CONDENSER UNIT FOR PROVIDING DIRECTED LIGHTING OF AN OBJECT TO BE MEASURED POSITIONED IN A MEASURED OBJECT POSITION, IMAGING DEVICE AND METHOD FOR RECORDING A SILHOUETTE CONTOUR OF AT LEAST ONE OBJECT TO BE MEASURED IN A MEASURING FIELD USING AN IMAGING DEVICE AND USE OF AN ATTENUATION ELEMENT

Abstract

A condenser unit for providing directed lighting of an object to be measured positioned in a measured object position, wherein the condenser unit comprises a light source for emitting a light beam and an optical element having a positive refractive power. The condenser unit further comprises at least one attenuation element arranged in a common optical axis with the light source and the optical element, which attenuation element comprises a location-dependent light intensity attenuation effect for the light beam incident on the attenuation element, more particularly wherein the light intensity attenuation effect declines from the optical axis towards an edge of the attenuation element.

Claims

1. A condenser unit for providing directed lighting of an object to be measured positioned in a measured object position, wherein the condenser unit includes the following features: at least one light source for emitting a light bundle; an optical element having a positive refractive force; and at least one attenuation element arranged in a common optical axis with the light source and the optical element, which has a location-dependent light intensity attenuation effect for the light bundle incident through the attenuation element (300), in particular wherein the light intensity attenuation effect decreases from the optical axis to an edge of the attenuation element.

2. The condenser unit as claimed in claim 1, characterized in that the attenuation element is made plate-shaped and/or the attenuation element is arranged on a side of the optical element facing toward or facing away from the light source.

3. The condenser unit as claimed in claim 1, wherein a second attenuation element arranged in the optical axis, which has a location-dependent light intensity attenuation effect for the light bundle incident through the second attenuation element, in particular wherein the second attenuation element is made plate-shaped and/or a light intensity attenuation effect of the second attenuation element decreases from the optical axis toward an edge of the second attenuation element and/or the attenuation element is arranged in the optical axis between the light source and the optical element and the optical element is arranged between the light source and the second attenuation element.

4. The condenser unit as claimed in claim 1, wherein the optical element is formed as a Fresnel lens.

5. The condenser unit as claimed in claim 1, wherein the attenuation element is arranged on a light entry surface or a light exit surface of the optical element.

6. The condenser unit as claimed in claim 1, wherein a ratio of a structural height of the optical element and an aperture opening of the optical element is less than 1, in particular less than 0.5.

7. The condenser unit as claimed in claim 1, wherein at least the attenuation element is designed as a gradient filter, an absorbing and/or reflecting binary filter, a scattering filter having periodic or randomly-distributed scattering elements, a diffractive or holographic optical element, and/or as a partial reflector.

8. The condenser unit as claimed in claim 1, wherein the light source is designed as at least one LED light source, a fiber, scattering, or converting light source, and/or in that the light source has an extension which is less than one-fifth of the focal length f of the optical element.

9. The condenser unit as claimed in claim 1, wherein a diffuser, a diffractive element, and/or an interference filter is provided in the optical axis to delimit an aperture of the condenser unit and/or the optical element.

10. An imaging device for optically measuring the object to be measured, which can be positioned and/or is positioned in the measured object position in a field of view, wherein the imaging device includes the following features: a condenser unit as claimed in claim 1 for lighting the object to be measured; an imaging optical unit; and an image sensor, wherein the imaging optical unit is designed to image the object to be measured on the image sensor and at least the attenuation element is designed to homogeneously light the image field assigned to the field of view on the image sensor.

11. A method for recording a silhouette contour of at least one object to be measured in a measuring position using an imaging device as claimed in claim 10, wherein the method includes the following steps: generating a lighting light bundle using the condenser unit and lighting the object to be measured using the lighting light bundle; imaging the silhouette of the object to be measured on an image sensor by means of an imaging optical unit, and recording the silhouette contour of the object to be measured using the image sensor.

12. The method as claimed in claim 11, characterized in that in the step of imaging, a silhouette of the object to be measured is imaged on the image sensor telecentric on the object side and/or telecentric on the image side.

13. A use of an attenuation element, which has a location-dependent light intensity attenuation effect for the light bundle incident through the attenuation element, for homogenizing the illumination of an image field on an image sensor of an imaging device, wherein the imaging device comprises: a condenser unit for providing collimated lighting of an object to be measured positioned in a measured object position in a field of view associated with the image field; an imaging optical unit; and the image sensor arranged in an image plane of the imaging optical unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Particularly advantageous exemplary embodiments are described hereinafter on the basis of the appended drawings. In the figures:

[0028] FIG. 1 shows a schematic illustration of an exemplary embodiment of an imaging device;

[0029] FIG. 2 shows a diagram of an exemplary intensity curve of the irradiance in the aperture plane of the optical element or in the plane of the object to be measured;

[0030] FIG. 3 shows a schematic illustration of a further exemplary embodiment of an imaging device;

[0031] FIG. 4 shows a schematic illustration of a further exemplary embodiment of an imaging device;

[0032] FIG. 5 shows a schematic cross-sectional illustration through an exemplary arrangement of a light source having an optical element arranged downstream in the optical path to explain the functionality of the attenuation element;

[0033] FIG. 6 shows an exemplary diagram to illustrate an efficiency plotted on the y axis in relation to an aspect ratio plotted on the x axis;

[0034] FIG. 7 shows a schematic illustration of a further exemplary embodiment of an imaging device;

[0035] FIG. 8 shows a schematic illustration of a further exemplary embodiment of an imaging device;

[0036] FIG. 9 shows a schematic illustration of a further exemplary embodiment of an imaging device;

[0037] FIG. 10 shows a flow chart of an exemplary embodiment of a method for recording a silhouette contour of at least one object to be measured in a measuring field using a variant presented here of an imaging device.

DETAILED DESCRIPTION

[0038] Identical and/or functionally identical elements are designated by identical and/or similar reference signs in the different figures, wherein a further extensive description of these elements is omitted for simplification and easier readability.

[0039] FIG. 1 shows a schematic illustration of an exemplary embodiment of an imaging device 10, as can be used as the fundamental arrangement for an exemplary embodiment of the approach presented here. The imaging device 10 comprises a condenser unit 100 for generating or providing a light bundle 105 having a small divergence. This is suitable in particular for lighting objects to be measured 110 in the object plane in a measurement position 001, which is to be measured with high accuracy by means of, for example, a telecentric detector unit 115 in the silhouette contour method. In this application, the smallest possible numeric aperture NA matched with the detection system 115 is advantageous. Such a condenser unit 100 consists here, for example, at least of a light source 120, such as an LED, laser diode, fiber, scattering, or converting light source, which is positioned, for example, in the focal point of an optical element 125. FIG. 1 thus shows an arrangement in which the condenser unit 100 outputs the light bundle 105 from a light source 120 on an optical element 125, such as a Fresnel lens, at which the light bundle 105 is collimated. The light source 120 consists here, for example, of a single emitting element. The size or width of the emitter or the light source 120 is selected, for example, in such a way that the numeric aperture NA of the final light bundle 105 is less than 0.1 upon the exit from the condenser unit 100. The light source 120 and the optical element 125 are arranged or aligned on a common optical axis 130.

[0040] An aperture or opening D can be understood as the largest extension of the beam path in an aperture plane perpendicular to the optical axis. The aperture plane can be the light exit-side main plane of the optical element. The structural height can be understood as the distance of the light source to the light exit-side surface (or its largest z coordinate if z is defined in the direction of the optical axis) of the optical element or the light exit surface of the attenuation element along the optical axis, depending on which measure is larger.

[0041] To achieve the most compact possible construction of the condenser unit 100 and thus also the imaging device 10, the optical element 125 is selected in such a way that its focal length is as small as possible in relation to its aperture. The smaller this ratio is selected to be, the more strongly the beam density of the collimated light bundle 105 drops toward the edges. This results because a natural vignetting=reduction of the irradiance of the aperture of the lens takes place with increasing distance to the optical axis (due to projection of the angle and increasing distance to the light source).

[0042] FIG. 2 shows a diagram of an exemplary intensity curve I of the irradiance plotted on the y axis in the aperture plane of the optical element, or in the (measuring) plane 001 of the object to be measured 110. The curve provided with the reference sign (a) of the profile of the light intensity I over the radial distance r from the optical axis 130 shows this high damping behavior in the edge areas having large distance r from the optical axis. The curve (a) thus shows an inhomogeneous distribution of the radiation density, which has negative effects on the measurement accuracy of the measurement of the object to be measured 110.

[0043] In contrast, an approximately constant level of the light intensity of the light bundle 105 would be desirable to achieve the most precise and detailed possible optical evaluation of the object to be measured 110 at the measuring position 001 by the detector unit 115, as shown in the curve having the reference sign (b) in FIG. 2. Such a curve (b) can be obtained according to the approach presented here by using a suitable attenuation element.

[0044] FIG. 3 shows a schematic illustration of a further exemplary embodiment of an imaging device 10, which includes an arrangement of the optical components in accordance with the illustration from FIG. 1, supplemented with an attenuation element 300 arranged in the optical path 130 in the condenser unit 100. The gradient of the beam density described with reference to FIG. 2 according to the curve (a) is thus corrected by an attenuation element 300 having location-dependent (light intensity) attenuation effect at a position between the light source 120 and the optical element 125 and/or at a position on a side of the optical element 125 facing away from the light source 120. In this way, the beam density or intensity of the light bundle 105 output by the condenser unit 100 can be corrected over the entire aperture of the condenser unit 100 to a predetermined intensity distribution, as shown in FIG. 2 according to the curve (b).

[0045] The attenuation element 300 at the position between the light source 120 and the optical element 125 and/or on the side of the optical element 125 opposite to the light source 120 can be implemented, for example, by a gradient filter (gray filter), binary filter (absorbing or reflecting), scattering filter having periodic or randomly-distributed scattering elements (diffractive or holographic optical elements), or a partial reflector (polarization-dependent, polarization-independent, or chromatic). It is furthermore also conceivable that the attenuation element 300 is vapor deposited or laminated as a layer on the optical element, and a very compact condenser unit 100 may be implemented in this way.

[0046] In the configuration or arrangement of the attenuation element 300 on the side of the optical element 125 facing away from the light source 100, as shown in FIG. 3, the light bundle 105 which originates from the light source 120 passes through the optical element 125 first and then the attenuation element 300. In this case, the size/width of the attenuation element 300 at the position following the optical element 125 approximately corresponds to that of the optical element 125. The precise distance of both elements, thus of the attenuation element 300 and optical element 125, can be selected freely.

[0047] In a second configuration, the attenuation element 300 is located at a position between the light source 120 and the optical element 125, the light bundle 105 passes through it first and subsequently passes the optical element 125. In this case, the size of the attenuation element 300 at the position between the light source 120 and the optical element 125 is related to its three-dimensional location. For the most uniform possible beam density of the emitted light bundle 105 over the entire aperture, the distance is accordingly to be adjusted accurately. If a partial reflector is used as an attenuation element 300 in this configuration, the surface around the optical element 125 is supposed to absorb the reflected light. Specific spatial and angle-dependent emission characteristics of the light bundle 105 may be achieved by the integration of (for example also multiple) attenuation elements 300 at a position between the light source 120 and the optical element 125 and/or a position on a side of the optical element 125 facing away from the light source 120. No deflection mirrors or beam splitters are required in the beam path and it is made possible that a compact vertical structural form of the condenser unit 100 can thus be achieved, substantially determined by the focal length of the optical element 125.

[0048] FIG. 4 shows a schematic illustration of a further exemplary embodiment of an imaging device 10, which includes an arrangement of the optical components according to the illustration from FIG. 3, supplemented by optical components of the detector unit 115 arranged in the optical path 130. The optical detection system or the detector unit 115 comprises as optical components an object-side optical element 400 (which comprises a lens, for example), a stop element 410 (for example an aperture), an image-side optical element 420 (for example also a lens again), and a surface sensor element or image sensor 430. The object-side optical element 400, the stop element 410, and/or the image-side optical element 420 can be combined as an imaging optical unit or imaging objective. The quality of the achieved lateral beam density of the light bundle 105 is defined here via the homogeneous illumination of a surface sensor element or an image sensor 430 in the optical detection unit 115 and its object-side numeric aperture.

[0049] This imaging device 10 can be used particularly advantageously in the silhouette contour method, wherein a silhouette of the object to be measured 110 results on the image sensor 430. To avoid the paradox of a homogeneously illuminated shadow, a field of view 440 and an image field 450 are defined. The field of view 440 designates in this case an object-side area, which can be imaged on the image sensor 430 by means of the imaging optical unit (according to the illustration from FIG. 4, for example, the object-side optical element 400, the stop element 410, and the image-side optical element 420). The image field 450 corresponds, for example, to the area illustrated in FIG. 4, which corresponds to an area visible due to the effect of the aperture 410 on the image sensor 430, an area visible through the aperture of the imaging optical unit, and/or a part of the image plane of the object-side field of view 440 delimited by the sensitive surface of the image sensor 430. The image field 450 can comprise, but does not have to, the entire sensitive surface of the image sensor 430. The homogeneity of the illumination of the image field 430 can advantageously be determined without the presence of an object to be measured 110.

[0050] To effect such a homogeneous illumination of the sensor 430, according to the approach presented here, the condenser unit 100 advantageously adapted to the imaging optical unit is used.

[0051] FIG. 5 shows a schematic cross-sectional illustration through an exemplary arrangement of a light source 120 having an optical element 125, which is designed here as a Fresnel lens, arranged downstream in the optical path 130. The light 105 emitted from the light source 120, which is designed as a single emitter having the numeric aperture NA.sub.LED, passes through the optical element 125, such as a Fresnel lens. The radial gradient of the beam density or the intensity distribution of the light bundle 105, which would result after the optical element 125 according to the curve (a) from the diagram of FIG. 2, is now corrected via the attenuation element 300 to achieve a homogeneous illumination and equalized to an approximately constant level, so that the condenser unit 100 has a light bundle 105 having a very homogeneous light distribution at a numeric aperture NA.sub.ill. The emission angle of the light source 120, which increases with the distance to the optical axis, is also apparent in FIG. 5, as well as the increasing distance to the optical element 125, which causes a reduction of the irradiance in the plane of the optical element 125 (natural vignetting).

[0052] The overall efficiency r of the condenser unit 100 may be determined here in a simple model via the following relationships: The collection efficiency η.sub.1 600 describes the proportion of the light emitted by the light source 120 which irradiates the effective aperture of the optical element 125. For a Lambertian emitter, the following results

[00001]$\begin{array}{cc}{\eta }_1={\mathrm{NA}}_{\mathrm{LED}}^2,& {\mathrm{NA}}_{\mathrm{LED}}=\sin \left(\mathrm{arc}\tan \left(\frac{D}{2f}\right)\right)\end{array}$

[0053] with the numeric aperture of the light source NA.sub.LED according to the illustration from FIG. 5, the diameter of the aperture opening D, and the focal length f of the optical element 125. The irradiance E(r) in the object plane results due to the natural vignetting of the lens or the optical element 125 as:

[00002]$E\left(r\right)={E_0\left[\cos \left(\mathrm{arc}\tan \left(\frac{r}{f}\right)\right)\right]}^4$

[0054] An ideally assumed attenuation element 300 at a position between the light source 120 and the optical element 125 and/or at a position on a side of the optical element 125 opposite to the light source 120 reduces the irradiance according to the homogeneity requirement (here 50%) to E′(r):

[00003]$E^{\prime }\left(r\right)=\{\begin{array}{cc}E\left(r\right)& E\left(r\right)<E_c\\ E_e& \mathrm{else}\end{array},E_c=2*E\left(D/2\right)$

[0055] The efficiency η.sub.2 610 results from the ratio of the optical radiation flux with attenuation element φ′ and without attenuation element φ as

η.sub.2=Φ′/Φ,Φ.sup.(′)=2π∫.sub.0.sup.D/2drrE.sup.(′)(r)

[0056] The overall efficiency η of the system is then the product of the individual efficiencies:

η=η.sub.1η.sub.2

[0057] FIG. 6 shows a diagram in which the aspect ratio is plotted on the x axis and an efficiency is plotted on the y axis. A nominal overall efficiency η of the condenser unit 100 can be calculated as a function of the aspect ratio f/D from the individual efficiencies η.sub.1 600 and η.sub.2 610 for an assumed requirement of a local intensity homogeneity (E′.sub.min/E′.sub.max) in the imaging system of 50%.

[0058] The concept presented here of a novel condenser unit 100 differs from other implementations of directed lighting with slight variation in the angle over the aperture (according to priority): due to the low aspect ratio (focal length of the optical element 125/diameter of the optical element 125) less than 1.

[0059] A high efficiency at low NA.sub.ill<0.1 in the outgoing beam bundle high homogeneity

[0060] In the condenser unit 100 presented here, in addition to the good setting of a homogeneous light distribution, furthermore a simple construction and a minor or absent alignment effort is particularly advantageous. A condenser unit 100 can be provided here which has a small numeric aperture (NA.sub.ill<0.1, which corresponds to a divergence angle±5.7°), a large diameter D of the illuminated surface (measuring field in the area of the object to be measured 110) with small structural height b of the condenser unit 100 and large lighting surface at the same time.

[0061] The approach presented here can be used for multiple different applications, for example for an adapted illumination for telecentric measuring objectives or for compact measuring microscopes having small aperture.

[0062] In the following description, particularly advantageous exemplary embodiments of the condenser unit 100 are explained once again, wherein the arrangement of the attenuation element 300 was omitted for reasons of clarity; however, it is to be noted here that the attenuation element 300 can be arranged both between the light source 120 and the optical element 125 and in the beam path after the optical element 125, as already described above.

[0063] FIG. 7 shows a schematic illustration of an exemplary embodiment of an imaging device 10, in which telecentric lighting parallel to the optical axis or the optical path 130 is provided (by aligning the light source 120 in the focal plane of the focusing lens as the optical element 125 orthogonally and symmetrically to the optical axis 130).

[0064] FIG. 8 shows a schematic illustration of an exemplary embodiment of an imaging device 10, in which telecentric lighting not parallel (i.e., oblique) to the optical axis 130 is carried out (for example by orthogonal displacement of the light source 120 or the emitter or the focusing lens as optical element 125 to the optical axis 130).

[0065] FIG. 9 shows a schematic illustration of an exemplary embodiment of an imaging device 10, in which non-telecentric lighting is provided (for example by axial defocusing of the light source 120 or the emitter or the focusing lens as optical element 125). This enables the adaptation of the condenser unit 100 to non-telecentric imaging objectives 115 as well.

[0066] FIG. 10 shows a flow chart of an exemplary embodiment of a method 1000 for recording a silhouette contour of at least one object to be measured in a measuring field using an imaging device according to a variant presented here, wherein the method 1000 includes a step 1010 of generating lighting light using the condenser unit 100 and lighting the object to be measured using the lighting light. Furthermore, the method 1000 comprises a step 1020 of imaging the silhouette of the object to be measured on an image sensor by means of an imaging device. Finally, the method 1000 comprises a step 1030 of recording the silhouette contour of the object to be measured using the image sensor.

[0067] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.