Spectral confocal distance measuring device

Abstract

The invention relates to a device for the spectral confocal measurement of distances from a plurality of points of a reflective surface (38) of an object (40). The device has: a light source (12) which generates a multicolor measurement light (ML); and a light pattern generation means (18) that generates a light pattern from the measurement light. An unchromatic-aberration-corrected objective lens (36) generates an image of the light pattern in an image plane (B1, B2, B3), the axial position of which is wavelength-dependent on the basis of longitudinal chromatic aberration. The device also has a static space filter (44), a cubic beam splitter (33) and a spectrometer (46), which spectrally analyzes the measurement light reflected by the surface (38). According to the invention, the device further comprises a spatial filter (26; 26 '; 26 '') having a plurality of pixels (28) and either forming the light pattern generating means (18) or being arranged in a plane (E2) optically conjugated to the static spatial filter (44), each pixel (28) being convertible to a first switching state in which the pixel (28) blocks the measurement light (ML) and to a second switching state in which the pixel (28) does not block the measurement light (ML).

Description

Technical Field

[0001] The invention relates to a device for spectral confocal distance measurement at a plurality of points preferably arranged along a line on the surface of a workpiece or other object. Background Art

[0002] Spectral confocal distance measuring devices have been used in industrial metrology for many years whenever the distance to a workpiece or other object needs to be measured contactlessly with high precision. In transparent objects, such devices can also measure wall thickness or other thicknesses, since a distance can usually be determined for each optical interface and the thickness is derived from the difference in the measured distances.

[0003] A conventional spectral confocal distance measuring device comprises a light source which generates polychromatic measuring light and is directed to an aperture plate with a very small aperture. The aperture is imaged onto the surface to be measured by an imaging optical system. At least a part of the imaging optical system has significant longitudinal chromatic aberration. Therefore, the aperture images of different colors are arranged in sequence on the optical axis of the imaging optical system. Only the spectral component of the measuring light whose aperture image is just on the surface to be measured is reflected back by this surface, so that this component can enter the same aperture or an aperture optically conjugate therewith. The wavelength of this spectral component is detected by means of a spectrometer. Each wavelength corresponds to a certain distance from the imaging optical system.

[0004] Although other spectral components are also partially reflected by the object surface, they cannot be focused by the imaging optical system into the same plate opening or an optically conjugate plate opening, and thus have no significant impact on the portion of the measurement light that is spectrally analyzed by the spectrometer.

[0005] US 2018 / 0038680 A1 discloses a spectral confocal measuring device with which distances or thicknesses can be measured simultaneously at multiple points. In addition, the conventional aperture plate is replaced here by a linear or planar arrangement of the ends of the optical fibers arranged linearly or planarly. If the distance or thickness is measured simultaneously at multiple locations, the measuring time is significantly shortened. In this case, even for larger surfaces, a complete surface profile can be created in a short time.

[0006] The lateral resolution of such multi-point measuring devices, i.e. the density of the measuring points on the object surface, is limited by the fact that the measuring light reflected from the object and incident on the end of one optically conjugated fiber must not simultaneously incident on an adjacent fiber. If this optical crosstalk occurs, the individual measuring points can no longer be assigned a single distance value. The main cause of the optical crosstalk is that even with optimally corrected imaging optics, for physical reasons the image of the fiber end is not completely sharp, but, due to the diffraction phenomenon, has the shape of a planar extended diffraction disk with several clearly identifiable secondary maxima.

[0007] Therefore, in the known spectral confocal distance measuring device, the distance between the ends of the optical fibers is relatively large, so that a high density of measuring points cannot be achieved. Summary of the invention

[0008] The object of the present invention is to provide a device for spectral confocal measurement of the distance to a plurality of points on the surface of an object, said device having a high lateral resolution.

[0009] The solution of the present invention to achieve the above-mentioned purpose is a device for spectral confocal measurement of the distance to a plurality of points on the surface of an object, the device having a light source, the light source being configured to generate polychromatic measurement light. The light pattern generating device is configured to generate a light pattern from the measurement light, the light pattern extending in one dimension or in two dimensions in a first plane. The objective lens, which has not been chromatically corrected, is configured to generate images of the light pattern in an image plane, the axial positions of these image planes being related to the wavelength based on the longitudinal chromatic aberration. The static spatial filter is arranged in a second plane and has a filtering function corresponding to the light pattern (but not necessarily the same), wherein the second plane is optically conjugate to the first plane. Preferably, a non-polarizing cubic beam splitter is arranged in the optical path between the light pattern generating device and the objective lens, and guides the measurement light reflected by the surface and passing through the objective lens to the spatial filter. The spectrometer has a plurality of input channels, which are configured to perform spectral analysis on the reflected measurement light corresponding to the points of the corresponding input channels passing through the static spatial filter. The analysis device is configured to calculate the distance from the point on the surface to the measurement device from the wavelength measured by the spectrometer. According to the present invention, the device also has a spatial filter that can be switched pixel by pixel, the spatial filter has multiple pixels, and either forms a light type generating device or is arranged in a third plane optically conjugate with the first plane and the second plane, wherein each pixel can be converted into a first switching state in which the pixel blocks the measuring light, and can be converted into a second switching state in which the pixel does not block the measuring light.

[0010] The spatial filter, which can be switched pixel by pixel, can at one point in time during the measurement block or deflect the part of the measurement light that causes optical crosstalk so that it does not reach the spectrometer. At another point in time, another part of the measurement light is suppressed. This makes it possible to achieve very high lateral resolutions by combining several consecutive measurements.

[0011] In the simplest case, the digitally switchable spatial filter pixel by pixel is controlled in such a way that it switches during measurement between a first switching configuration, in which two adjacent pixels are not in the same switching state, and a second switching configuration, in which the second switching configuration is complementary to the first switching configuration. As a result, only two individual measurements are required.

[0012] To achieve higher lateral resolution, a larger distance between active pixels may be required, so that in each switching configuration, at least n=2, 3, ... pixels between two active pixels are in an inactive switching position. In this case, there must be n+1 different switching configurations in sequence until all pixels are in an active switching position.

[0013] The control of the different switching configurations depends not only on the required lateral resolution, but also on the characteristics of the surface of the object to be measured. In surfaces with a good signal-to-noise ratio, more crosstalk can be tolerated as appropriate, so that at a certain point in time, half or even all of the pixels of the spatial filter can be in the active second switching state. The more disturbing the crosstalk is, the greater the distance between the pixels that are in the active second switching state at a given point in time should be.

[0014] The optical conjugation between the third plane where the spatial filter that can be digitally switched pixel by pixel is located and the first plane where the light type generating unit is located ensures that the pixels of the spatial filter that can be digitally switched pixel by pixel can correspond to each measurement point in a single manner. Planes that can be converted to each other by optical imaging are called optical conjugates. Therefore, an objective lens having one or more lenses or mirrors is usually provided between two optically conjugated planes, and the objective lens realizes optical imaging. However, as an alternative to the objective lens, optical conjugation can also be realized by other optical systems in special cases. An example is the opposite ends of an optical fiber, which can be regarded as optically conjugated because the point-shaped light distribution at the two ends is the same. Therefore, optical images can also be generated using an optical fiber bundle, such as a known endoscope. Two planes that are adjacent to each other can also be regarded as optically conjugated in a broad sense.

[0015] If the spatial filter that can be digitally switched pixel by pixel is independent of the light pattern generating device and arranged in the third plane, then the spatial filter can be in the optical path between the light pattern generating device and the cubic beam splitter. The advantage of this arrangement is that the image of the light pattern is clearer than after re-imaging through the objective lens.

[0016] In this case, the device preferably has an imaging optical system that images the first plane onto a third plane. The advantage of such an imaging optical system lies primarily in that the light pattern generating device comprises a layout of an optical fiber end, or comprises a light shield having at least one opening. The measuring light is usually emitted from the optical fiber or the opening in a strongly divergent manner. If a spatial filter that can be digitally switched pixel by pixel is arranged directly in front of the optical fiber end or the light shield opening, an optical conjugation in a broad sense will occur. However, many particularly suitable spatial filters that can be digitally switched pixel by pixel (such as micromirror arrays) cannot be arranged close to the light pattern generating device to a degree that can still be called optical conjugated. The imaging optical system allows the use of large numerical apertures on the one hand, and on the other hand allows the use of micromirror arrays and other switchable spatial filters, which can only be arranged at a distance from the light pattern generating device due to beam folding or the required installation space.

[0017] The light pattern may include a plurality of two-dimensionally distributed light spots, or at least one continuous light beam or a light beam composed of light spots. The continuous light beam is divided into individual measurement points by pixels of a switchable spatial filter.

[0018] In one embodiment, the light pattern generating device comprises a planar arrangement of micro-converging lenses. The converging lenses focus the measuring light onto corresponding pixels of the switchable spatial filter and thereby form an optical conjugate in a broad sense.

[0019] In another embodiment, a spatial filter that can be digitally switched pixel by pixel forms the light pattern generating means. This structure is particularly simple and allows the use of a spatial filter in the form of a micromirror array without the need for an additional imaging optical system.

[0020] In this case, the spatial filter should be illuminated with light whose angular distribution matches the numerical aperture of the uncorrected objective. This is particularly effective if the measurement light propagates as a free beam between the light source and the spatial filter, which can be digitally switched pixel by pixel.

[0021] In order to avoid light loss, the spatial filter used as the light pattern generating device should be illuminated by the light source in such a way that as much light as possible enters the spatial filter. Depending on the specific type of light source, a simple light collecting system is sufficient to collect the light emitted from the light exit surface of the light source so that it enters the spatial filter in a low-loss manner. If the light pattern generated by the spatial filter includes light rays composed of a plurality of light points, the light collecting system can be constructed as a cylindrical lens or as an anamorphic lens in other ways.

[0022] In one embodiment, a collimator is arranged in the optical path between the light pattern generating device and the cubic beam splitter, which collimates the measurement light entering the cubic beam splitter. In this case, based on confocal imaging, the measurement light reflected from the object also passes through the cubic beam splitter in a collimated manner. The advantage of collimated passage is that, as a result, the cubic beam splitter does not generate spherical aberration.

[0023] The spatial filter that can be digitally switched pixel by pixel is preferably a micromirror array. Alternatively, it can also refer to a transmissive MEMS component as described in US 8,054,527 B2. It is also possible to consider using an LCD panel as a spatial filter that can be digitally switched pixel by pixel, but it has disadvantages due to the polarization properties.

[0024] For the same reasons, the cubic beam splitter is advantageously non-polarizing. In this case, the graduation rate of the cubic beam splitter is independent of the polarization state and thus also independent of the properties of the object surface.

[0025] In one embodiment, the multicolor light source comprises a light emitter as known from EP 3 764 056 A1 (corresponding to US 10,731,965 B1). Such a light source preferably has a long strip-shaped light exit surface. If optical fibers are used to guide light, their ends can form a rectangular or circular layout and receive light emitted from adjacent square or circular light exit surfaces of the light emitter.

[0026] In luminophore-based light sources, a luminescent substance, called a luminophore, is excited by means of a pump source (usually a laser or LED), which emits light by a physical process (especially phosphorescence, fluorescence or scintillation). The advantage of this type of light source is that it can illuminate the entire confocal aperture and has high efficiency and high light output.

[0027] To reduce optical crosstalk caused by scattered light, etc., other spatial filters may be arranged at positions optically conjugated to the first, second and third planes.

[0028] The spectrometer can be synchronized with a spatial filter that can be digitally switched pixel by pixel, so that the input channel corresponding to the pixel in the second switching state is logically or physically deactivated. This prevents measurement light entering adjacent input channels due to crosstalk from being taken into account in the analysis. In the simplest case, the deactivation of the relevant input channel is implemented in such a way that the intensities measured there are not read out.

[0029] If a spatial filter that can be digitally switched pixel by pixel is arranged in the optical path between the light source and the cubic beam splitter, another spatial filter that can be digitally switched pixel by pixel can be arranged in a fourth plane in the optical path between the cubic beam splitter and the spectrometer, the fourth plane being optically conjugate to the first plane and the second plane. Each pixel of the other spatial filter that can be digitally switched pixel by pixel can be switched to a first switching state in which the pixel blocks the measurement light, and can be switched to a second switching state in which the pixel does not block the measurement light.

[0030] The background to this measure is that the image of the light pattern loses sharpness with each optical imaging. For example, if two adjacent diffraction disks overlap only to a negligible extent on the object surface, this overlap may already be noticeable after re-imaging through the objective at the height of the spectrometer. The further spatial filter, which can be digitally switched pixel by pixel, can provide a remedy here by cutting off the relevant light beams again so that no crosstalk occurs at the spectrometer even after re-imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The embodiments of the present invention are described in detail below with reference to the drawings.

[0032] Figure 1 is a schematic longitudinal cross section of a distance measuring device according to a first embodiment of the present invention;

[0033] Figure 2 For Figure 1 A top view of an aperture plate used as a light pattern generating device in the device shown;

[0034] Figure 3a and Figure 3b for Figure 1 Enlarged schematic cross-sections of different switching configurations of a transmissive MEMS spatial filter included in the illustrated device;

[0035] Figure 4 To be available in Figure 1 A top view of another embodiment of an aperture plate used as a light pattern generating device in the device shown;

[0036] Figure 5 To be available in Figure 1 A top view of another embodiment of an aperture plate used as a light pattern generating device in the device shown;

[0037] Figure 6 is a schematic longitudinal cross section of a distance measuring device according to a second embodiment of the present invention;

[0038] Figure 7a and Figure 7b for Figure 6Enlarged schematic cross-sections of different switching configurations of the reflective MEMS spatial filter included in the illustrated device;

[0039] Figure 8 A schematic diagram of an embodiment in which the light pattern generating device is formed by linearly arranged micro-lenses;

[0040] Figure 9a and Figure 9b Basis for other options for possible switching configurations Figure 3a and Figure 3b Schematic diagram of

[0041] Fig.10 A part of another technical variant having two transmissive MEMS spatial filters; and

[0042] Fig.11 is a schematic longitudinal section of a distance measuring device according to a third embodiment of the present invention, in which a spatial filter which can be digitally switched pixel by pixel forms the light pattern generating means. DETAILED DESCRIPTION

[0043] 1. Structure of the measuring device

[0044] Figure 1 A schematic meridional section through a distance measuring device according to the invention, designated as a whole by 10, is shown according to a first embodiment.

[0045] The device 10 has a light source 12, which generates polychromatic measurement light ML. The measurement light ML preferably has a continuous spectrum. However, in principle, it is also possible to use a comb spectrum or other discrete spectrum as long as the wavelength peaks are close enough. In the embodiment shown, the light source 12 includes a superluminescent diode 14 and a converging lens 16 arranged behind it in the light propagation direction.

[0046] The measurement light ML generated by the light source 12 is incident on the light pattern generating device 18, and the light pattern generating device generates a light pattern from the incident measurement light ML. In the illustrated embodiment, the light pattern generating device 18 includes an aperture plate 20, Figure 2 The orifice plate 20 has a plurality of plate openings 22 arranged along a line. When irradiated with the measurement light ML, the plate openings 22 are point light sources, and the measurement light ML radiates from these point light sources.

[0047] The aperture plate 22 is arranged in a first plane E1, which coincides with the object plane of the imaging optical system 24. In the embodiment shown, the imaging optical system 24 is constructed as a 4f optical system. The characteristic of this 4f optical system is that the two objectives or lenses L1 and L2 are arranged so that the rear focal plane of lens L1 coincides with the front focal plane of lens L2. This leads to the formation of a telecentric optical path on both sides, as a result of which the angular distribution at the plate opening 22 is transmitted to the image plane E2 of the imaging optical system 24 without tilting. If, as in the embodiment shown, the focal lengths of lenses L1 and L2 are equal, the imaging ratio β=-1.

[0048] A transmissive MEMS spatial filter 26 is arranged in the image plane E2 of the imaging optical system 24, wherein MEMS is the abbreviation for micro-electromechanical system. Such a filter 26 comprises a large number of regularly arranged elements or pixels 28, which can be individually mechanically moved to selectively open or block the optical path. Suitable examples of such MEMS filters are known and are described, for example, in US 2006 / 0012781 A1. As an alternative, LCD panels can also be used, but they have a polarizing effect, which can be disadvantageous for some measurement tasks.

[0049] Figure 3a and Figure 3b An enlarged schematic cross section of the transmissive MEMS spatial filter 26 is shown. In the illustrated embodiment, the pixels 28 of the transmissive MEMS spatial filter 26 are arranged along a line so that each pixel 28 corresponds to exactly one plate opening 22 of the light pattern generating device 18. This correspondence is caused by the imaging of the plate opening 22 on the pixel 28 caused by the imaging optical system 24.

[0050] The independent switchability of each pixel 28 is Figure 3a Pixels 28 with a dark background are in a first switching state, in which the pixels 28 block the measuring light ML. Pixels 28 with a light background are in a second switching state, in which the pixels 28 are transparent to the measuring light ML. The switching states of the pixels 28 are preset by the control and analysis device 30. Figure 3a and Figure 3b A comparison of the EM images clearly shows that the transitions between the different switching states are usually carried out within a few microseconds.

[0051] against Figure 3a The pixel 28 in the second switching state shown on the far left shows with other beams 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 only filters in the location space, not in the angle space. Therefore, the measurement light ML is emitted at the output end of the pixel 28 with the numerical aperture NA of the imaging system 24.

[0052] Therefore, the pixels 28 of the transmissive MEMS spatial filter 26 are also point light sources, but unlike the plate openings 22 of the light pattern generating device 18, these point light sources can be turned on and off individually.

[0053] Figure 3a and Figure 3b Two different switching configurations are shown, between which switching configurations can be switched in this embodiment. Figure 3a In the first switching configuration shown, no two adjacent pixels 28 are in the same switching state. The switching state thus alternates between the pixels. Figure 3b The second switching configuration shown is Figure 3a The first switching configuration of is complementary. Therefore, the two adjacent pixels 28 here are also not in the same switching state, and the switching state is also alternated between pixels. However, the switching pattern is staggered by one pixel, so that Figure 3a and Figure 3b The two switching configurations are switched between by switching each pixel 28 to the other switching state. Advantages associated with the transmissive MEMS spatial filter 26 and the switching configuration switching are described in Section 2 below.

[0054] A collimator lens 32 is arranged in the optical path behind the transmissive MEMS spatial filter 26 , and the front focal plane of the collimator lens coincides with the plane E2 . Therefore, the ray beam emitted from the pixel 28 is collimated after passing through the collimator lens 32 .

[0055] The collimated beam of rays is incident on a non-polarizing cubic beam splitter 33, which has a beam splitter surface 34 arranged at an angle of 45° relative to the optical axis. A preset component of the emitted light, for example 50%, is reflected at the beam splitter surface and lost in the measurement. The remaining measurement light ML passes through the cubic beam splitter without deflection based on the collimated light path and is incident on an unchromatically aberration-uncorrected objective lens 36, which has an object plane at infinity. The objective lens 36, together with the imaging optical system 24 and the collimating lens 32, images the plate port 22 arranged in the plane E1 in image planes B1 to B3 based on their longitudinal chromatic aberration, and the axial positions of these image planes are related to the wavelength. This is Figure 2 In the figure, each wavelength corresponds to exactly one image plane. If (as in the present embodiment) the spectrum generated by the light source 12 is continuous, a series of continuous image planes will be generated.

[0056] If the image of the plate opening 22 is in an image plane, at the height of which the at least partially reflecting surface 38 of the object 40 is located, the outgoing beam is reflected back on itself there and returns to the splitting surface 34 of the cubic beam splitter 33 via the objective lens 36 along the same path. For the case shown here, for example, the image at the plate opening 22 is in the wavelength of the image plane B2, and the plate opening 22 located on the optical axis OA of the device 10 satisfies the above prerequisite. For the beam 43 passing through the other plate opening 22, the image at the relevant plate opening 22 is in another wavelength in the image plane B1, and here the object 40 at the bottom satisfies the above prerequisite. Of course, not only light of a single wavelength is reflected on the surface 38. But only a measuring beam of one wavelength is reflected by itself, because only the focus of this wavelength is exactly on the surface 38.

[0057] A predetermined component of the reflected measurement light ML is reflected 90° at the beam splitter 34 and is focused by the converging lens 42 onto a static spatial filter 44, which is arranged in the third plane E3 and has a filtering function corresponding to the light type. The static spatial filter 44 allows the measurement light ML to pass through (or allows reflection in the case of a reflective spatial filter) at some positions, and blocks the measurement light ML at other positions. In the simplest case, the static spatial filter 44 refers to the same aperture plate used for the plate opening of the light type generating device 18, which is reduced or enlarged according to the image ratio of the optical system in between. That is, the entire optical system in the optical path between the light type generating device 18 and the static spatial filter 44, that is, the imaging optical system 24, the collimating lens 32, the objective lens 36 and the focusing lens 42, enables the light type generating device 18 to be imaged on the static spatial filter 44. Therefore, the planes E1, E2 and E3 are optically conjugated. An intermediate image is generated in the image planes B1 to B3 at the height of the transmission MEMS spatial filter 26 and on the surface 38 of the object 40.

[0058] The static spatial filter 44 ensures that only the measuring light beam which is reflected by itself at a specific wavelength at the surface 38 can be further analyzed. The measuring light ML which does not meet this condition is blocked by the static spatial filter 44 according to the spectral confocal measurement principle.

[0059] A spectrometer 46 having a plurality of input channels is arranged in the optical path after the static spatial filter 44, and performs spectral analysis on the reflected measurement light ML corresponding to the points of the respective input channels that have passed through the static spatial filter 44. The spectrometer 46 generally includes a dispersive optical element, such as a grating or a prism 47, and a photosensitive chamber in a row arrangement 48 for each input channel. Figure 1 Since such a spectrometer 46 is known, no further description is required.

[0060] 2. Function

[0061] As is known for spectral confocal measuring devices, during the measurement, the control and analysis device 30 calculates the distance from points on the surface 38 to the measuring device 10 from the wavelength measured by the spectrometer 46. These points are images of point light sources, i.e., plate openings 22. Each point light source is assigned a separate input channel, so that the distance measurement can be carried out for all point light sources simultaneously in principle.

[0062] However, when all point light sources are measured at the same time, optical crosstalk may occur if the point light sources are very close to each other. The reason is that even in the case of optimal optical imaging, the images of the point light sources will still be blurred by diffraction and may overlap. This is schematically shown in the enlarged section C of the static spatial filter 44. It can be seen in section C that the gray background light beam LB in plane E3 is not focused on a single plate opening 22', but partially spans two adjacent plate openings 22", 22"'. The measurement light ML entering the wrong plate opening 22", 22"' will be detected by the corresponding input channel of the spectrometer 46 and distort the distance measurement. For example, not only does the light beam LB' represented by the dotted line fall into the plate opening 22"', but also part of the light beam LB will fall into the plate opening.

[0063] Optical crosstalk can be prevented by increasing the distance between the point light sources (here, the plate openings 22 ), but this measure is at the expense of the lateral resolution of the device 10 .

[0064] Therefore, according to the invention, the control and analysis device 30 controls the transmissive MEMS spatial filter 26 in such a way that the measurement is divided into two partial measurements. In the first partial measurement, the pixels 28 of the transmissive MEMS spatial filter 26 are in Figure 3a and Figure 3b In the second part of the measurement, the pixel 28 is in another switching configuration. Figure 1 For the adjacent light beam LB' represented by a dotted line in local C in the figure, this means that the propagation of this light beam is blocked by the transmissive MEMS spatial filter 26 and cannot enter the input channel of the spectrometer 46 that does not correspond to this light beam LB'; this also applies accordingly to other light beams adjacent to the light beam LB on the other side that are not shown in local C.

[0065] At the same time, the spectrometer 46 is synchronized with the spatial filter 26 which can be digitally switched pixel by pixel, so that two input channels corresponding to adjacent plate ports 22" are deactivated. Therefore, the components of the light beam LB falling on the photosensitive chambers of these two input channels are not analyzed.

[0066] Therefore, by dividing the measurement into two individual measurements, between which Figure 3a and Figure 3bThe optical crosstalk can be most effectively prevented by switching between the switching configurations shown. In this way, a high lateral resolution can be achieved while the measuring time is substantially doubled. The control and analysis device 30 can be programmed in such a way that this mode is only used for measurements in the following cases: a high lateral resolution is required and the object has a surface that is particularly susceptible to optical crosstalk. If the requirements for the lateral resolution are lower, Figure 3a and Figure 3b A measurement is performed in one of the switching configurations shown.

[0067] 3. Other embodiments

[0068] Figure 4 Show according to Figure 2 The slit plate 20' has a slit-shaped plate opening 22', which can be used as Figure 2 The illustrated alternative to the aperture plate 20 is used as the light pattern generating device 18 . The propagation of the measuring light ML which could lead to optical crosstalk is likewise blocked here by the transmissive MEMS spatial filter 26 .

[0069] Figure 5 Show according to Figure 2 3 , which can also be used as a 2D well plate 20 ″ Figure 2 An alternative to the aperture plate 20 is shown for use as the light pattern generating means 18. In a 2D aperture plate 20", the plate openings 22" are divided into a regular two-dimensional grid.

[0070] In this case, the transmissive MEMS spatial filter 26 must have a corresponding two-dimensional layout of pixels 28, so that each plate opening 22" corresponds to a switchable pixel. The static spatial filter 44 and the spectrometer 46 are also correspondingly expanded to two dimensions, which is known in the prior art.

[0071] Figure 6 A second embodiment of the measuring device is shown, which is indicated as a whole by 10 ′. Figure 1 The device 10 shown differs mainly in the following aspects:

[0072] On the one hand, instead of a superluminescent diode, a light emitter 52 is used as the light source 12, which in the illustrated embodiment has an elongated light exit surface and is illuminated by a pump source 54, which can be, for example, a laser. In the illustrated embodiment, the polychromatic measurement light emitted by the light exit surface of the light emitter 52 is first collimated and then coupled into the ends of the parallel optical fibers 56 arranged in a linear manner by means of a cylindrical lens 55. A particularly high light intensity can be achieved with the light emitter 52. In a technical variant, the light emitter 52 has a circular or square light exit surface. In this case, the ends of the optical fibers 56 do not form a linear arrangement, but a circular or square arrangement; in this technical variant, a cylindrical lens 55 is not required.

[0073] 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 paper surface and represent the light pattern generating device 18 at the same time. The imaging optical system 24 images the optical fiber ends onto the switchable spatial filter 26' through the plane polarizer 58, which is constructed as a one-dimensional digital micromirror array (DMD, digital micromirror device) in the embodiment shown. The micromirror array is perpendicular to the paper surface. Figure 6 Extension of paper.

[0074] In this embodiment, the static spatial filter 44 is likewise formed by the ends of a linearly arranged optical fiber 60 , wherein the line here likewise runs perpendicular to the paper plane. The optical fiber 60 guides the measuring light to the spectrometer 46 .

[0075] Fiber optic connectors 62, 62', 64, 64' can be integrated into the optical fibers 56, 60. In this way, the parts of the device 10' outlined with a dashed line, which form the mobile measuring head 66 and the stationary control device 68, can be installed in separate housings.

[0076] Figure 7a and Figure 7b Based on Figure 3a and Figure 3b The view of 2 shows two switching configurations of the reflective switchable spatial filter 26 '. Each pixel 28 is composed of a micromirror that exhibits two stable switching states. The gray background pixel 28 is in the second switching state and reflects the incident measurement light ML in such a way that it falls on the absorber. The white background pixel 28 reflects the incident measurement light ML in such a way that it can enter the objective lens 36 through the cubic beam splitter 33.

[0077] Figure 8 An embodiment is shown in a schematic diagram, in which the light pattern generating device 18 is formed by a linearly arranged microlens 70. The light source includes a collimating lens 72, which collimates the measurement light to the microlens 70. These microlenses focus the measurement light ML onto the corresponding pixels 28 of the transmissive MEMS spatial filter 26. Therefore, in this embodiment, the imaging optical system 24 is not required. Since the microlens 70 is arranged directly in front of the transmissive MEMS spatial filter 26, the plane E1 of the microlens 70 coincides with the plane E2 to a certain extent, which is equivalent to optical conjugation. Among them, the numerical aperture NA of the microlens 70 matches the numerical aperture NA of the objective lens 36.

[0078] Figure 9a and Figure 9b Based on Figure 3a and Figure 3bThe schematic diagram of FIG. 4 shows other possible switching configurations. If the images of the point light sources at the height of the static spatial filter 44 are particularly large, it may be the case that these images extend not only over the immediately adjacent aperture 22', but also over two or even three adjacent apertures 22'. In this case, the measurement should be divided into not only two, but three or more individual measurements in order to prevent optical crosstalk.

[0079] exist Figure 9a and 9b In FIG. 1 , it is assumed that there are four individual measurements in total. Therefore, in each switching configuration, of four adjacent pixels 28 in one direction, only one is always in the second switching state, while the other three are in the first switching state and block the incident measurement light. Figure 9a and Figure 9b Two of the four switching states that need to be set in sequence are shown.

[0080] Fig.10 A part of another technical variant; the device 10 is not in Fig.10 The portion shown corresponds to Figure 1 part of .

[0081] In this technical variant, in the optical path between the cubic beam splitter 33 and the spectrograph 46, another transmissive MEMS spatial filter 74 is arranged in a fourth plane E4, which is optically conjugate with the first plane E1 and the second plane E2. Another imaging optical system 75 images the transmissive MEMS spatial filter 74 in plane E4 onto the static spatial filter 44 in plane E3. The pixels of the other transmissive MEMS spatial filter 74 also have the following characteristics: a first switching state that can be converted into a pixel blocking the measurement light ML, and a second switching state that can be converted into a pixel not blocking the measurement light ML. In a technical variant, the static spatial filter 44 is not required; in this case, an input slit of the spectrograph 46 is provided in plane E3.

[0082] This further transmissive MEMS spatial filter 74 is advantageous in the following cases: the input channels in the spectrograph cannot be deactivated individually, and the images of the point light sources partially overlap on the static spatial filter 44 despite the MEMS spatial filter 26 being arranged in front in the optical path behind the objective lens 34. The further transmissive MEMS spatial filter 74 “cleans up” the light distribution and thereby ensures that the images of the point light sources do not overlap on the static spatial filter 44. The switching configuration of the further transmissive MEMS spatial filter 74 always matches the switching configuration of the transmissive MEMS spatial filter 26 in front.

[0083] If, however, the spectrometer has input channels that can be individually deactivated, the further transmissive MEMS spatial filter 74 may not be provided.

[0084] Fig.11 Show according to Figure 1 A second embodiment of a measuring device for a view of a light pattern is shown in FIG. 1 , which is denoted as a whole by 10”. In the aforementioned embodiment, the spatial filters 26, 26' that can be digitally switched pixel by pixel are components independent of the light pattern generating device 18, while in the device 10", the spatial filter 26" that can be digitally switched pixel by pixel forms the light pattern generating device 18. In this way, there is no need for a separate light pattern generating device, and thus there is no need for an imaging optical system that images the light pattern generating device onto the spatial filter 26" that can be digitally switched pixel by pixel.

[0085] In the illustrated embodiment, in the device 10 ″, the measurement light ML generated by the light source 14 is first collimated by a focusing lens 16. Another focusing lens 16 ′ focuses the measurement light ML so that it just completely illuminates the spatial filter 26 ″ which can be digitally switched pixel by pixel. Fig.11 In the figure, it is assumed that the spatial filter 26" which can be digitally switched pixel by pixel is square and the measuring light ML illuminates a circular area. In a linear spatial filter which can be digitally switched pixel by pixel, that is, which extends only in one direction, the converging lens 16' can be constructed as a cylindrical lens or another deformable optical element which has different refractive powers in orthogonal directions. In this way, the linear spatial filter can be illuminated in a strip shape to minimize light losses. Alternatively, a light source with an elongated light exit surface can be used, which is imaged onto the linear spatial filter which can be digitally switched pixel by pixel and illuminates this spatial filter accordingly.

Claims

1. A device for spectral confocal measurement of distances to a plurality of points on a surface (38) of an object (40) at least partially reflecting incident measurement light (ML), the device comprising: a) a light source (12) configured to generate polychromatic measuring light (ML), b) a light pattern generating device (18) configured to generate a light pattern from the measuring light, the light pattern extending in one dimension or in two dimensions in a first plane (E1), c) an objective lens (36) not corrected for chromatic aberration, which is configured to generate an image of the light pattern in an image plane (B1, B2, B3), the axial position of the image plane being wavelength-dependent based on longitudinal chromatic aberration, d) a static spatial filter (44) arranged in the second plane (E3) and having a filtering function corresponding to the light pattern, wherein: The second plane (E2) is optically conjugate with the first plane (E1), e) a cubic beam splitter (33) arranged in the optical path between the light pattern generating device (18) and the objective lens (36) and guiding the measurement light (ML) reflected by the surface (38) and passing 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 configured to perform a spectral analysis on the reflected measurement light corresponding to a point of the corresponding input channel that has passed through the static spatial filter (44), and g) an analysis device (30) configured to calculate the distance from a point on the surface (38) to the device (10; 10') from the wavelength measured by the spectrometer (46), Features A spatial filter (26; 26'; 26") capable of digitally switching pixel by pixel, the spatial filter having a plurality of pixels (28), and the spatial filter either forming the light pattern generating device (18) or being arranged in a third plane (E2) optically conjugated to the first plane (E1) and the second plane (E3), wherein each pixel (28) can be switched to a first switching state in which the pixel (28) blocks the measuring light (ML), and can be switched to a second switching state in which the pixel (28) does not block the measuring light (ML).

2. The device according to claim 1, characterized in that In the case of a measurement, the spatial filter (26; 26'; 26") which can be digitally switched pixel by pixel is switched between a first switching configuration and a second switching configuration, wherein in the first switching configuration two adjacent pixels (28) are not in the same switching state, and wherein the second switching configuration is complementary to the first switching configuration.

3. The device according to any one of claims 1 or 2, characterized in that The spatial filter (26") which can be digitally switched pixel by pixel forms the light pattern generating device (18), and the measuring light (ML) propagates as a free beam between the light source (14) and the spatial filter (26") which can be digitally switched pixel by pixel.

4. The device according to claim 1 or 2, characterized in that: The spatial filter (26; 26') which can be digitally switched pixel by pixel is independent of the light pattern generating device (18) and is arranged in the third plane (E2).

5. The device according to claim 4, characterized in that The spatial filter (26; 26') which can be digitally switched pixel by pixel is arranged in the optical path between the light pattern generating device (18) and the cubic beam splitter (33).

6. The device according to any one of claims 4 or 5, characterized in that The device (10; 10') has an imaging optical system (24) for imaging the first plane (E1) onto the third plane (E2).

7. The device according to any one of claims 4 to 6, characterized in that The light pattern comprises a plurality of two-dimensionally distributed light spots (22; 22"), or at least one continuous light beam (20; 22') or a light beam composed of light spots.

8. The device according to any one of claims 4 to 7, characterized in that The light pattern generating device (18) comprises an arrangement of ends of optical fibers (56).

9. The device according to any one of claims 4 to 7, characterized in that The light pattern generating device (18) comprises a light shielding plate (20; 20'; 20") having at least one opening (22; 22', 22").

10. The device according to any one of claims 4 to 7, characterized in that The light pattern generating device (18) comprises a planar arrangement of micro-converging lenses (70).

11. The device according to any one of the preceding claims, characterized in that A collimator (32) is arranged in the optical path between the light pattern generating device (18) and the cubic beam splitter (33), and the collimator collimates the measurement light (ML) entering the cubic beam splitter (33).

12. The device according to any one of the preceding claims, characterized in that The spatial filter (26') capable of digital switching pixel by pixel is a micromirror array.

13. The device according to any one of the preceding claims, characterized in that The polychromatic light source (12) comprises a luminescent body (52).

14. The device according to any one of the preceding claims, characterized in that The spectrometer (46) is connected to a spatial filter (26; 26'; 26″) so that the input channel of the pixel (28) corresponding to the second switching state is deactivated.

15. The device according to any one of the preceding claims, characterized in that The spatial filter (26; 26'; 26") which can be digitally switched pixel by pixel is arranged in the optical path between the light source (14) and the cubic beam splitter (33), Another spatial filter (74) that can be digitally switched pixel by pixel is arranged in a fourth plane (E4) in the optical path between the cubic beam splitter (33) and the spectrometer (46), the fourth plane being optically conjugate to the first plane (E1) and the second plane (E2), and Each pixel of the further spatial filter (74) which can be digitally switched pixel by pixel can be switched into a first switching state in which the pixel blocks the measuring light (ML) and into a second switching state in which the pixel does not block the measuring light (ML).

Images