Sensor device for monitoring a laser processing process and a laser processing system with the same

Abstract

The present invention relates to a sensor device for monitoring a laser processing process, the sensor device comprising: at least one filter module for filtering a process beam generated during the laser processing process, and a sensor unit for detecting the intensity of the filtered process beam in at least two measuring channels by means of at least two photosensors, wherein the filter module is configured to adapt at least a partial wavelength range of the process beam that can be detected in one of the measuring channels of the sensor unit. A laser processing system with the sensor device is also specified.

Description

[0001] The present invention relates to a sensor device for monitoring a laser processing process, in particular a sensor device for monitoring a laser processing process (in particular a laser welding process) with optical filtering of the optical process emissions, and a laser processing system with the sensor device. Technical background

[0002] In a laser processing system, also known as a laser processing unit, the laser beam emitted from a laser beam source or the end of a laser fiber is directed onto the workpiece using beam guidance and focusing optics. The processing can include laser welding or laser cutting. The laser processing system can include a laser processing head, such as a laser welding head or a laser cutting head, in which the optics are arranged. The laser processing process can, for example, include a laser welding process and a laser cutting process.

[0003] To ensure the quality of the processing, it is essential to continuously monitor the laser processing process. This monitoring is typically achieved by capturing and analyzing the optical process emissions generated during the laser processing, i.e., light reflected back from the process. These optical process emissions include laser radiation backscattered or reflected from the workpiece (so-called laser back reflection), radiation generated in the (near-)infrared wavelength range (so-called infrared wavelength range), e.g., containing thermal radiation from a melt pool, and radiation generated in the visible wavelength range, e.g., containing radiation from a plasma generated during processing. These optical process emissions can also be referred to as process radiation or process beam.

[0004] The process beam is typically detected by photodiodes. These photodiodes can be part of a sensor unit mounted on the laser processing head. The process beam is coupled into the sensor unit via the laser processing head. Within the sensor unit, the process beam is split into partial beams with different wavelength ranges by a beam splitter arrangement with one or more beam splitters featuring a wavelength-selective coating, or by optical filters downstream of the beam splitter arrangement. The photodiodes each detect the intensity of a corresponding partial beam with the specified wavelength range and generate a corresponding sensor signal. This sensor signal represents the average intensity of the respective wavelength range. Changes in the measured intensity relative to reference data indicate errors that may have occurred during the laser processing operation.For monitoring purposes, the sensor signal profiles are compared with predefined envelopes and / or threshold values, and an error is reported if a sensor signal lies outside the envelopes or exceeds or falls below a threshold value. Error detection can be further optimized by evaluating the intensity of different wavelength ranges.

[0005] To ensure versatile application possibilities for the sensor unit in process monitoring, it is usually designed with relatively broadband measurement channels. Typical sensor units have one measurement channel each for the visible wavelength range, the infrared wavelength range, and for the laser beam wavelength (also called the "back-reflection wavelength range"), which generally enables good process monitoring and, due to the broadband design, is not limited to predefined applications. Because of the broadband measurement channels (e.g., with a width of approximately 500 nm or more), only the total intensity of the corresponding partial beam can be detected across a large, i.e., broadband, wavelength range (so-called integral sensor signal or integral intensity measurement) and used for process monitoring.

[0006] In certain cases, however, a more precise definition of the measurement channels or a higher spectral resolution is advantageous for fault detection or process monitoring. However, retrofitting a typical sensor unit, which is often a self-contained functional unit, is not easily possible. In this case, replacing the sensor unit would be necessary.

[0007] For example, the sensor unit records the sensor signal for the visible spectrum in the wavelength range of 350 nm to 850 nm, the sensor signal for the laser back reflection in the wavelength range of 1000 nm to 1100 nm, and the sensor signal for the infrared wavelength range in the wavelength range greater than 1200 nm. Intensity changes of different wavelengths contained in the respective measurement channel cannot be distinguished, which reduces the error sensitivity due to the lower relative change signal. In the worst case, certain errors cannot be detected at all, where the intensity changes of different wavelengths in the measurement channel cancel each other out.

[0008] Furthermore, the different wavelength ranges of the partial beams partially overlap, as complete separation of the wavelength ranges is not possible with the beam splitter. When measuring the intensity of the respective partial beams—a phenomenon exacerbated by the broadband spectral sensitivity of the photosensors—crosstalk occurs, meaning the photosensors also detect the intensity of unwanted wavelength ranges. To remove the unwanted wavelength ranges from a partial beam, additional filters must be placed after the beam splitter.

[0009] On the other hand, it is often desirable for other economic and / or technical reasons to provide a sensor unit that has measurement channels with the broadest possible spectral sensitivity in the three wavelength ranges mentioned, in order to enable a sensor unit that can be used as universally as possible for process monitoring. Summary of the invention

[0010] The inventors have recognized that such integral intensity measurement, or intensity measurement in a broadband wavelength range, can be disadvantageous for precise monitoring of laser processing processes, especially laser welding processes.

[0011] Since the sensor signal corresponds to the average intensity of the process beam in the detected wavelength range, no changes are detectable in the sensor signal for certain process errors, even though there is a change in intensity at individual wavelengths in the wavelength range.

[0012] This will be demonstrated using Fig. 9 explained. Fig. Figure 9 shows a diagram illustrating the intensity of the process beam during laser welding in a broadband wavelength range (λ1 to λ3), for example, the visible wavelength range. The solid line shows the intensity of the process beam as a function of wavelength λ at a time when a process error occurs, while the dashed line shows the intensity for laser welding without the process error. On the left side of the diagram (partial wavelength range λ1 to λ2), the process error results in a decrease in intensity compared to the case without the process error, while on the right side (partial wavelength range λ2 to λ3), the intensity increases compared to the case without the process error. However, if only a sensor signal for the intensity in the large or small wavelength range is used, the diagram will show a different result.Since the broadband wavelength range between λ1 and λ3 is captured, changes within the individual sub-wavelength ranges λ1 to λ2 and λ2 to λ3 cannot be detected because the intensity changes in the two sub-wavelength ranges cancel each other out. Consequently, the process error and a defectively welded workpiece resulting from the process error cannot be detected.

[0013] It is therefore an object of the present invention to provide a sensor device that enables improved, in particular more precise, monitoring of a laser processing process and that enables improved detection of process errors.

[0014] It is an object of the present invention to provide a sensor device that enables the monitoring of a laser processing process based on intensities of a process beam, which are detected independently and separately for several different wavelength ranges.

[0015] It is an object of the present invention to provide a sensor device with a high spectral resolution with respect to material-specific emission ranges, in particular in the visible wavelength range.

[0016] It is an object of the present invention to provide a sensor device whose spectral sensitivity can be adapted for process monitoring of various laser processing processes.

[0017] It is an object of the present invention to provide a sensor device that can be used flexibly for process monitoring.

[0018] It is particularly an object of the present invention to provide a sensor device that makes it possible to individually adapt, in particular to design as narrowband, a partial wavelength range of the process beam that can be detected in a measuring channel for monitoring the laser processing process.

[0019] It is an object of the present invention to provide a sensor device that makes it possible to individually design and / or adjust the amplification of a sensor signal for different wavelength ranges of the process beam.

[0020] It is also an object of the invention to provide a laser processing system with such a sensor device.

[0021] At least one of these problems is solved by the subject matter of the independent claims. Advantageous embodiments and further developments are the subject matter of dependent claims.

[0022] The present invention is based on the understanding that monitoring a laser processing operation is disadvantageous if the intensity of the process beam is only measured in large, broadband measurement channels. This means that certain effects or defects of the laser processing operation cannot be detected because the measured intensity only represents the average intensity within the broadband measurement channel. Furthermore, relying solely on broadband measurement channels makes precise design and adjustment of the monitoring system difficult or impossible. A measurement channel can be defined as a spectral wavelength range for which the sensor unit is configured to acquire a corresponding sensor signal. The sensor unit can have multiple measurement channels and thus acquire multiple sensor signals. The sensor signal can then be evaluated and / or recorded.For example, the sensor unit can have one measurement channel each in the visible wavelength range, the infrared wavelength range, and the back-reflect wavelength range. The width of a measurement channel is determined by the spectral sensitivity of the corresponding photodiodes themselves, as well as by optical elements of the sensor device, such as filters or beam splitters, in the beam path of the process beam or a partial beam thereof upstream of the corresponding photodiode. A measurement channel, therefore, does not exclusively represent the spectral sensitivity range of a photosensor.

[0023] The present invention is based on the idea of ​​filtering the process beam in a sensor device with a sensor unit using a filter module such that at least one partial wavelength range of the process beam, detectable in one of the measuring channels of a sensor unit of the sensor device, is adapted within the (continuous) spectrum of the process beam. Thus, by means of the filter module, a partial wavelength range detectable by a measuring channel is adapted within the spectrum of the process beam, in particular by limiting and / or narrowing it on one or both sides. The adapted partial wavelength range is narrower than the unadapted partial wavelength range. In other words, the adapted partial wavelength range detectable in one measuring channel is narrower than the measuring channel (or the wavelength range of this measuring channel) itself.

[0024] Subsequently, the intensity of the process beam filtered by the filter module can be individually or separately recorded in the respective measuring channels using the photosensors of the sensor unit.

[0025] Compared to conventional solutions, the present invention offers the possibility of expanding an existing sensor unit by adding a filter module. The "pre-filtering" in the filter module, in combination with the downstream elements of the sensor unit, e.g., optical filters, beam splitters, etc., allows for a customized adjustment of the sensor device with respect to one or more measurement channels for a specific application. Unlike optical filters in a partial beam after a beam splitter in the sensor unit, the filter module is positioned upstream of these elements of the sensor unit.

[0026] It is not essential to the invention whether the filter module is provided within the sensor unit itself, or whether the filter module is a separate component positioned in the process beam path upstream of the sensor unit. In the latter case, existing sensor units without a pre-existing filter module can be retrofitted. In this case, the filter module can have a self-contained, enclosed housing with optical input and output and be positioned upstream of the sensor unit. This enables a modular design of the sensor unit or sensor device.

[0027] The filter module is thus to be understood as a supplementary component to a sensor unit with predefined measurement channels, serving to optimize the existing (broadband) measurement channels for specific processes. The resulting, adapted partial wavelength ranges of the process beam, which can be detected in the respective measurement channels, are narrower compared to the sensor unit without the filter module. This increases the spectral resolution of the sensor unit with respect to the respective individual measurement channels. The spectral resolution of the sensor device according to the invention can then be determined by both the sensor unit and the optical filtering in the filter module.For example, for an existing sensor unit, a single long-pass filter in the filter module can be a possible filter design to limit the visible wavelength range of the measurement channel (by setting a new lower measurement range limit) without changing the other measurement channels.

[0028] The filter module allows existing sensor units with broadband measurement channels to be retrofitted or supplemented for the precise detection of intensity in a narrowband wavelength range. Furthermore, it enables a modular design of the sensor unit or sensor device. This allows the sensor unit to be used with different filter modules for various predefined laser processing processes, each requiring monitoring in a different narrowband wavelength range. In this case, the filter module can be designed as a filter cartridge or as a filter insert within a filter cartridge. The filter module can therefore be a coaxial filter cartridge module with a filter insert containing at least one filter. This allows for a simple, modular, and cost-effective process-specific design of the sensor unit.

[0029] By individually measuring the intensity in a specific, narrower partial wavelength range of the process beam, more precise monitoring of the laser processing process is enabled. This is because the intensity in this wavelength range is measured without superposition, allowing certain process errors to be detected for the first time or more effectively. In particular, the intensity of the process beam can be measured and monitored at one or more specific material-related emission wavelengths.

[0030] The acquisition, processing, and / or evaluation of the adapted partial wavelength range can be performed separately from the other partial wavelength ranges of the process beam, and thus individually. The corresponding sensor signals can be amplified separately and / or differently from one another. This allows each generated sensor signal to be subjected to individual amplification. The present invention, for example, allows individual amplification of the sensor signals of the wavelength ranges over a wide order of magnitude, for example by a factor of 10 to 10 7 or 10 8 .

[0031] The term "visible wavelength range" refers to a range of wavelengths that predominantly consist of wavelengths in the visible spectrum of light. Specifically, the visible wavelength range can be or encompass wavelengths between 350 nm and 850 nm, between 390 nm and 850 nm, or between 380 nm and 800 nm.

[0032] The term "infrared wavelength range" refers to a range of wavelengths that include wavelengths in the infrared spectral range. In particular, the infrared wavelength range can be or encompass a wavelength range greater than 1200 nm, especially between 1200 nm and 2100 nm.

[0033] The term "back-reflection wavelength range" refers to a wavelength range that encompasses the wavelength of the laser beam, which lies, for example, between 1000 nm and 1100 nm.

[0034] Furthermore, a "visible partial beam" refers to a partial beam in the visible wavelength range, an "infrared partial beam" to a partial beam in the infrared wavelength range, and a "back-reflection partial beam" to a partial beam in the back-reflection wavelength range. "Non-overlapping" wavelength ranges mean that no wavelength from one wavelength range is contained in the other. "Non-overlapping" is synonymous with "completely different."

[0035] A partial wavelength range of the process beam that can be detected and / or is detected in one of the sensor unit's measurement channels can be referred to as a measurement channel wavelength range (of the process beam). For example, if the sensor unit has three measurement channels, the process beam's spectrum can comprise three measurement channel wavelength ranges. For the purposes of this disclosure, detecting a wavelength range or a (partial) beam means detecting the intensity within that wavelength range or the intensity of the (partial) beam.

[0036] If elements are numbered, for example by "first element", "second element", "third element", etc., this numbering is not intended to indicate a preferred order, but merely to distinguish the elements.

[0037] According to one aspect of the present disclosure, a sensor device for monitoring a laser processing process for machining a workpiece using a laser beam is specified. The sensor device comprises at least one filter module for filtering a process beam generated during the laser processing process, and a sensor unit for detecting the intensity of the filtered process beam in at least two measurement channels by means of at least two photosensors. The filter module is configured to adapt at least a partial wavelength range of the process beam that can be detected in one of the measurement channels of the sensor unit (measurement channel wavelength range of the process beam).

[0038] The adjustment can be achieved by limiting at least one partial wavelength range on one or both sides, in particular by filtering the wavelengths that lie outside the desired partial wavelength range.

[0039] Other measurement channel wavelength ranges or wavelength ranges of other measurement channels are preferably not adapted by the filter module, i.e., they pass through the filter module essentially unchanged.

[0040] According to another aspect of the present disclosure, a laser processing system is specified. The laser processing system comprises a laser processing head, configured to direct a laser beam onto a workpiece to perform a laser processing process, and a sensor device according to aspects and embodiments of the present disclosure.

[0041] The aspects of the present disclosure may exhibit one or more of the following optional features.

[0042] The sensor unit can include at least two photosensors.

[0043] The filter module can be arranged, particularly coaxially, in the beam path of the process beam. The filter module can be arranged in the beam path of the process beam upstream of the sensor unit. The sensor unit can be arranged in the beam path of the process beam. The sensor unit can be arranged in the beam path of the process beam filtered by the filter module.

[0044] The filter module and the sensor unit can be arranged coaxially. The filter module can be arranged coaxially in the beam path of the process beam upstream of the sensor unit. The filter module can be arranged in the beam path of the process beam, particularly upstream of the first beam splitter and / or upstream of a focusing optic of the sensor unit. The filter module and the sensor unit can be arranged on the same axis.

[0045] In particular, an optical axis of the filter module and an optical axis of the sensor unit can be coaxial to each other and / or each coaxial to an optical axis of the sensor device and / or a beam axis of the process beam entering the sensor device.

[0046] The optical axis of the filter module can be defined as a central axis of the filter module. The sensor unit can include focusing optics through which the process beam enters the sensor unit. In this case, the optical axis of the sensor unit can be defined by the focusing optics of the sensor unit. The sensor device can have an optical input, and the optical axis of the sensor device can also be defined as a central axis of the optical input. Furthermore, the sensor device can include focusing optics, such as a focusing lens, for focusing the process beam entering the sensor device. In this case, the focusing optics can define an optical axis of the sensor device.

[0047] The filter module and / or its components, particularly optical elements such as optics, lenses, or optical filters, can be designed to be inserted and / or replaced within the sensor device. The filter module can be designed to be inserted between the sensor unit and the housing of a laser processing head.

[0048] The filter module can be designed as a filter cartridge and / or a filter insert. A filter cartridge can, in particular, refer to a filter module sealed by protective glass. This simplifies the modular design of the sensor device. The filter insert can be inserted into a housing of the sensor device. The filter insert or filter cartridge can comprise one or more individual filters.

[0049] The sensor device may further comprise the housing. The housing may define the exterior of the sensor device. The housing or the sensor device may have an optical inlet for introducing the process beam into the housing or the sensor device. The at least one filter module and / or the sensor unit may be arranged within the housing or be designed to be inserted into it.

[0050] Alternatively or additionally, the filter module and the sensor unit can each comprise their own housing, and / or can be designed as independent and / or self-contained components.

[0051] The sensor device may include a coupling device for connecting the sensor device to a laser processing head. The coupling device may be arranged on and / or attached to the housing. The coupling device may include an optical input.

[0052] The at least one adapted measurement channel wavelength range of the process beam can be 250 nm or less, in particular 100 nm or less, in particular 50 nm or less, in particular 25 nm or less, in particular 10 nm or less. In other words, the adapted partial wavelength range can have a spectral width of 250 nm or less, in particular 100 nm or less, in particular 50 nm or less, in particular 25 nm or less, in particular 10 nm or less.

[0053] The adapted measurement channel wavelength range can include visible or (near) infrared wavelengths. The adapted measurement channel wavelength range can include at least one wavelength selected from: 400 nm, 500 nm, 600 nm, 700 nm, 750 nm, 800 nm, a wavelength equal to or greater than 1200 nm, a wavelength equal to or greater than 1300 nm, a wavelength of an emission line of aluminum oxide, a wavelength of an emission line of iron oxide, an atomic emission line of a machining material or an alloying component of a machining material, and a wavelength of an atomic emission line, in particular of copper, aluminum, or iron. In particular, a mean or central wavelength of the adapted measurement channel wavelength range can correspond to one of the wavelengths listed.

[0054] The sensor device can include at least one beam splitter. The at least one beam splitter, i.e., one or more beam splitters, can form a beam splitter arrangement. The beam splitter can be configured to extract a partial beam from the filtered process beam. The partial beam can comprise a wavelength or wavelength range within the at least one matched measurement channel wavelength range. Alternatively or additionally, the at least one partial beam can comprise a wavelength or wavelength range corresponding to another measurement channel, i.e., a measurement channel that does not include the said partial wavelength range of the process beam, and / or a wavelength or wavelength range within a non-matched measurement channel wavelength range of the process beam.

[0055] For example, a first coupled partial beam may cover a wavelength range in the matched measurement channel wavelength range, and / or a second coupled partial beam may cover a wavelength range in a non-matched measurement channel wavelength range.

[0056] A first photosensor of the sensor unit can be configured to detect the intensity of the first partial beam. A second photosensor of the sensor unit can be configured to detect the intensity of the second partial beam.

[0057] For example, a coupled partial beam can comprise a first wavelength range within the adapted measurement channel wavelength range and a second wavelength range that differs from the first. The sensor unit can include a so-called sandwich photodiode (two-color sandwich photodiode) as one of the photosensors. A first photodiode of the sandwich photodiode can be configured to detect the intensity of the partial beam in the first wavelength range and can be transparent to wavelengths in the second wavelength range. A second photodiode of the sandwich photodiode can be positioned downstream of the first photodiode in the beam propagation direction and / or be configured to detect the intensity of the partial beam in the second wavelength range.

[0058] The at least one beam splitter can have a wavelength-specific coating.

[0059] The multiple photosensors can be configured to detect the intensity of a corresponding portion of at least one of the beams. Each photosensor can be configured to generate a corresponding sensor signal based on the detected intensity. A sensor signal, in particular its strength, can represent the intensity of the detected wavelength range. The sensor signals can be analog or digital signals. The sensor signals can be voltage signals.

[0060] Each of the photosensors can include or be one of at least one of the following elements: a photosensitive chip, a photosensitive element, a photodiode, a photodiode array, a camera, a pixel array, a CMOS chip, a CCD chip, a spectrometer, a sandwich photodiode, and an optical sensor.

[0061] The width of the spectral sensitivity range (also called spectral sensitivity) of the photosensors, especially the first photosensor, can be 500 nm or more, especially 750 nm or more.

[0062] The filter module can comprise at least one filter. The filter module can comprise one or more filters. The at least one filter can be configured as a notch filter, a long-pass filter, a short-pass filter, a multibandpass filter, or a multi-notch filter. The sensor device can comprise multiple filter modules.

[0063] A transmission wavelength range of the filter module or filter can define a wavelength range that is transmitted through the filter module or filter. The filter module or filter can also have a blocking wavelength range. The blocking wavelength range can define a wavelength range that is not transmitted or is blocked by the filter module or filter. A blocking wavelength range can be spectrally positioned between two transmission wavelength ranges. That is, the two transmission wavelength ranges can be spectrally separated by the blocking wavelength range. In this way, the filter module can be designed to be process-specific, in order to adapt to a broadband measurement channel wavelength range of the process beam. The respective transmission wavelength ranges of the filter module can be defined as non-overlapping.

[0064] At least one of the transmission wavelength ranges of the filter module can be a unidirectional (i.e., semi-open) wavelength range. This transmission wavelength range can be 100 nm or more, in particular 500 nm or more, wide. In other words, this transmission wavelength range can have a spectral width of 100 nm or more, in particular 500 nm or more.

[0065] The filter module can include a multibandpass filter. Alternatively or additionally, the filter module can include a longpass filter and a notch filter. The filter module can have a first transmission wavelength range and a second transmission wavelength range. The first transmission wavelength range can be narrowband. The second transmission wavelength range can be broadband. The first transmission wavelength range can be within the visible wavelength range. The second transmission wavelength range can include wavelength ranges in the back-reflection and infrared wavelength ranges.The first transmission wavelength range and the second transmission wavelength range can be separated from each other by a blocking wavelength range.

[0066] The laser processing system comprises a laser processing head, configured to project a laser beam onto a workpiece for laser processing, and a sensor device according to one of the preceding embodiments. The laser processing head may include at least one beam splitter for decoupling the process beam from the laser beam path and / or for decoupling the process beam to the sensor device. The beam splitter of the laser processing head may be located within the housing of the laser processing head. The beam splitter may be located in the laser beam path and in the beam path of the process beam generated during the laser processing process and entering the laser processing head. The beam splitter may be arranged to decoupling the process beam from the laser beam path to the sensor device.

[0067] The laser processing system may also include a control unit. The control unit may be configured to receive and / or adjust the gain and / or evaluate the sensor signals. In particular, the control unit may be configured to evaluate the sensor signals separately. The control unit may also be configured to control the laser processing process and / or to regulate and / or monitor the laser processing process based on the sensor signals. In particular, the control unit may be configured to detect, based on the sensor signals, whether a process error has occurred in the laser processing process.

[0068] The control unit can be configured to evaluate and / or record the sensor signals. In particular, the evaluation of the sensor signals can be performed separately for each sensor signal. Consequently, each wavelength range and / or each measurement channel can be evaluated and monitored independently. The control unit can also be configured to convert the (analog) sensor signals into digital signals.

[0069] The laser processing system, in particular the control unit, can be set up to adjust an individual gain for each sensor signal.

[0070] The laser processing process can include or be laser welding, laser cutting, laser brazing, or laser cladding on a workpiece. The workpiece can be a metallic workpiece.

[0071] According to another aspect of the present disclosure, a sensor device for monitoring a laser processing process for processing a workpiece using a laser beam is specified.The sensor device comprises at least one filter module configured to filter the process beam generated during the laser processing process, wherein the at least one filter module has at least one narrowband transmission wavelength range, and at least one broadband transmission wavelength range and / or at least one further narrowband transmission wavelength range, and a sensor unit for detecting the intensity of the filtered process beam, comprising at least one beam splitter configured to divide the filtered process beam into at least two partial beams, and at least two photosensors, each of which is configured to detect the intensity of a corresponding partial beam of the at least two partial beams.

[0072] According to a further aspect of the present disclosure, a sensor device for monitoring a laser processing process for machining a workpiece using a laser beam is specified. The sensor device comprises a filter module or several filter modules for filtering a process beam generated during the laser processing process, wherein the filter module has at least one narrowband transmission wavelength range and at least one broadband transmission wavelength range, and a sensor unit for detecting the intensity of the filtered process beam, wherein the sensor unit comprises at least one beam splitter for extracting a first partial beam with the narrowband transmission wavelength range from the filtered process beam and a first photosensor for detecting the intensity of the first partial beam. Brief description of the characters

[0073] Embodiments of the present disclosure are described below with reference to the figures. The figures show: Fig. 1 a laser processing system according to embodiments of the present disclosure; Fig. 2A, Fig. 2B Schematic views of a sensor device according to embodiments of the present disclosure; Fig. 3A, Fig. 3B Schematic views of a sensor device according to embodiments of the present disclosure; Fig. 4A, Fig. 4B Schematic views of a sensor device according to embodiments of the present disclosure; Fig. 5A, Fig. 5B Schematic views of a filter module according to embodiments of the present disclosure; Fig. 6A-6C Diagrams illustrating a transmission spectrum of a filter module and adapted measurement channel wavelength ranges according to embodiments of the present disclosure; Fig. 7A, Fig. 7B Diagrams illustrating a transmission spectrum of a filter module and adapted measurement channel wavelength ranges according to embodiments of the present disclosure; Fig. 8A, Fig. 8B Diagrams illustrating a transmission spectrum of a filter module and of adapted measurement channel wavelength ranges according to embodiments of the present disclosure; and Fig. 9 a diagram to illustrate a sensor signal for the intensity of the process beam during laser welding in a broadband wave range. Detailed description

[0074] Corresponding elements and sizes are always provided with the same reference symbols in all figures.

[0075] Unless otherwise noted, the same reference symbols are used for identical and equivalent elements in the following text. Redundant descriptions of recurring features are avoided. The various embodiments and features of the figures described below are expressly combinable and should not be understood as complete embodiments.

[0076] Fig. Figure 1 shows a laser processing system according to embodiments of the present disclosure.

[0077] The laser processing system 10 is set up to perform a laser processing process and includes a laser processing head 12. To perform a laser processing process, a laser beam (not shown) is directed onto a workpiece 14 by means of the laser processing head 12, which may include collimating, focusing, and / or beam-shaping optics. This causes the material of the workpiece 14 to heat up, melt, and possibly vaporize. The workpiece 14 can be a metallic workpiece and may, in particular, be made of iron, stainless steel, or aluminum. The laser processing process may include laser welding, laser cutting, laser brazing, or laser cladding.

[0078] During the laser processing process, a process beam 16 is generated, which enters the laser processing head 12 and is coupled out from a beam path of the laser beam (not shown) by a beam splitter 17. The process beam 16 comprises the laser radiation backscattered or reflected by the workpiece 14, radiation in the infrared wavelength range of light, e.g., thermal radiation from a melt pool, and radiation in the visible wavelength range of light, e.g., radiation from a plasma generated by the processing. The process beam typically has a continuous wavelength spectrum.

[0079] To extract the process beam 16, the laser processing head 12 can have a first coupling device 18 and an optical output (not shown). The optical output can be combined with the first coupling device 18. The process beam is extracted via the optical output of the laser processing head 12.

[0080] The laser processing system 10 further comprises a sensor device 20 for monitoring the laser processing process according to embodiments of the present disclosure. The sensor device 20 can also be referred to as a detector. Monitoring is carried out by detecting the intensity of the process beam 16 generated during the laser processing process. The sensor device 20 includes an optical input (not shown) for introducing or coupling the process beam 16 into the sensor device 20. The sensor device 20 can further comprise a second coupling device 24 for coupling the sensor device 20 to the laser processing head 12. The coupling device 24 can be combined with the optical input and / or the coupling device 24 can include the optical input.

[0081] The beam splitter 17 for extracting the process beam can be arranged downstream of a focusing optic (not shown) of the laser processing head in the beam path of the process beam 16 within the laser processing head 12. The process beam 16 can thus be coupled into the sensor device 20 in a collimated state. Furthermore, the sensor device 20 and / or the sensor unit 28 can include a focusing optic, for example, a focusing lens, for focusing the process beam 16 coupled into the sensor device 20. The beam axis 27 of the process beam 16 can coincide with an optical axis of the focusing optic. The focusing optic can be used to focus the process beam 16 or partial beams, described later, onto photosensors, also described later.

[0082] The in Fig. The laser processing system 10 shown in Figure 1 can further include a control unit 50 that receives the sensor signals from all photosensors. The control unit 50 can be configured to regulate the laser processing process based on the received sensor signals. In particular, the control unit can be configured to detect, based on the received sensor signals, whether a process error has occurred in the laser processing process. The control unit can also be configured to set an individual gain for each sensor signal.

[0083] The control unit can also be configured to evaluate and / or record the sensor signals. The evaluation of the sensor signals can be performed separately for each sensor signal or independently of the other sensor signals. Consequently, each wavelength range can be evaluated and monitored separately.

[0084] The sensor device 20 is described in detail below.

[0085] Fig. 2A, Fig. Figure 2B shows schematic views of a sensor device for monitoring a laser processing process for processing a workpiece using a laser beam according to embodiments of the present disclosure.

[0086] The sensor device 20 comprises a filter module 32 and a sensor unit 28 with at least one beam splitter 30 and at least one first photosensor 31a and a second photosensor 31b, which can be, for example, photodiodes. The filter module 32 is arranged to filter the process beam 16 generated during the laser processing process and coupled into the sensor device 20.

[0087] A beam axis 27 of the process beam 16, or beam axes of partial beams 36a, 36b of the process beam 16, are illustrated by lines extending from the optical input (not shown). The filter module 32 and the sensor unit 28 are arranged in the beam path of the process beam 16, or along the beam axis 27 of the process beam 16. More precisely, the filter module 32 is arranged along the beam path of the process beam 16 upstream of the sensor unit 28. The filter module 32 can be arranged in the beam path of the process beam entering or coupled into the sensor device 20, and optionally in the beam path of the process beam focused by a focusing optic (not shown). The sensor unit 28 is arranged in the beam path of the process beam filtered by the filter module 32.

[0088] The filter module 32 is arranged coaxially in front of the sensor unit 28. The filter module 32 and the sensor unit 28 are arranged coaxially with respect to the beam axis 27. In particular, the optical axis of the filter module 32 and the optical axis of the sensor unit 28 are arranged coaxially with each other and each coaxially with respect to the beam axis 27 of the process beam. The optical axis of the filter module 32 can be defined as a central axis of the filter module 32. The optical axis of the sensor unit 28 can be defined as a central axis of one of the elements of the sensor unit 28. For example, the optical axis of the sensor unit 28 is defined by the central axis 37 of the beam splitter 30. Any beam offset of the process beam 16 caused by the beam splitter can be neglected here. The photosensor 31a is arranged coaxially with respect to the beam axis of the partial beam 36a. The photosensor 31b is arranged coaxially with respect to the beam axis of the partial beam 36b.

[0089] The beam splitter 30 of the sensor unit 28 is configured to split the filtered process beam into a first partial beam 36a and a second partial beam 36b (which can also be described as coupling the partial beams out of the process beam) and direct them onto the photosensors 31a and 31b. For this purpose, the beam splitter 30 can have a corresponding wavelength-specific coating. The first photosensor 31a is configured to detect the intensity of the first partial beam 36a, and the second photosensor 31b is configured to detect the intensity of the second partial beam 36b.

[0090] The purpose of the filter module is to adapt, in particular to restrict, the measurement channel wavelength range of the process beam for at least one of the measurement channels for improved process monitoring.

[0091] The in Fig. 2A and Fig. The sensor unit 28 shown in Figure 2B detects two (broadband) measurement channels using the two photosensors 31a, 31b and generates corresponding sensor signals. The sensor device 20 therefore comprises two measurement channels. The process beam 16 is split, as shown, into two partial beams 36a, 36b by the beam splitter 30, each partial beam encompassing wavelengths in one of the two measurement channels. The intensity of each partial beam 36a, 36b is detected by one of the photosensors 31a, 31b.

[0092] The present disclosure is not limited to this, however. The sensor unit 28 can be configured to detect multiple measurement channel wavelength ranges using photosensors arranged in the beam path of a partial beam of the process beam 16. This is possible, for example, using "two-color sandwich photodiodes," which have two photosensitive chips arranged one behind the other with different spectral sensitivity ranges. This enables the separate detection of a first, for example visible, wavelength range and a second, for example (near)infrared, wavelength range within a single partial beam.

[0093] Furthermore, the present disclosure is not limited to two measurement channels. A sensor unit can also comprise more than two, in particular three or four, measurement channels.

[0094] The sensor unit 28 may include at least one focusing optic and / or optical filters (not shown).

[0095] The filter module 32 can be designed as a standalone component and / or as a filter cassette, and can in particular be designed to be inserted into or replaced by the sensor device 20. This is shown in Fig. 2B is illustrated by a double arrow on filter module 32.

[0096] Fig. 3A and Fig. Figure 3B shows schematic views of a sensor device for monitoring a laser processing process for processing a workpiece using a laser beam according to further embodiments of the present disclosure.

[0097] The embodiments of Fig. 3A and Fig. 3B differ from the embodiments of Fig. 2A and 2B are essentially characterized by the presence of several beam splitters 30a, 30b and three photosensors 31a-c. The embodiment of the sensor device 20 is configured to acquire sensor signals for three measurement channels using the three photosensors 31a-c. The sensor device 20 of Fig. 3A and Fig. 3B therefore comprises three measurement channels.

[0098] The beam splitters 30a and 30b of the sensor unit 28 are configured to extract the first to third partial beams 36a-c from the filtered process beam 16 and direct them to the corresponding first to third photosensors 31a-c. For example, the first beam splitter 30a extracts a first partial beam 36a to the first photosensor 31a. The first photosensor 31a is configured to detect the intensity of the first partial beam 36a. The second beam splitter 30b splits the portion of the process beam transmitted by the first beam splitter 30a into the second partial beam 36b and the third partial beam 36c. The second photosensor 31b is configured to detect the intensity of the second partial beam 36b, and the third photosensor 31c is configured to detect the intensity of the third partial beam 36c. Photosensor 31a is arranged coaxially to the beam axis of partial beam 36a. Photosensor 31b is arranged coaxially to the beam axis of partial beam 36b.The photosensor 31c is arranged coaxially to the beam axis of the partial beam 36c.

[0099] The photosensors 31a, 31b and, if applicable, 31c are each configured to generate a corresponding sensor signal, for example, an analog voltage signal, based on the intensity detected. For example, the voltage level can be a measure of the intensity of the respective detected wavelength range.

[0100] Fig. 4A and Fig. Figure 4B shows schematic views of a sensor device for monitoring a laser processing process for processing a workpiece using a laser beam according to further embodiments of the present disclosure.

[0101] The in Fig. 4A and Fig. The sensor devices shown in 4B differ from those in Fig. 2A and Fig. 2B and Fig. 3A and Fig. The sensor devices shown in Figure 3B 20 are characterized by the presence of three or more beam splitters or four or more photosensors. The Fig. 5A and Fig. The sensor unit 28 shown in 5B can therefore include four or more measurement channels.

[0102] Fig. 5A, Fig. Figure 5B shows schematic views of a filter module according to embodiments of the present disclosure. Fig. Figure 5A shows a filter module 32, which is designed as a filter cassette. The filter module 32 has three filters 35. Each of the filters 35 is designed as a filter module that can be inserted into the filter cassette, as illustrated by the double arrows in the figure. Fig. 5B shows a filter module 32, which differs from the one in Fig. The filter module shown in 5A differs in that it has more than three filters 35.

[0103] Fig. Figures 6A-6C show diagrams illustrating a transmission spectrum of a filter module and adapted measurement channel wavelength ranges according to embodiments of the present disclosure.

[0104] The grey areas 34a, 34b, 34c in the Fig. 6A and Fig. Figure 6B illustrates partial wavelength ranges of the process beam that can be detected in a measurement channel of the downstream sensor unit (measurement channel wavelength ranges). Accordingly, the sensor unit comprises three measurement channels. The measurement channel wavelength range 34a for the first measurement channel of the sensor unit is to be adjusted to reflect the Fig. The narrower measurement channel wavelength range 34a' shown in Figure 6C is obtained. The measurement channel wavelength range 34a or 34a' can include wavelengths or wavelength ranges in the visible wavelength range. The measurement channel wavelength range 34b can include wavelengths or wavelength ranges in the back-reflection wavelength range. The measurement channel wavelength range 34c can include wavelengths or wavelength ranges in the infrared wavelength range.

[0105] As in Fig. As shown in Figure 6A, a bandpass filter with a narrowband transmission wavelength range in the first measurement channel wavelength range 34a can be provided in the filter module 32. The bandpass filter further comprises a broadband transmission wavelength range encompassing the second and third measurement channel wavelength ranges 34b, 34c of the process beam. The bandpass filter can be configured as a multibandpass filter or include one.

[0106] The narrowband transmission wavelength range is or encompasses a wavelength range in the visible wavelength range. The broadband transmission wavelength range encompasses wavelength ranges in the back-reflection wavelength range and in the infrared wavelength range.

[0107] This allows the second and third measurement channel wavelength ranges 34b, 34c to pass through the filter module largely unchanged.

[0108] Alternatively, as in Fig. As shown in Figure 6B, a long-pass filter and a notch filter can be provided in filter module 34. The superposition of the transmission wavelength ranges of these filters yields the same result as in Figure 6B. Fig. 6A shows the transmission spectrum of the filter module.

[0109] The in Fig. 6A and Fig. The filter module discussed in 6B adapts the measurement channel wavelength range 34a by limiting the measurement channel wavelength range on both sides.

[0110] Fig. 7A and Fig. Figure 7B shows diagrams illustrating a transmission spectrum of a filter module and adapted measurement channel wavelength ranges according to embodiments of the present disclosure.

[0111] In Fig. 7B is the narrower measurement channel wavelength range 34a' shown, starting from the in Fig. The measurement channel wavelength range 34a shown in 7A can be obtained.

[0112] For this purpose, (only) a long-pass filter is provided in filter module 34. The long-pass filter is designed such that the measurement channel wavelength range 34a is limited only on one side, namely its lower side. The upper side is defined by the measurement channel of the sensor unit, which is determined or limited not only by the spectral sensitivity range of the corresponding photosensor, but also by other optical elements such as beam splitters and optical filters of the sensor unit.

[0113] Fig. 8A and Fig. Figure 8B shows diagrams illustrating a transmission spectrum of a filter module and adapted measurement channel wavelength ranges according to embodiments of the present disclosure.

[0114] The in Fig. The narrower measurement channel wavelength ranges 34a' and 34c' shown in Figure 8B are intended to be derived from those in Fig. The measurement channel wavelength ranges 34a and 34c shown in 8A can be obtained.

[0115] A multibandpass filter is provided in the filter module for this purpose. Alternatively, a longpass filter, two notch filters, and a shortpass filter can be provided. The multibandpass filter comprises a first narrowband transmission wavelength range in the first measurement channel wavelength range 34a, a second broadband transmission wavelength range encompassing the second measurement channel wavelength range 34b, and a third narrowband transmission wavelength range located in the third measurement channel wavelength range 34c.

[0116] This allows the second measurement channel wavelength range 34b to pass through the filter module largely unchanged.

[0117] The present invention implements a process-specific spectral evaluation of process radiation. This is achieved by pre-filtering through at least one filter, which is integrated into a filter module upstream of the sensor unit. According to the present invention, a universally applicable, broadband (coaxial) multi-channel sensor device, which offers great flexibility and universal applicability precisely because of its broadband sensitivity, is combined with a filter module to ensure comprehensive yet precise process monitoring. This enables the use of a universal broadband (coaxial) multi-channel detector while simultaneously allowing for the flexibility of individual, process-specific spectral filtering for improved fault detection. Retrofitting existing broadband multi-channel detectors with a corresponding filter module is also possible.

Claims

[1] Sensor device (20) for monitoring a laser processing process, the sensor device (20) comprising: - at least one filter module (32) for filtering a process beam (16) generated during the laser processing process, and - a sensor unit (28) for detecting the intensity of the filtered process beam (16) in at least two measurement channels by means of at least two photosensors (31a-c), wherein the filter module (32) is configured to adapt at least a partial wavelength range of the process beam that can be detected in one of the measuring channels of the sensor unit (28). [2] Sensor device according to claim 1, wherein the filter module (32) is arranged in the beam path of the process beam (16) in front of the sensor unit (28) and / or wherein the filter module (32) and the sensor unit (28) are arranged on an axis and / or coaxially to each other. [3] Sensor device according to one of the preceding claims, wherein the filter module (32) and / or elements contained therein are provided interchangeably in the sensor device (20), and / or wherein the filter module (32) is designed as a filter cassette and / or as a filter insert. [4] Sensor device according to one of the preceding claims, further comprising a housing with an optical inlet for introducing the process beam (16) into the housing, wherein the filter module (32) and the sensor unit (28) are arranged inside the housing. [5] Sensor device according to one of the preceding claims, wherein the at least one adapted partial wavelength range (34a', 34c') of the process beam (16) has a spectral width of 250 nm or less, a spectral width of 100 nm or less, a spectral width of 50 nm or less, a spectral width of 25 nm or less, or a spectral width of 10 nm or less. [6] Sensor device according to one of the preceding claims, wherein the at least one adapted partial wavelength range (34a', 34c') of the process beam (16) (33a) includes at least one wavelength selected from: 400 nm, 500 nm, 600 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 1200 nm, 1300 nm, a wavelength of an emission line of aluminium oxide, a wavelength of an emission line of iron oxide, and a wavelength of an atomic emission line, in particular of copper, aluminium or iron. [7] Sensor device according to one of the preceding claims, further comprising at least one beam splitter (30a,b), wherein at least one beam splitter (30a,b) is set up to couple out at least one partial beam (36a-c) from the filtered process beam (16) according to one of the measuring channels of the sensor unit (28). [8] Sensor device according to claim 7, wherein the at least two photosensors (31a-c) are configured to detect an intensity of a corresponding of the at least one partial beam (36a-c). [9] Sensor device according to one of the preceding claims, wherein each photosensor (31a-c) comprises at least one of the following elements: a photosensitive chip, a photosensitive element, a photodiode array, a camera, a pixel array, a CMOS chip, a CCD chip, a spectrometer, and an optical sensor. [10] Sensor device according to one of the preceding claims, wherein the filter module (32) comprises at least one filter (35) selected from: notch filter, long-pass filter, short-pass filter, multi-band-pass filter and multi-notch filter. [11] Sensor device according to one of the preceding claims, wherein the filter module (32) comprises a multibandpass filter or the filter module comprises a longpass filter and a notch filter, and / or wherein the filter module has a first transmission wavelength range which is or includes a wavelength range in the visible wavelength range, and wherein the filter module has a second transmission wavelength range which includes wavelength ranges in the back-reflection wavelength range and in the infrared wavelength range. [12] Laser processing system (10), comprising: - a laser processing head (12) configured to direct a laser beam onto a workpiece (14) to perform a laser processing process, and - a sensor device (20) according to one of the preceding claims. [13] Laser processing system according to claim 12, wherein the laser processing head (12) comprises at least one beam splitter (17) configured to decouple the process beam (16) from the beam path of the laser beam to the sensor device (20). [14] Laser processing system according to claim 12 or 13, wherein the photosensor (31a-c) is configured to generate a sensor signal based on the detected intensity, and wherein the laser processing system (10) further comprises a control unit (50) which is configured to evaluate and / or record the sensor signal and / or to monitor and / or control the laser processing process based on the sensor signal.

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