JP7410853B2 - Method and device for non-contact measurement of distance to a surface or distance between two surfaces - Google Patents

Description

The present invention relates to a measuring device and method for non-contact measurement of the distance to a surface or the distance between two surfaces, in which case polychromatic light is directed towards the object to be measured and is reflected from the object. The measurement light is spectrally analyzed. The invention relates in particular to the problem of reducing the loss of measurement accuracy due to thermal effects.

A problem that often arises in measurement technology is determining the distance between a reference point and the surface of a solid or liquid object to be measured. Depending on the measurement task, only one or a few points on the surface or a large number of closely spaced points are measured. In the latter case, a typological one-dimensional or two-dimensional height profile of the surface to be measured is derived from the distance measurements. In this way, it is possible, for example, to demonstrate the roughness of a precisely machined surface or to determine a roughness index. In these measurements, it is usually not important to measure the spacing absolutely; only relative spacing changes are detected with high accuracy.

The same is true when trying to measure the spacing between surfaces and especially the thickness of optically transparent layers. Even in this case, absolute spacing for the reference points is not required. This is because the thickness of a layer results from the difference in spacing values for the surfaces that define the layer.

In this context, not only layers of material that are supported by or fixed to a solid body are referred to as layers, but also thin solid structures that do not require support. Examples thereof are the walls of disks or bottles or similar objects made of glass or semiconductor material.

In addition to capacitive or other electrical measuring principles, in particular optical measuring principles are also used to measure distances without contact. This is because a particularly high measurement accuracy is thereby obtained. In one such optical measurement principle, polychromatic measurement light is directed onto the measurement object by an optical measurement head. Measurement light reflected from the surface of the object to be measured is received by a measurement head and supplied to a spectrograph which spectrally analyzes the reflected measurement light. From the spectral composition of the measurement light, the distance to the surface of the measurement target can be estimated. Since each optical interface between two media with different refractive indices reflects a part of the incident light, it is thus possible to Spacing can also be determined. The only condition for this is that the optical medium through which the measuring light is transmitted is sufficiently transparent for the measuring light used.

In the first type of measuring device used with this measuring principle, a chromatically confocal measuring concept is utilized. This type of measuring device has a measuring head that has a color-uncorrected optical system that focuses the measuring light onto the surface of the object to be measured. The chromatic longitudinal aberrations of the optical system, which can have lenses made of glass with strong dispersion and/or diffractive optical elements, focus the spectral components of the measurement light onto different focal planes. The confocally arranged diaphragm ensures that only those spectral components of the measuring light whose focal plane lies precisely on the surface of the object to be measured reach the spectrograph and can be spectrally analyzed there. A spectrograph has a grating or other dispersive optical element and a detector that has a large number of light-sensitive cells. Since each photosensitive cell is associated with a very narrow wavelength range, it is possible to directly assign spacing values to the individual cells of the detector. The correspondence between spacing values and cells can be determined via calibration, as described in DE 10 2004 049 541 A1.

In other types of measuring devices, in which the measuring light reflected from the surface of the object to be measured is spectrally analyzed, the concept of optical interference is used. The measurement light reflected from the measurement object interferes with the measurement light reflected within the reference arm. Due to the interference, the reflected measuring light is spectrally modulated, and the determined spacing value can then be derived from the modulation frequency. For this purpose, the measuring light reflected from the object and interfering with the measuring light reflected in the reference arm is spectrally detected in a spectrograph and inversely Fourier transformed.

The two types of optical measurement devices mentioned above are often used for quality assurance within manufacturing environments. In a manufacturing environment, of course, ambient temperatures vary significantly. The measuring device is therefore typically operable over a temperature range between +5°C and +60°C.

The problem then arises that different ambient temperatures have a direct effect on the measured distance values. When the temperature changes, thermal expansion of the optical element results in changes in important optical parameters such as the radius of curvature and the spacing between the optical interfaces. Furthermore, the refractive index of lenses and other refractive optical elements is directly dependent on temperature. The refractive index of the air or other gas through which the measurement light propagates itself depends on the temperature - albeit to a much lesser extent than in a fixed body. Furthermore, thermal expansion of the holder that secures the optical element to the housing can lead to a change in the position of the optical element, which likewise affects the operation of the optical system.

In order to compensate for thermally-based measurement errors, EP 2 369 294 (B1) proposes a chromatically uncorrected optical system included in the measurement head to compensate for the effects of individual optical elements on temperature changes. It is proposed to design such that changes in optical effects are mutually compensated.

It is known from EP 2 149 028 (B1) to allow for thermally induced changes in the measured values, but to compensate for these changes in a subsequent correction step. To obtain the correction value, the spectral composition of the measurement light components reflected at the optical surfaces in the measurement head is determined using a spectrograph. It is assumed that the distance of this surface to the end of the optical fiber, into which the reflected measuring light is coupled, depends on the temperature in the measuring head. In this way, the temperature is measured indirectly via the distance from the optical surface in the measuring head, so that the influence of the temperature can be taken into account in subsequent measurements on the measuring object.

In a similar manner, temperature-dependent effects in the measuring head are also taken into account in the measuring device known from DE 102015118069 A1. In order to determine the effect of temperature changes, the reflections at the external boundary surfaces of the measuring head are used instead of the reflections at the internal, fixed optical boundary surfaces of the measuring head. In an embodiment, the measuring light in the additional measuring arm is directed onto a stepped reflective surface, the height of the step along the optical axis being precisely known. If the distance value measured between two surfaces changes, this effect is assigned to the changed temperature and used to determine the correction factor. Then, in subsequent measurements, the measured spacing value is multiplied by the correction factor.

U.S. Pat. No. 9,541,376 (B2) addresses the problem of how changes in the spectrograph affect the measurement accuracy of a spacing measurement device operating according to the chromatically confocal measurement principle. We are fundamentally working on this. To solve this problem, it is proposed to detect both the +1 and -1 diffraction orders with the spectrograph detector, rather than the +1 or -1 diffraction orders. Spacing information is derived from the spacing between the photosensitive cells of the detector where the maxima of the two diffraction orders occur. If the position of the grating and/or the detector changes due to temperature changes, this often causes the maxima of the diffraction orders to shift by the same amount, so that the spacing between the maxima remains constant. Temperature changes do not affect the measurement accuracy since only this interval is included in the subsequent evaluation.

Of course, the disadvantage of this known concept is that two diffraction orders have to be evaluated by the detector. Thereby, the spectral resolution and therefore the measurement accuracy are also reduced when the number of photosensitive cells provided is equal.

German Patent Application No. 102004049541 (A1) European Patent No. 2369294 (B1) European Patent No. 2149028 (B1) specification German Patent Application No. 102015118069 (A1) US Patent No. 9541376 (B2)

It is an object of the invention to provide a measuring device and a method for non-contact measurement of the distance to a surface or the distance between two surfaces, in which temperature changes in the spectrometer do not affect the measurement accuracy, or at least to a much lesser extent than before. The goal is to improve it so that it works. There is no need to accept the losses in spectral resolution and the associated measurement accuracy that had to be accepted in known solutions.

Regarding the measuring device, the problem mentioned above is solved by a measuring device for non-contact measurement of a distance to a surface or a distance between two surfaces, which has a measuring light source arranged to generate polychromatic measuring light. be done. The measuring device further includes an optical measuring head, the measuring head directing the measuring light generated from the measuring light source towards the measuring object and receiving the measuring light reflected from the measuring object. It's arranged. Furthermore, the measuring device has a spectrograph, which spectrograph is arranged to spectrally analyze the measuring light reflected from the measuring light and received by the optical measuring head, in which case A spectrograph has a dispersive optical element and a detector with a large number of photosensitive cells. The evaluation device of the measuring device is arranged to calculate the distance value from the measuring signals of at least some of the photosensitive cells. According to the invention, the measuring device has a calibration light source arranged to generate calibration light having a known spectral composition. The calibration light can be directed onto the detector through the dispersive optical element without being previously reflected in the optical path leading to the measurement object. The evaluation device is arranged to derive a correction value from a spectral change caused by the calibration light in at least some of the photosensitive cells of the detector, and by which correction value the at least some of the photosensitive cells and A predetermined correspondence between the wavelength or a variable derived from the wavelength is modified.

The invention starts from the recognition that temperature variations within the spectrograph are an important factor for measurement accuracy. In that case, it is taken into account that different temperatures can prevail in the measuring head and in the spectrograph. For example, an evaluation device is often arranged in the immediate vicinity of the spectrograph, which evaluation device usually has a large number of electronic components. The heat losses generated from them can lead to higher temperatures prevailing in the spectrograph than in the measurement head.

In order to be able to detect the effects of temperature changes in the spectrograph and take them into account in subsequent measurements, according to the invention, a calibration light with a known spectral composition is applied to the dispersion of the spectrograph. is directed through an optical element to its detector. In this way, a unique relationship is formed between the spectrum of the calibration light and the photosensitive cells of the detector. If a change in temperature results in a change in the position of a photosensitive cell, the maximum intensity in the spectrum of the calibration light will occur in another photosensitive cell. According to the invention, this displacement is directly taken into account when evaluating the measurements on the subsequent measurement object by modifying the predetermined correspondence between the photosensitive cell and the wavelength or variables derived from the wavelength. be done. In the simplest case, a modified mapping of this kind can be considered such that a given photosensitive cell no longer corresponds to the original predetermined wavelength, but to a modified wavelength. Since the desired spacing information is encoded within the spectrum of the measurement light, correct detection of the spectrum as a result of the corrected mapping automatically provides a temperature-independent measurement of the spacing. This direct method of calibration is effective compared to the idea that the effects of temperature changes are derived from interval measurements.

Since the calibration light is supplied to the spectrograph without being previously reflected in the optical path leading to the measurement object, only the effects of temperature changes within the spectrograph are detected by means of the calibration light. The possibility afforded by the invention to be able to determine the influence of temperature changes in the spectrograph independently of the influence of temperature changes in the measuring head is advantageous for several reasons. . As in the case of the above-mentioned Patent Document 3 (European Patent No. 2149028 (B1)), when temperature changes inside the spectrograph and inside the measurement head are detected in combination, only the overlap of the two effects is detected. Detected. Since the two effects usually require different correction measures when evaluated, an optimal correction cannot be carried out when temperature changes are detected in combination. That is, for example, for wavelengths associated with reflective surfaces in the measuring head mentioned above, it may happen that the effects in the measuring head and in the spectrograph cancel each other out, so that no temperature change is detected. However, for other wavelengths, there may be an absolute need for correction, which is not recognized when detecting a combination of effects based on Patent Document 3.

Separate detection of temperature changes is also advantageous with respect to the modular construction of the measuring device. Precisely if the effects caused by temperature changes in the spectrograph are predominant compared to the effects in the measuring head, the correction is carried out irrespective of whether the measuring head has means for sensing temperature or not. It is effective if you can do it. The measuring device according to the invention therefore does not require a special measuring head, can be driven by any measuring head, and is therefore universally usable.

In order to be able to feed the calibration light to the dispersive optics of the spectrograph, a light splitting device is generally introduced in the optical path, with which the calibration and measurement light are commonly distributed. It is necessary to supply the optical elements with the same characteristics. The light splitting device can be, for example, a beam splitter cube or a fiber coupler.

Most advantageously, the evaluation device is arranged to derive the correction value from the change in position of the intensity pattern generated by the calibration light on at least a portion of the photosensitive cells of the detector. This type of pattern usually consists of a series of local maxima and minima. In the simplest case, this type of intensity pattern consists of individual (local) maxima or minima.

Calibration according to the invention is most easily carried out when the calibration light has a temporally stable and temperature-independent spectral composition. To this end, the calibration light source must have the property of generating calibration light with a spectral composition that does not change, regardless of the ambient temperature. However, it is also conceivable in principle to use calibration light with a temperature-dependent spectral composition. However, in that case, not only the temperature within the spectrograph but also the temperature dependence of the spectral composition must be known precisely so that it can be taken into account in the calculations during the evaluation.

In the simplest case, the calibration light source is a narrowband light source, for example a laser diode. An even smaller temperature dependence of the spectral composition is obtained if the calibration light source comprises a (possibly broadband) light source and a temperature-stable monochromator, for example a Fabry-Perot interferometer.

A particularly simple possibility to generate calibration light with a temporally stable and temperature-independent spectral composition is the arrangement of a broadband light source and a reflective surface that spectrally modulates the intensity of the calibration light by the formation of interferences. and using a calibrated light source with Therefore, unlike the use of laser diodes, this calibrated light source does not have a single maximum intensity at a given wavelength, but rather a relatively broad spectrum, but the spectrum has multiple local intensity maxima due to modulation. The detector of the spectrograph then detects not only the individual maximum intensity position, but also a plurality of maximum intensity positions. An arrangement of this type can be formed, for example, as plane-parallel plates of optically transparent material. If the plate is made of thermally non-conductive glass, the thickness change with temperature variations is compensated by the refractive index change in the opposite direction, so that the optical thickness of the plate and thus the modulation frequency remain constant. Instead of a glass plate, an air gap of thickness d can also be used for spectral modulation. This air gap can be formed, for example, between a first transparent, partially reflective plate on the underside and a second reflective plate. The spacing between the plates is adjusted by space holders, which are made of a material with low thermal expansion (quartz glass or Zerodur). The spectral modulation thereby generated by the air gap is not particularly temperature dependent.

Calibration can be performed simultaneously with spacing measurements if the calibration light and measurement light have non-overlapping spectra. In particular, the spectrum of the calibration light can be of shorter wavelength than the spectrum of the measurement light. If the spectra overlap, calibration must be performed in the time interval between distance measurements. This is because otherwise the spacing measurements would be distorted by the calibration light. Overlapping here is also a special case of identity (and thus complete overlap).

Even if the spectra of the calibration light and measurement light overlap, the calibration light with a certain wavelength is incident on a photosensitive cell and the reflected measurement light with the same wavelength is not allowed to enter the cell, so that the dispersive optical element Simultaneous calibration and measurement is possible if the calibration light can be directed through the detector to the detector. Preferably, the reverse also holds true, ie no reflected measuring light can enter a photosensitive cell into which a calibration light having the same wavelength can enter. This means, for example, that the calibration light and the measurement light are polarized differently and that the polarization filter ensures on the photosensitive cell that the calibration light and the reflected measurement light cannot be incident on the same cell. This can be achieved by

Since polarizing filters introduce optical losses, it is often more effective to have the calibration light enter the dispersive optical element from a different direction than the reflected measurement light. Thereby, the calibration light can take a different route than the measurement light behind the dispersive optical element and be spatially separated therefrom. The photosensitive cell then has a first cell and a second cell, on the first cell only the calibration light can be incident, and the first cell is in the first column. , and only reflected measurement light can be incident on the second cell, and the second cell is arranged in a second row extending parallel to the first row. located along.

In this context, the concept of calibration light source should be interpreted broadly. In particular, it is unnecessary for the calibration light and the measurement light to be generated from different optical components. In embodiments, the calibration light source and the measurement light source use the same optical components to generate the light. In that case, the calibration light source has, for example, a beam splitter that supplies a part of the light generated by the optical component as measuring light to the measuring head and another part of the light to a monochromator; The monochromator generates calibration light from the light by spectral filtering. Alternatively, this portion of the light can be directed to a plane-parallel plate to generate a modulated calibration light spectrum. In this way the calibration light source does not require dedicated optical components. In that case, of course, there is no measuring object in the optical path during the calibration, or the optical path leading to the measuring object is blocked, so that on the one hand the measuring light is reflected in the optical path leading to the measuring object. must be guaranteed to reach the detector.

It is particularly advantageous if two calibration light sources are provided and arranged to generate calibration light with different spectral compositions. The calibration light generated by the two calibration light sources is then simultaneously directed through the dispersive optical element to the detector without being previously reflected in the optical path leading to the measurement object. In this way, a temperature-based position change of the photosensitive cell is detected, which is not described as a uniform location-independent displacement (offset). When first and second calibration lights with different spectral compositions are used, a linear dependence of the displacement on the wavelength is detected, thereby establishing a correspondence between the photosensitive cell and the wavelength or a variable derived from the wavelength. will be taken into account when revising the assignment. In this case, the spectra of the calibration light generated by the two calibration light sources will of course not overlap. Ideally, the spectrum of the measurement light lies between the spectra of the first and second calibration light generated by the two calibration light sources.

Another possibility of providing measurement signals generated by the calibration light at different locations on the detector is to use a diffraction grating as a dispersive optical element and to divide the spectrum of the calibration light into two parts of the calibration light by the detector. The problem lies in choosing such that two different diffraction orders are detectable. Again, the point where the calibration light enters the detector is located outside the area reserved for the measurement light, ideally located at and between its opposite ends.

The subject of the invention furthermore relates to a method for contact-free measurement of a distance to an object or a distance between two surfaces, comprising the following steps:
a) polychromatic measuring light is generated;
b) measurement light is directed onto the measurement object by an optical measurement head, and measurement light reflected from the measurement object is received by the optical measurement head;
c) detection in which the measuring light reflected from the measuring object and received by an optical measuring head is spectrally analyzed in a spectrograph, said spectrograph being equipped with dispersive optical elements and a number of photosensitive cells; having a vessel;
d) spacing values are calculated from the measurement signals of at least some of the photosensitive cells, using a predetermined correspondence between at least some of the photosensitive cells and wavelengths or variables derived from the wavelengths; is;
e) calibration light is generated, having a known spectral composition;
f) the calibration light is directed through a dispersive optical element onto the detector without being previously reflected in the optical path leading to the measurement object;
g) deriving a correction value from the spectral changes produced by the calibration light on at least some of the photosensitive cells of the detector;
h) the predetermined correspondence is modified by the correction value;
i) At least steps a) to d) are repeated, with the mapping modified in step h) being used in step d).

The explanations given above for the measuring device and the indications for preferred embodiments apply equally to the method.

It is particularly advantageous if the calibration light has a temporally stable and temperature-independent spectral composition.

The calibration light is generated in step e) by a temperature stable monochromator, which monochromator is illuminated by a broadband light source.

A calibration light source for generating calibration light has a broadband light source and a plate of optically transparent material that spectrally modulates the intensity of the calibration light by creating interference.

The calibration light and the measurement light preferably have non-overlapping spectra, in which case the spectrum of the calibration light can in particular be shorter-wave than the spectrum of the measurement light. In this case, it is possible to direct the calibration light to the detector simultaneously with the measurement light and perform a spectral analysis.

If the calibration light and measurement light have overlapping spectra, the calibration light should not be directed to the detector at the same time as the measurement light.

A part of the measurement light generated from the measurement light source can be branched. By means of spectral filtering, calibration light is then generated from the branched part of the measuring light.

In an embodiment, first and second calibration lights having different spectral compositions are generated and simultaneously directed through a dispersive optical element to the detector without being previously reflected in an optical path leading to the measurement object. . The spectra of the first and second calibration light then preferably do not overlap.

If the dispersive optical element is a diffraction grating, the spectrum of the calibration light can be selected such that two different diffraction orders of the calibration light can be detected by the detector.

Calibration with calibration light can be performed at relatively large time intervals. This is because temperature usually changes relatively slowly. However, it is also possible to carry out the calibration with a calibration light at the same time (for example in the case of different spectra) or immediately or before each measurement. In this case, in step i) not only steps a) to d) but also all previous steps a) to h) are repeated.

Definitions Polychromatic light is light that is spectrally broadband and can contain, for example, more than one color, or has more than one narrowband spectral component, such as, for example, produced by a comb filter.

A dispersive optical element is an optical element in which the optical property that comes into play for its function, such as the refractive index or the angle of diffraction, exhibits a sharp dispersion, and where dispersion is desirable for its function. A normal lens made of glass is therefore not a dispersive optical element - although its refractive power is wavelength dependent to a small extent. On the other hand, it exhibits significant dispersion and, in the case of dispersive prisms or diffraction gratings so designed, refracts or diffracts light of different wavelengths with different intensities.

Embodiments of the present invention will be described in detail below with reference to the drawings.

1 schematically shows a device for measuring distances according to the prior art; 1 schematically shows how the pixels of the detector included in the spectrograph detect the maximum intensity in the spectrum, in particular before or after an increase in temperature; 1 schematically shows how the pixels of the detector included in the spectrograph detect the maximum intensity in the spectrum, in particular before or after an increase in temperature; 1 schematically shows how the pixels of a detector included in a spectrograph detect two maximum intensities in a spectrum, in particular before and after a temperature increase; 1 schematically shows how the pixels of a detector included in a spectrograph detect two maximum intensities in a spectrum, in particular before and after a temperature increase; In a schematic representation similar to FIG. 1, a first embodiment of the invention is shown, using the principle of color confocal measurement. 2 shows a second embodiment of the invention, also using the principle of color confocal measurement and in which the calibration light source comprises a monochromator; 3 shows a variant for the calibration light source with two different monochromators; 2 shows a variant for a calibration light source with a glass plate for generating spectrally modulated calibration light; Figure 2 shows the spectrum of the calibration light source generated by the glass plate. 2 shows a variant for the calibration light source, in which the calibration light is focused onto the glass plate; Figure 3 shows a variant for the calibration light source in which the calibration light passes through the glass plate. 3 shows a third embodiment of the invention, which similarly uses the principle of color confocal measurement and in which the calibration light is generated by the same optical element as the measurement light. A fourth embodiment of the invention is shown, which similarly uses the principle of color confocal measurement and in which the calibration light and the measurement light propagate in free space. 5 shows a fifth embodiment of the invention, in which the measurement device uses an interferometric measurement principle; A sixth embodiment is shown in which the calibration light and the measurement light can be incident on the same pixel of the detector.

1. Measuring Principle and Problem Statement FIG. 1 shows a diagrammatic representation of a measuring device 10 according to the prior art. The measurement light source 11 generates polychromatic measurement light 12, which is directed onto the measurement object 18 via a light splitting device 14 and a measurement head 16, which can be, for example, a beam splitter cube. In FIG. 1, the part of the measuring light 12 reflected from the surface 19 of the measuring object 16 is indicated by a black arrow and has the reference numeral 12'. The reflected measurement light 12' is received by the measurement head 16 and directed by the light splitting device 14 to the spectrograph 20. Spectrograph 20 has a dispersive optical element 22, which can be a diffraction grating or a diffusing prism. Furthermore, spectrograph 20 has a detector 24 that includes a number of photosensitive cells 26 . The photosensitive cells 26 are arranged along straight or curved lines and are referred to below as pixels. The signals generated by the pixels are evaluated by an evaluation device 28 and a spacing value for the surface 19 is calculated based thereon.

In the measurement, the reflected measurement light 12' is deflected by a dispersive optical element 22, the deflection angle being dependent on the wavelength of the reflected measurement light 12'. If the reflected measuring light 12' is monochromatic, as is the case in a color confocal measuring device, it is indicated by the black highlighted pixel 26' in FIG. is incident on one or a few pixels 26 of the detector 24, as shown in FIG. In a measuring device in which the reflected measuring beam 12' interferes with the measuring beam previously reflected in a reference arm (not shown), a broad spectrum is obtained on the detector 24, which Spectrally modulated. The detector 24 then detects a number of maximum intensities, each distance between the measuring object 18 and the measuring head 16 being associated with a modulation frequency. A desired spacing value is calculated from the signal generated by the detector 16 by means of a Fourier transformation, which is known per se in the prior art.

In the following, for the sake of simplicity, it will be assumed that the measuring device 10 operates according to the principle of color confocal measurement. However, all considerations also apply mutatis mutandis to interferometrically operated measuring devices.

FIG. 2 shows a plurality of pixels 26 of the detector 24 and also shows the intensity distribution generated by the dispersive optical element 22 from the reflected measurement light 12'. It is recognized that the spectral intensity distribution is spread across multiple pixels 26. Each pixel 26 generates an electrical signal, which signal is dependent on the intensity of the light it generates, preferably linearly or according to a complex characteristic curve. By comparing the output signals of the pixels 26, it is easily determined on which pixel 26 the highest intensity is achieved. In FIG. 2a, this pixel is marked in black and designated 26'. A predetermined wavelength can be associated with this pixel. In a color confocal measuring device, each wavelength is associated with an interval, so the interval value can be directly derived from information about which pixel the maximum intensity occurs. The correspondence between pixels p and wavelengths λ may have the form of a correspondence table, for example, as shown below:

Each pixel p ₁ is associated with a predetermined wavelength λ ₁ . The use of a correspondence table is particularly effective when the relationship between pixels and wavelengths cannot be expressed in a simple equation. The correspondence table is established by the manufacturer of the measuring device through a calibration in which it is determined to which pixel the light of wavelength λ from the diffusing optical element 22 is directed by a tunable calibration light source. This calibration is performed at precisely specified temperatures.

If the temperature increases within the spectrograph 20, for example by an electronic evaluation device 28 that is directly adjacent and generates heat losses, the relative position between the pixel 26 and the spectrum changes with the maximum intensity contained therein. do. The cause may be a change in the position of the pixel 26 and/or the diffusing optical element 22. As a comparison of FIGS. 2a and 2b shows, with this type of change in relative position, the maximum intensity no longer occurs on the pixel 26', but on an adjacent or even more distant pixel 26''.

In order to avoid the associated measurement inaccuracies, according to the invention the correspondence table between pixels and wavelengths is modified. For example, for every pixel, if the shift is Δp pixels, the following correction calculation is performed:

In that case, p _1,korr is the corrected pixel number, and p ₁ is the original pixel number. In that case, the following corrected correspondence rule for wavelength results:

Therein, λ _1,korr is the corrected wavelength for the signal at pixel p ₁ and λ(p ₁ ) is the value resulting from the original correspondence table.

However, often temperature changes within the spectrograph 20 do not simply result in a displacement Δp that is the same for all pixels 26, as shown in FIGS. 2a and 2b. Rather, the displacements for different pixels of detector 24 may be of different magnitudes.

This case is illustrated in Figures 3a and 3b. In FIG. 3a, two maximum intensities are suggested at locations far apart from each other on the detector 24. At the initial temperature, these maximum intensities are located at pixels 26-1' and 26-2'. However, if the temperature increases, the shift may be of a different magnitude, as shown in Figure 3b. The maximum intensity shown on the left is shifted to the left by one pixel, while the maximum intensity shown on the right is shifted to the right by three pixels. This type of wavelength-dependent pixel displacement Δp=Δp(λ) is referred to below as a scaling error.

If a wavelength-independent displacement Δp=cost exists in the color confocal measuring device, this has a direct effect on the measured spacing value. This is because each pixel is directly associated with a spacing value. When the spacing between the surfaces of the transparent body is measured, offsets in the spacing values are no longer noticeable due to difference formation. The spacing measurement between two surfaces also applies if a scaling error (Δp=Δp(λ)) occurs. This is because in this case, based on the wavelength dependence of the displacement, erroneous spacing values are no longer calculated.

In an interferometric measuring device, if the displacement is independent of wavelength, Δp=cost, which likewise leads to an error in the distance measurement. As in the color confocal measurement method, scaling errors lead to measurement inaccuracies when measuring the distance between two surfaces of the object to be measured. Details thereof are explained below in connection with the fifth embodiment.

2. First Embodiment FIG. 4 shows a first embodiment for a measuring device 10 according to the invention in a representation according to FIG. Like the measuring device shown in FIG. 1 and known in the prior art, it has a measuring light source 11, a light splitting device 14, a measuring head 16 and a spectrograph 20, the spectrograph being dispersive. optical element 22 and a detector 24 with pixels 26.

Additionally, the measuring device 10 according to the invention has a calibration light source 30, which in the illustrated embodiment is designed to generate calibration light. The calibration light has two mutually separated narrowband spectral components, which are referred to below as first and second calibration light.

A first calibration light 32a with wavelength λa is indicated by pixel 32a and a second calibration light 32b with wavelength λb is indicated by pixel 32b. The first and second calibration lights 32a, 32b pass through the light splitting device 14, through the dispersive optical element 22 and onto the detector 24 without being previously reflected in the optical path leading to the measurement object 18. directed towards. The dispersive optical element 22 deflects the calibration light according to the wavelength so that the maximum intensity of the first calibration light 32a is directed to the first pixel 26a and the maximum intensity of the second calibration light 32b is directed to the second pixel 26b. incident on the It is assumed here that the calibration light source 30 is designed such that the first and second calibration lights 32a, 32b have a temporally stable and temperature-independent spectral composition. The wavelengths λa, λb are therefore constant at all temperatures occurring during normal operation.

If, within the spectrograph 20, the relative position between the pixels 26 and the spectrum changes upon temperature changes, this is directly detected using the calibration lights 32a, 32b. In that case, the same idea as explained above with respect to FIGS. 3a and 3b is used. Therefore, for each of the two wavelengths λa, λb, it is determined which pixel the calibration light impinges on. By comparing with the original correspondence table, it is possible to easily determine how large the pixel displacement Δp is when the temperature changes for the two wavelengths. If the displacements are the same at the two wavelengths, a particularly simple correction occurs according to equation (1) since there is a wavelength-independent displacement (Δp=cost).

If the displacement is wavelength dependent, the corrected pixel number p _korr is calculated by the following linear formula:

In that case Δp(λa) and Δp(λb) are the displacements measured using the calibration beams 32a, 32b for the two wavelengths λa, λb, and p _mess is the pixel where the highest intensity was measured. . From the corrected pixel positions, corrected spacing values can then be easily calculated in color confocal spacing measurements.

Instead of calibration light having two different wavelengths, calibration light having only one wavelength can be used so that it is incident on the detector 26 at two different locations. For example, if a diffraction grating is used as the dispersive optical element 22, this is designed in such a way that both the +1st order diffraction and the -1st order diffraction of the calibration light can be detected by the detector 26. be able to. In this way, two far apart locations are obtained which are impinged by the calibration light of known wavelength on the detector 24 as well. Ideally, the pixels on which the measuring light is incident in distance measurements are between these locations. In this way, the spacing measurement is not disturbed by the calibration, and at the same time the locations where the calibration light impinges on the detector 24 are maximally separated from each other, which is the linear function described by equation (3). Be effective in making decisions. If the spectra of the calibration light and measurement light overlap, the calibration light may be incident on the same pixel as the measurement light, thereby distorting the measurement. In order to avoid this, the calibration has to be carried out in this case within the period between measurements with the measuring light. Alternatively, suitable measures can prevent the calibration light from entering the same pixel as the measurement light, despite the spectral overlap. Details thereof are explained further below in connection with the sixth embodiment.

If the calibration light source 30 only generates calibration light with a unique wavelength, no scaling error is thereby defined. Therefore, in measurement devices where scaling errors do not occur or are negligible, it is sufficient to generate a calibration light having only one wavelength.

3. Second Embodiment FIG. 5 shows in a schematic representation a second embodiment for a measuring device 10 operating according to the color confocal measurement principle. The measurement light source 11 consists of an LED 34 which generates polychromatic light having a wavelength between approximately 500 nm and 700 nm. The measuring light 12 is coupled into an optical fiber 38 by a condensing lens 36 and reaches the measuring head 16 via a light splitting device formed as a fiber coupler 40 . The measuring light 12 then leaves the optical fiber 39 and is directed onto the measuring object 18 by a non-color-corrected objective consisting of two lenses 42, 44. Due to the chromatic longitudinal aberration of the objective lens, the emerging measuring beam 12 is focused in different wavelength planes, which is illustrated for three different wavelengths in FIG. The measuring light 12 reflected on the surface 19 of the measuring object 18 returns via the measuring head 18 into the optical fiber 39 and is fed via a fiber coupler 40 to another optical fiber 41 leading to the spectrograph 20 .

In the illustrated embodiment, the calibration light source 30 includes a broadband LED 46 that produces light in the blue-violet spectral region. Calibration light 32 is collimated by condenser lens 48 and passes through monochromator 50, which filters a narrow frequency band from the spectrum of calibration light 32. The now monochromatic calibration light 32 is coupled by a condensing lens 52 into an optical fiber 54 , which is coupled with a fiber coupler 40 to guide the calibration light through an optical fiber 41 to the spectrograph 20 .

In the spectrograph 20, the calibration light 32 and the measurement light 12 are also collimated by a condenser lens 55 and directed onto a dispersive optical element, which is formed as a reflection grating 56. The light reflected and diffracted therein is directed via a further condensing lens 57 onto a detector 24 with pixels 26, which detector is connected to an evaluation device 28.

Therefore, in this embodiment, the calibration light source 30 only generates calibration light having a unique wavelength, so that wavelength-dependent pixel displacements cannot be detected.

FIG. 6 shows a calibration light source 30 according to a variant, in which a monochromator 50 consisting of two separating parts is arranged behind the lens 48 in the collimated optical path. The two separating members are arranged in the optical path in such a way that half of the calibration light 32 passes through the separating member 50a and the other half passes through the separating member 50b. The two separating members 50a, 50b have different filtering effects, so that in the embodiment shown in FIG. 6, first and second calibration lights 32a, 32b with different wavelengths are generated.

The separation members 50a, 50b can be, for example, Fabry-Perot interferometers. Possible assembly configurations for this type of interferometer include plates with plane-parallel and partially reflectively coated surfaces. The wavelength of light that can pass through the interferometer depends on the thickness of the plate. Different plate thicknesses therefore provide different spectral filtration.

Another variation of the calibration light source 30 is shown in FIG. In this variant, the calibration light is not composed of one or two monochromatic components, but is polychromatic exactly like the measurement light 12. In order to nevertheless be able to assign wavelengths to the pixels 26 of the detector 24, the spectrum (p) of the calibration light is modulated, as shown in FIG. If the maximum intensities are far enough apart from each other, they can be resolved by the detector 24 with sufficient precision and mapped to individual pixels.

As FIG. 7 shows, in order to generate spectral modulation, broadband calibration light generated by LED 46 is directed through an aperture 51, a beam splitter cube 53 and a condenser lens 59 to a transparent plate 58; Its rear side 60 fully reflects the calibration light 32 and its front side 62 partially reflects it. The interference of the reflected calibration light 32 at the rear side 60 and the front side 62 results in the spectral modulation shown in FIG. 8, the variable part of which is
is proportional to. In equation (4), n is the refractive index of the plate 58, and d is the thickness.

If the thickness d and the refractive index n of the plate 58 do not change with temperature, the wavelength at which maximum interference occurs will remain constant. The plate 58 is therefore preferably made of glass, the coefficient of thermal expansion and the change in the refractive index being negligible at the temperatures normally occurring. The modulation frequency and thus the location of the maximum intensity on the detector 26 then remains constant over a wide temperature range, even if the emission spectrum of the LED 46 changes, especially when the temperature changes.

Another possibility consists in using a thermally non-conducting glass for the plate 58, in which the thermally induced geometric thickness increase is at least substantially in the opposite direction of the refractive index. compensated by a decrease in In this way, the optical thickness of the plate 58, which is defined by the product of the geometric thickness and the refractive index, and which defines the modulation frequency, remains constant with high precision even when the temperature changes. Examples of thermally non-conductive glasses of this type are, for example, Schott's N-PK51 and N-FK51A.

With this type of modulated spectrum, also two locations on the detector 26 are illuminated, between which there are pixels illuminated by the measuring light. In the simplest case, two diffraction orders of the calibration light are therefore detected by the detector 26, which was already explained above in connection with the first embodiment.

A spectral filter 64 is drawn in FIG. 7 by a dashed line, which only passes wavelengths smaller than the limiting wavelength. The limit wavelength is shorter than the minimum wavelength of the measurement light 12. In this way, it is ensured that calibration light that is within the spectrum of the measurement light cannot reach the detector 24. The calibration light 32 therefore does not impair the original distance measurement. This kind of spectral filter 64 is effective when the spectrum of the LED 46 of the calibration light source 30 overlaps with the spectrum of the LED 34 of the measurement light source 11. If there is no spectral overlap, the spectral filter 64 can be omitted.

FIG. 9 shows another variant of the calibration light source 30, which differs from the variant shown in FIG. It's different.

In the variant of the calibration light source 30 shown in FIG. 10, in contrast to the variants shown in FIGS. 7 and 9, the plate 58 is passed transparently. The construction of the calibration light source 30 is thereby simplified. This is because beam splitter cube 53 is not required.

4. Third Embodiment In the embodiments described above, various optical elements generate the measurement light and the calibration light. In this way, it is ensured particularly simply that the spectra do not overlap and that calibration can be carried out even between measurements.

The measurement light and the calibration light can be generated from the same optical element if sufficient time is provided to carry out regular calibration between distance measurements. FIG. 11 shows an embodiment of this type of structure, in which the calibration light source 30 simply consists of the condenser lens and plate 58 of the embodiment shown in FIG. Measuring light 12 generated by measuring light source 11 is fed via fiber coupler 40 to calibration light source 30 and directed toward plate 58 . The calibration light is then subjected to spectral modulation, as explained above with respect to FIG. The spectrally modulated calibration light then passes into the spectrograph 20 via an optical fiber 41, as in the embodiment shown in FIG. By omitting the LED 46 in the calibration light source, the structure of the calibration light source 30 is simplified.

If part of the measuring light is branched off using a spectral filter and fed to the spectrograph, additional optical elements for generating the light can also be dispensed with. In this case, the calibration is performed at the same time as the distance measurement. Of course, in this variant less bandwidth is provided for the spacing measurement, thereby reducing the measurement area for the spacing measurement.

5. Fourth Embodiment FIG. 12 shows another embodiment for the measuring device 10 according to the invention, which substantially corresponds to the variant shown in FIG. Between the measurement light source 11, the calibration light source 30, the measurement head 16 and the spectrograph 20, the measurement light 12 and the calibration light 32 propagate, but not in optical fibers but in free space. The fiber coupler of the embodiment shown in FIG. 5 is therefore replaced by a beam splitter cube 40'.

The optical path within spectrograph 20 is further folded such that measurement light 12 and calibration light 32 pass through the same lens 56 both before and after diffraction at reflection grating 56.

The measuring light 12 emerges from an exit window 70 of the measuring light source, which is not otherwise shown in this example, and is directed to the measuring head 16 via two apertures 72, 74 and via a beam splitter cube 40'.

6. Fifth Embodiment All the embodiments described so far of the measuring device according to the invention are based on the principle of confocal-chromatic distance measurement. However, as already defined above, the invention can also be used in an interferometric device for measuring distances. In devices of this type, the measuring head 16 does not have distinctly colored longitudinal aberrations. Instead, the spacing information is obtained from the spectrum of the reflected measurement beam 12' after it interferes with the reference beam.

FIG. 13 shows an embodiment of this type of measuring device 10. This corresponds approximately to the embodiment shown in FIG. What has been done is different. In the reference arm 80, the measurement light 12 generated by the measurement light source 11 is reflected by a mirror 86 and interferes in the fiber coupler 84 with the measurement light 12' reflected from the surface 19 of the measurement object 18. This interference is detected within spectrograph 20 and generates a modulated spectrum onto detector 24. Modulation frequencies, each associated with an interval value, can be obtained from the spectrum by inverse Fast Fourier Transformation (IFFT). For further details, reference is made to German Patent Application No. 102016005021 (A1) of the applicant.

In order to be able to perform the inverse FFT, the phase-dependent intensities p int(Ki) must first be derived from the intensity values P _{int(pi) measured} from the individual pixels p _i . In that case, the wave number k is given by the formula
is combined with the wavelength λ by , where n(λ) represents the diffusion of the medium in which the measuring object 18 consists and, if appropriate, the measuring light enters. The wavelength λ is again mapped to the pixel number p via the correspondence table p ₁ =p ₁ (λ ₁ ) described in Section 1. In order to correct the pixel number p, the pixel number p _korr corrected according to equations 1 or 3 is used here as well. The result is a modified correspondence between wavenumber k and pixel number p, which converts the pixel-dependent intensity p _int(pi) into phase-dependent intensity p _int(ki). is necessary.

7. Sixth Embodiment In the embodiments described above, either the spectra of the calibration light and the measurement light must be non-overlapping, or the calibration cannot be performed at the same time as the measurement.

As already briefly described in connection with the first embodiment, with a suitable beam guide it is possible to perform a calibration during the measurement with the measuring light, despite the superposition of the spectra of the calibration light and the measuring light. . In this way, for example for individual measurements, a correspondence table can be used which is defined simultaneously with the calibration light.

FIG. 14 schematically shows a part of the spectrometer 20. A dispersive optical element can be seen, which is here formed as a transmission grating 84 for reasons of particular ease of display. The transmission grating 84 is placed in the collimated optical path, as is the reflection grating 56 shown in FIGS. 5, 11 and 12. As in other embodiments, a condenser lens 57 focuses the diffracted light onto the detector 24.

Unlike the embodiments described above, the detector 24 has two pixel rows 86, 88 instead of just one. In the illustrated example, first pixels 26-1 are arranged along a first pixel row 86 through which an optical axis 90 parallel to the z-direction extends; Only the measurement light 12' can be incident on the. A second pixel 26-2 is disposed along a second pixel row 88, displaced along the x direction but extending parallel to the first pixel row 86, on which Only the calibration light 32 can be incident.

In this embodiment as well, the measuring light 12' enters the dispersive optical element (transmission grating 84) parallel to the axis. Since the diffractive structure of the transmission grating 84 extends along the x direction, the measuring beam 12' is deflected in the yz plane according to the wavelength and is focused by the condenser lens 57 on the first pixel of the first pixel row 86. 26-1, which is also the case in the embodiments described above.

The calibration light 32, which is collimated therewith and is indicated by a dashed line in FIG. 14, is in this embodiment incident on the transmission grating 84 not axially parallel, but at an angle different from zero with respect to the xz plane. The condensing lens 57 thereby directs the calibration light 32 diffracted in the yz plane not onto the pixel 26-1 of the first pixel row 86, but onto a second pixel 26-1, which is disposed displaced in the x direction relative to it. Focus on the second pixel 26-2 of pixel row 88. Therefore, as envisaged in FIG. 14, due to the different directions of incidence, the calibration light 32 and the measurement light 12' can be focused on the same pixel even if the wavelength and therefore the diffraction angle are the same. I can't. In this embodiment, therefore, calibration and measurement can be performed simultaneously, even if the calibration light 32 and the measurement light 12' have equal spectra. This idea can therefore be combined particularly well with the embodiment shown in FIG. 11, in which the calibration light 32 and the measurement light 12' are generated from the same LED and therefore have the same spectrum.

Since the two pixel rows 86, 88 are located within the same detector 24 and, in particular, directly adjacent in the illustrated embodiment, the pixels within the two pixel rows 86, 88 always have the same y position. have. Thereby, from the position of the second pixel 16-2 supplied with the calibration light 32, the position of the first pixel 26-1 arranged below it can be directly estimated. For evaluation purposes, therefore, it is not distinguished whether the calibration light 32 is incident on the first pixel 26-1 or on the second pixel 26-2 arranged above it.

In order to be able to direct the calibration beam 32 and the measurement beam 12' from different directions onto the dispersive optical element, the calibration beam 32 can be directed into a dedicated can be guided through fibers. In this case, the two ends of the fiber are arranged side by side in the focal plane of the condenser lens 55 . In the embodiment shown in FIG. 14, the displacement of the fiber end is provided along the x direction.

In an arrangement with free beam propagation, as illustrated in FIG. 12, the aperture 51 of the calibration light source 30 may be moved perpendicular to the paper plane.

Of course, beam tilt can also be provided in other ways, for example by using a wedge prism.

The desired spatial separation of the calibration and measurement light on the detector is not only ensured by the different directions of incidence of the calibration and measurement light on the dispersive optical element. Alternatively, it is conceivable, for example, for the calibration light and the measurement light to be polarized differently, for example orthogonally linearly or vice versa. In that case, a suitable polarizing filter placed immediately before or above the pixels 26-1, 26-2 is used to prevent the calibration light from entering the reflected measurement light having the same wavelength. Make it incident only on pixels and vice versa.
The invention disclosed herein includes the following.
[Aspect 1]
A measuring device for non-contact measurement of the distance to a surface (19) or the distance between two surfaces,
comprising a measurement light source (11) arranged to generate a polychromatic measurement light (12);
Optical measurement arranged to direct the measurement light (12) generated from the measurement light source (11) towards the measurement object (18) and to receive the measurement light (12') reflected from the measurement object (18) having a head (16);
a spectrograph (20) arranged to spectrally analyze the measurement light (12') reflected from the measurement object (18) and received by the optical measurement head (16); a spectrograph (20) has a dispersive optical element (22) and a detector (24) with a number of photosensitive cells (26);
comprising an evaluation device (28) arranged to calculate an interval value from the measurement signals of at least some of the photosensitive cells (26);
In things,
The measuring device (10) has a calibration light source (30) arranged to generate a calibration light (32) having a known spectral composition, in which case the calibration light (32) can be directed through the dispersive optical element (20) to the detector (24) without being previously reflected in the optical path leading to the measurement object (18), and
The evaluation device (28) is further arranged to derive a correction value from the spectral changes generated in at least some of the photosensitive cells (26) of the detector (24) by the calibration light (32). , the correction value modifies a predetermined association between at least a portion of the photosensitive cell (26) and a wavelength or a variable derived from the wavelength;
A measuring device characterized by:
[Aspect 2]
such that the evaluation device (28) derives the correction value from the change in position of the intensity pattern generated by the calibration light (32) on at least a portion of the photosensitive cells (26) of the detector (24); The measuring device according to aspect 1, wherein the measuring device is arranged.
[Aspect 3]
3. Measuring device according to aspect 1 or 2, characterized in that the calibration light (32) has a temporally stable and temperature-independent spectral composition.
[Aspect 4]
4. Measuring device according to claim 3, characterized in that the calibration light source (30) comprises a broadband light source (46) and a temperature-stable monochromator (50).
[Aspect 5]
Embodiment 3, characterized in that the calibration light source (30) comprises a broadband light source (46) and an arrangement of reflective surfaces, said arrangement spectrally modulating the intensity of the calibration light by the generation of interference. Measuring device as described.
[Aspect 6]
6. The measuring device according to any one of aspects 1 to 5, characterized in that the calibration light (32) and the measurement light (12) have non-overlapping spectra.
[Aspect 7]
Embodiment 1 characterized in that the calibration light (32) and the measurement light (12) have overlapping spectra, but the calibration light (32) cannot be directed to the detector (24) at the same time as the measurement light (12). The measuring device according to any one of 5 to 5.
[Aspect 8]
the calibration light (32) and the measurement light (12) have at least partially overlapping spectra, and
The calibration light (32) is dispersed in such a way that the calibration light (32) having a certain wavelength is incident on a photosensitive cell where the reflected measurement light (12') having the same wavelength cannot be incident. to the detector (24) through the optical element (20) of the
The measuring device according to any one of aspects 1 to 5, characterized in that:
[Aspect 9]
the calibration light (32) is incident on the dispersive optical element (20) from a different direction than the reflected measurement light (12'), and
Preferably a photosensitive cell (26) comprises a first cell (26-1) and a second cell (26-2), with only the calibration light (32) being incident on said first cell. and the first cell is arranged along a first row (86), and only reflected measurement light (12') can be incident on the second cell; and said second cells are arranged along a second row (88) extending parallel to the first row (86).
The measuring device according to aspect 8, characterized in that:
[Aspect 10]
The calibration light source (30) includes a beam splitter (40) that splits a part of the measurement light (12) generated from the measurement light source (11), and a monochromator (50) or a plane-parallel plate according to aspect 5 ( 58) The measuring device according to any one of aspects 1 to 9, characterized in that it has the following.
[Aspect 11]
Two calibration light sources are provided, arranged to generate calibration light with different spectral compositions, in which case the calibration light (32) generated from the two calibration light sources (30) has previously detected the object to be measured ( Any of the embodiments 1 to 10, characterized in that it can simultaneously be directed through the diffusive optical element (20) to the detector (24) without being reflected in the optical path leading to (18). Measuring device as described in one.
[Aspect 12]
the dispersive optical element is a diffraction grating (50), and
Any one of embodiments 1 to 10, characterized in that the spectrum of the calibration light (32) is selected such that two different diffraction orders of the calibration light are detectable by the detector (24). Measuring device described in.
[Aspect 13]
A method for non-contact measurement of the distance to a surface (19) or between two surfaces, comprising the steps of:
a) polychromatic measuring light (12) is generated;
b) The measurement light (12) is directed onto the measurement object (18) by the optical measurement head (16), and the measurement light (12') reflected from the measurement object (18) is directed to the measurement object (18) by the optical measurement head (16). received by (16);
c) The measuring light (12') reflected from the measuring object (18) and received by the optical measuring head (16) is spectrally analyzed in a spectrograph (20), said spectrograph being comprising an optical element (22) and a detector (14) comprising a number of photosensitive cells (26);
d) from the measurement signals of at least some of the photosensitive cells (26) a distance value is calculated, in which case a predetermined interval value between at least some of the photosensitive cells and the wavelength or a variable derived from the wavelength; The mapping is used;
e) a calibration light (32) is generated having a known spectral composition;
f) directing the calibration light (32) through the dispersive optical element (22) onto the detector (24) without the calibration light (32) being previously reflected in the optical path leading to the measurement object (18); Re;
g) deriving a correction value from the spectral changes produced by the calibration light (32) on at least some of the photosensitive cells (26) of the detector (24);
h) the predetermined correspondence is modified by the correction value;
i) at least steps a) to d) are repeated, where in step d) the mapping modified in step h) is used;
A method with steps.
[Aspect 14]
A method according to aspect 13, having the characteristics of any one of aspects 1 to 12.

10 Measuring device 11 Measuring light source 12 Measuring light 12' Reflected measuring light 14 Light splitting device 16 Measuring head 18 Measuring object 19 Surface 20 Spectrometer 22 Dispersive optical element 24 Detector 26 Photosensitive cell (pixel)
28 Evaluation device 30 Calibration light source 32 Calibration light 34 LED of measurement light source
36 Condenser lens 38 Optical fiber 39 Optical fiber 40 Fiber coupler 40' Beam splitter cube 41 Optical fiber 42 Condenser lens 44 Condenser lens 46 Calibration light source LED
48 Condenser lens 50 Monochromator 51 Aperture 52 Condenser lens 53 Beam splitter cube 54 Optical fiber 55 Condenser lens 56 Reflection grating 57 Condenser lens 58 Plate 59 Condenser lens 60 Back side 62 Front side 64 Spectral filter 70 Exit window 72 Aperture 74 Aperture 80 Reference arm 82 Mirror 84 Transmission grating 86 First pixel row 88 Second pixel row 90 Optical axis

Claims (8)

A measuring device for non-contact measurement of the distance to a surface (19) or the distance between two surfaces,
comprising a measurement light source (11) arranged to generate a polychromatic measurement light (12);
an optical device arranged to direct the measurement light (12) generated from the measurement light source (11) towards the measurement object (18) and to receive the measurement light (12') reflected from the measurement object (18); a measuring head (16),
a spectrograph (20) arranged to spectrally analyze the measurement light (12') reflected from the measurement object (18) and received by the optical measurement head (16); The spectrograph (20) then has a dispersive optical element (22) and a detector (24) with a number of photosensitive cells (26);
comprising an evaluation device (28) arranged to calculate an interval value from the measurement signals of at least some of the photosensitive cells (26);
In things,
The measuring device (10) has a calibrated light source (30), the calibrated light source (30) having a broadband light source (46) and an arrangement of reflective surfaces, the arrangement being configured to prevent the occurrence of interference. spectrally modulating the intensity of the calibration light by, said calibration light source (30) being arranged to generate calibration light (32) having a known spectral composition that is both temporally stable and temperature independent; The calibration light (32) can then be directed through a dispersive optical element (20) to the detector (24) without being previously reflected in the optical path leading to the measurement object (18). and said evaluation device (28) is further adapted to derive a correction value from spectral changes produced in at least some of the photosensitive cells (26) of said detector (24) by said calibration light (32). the correction value modifies a predetermined association between at least a portion of the photosensitive cell (26) and a wavelength or a variable derived from the wavelength;
The calibration light (32) and the measurement light (12) have spectra that at least partially overlap, and the calibration light (32) has a certain wavelength and the calibration light (32) has a reflection having the same wavelength. the measured measuring light (12') can be directed through the dispersive optical element (20) to the detector (24) in such a way that it is incident on a photosensitive cell that cannot enter;
the calibration light (32) is incident on the dispersive optical element (20) from a different direction than the reflected measurement light (12'), and
The photosensitive cell (26) has a first cell (26-1) and a second cell (26-2), and only the calibration light (32) is incident on the first cell. and the first cell is arranged along the first row (86), and only the reflected measurement light (12') can enter the second cell. , and the second cells are arranged along a second row (88) extending parallel to the first row (86).
A measuring device characterized by: The evaluation device (28) derives a correction value from the change in position of the intensity pattern generated by the calibration light (32) on at least a portion of the photosensitive cells (26) of the detector (24). Measuring device according to claim 1, characterized in that it is arranged so as to guide the measuring device. The measuring device according to claim 1 or 2, characterized in that the calibration light (32) and the measurement light (12) have non-overlapping spectra. Although said calibration light (32) and said measurement light (12) have overlapping spectra, said calibration light (32) cannot be directed to said detector (24) at the same time as said measurement light (12). The measuring device according to claim 1 or 2, characterized in that: The calibration light source (30) includes a beam splitter (40) for splitting a part of the measurement light (12) generated from the measurement light source (11), and a monochromator (50) or a plane-parallel plate (58). The measuring device according to claim 1 or 2, characterized in that it has: Two calibration light sources are provided, arranged to generate calibration light with different spectral compositions, in which case the calibration light (32a, 32b) generated from the two calibration light sources (30) has been previously Claim characterized in that it can simultaneously be directed through the dispersive optical element (20) to the detector (24) without being reflected in the optical path leading to the measurement object (18). The measuring device according to item 1 or 2. the dispersive optical element is a diffraction grating (50), and the spectrum of the calibration light (32) is such that two different diffraction orders of the calibration light are detectable by the detector (24); The measuring device according to claim 1 or 2, wherein the measuring device is selected. A method for non-contact measurement of a distance to a surface (19) or a distance between two surfaces, the method comprising:
a) a polychromatic measurement light (12) is generated;
b) said measurement light (12) is directed onto a measurement object (18) by an optical measurement head (16), and the measurement light (12') reflected from said measurement object (18) is directed by an optical measurement head (16) onto a measurement object (18); a step received by a measuring head (16);
c) the measurement light (12') reflected from the measurement object (18) and received by the optical measurement head (16) is spectrally analyzed in a spectrograph (20), and the spectrograph having a dispersive optical element (22) and a detector (14) with a number of photosensitive cells (26);
d) from the measurement signals of at least some of the photosensitive cells (26) a distance value is calculated, in which case a predetermined interval value between at least some of the photosensitive cells and the wavelength or a variable derived from the wavelength; the steps in which the mapping is used;
e) generating by a calibration light source (30) a calibration light (32) having a known temporally stable and temperature-independent spectral composition, said calibration light source (30) comprising a broadband light source (46); ) and an arrangement of reflective surfaces, said arrangement spectrally modulating the intensity of the calibration light by generating interference;
f) the calibration light (32) passes through the dispersive optical element (22) to the detector (24) without being previously reflected in the optical path leading to the measurement object (18); ) a step directed upward;
g) deriving a correction value from the spectral changes produced by the calibration light (32) on at least some of the photosensitive cells (26) of the detector (24);
h) the predetermined correspondence is modified by the correction value;
i) at least steps a) to d) are repeated, in which case in step d) said mapping modified in step h) is used;
has
The calibration light (32) and the measurement light (12) have spectra that at least partially overlap, and the calibration light (32) has a certain wavelength and the calibration light (32) has a reflection having the same wavelength. the measured measuring light (12') can be directed through the dispersive optical element (20) to the detector (24) in such a way that it is incident on a photosensitive cell that cannot enter;
the calibration light (32) is incident on the dispersive optical element (20) from a different direction than the reflected measurement light (12'), and
The photosensitive cell (26) has a first cell (26-1) and a second cell (26-2), and only the calibration light (32) is incident on the first cell. and the first cell is arranged along a first row (86), and only the reflected measurement light (12') can enter the second cell. , and wherein the second cells are arranged along a second row (88) extending parallel to the first row (86).

Images