, such as a windshield, a visual aid, a cockpit glazing, a helmet visor, or the like, includes detecting a first imaging of a first line grating through the transparent object at at least one predetermined point of the object using a camera and determining a line spacing of the first imaging, the rotation of the lines relative to the first line grating or both through use of a computing unit on the basis of the first imaging at the at least one specified point and using the line spacing or rotation of lines to determine the refractive power at the at least one predetermined point of the transparent object.

Claims

1. A method for determining a refractive power of a large-surface-area transparent object, the method comprising the steps of: capturing a first imaging of a first line grating through the transparent object using a camera at at least one predetermined point of the transparent object; using the central processing unit to determine a line spacing of the first imaging transverse to lines of the first line grating at the at least one predetermined point; capturing a second imaging of a second line grating and a third imaging of a third line grating through the object using the camera, wherein lines of the second line grating extend at an angle not equal to 0° with respect to the lines of the first line grating and lines of the third line grating extend at an angle not equal to 0° with respect to the lines of the first line grating and extend at an angle not equal to 0° with respect to the lines of the second line grating; using the central processing unit to determine respective line spacings of the second imaging and the third imaging transversely to the respective lines of the second line grating and third line grating, based on the second imaging and the third imaging and a rotation of the lines relative to the respective second line grating and third line grating; and using the central processing unit to calculate the refractive power in every azimuthal direction at the at least one predetermined point of the transparent object based on the determined line spacings and the rotation of the lines relative to the respective first line grating, second line grating and third line grating.

2. The method according to claim 1, wherein determining the line spacing for the first imaging is carried out perpendicular to the first line grating, determining the line spacing for the second imaging is carried out perpendicular to the second line grating and determining the line spacing for the third imaging is carried out perpendicular to the third line grating.

3. The method according to claim 1, further comprising moving the transparent object past the first line grating, the second line grating and the third line grating one after the other, and past the associated camera.and the first line grating, the second line grating and the third line grating extend parallel to one another.

4. The method according to claim 3, wherein the first line grating, the second line grating and the third line grating extend parallel to one another.

5. The method according to claim 1, wherein the first line grating, the second line grating and the third line grating are generated by a light wall having a matrix of light source elements.

6. The method according to claim 5, wherein the light source elements comprise light emitting diodes (LEDs) or organic light emitting diodes (OLEDs).

7. The method according to claim 1, wherein an inclination of the transparent object with respect to an optical axis of the camera is additionally taken into account in the calculation of the refractive power in every azimuthal direction at the at least one predetermined point.

8. The method according to claim 1, wherein the large-surface-area transparent object comprises any of a windshield, a visual aid, a cockpit and a helmet visor.

9. A device for determining a refractive power of a large-surface-area transparent object, comprising: a camera; a central processing unit; a first line grating defined by first grating lines; a second line grating defined by second grating lines, which second grating lines extend at an angle not equal to 0° with respect to the lines of the first line grating; and a third line grating defined by third grating lines, which third grating lines extend at an angle not equal to 0° with respect to the lines of the first line grating and with respect to the lines of the second line grating; wherein the camera captures a first imaging of the first line grating through the transparent object at at least one predetermined point of the object, wherein the central processing unit processes the first imaging to determine a line spacing of the first imaging transversely to the first grating lines at the particular point; wherein the camera captures a second imaging of the second line grating and a third imaging of the third line grating through the transparent object; and based on the second imaging and the third imaging, the central processing unit determines a line spacing of the second imaging transversely to the second grating lines and a line spacing of the third imaging transversely to the third grating lines; and based on the determined line spacings and with consideration for the rotation of the lines relative to the respective line grating, the central processing unit determines the refractive power in every azimuthal direction at the at least one predetermined point of the transparent object.

10. The device according to claim 9, wherein one or more of the first line grating, the second line grating and the third line grating extend parallel to one another or are disposed in a common plane.

11. The device according claims 9, wherein the camera is a matrix camera or a line scan camera.

12. The device according to claim 9, wherein the large-surface-area transparent object comprises any of a windshield, a visual aid, a cockpit and a helmet visor.

13. The device according to claim 9, wherein a separate camera is provided for each line grating of the first line grating, the second line grating and the third line grating.

14. The device according to claim 9, further comprising a light wall having a matrix made from light source elements comprising light emitting diodes (LEDs) or organic light emitting diodes (OLEDs) generates the first line grating, the second line grating and the third line grating one after the other by switching.

15. The device according to claim 14, wherein the light source elements comprise light emitting diodes (LEDs) or organic light emitting diodes (OLEDs).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in the following in greater detail on the basis of exemplary embodiments and with reference to the figures. All the features that are described and/or graphically depicted form the subject matter of the invention, either alone or in any combination, independently of their wording in the claims or their back-references.

(2) Schematically in the drawings:

(3) FIG. 1 shows the distortion of a circular disk by the refractive power of a transparent object into an ellipse according to a method according to the prior art,

(4) FIG. 2 shows the behavior of the lens model at any point of the object having two principal curvatures k.sub.1 and k.sub.2 in a stationary coordinate system,

(5) FIG. 3 shows a perspective view from the side of a section of a transparent object, e.g., a windshield, subdivided into points (volume elements),

(6) FIG. 4 shows photographs of the imaging of a line grating through a cylindrical lens for a horizontal grating (a)), a grating rotated obliquely to the right (b)) and a grating rotated obliquely to the left (c)) for arrangements of the cylindrical lens at various angles relative to the horizontal (see header),

(7) FIG. 5 shows a view from the side of an exemplary embodiment of a device according to the invention,

(8) FIG. 6 shows a schematic diagram, in a view from the direction of the camera, of the procedure for a first exemplary embodiment of a method according to the invention,

(9) FIG. 6a shows a view from the front of a striated line grating,

(10) FIG. 7 shows a detailed view of the imaging of a line grating through a lens according to the method according to the invention,

(11) FIG. 8 shows a view from the direction of the camera of a device according to the invention for the first exemplary embodiment, represented in FIG. 6, of a method according to the invention,

(12) FIG. 9 shows a view from the direction of the camera of a second exemplary embodiment of a method according to the invention,

(13) FIG. 10 shows the change of the position vector in two planes at a point in the lens coordinate system when the object is tilted,

(14) FIG. 11 shows curves for calculated refraction indices in [m.sup.−1] for a horizontal grating, a right grating, and a left grating, wherein the scanning direction extends perpendicular to the grating lines in each case (for M.sub.l<M.sub.r it follows that φ<90°, for M.sub.l>M.sub.r it follows that φ>90°), plotted against the azimuthal angle which a lens can assume at a point of an object,

(15) FIG. 12 shows the representation according to FIG. 10, but with k.sub.1=0.6 m.sup.−1,

(16) FIG. 13 shows the curves according to FIG. 11 in a representation according to FIG. 10, but with a distance a between the line grating and the transparent object of 0.4 m,

(17) FIG. 14 shows the representation according to FIG. 10 for a spherical lens, wherein k.sub.1=k.sub.2=0.08 m.sup.−1,

(18) FIG. 15 shows the amplification factor for determining the refractive index plotted against the inclination angle ξ of the transparent object made from glass having a refractive index n=1.5, and

(19) FIG. 16 shows the curves according to FIG. 11 with k.sub.1=0.08 m.sup.−1, k.sub.2=−0.02, a grating rotation of ε.sub.1=45°, ε.sub.2=−45° and an inclination ξ=50° and a=1 m.

DETAILED DESCRIPTION OF THE INVENTION

(20) The exemplary embodiment of a device according to the invention shown in FIG. 5 shows a transparent object, e.g., in the form of a windshield 10 for a motor vehicle, which is disposed between a horizontal, striated line grating 14 and a camera 16. The horizontal line grating 14 is illuminated on the side opposite the windshield 10 by a light source 12, e.g., in the form of a fluorescent lamp, which has a constant intensity along its length. The pattern of the line grating 14 is refracted at the windshield and is imaged onto the camera 16. A striated line grating used for such a measurement is shown in greater detail in FIG. 6a.

(21) In a first exemplary embodiment of the method according to the invention, three striated line gratings 13, 14, and 15, which are rotated relative to one another and which are represented in FIGS. 6 and 8, are used to determine the local refractive index over the entire windshield 10, which is composed of a multiplicity of points (volume elements) 11, as represented in a cutout in FIG. 3. The right line grating 13 is rotated through the angle ε.sub.1=−30° relative to the horizontal line grating and the left line grating 15 is rotated through the angle ε.sub.2=30°. The lines of the line gratings 13, 15 are also rotated relative to the horizontal about the same respective angles.

(22) A striated line grating 14 used for such a measurement is also represented in FIG. 6a. The striated line gratings 13, 15, which are rotated only with respect to the line grating 14, are also rotated in an analogous manner.

(23) As was extensively described above in the general part of the description, three independent measurements must be performed successively or simultaneously using three line gratings rotated relative to one another (cf. FIGS. 6 and 8), which are arranged in a plane, for each point 11 of the windshield 10 in order to determine the curvatures k1, k2 and the angle φ or the refractive index. For this purpose, the windshield 10 is moved past the line gratings 13, 14, 15, which are arranged side-by-side or above one another, at a certain, predetermined speed. In the case shown in FIG. 8, the windshield has already been moved by the distance V1 for analysis purposes. The motion direction of the windshield 10 is indicated in FIG. 8 by the arrow 27. For the horizontal line grating 14, the point 11.1 is located at the grating position y.sub.1 and at the advance of the glass pane V1. The following equations result from the geometric relationships in FIG. 8:

(24) $\begin{array}{cc}L2=\frac{y_1}{\cos \mathrm{.Math.}}S2=y_1.Math.\mathrm{tg}\mathrm{.Math.}L3=\frac{y_1}{\cos \lambda }S3=y_1.Math.\mathrm{tg}\lambda & \left(14\right)\end{array}$

(25) The measured value associated with the point 11.2 on the right line grating 13 is obtained at the position L2 and the advance Vr=V1−S2. On the left line grating, the measurement is carried out at the position L3 and the advance Vl=V1+S3.

(26) As an alternative, the refractive index can also be measured in the vicinity of the horizontal grating 14′ by means of an oblique line grating 13′, 15′, as shown in FIG. 9. In this exemplary embodiment, the line gratings 13′, 15′ extend parallel to the line grating 14′, although the lines of the particular gratings are rotated relative to one another. In this case, the line spacing after the imaging through the windshield 10 is determined (scanned) by means of a matrix camera at every point perpendicular to the grating lines of the line gratings 13′, 15′. The particular scanning direction is indicated in the center of the line grating 13′, 14′, 15′ using one or more lines 28, 29, 30, respectively. Such an arrangement has the advantage that three measurements can be carried out for every point 11 of the windshield 10, which measurements differ only with regard to the advance of the glass pane, which corresponds to the separation of the line gratings 13′, 14′, 15′.

(27) As another alternative, switchable lighting means can be used to generate the line gratings 13′, 14′, 15′ at a point and to capture the three imagings at this point. In this exemplary embodiment, the switchable lighting means can also be used to generate the two oblique line gratings 13′, 15′ in temporal succession, e.g., at the point of the horizontal line grating 14′. Three imagings would then have to be captured by a matrix camera, also in temporal succession. The imagings can be evaluated in the desired scanning directions.

(28) In FIG. 8, the following should apply: ε.sub.1=ε.sub.2=ε. If the lens is rotated in front of the grating, the left line grating 15 would not start the measurement at φ as it would with the horizontal line grating, but rather at φ+ε. With regard to the right line grating 13, the measurement begins at φ−ε. (In FIG. 9, the right line grating 15′ and the left line grating 13′ are interchanged as compared to FIG. 8.)

(29) Based on the relationships in FIG. 9, the refractive power for each point is calculated from the measured values M.sub.h, M.sub.l and M.sub.r using the following equations:

(30) $\begin{array}{cc}{M}_h=\left[\frac{\mu .Math.\cos \left(\beta -\phi \right)}{\cos \beta .Math.\cos \phi }-1\right].Math.g=-\left[\frac{v.Math.\sin \left(\beta -\phi \right)}{\cos \beta .Math.\sin \phi }+1\right].Math.g{M}_l=\left[\frac{\mu .Math.\cos \left(\beta -\phi -\lambda \right)}{\cos \beta .Math.\cos (\phi +\lambda )}-1\right].Math.g=-\left[\frac{v.Math.\sin \left(\beta -\phi -\lambda \right)}{\cos \beta .Math.\sin \phi \left(\phi +\lambda \right)}+1\right].Math.g{M}_r=\left[\frac{\mu .Math.\cos \left(\beta -\phi +\lambda \right)}{\cos \beta .Math.\cos \left(\phi -\lambda \right)}-1\right].Math.g=-\left[\frac{v.Math.\sin \left(\beta -\phi +\lambda \right)}{\cos \beta .Math.\sin \phi \left(\phi -\lambda \right)}+1\right].Math.g& \left(15\right)\end{array}$

(31) In the following, the measured values are graphically depicted using the following parameters: ε.sub.1=ε.sub.2=45°, k.sub.1=0.080, k.sub.2=−0.020, a=1 m, g=1 mm.

(32) This results in the curves in FIG. 11, in which the curve for the measured value M.sub.r is labeled with reference number 33, the curve for the measured value M.sub.h is labeled with the reference number 34, and the curve for the measured value M.sub.l is labeled with the reference number 35, wherein M.sub.l<M.sub.r applies when φ<90°. M.sub.l>M.sub.r applies when φ>90°. The x-axis 32 in the diagram in FIG. 11 indicates the angle of rotation of the lens formed at the particular point, in [°], and the y-axis 31 indicates the measured value M.sub.h, M.sub.r and M.sub.l in [m.sup.−1].

(33) The curves become distorted when it is assumed that k.sub.1=0.6 m.sup.−1, as shown in FIG. 12. If the focal length of the lens is equal to the distance a between line gratings 13′, 14′, 15′ and the windshield 10, a measurement is no longer meaningful. The distance a should be less than the focal length of the lens. It therefore makes sense to shorten the distance a in a timely manner as the refractive powers increase.

(34) These distortions are avoided when the distance a between the line gratings 13′, 14′, 15′ and the windshield 10 is shortened to 0.4 m. This is shown in the curves in FIG. 13.

(35) For a spherical lens, all the measured values are the same when the line spacings of the line gratings 13′, 14′, 15′ are the same. This is illustrated in FIG. 14. The set of parameters used to calculate the curves in FIG. 11 was changed by k.sub.1=k.sub.2=0.08 m.sup.−1.

(36) The methods described so far relate to the measurement of a vertically positioned glass pane in front of a vertical grating. In many cases, it is necessary to measure a slanted (tilted) windshield 10, e.g., in the installed position. The measurement arrangement used for this purpose is represented in FIG. 5. FIG. 11 further shows the change in refractive power of a lens at a point when the object is slanted by the angle ξ about the x-axis of the three-dimensional coordinate system having the axes x, y and z.

(37) For glass having the refractive index n=1.5, the equation (12) indicated above can be used to calculate the amplification factor V, which is represented in FIG. 14 by the curve 47 over the axis 42, wherein the angle of inclination ξ of the windshield 10 is plotted on the axis 42. This is taken into account by the non-illustrated central processing unit in the determination of the refractive power at the points 11 of the windshield 12. It is also apparent from FIG. 5 that, due to the slant of the windshield 10 relative to the optical axis 17, the distance a.sub.o of the windshield 10 to the line grating 14 in the region of an upper edge beam 18 changes to the distance a in the region of the optical axis 17 and ultimately to the distance a.sub.u in the region of a lower edge beam 19 of the imaging. This distance change of the slanted windshield 10 along its entire height has already been taken into account in the formulas.

(38) A lens rotated from the plane E.sub.1 into the plane E.sub.2 can assume all possible azimuthal positions as is the case for the lens in the plane E.sub.1. The lens is rotated through the angle φ in order to visualize the possible measured values. Greater extreme values are obtained with the vertical scan (M.sub.h) than with the scans performed at a rotated angle (M.sub.r, M.sub.l). A principal curvature with maximum rotation is measured only with the vertical scan. If the glass pane is not slanted, the extreme values for all measurements are the same.

(39) FIG. 16 corresponds to the above-described FIG. 11, with the following parameters: k.sub.1=0.08, k.sub.2=−0.02, Grating rotation ε.sub.1=45° (curve 33″″) and ε.sub.2=−45° (curve 34″″), Glass pane inclination ξ=50° and Distance: grating−center of glass pane a=1 m,

(40) wherein the object (glass pane) was slanted by the angle ξ with respect to the optical axis. The measurement is carried out in the center of the glass pane. The curve labeled with reference number 35″″ corresponds to measurements carried out using the vertical grating. In this case, the extreme values of the curves 33″″ and 34″″ are the same, because the gratings were rotated through the same angle symmetrically with respect to the vertical grating. These extreme values are lower, however, than the extreme values for the measurement carried out using the vertical grating (see curve 35″″). The reason for the different extreme values for a vertical scan and for the scan carried out with the rotated grating is that, when a cylindrical lens is rotated in the E.sub.2 plane, only the vertical grating scans the principal curvature during the maximum rotation. The principal curvatures are not scanned with the rotated gratings during the maximum rotation.

LIST OF REFERENCE NUMBERS/LIST OF VARIABLES

(41) 5 stationary coordinate system 7 circular disk 9 ellipse 10 windshield 11 point (volume element) of the windshield 10 11.1, 11.2 point (volume element) of the windshield 10 11.3 point (volume element) of the windshield 10 12 light source 13, 14, 15 line grating 13′, 14′, 15′ line grating 16 camera 17 optical axis of the camera 16 18, 19 edge beam 23 line grating of the imaging 25 coordinate system of the imaging 27 arrow 28, 29, 30 direction in which the line spacing of the particular line grating in the imaging is determined 31 y-axis (measured value in m.sup.−1) 32 x-axis (angle of rotation in °) 33, 33′ curve for the measured value M.sub.r 33″, 33′″, curve for the measured value M.sub.r 33″″ curve for the measured value M.sub.r 34, 34′ curve for the measured value M.sub.h 34″, 34′″ curve for the measured value M.sub.h 34″″ curve for the measured value M.sub.h 35, 35′ curve for the measured value M.sub.l 35″, 35′″ curve for the measured value M.sub.l 35″″ curve for the measured value M.sub.l 41 y-axis (amplification factor) 42 x-axis (angle of inclination in °) 47 curve for the amplification factor for glass (refractive index 1.5) a, a.sub.o, a.sub.u distance of windshield 10 from the line grating 14 d line spacing of the line grating 23 of the imaging d.sub.s line spacing of the line grating 23 of the imaging measured in a direction perpendicular to the line grating 13 e, e.sub.1, e.sub.1″ coordinates of a point on the line grating 13 e.sub.2, e.sub.2″, s coordinates of a point on the line grating 13 F amplification factor f focal length of a lens g line spacing of the line grating 13 k curvature k1, k2 curvature in the direction of the main axes L2, L3 distance M.sub.h, M.sub.l, M.sub.r measured values of the line grating imaging n index of refraction/refractive index S2, S3 distance V1, Vr, Vl distance of a displacement x, x′, x″, y, y′, y″, z, z″ coordinates β angle of rotation of the line grating 23 of the imaging for the stationary coordinate system γ angle in the stationary coordinate system 5 ξ angle of inclination of the windshield 10 relative to the optical axis 17 ε, ε.sub.1, ε.sub.2 angle of rotation of the line grating 13 relative to the horizontal line grating 14 φ angle of rotation of the lens relative to the stationary coordinate system 5 λ, λ.sub.1, λ.sub.2 angle of rotation of the line grating 15 relative to the horizontal line grating 14 ν, μ factors of the imaging σ angle of rotation of the line grating 13 relative to the stationary coordinate system 5