Title of Invention

METHOD OF OPERATING A INTERFEROMETRIC SYSTEM WITH ONE OR MULTIPLE MIRRORED ZONE

Abstract

The invention is with regard to an interferometric system with an illumination arm that has a light source and lighting optics with which to form an illuminating path of rays, an object arm that has a reference element for measuring an object that has an object surface to be measured to form an image-forming path of rays, whereby the object to be measured exhibits a object surface that is not directly accessible to illumination, a reference arm with a reference element and a detector arm with a detector and a beam splitter, whereby the reference element has one or more mirrored zones. Components that have undercut surfaces lying in the illumination direction can thus be measured in one single measurement procedure.

Full Text

INTERFEROMETRIC SYSTEM WITH COMPARISON PLATE WITH A MIRRORED ZONE Prior Art The invention is with regard to an interferometric system with an illumination arm that has a light source and lighting optics with which to form an illuminating path of rays, an object arm that has a reference element for measuring an object that has an object surface to be measured for formation of an image-forming path of rays, whereby the object to be measured exhibits a object surface that is not directly accessible to illumination, a reference arm with a reference element and a detector arm with a detector and a beam splitter. The invention is, furthermore, with regard to a measuring process that can be accomplished using the device. Manufacture of precision parts demands measuring methods for registering the geometry and the condition of the parts, which ensure the quality of the corresponding parts. Optical measuring methods such as, for example, picture imaging, image evaluation, interferometry, especially white light interferometry, make an important contribution here. The principle of the white light interferometer is based on using a short coherent light source for illumination of an imaging system. In addition to the normal imaging lens, the imaging system has a reference arm through which a part of the radiated light passes. If the path of light Λ0 in the object arm and the path in the reference arm ΛR now exhibit a difference that is less than the coherence length lc of the light i.e. then the light fields that are re-merged, can exhibit a measurable interference, which is utilised in that the path difference of the light fields, defined by moving the object or the reference element along the optical axis, is changed during measurement. The intensity of the re-merged light fields is simultaneously measured by a laminar-measuring detector, usually a CCD camera. Since a constructive or destructive interference can only take place within the coherence length of the white light source, the pixel evaluation of intensity modulation created through interference supplies the intensity correlogram, precise information regarding height for each individual pixel. This results in complete height information of the object, executed for the entire pixel field. Commercial white light interferometers, typically, exhibit the following specifications: The height resolution Az is specified through the middle wavelength of light λ m used, the coherence length lc and the type of correlogram evaluation algorithm. Typical parameters such as λ = 600 nm, lc - 2 μm make values of Az = 1 nm possible. Lateral resolution 5 is equal to that of a conventional imaging system and is principally restricted by λm and the numeric aperture NA of the imaging optics. δ > 0.61 λm/NA (2) The maximum measurable total height difference zmax is determined by the technical feasibility of creating a path difference in the reference arm and object arm that is guided precisely over the entire stretch. Today, regulated piezo systems make values of zmax Conventional interferometers, especially white light interferometer systems, can be used for the above described tasks when the locations to be measured are easily accessible and exhibit a predominantly even geometry. If this is not the case, then an interferometer, which has a special lens that is aligned to the object to be measured, is used. The disadvantage with this type of interferometer, however, is that the undercuts at the object to be measured lie in the shadow area of the illumination and can, thus, not be registered. The object has to be disassembled and be recorded in a second measuring procedure in order to measure this surface. The objective of the invention is to provide an interferometric system, which will enable three-dimensional measuring of objects which have surfaces that are difficult to access, using only one single photograph. Advantages of the Invention The objective of the invention relating to the device is met in that the reference element exhibits one or more mirrored zones. Using this, light rays can reach the undercut surfaces which can thus be measured in the same measuring procedure as the rest of the surfaces. The position of the undercut surfaces relative to the remaining surfaces can be determined in particular. Undercuts of any shape, even those with uneven surfaces can be measured by aligning the mirrored zone to the object to the effect that the mirrored zone is designed in each case in a half angle to the vertical line to the optical axis of the image-forming path of rays in the manner of a partial surface of the object surface to be measured. A design that is particularly not sensitive to environmental impact such as temperature influences has the mirrored zone connected to the reference element in one piece. If the mirrored zone is designed as a separated unit and if it is mechanically connected to the reference element by, for example, pasting or screwing, it can be aligned in a separate processing step, to the shape of the object surface and, if necessary, be re-used in the case of a similar type of object in another reference element. In a preferred design, a second comparison plate for measuring of the object surface is formed in the reference element apart from the mirrored zone. This accomplishes determination of the relative position of an object surface that is accessible in the usual measurement process and a surface that is usually not accessible. If at least one second comparison plate is executed in the reference element apart from the mirrored zone, for measuring at least one second object surface, then the position of all object surfaces one is interested in, with reference to the reference element, can be determined in one depth scan. The objective of the invention regarding the process is met in that light rays reflected from an object surface are brought to interfere with light rays reflecting from an associated comparison plate, while light rays reflected from the object surface that is not accessible to direct illumination are reflected in addition through a mirrored zone and then brought into interference with light rays reflected from an associated comparison plate. Components with undercuts can, thus, be measured in one measurement process and the relative position of the undercuts in particular can be determined with regard to the remaining surface. Drawings The invention is explained in greater detail by means of the exemplary embodiments illustrated in the figures. Figure 1 is a schematic presentation of a white light interferometer configuration in accordance with prior art. Figure 2 is a schematic illustration of an interferometric system in an inventive design. Figure 3 schematically presents an interferometric system that is suited to simultaneous measuring of surfaces facing and turned away from the object. Description of the Exemplary Embodiments The interferometric system 1 of a white light interferometer configuration schematically illustrated in Figure 1, in accordance with prior art, comprises an object arm 40 at which the surface of an object 41 is located, an illumination arm 20 that has a light source 21 and illuminating optics 22, which form an illuminating path of rays 60 and which is constructed by one or several lenses. The interferometric system 1 exhibits a reference arm 10 with a reference element, located orthogonal to the illumination arm 20 and to the object arm 40, this arm being mechanically coupled to an adjusting element 12, usually to a piezo system. A detector arm 30 lies opposite the reference arm 10, this detector arm usually exhibiting a laminar-measuring detector 31 such as, for example, a CCD camera, as well as a lens 32 for imaging of intensity-distribution in image-forming path of rays 70, this intensity-distribution having to be evaluated. An evaluation device (that is not illustrated in detail) is present for evaluation. A beam splitter 50 thereby splits the different light rays and/or re-merges them so that the light rays from the reference am 10 and those from the object arm 40 can interfere in the detector arm 30 at the detector 31 in the manner described above. Scanning of object can thus take place by moving the reference element 11 with the adjusting element 12 or, alternatively, by moving the object 41 with a similar adjusting element. The architecture of an interferometric system 1, in accordance with prior art, permits only measuring of surfaces at object 41, that are directly accessible to illumination. Undercuts in object 41 require that the object be disassembled and the surfaces as well as other object surfaces be measured in a second procedure in order to determine the position of the undercuts with regard to object surfaces measured in the first step. Compared to this, Figure 2 schematically presents an interferometric system 1 in which object surfaces 45 at object 41 that are not directly accessible to illumination can be measured in accordance with the invention. For this purpose, the object 41 is connected to a reference element 42 that has at least one mirrored zone 46. Light passes through a lens 48 in the direction of the object 41 from the illumination arm 20 that is not illustrated here. That portion near the mirrored zone 46 is reflected in the direction of the object surface 45 that is not accessible to illumination. Reflected back from this location and via the mirrored zone 46, the same passes through the lens 48 and is guided via the beam splitter 50 that is not illustrated here, to the detector 31 that is also not illustrated here. A comparison plate 47 whose reflected light runs the same optical path length, as that reflected from the object surface 45 serves as reference for the object surface 45 and therewith creates the same interference fringe pattern. Figure 3 illustrates a design for the interferometric system 1 that facilitates measurement of a complete object 41 with undercuts. For this purpose, the lens 48 in the object arm is brought at least to a second position, represented here by lens 49. This causes depth sensing of the object 41. While the object surface 43 and the associated comparison plate 44 contribute to interference when in the position of lens 48, the object surface 45 is measured using the mirrored zone 46 and the associated comparison plate 47 when in the position of lens 49. All surfaces of the object 41 that one is interested in can be measured in this manner, relative to one another. All surfaces of the object one is interested in can thus be reached in a corresponding design of the reference element 42 with mirrored zones 46. Claims 1. Interferometric system (1) with an illumination arm (20) that has a light source (21) and lighting optics (22) with which to form an illuminating path of rays (60), an object arm (40) that has a reference element (42) for measuring an object (41) that has an object surface (45) to be measured to form an image-forming path of rays (70), whereby the object (41) to be measured exhibits a object surface (45) that is not directly accessible to illumination, a reference arm (10) with a reference element (11) and a detector arm (30) with a detector (31) and a beam splitter (50), characterized in that, the reference element (42) has one or several mirrored zones (46). 2. Device according to Claim 1, characterized in that, the mirrored zone (46) is aligned to the object (41) in such a manner that, in each case, the mirrored zone (46) is designed in a half angle to the vertical line to the optical axis of the image-forming path of rays (70) in the manner of a partial surface of the object surface (45) to be measured. 3. Device according to one of Claims 1 or 2, characterized in that, the mirrored zone (46) is connected to the reference element (42) in one piece. 4. Device according to one of Claims 1 or 2, characterized in that, the mirrored zone (46) is designed as a separated unit and is mechanically connected to the reference element (42) by, for example, pasting or screwing. Device according to one of Claims 1 to 4, characterized in that, a second comparison plate (47) is designed apart from the mirrored zone (46) for measurement of the object surface (45). Device according to one of Claims 1 to 5, characterized in that, at least one second comparison plate (44) is designed apart from the mirrored zone (46) for measuring at least one second object surface (43). Process for operating an inferometric system (1) with an illumination arm (20) that has a light source (21) and lighting optics (22) with which to form an illuminating path of rays (60), with an object arm (40) that has a reference element (42) for measuring an object (41) that has an object surface (45) to be measured to form an image-forming path of rays (70), whereby the object (41) to be measured exhibits a object surface (45) that is not directly accessible to illumination, a reference arm (10) with a reference element (11) and a detector arm (30) with a detector (31) and a beam splitter (50), characterized in that, light rays reflected from an object surface (43) are brought to interfere with light rays reflecting from an associated comparison plate (44), while light rays reflected from the object surface (45) that is not accessible to direct illumination are reflected in addition through a mirrored zone (46) and then brought into interference with light rays reflected from an associated comparison plate.

Documents:

1179-CHENP-2007 AMENDED PAGES OF SPECIFICATION 08-07-2013.pdf

1179-CHENP-2007 AMENDED CLAIMS 08-07-2013.pdf

1179-CHENP-2007 CORRESPONDENCE OTHERS 16-04-2013.pdf

1179-CHENP-2007 ENGLISH TRANSLATION 08-07-2013.pdf

1179-CHENP-2007 FORM-1 08-07-2013.pdf

1179-CHENP-2007 FORM-3 08-07-2013.pdf

1179-CHENP-2007 OTHER PATENT DOCUMENT 08-07-2013.pdf

1179-CHENP-2007 POWER OF ATTORNEY 08-07-2013.pdf

1179-CHENP-2007 CORRESPONDENCE OTHERS 28-03-2014.pdf

1179-CHENP-2007 EXAMINATION REPORT REPLY RECEIVED 08-07-2013.pdf

1179-CHENP-2007 FORM-1 28-03-2014.pdf

1179-chenp-2007-abstract.pdf

1179-chenp-2007-claims.pdf

1179-chenp-2007-correspondnece-others.pdf

1179-chenp-2007-description(complete).pdf

1179-chenp-2007-drawings.pdf

1179-chenp-2007-form 1.pdf

1179-chenp-2007-form 3.pdf

1179-chenp-2007-form 5.pdf

1179-chenp-2007-pct.pdf

1179-CHENP-2007-Petition for POR.pdf