DE202021100643U1 - Spectrally sensitive optoelectronic device for monitoring a surveillance area - Google Patents

Abstract

Device (10, 40, 70, 100, 140) for monitoring a surveillance area (12, 154).
- at least one reference structure (30, 90, 130, 152) for generating reference light (32, 52, 82, 132, 160) with a predetermined spectral characteristic,
- at least one light receiver (20, 62, 92, 120, 144a, ..., 144n) for detecting received light (38, 58, 88, 138, 158) from the monitored area (12, 154) and for generating received signals the received light (38, 58, 88, 138, 158), wherein the received light (38, 58, 88, 138, 158) the reference light (32, 52, 82, 132, 160) and/or from objects (34, 162 ) includes object light (36, 56, 86, 136, 164) remitted and/or reflected in the monitored area (12, 154),
- A control and evaluation unit (24, 124, 150) for controlling the light receiver (20, 62, 92, 120, 144a, ..., 144n) and for receiving the received signals, characterized in that the control and evaluation unit ( 24, 124, 150) is designed to determine a detected spectral characteristic of the received light (38, 58, 88, 138, 158) from the received signals, the detected spectral characteristic of the received light (38, 58, 88, 138, 158) to compare it with the specified spectral characteristic of the reference light (32, 52, 82, 132, 160) and to trigger a safety-related action if the detected spectral characteristic deviates from the specified spectral characteristic.

Description

The invention relates to a spectrally sensitive optoelectronic device for monitoring a surveillance area according to the preamble of claim 1.

The primary goal of safety technology is to protect people from sources of danger, such as those presented by machines in an industrial environment. The machine is monitored with the help of sensors, and accordingly, if there is a situation where a person threatens to come dangerously close to the machine, an appropriate safety measure is taken.

Conventionally, primarily optoelectronic sensors such as light grids or laser scanners are used for safety-related monitoring. More recently, 3D cameras have been added. Sensors used in safety technology must work particularly reliably and therefore meet high safety requirements, for example the EN 13849 standard for machine safety and the IEC61496 or EN61496 device standard for electro-sensitive protective equipment (ESPE). A number of measures must be taken to meet these safety standards, such as reliable electronic evaluation using redundant, diverse electronics, function monitoring or special monitoring of the contamination of optical components.

A common protection concept provides for protective fields to be configured that operating personnel are not allowed to enter while the machine is in operation. An optoelectronic safety sensor captures geometric information about its surroundings and relates this to an internally stored geometry of a protective field. Specifically, preconfigured protective fields or protective volumes are programmed, and an intersection of the measured surrounding contour with these protective areas is detected. If the sensor detects an inadmissible intrusion into the protective field in this way, such as an operator's leg, the machine is prompted to switch to a safe state.

the EP 0 793 208 A2 describes a spectral detection for a safety-related application, wherein an intrusion of an object (for example the intrusion of a hand into a machine) is determined by detecting thermal radiation. Exemplary embodiments with detection in the optical wavelength range are also described, with a predetermined spectral signature of the interfering object being recognized in each case. Therefore, for example, to detect a hand, a reflector with a known spectral signature must be arranged on the hand (eg on a glove).

From the EP 2 064 480 B1 a machine tool monitoring device is known which, based on a spectral evaluation, can make a distinction between a material to be processed and human tissue and derive safety-critical actions. It is therefore also necessary here to determine the spectral signature of the interfering object. The device mentioned works with ultra-broadband (or Ultra Wide Band or UWB) signals which have a frequency spectrum with a center frequency in the frequency range from 1 GHz to 15 GHz (ie in the radar range), so that the spatial resolution is limited.

the EP 2 233 818 B1 describes a safety sensor that can reliably distinguish a safety-critical object from other, non-safety-critical objects by means of a spectral analysis carried out in the safety sensor.

The methods from the prior art mentioned are based on the recognition of known spectral signatures of objects in order to detect their intrusion into a surveillance area. The disadvantage here is that the spectral signatures of the objects must be known or learned, or the objects must be marked with known spectral signatures.

It is therefore the object of the invention to specify an improved spectrally sensitive optoelectronic device for monitoring a monitoring area.

The invention is based on the basic idea that a monitoring area has at least one reference structure that generates light with a predetermined spectral characteristic (also referred to below as “reference light”), which is received by one or more light receivers of a spectrally sensitive optoelectronic sensor (also referred to below as “ Spectral sensor") is detected and converted into received signals.

The reference light can be generated passively by the reference structure (for example by remission and/or reflection of transmitted light or by luminescence induced by transmitted light) or actively (for example by a reference light source).

The term "spectral characteristic" is to be understood as the spectral composition of light, in particular the light emitted, remitted and/or reflected by the reference structure and/or objects in the monitored area, which is detected by the light receiver as received light.

If there is no object in the monitored area, the reference light reaches the light receiver as received light with unchanged, specified spectral characteristics. An object encroaching on the monitoring area between the reference structure and the spectral sensor leads to a changed or completely unspecific spectral characteristic of the received light, which can be detected by the spectral sensor. A control and evaluation unit is designed to compare the detected spectral characteristic of the received light with the specified spectral characteristic of the reference light. In the event of a predetermined deviation of the detected spectral characteristic from the specified spectral characteristic, the control and evaluation unit can trigger a safety-related action. The principle of negative classification is thus applied, with elements that are not safety-relevant being detected first and a fault in the detection being evaluated as a safety-critical event.

The reference structure can be designed, for example, as a reference surface that forms a background of a surveillance area to be monitored. In a further embodiment, the reference structure can be arranged at the edges of the surveillance area to be monitored. The area to be monitored by the spectral sensor is then limited to these edges, and entry and/or exit of an object into or out of the monitored area can be detected.

The spectral characteristic of the reference light can have a continuous wavelength spectrum or discrete wavelengths or wavelength ranges. Continuous spectra or discrete wavelengths or wavelength ranges can be, for example, in the visible (VIS, 450nm - 780nm) or in the near-infrared (NIR, 800nm - 2500nm) wavelength range.

The reference light can be generated in different ways. On the one hand, a transmitted light source can illuminate the reference structure with transmitted light, in which case the transmitted light can have a predetermined spectral composition. The spectral composition of the transmitted light can be broadband, have discrete wavelengths or wavelength ranges, or change over time (frequency chirp). By remission and/or reflection of the transmitted light, the reference structure generates reference light with a predetermined spectral characteristic that results from the spectral composition of the transmitted light and the reflection and/or remission behavior of the reference structure. The reference light can be detected by the spectrally sensitive optoelectronic sensor. If, when an object enters the monitored area, there is a change in the spectral composition of the light detected by the spectral sensor due to the remission and/or reflection properties of the object, a safety-related action can be triggered as described above. The remission and/or reflection properties of the reference structure can preferably be selected in such a way that they differ from the remission and/or reflection properties of the objects to be detected.

In an alternative embodiment, the reference light can be generated by luminescence of the reference structure. The reference structure can have one or more luminescent, in particular fluorescent materials, which are illuminated with preferably ultraviolet or blue transmitted light and emit wavelength-shifted reference light to the transmitted light. By suitably selecting the luminescent material or materials, reference light with a predetermined spectral characteristic can be generated. The luminescent materials can preferably be selected in such a way that the spectral characteristic of the reference light clearly differs from the spectral characteristic of the transmitted light remitted and/or reflected as object light by the objects to be detected.

In the NIR spectral range, the spectral characteristics of the reference light can be generated, for example, by absorption spectra that result from the excitation of harmonics and combination vibrations in organic molecular bonds (OH, CH, NH, C=O, SH) of a material of the reference structure. The material can preferably be selected in such a way that the spectral characteristic of its absorption spectrum clearly differs from the spectral characteristic of the absorption spectra of the objects to be detected. If, for example, the intervention of a hand is to be detected as a security-relevant intervention, plastics, wood or other organic materials are preferably suitable as materials for the reference structure, since these are clearly distinguishable from human skin with regard to their spectral characteristics.

In the case of a spectral characteristic that is characterized by discrete wavelengths or wavelength ranges, selected characteristic absorption bands of the material can serve as a reference. In this case, a spectral analysis through targeted detection can be less discrete Wavelengths or wavelength ranges are accelerated and ambiguous spectral regions in which the reference structure and the objects to be detected emit light with similar spectral characteristics are avoided.

In a further embodiment, the reference structure can have at least one reference light source with a predetermined spectral characteristic for generating the reference light.

The reference structure can have a large number of substructures, it being possible for the substructures to generate reference light with different spectral characteristics. The partial structures can form a pattern, for example two ring-shaped zones arranged in a circle around an object to be monitored. If the object moves out of the surveillance area, there will first be a change in the spectral characteristic of the reference light in the inner zone. If the object moves further, there will also be a change in the spectral characteristic of the reference light in the outer zone. In this way, additional location information can be determined from a change in the spectral characteristic of the reference light, and the monitoring of the monitored area can thus be improved.

The spectrally sensitive optoelectronic sensor is preferably designed as an imaging spectral sensor, so it can determine spatially resolved spectral data of objects in the monitored area and in particular of the reference structure, for example by point-by-point scanning with a scanning spectrometer. In a further embodiment, the spectrally sensitive optoelectronic sensor can be designed as a multispectral or hyperspectral camera or as a multiphysical 3D camera. The sensor can also be designed as an arrangement of one or more spectrally sensitive point or line sensors, for example Fabry-Perot interferometers.

The spectral sensor can be set up to evaluate discrete wavelengths or wavelength ranges (multispectral evaluation) instead of the entire wavelength spectrum of the received light, as a result of which the amount of data is reduced and the evaluation is simplified and accelerated.

In one embodiment, the spectral sensor can be designed in such a way that the light receiver receives a time sequence of light of discrete wavelengths or wavelength ranges, for example by the reference structure being illuminated with a time sequence of transmitted light of discrete wavelengths or wavelength ranges or actively emitting it itself. The discrete wavelengths or wavelength ranges can also overlap. A spectral splitting of the received reference light is then not necessary, the spectral sensitivity results from the time-resolved detection and the a priori information about the time sequence of the wavelengths of the transmitted light. For this purpose, the control and evaluation unit can synchronize the light transmitter and light receiver.

The control and evaluation unit can be designed for a teach-in mode in which the specified spectral characteristic of the reference light is taught in when the monitoring area is free. This can be done during production or later in the field. In production, for example, devices in which the reference structure, light transmitter and light receiver are already combined in one module can be calibrated. In the field, teaching in or calibrating the specified spectral characteristics can be part of a calibration or maintenance process, with environmental conditions of the device, for example external light sources, being able to be taken into account in particular.

A filter for filtering the transmitted light can be connected upstream of the light receiver. Influencing of the spectral analysis of the received light by transmitted light and/or ambient light can thus be reduced.

The spectral sensor can also be set up to record spatial data such as the size or shape of the objects in addition to the spectral data of the objects and/or the reference structure. This allows objects to be classified according to size or shape, for example. If both spectral data and spatial data are recorded, a diverse evaluation of the recorded data is possible.

The spectral sensor can also be designed to link and logically process spectral data of the objects and/or the reference structure or evaluation results such as the deviation of the detected spectral characteristic from the specified spectral characteristic of the received light with results from other safety sensors such as light grids. The security of a system comprising a plurality of security sensors can thus be increased.

• 1 eine schematische Darstellung einer Ausführungsform der erfindungsgemäßen Vorrichtung
• 2 eine schematische Darstellung einer alternativen Ausführungsform der erfindungsgemäßen Vorrichtung
• 3 eine schematische Darstellung einer weiteren Ausführungsform der erfindungsgemäßen Vorrichtung mit einer mehrere Teilstrukturen aufweisenden Referenzstruktur
• 4 eine schematische Darstellung einer Ausführungsform der erfindungsgemäßen Vorrichtung mit einer Referenzstruktur, die eine eigene Lichtquelle aufweist
• 5 eine schematische Darstellung einer Ausführungsform der erfindungsgemäßen Vorrichtung als Lichtgitter

The invention is explained in more detail below, also with regard to further features and advantages, by way of example on the basis of embodiments and with reference to the attached drawing. The illustrations of the drawing show in:

• 1 a schematic representation of an embodiment of the device according to the invention
• 2 a schematic representation of an alternative embodiment of the device according to the invention
• 3 a schematic representation of a further embodiment of the device according to the invention with a reference structure having a plurality of substructures
• 4 a schematic representation of an embodiment of the device according to the invention with a reference structure having its own light source
• 5 a schematic representation of an embodiment of the device according to the invention as a light grid

1 shows a schematic representation of an embodiment of a device 10 according to the invention for monitoring a monitored area 12 . A control and evaluation unit 24 is connected to the transmitted light source 16 and the light receiver 20 and set up to control the transmitted light source 16 and the light receiver 20 and to receive received signals from the light receiver 20 . The control and evaluation unit 24 can evaluate the received signals and, based on the evaluation, trigger a safety-related action via an interface 26, for example activating a warning light, switching off a machine or sending a signal to a higher-level safety controller.

Transmitted light 28 emitted by the transmitted light source 16 with a spectral characteristic that includes a large number of wavelengths (polychromatic transmitted light) is projected by the transmitting optics 18 onto a reference structure 30 arranged in or at the edge of the monitoring area 12 and is projected by the reference structure 30 as reference light 32 remitted and/or reflected with a predetermined spectral characteristic. The reference structure 30 therefore generates the reference light 32 by remission and/or reflection of the transmitted light 28, the specified spectral characteristics of the reference light 32 resulting from the spectral composition of the transmitted light 28 and the remission and/or reflection behavior of the reference structure 30. If there is an object 34 in the monitored area 12 , the transmitted light 28 is remitted and/or reflected by the object 34 as object light 36 . Reference light 32 and/or object light 36 travel back to the sensor 16 as received light 38 and are imaged by the receiving optics 22 onto the light receiver 20 and detected by the latter. The light receiver 20 is designed as a multispectral or hyperspectral camera and has a large number of receiving elements 20a, 20b arranged in a matrix, with each receiving element 20a, 20b being able to determine an intensity and spectral composition of the received light 38 detected by the receiving element 20a, 20b, which as received signals from the Control and evaluation unit 24 are received. The control and evaluation unit 24 is designed to determine a detected spectral characteristic of the received light 38 from the received signals and to compare this with the specified spectral characteristic of the reference light 32 stored in the control and evaluation unit. The specified spectral characteristic of the reference light 32 can be determined theoretically (from the known spectral composition of the transmitted light 28 and the remission and/or reflection behavior of the reference structure 30) or in a learning process. If an object 34 is located in the monitored area 12 , the reference light 32 is mixed with the object light 36 , so that the spectral characteristic of the received light 38 differs from the specified spectral characteristic of the reference light 32 . In this way, an intervention by the object 34 in the monitored area 12 can be detected and the control and evaluation unit 24 can trigger a safety-related action.

2 shows a schematic representation of an alternative embodiment of a device 40 according to the invention for monitoring a monitoring area 12. In contrast to that in FIG 1 In the embodiment described, the sensor 44 has a plurality of transmitted light sources 46a, 46b, 46c, each transmitted light source 46a, 46b, 46c emitting transmitted light 48 of a predetermined discrete wavelength (or a wavelength range) that differs from the wavelengths (or wavelength ranges) of the other Transmission light sources emitted transmission light is at least partially different. The transmitted light sources 46a, 46b, 46c are activated alternately, so that only one of the transmitted light sources 46a, 46b, 46c emits transmitted light 48, which is projected from the transmission optics 50 onto a reference structure 30 arranged in or at the edge of the monitored area 12 and from the reference structure 30 is remitted and/or reflected as reference light 52 with a predetermined spectral characteristic. If an object 34 is located in the monitored area 12, the transmitted light 48 is remitted and/or reflected by the object 34 as object light 56. Reference light 52 and/or object light 56 travel back to the sensor 44 as received light 58 and are imaged by the receiving optics 60 onto the light receiver 62 and detected by the latter. In contrast to in the 1 In the embodiment described, the light receiver 60 does not have to operate spectrally selectively, but rather only be designed to measure an intensity of the received light 58 . The control and evaluation unit 24 is set up to synchronize the transmitted light sources 46a, 46b, 46c and the light receiver 60 in such a way that the received signals generated by the light receiver 60 are assigned the respective wavelength of the transmitted light 46 and the spectral characteristics of the received light 58 are thus recorded can. The recorded spectral characteristic of the received light 58 can then be used as in 1 shown exemplary embodiment can be compared with a predefined spectral characteristic of the reference light 52 stored in the control and evaluation unit. The specified spectral characteristic of the reference light 52 can be determined theoretically (from the known spectral composition of the transmitted light 48 and the remission and/or reflection behavior of the reference structure 30) or in a learning process. If an object is located in the monitored area 12 , the reference light 52 is mixed with the object light 56 so that the spectral characteristic of the received light 58 differs from the specified spectral characteristic of the reference light 52 . In this way, an intervention by the object 34 in the monitored area 12 can be detected and the control and evaluation unit 24 can trigger a safety-related action.

3 shows a schematic representation of an alternative embodiment of a device 70 according to the invention for monitoring a monitoring area 12. In contrast to in the 1 and 2 In the exemplary embodiments shown, the reference structure 90 has two partial structures 90a, 90b, which are designed as fluorescent areas. After being illuminated by the transmitted light 78 emitted by the transmitted light source 76, the fluorescent regions of the partial structures 90a, 90b emit reference light 82a, 82b, which is red-shifted in relation to the transmitted light 78, ie has a longer wavelength. The wavelengths of the transmitted light 78 can be adapted to the fluorescence properties of the fluorescent areas of the partial structures 90a, 90b. A filter 94 for filtering the transmitted light 78 is connected upstream of the light receiver 92 . The light receiver 92 is designed to be spectrally sensitive, for example as in FIG 1 described embodiment as a multispectral or hyperspectral camera and has a multiplicity of receiving elements 92a, 92b arranged in a matrix, wherein each receiving element 92a, 92b can determine an intensity and spectral composition of the received light 88 detected by the receiving element, which is received as received signals by the control and evaluation unit 24 will. In principle, however, the use of a non-spectrally selective light receiver with an arrangement of alternately activated transmission light sources as in 3 described embodiment possible, wherein the transmitted light sources alternately emit transmitted light with wavelengths adapted to the fluorescence properties of the fluorescent regions, and the detection of the received light is synchronized with the activation of the transmitted light sources. As explained in relation to the previous exemplary embodiments, an intervention by an object 34 in the monitored area 12 leads to a change in the spectral characteristics of the received light 88, in this exemplary embodiment essentially because the substructures 90a, 90b of the reference structure 90 designed as fluorescent areas are designed in this way that their fluorescence properties differ from those of the object 34 to be detected, so that the spectral characteristic of the received light 88 differs from the specified spectral characteristic of the reference light 82 when the object 34 enters.

The partial structures 90a, 90b of the reference structure 90 of the exemplary embodiment are designed as concentric, circular fluorescent regions with different fluorescence properties, so that the spectral characteristics of the reference light 82a, 82b generated by the two partial structures 90a, 90b differ. When the object 34 enters the monitoring area 12, the spectral characteristic of the received light 88 changes depending on the coverage of the partial structures 90a, 90b by the object 34, so that a change in the spectral characteristic of the received light 88 changes a position of the object 34 in relation to a center point 94 of the concentric, circular partial structures 90a, 90b can be determined

In 4 a further embodiment of a device 100 according to the invention is shown. In contrast to the previous exemplary embodiments, the reference structure 130 has its own light source. The reference light 132 is therefore not generated by remission or reflection of transmitted light or by luminescence (e.g. fluorescence) excited by transmitted light, but rather the reference structure 130 has a reference light source 116 controlled by the control and evaluation unit 24, which actively emits reference light 132 with a predetermined spectral characteristic emits. If an object 34 enters the monitoring area 12, the object light 136 emitted by the object 34, for example reflected ambient light, mixes with the reference light 132 and reaches the light receiver 120 as received light 138, which, due to the mixture, has a spectral characteristic that differs from the specified spectral Characteristic of the reference light 132 deviates. Consequently the intervention of an object 34 in the monitored area 12 can be detected as in the exemplary embodiments described above. Like the transmission light sources described above, the reference light source 116 can emit broadband reference light or can include several reference light sources emitting reference light of discrete wavelengths or wavelength ranges, the latter being able to be activated alternately by the control and evaluation unit 24 . Likewise, different substructures of the reference structure 130 can be compared to in 3 The embodiment shown emit reference light with different spectral characteristics, for example by reference light sources with reference light with different spectral characteristics being assigned to the different areas.

5 shows another possible embodiment of the invention as a scanning light grid 140. The light grid 140 has a transmitting and receiving module 142 with a plurality of light receivers 144a, ..., 144n and associated receiving optics 146a, ..., 146n and a light transmitter 148 with associated Transmission optics 150 on. The light transmitter 148 and the light receivers 144a, . . . , 144n are connected to a control and evaluation unit 150. A reference structure 152 is arranged opposite the transmission and reception module 142 , so that the area between the transmission and reception module 142 and the reference structure 152 forms a monitoring area 154 . As is usual with a scanning light grid, control and evaluation unit 150 is set up to calculate the light propagation times between the emission of transmitted light 156 and the reception of received light 158, which consists of transmitted light 152 remitted and/or reflected by objects in monitoring region 150 and/or reference structure 148 is formed to determine. If an object enters the monitored area 150 between a transmitting and receiving module 142 and the reference structure 148, the light propagation time is shortened, as a result of which an intervention by the object in the monitored area can be detected. In addition to measuring the light propagation time, the spectral characteristics of the received light 158 can be detected according to the invention, for example comparable to that in 2 described embodiment. For this purpose, the light transmitter 148 has a multiplicity of transmitted light sources 148a, 148b, 148c, which emit transmitted light 156 with a predetermined discrete wavelength (or a wavelength range) which differs from the wavelengths (or the wavelength ranges) of the transmitted light emitted by the respective other transmitted light sources at least partly different. The transmission light sources 148a, 148b, 148c are activated alternately, so that only one of the transmission light sources 148a, 148b, 148c emits transmission light 156, which is projected by the transmission optics into the monitoring area 154 and by the opposite reference structure 152 as reference light 160 with a predetermined spectral Characteristic is remitted and / or reflected. If an object 162 is located in the monitoring area 154, the transmitted light 156 is remitted and/or reflected by the object 162 as object light 164. Reference light and/or object light return to the sensor as received light 158 and are detected by light receivers 144a, . . . , 144n. The control and evaluation unit 150 is set up to synchronize the transmitted light sources 148a, 148b, 148c and the light receivers 144a, ..., 144n in such a way that the received signals of the light receivers 144a, ..., 144n are assigned the respective wavelength of the transmitted light 156 is assigned and thus the spectral characteristic of the received light 158 can be detected. The recorded spectral characteristic of the received light 158 can be compared with the predefined spectral characteristic of the reference light 160 stored in the control and evaluation unit 150 . Object recognition is thus possible in a diverse manner both by measuring the light propagation time and by detecting the spectral characteristics of the received light 158 .

The latter exemplary embodiment relates to a scanning light grid with a central light transmitter 148 and a large number of light receivers 144a, ..., 144n, the transmitted light emitted by the light transmitter 148 being used both for the scanning function of the light grid by analyzing the light propagation time and for the spectral Monitoring of the monitoring area 154 is formed. Of course, other variants of a combination of the device according to the invention with known light grids are also conceivable here. Thus, in the exemplary embodiment shown above, a plurality of light transmitters 148, in particular one light transmitter 148 per light receiver 144a, . . . , 144n, can be provided. Furthermore, a conventional scanning (or non-scanning) light grid can also be combined with spectral monitoring according to the invention, it being possible for the spatial monitoring by the light grid to take place in a different wavelength range than the spectral monitoring. The light receiver of the light grid and the light receiver for spectral monitoring can have optical bandpass filters to reduce interference signals from the respective other light emitters, so that spectral monitoring can take place simultaneously with spatial monitoring. The spectral and spatial monitoring results can then be combined and logically processed, increasing the security of the system.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 0793208 A2 [0005]
• EP 2064480 B1 [0006]
• EP 2233818 B1 [0007]

Claims (10)

Device (10, 40, 70, 100, 140) for monitoring a monitored area (12, 154) with - at least one reference structure (30, 90, 130, 152) for generating reference light (32, 52, 82, 132, 160) with a predetermined spectral characteristic, - at least one light receiver (20, 62, 92, 120, 144a, ..., 144n) for detecting received light (38, 58, 88, 138, 158) from the monitored area (12, 154) and for generating received signals from the received light (38, 58, 88, 138, 158), the received light (38, 58, 88, 138, 158) the reference light (32, 52, 82, 132, 160) and/or object light (36, 56, 86, 136, 164) remitted and/or reflected by objects (34, 162) in the surveillance area (12, 154), - a control and evaluation unit (24, 124, 150) for controlling the light receiver (20, 62, 92, 120, 144a, ..., 144n) and for receiving the received signals, characterized in that the control and evaluation unit (24, 124, 150) is designed to, from the Emp capture signals to determine a detected spectral characteristic of the received light (38, 58, 88, 138, 158), the detected spectral characteristic of the received light (38, 58, 88, 138, 158) with the predetermined spectral characteristic of the reference light (32, 52, 82, 132, 160) and to trigger a safety-related action if the detected spectral characteristic deviates from the specified spectral characteristic. device (10, 40, 70, 140). claim 1 , characterized in that the device (10, 40, 70, 140) has at least one transmitted light source (16, 46a, 46b, 46c, 76, 148a, 148b, 148c) for illuminating the reference structure (30, 90, 152) with transmitted light ( 28, 48, 78, 156). Device (40, 140) according to claim 2 , characterized in that the device (40, 140) has a plurality of transmission light sources (46a, 46b, 46c, 148a, 148b, 148c). device (10, 40, 70, 140). claim 2 , characterized in that the reference light (32, 52, 82, 160) is generated by remission and/or reflection of the transmitted light (28, 48, 78, 156) on the reference structure (30, 90, 152). device (10, 40, 70, 140). claim 2 , characterized in that the reference light (32, 52, 82, 160) is generated by luminescence, in particular by fluorescence of the reference structure (30, 90, 152). Device according to one of claims 2 until 5 , wherein the control and evaluation unit (24, 150) is designed to control the at least one transmission light source (16, 46a, 46b, 46c, 76, 148a, 148b, 148c). Device (100) according to claim 1 , characterized in that the reference structure (130) for generating the reference light (132) has at least one reference light source (116). Device (100) according to claim 7 , wherein the control and evaluation unit (124) is designed to control the reference light source (116). Device (10, 40, 70, 100, 140) according to one of the preceding claims, characterized in that the reference structure (30, 90, 130, 152) at least partially delimits the monitoring area (12, 154). Device (70) according to one of the preceding claims, characterized in that the reference structure (90) has at least two substructures (90a, 90b), a first substructure (90a) generating first reference light (82a) with a first predetermined spectral characteristic, and a second partial structure (90b) generates second reference light (82a) with a second predetermined spectral characteristic.

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