WO2018046183A1

WO2018046183A1 - Method and device for operating a spectrometer

Info

Publication number: WO2018046183A1
Application number: PCT/EP2017/069295
Authority: WO
Inventors: Ralf Noltemeyer; Martin HUSNIK; Eugen BAUMGART; Christian Huber; Benedikt Stein
Original assignee: Robert Bosch Gmbh
Priority date: 2016-09-06
Filing date: 2017-07-31
Publication date: 2018-03-15
Also published as: DE102016216842B4; DE102016216842A1

Abstract

The invention relates to a device (102) for operating a spectrometer (100), wherein the device (102) comprises a determination device (122) for determining a compensation value (126) for compensating an offset (120) of a spectrum (104) detected by the spectrometer (100) using an angle value (128), and a compensating device (124) for compensating the spectrum (104) using the compensation value (126) in order to obtain an angle-compensated spectrum (130), wherein the angle value (128) represents an angle of incidence (116) of light (106) which is incident on the spectrometer (100) during the detection of the spectrum (104).

Description

Description title

Method and apparatus for operating a spectrometer prior art

The invention is based on a device or a method according to the preamble of the independent claims. The subject of the present invention is also a computer program.

Disclosure of the invention

In a spectrometer, a detected spectrum may have an offset when the light falls obliquely on the spectrometer.

Against this background, the method presented here introduces a method for operating a spectrometer, furthermore a device which uses this method, a spectrometer, and finally a corresponding computer program according to the main claims. The measures listed in the dependent claims are advantageous

Further developments and improvements of the device specified in the independent claim possible.

The wavelength error caused by obliquely incident light when detecting a spectrum depends on an angle of incidence of the light. Therefore, in the approach presented here, the angle of incidence is determined and used to determine a compensation value for the spectrum. The compensation value is applied to the offset spectrum and the spectrum is shifted. A method for operating a spectrometer is presented, the method comprising the following steps:

Determining a compensation value for compensating for an offset of a spectrum sensed by the spectrometer using an angle value, the angle value representing an angle of incidence of light incident on the spectrometer during acquisition of the spectrum; and

Compensating the spectrum using the compensation value to obtain an angle compensated spectrum.

This method can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example in a control unit.

Furthermore, an apparatus for operating a spectrometer is presented, the apparatus having the following features: a determination device for determining a compensation value for compensating an offset of a spectrum detected by the spectrometer using an angle value, the angle value representing an angle of incidence of light which during collapsing the spectrum onto the spectrometer; and compensation means for compensating the spectrum using the compensation value to obtain an angle compensated spectrum.

A spectrometer can be understood as a component which has a spectral element in an optical path in front of a detector. A spectrum is an intensity course over a wavelength range. The spectrum can be recorded in parallel or serially. In the parallel recording, the entire spectrum is spatially resolved by the spectral element and a plurality of Captured intensity values with multiple pixels in a single timeslot. In the case of serial recording, the spectral element only passes through and covers a limited wavelength range of the incident light

Intensity value of the wavelength range is detected. In several time slots successively different wavelength ranges are transmitted and the resulting intensity values recorded. The spectrum is composed of the consecutively recorded intensity values. The angle value can be detected using an angle sensor.

Compensation values can be stored in a table.

The device may comprise an angle detection device which is designed to detect an angle of incidence of light incident on the spectrometer during acquisition of the spectrum and to map it in the angle value. The angle detection device can be integrated in the spectrometer. Thus, the actual angle of incidence can be detected during the acquisition of the spectrum.

The angle detector may include a photodetector having a pixel array with a plurality of pixels each providing an intensity value, the angle detector being configured to determine the angle value using the intensity values. The angle may be determined using a centroid of light incident on the detector. The photodetector can use the light that is used to capture the spectrum. This can avoid a systematic error. A totality of

Intensity values can be used to capture the spectrum.

The device may comprise a lighting device which is arranged laterally offset from the photodetector, wherein the pixels are aligned on an axis between the illumination device and the photodetector. An illumination device can have, for example, an LED. The illumination device may be aligned obliquely to an optical axis of the optical element. By the illumination device, the angle of incidence of the incident light is related to a distance between a lit object and the spectrometer. The spectrometer can be used for distance measurement.

The photodetector may be configured to detect the spectrum. The photodetector can use the light that is used to capture the spectrum. This can avoid a systematic error.

The pixels can be arranged two-dimensionally flat. Pixels oriented in a first direction can detect the spectrum. Transversely aligned pixels can provide the intensity values. Due to the planar arrangement of the pixels, the spectrum and the angle of incidence can be detected in parallel.

Furthermore, a spectrometer is presented with a device according to the approach presented here.

A spectral element of the spectrometer can be designed as a linearly variable filter. Through the linear variable filter, the spectrum can be recorded in parallel.

The spectral element of the spectrometer can be called micromechanical

Interferometer be formed. Through the interferometer, a simple photodetector can be used.

Also of advantage is a computer program product or computer program with program code which can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and for carrying out, implementing and / or controlling the steps of the method according to one of the above

described embodiments, in particular when the program product or program is executed on a computer or a device.

Embodiments of the approach presented here are shown in the drawings and explained in more detail in the following description. It shows: 1 is a block diagram of a spectrometer with an apparatus for operating according to an embodiment;

FIG. 2 is an illustration of angle detection using a pixel array according to an embodiment; FIG.

3 shows an illustration of an illumination spot incident centrally on a photodetector according to an exemplary embodiment;

Fig. 4 is an illustration of a detected spectrum;

5 shows representations of off-center incident on a photodetector according to an embodiment illumination spots.

Fig. 6 is an illustration of a spectrum with offset;

7 shows an illustration of a spectrometer with a linearly variable filter according to an exemplary embodiment;

8 shows an illustration of a spectrometer with an interferometer according to an exemplary embodiment; and

9 is a flowchart of a method for operating a

Spectrometer according to one embodiment.

In the following description of favorable embodiments of the present invention are for the in the various figures

represented and similar elements acting the same or similar

Reference numeral used, wherein a repeated description of these elements is omitted.

1 shows a block diagram of a spectrometer 100 with an apparatus 102 for operating according to an exemplary embodiment. The spectrometer 100 is configured to detect a spectrum 104 of incident light 106. For this purpose, the spectrometer 100 has a spectral element 108. The spectral element 108 is configured to separate the incident light 106 into its contained wavelengths. A photodetector 110 images radiation intensities of the wavelengths in intensity values 112. A detection device 114 detects the intensity values and maps them in the spectrum 104.

The spectral element is angle sensitive. If the incident light is incident at an angle of incidence 116 obliquely to a working axis 118 of the spectrometer 100, the separated wavelengths are shifted by an angle-dependent offset 120. This offset 120 is thus also shown in the spectrum 104. The spectrum 104 thus has the offset 120.

The device 102 has a determination device 122 and a

Compensation device 124. The determination device 122 is designed to determine a compensation value 126 for compensating the offset 120 using an angle value 128. The angle value 128 represents the angle of incidence 116 during the detection of the spectrum 104. The compensation device 124 is configured to compensate the spectrum 104 using the compensation value 126

angle compensated spectrum 130.

In one embodiment, the device 102 has a

Angle detection device 132 on. The angle detection device 132 is designed to detect the angle of incidence 116 and to map it in the angle value 128. For example, the angle detection device 132 may be arranged next to the spectral element 108. Here is the

Angle detection device 132 part of the spectrometer 100th

The angle detector 132 comprises the photodetector 110. The photodetector 110 has a pixel field 134 with a plurality of pixels 136. The pixels 136 each form the incident in the region of the pixel 136

Radiation intensity of the light 106 in an intensity value 112 from. Since the position of each pixel 136 relative to the working axis 118 is known, in a determination device 138 of the angle detection device 132 from the simultaneously detected intensity values 112 of the individual pixels 136 on the Angle of incidence 116 can be closed. The determination device 138 maps the angle of incidence 116 in the angle signal 128 and combines the simultaneously detected intensity values 112 into an intensity value 112.

In one embodiment, the spectral element 108 is formed as an interferometer 108. The interferometer 108 has two mirrors spaced apart by a gap. A gap width 140 of the gap determines a wavelength transmitted through the interferometer 108. A drive device 142 is configured to adjust the gap width 140 in response to a control signal 144, the gap width.

Control signal 144 may be provided by detector 114 to adjust gap width 140 to a new wavelength when a wavelength is detected.

In one embodiment, Fig. 1 shows a device 100 and a miniature spectrometer 100, consisting of a non-illustrated

Light source, a spectral element 108 with a limited aperture and a photodetector 110, as at least two-part photodiode, quadrants

Photodiode or detector array 134 is executed. In the

Angle determination device 132, a difference signal 112 of the photodiode 110 is used to determine the main angle of incidence 116.

The spectral element 108 may be a micromechanical Fabry-Perot

Interferometer device 108 be. The interferometer then consists of at least two spaced apart by a gap, superimposed mirror elements. The knowledge of the main angle of incidence is used to correct the spectral offset 120.

The spectral element 108 may also be a linearly variable filter 108 with a wavelength change in X. Then, the detector 110 a

two-dimensional detector array 134 with pixels 136 in X for the wavelength and pixels 136 in Y for the angle correction. The difference of detector lines is used to detect the main angle of incidence 116. The knowledge of the main incident angle 116 is used to correct the spectral offset 120. The approach presented here makes compensation more dependent on the angle and thus more distance-dependent in the case of an eccentric lighting approach

Wavelength offset error 120 is achieved in spectrometers 100. By the

Compensation of the wavelength offset 120 may provide higher accuracy of the

Wavelength spectrum 130 at different distances, and thus a greater robustness of the system 100 in handling by the end user can be achieved.

FIG. 2 shows an illustration of angle detection using a pixel array 134 according to one embodiment. The angle of incidence 116 is detected at a spectrometer 100, as shown for example in Fig. 1. The spectrometer 100 here comprises an illumination device 200, which is arranged laterally offset from the photodetector 110. The

Lighting device 200 is aligned obliquely to the working axis 118. An illumination axis 202 of the illumination device 200 intersects the working axis 118. An illumination beam of the illumination device 200 is divergent. As a distance 204 between the spectrometer 100 and an illuminated object becomes smaller, an illuminated area 206 on the object travels along the illumination axis 202 in the direction of

Lighting device 200. In this case, the illuminated area 206 is smaller. As the distance 204 increases, the illuminated area 206 travels away from the illumination device 200 along the illumination axis 202. At this time, the illuminated area 206 becomes larger. In other words, through the oblique illumination axis 202, the angle of incidence 116 between the spectrometer 100 and the illuminated area 206 changes as the distance 204 changes. The illuminated area 206 may be referred to as a target. When the reflected light 206 in the illuminated area 106 by a

Aperture diaphragm 208 or lens optics 208 is incident on the photodetector 110, a position of an illumination spot caused by the reflected light 106 on the photodetector 110 changes with the angle of incidence 116. Here, the pixel field 134 has two neighboring pixels 136. The pixels are along a connecting line between the illumination device 200 and the Photodetector 110 aligned. Depending on the position of the

Illumination spots, a light intensity of the light 106 on the pixels 136 changes. The light intensity is again mapped in the intensity values of the pixels 136.

A typical eccentric light arrangement is shown in FIG. If 204 is measured at different distances, it will happen

different input angles 116. Between the pinhole 208 and the detector 110 is integrated as not shown spectral element, for example, a Fabry Perot filter, which responds sensitively to input angle changes. Input angle deviations from the detector axis 118 are always shifted to shorter wavelengths.

FIG. 3 shows an illustration of an illumination spot 300 incident centrally on a photodetector 110 according to an exemplary embodiment

Photodetector 110 essentially corresponds to the representations in FIGS. 1 and 2. Here, the pixel field 134 is circular and has four equal pixels 136. The pixels 136 are circular sector-shaped. The illumination spot 300 strikes the pixel field 134 substantially in the center. As a result, an illuminated area per pixel 136 is substantially identical. The pixels 136 convert the incidental portion of the light from the illumination spot 300 in FIG

Substantially the same electrical intensity values.

When using a pinhole or a lens system, the illumination spot 300 shifts laterally, depending on the distance on the detector 110. A pixel array 134 or a detector 110 divided into at least two parts may reflect the different centroids of the reflected

Measure illumination spots 300 on the detector 110. Here are the

Focal points measured using the four sectors 136. This difference is a measure of the angle of incidence and thus the distance of the target. Based on this data, the respective spectrum offset can be corrected by means of signal processing as in FIG.

Four-part detectors 110 may give an indication of sample homogeneity since lateral sectors 136 should have the same signal. Strength Differences may indicate a target inhomogeneity. Furthermore, it can be checked whether the illumination path or the mechanical

Positioning of the pinhole to the detector 110 has been changed.

At large incident angle intervals, it is advantageous that the

Focus analysis of the illumination spot 300 is performed over the entire spectrum, because different wavelengths and different angles of incidence are measured at the same time. Heavily varying spectra could lead to different measurement results depending on the setting of the spectral element. By measuring the entire spectrum and comparing the centroid positions, a plausibility check can be made

Measurement result can be achieved.

FIG. 4 shows a representation of a detected spectrum 104. The spectrum 104 is plotted in a diagram which has plotted the wavelength λ on the abscissa and an intensity on the ordinate. The measured spectrum 104 has been detected by light incident substantially perpendicular to a spectral element. For example, the spectrum 104 has been detected at the illumination spot shown in FIG. The spectrum 104 corresponds to an actual spectrum 400 or target spectrum due to the vertically incident light.

FIG. 5 shows illustrations of off-center illumination spots 300 impinging on a photodetector 110 according to an exemplary embodiment

Photodetector 110 is shown twice and essentially corresponds to the photodetector in FIG. 3. Here, the light has dropped obliquely through an optical system or aperture arranged in front of detector 110. The illumination spot 300 is thus shifted laterally on the pixel field 134. Here are the shares in the

Lighting spots 300 each unevenly distributed to the pixels 136 of the pixel array 134. Thus, the pixels 136 provide different intensity values.

FIG. 6 shows a representation of a spectrum 104 with offset 120. The spectrum 104 is plotted as in FIG. 4 in a diagram which has plotted the wavelength λ on the abscissa and an intensity on the ordinate. The

Spectrum 104 is light incident obliquely on a spectral element been recorded. For example, the spectrum 104 has been detected at one of the illumination spots shown in FIG. The intensity values of the spectrum 104 are shifted by the offset 120 relative to the actual spectrum 400.

Since the angle value of the angle of incidence can be determined using the different intensity values of the pixels in FIG

Correction value for compensating the offset 120 are read out, for example, from a stored table. Likewise, the correction value can be calculated by a calculation rule. The detected spectrum 104 can thus be shifted by the correction value in order to obtain the compensated spectrum 130, which essentially corresponds to the actual spectrum 400.

FIG. 7 shows a representation of a spectrometer 100 with a linearly variable filter 108 according to one exemplary embodiment. The spectrometer essentially corresponds to the spectrometer in FIG. 1. The pixel field 134 is embodied here as a matrix with pixels 136 in rows and columns. In this case, the rows are aligned with a filter direction of the linearly variable filter 108 or an x-direction, while the columns are oriented transversely to the filter direction or in ay direction. The linearly variable filter 108 has two dielectric mirrors 700, which have a decreasing distance from one another via the filter direction. The distance determines a transmitted wavelength. Due to the decreasing distance, the filter 108 passes through a wavelength profile in the filter direction, whereby the rows of the pixel field 134 detect the spectrum 104. The columns of the pixel array 134 detect the angle of incidence.

FIG. 8 shows a representation of a spectrometer 100 with an interferometer 108 according to one exemplary embodiment. The spectrometer corresponds to

Essentially the spectrometer in Fig. 2. The pixel array 134 is formed here as a matrix with pixels 136 in rows and columns. The interferometer 108 acts as the pinhole 208. The interferometer 108 passes one resonance wavelength and its harmonics at a time. The harmonics can be filtered out. The spectrum is chronologically consecutive subsequent individual measurements at each different transmitted wavelengths detected. In contrast to FIG. 7, both the rows and the columns detect the angle of incidence 116. The angle of incidence 116 is detected in two spatial directions.

In other words, FIG. 8 shows a spectrometer 100 with a Fabry-Perot interferometer 108 for distance measurement and for incident angle measurement.

Micromechanical Fabry-Perot interferometers (FPI) 108 consist of two mirror elements, which are arranged on a substrate above a through hole. Interferometers 108 may also be constructed of two substrates with through holes. The light beam 106 should be routed vertically through the sandwich design with two highly reflective mirrors, narrowband regions being transmitted around a resonant wavelength and their overtones depending on the distance between the two mirrors. By varying the distance, the desired resonant wavelength can be adjusted, measured in a subsequent detector 110, and a spectrum can thus be recorded serially. An additional band pass filter located in front of it can filter out the desired order so that errors due to other orders are minimized.

In Fabry-Perot interferometers (FPI) 108 as a linear variable filter 108 or mechanically tunable interferometer 108, a variation of the angle of incidence 116 of the light beam 106 causes a shift in the measured one

Wavelength. At the same time light rays 106 with different angles of incidence 116 on the spectral element 108, the possible

Wavelength resolution reduced. Spectra with strong

Transmissionsvariationen or absorption variations in a narrow wavelength range are therefore no longer well resolved. Is this

Distribution of the angle of incidence 116, however, centered by a certain angle 116 away from the normal 118, this leads to a shift of the entire spectrum, ie a wavelength offset error. In triangulation methods, the illumination axis and optical axis 118 of the detector 110 are different. In the case of vertical displacements of the target 206, the illumination spot is displaced laterally, which is measured by the detector 110.

In the approach presented here, a triangulation method is combined with the spectrum measurement technique.

In the case of spectrometers 100, the offset of the wavelength shift increases, the more dense the target 206 or object on the wavelength

Spectrometer 100 is positioned. With the same lateral displacement to the optical axis 118 of the spectrometer 100, this results in an increase of the angle of incidence 116 to the surface normal 118.

The closer the object can be positioned to the spectrometer 100, the more reflected power is collected and the signal to noise ratio can be improved. In this case, a collection of photons of an illuminating body with a certain angle of incidence and reflection, absorption or destructive interference of the unnecessary photons, so that no false signals are generated. An eccentric illumination of the target takes place in order to generate a lateral displacement of the illumination region 206 in relation to the optical axis 118 of the spectrometer 100. This shift produces a photon angle of incidence change on the

Spectrometer 100, which leads to an offset shift of the wave detection. The measurement of the illumination spot position is effected, for example, via the light centroid at the location of the detector 110. The device according to the approach presented here carries out a correction of the wavelength spectrum offset as a function of the illumination spot position on the detector 110. In one embodiment, the spectral element 108 is a linearly variable filter 108, as in FIG. 7. The illumination 200 is arranged eccentrically. A variation of the sample spacing results in a varying angle of incidence 116 of the diffusely reflected radiation. In each line, the linearly variable filter 108 provides a map of the spectrum. The variation of the angle 11 provides for a Displacement of the difference signal between the lines, from which the angle 116 can be determined.

9 shows a flowchart of a method 900 for operating a spectrometer according to an exemplary embodiment. The method 900 includes a step 902 of determining and a step 904 of compensating. In step 902 of the determination, a compensation value for compensating an offset of a spectrum detected by the spectrometer is subjected to

Using an angle value determined. The angle value represents an angle of incidence of light incident on the spectrometer during acquisition of the spectrum. In step 904 of compensating, the spectrum is compensated using the compensation value to obtain an angle compensated spectrum.

If an exemplary embodiment comprises a "and / or" link between a first feature and a second feature, then this is to be read so that the embodiment according to one embodiment, both the first feature and the second feature and according to another embodiment either only first feature or only the second feature.

Claims

claims

A device (102) for operating a spectrometer (100), the device (102) having the following features: a detection device (122) for determining a

Compensation value (126) for compensating for an offset (120) of a spectrum (104) detected by the spectrometer (100)

Using an angle value (128), the angle value (128) representing an angle of incidence (116) of light (106) incident upon the spectrometer (100) during detection of the spectrum (104); and compensating means (124) for compensating the

Spectrum (104) using the compensation value (126) to obtain an angle compensated spectrum (130).

2. Device (102) according to claim 1, with a

Angle detecting means (132) adapted to detect the angle of incidence (116) of light (106) incident on the spectrometer during detection of the spectrum (104) and to map it in the angle value (128).

3. Device (102) according to claim 2, wherein the

Angle detecting means (132) comprises a photodetector (110) having a pixel array (134) with a plurality of each one intensity value (112) providing pixels (136), wherein the

Angle detection device (132) is designed to under

Using the intensity values (112) to determine the angle value (128).

The apparatus (102) of claim 3, further comprising illumination means (200) disposed laterally offset from the photodetector (110), the pixels (136) being disposed on an axis between the

Lighting device (200) and the photodetector (110) are aligned.

5. Device (102) according to one of claims 3 to 4, wherein the pixels (136) are arranged two-dimensionally flat, wherein in a first direction aligned pixels (136) are formed to detect the spectrum (104) and transversely thereto aligned pixels (106) are configured to provide the intensity values (112).

6. Device (102) according to one of claims 3 to 5, wherein the

Photodetector (110) is adapted to detect the spectrum (104).

7. spectrometer (100) with a device (102) according to one of

Claims 1 to 6.

8. Spectrometer (100) according to claim 7, in which a spectral element (108) of the spectrometer (100) is designed as a linearly variable filter (108).

9. spectrometer (100) according to claim 7, wherein a spectral element (108) of the spectrometer (100) is designed as a micromechanical interferometer (108).

10. A method (900) for operating a spectrometer (100), the method (900) comprising the following steps:

Determining (902) a compensation value (126) for compensating an offset (120) of one detected by the spectrometer (100)

Spectrum (104) using an angle value (128), wherein the angle value (128) represents an angle of incidence (116) of light (106), which has collapsed onto the spectrometer (100) during acquisition of the spectrum (104); and

Compensating (902) the spectrum (104) using the compensation value (126) to obtain an angle compensated spectrum.

A computer program configured to execute the method (900) of claim 10.

12. A machine-readable storage medium on which the computer program according to claim 11 is stored.