Chromatic confocal distance measuring device
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- PRECITEC OPTRONIK GMBH
- Filing Date
- 2023-06-28
- Publication Date
- 2026-06-02
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to an apparatus for performing chromatic confocal ranging at a plurality of points preferably arranged on a straight line on the surface of a workpiece and other objects.
Background Art
[0002] When it is necessary to measure the distance to a workpiece or other object non - contact and with high precision, chromatic confocal ranging devices have been used in industrial measurement technology for many years. For transparent objects, usually, the distance can be measured for each optical interface, and since the thickness can be obtained from the difference in the measured distances, such devices can also measure wall thickness and other thicknesses.
[0003] Conventional chromatic confocal ranging devices include a light source that generates measurement light of multiple colors and is aligned with a pinhole plate having very small openings. The openings are imaged on the surface of the measurement object by an imaging optical system. There is a significant longitudinal chromatic aberration in at least a part of the imaging optical system. Therefore, images of the openings of different colors are sequentially arranged on the optical axis of the imaging optical system. Only the spectral part of the measurement light for which the opening image is exactly on the surface of the measurement object is reflected by the surface, and thereby, this part can enter the same opening or an optically conjugate opening thereto. The wavelength of the spectral part is detected by a spectrometer. Here, each wavelength corresponds to a specific distance from the imaging optical system.
[0004] Other spectral parts are also partially reflected by the surface of the object, but since they cannot be focused by the imaging optical system on the same opening or an optically conjugate opening thereto, they do not significantly affect the part of the measurement light for which spectral analysis is performed by the spectrometer.
[0005] According to US 2018 / 0038680 A1, a chromatic confocal measuring device is known, and distances or thicknesses can be measured simultaneously at multiple points using this measuring device. Also, here, a general pinhole plate is replaced with a linear or planar array at the end of an optical fiber. If distances or thicknesses are measured simultaneously at multiple positions, the measurement time is significantly shortened. In this case, even for a large surface, a complete surface shape can be created in a short time.
[0006] The lateral resolution of such a multi-point measuring device, that is, the density of measurement points on the surface of an object, is restricted such that the measurement light reflected from the object and incident on the end of one optically conjugate optical fiber should not be incident on an adjacent optical fiber simultaneously. When such optical crosstalk occurs, each measurement point cannot correspond to a single distance value. Optical crosstalk is mainly due to physical reasons such that even when the imaging optical system is optimally calibrated, the image of the end of the optical fiber cannot be made completely sharp, leading to having the shape of a diffraction disk that extends planar based on the diffraction phenomenon, and the diffraction disk has a plurality of secondary maxima that can be clearly identified.
[0007] Therefore, in a known chromatic confocal distance measuring device, since the distance of the end of the optical fiber is relatively large, a high density of measurement points cannot be realized. SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a device for chromatically confocal measuring distances to a plurality of points on the surface of an object, which has a high lateral resolution.
[0009] The solution means for achieving the above object of the present invention is used for chromatic confocal measurement of distances to a plurality of points on the surface of an object, and includes a light source arranged to generate measurement light of a plurality of colors, a light pattern generation device arranged to generate a light pattern extending one-dimensionally or two-dimensionally in a first plane from the measurement light, an objective lens arranged to generate an image of the light pattern in an image plane whose axial position has wavelength dependence due to longitudinal chromatic aberration and whose chromatic aberration is not corrected, a static spatial filter arranged in a second plane optically conjugate to the first plane and having a filtering function corresponding to (but not necessarily the same as) the light pattern, a preferably non-polarizing cube beam splitter arranged in the optical path between the light pattern generation device and the objective lens to guide the measurement light reflected from the surface and passing through the objective lens to the spatial filter, a spectrometer having a plurality of input channels, each of which is arranged to perform spectral analysis on the reflected measurement light passing through a point of the static spatial filter corresponding to each input channel, and an analysis device arranged to calculate the distance from a point on the surface to the measuring device based on the wavelength measured by the spectrometer. According to the present invention, the device further includes a spatial filter having a plurality of pixels and being switchable for each pixel, which forms the light pattern generation device or is arranged in a third plane optically conjugate to the first plane and the second plane, and each pixel is switchable between a first switching state in which the pixel blocks the measurement light and a second switching state in which the pixel does not block the measurement light.
[0010] The pixel-switchable spatial filter can block or deflect a portion of the measurement light that causes optical crosstalk at a specific time during measurement so that it cannot reach the spectrometer. Another portion of the measurement light is suppressed at another time. In this way, extremely high lateral resolution can be achieved by combining a plurality of consecutive measurements.
[0011] In the simplest scenario, during measurement, a spatially digital switchable spatial filter that can be digitally switched pixel by pixel between a first switching arrangement and a second switching arrangement is controlled such that in the first switching arrangement, two adjacent pixels do not have the same switching state, and the second switching arrangement is complementary to the first switching arrangement. Thereby, only two individual measurements are required.
[0012] To achieve a higher horizontal resolution, in each switching arrangement, it may be necessary to increase the distance between active pixels such that there are at least n = 2, 3,... inactive switching positions between two active pixels. In this case, n + 1 different switching arrangements need to exist sequentially until all pixels are in the active switching position.
[0013] The control of different switching arrangements depends not only on the required horizontal resolution but also on the characteristics of the surface of the object being measured. On a surface with a good signal-to-noise ratio, more crosstalk can be tolerated if necessary, such that at a specific time point, up to half or even all of the pixels of the spatial filter can be in the active second switching state. The greater the interference of crosstalk, the greater the distance between the pixels in the active second switching state at a given time point should be.
[0014] By the optical conjugation between the third plane where a spatially switchable filter that can be digitally switched for each pixel is arranged and the first plane where the light pattern generation unit is arranged, it is ensured that the pixels of the spatially switchable filter that can be digitally switched for each pixel can correspond one-to-one to each measurement point. Planes that can be switched mutually by optical imaging are called optical conjugates. Therefore, an objective lens including one or a plurality of lenses or mirrors is usually provided between two optically conjugate planes, and the objective lens realizes optical imaging. However, instead of the objective lens, in special situations, optical conjugation can also be realized by other optical systems. As an example, the opposing ends of an optical fiber can be mentioned, and since the dot-like light distributions of these two ends are the same, they can be regarded as optical conjugates. Therefore, for example, an optical image can also be generated by an optical fiber bundle like a known endoscope. Two adjacent planes can also be regarded as optical conjugates in a broad sense.
[0015] When a spatially switchable filter that can be digitally switched for each pixel is arranged in the third plane independently of the light pattern generation device, the spatial filter may be in the optical path between the light pattern generation device and the cube beam splitter. The advantage of such an arrangement is that the image of the light pattern is sharper than the image re-imaged by the objective lens.
[0016] In this case, it is preferable that the device has an imaging optical system that images the first plane onto the third plane. The main advantage of such an imaging optical system is that the light pattern generating device includes an arrangement of the ends of optical fibers or a light-shielding plate having at least one opening. The measurement light is generally emitted from the optical fiber or the opening so as to strongly diverge. When a spatially switchable filter that can be digitally switched for each pixel is directly arranged in front of the end of the optical fiber or the opening of the light-shielding plate, an optical conjugation in a broad sense occurs. However, many particularly suitable spatially switchable filters that can be digitally switched for each pixel (for example, a micro mirror array) still cannot be arranged close enough to the light pattern generating device to the extent that it can be called optical conjugation. While the imaging optical system can utilize a large numerical aperture, it can use a micro mirror array and other switchable spatial filters, and these filters can only be arranged at a position away from the light pattern generating device due to the folding of the light beam or the required mounting space.
[0017] The light pattern may include a plurality of light points two-dimensionally distributed, or at least one continuous light ray or a light ray composed of light points. The continuous light ray is divided into each measurement point by the pixels of the switchable spatial filter.
[0018] In one embodiment, the light pattern generating device includes a planar arrangement of micro focusing lenses. The focusing lens forms an optical conjugation in a broad sense by focusing the measurement light onto the corresponding pixels of the switchable spatial filter.
[0019] In another embodiment, the spatially switchable filter that can be digitally switched for each pixel forms the light pattern generating device. Such a structure is very simple and can use a micro mirror array type spatial filter without the need for an additional imaging optical system.
[0020] In this case, the spatial filter should be illuminated with light having an angular distribution that matches the numerical aperture of the objective lens with uncorrected chromatic aberration. This is particularly effective when the measurement light propagates as a free beam between the light source and the spatially filter that can be digitally switched for each pixel.
[0021] To avoid light loss, the spatial filter used as the light pattern generator should be illuminated using the light source so as to allow as much light as possible to enter the spatial filter. Depending on the specific type of the light source, a simple focusing system alone is sufficient to focus the light from the light emitting surface of the light source and to cause it to enter the spatial filter with low loss. When the light pattern generated by the spatial filter includes light rays composed of a plurality of light spots, the focusing system can be constructed as a cylindrical lens or can be constructed as an anamorphic lens by other means.
[0022] In one embodiment, a collimator for collimating the measurement light incident on the cube beam splitter is disposed in the optical path between the light pattern generator and the cube beam splitter. In this case, based on confocal imaging, the measurement light reflected from the object is similarly collimated and passes through the cube beam splitter. The advantage of being collimated and passing through is that it does not cause spherical aberration in the cube beam splitter.
[0023] The spatially filter that can be digitally switched for each pixel is preferably a micro mirror array. Alternatively, it may refer to the transmissive MEMS component described in US 8,054,527 B2. Although it is also possible to consider using an LCD panel as a spatially filter that can be digitally switched for each pixel, the LCD panel has drawbacks due to its polarization characteristics.
[0024] For the same reason, it is advantageous for the cube beam splitter to be non-polarizing. In this case, since the splitting ratio of the cube beam splitter does not depend on the polarization state, it also does not depend on the characteristics of the surface of the object.
[0025] In one embodiment, the multi-color light source includes a light emitter as known from EP 3764056 A1 (corresponding to US 10,731,965 B1). Such a light source preferably has an elongated light-emitting surface. When guiding light through an optical fiber, its end forms a rectangular or circular array and can receive light emitted from adjacent rectangular or circular light-emitting surfaces of the light emitter.
[0026] In a light source based on a light emitter, a light-emitting substance called a light emitter is excited by a pump source (usually referring to a laser or an LED), and the light-emitting substance emits light through a physical process (especially phosphorescence, fluorescence, or scintillation). The advantage of such a light source is that it can illuminate the entire confocal aperture and has high efficiency and high light output.
[0027] In order to reduce optical crosstalk due to scattered light or the like, other spatial filters may be arranged at positions optically conjugate to the first, second, and third planes.
[0028] The spectrometer can be synchronized with a spatially filter digitally switchable for each pixel such that the input channels corresponding to the pixels in the second switching state become logically or physically inactive. Thereby, it is prevented that the measurement light incident on adjacent input channels due to crosstalk is considered during analysis. In the simplest scenario, the inactivation of the relevant input channels is implemented such that the intensities measured at these locations are not read.
[0029] When a spatially filter digitally switchable for each pixel is arranged in the optical path between the light source and the cube beam splitter, another spatially filter digitally switchable for each pixel may be arranged in a fourth plane in the optical path between the cube beam splitter and the spectrometer, and the fourth plane is optically conjugate to the first and second planes. Each pixel of the other spatially filter digitally switchable for each pixel is switchable between a first switching state in which the pixel blocks the measurement light and a second switching state in which the pixel does not block the measurement light.
[0030] The background of this solution is that the image of the optical pattern loses sharpness each time an optical imaging is performed. For example, when two adjacent diffraction disks overlap negligibly on the surface of an object and are re-imaged by an objective lens at the height of a spectrometer, the overlap may already be obvious. Here, a spatial filter that can be digitally switched for each different pixel can specifically provide improvements such as the spatial filter re-blocking the relevant light beam so that crosstalk does not occur in the spectrometer even after re-imaging.
Brief Description of the Drawings
[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
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Mode for Carrying Out the Invention
[0032] 1. Structure of the measuring device FIG. 1 shows a schematic meridional cross-section of a distance measuring device according to a first embodiment of the present invention, which is represented by 10 as a whole.
[0033] The device 10 has a light source 12 that generates measurement light ML of a plurality of colors. Here, the measurement light ML preferably has a continuous spectrum. However, in principle, if the wavelength peaks are close enough, the use of a comb-like spectrum or other discrete spectra can be considered as well.
[0034] In the illustrated embodiment, the light source 12 includes a superluminescent diode 14 and a focusing lens 16 arranged behind it along the optical propagation direction.
[0035] The measurement light ML generated from the light source 12 is incident on an optical pattern generation device 18, and the optical pattern generation device generates an optical pattern by the incident measurement light ML. In the illustrated embodiment, the optical pattern generation device 18 includes a pinhole plate 20, and FIG. 2 shows a top view of the pinhole plate. The pinhole plate 20 has a plurality of openings 22 arranged in a straight line. When irradiated with the measurement light ML, the openings 22 become point light sources, and the measurement light ML diverges from these point light sources.
[0036] The aperture 22 is arranged in a first plane E1 that overlaps with the object plane of the imaging optical system 24. In the illustrated embodiment, the imaging optical system 24 is constructed as a 4f optical system. The characteristic of such a 4f optical system is that two objective lenses or lenses L1 and L2 are arranged such that the rear focal plane of lens L1 and the front focal plane of lens L2 overlap. As a result, telecentric optical paths are formed on both sides, and as a result, the angular distribution at the aperture 22 is transmitted to the image plane E2 of the imaging optical system 24 without tilting. As shown in the embodiment, when the focal lengths of lenses L1 and L2 are equal, the imaging scale β = -1.
[0037] A transmissive MEMS spatial filter 26 is arranged in the image plane E2 of the imaging optical system 24, where MEMS is an abbreviation for microelectromechanical system. Such a filter 26 includes a large number of regularly arranged elements or pixels 28, and these elements or pixels can be mechanically moved separately so as to selectively open or block the optical path. Appropriate examples of such MEMS filters are known, for example, as described in US 2006 / 0012781 A1. As an alternative method, an LCD panel may be used, but due to its polarization effect, it may be disadvantageous for some measurement operations.
[0038] Figures 3a and 3b show schematic enlarged cross-sections of the transmissive MEMS spatial filter 26. In the illustrated embodiment, the pixels 28 of the transmissive MEMS spatial filter 26 are arranged in a straight line such that each exactly corresponds to one of the apertures 22 of the light pattern generator 18. Such a correspondence relationship is generated by the imaging of the aperture 22 at the pixel 28 by the imaging optical system 24.
[0039] The independent switchability of each pixel 28 is shown with a light and a dark background in Fig. 3a. The pixels 28 with a dark background are in the first switching state, in which state the pixels 28 block the measurement light ML. The pixels 28 with a light background are in the second switching state, in which state the pixels 28 become transparent to the measurement light ML. The switching state of the pixels 28 is preset by the control and analysis device 30. The switching between different switching states clearly found from the comparison between Fig. 3a and Fig. 3b is usually carried out within a few microseconds.
[0040] For the pixels 28 in the second switching state shown at the leftmost end of Fig. 3a, other beams show that the angular distribution of the measurement light ML remains unchanged when passing through the transmissive MEMS spatial filter 26. Therefore, the transmissive MEMS spatial filter 26 filters only in the point space and does not filter in the angular space. Therefore, the measurement light ML is emitted at the numerical aperture NA of the imaging system 24 at the output end of the pixel 28.
[0041] Therefore, the pixels 28 of the transmissive MEMS spatial filter 26 are also point light sources, but different from the openings 22 of the light pattern generator 18, these point light sources can be separately opened and blocked.
[0042] Figs. 3a and 3b show two different switching arrangements, and in this embodiment, it is possible to switch between these two switching arrangements. In the first switching arrangement shown in Fig. 3a, no two adjacent pixels 28 will be in the same switching state. Thereby, the switching states alternate between pixels. The second switching arrangement shown in Fig. 3b is complementary to the first switching arrangement in Fig. 3a. Therefore, here no two adjacent pixels 28 will be in the same switching state either, and the switching states also alternate between pixels. However, when the switching mode is offset by one pixel, it is possible to switch between the two switching arrangements shown in Figs. 3a and 3b, specifically, to switch each pixel 28 to a different switching state. In 2. below, the advantages regarding the switching of the transmissive MEMS spatial filter 26 and the switching arrangement will be described.
[0043] A collimating lens 32 having a front focal plane overlapping the plane E2 is disposed in the optical path behind the transmissive MEMS spatial filter 26. Therefore, the beam emitted from the pixel 28 is collimated when passing through the collimating lens 32.
[0044] The collimated beam is incident on an unpolarized cube beam splitter 33, and the cube beam splitter has a splitting surface 34 inclined at 45° with respect to the optical axis. A predetermined portion of the emitted light, for example 50%, is reflected by the splitting surface and lost during measurement. The remaining measurement light ML passes through the cube beam splitter without being deflected based on the collimated optical path and is incident on an objective lens 36 with uncorrected chromatic aberration, and the objective lens has an object plane at infinity. The objective lens 36, together with the imaging optical system 24 and the collimating lens 32, forms an image of the aperture 22 disposed in the plane E1 from the image plane B1 to B3 based on longitudinal chromatic aberration, and the axial positions of these image planes depend on the wavelength. This is shown by different dashed lines in FIG. 2. Here, each wavelength exactly corresponds to one image plane. When the spectrum generated from the light source 12 (as in this embodiment) is continuous, a continuous series of image planes is produced.
[0045] When the image of the aperture 22 is in one image plane and at least a part of the reflecting surface 38 of the object 40 is provided at the height of the image plane, the emitted light beam is reflected here and returns to itself, passes through the objective lens 36 along the same path, and returns to the splitting surface 34 of the cube beam splitter 33. For the arrangement shown here, for example, at the wavelength where the image of the aperture 22 is in the image plane B2, the aperture 22 on the optical axis OA of the apparatus 10 satisfies the above-mentioned prerequisite. For the light beam 43 passing through another aperture 22, at another wavelength where the image of the related aperture 22 is in the image plane B1, here the lowermost object 40 satisfies the above-mentioned prerequisite. Of course, not only the light of a single wavelength is reflected by the surface 38. However, there is only one wavelength at which the measurement light beam is reflected by itself, because only the focus of this wavelength is accurately positioned on the surface 38.
[0046] A predetermined portion of the reflected measurement light ML is reflected by 90° at the spectroscopic surface 34 and focused by the focusing lens 42 onto the static spatial filter 44, which is arranged in the third plane E3 and has a filtering function corresponding to the light pattern. The static spatial filter 44 allows the transmission of the measurement light ML at some positions (or allows reflection when a reflective spatial filter is employed), while blocking the measurement light ML at the remaining positions. In the simplest scenario, the static spatial filter 44 refers to the same pinhole plate used for the aperture of the light pattern generator 18, and is optionally reduced or enlarged according to the image scale of the optical system therebetween. That is, the entire optical system in the optical path between the light pattern generator 18 and the static spatial filter 44, namely the imaging optical system 24, the collimating lens 32, the objective lens 36, and the focusing lens 42, causes the light pattern generator 18 to be imaged onto the static spatial filter 44. Therefore, the planes E1, E2, and E3 are optically conjugate. At the height of the transmissive MEMS spatial filter 26, an intermediate image is formed within the image planes B1 to B3 on the surface 38 of the object 40.
[0047] The static spatial filter 44 ensures that only the measurement light beam reflected by itself at the surface 38 at a specific wavelength can be further analyzed. The measurement light ML that does not meet this condition is blocked by the static spatial filter 44 based on the chromatic confocal measurement principle.
[0048] A spectrometer 46 having a plurality of input channels is arranged in the optical path behind the static spatial filter 44. The plurality of input channels perform spectral analysis on the reflected measurement light ML that has passed through the points of the static spatial filter 44 corresponding to each of the input channels. The spectrometer 46 generally includes a dispersive optical element such as a diffraction grating or a prism 47, as schematically shown in FIG. 1, and includes a photosensitive chamber arranged in a columnar configuration 48 for each input channel. Since such a spectrometer 46 is known, no further explanation is required.
[0049] 2. Function As is known for a chromatic confocal measuring device, during measurement, the control and analysis device 30 calculates the distance from a point on the surface 38 to the measuring device 10 based on the wavelength measured by the spectrometer 46. These points are the image of the point light source, i.e., the aperture 22. Here, each point light source corresponds to one input channel so that distance measurement can be performed for all point light sources simultaneously in principle.
[0050] However, when distance measurement is performed simultaneously for all point light sources, if the distance between the point light sources is short, there is a possibility of causing optical crosstalk. The reason is that even when optimally optically imaged, the image of the point light source may be blurred due to diffraction and may overlap. This is schematically shown in the enlarged portion C of the static spatial filter 44. From portion C, it can be seen that the light beam LB of the gray background on the plane E3 is not focused on a single aperture 22', but partially straddles two adjacent apertures 22", 22"'. The measurement light ML incident on the incorrect apertures 22", 22"' is detected by the corresponding input channel of the spectrometer 46 and distorts the distance measurement. For example, not only the light beam LB' shown by the dashed line is incident on the aperture 22"', but the light beam LB is also partially incident on the aperture.
[0051] Optical crosstalk may be prevented by increasing the distance between the point light sources (here the apertures 22). However, this solution is achieved at the expense of the lateral resolution of the device 10.
[0052] Accordingly, according to the present invention, the control and analysis device 30 controls the transmissive MEMS spatial filter 26 so as to divide the measurement into two partial measurements. In the first partial measurement, the pixels 28 of the transmissive MEMS spatial filter 26 are in the two switching arrangements shown in FIGS. 3a and 3b. In the second partial measurement, the pixels 28 are in another switching arrangement. For the adjacent optical beam LB' indicated by the broken line in part C in FIG. 1, this means that the propagation of the optical beam is blocked by the transmissive MEMS spatial filter 26 and cannot be incident on the input channel of the spectrometer 46 that does not correspond to this optical beam LB'. Accordingly, the same applies to the other optical beams adjacent to the optical beam LB on the other side not shown in part C.
[0053] At the same time, the spectrometer 46 is synchronized with the spatially digitally switchable filter 26 on a pixel-by-pixel basis such that the two input channels corresponding to the adjacent openings 22" are deactivated. Accordingly, the portion of the optical beam LB incident on the photosensitive chambers of these two input channels is not analyzed.
[0054] Accordingly, by dividing the measurement into two separate measurements and switching between the switching arrangements shown in FIGS. 3a and 3b during these two separate measurements, optical crosstalk can be most effectively prevented. Thereby, a high lateral resolution can be achieved when the measurement time is approximately doubled. Here, the control and analysis device 30 may be programmed so that this mode is applied only to measurements where a high lateral resolution is required and optical crosstalk is very likely to occur on the surface of the object. When the requirement for lateral resolution is low, one measurement is performed in any of the switching arrangements shown in FIGS. 3a and 3b.
[0055] 3. Other Embodiments FIG. 4 shows a slit plate 20' having a slit-shaped opening 22' from the perspective of FIG. 2, and the slit plate 20' can be used as the light pattern generating device 18 instead of the pinhole plate 20 shown in FIG. 2. The propagation of the measurement light ML that can cause optical crosstalk is similarly blocked here by the transmissive MEMS spatial filter 26.
[0056] FIG. 5 shows a 2D pinhole plate 20” from the viewpoints of FIGS. 2 and 3, and the 2D pinhole plate 20” can similarly be used as the light pattern generator 18 instead of the pinhole plate 20 shown in FIG. 2. In the 2D pinhole plate 20”, the openings 22” are divided into a regular two-dimensional grid.
[0057] In this case, the transmissive MEMS spatial filter 26 needs to have pixels 28 arranged two-dimensionally accordingly such that each opening 22” corresponds to one switchable pixel. As is known in the prior art, the static spatial filter 44 and the spectrometer 46 are similarly extended two-dimensionally accordingly.
[0058] FIG. 6 shows a second embodiment of the measuring device denoted as 10’. The differences between this embodiment and the device 10 shown in FIG. 1 are mainly as follows.
[0059] On the one hand, a light emitter 52 is used as the light source 12 instead of the superluminescent diode. The light emitter has an elongated light-emitting surface in the illustrated embodiment and is illuminated by a pump source 54, which may refer to a laser, for example. In the illustrated embodiment, the measurement light of multiple colors emitted from the light-emitting surface of the light emitter 52 is collimated and then input and coupled into a linear array at the end of the parallel optical fiber 56 by the cylindrical lens 55. A very high light intensity can be achieved by using the light emitter 52. In one technical variant, the light emitter 52 has a circular or rectangular light-emitting surface. In this case, the ends of the optical fiber 56 form a circular or rectangular array instead of a linear array, and in this technical variant, the cylindrical lens 55 is not required.
[0060] The measurement light ML introduced into the optical fiber 56 is emitted at the opposite ends of the optical fiber 56. These ends are arranged along a line extending perpendicular to the plane of the paper and simultaneously represent the optical pattern generation device 18. The imaging optical system 24 images the end of the optical fiber onto a spatial filter 26' whose end can be switched by a planar polarization mirror 58. The spatial filter is constructed as a one-dimensional digital micromirror device (DMD) in the illustrated embodiment. Here, the micromirror array extends perpendicular to the plane of the paper in FIG. 6.
[0061] In this embodiment, the static spatial filter 44 is similarly formed by a linear array of the ends of the optical fiber 60, where the line also extends perpendicular to the plane of the paper. The optical fiber 60 guides the measurement light to the spectrometer 46.
[0062] Optical fiber plugs 62, 62', 64, 64' may be integrated into the optical fibers 56, 60. Thereby, the portions outlined by the dashed lines of the device 10' can be attached to a separate housing, and these portions form the movable measurement head 66 and the fixed control device 68.
[0063] FIGS. 7a and 7b show two switching arrangements of the reflective switchable spatial filter 26' from the viewpoints of FIGS. 3a and 3b. Each pixel 28 is composed of a micromirror presenting two stable switching states. The pixels 28 with a gray background are in the second switching state and reflect the incident measurement light ML so as to hit the absorber. The pixels 28 with a white background reflect the incident measurement light ML so that it can pass through the cube beam splitter 33 and enter the objective lens 36.
[0064] FIG. 8 schematically shows an embodiment, in which the optical pattern generator 18 is formed by a linear array of microlenses 70. The light source includes a collimating lens 72 that collimates the measurement light and aligns it with the microlenses 70. These microlenses focus the measurement light ML onto corresponding pixels 28 of the transmissive MEMS spatial filter 26. Therefore, in this embodiment, an imaging optical system 24 is not required. Since the microlenses 70 are directly disposed in front of the transmissive MEMS spatial filter 26, the plane E1 and the plane E2 of the microlenses 70 overlap to some extent and correspond to optical conjugation. Here, the numerical aperture NA of the microlenses 70 coincides with the numerical aperture NA of the objective lens 36.
[0065] FIGS. 9a and 9b are schematic diagrams according to FIGS. 3a and 3b, showing other forms of possible switching arrangements. When the images of the point light source at the height of the static spatial filter 44 are very large, these images may extend not only above the adjacent openings 22', but also above two or even three adjacent openings 22'. In this case, in order to prevent optical crosstalk, the measurement should be divided not only into two, but into three or more individual measurements.
[0066] In FIGS. 9a and 9b, assume that there are a total of four individual measurements. Therefore, in each switching arrangement, among four adjacent pixels 28 in one direction, only one is always in the second switching state, and the remaining three are in the first switching state and block the incident measurement light. FIGS. 9a and 9b show two of the four switching states that need to be set sequentially.
[0067] FIG. 10 shows a part of another technical modification, and the part of the device 10 not shown in FIG. 10 corresponds to the part in FIG. 1.
[0068] In a modified example of this technology, in the optical path between the cube-shaped beam splitter 33 and the spectroscope 46, another transmissive MEMS spatial filter 74 is arranged in a fourth plane E4 optically conjugate to the first plane E1 and the second plane E2. Another imaging optical system 75 images the transmissive MEMS spatial filter 74 in the plane E4 onto the static spatial filter 44 in the plane E3. The pixels of the other transmissive MEMS spatial filter 74 also have the property of being switchable between a first switching state in which the pixels block the measurement light ML and a second switching state in which the pixels do not block the measurement light ML. In one technical modification example, the static spatial filter 44 is not required, and in this case, an input slit of the spectroscope 46 is provided in the plane E3.
[0069] Such another transmissive MEMS spatial filter 74 is advantageous when the input channels in the spectroscope cannot be individually deactivated and the image of the point light source still partially overlaps on the static spatial filter 44 even though the MEMS spatial filter 26 is arranged in front in the optical path behind the objective lens 34. The said another transmissive MEMS spatial filter 74 guarantees that the image of the point light source does not overlap on the static spatial filter 44 by "cleaning up" the light distribution. Here, the switching arrangement of the said another transmissive MEMS spatial filter 74 always coincides with the switching arrangement of the front transmissive MEMS spatial filter 26.
[0070] When the spectroscope has individually deactivatable input channels, the said another transmissive MEMS spatial filter 74 may not be provided.
[0071] FIG. 11 shows a second embodiment of a measuring device representing the whole at 10" from the perspective of FIG. 1. In the above embodiment, the spatially switchable filters 26, 26' that can be digitally switched for each pixel are an assembly independent of the light pattern generating device 18. Also, in the device 10", the spatially switchable filter 26" that can be digitally switched for each pixel forms the light pattern generating device 18. Thereby, since a separate light pattern generating device is not required, an imaging optical system for imaging the light pattern generating device onto the spatially switchable filter 26" that can be digitally switched for each pixel is not required.
[0072] In the illustrated embodiment, in the device 10", the measurement light ML generated by the light source 14 is first collimated by the focusing lens 16. Another focusing lens 16' focuses the measurement light ML so as to completely illuminate the spatially switchable filter 26" that can be digitally switched for each pixel. In FIG. 11, assume that the spatially switchable filter 26" that can be digitally switched for each pixel is rectangular and the measurement light ML illuminates a region surrounded by a circle. For a linearly spatially switchable filter that extends only along one direction and can be digitally switched for each pixel, the focusing lens 16' may be constructed as a cylindrical lens or other deformed optical element, and the element has different refractive powers in the orthogonal directions. Thereby, strip-shaped illumination of the linear spatial filter becomes possible, and light loss can be minimized. Alternatively, a light source having an elongated light emitting surface can be used, and the light source is imaged onto the linearly spatially switchable filter that can be digitally switched for each pixel and illuminates the spatial filter accordingly.
Claims
1. It is used to chromatically confocally measure the distance of incident measurement light (ML) to multiple points on the reflective surface (38) of an object (40), at least partially. a) A light source (12) arranged to generate multiple colored measurement light (ML), b) A light pattern generating device (18) arranged to generate a light pattern extending in one or two dimensions within a first plane (E1) from the measurement light, c) An objective lens (36) whose axial position is wavelength-dependent due to longitudinal chromatic aberration and which generates an image of the light pattern within an image plane (B1, B2, B3), and whose chromatic aberration is not corrected, d) A static spatial filter (44) disposed in a second plane (E3) optically conjugate to the first plane (E1) and having a filtering function corresponding to the light pattern, e) A cube-shaped beam splitter (33) is positioned in the optical path between the light pattern generating device (18) and the objective lens (36) and guides the measurement light (ML) that has been reflected by the surface (38) and passed through the objective lens (36) to the static spatial filter (44), f) A spectrometer (46) having a plurality of input channels, each of which is arranged to perform spectral analysis on reflected measurement light that has passed through a point of the static spatial filter (44) corresponding to each of the plurality of input channels, g) An analytical device (30) arranged to calculate the distance from a point on the surface (38) to the apparatus (10, 10') based on the wavelength measured by the spectrometer (46), h) A device comprising: a plurality of pixels (28) that form the light pattern generating device (18), or a third plane (E2) that is optically conjugate to the first plane (E1) and the second plane (E3), and a digitally switchable spatial filter (26, 26', 26") that is arranged in a third plane (E2) that is optically conjugate to the first plane (E1) and the second plane (E3), The apparatus is characterized in that each pixel (28) can be switched between a first switching state in which the pixel (28) blocks the measurement light (ML) and a second switching state in which the pixel (28) does not block the measurement light (ML).
2. The apparatus according to claim 1, characterized in that, during measurement, the digitally switchable spatial filters (26, 26', 26") for each pixel are switched between a first switching configuration and a second switching configuration, in which case, in the first switching configuration, two adjacent pixels (28) do not enter the same switching state, and the second switching configuration is complementary to the first switching configuration.
3. The apparatus according to claim 1 or claim 2, characterized in that the spatial filter (26") which can be digitally switched for each pixel forms the light pattern generating device (18), and the measurement light (ML) propagates as a free beam between the light source (14) and the spatial filter (26") which can be digitally switched for each pixel.
4. The apparatus according to claim 1 or claim 2, characterized in that the spatial filters (26, 26') that can be digitally switched for each pixel are arranged in the third plane (E2) independently of the light pattern generating apparatus (18).
5. The apparatus according to claim 4, characterized in that the digitally switchable spatial filters (26, 26') for each pixel are arranged in the optical path between the light pattern generating device (18) and the cube-shaped beam splitter (33).
6. The apparatus according to claim 4, characterized in that the apparatus (10, 10') has an imaging optical system (24) that images the first plane (E1) onto the third plane (E2).
7. The apparatus according to claim 4, characterized in that the light pattern includes a plurality of two-dimensionally distributed light points (22, 22"), or at least one continuous or light-point-based ray (20, 22').
8. The apparatus according to claim 4, wherein the light pattern generating apparatus (18) includes an arrangement of the ends of optical fibers (56).
9. The apparatus according to claim 4, wherein the light pattern generating apparatus (18) includes a light shielding plate (20, 20', 20") having at least one opening (22, 22', 22"), the apparatus according to claim 4.
10. The apparatus according to claim 4, wherein the light pattern generating apparatus (18) includes a planar arrangement of micro-focusing lenses (70).
11. The apparatus according to claim 1 or claim 2, characterized in that a collimator (32) for collimating the measurement light (ML) incident on the cube-shaped beam splitter (33) is arranged in the optical path between the light pattern generating device (18) and the cube-shaped beam splitter (33).
12. The apparatus according to claim 1 or claim 2, characterized in that the spatial filter (26') that can be digitally switched for each pixel is a micromirror array.
13. The apparatus according to claim 1 or claim 2, characterized in that the multiple-color light source (12) includes a light-emitting element (52).
14. The apparatus according to claim 1 or 2, characterized in that the spectrometer (46) is synchronized with a spatial filter (26, 26', 26") that can be digitally switched on a pixel-by-pixel basis, such that the input channel corresponding to the pixel (28) in the second switched state becomes inactive.
15. The digitally switchable spatial filters (26, 26', 26") for each pixel are arranged in the optical path between the light source (14) and the cube-shaped beam splitter (33). A digitally switchable spatial filter (74) for each individual pixel is located in a fourth plane (E4) in the optical path between the cube-shaped beam splitter (33) and the spectrometer (46), the fourth plane being optically conjugate to the first plane (E1) and the second plane (E2). The apparatus according to claim 1 or claim 2, characterized in that each pixel of the spatial filter (74), which is digitally switchable for each separate pixel, is switchable between a first switching state in which the pixel blocks the measurement light (ML) and a second switching state in which the pixel does not block the measurement light (ML).