DE102011111542A1 - Determination of subapertures on a test specimen for surface measurements on the specimen - Google Patents

Abstract

For determining the position of subapertures on a test object, steps a) generate a data set from a subaperture measurement of the test object (1) with a measuring device (2), b) calculate the coordinates of at least one position of the test object (1) or of the interferometer (2) in a first at least two-dimensional, preferably three-dimensional coordinate system, c) extension of the data set obtained from step a) by the coordinates obtained in step b). Using a test object having a surface with first and second markings (3) or an interferometer (2) having a surface with first and second markings (3), a step a) of capturing at least one first two-dimensional image from a first recording field is carried out, which detects the first and second marks (3). The calculation in step b) consists of positions of the first and second markings (3) on the first images by triangulation. The orientation advantageously serves a stitching method. The invention also relates to a position determination adapted device.

Description

The invention relates to a method for determining the position of subapertures in surface and passage measurements of optical electromagnetic waves on the specimen, in particular a large optical element, with an optical measuring device, in particular an interferometer. The invention further relates to the method adapted computer programs and devices. The invention is generally applicable to property determinations with raster-like measurement of patches and joining the measurement of patches of the test piece to an overall image in a stitching process. Property determinations in particular are refractive index homogeneity measurements by interferometry or voltage measurement.

Requirements for the homogeneity of large lens systems, as they are used for example in astronomy, are getting higher. The patent US 4,594,003 describes a Fizeau interferometer for testing optical components.

Homogeneity measurements of large lens systems with lens diameters over 800 mm, z. B. with lens diameters of 1 to 1.5 m, such interferometers of the prior art do not allow.

The so-called stitching method is known from photography. An overall picture is composed of several single pictures. By means of this as stitching it is possible to determine individual large parts of an object and to represent an exact overall picture of this object.

WO 2007/023042 A1 shows raster-type interferometric measurements. This is done by measurements of subapertures, from which a total interferogram is obtained in a stitching process. The grid-like measurement of a test specimen thereby harbors sources of error due to a rotation or displacement of the raster-like detected measuring ranges or measuring surfaces against each other. In order to avoid this, corresponding overlaps of the measuring surfaces were used.

By marking by means of two crosses or also several crosses, the crosses can be brought to coincidence by the grid-like detected measuring areas, in order to reconstruct an overall interferogram. However, this procedure has the disadvantage that measurements can not be carried out in the area of the markings.

Without marking, z. B. by means of two or more crosses are weak contrasts in the overlapping areas sources of error. Calculations for a stitching method to reconstruct an overall interferogram are complex, expensive, and error prone.

In an alternative solution, a highly accurate DUT transfer and positioning system is used to reconstruct an overall interferogram. However, this requires a high expenditure on equipment. Although a corresponding solution with a defined movement of the test object with an exact positioning system can be sufficiently accurate, such techniques are very costly, especially when very large parts, e.g. B. with diameters in the range of 1.6 m with a typically necessary accuracy of <0.1 mm must be moved. Because of a much larger space requirements also require corresponding systems for standard interferometers a massive conversion of the existing transfer systems. Each interferometer requires a special solution.

In the WO 2007/023042 A1 a position determination is described for subaperture measurements. In this case, first a data set is generated from a subaperture measurement of a test object with an interferometer, then coordinates of a position of the test object in a first coordinate system are calculated and then the data set from the subaperture measurement is expanded by the coordinates obtained in the previous step. In this case, coordinates of a further position of the test object are determined in a further subaperture measurement in the first coordinate system on the basis of overlaps of the measuring ranges of the subaperture measurements.

The object of the invention is to overcome disadvantages of the prior art. A further object of the invention is to enable a grid-like surface measurement which is superior in terms of reliability, equipment complexity and speed, in particular a measurement for optical elements or specimens.

• a) Erzeugen eines Datensatzes aus einer Subaperturmessung des Prüflings mit einer Messvorrichtung,
• b) Berechnung der Koordinaten wenigstens einer Position des Prüflings oder des Interferometers in einem ersten Koordinatensystem und gegebenenfalls Konvertierung dieser Koordinaten in Koordinaten eines zweiten Koordinatensystems,
• c) Erweiterung des aus Schritt a) erhaltenen Datensatzes um die in Schritt b) erhaltenen Koordinaten.

The invention therefore relates to a method and a device having the features of the independent claims. The invention therefore relates in particular to the position determination of subapertures in a recording field and a measuring field, comprising the steps

• a) generating a data record from a subaperture measurement of the test object with a measuring device,
• b) calculating the coordinates of at least one position of the specimen or the interferometer in a first coordinate system, and if necessary, conversion of these coordinates into coordinates of a second coordinate system,
• c) extension of the data set obtained from step a) by the coordinates obtained in step b).

A preferred measuring device is z. B. an interferometer. Triangulation methods for position determination in a coordinate system are known per se. For example, the article describes Wieland, Th., "Examination of a Linear Direct Method for Camera Calibration", Vision and Voice Magazine 6 (1992), No. 1, pp. 31-36, ISSN: 0936-8469 Stereo Triangulation Method with CCD Cameras , The methods find application in the automated manufacture of vehicles where computers are controlled by a 3-D survey. In this case, measuring points are arranged at certain common prominent points on the vehicle blank. Such devices are offered for example by the Institute of Optical Precision Engineering (IOF) in Jena (Germany) under the name Kolibri or the company GOM under the name ATOS. An overview of such procedures offers the Hochschule Bochum, Department of Surveying and Geoinformatics, Lennershofstraße 140, 44801 Bochum, DE, in the article by Heinz-Jürgen Przybilla entitled "Strip Projection - Basics, Systems and Applications" , which is also available on the Internet at the University of Bochum at: http://www.hochschulebochum.de/fileadmin/media/fb_v/labore/photogrammetrie/Artikel/Veroeffentlichungen/Przybilla/Streifenprojektion.pdf.

Corresponding triangulation methods, stereotriangulation methods or devices used therefor and computer programs are applicable to the present invention.

• – dass als Prüfling ein Prüfling mit einer Oberfläche mit ersten und zweiten Markierungen oder als Interferometer ein Interferometer mit einer Oberfläche mit ersten und zweiten Markierungen verwendet wird,
• – dass in einem weiteren Schritt n) wenigstens ein erstes zweidimensionales Abbild aus einem ersten insbesonders otpischen Aufnahmefeld erstellt wird, das die ersten und zweiten Markierungen von Prüfling und/oder Messvorrichtung erfasst und
• – dass die Berechnung in Schritt b) aus Positionen der ersten und zweiten Markierungen auf den ersten Abbildern durch Triangulation erfolgt.

Using triangulation methods, the invention provides

• In that a specimen having a surface with first and second markings or an interferometer having a surface with first and second markings is used as the specimen,
• - That in a further step n) at least a first two-dimensional image from a first especially otpischen recording field is created, which detects the first and second marks of the test piece and / or measuring device and
• - That the calculation in step b) from positions of the first and second marks on the first images by triangulation takes place.

According to the invention, it is preferable for the recording field to be larger than the measuring field in which, in particular, physical properties of the test object are recorded or measured. In addition, it is preferred that the markings are arranged outside the measuring field.

Interferometer as in the patent US 4,594,003 can be used for the invention.

In particular, a distance between the surface with first and second markings and the camera can be calculated on the basis of a distance between a first and a second mark in the further step n) acquired image.

While state-of-the-art prior art interferometer measurement systems provide positional determinations over highly accurate positioning devices, the present invention, by utilizing cameras and triangulation methods for positional determination, allows a raster-like surface measurement superior in the combination of reliability, equipment complexity and speed.

The system of the first and second mark on the test piece or measuring device (eg interferometer) can also be combined with markings on a test fixture of the test object. In this way it is possible to determine the position of the specimen absolutely to the position of the measuring fixture or the interferometer. The minimum requirements for the number of markings in the recording field is two, preferably at least three, and these are especially not in the optical measuring field of the measuring device.

The invention can be used wherever a property determination of parts by scanning small areas and then assembling the partial results.

As the test specimen, a specimen having a surface having first and second markers and / or an interferometer having a surface with third and fourth marks may be used, or an interferometer having a surface having first and second marks and a specimen having a surface may also be used to be used with third and fourth marks.

• a'') Erfassen eines zweiten zweidimensionalen Abbildes aus einem zweiten Aufnahmefeld, das die dritten und vierten Markierungen erfasst, wobei sich erste und zweite Aufnahmefelder überlappen,
• b') Berechnung der Koordinaten wenigstens einer Position der die dritten und vierten Markierungen aufweisenden Oberfläche in dem zweiten dreidimensionalen Koordinatensystem durch Stereotriangulation, wobei in Schritt b) eine Konvertierung der Koordinaten in Koordinaten des zweiten dreidimensionalen Koordinatensystems erfolgt oder ein Schritt b'') der Konvertierung der in Schritt b') berechneten Koordinaten in Koordinaten des ersten dreidimensionalen Koordinatensystems und des Ersetzens der in Schritt c) erhaltenden Koordinaten in dem erweiterten Datensatz durch diese konvertierten Koordinaten erfolgt.

In the first recording field, the third and fourth markings are detected, the method preferably further comprising the following steps:

• a '') detecting a second two-dimensional image from a second recording field that detects the third and fourth marks, wherein first and second recording fields overlap,
• b ') Calculation of the coordinates of at least one position of the third and fourth marks having surface in the second three-dimensional coordinate system by stereotriangulation, wherein in step b) a conversion of the coordinates takes place in coordinates of the second three-dimensional coordinate system or a step b'') of the conversion the coordinates calculated in step b ') take place in coordinates of the first three-dimensional coordinate system and the replacement of the coordinates obtained in step c) in the extended data set by these converted coordinates.

• d) Ausgabe des erweiterten Datensatzes an eine Datenverarbeitungseinheit,
• e) Versetzen des Prüflings bzw. des Interferometers,
• f) Wiederholen der Schritte a) bis d) und optional wenigstens eine Wiederholung der Schritte e) und f).

Grid-like measurements according to the invention preferably also comprise the steps

• d) output of the extended data record to a data processing unit,
• e) displacing the test piece or the interferometer,
• f) repeating steps a) to d) and optionally at least one repetition of steps e) and f).

It is also possible to displace the device under test and the interferometer, whereby position determinations of the device under test and the interferometer are provided by stereotriangulation.

In the grid-like measurements according to the invention, steps n) and n ") can be carried out with a camera, and the camera is aligned with the first recording field for step n). There is a realignment of the camera on the second recording field or step n) and n '') done with one camera, preferably simultaneously.

In the grid-like surveys according to the invention, the first coordinate system is a three-dimensional coordinate system and the calculation in step b) is performed from positions of the first and second markings on the first and second images by stereotriangulation.

The invention is particularly suitable for a test specimen in the form of an optical window, in particular with a diameter of more than 800 mm, preferably more than 1000 mm, in particular preferably between 1 and 1.5 m.

In this case, markings are preferably arranged in an edge region of a surface of the test object or optical element which is cut through the optical axis of the lens, preferably an edge region centered on the optical axis, which occupies not more than 10, in particular not more than 5%, of this surface , In particular, areas are used for markings that are no longer needed in the lens in use and are often covered anyway by a lens mount.

Preferably, the markings on the outer surfaces of the specimen, which are not optically effective, attached.

According to the invention, a simple and reliable stitching method is provided. In this case, the generation of an overall interferogram is carried out by arranging subinterferograms from the extended data records of a method according to the invention in accordance with the coordinates of these extended data records obtained in step b) or b ') of the method.

The total interferogram is thus reconstructed in a coordinate system from the sub-interferograms on the basis of positions of the measured subapertures in this coordinate system.

The invention also relates to a computer program which contains control commands and algorithms for carrying out the method according to the invention. Preferably, the method is automatically performed by the program.

• – ein Interferometer mit einem Strahlengang, in dem ein Messbereich des Interferometers angeordnet ist,
• – eine Halterung zur Anordnung eines Prüflings in wenigstens zwei Positionen, in denen der Prüfling den Messbereich des Interferometers überlappt,
• – Stellmittel, die mit der Halterung oder dem Interferometer verbunden sind, zur Einstellung einer der wenigstens zwei Positionen des Prüflings,

sowie
wenigstens eine Kamera mit einem ersten Aufnahmebereich in einer ersten Kameraposition und einem zweiten Aufnahmebereich in einer zweiten Kameraposition, wobei die ersten und zweiten Aufnahmebereiche Markierungen auf dem Prüfling und/oder dem Interferometer erfassen, und Positioniermittel, die mit der Kamera verbunden sind, zum Versetzen der Kamera aus der ersten Kameraposition in die zweite Kameraposition oder wenigstens eine erste Kamera mit einem ersten Aufnahmebereich und wenigstens eine zweite Kamera mit einem zweiten Aufnahmebereich, wobei die ersten und zweiten Aufnahmebereiche Markierungen auf dem Prüfling und/oder dem Interferometer erfassen.The invention also relates to a subaperture measuring device having a data processing unit with such a computer program. The device comprises

• An interferometer with a beam path in which a measuring range of the interferometer is arranged,
• A holder for arranging a test object in at least two positions in which the test object overlaps the measuring range of the interferometer,
• Adjusting means, which are connected to the holder or the interferometer, for adjusting one of the at least two positions of the test object,

such as
at least one camera having a first recording area in a first camera position and a second recording area in a second camera position, wherein the first and second recording areas detect marks on the specimen and / or the interferometer, and positioning means, which are connected to the camera, for displacing the camera Camera from the first camera position in the second camera position or at least a first camera with a first receiving area and at least a second camera with a second receiving area, wherein the first and second receiving areas detect markings on the specimen and / or the interferometer.

The invention is in principle applicable to all measuring systems in which the entire measuring field of a test specimen by measuring in particular physical properties and composition of sub-areas is generated. It is basically irrelevant whether the measuring system or the test object is moved. Conceivable are homogeneity measuring devices, stress birefringence measuring devices, defect detection systems or the like.

Typical physical properties are in particular optical properties such. B. surface homogeneities, refractive indices, stresses, in particular material stresses, as well as deviations and defects. Especially suitable is the method and the device for determining the refractive index homogeneity by means of interferometry and for refractive index measurement. In this case, a Gesamtinterferogramm is generated from the data sets of step c), in particular using the device according to the invention.

The inventive method and the device is particularly suitable for measuring the refractive index homogeneity by interferometry or for voltage measurement.

The invention will be illustrated below with reference to the drawing with reference to an embodiment showing further aspects and advantages of the invention.

1 schematically shows an arrangement of interferometer, cameras, markers and DUT according to a device according to the invention.

A Subaperturmessvorrichtung according to the in 1 The arrangement shown comprises an interferometer 2 with a beam path in which a measuring range 7 of the interferometer is arranged. The beam path passes through a socket 8th to a test object arranged in the beam path 1 , As an example, an optical window as a test object 1 shown.

The examinee 1 himself is in one in the 1 clamped not shown bracket. Also in 1 not shown adjusting means which are connected to the holder, allow movement of the specimen in a plane orthogonal to the beam path. Parallel to this plane points the interferometer 2 two marks 3 on. The adjusting means comprise a first linear motor connected directly to one end of the sample holder and a second linear motor having a direction of movement orthogonal to that of the first linear motor and connected to the first linear motor. First and second linear motor thus enable a controlled two-dimensional movement of the DUT holder.

The test object has two cross-shaped markings in an edge region on the surface facing the cameras 3 ,

The subaperture measuring device further comprises a not in 1 represented data processing unit and two cameras 5 passing through their lenses 6 Record recording fields. Every camera 5 has a recording field within its limits 4 two marks 3 of the test specimen and at least two markings 3 of the interferometer 2 be recorded. Both image fields capture two equal marks on the interferometer. The cameras are fixed relative to each other and firmly connected. They are attached to a tripod and aligned in accordance with the above-described features of their recording fields relative to the interferometer and the DUT. You can also focus freehand in a fast shooting mode according to the features described above.

The data processing unit in the form of a PC communicates via interfaces with the cameras, the linear motors and the interferometer. To output control signals and process measurement signals via the interfaces, the data processing unit is equipped with a computer program for executing the following sequence of steps:
S1: detection of at least one first two-dimensional image from the recording field of one of the cameras,
S2: acquiring a second two-dimensional image from the recording field of the other camera,
S3: generating a data record from a subaperture measurement of the test object with the interferometer,
54: calculation of the coordinates of at least one position of the test object in a coordinate system,
S5: calculating the coordinates of at least one position of the surface having the third and fourth marks in a second three-dimensional coordinate system by stereotriangulation,
S6: extension of the data record obtained from step S3 by the coordinates obtained in step S4,
S7: conversion of the coordinates calculated in step S5 into coordinates of the first three-dimensional coordinate system,
S8: replacing the coordinates obtained in step S4 in the extended data set by the converted coordinates obtained in step S7,
S9: storing the extended data record,
S10: displacing the test piece,
S11: Repeat steps S1 to S9 and
S12: repetition of steps S10 and S11 until data records for a complete interferogram of the measured surface of the test object are obtained;
S13: Generate a total interferogram from the extended data sets by arranging subinterferograms from the extended ones Records according to converted coordinates obtained in step S7 in these records,
S14: Output of the total interferogram to a screen.

Since suitable markings are applied at suitable points of the measuring device and on the test object (on the side edge or in the area outside the optically effective surface) and a 3D coordinate measuring system is used via two special cameras, the position of the test object can be absolutely determined by the markings under the interferometer Avoiding disadvantages of the prior art can be determined. For each Subaperturmessung thereby an exact position can be determined. In this case, the test piece or interferometer can be rotated or moved. The position of the subapertures to each other can be passed to appropriate computer programs for stitching or measuring.

By suitable positioning of the markings no measuring field is shaded. The positioning accuracy of 3D measuring systems is <0.1 mm, preferably <0.05 mm and especially 0.001 mm. Such cameras are usually calibrated on fixed markers. If you apply markings directly to the interferometer, the cameras can be absolutely calibrated in the room. The location of the cameras is freely selectable, as far as enough marks in the field of view. This allows this system to be used universally on any interferometer. It is adjusted to a suitable location of the measuring marks and the cameras.

Projected markers can also be used.

There is a high positioning accuracy, z. B. <0.1 mm, preferably <0.05 mm and especially 0.001 mm, by a simple construction with a small footprint with little retooling of existing measuring systems possible.

LIST OF REFERENCE NUMBERS

1

examinee

2

interferometer

3

marks

4

Limits of the recording field

5

camera

6

camera lens

7

Measuring range of the interferometer

8th

version

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 4594003 [0002, 0016]
• WO 2007/023042 A1 [0005, 0009]

Cited non-patent literature

• Wieland, Th., "Examination of a Linear Direct Method for Camera Calibration", Vision and Voice Magazine 6 (1992), No. 1, pp. 31-36, ISSN: 0936-8469 Stereo Triangulation Method with CCD Cameras [0012]
• Hochschule Bochum, Department of Surveying and Geoinformatics, Lennershofstraße 140, 44801 Bochum, DE, in the article by Heinz-Jürgen Przybilla entitled "Strip Projection - Fundamentals, Systems and Applications" [0012]
• http://www.hochschulebochum.de/fileadmin/media/fb_v/labore/photogrammetrie/Artikel/Veroeffentlichungen/Przybilla/Streifenprojektion.pdf. [0012]

Claims (10)

Method for determining the position of subapertures in a measuring field on a test object, comprising the steps of a) generating a data record from a subaperture measurement of the test object ( 1 ) with a measuring device ( 2 b) calculation of the coordinates of at least one position of the test piece ( 1 ) or the measuring device ( 2 ) in a first at least two-dimensional, preferably three-dimensional coordinate system and, if appropriate, conversion of these coordinates into coordinates of a second coordinate system, c) extension of the data set obtained from step a) to the coordinates obtained in step b), characterized in that the test object ( 1 ) a surface with first and second markings ( 3 ) and / or the measuring device ( 2 ) a surface with first and second markings ( 3 ), and in that a further step n) creates at least one first two-dimensional image from a first recording field, which comprises the first and second markings ( 3 ) and that the calculation in step b) consists of positions of the first and second markings ( 3 ) on the first images by triangulation. A method according to claim 1, characterized in that the sub-apertures comprise a recording field for determining the position of the specimens and a measuring field for determining or measuring physical properties of the specimen, wherein the recording field is greater than the measuring field and wherein the markings ( 3 ) are arranged in the recording field but outside the measuring field. Method according to Claim 1 or 2, characterized in that both the test specimen ( 1 ) as well as the measuring device ( 2 ) two markings each ( 3 ), so that third and fourth markings ( 3 ) and that in the first recording field the third and fourth markings ( 3 ) and the method further comprises the steps of: a '') acquiring a second two-dimensional image from a second capture field comprising the third and fourth markers ( 3 ), wherein first and second recording fields overlap, b ') calculation of the coordinates of at least one position of the third and fourth markings ( 3 ) in the second three-dimensional coordinate system by stereotriangulation, wherein in step b) a conversion of the coordinates into coordinates of the second three-dimensional coordinate system or a step b '') of the conversion of the calculated in step b ') coordinates in coordinates of the first three-dimensional coordinate system and replacing the coordinates obtained in step c) in the extended data set by these converted coordinates. Method according to claim 1 to 3, comprising the additional steps d) output of the extended data record to a data processing unit, e) transfer of the test object ( 1 ) and / or the interferometer ( 2 f) repeating steps a) to d) and optionally at least one repetition of steps e) and f). Method according to one of claims 4 to 6, wherein step n) and n '') with a camera ( 5 ) and the camera ( 5 ) is aligned for step a) on the first recording field, wherein the method further comprises a step a ') realignment of the camera ( 5 ) on the second recording field. Method according to one of claims 4 to 6, wherein step n) and n '') each with a camera ( 5 ), preferably be carried out simultaneously. Method according to one of claims 4 to 8, wherein the first coordinate system is a three-dimensional coordinate system and the calculation in step b) from positions of the first and second markings ( 3 ) on the first and second images by stereotriangulation. Method according to one of the preceding claims, wherein the test object ( 1 ) is an optical element, in particular with a diameter over 800 mm, preferably over 1000 mm, in particular preferably between 1 and 1.5 m. Method according to claim 10, characterized in that markings ( 3 ) of a specimen, which is cut through the optical axis of the specimen, are arranged in an edge region, preferably an edge region centered on the optical axis, which occupies not more than 10%, in particular not more than 5%, of this surface. Subaperture measuring device, comprising - an interferometer ( 2 ) with a beam path in which a measuring range ( 7 ) of the interferometer ( 2 ), - a holder for arranging a test object ( 1 ) in at least two positions, in which the test object covers the measuring range of the interferometer ( 2 ), - adjusting means connected to the holder or the interferometer ( 2 ), for adjusting one of the at least two positions of the test object, and - a data processing unit, characterized in that the data processing unit comprises a computer program which comprises control commands and algorithms for carrying out the method according to claim 1 and the subaperture measuring device at least one camera ( 5 ) having a first receiving area in a first camera position and a second receiving area in a second camera position, the first and second receiving areas having markings ( 3 ) on the test piece ( 1 ) and / or the interferometer ( 2 ) and positioning means connected to the camera ( 5 ), for moving the camera ( 5 ) from the first camera position to the second camera position or the at least one first camera ( 5 ) with a first receiving area and at least one second camera ( 5 ) with a second receiving area, wherein the first and second receiving areas mark ( 3 ) on the test piece ( 1 ) and / or the interferometer ( 2 ) to capture.

Images