AT521298A1 - Process for the optical detection of the geometry of a workpiece - Google Patents

Abstract

The invention relates to a method for optically detecting the geometry of a workpiece (1) with a cavity (4) and at least one bore (7), characterized by the following method steps: A) introducing an illumination source (12) into the cavity (4); B) illuminating at least one area (13) to be measured of the surface (5) of the bore (7) through a proximal bore opening (7a) by means of the illumination source; C) arranging an optical system in a region (9) of an outer surface (3) of the workpiece and a distal drilling opening (7b); D) collecting several representations of the area to be measured in the form of the light reflected from the surface and emerging from the distal drilling opening (RL); E) taking images of the captured representations of the surface in an image sensor, the focus point of the optics being continuously shifted in relation to the area of the surface to be measured between the taking of the images; and F) evaluating the images recorded by the image sensor by combining the images into a 3D model of the surface.

Description

Method for optically recording the geometry of a workpiece

The invention relates to a method for optically detecting the geometry of a workpiece, in particular an injection nozzle of an internal combustion engine, with a cavity and at least one bore between a proximal bore opening in the surface of the cavity and a distal bore opening in an outer surface of the workpiece.

The geometry of workpieces, particularly in the field of high technology, is often complex and cannot be measured with known measuring devices and measuring methods without destruction or only to a very limited extent. However, this geometry often plays an important role in the function of the workpiece. For example, the geometry of injection nozzles, especially that of the holes in the spray holes, is of central importance in diesel injection systems, since the injection nozzle forms the most important interface between the injection system and the combustion chamber. The micro-geometry of the spray holes can vary widely, for example in terms of angle, position, diameter, shape, edge rounding, channel length and K-factor (taper), and very tight tolerances make the measurement task even more difficult.

Optical measurement technology, in particular with focus variation, represents a quick and non-destructive solution for the measurement of such microgeometries. With focus variation, an image stack of an area to be measured is evaluated in such a way that for each pixel that image is determined from the recorded image stack on which this pixel or the associated area has the maximum sharpness. The image stack is usually generated by a relative movement between the area to be measured and the optics of the measuring system, recorded by an image sensor and combined in an evaluation unit to form a 3D model. This technology is described in ISO standard 25178-6 for the topographic measurement of surfaces and in EP 2 132 524 B1.

Local image contrast and, consequently, optimal illumination of the area to be measured are of particular importance for the optical detection of geometries, in particular of complex micro-geometries and using focus variation. When using known types of lighting, for example coaxial or ring light 2/16

Illumination, the amount of reflected light is usually too small with such geometries.

In addition, the optical detection of such geometries leads to additional difficulties which reduce the amount of light reflected and, as a result, the signal. These occur especially when the surface to be measured is essentially parallel to the direction of illumination, which is basically the case when detecting spray holes in injection nozzles. Firstly, less light falls into the numerical aperture of the lens, and secondly, the surface of the bore reflects or scatters a large part of the light from the direction of illumination and thus away from the lens.

Due to the above disadvantages, it has so far not been possible to satisfactorily detect a large number of complex (micro) geometries using optical measuring systems or methods. The present invention is therefore based on the object of overcoming these disadvantages of the prior art and for the first time making it possible to satisfactorily record such geometries.

This object is achieved by providing a method for optically detecting the geometry of a workpiece in accordance with the features of claim 1. Advantageous embodiments of the invention result from the subclaims.

The process according to the invention is characterized by the following process steps:

A) inserting an illumination source of a measuring system into the cavity;

B) illuminating a region of the surface of the bore to be measured through the proximal bore opening by means of the illumination source;

C) arranging an optical system of the measuring system in a region of the outer surface of the workpiece and the distal drilling opening;

D) collecting several representations of the area to be measured in the form of the light reflected from the surface and emerging from the distal drilling opening with the optics;

E) taking images of the representations of the surface captured by the optics in an image sensor of the measuring system, the focus point of the optics being continuously shifted in relation to the area of the surface to be measured between the taking of the images; and

F) Evaluation of the images recorded by the image sensor by combining the images into a 3D model of the surface.

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The method according to the invention enables the non-destructive measurement of complex (micro) geometries, for example spray holes of injection nozzles, with high accuracy and speed. By introducing the illumination source into the cavity of the workpiece, a surface can be illuminated and recorded, among other things, in the direction of the optics of the measuring system, wherein a sufficient amount of light reflected from the surface can be detected. By using the measuring principle of focus variation, the surface is also advantageously captured three-dimensionally.

The entire surface of the bore, in particular the entire surface of the cavity, is expediently illuminated.

The illumination source is expediently introduced through a distal cavity opening, which is located in the outer surface of the workpiece, and / or into a proximal region of the cavity.

In a preferred embodiment, the position of a lens of the optics and / or the orientation of an optical axis of the optics is / are varied during the taking of an image and / or between the taking of images. Since different surface inclinations reflect the light differently, the topography of the sample can be inferred by varying the position of the objective and / or the alignment of the optical axis. The advantage of this is that just a few images are sufficient to characterize the surface.

In a preferred embodiment, the optics are arranged at least during the taking of an image in such a way that the optical axis is essentially parallel to the surface and / or to a longitudinal axis of the bore. As a result, the light yield of the light reflected from the surface and emerging from the distal drilling opening can be increased.

The invention further provides for the illumination intensity and / or the illumination position of the illumination source to be varied at least during the taking of an image and / or between the taking of images. In this way, images with different sensitivity settings of the image sensor or different lighting intensity can be used on surfaces with very different reflection properties. This enables a higher radiometric dynamics of the surfaces to be imaged. Since different surface inclinations / 16 reflect the light differently, the topography of the sample can be determined by varying the lighting position.

In a further embodiment of the invention, the area of the surface to be measured is intermittently illuminated during the shifting process of the focus point, the area of the surface to be measured preferably being essentially only illuminated when the image sensor takes an image. The advantage here is that the illumination source and the workpiece are exposed to less heat development within the cavity.

The cavity expediently has at least one prismatic, in particular a cylindrical, at least one conical and / or at least one spherical section.

The cavity particularly expediently has a prismatic and a conical section, the conical section being arranged in the proximal region of the cavity and having at least one bore.

Alternatively, the cavity particularly expediently has a prismatic, a conical and a spherical section, the spherical section being arranged in the proximal region of the cavity and having at least one bore, and the conical section being arranged between the prismatic section and the spherical section.

The lighting source expediently has at least one element from the following group: halogen lamp, LED, OLED, QLED, laser diode, optical waveguide, laser.

In order to improve the lighting, the geometry of the lighting source is preferably designed to be compatible with the cavity.

The illumination source preferably has an interface to the cavity, in particular to the cavity opening. By means of a flange, for example, the lighting can hereby be introduced into a predetermined and fixed insertion depth and / or insertion position.

In a further embodiment of the invention, the outer surface of the workpiece is additionally determined using tactile or optical 3D measurement methods. Here, the outer surface is expediently illuminated, in particular by means of coaxial or ring light illumination. The additionally recorded images of the outer surface are evaluated by combining the images into a 3D model of the outer surface. In this way, the entire workpiece can be characterized, the area of the outer surface in which the distal drilling opening is located, for example, being of particular interest. In this way, among other things, the angle of the bore (s), for example in relation to the outer surface, can be determined.

The invention will now be explained in more detail on the basis of non-limiting exemplary embodiments with reference to the accompanying drawings. The schematic drawings show:

Figure 1 is a sectional view through a workpiece which is formed as part of an injection nozzle of an internal combustion engine.

2A and 2B show disadvantages that occur in measuring systems and measuring methods known from the prior art; and

3 shows a sectional view through a workpiece, in particular through a borehole of an injection nozzle of an internal combustion engine, while carrying out a method according to the invention for optically detecting the geometry of the workpiece.

Referring to FIG. 1, a section along a section plane through a section of a workpiece 1 is shown, the section plane being parallel to the plane of the drawing. In the example shown, the workpiece 1 is an injection nozzle of an internal combustion engine. The workpiece 1 can have any geometry or microgeometry that can be detected using the method according to the invention, a person skilled in the art being familiar with such geometries or microgeometries.

The workpiece 1 comprises a body 2 which is delimited by an outer surface 3. The workpiece 1, or the body 2, has a cavity 4 with a surface 5, the cavity 4 being accessible via a cavity opening 6 which is located in the outer surface 3 of the workpiece 1.

In the example shown in FIG. 1, the cavity 4 has a cylindrical section 4a, a conical section 4b and a spherical section 4c. The conical section 4b is arranged between the prismatic section 4a and the spherical section 4c. The spherical section 4c is arranged in a proximal region 4d of the cavity 4.

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The workpiece 1 has in the proximal region 4d two cylindrical bores 7 with a surface 5, each of which extends from a proximal bore opening 7a through the body 2 to a distal bore opening 7b. Since the workpiece 1 in the example shown in FIG. 1 is in one piece, the surface 5 corresponds to the holes 7 with respect to the material of the surface 5 of the cavity 4. Surface parameters such as roughness and, as a result, reflection properties can differ.

The cavity 4 can have any geometry, micro-geometry and / or any combination of prismatic, conical and / or spherical sections, a person skilled in the art being familiar with such geometries, micro-geometries and / or combinations of sections. For example, the cavity 4 can alternatively have a prismatic section 4a and a conical section 4b, the conical section 4b being arranged in the proximal region 4d of the cavity 4 and having the bores 7.

The workpiece 1 and / or the cavity 4 can have any number of bores 7, for example one, three, four, five, six, seven, eight, nine, ten or more than ten bores 7, the bores 7 being any Can have shape and geometry, a person skilled in the art knows such shapes and geometries.

FIG. 2A and FIG. 2B show disadvantages that can occur when the geometry of a bore 7 is detected using measurement methods known from the prior art. The diameter and / or the clear surface of the distal drilling opening 7b is / are usually smaller than the diameter and the numerical aperture NA of an objective 8 of an optical system of a measuring system. In FIG. 2A, the objective 8 is arranged in a region 9 of the outer surface 3 of the workpiece 1 and the distal drilling opening 7b and an optical axis 10 of the objective 8 or the optics is essentially parallel to the surface 5 and / or to a longitudinal axis 11 of the bore 7. When collecting a representation of the surface 5 of the borehole 7, the illumination is inevitably shadowed, which takes place along an illumination direction BR essentially from above through the distal borehole opening 7b, as a result of which the effective numerical aperture ENA is considerably smaller than the actual one numerical aperture NA of the objective 8. FIG. 2B shows the situation in an enlarged section and with further details. The light EL incident along the direction of illumination BR is largely scattered away from the surface 5 of the bore 7 from the direction of illumination BR (scattered light GL) and / 16 only a small part which can be used (reflected light RL) is reflected back in the direction of the lens 8 and can be captured by the lens 8 and the optics.

An implementation of a method according to the invention for optically detecting the geometry of the workpiece 1 is explained below with reference to FIG. 1 and FIG. 3:

In a method step A), an illumination source 12 of a measuring system (not shown) is introduced into the proximal area 4d of the cavity 4, for example through the distal cavity opening 6. The illumination source 12 can alternatively be in each area or in several areas of the cavity 4 and / or be introduced through one of the holes 7

In a method step B), at least one area 13 of the surface 5 of the bore 7 to be measured is illuminated by the proximal bore opening 7a by means of the illumination source 12. The surface 5 of the bore 7, in particular the area 13 to be measured, reflects the light EL incident on the surface 5 along one or more illumination direction / s BR as reflected light RL through the bore 7 in the direction of the distal bore opening 7b. The area 13 to be measured can also be a defined point of the surface 5 of the bore 7. The entire surface 5 of the bore 7, in particular the entire surface 5 of the cavity 4, is expediently illuminated or illuminated by means of the illumination source 12. The area 13 to be measured is then in each case a point, area or section of this illuminated surface 5. The illumination source 12 can be designed as an non-directional point light source, in particular as an LED, or as a plurality of directional light sources, for example LASER light sources, along a plurality of illumination directions BR ,

In a method step C), an objective 8 is arranged in the area 9 of the outer surface 3 of the workpiece 1 and the distal drilling opening 7b. The objective 8 is part of an optical system of the measuring system, which is arranged along an optical axis 10. The arrangement can be such that the optical axis 10 is essentially parallel to the surface 5 and / or to the longitudinal axis 11 of the bore 7. The surface 5 of the bore 7, in particular the area 13 to be measured, reflects the incident light EL as reflected light RL in the direction of the objective 8. As a result, the light yield is significantly improved in comparison to measurement methods known from the prior art and the detection of a bore 7 of an injection nozzle of an internal combustion engine is only possible.

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Process steps B) and C) can be carried out in any time sequence or essentially simultaneously.

In a method step D), a plurality of representations of the area 13 to be measured are captured with the optics of the measuring system in the form of the light RL reflected by the surface 5 and emerging from the distal drilling opening 7b.

In a method step E), images of the representations of the surface 5 captured by the optics are captured in an image sensor of the measuring system. The images (image data) recorded by the image sensor can be transmitted, for example, via a data bus of the measuring system to an evaluation unit of the measuring system, where they are evaluated in a method step F). Between the taking of the images, the focal point of the optics is continuously shifted in relation to the area 13 of the surface 5 to be measured. The image sensor then captures images during the continuous focus point shifting process. To achieve this, a measurement controller of the measurement system can detect the current position of the focus point in relation to the area 13 to be measured on the surface 5 and send a trigger signal to the image sensor at defined positions in order to trigger the taking of an image in the image sensor. Due to the focus variation and a shallow depth of field of the optics, different areas of the surface 5 can be imaged sharply in the image sensor. The images recorded by the image sensor are evaluated by combining the images into a 3D model of the surface 5.

The focus point of the optics can be shifted, for example, by using liquid lenses for focal length control and / or by changing the relative distance between the optics and the area 13 to be measured or the surface 5. A person skilled in the art knows the specified and comparable alternative possibilities.

Process steps D), E and F) can be carried out in a repeatedly repeated sequence and / or essentially simultaneously.

In order to improve the images or the 3D model of the surface 5, the position of the lens 8 and / or the orientation of the optical axis 10 can be varied between the taking of images. In addition, the illumination intensity and / or the illumination position of the illumination source 12 can be varied during the acquisition of an image and / or between the acquisition of images. Because / 16 different surface inclinations reflect the light differently, can

Variation of the lighting position can be inferred from the topography of the surface 5.

The area 13 of the surface 5 to be measured can be illuminated intermittently during the shifting process of the focus point and / or the illumination intensity of the illumination source 12 can vary, which enables a higher radiometric dynamic of the surfaces 5 for surfaces 5 with widely differing reflection properties.

The illumination source 12 can have at least one element from the following group: halogen lamp, LED, OLED, QLED, laser diode, optical waveguide, laser. A person skilled in the art knows the specifics and advantages of the respective elements.

The geometry of the illumination source 12 can be designed to be compatible with the cavity 4 in order to optimally illuminate the area 13 to be measured and / or the surface 5. In addition, the illumination source 12 can have an interface to the cavity 4, in particular to the cavity opening 6, for example an insertion flange or threaded flange, as a result of which the illumination source 12 can be introduced in a targeted and fixed manner into the cavity 4, for example into the proximal region 4d.

The method according to the invention can be expanded and / or combined with focus variation methods or other optical or tactile 3D measurement methods, so that the outer surface 3 of the workpiece 1 can also be determined. For this purpose, the outer surface 3 is additionally illuminated in method step B), in particular by means of coaxial or ring light illumination. In method steps D), E) and F), the additionally captured representations and recorded images of the outer surface 3 are evaluated by combining the images to form a 3D model of the outer surface 3.

The previously described method steps according to the invention and advantageous additional measures can be combined depending on the application. An optimal solution can therefore be found for each workpiece 1 or geometry.

Claims (16)

claims: 1. A method for optically detecting the geometry of a workpiece (1), in particular an injection nozzle of an internal combustion engine, with a cavity (4) and at least one bore (7) between a proximal bore opening (7a) in the surface (5) of the cavity (4 ) and a distal drilling opening (7b) in an outer surface (3) of the workpiece (1), characterized by the following method steps: A) introducing an illumination source (12) of a measuring system into the cavity (4); B) illuminating at least one area (13) to be measured of the surface (5) of the bore (7) through the proximal bore opening (7a) by means of the illumination source (12); C) arranging an optical system of the measuring system in a region (9) of the outer surface (3) of the workpiece (1) and the distal drilling opening (7b); D) collecting a plurality of representations of the area (13) to be measured in the form of the light (RL) reflected by the surface (5) and emerging from the distal drilling opening (7b) with the optics; E) taking images of the representations of the surface (5) captured by the optics in an image sensor of the measuring system, the focus point of the optics being continuously shifted in relation to the area (13) of the surface (5) to be measured between the taking of the images ; and F) Evaluation of the images recorded by the image sensor by combining the images into a 3D model of the surface (5). 2. The method according to claim 1, wherein the entire surface (5) of the bore, in particular the entire surface (5) of the cavity (4), is illuminated. 3. The method according to claim 1 or 2, wherein the illumination source (12) through a distal cavity opening (6), which is located in the outer surface (3) of the workpiece (1), is introduced. 4. The method according to any one of claims 1 to 3, wherein the illumination source (12) is introduced into a proximal region (4d) of the cavity (4). 5. The method according to any one of claims 2 to 4, wherein the position of a lens (8) of the optics and / or the orientation of an optical axis (10) of the optics is varied during the taking of an image and / or between the taking of images / become. 11/16 6. The method according to any one of claims 1 to 5, wherein the optics is arranged at least during the recording of an image such that the optical axis (10) substantially parallel to the surface (5) and / or to a longitudinal axis (11) of the bore (7) is. 7. The method according to any one of claims 2 to 6, wherein the illumination intensity and / or the illumination position of the illumination source (12) is / are varied at least during the acquisition of an image and / or between the acquisition of images. 8. The method according to any one of claims 2 to 7, wherein the illumination of the area to be measured (13) of the surface (5) is carried out intermittently during the displacement process of the focus point. 9. The method according to any one of claims 1 to 8, wherein the cavity (4) has at least one prismatic, in particular a cylindrical, at least one conical and / or at least one spherical section (4a, 4b, 4c). 10. The method according to claim 9, wherein the cavity (4) has a prismatic and a conical section (4a, 4b), wherein the conical section (4b) is arranged in the proximal region (4d) of the cavity (4) and the at least one Has bore (7). 11. The method according to claim 9, wherein the cavity (4) has a prismatic, a conical and a spherical section (4a, 4b, 4c), the spherical section (4c) being arranged in the proximal region (4d) of the cavity (4) and which has at least one bore (7), and wherein the conical section (4b) is arranged between the prismatic section (4a) and the spherical section (4c). 12. The method according to any one of claims 1 to 11, wherein the lighting source (12) has at least one element from the following group: halogen lamp, LED, OLED, QLED, laser diode, optical waveguide, laser. 13. The method according to any one of claims 1 to 12, wherein the geometry of the illumination source (12) is compatible with the cavity (4). 14. The method according to any one of claims 1 to 13, wherein the illumination source (12) has an interface to the cavity (4), in particular to the cavity opening (6). 12/16 15. The method according to any one of claims 1 to 14, wherein additionally the outer surface (3) of the workpiece (1) is determined using tactile or optical 3D measurement methods. 16. The method according to claim 15, wherein the outer surface (3) is additionally illuminated, in particular by means of coaxial or ring light illumination, and wherein the additionally recorded images of the outer surface (3) are evaluated by combining the images to form a 3D model of the outer surface (3).