Method for monitoring a laser processing process, and laser processing system

Abstract

A method for monitoring a laser processing system is specified. The method comprises the steps of: acquiring, in a monitoring period, measured values of a measured variable of the laser processing process; comparing the measured values with value ranges of the measured variable of a plurality of process levels; determining whether the measured values lie in one of the value ranges of the process levels; and, if the measured values lie in one of the value ranges of the process levels, setting the process level, in the value range of which the measured values lie, for monitoring the process.

Description

[0001] Method for monitoring a laser processing process and laser processing system

[0002] The present disclosure relates to a method for monitoring a laser processing process. Furthermore, the present disclosure relates to a laser processing system and a computer program product configured to carry out the method.

[0003] background

[0004] In a laser processing system, also known as a laser processing machine or simply a machine, a laser beam is directed at the workpiece to be processed. The processing can include laser welding, laser cutting, laser engraving, or laser hardening.

[0005] To ensure the quality of the processing, the laser processing process can be monitored. A sensor or sensor unit can detect process emissions generated during the laser processing. The sensor data can be compared with specified limit values ​​and / or envelopes. If the sensor data lies outside the envelopes or exceeds or falls below a limit, a fault in the laser processing process is detected.

[0006] A faultless laser processing process can occur even if the sensor data lie outside the specified envelope curves or exceed or fall below the limit values. For example, the sensor data for a "cold" system, i.e., a system with a short operating time, can differ significantly from the sensor data for a "warm" system, i.e., a system with a longer operating time. In both cases, however, the laser processing process can proceed without faults. Sensor data indicating faultless operation can also differ significantly between different laser processing processes, different positions in a scan field of a laser scanner system, different component tolerances of the laser processing system, and / or different production or material batches. Disclosure of the Invention

[0007] It is an object of the present disclosure to provide a method and / or a laser processing system by which monitoring of a laser processing process, in particular online monitoring, is improved.

[0008] A further object of the present disclosure is to provide a method and / or a laser processing system by which error detection of the laser processing process is improved. In particular, an object of the present disclosure is to provide a method and / or a laser processing system by which false error detection is reduced.

[0009] A further object of the present disclosure is to provide a method and / or a laser processing system by which monitoring of the laser processing process is improved.

[0010] A further object of the present disclosure is to provide a method and / or a laser processing system by means of which reliable process monitoring is possible in an automated manner, regardless of the state of the system or individual components.

[0011] One or more of these objects are achieved by the subject matter of the independent claims. Advantageous embodiments and further developments are specified in the dependent claims.

[0012] The present disclosure is based on the idea that a stably set laser processing process can run at different process levels (process windows) for various reasons, e.g. due to a dependence on a scan field position in a laser scanner system, tolerance of a clamping device for fixing components, component tolerances, a temperature (cold / warm system). Accordingly, the present disclosure provides a method and a laser processing system for monitoring a laser processing process online that runs at different process levels. To ensure this, according to one aspect of the present disclosure, previously (automatically or manually) learned or defined process levels (process windows) can be automatically adjusted based on sensor data orMeasured values ​​are detected and (previously automatically or manually) determined parameters for process monitoring are automatically adjusted to the detected process level.

[0013] A method for monitoring a laser processing process is specified. The method comprises the steps of: recording, within a monitoring period, measured values ​​of a measurand of the laser processing process, comparing the measured values ​​with value ranges of the measurand of several process levels, determining whether the measured values ​​lie within one of the value ranges of the process levels, and if the measured values ​​lie within one of the value ranges of the process levels, setting the process level for process monitoring in whose value range the measured values ​​lie, and monitoring the laser processing process based on at least one parameter assigned to the set process level. The method can be carried out for each measurand of the laser processing process that is to be used for process monitoring. The monitoring period can be during the execution of the laser processing process.

[0014] In other words, according to the present disclosure, a method for monitoring a laser processing process based on at least one measured variable of the laser processing process comprises the following steps for each measured variable in a monitoring phase or in a monitoring period: capturing measured values ​​of the measured variable of the laser processing process; comparing the measured values ​​with (predetermined) value ranges of several (predetermined) process levels; determining whether the measured values ​​lie within one of the (predetermined) value ranges of the (predetermined) process levels; if the measured values ​​lie within one of the (predetermined) value ranges of the (predetermined) process levels, setting the process level for process monitoring in whose value range the measured values ​​lie; and monitoring the laser processing process based on at least one parameter associated with the set process level.

[0015] Also specified is a laser processing system for carrying out a laser processing process. The laser processing system comprises a laser processing head with at least one sensor unit, wherein the sensor unit is configured to record measured values ​​of a measured variable of the laser processing process within a monitoring period. The laser processing system comprises a control device. The control device is configured to: compare the measured values ​​with value ranges of multiple process levels; determine whether the measured values ​​lie within one of the value ranges of the process levels, and if the measured values ​​lie within one of the value ranges of the process levels; set the process level for process monitoring in whose value range the measured values ​​lie; and monitor the laser processing process based on at least one parameter associated with the set process level.The laser processing system may further comprise a scanning device for deflecting a processing laser beam to different positions within a scanning field of the scanning device. The scanning device may, for example, comprise at least one, preferably two, mirror elements that can be pivoted about at least one axis by means of a drive (e.g., a galvo drive).

[0016] The laser processing system, in particular the control device, can be configured to perform any method step or method disclosed herein. In particular, the sensor unit and / or the control device is configured to perform a method step disclosed herein.

[0017] Further provided is a computer program product comprising instructions that cause a laser processing system to perform a method disclosed herein.

[0018] The method may be any method disclosed herein. The laser processing system may be any laser processing system disclosed herein.

[0019] By comparing measured values, for example, recorded by a sensor, with multiple value ranges from different process levels, different properties or configurations of the laser processing process or laser processing system can be taken into account during process monitoring. For example, the measured values ​​may lie outside a first value range defined for a "warm" system (first process level), and the measured values ​​may lie within a second value range defined for a "cold" system (second process level). If the measured values ​​were only compared with the value range of the first process level ("warm" system), a malfunction of the process or system could be falsely detected, even though the process is running stably or error-free on a "cold" system. This improves the operation and monitoring of the laser processing process.Analogously, this applies to components of the laser processing system from different batches, workpieces from different batches or properties (material, alloy, dimensions, etc.), for different users, component tolerances, etc.

[0020] In particular, in a laser processing system with a scanning device for deflecting the processing laser beam (i.e., a laser scanner system), the measured values ​​of the observed measurand can experience a (sudden) change from one process level to another process level due to a change in the scanning position in the scanning field of the scanning device. The scanning position can, for example, influence measured values ​​of a radiation intensity of process emissions, e.g., thermal radiation, due to a different angle and / or distance from the corresponding sensor unit. According to the present disclosure, an automatic adjustment of the process level is proposed to ensure automatic and continuous process monitoring.

[0021] The monitoring period can be any interrupted or uninterrupted period. In particular, the monitoring period can be an uninterrupted or continuous period. The monitoring period can be part of a longer or larger monitoring period. The monitoring period is preferably shorter than 1 minute, more preferably shorter than 10 seconds, more preferably shorter than 1 second, more preferably shorter than 300 ms. The monitoring period can be a period of complete laser processing of one or more workpieces, for example, a complete welding of two workpieces.

[0022] The measured values ​​can be recorded by a sensor or a sensor unit. The measured values ​​can be individual measurements (digital measurement signal) or continuous measurements (analog measurement signal). A large number of measured values ​​can be recorded during the monitoring period. The measured values ​​can represent a trend. A trend can be created based on the measured values. The trend can be compared with the value ranges of the process levels. The trend can be a time trend.

[0023] The measured variable of the laser processing process can be any desired measured variable, in particular a measured variable of the laser processing process. In particular, the measured variable can be a temperature, a pressure, an intensity of electromagnetic radiation, and / or an intensity of an optical process emission. Measured values ​​of several measured variables can be recorded. Different sensors can be provided for this purpose.

[0024] For each process level, there is at least one value range or exactly one value range. This means that each process level can be assigned exactly one value range. The number of value ranges and process levels can be the same. Each of the value ranges contains values ​​of the measurand. Each process level can be assigned a different value range, or each process level can be assigned a different value range. For each measurand, multiple process levels can be defined or present. This means that for each measurand, the measured values ​​recorded for this measurand can be compared with value ranges of multiple, i.e., different, process levels.

[0025] In general, different process levels may differ in at least one property or in at least one configuration of the laser processing process or the laser processing system.

[0026] None of the value ranges can completely overlap with any other of the value ranges. One value range can partially overlap another value range. Preferably, the value ranges are completely spaced apart from one another, i.e. the value ranges can be completely non-overlapping or not overlapping. The value ranges can be spaced apart from one another at least at one point in time or in one time period in the laser processing process, i.e. the value ranges can be non-overlapping or not overlapping at least at one point in time or in one time period in the laser processing process. In this case, each measured value of the measurand can be clearly assigned to a value range or a process level. The value ranges and / or the parameters for process monitoring can be stored or saved in a memory of the laser processing system.

[0027] The measured values ​​can be compared with at least 2, preferably at least 5, more preferably at least 10, more preferably at least 50, different value ranges. The measured values ​​can be compared with at most 100, preferably at most 50, more preferably at most 10, different value ranges. In particular, the number of value ranges with which the measured values ​​are compared is between 2 and 100. In general, the number of value ranges with which the measured values ​​are compared can be selected such that a clear assignment of the measured values ​​to (exactly) one value range is possible.

[0028] The comparison of the measured values ​​with the value ranges can be performed in real time. In particular, the comparison of the measured values ​​with the value ranges is performed in less than 1 s, preferably less than 500 ms, more preferably less than 200 ms.

[0029] When determining whether the measured values ​​lie within one of the value ranges of the process levels, it can be determined whether the measured values, particularly within the monitoring period, lie predominantly or completely within one of the value ranges of the process levels.

[0030] If the measured values ​​are within one of the value ranges of the process levels, the laser processing process can be monitored at that process level. This means that a process level can be selected or identified based on the measured values ​​during the monitoring period. The laser processing process can then be monitored based on the at least one process monitoring parameter of the selected or identified process level.

[0031] The method can include: if the measured values ​​do not lie within any of the value ranges of the (known or predetermined) process levels, detecting that an unknown process level exists. For example, the existence of an unknown process level can occur if measured values ​​from multiple laser processing processes lie in a new value range (i.e., not yet assigned to a process level) and / or are similar. In this case, the unknown process level can be learned by determining a value range for the unknown process level for the measured variable and determining at least one parameter for monitoring the laser processing process and assigning it to the (previously) unknown process level.

[0032] Alternatively or additionally, the procedure may include: if the measured values ​​do not lie within any of the value ranges of the process levels, detecting that there is or was a fault in the laser processing process or that the laser processing process is or was faulty.

[0033] As a result of the determination, it can be determined that the measured values ​​(completely) do not lie within any of the value ranges. In other words, it can be determined that the measured values ​​(completely) lie outside all value ranges. In this case, an error can be detected.

[0034] As a result of the determination, it can also be determined that the measured values ​​lie (entirely) within (exactly) one of the value ranges of the process levels. In this case, the laser processing process can be monitored based on the detected process level. In particular, the monitoring is carried out based on a parameter assigned to the process level.

[0035] Also, as a result of the determination, it can be determined that the measured values ​​(within the monitoring period) are only partially, exactly partially, or at most partially, or at least partially within a value range. In other words, it can be determined that some of the measured values ​​are within a value range and others are outside the value range. If a limit value is exceeded for a number of measured values ​​within a value range, or a limit value is exceeded for a period of measured values ​​within the value range, it can be recognized that an error exists. If a limit value is exceeded for a number of measured values ​​outside a value range, or a limit value is exceeded for a period of measured values ​​outside the value range, it can be recognized that an error exists.If a limit is exceeded for a number of measured values ​​outside a range, or if a limit is exceeded for a period of measured values ​​outside the range, the process level can be detected or identified. If a limit is exceeded for a number of measured values ​​within a range, or if a limit is exceeded for a period of measured values ​​within the range, the process level can be detected or identified.

[0036] It can be provided that a process level is detected if at least 90% of the measured values ​​during the monitoring period are within the value range of the process level. Alternatively or additionally, it can be provided that faulty operation or an error is detected if at least 10% of the measured values ​​during the monitoring period are not within any of the value ranges.

[0037] Based on the detected process level, the process can be monitored. Each process level can be assigned one or more parameters. The parameter can also be referred to as a monitoring parameter. The parameter can include a statistical value, a mathematical function, etc. The parameter can be assigned a value or a range of values. The value or range of values ​​can specify a maximum permissible deviation.

[0038] For example, at least one reference curve for the set process level can be specified for the measured values ​​of the measurand. In particular, an upper and a lower reference curve can be specified, and / or a mean value reference curve. The parameter can be or comprise a (maximum) amplitude with which the measured values ​​exceed or fall below this reference curve. If a specified value (e.g. limit value) for the parameter, i.e. for the (maximum) amplitude, is exceeded, an error can be detected. Alternatively or additionally, the parameter can be or comprise a (maximum) area that includes the measured values ​​lying above or below this reference curve with the reference curve. If a specified value (e.g. limit value) for the parameter, i.e. for the (maximum) area is exceeded, an error can be detected. Alternatively or additionally, the parameter can be an area below the measured values ​​orbe or include an integral of the measured values ​​during a laser processing process. If a specified value (e.g. limit value) for the parameter, i.e. for the area or the integral, is exceeded or undershot, an error or no error can be detected. The area or the integral can be understood as the integral of the time course of the measured values ​​or the measurement signal. Alternatively or additionally, the parameter can be or include an outlier frequency, i.e. a frequency or number of measured values ​​that lie above or below the reference curve. If a specified value (e.g. limit value) for the parameter, i.e. for the outlier frequency, is exceeded, an error can be detected. The outlier frequency can be understood as the number or period of measured values ​​above the upper reference curve and below the lower reference curve. The outlier frequency can be an absolute or relative value.Alternatively or additionally, the parameter can be or include a quadratic deviation from a specified reference curve (e.g., a mean reference curve). If a specified value (e.g., limit value) for the parameter, i.e., the quadratic deviation, is exceeded, an error can be detected. To determine the quadratic deviation, a deviation of a measured value or measurement signal from the reference curve can be squared.

[0039] If an error is detected, an error message can be output, particularly to a user. The error message can be a visual or acoustic signal. In particular, the error message can be a graphical representation on a display of the laser processing system. Based on the error message, the user can modify the laser processing process. Alternatively or additionally, the laser processing process can be modified if an error is detected. For example, the laser processing process can be interrupted or shut down. Likewise, the laser processing process can be controlled or regulated, particularly based on the result of the comparison of the measured values ​​with the value ranges.

[0040] Each of the value ranges can be defined by specified limits. In particular, each of the value ranges can be defined by two curves.

[0041] At least one limit value can be specified for each of the value ranges. In particular, at least two limit values ​​can be specified for each of the value ranges. A first limit value can be an upper limit value, and the second limit value can be a lower limit value. The value range can be specified between the first limit value and the second limit value. Each of the limit values ​​can be specified or set by a user or operator of the laser processing system or by a manufacturer of the laser processing system. Each of the limit values ​​can be specified or set automatically by the laser processing system.

[0042] Each of the limit values ​​can be a gradient or a curve. Preferably, each of the limit values ​​is an envelope (also referred to as a "reference curve" or "reference" for short). An upper envelope and a lower envelope can be defined for each value range. The value range can be defined between the upper and lower envelopes. The value range can have a mean value, for example, a mean value curve.

[0043] The method may comprise, for each measured variable (e.g., in a recording phase): acquiring, e.g., in a recording period or in a recording phase, measured values ​​of the measured variable; determining a value range for at least one process level or for each of the process levels based on the measured values ​​in the recording period. This allows new or as yet unknown process levels to be defined. The method may further comprise: determining at least one parameter for monitoring the laser processing process and assigning it to the corresponding process level.

[0044] The acquisition period can be referred to as a recording phase or be contained within a recording phase. The acquisition period of the laser processing can be any interrupted or uninterrupted period. In particular, the acquisition period is an uninterrupted or continuous period. The acquisition period can be part of a longer or larger acquisition period. The acquisition period is preferably longer than 1 hour, preferably longer than 4 hours, more preferably longer than 12 hours, more preferably at least 24 hours. The acquisition period can be longer than the monitoring period.

[0045] A laser processing process can be performed during the detection period. Preferably, the same laser processing process is performed during the detection period as during the monitoring period. The laser processing process during the monitoring period can be a part or section of the laser processing process during the detection period.

[0046] During the acquisition period, measured values ​​of the same measurand can be recorded as during the monitoring period. In particular, the same sensor or sensor unit is used to record measured values ​​during the acquisition period as during the monitoring period.

[0047] During the recording period, measured values ​​of the measurand can be recorded for more than one process level, especially for a number of process levels. Based on the measured values ​​in the recording period, several value ranges for different process levels can be determined. Each value range can be assigned to or linked to a process level.

[0048] The recording period and the monitoring period can be separated (in time). The recording period and the monitoring period cannot occur simultaneously. The recording period and the monitoring period cannot overlap (in time). The recording period and the monitoring period can be adjacent to each other. The recording period can precede the monitoring period.

[0049] A parameter for monitoring the laser processing process can be assigned to each process level. The assignment can be done manually or automatically. The parameter can be the same for all process levels. In this case, however, the value or value range assigned to the parameter can be different. Likewise, the parameters of at least two process levels can be different. The parameters of all process levels can be different.

[0050] The recording of measured values ​​during the recording period can be performed multiple times for different process levels. Alternatively or additionally, the determination of value ranges can be performed multiple times for different process levels. Alternatively or additionally, the assignment of at least one parameter for monitoring the laser processing process to one or each of the process levels can be performed multiple times for different process levels.

[0051] For example, measured values ​​for a first process level can be recorded in the recording period, and measured values ​​for a second process level can be recorded in the recording period. In general, measured values ​​for a variety of process levels can be recorded. A value range can be determined for measured values ​​for each process level, so that respective value ranges for multiple process levels can be determined from measured values ​​in a (continuous) recording period. A parameter can be assigned to each process level. The laser processing process can be monitored based on the parameter.

[0052] The recording of measured values ​​during the recording period can be performed before commissioning the laser processing system. Alternatively or additionally, the determination of value ranges can be performed before commissioning the laser processing system. Alternatively or additionally, the assignment of at least one parameter for monitoring the laser processing process to one or each of the process levels can be performed before commissioning the laser processing system.

[0053] During the recording period, a predefined laser processing program can be executed. Laser processing processes with different process levels can be performed in the laser processing program. The laser processing program can comprise at least two different process levels, preferably at least five different process levels. The laser processing program can be specified or can be specified by a manufacturer of the laser processing system or by a user of the laser processing system.

[0054] Further recording of measured values ​​in a recording period can be carried out after the recording of measured values ​​in a monitoring period, e.g. if an unknown process level exists. Alternatively or additionally, further determination of value ranges can be carried out after the recording of measured values ​​in a monitoring period. Alternatively or additionally, the assignment of at least one parameter for monitoring the laser processing process to one or each of the process levels can be carried out after the recording of measured values ​​in a monitoring period. Likewise, further determination of value ranges can be carried out after an initial determination of value ranges, wherein preferably at least one monitoring period lies between the further determination of value ranges and the initial determination of value ranges. In other words, after a monitoring phase, a change can be made back to a setting phase.

[0055] The further recording and / or further determination of value ranges and / or the further assignment of parameters can be carried out after a change in the laser processing system and / or after a change in the laser processing process.

[0056] The number of value ranges of the process levels, especially in a memory of the laser processing system, can change or remain the same through the further determination of value ranges. In other words, through the further determination of value ranges, value ranges can be determined that supplement previously determined value ranges, or previously determined value ranges can be replaced by further determined value ranges.

[0057] In general, the number of considered value ranges, i.e., the number of value ranges with which measured values ​​are compared, can be variable. The number can be increased or decreased. Changing the number of considered value ranges can be automated, particularly based on an error detection rate.

[0058] The change in the laser processing process may involve a change in a component of the laser processing system. For example, a component (e.g., a lens or protective glass) of the laser processing system may be replaced. This may slightly alter the laser processing process, making it advisable to update or add value ranges for process levels. The change in the laser processing process may also be due to aging or wear of a component of the laser processing system. The change in the laser processing process may be caused by a batch change of a component.

[0059] The further recording and / or further determination of value ranges and / or the assignment of parameters can be initiated by a user or carried out automatically, for example, automatically after a component of the laser processing system is changed. The value ranges and / or the parameters of the process levels can be determined using one or more statistical methods. For example, a box plot analysis or a frequency distribution can be performed for this purpose. Other, known statistical methods are possible. The value ranges can be determined based on the recorded measured values ​​for the measurand in the recording period using one or more statistical methods.

[0060] For example, a mean curve can be determined based on measured values ​​in the recording period. For the mean curve, curves can be determined as limit values. The curves can be envelope curves. The envelope curves can comprise an upper envelope and a lower envelope, with the mean curve lying between the upper envelope and the lower envelope. The mean curve and / or the envelope curves can be determined using a statistical method, e.g. a box plot analysis. The mean curve can comprise mean values ​​and / or median values ​​of the measured values ​​recorded for the measured variable during the recording period. In the recording period, the respective limit value can be set based on the mean curve determined for the measured variable and / or on the envelope curves determined for the measured variable.In particular, the upper envelope can be defined such that it has a predefined first distance from the mean value curve, and the lower envelope can be defined such that it has a predefined second distance from the mean value curve. The first distance and the second distance can be equal or different in magnitude. The envelopes can define a respective value range of a process level.

[0061] Before comparing the measured values ​​with the value ranges of the process levels, the process levels can be selected. The measured values ​​can then be compared with the value ranges of the selected process levels.

[0062] The selection may be based on at least one of the following information: information about the laser processing system, information about the laser processing process, information about the temperature of the laser processing system, information about the operating time of the laser processing system, information about the pressure in and / or outside the laser processing system, information about a user of the laser processing system, information about aging and / or wear of at least one component of the laser processing system, a component tolerance of one or more components of the laser processing system, a batch of workpieces to be processed in the laser processing process and / or a scan field position.

[0063] The selection can be made based on user input. Alternatively or additionally, the selection can be made automatically based on information from the laser processing system and / or the laser processing process. For example, the laser processing system may know the current operating time, and this information can be used for the selection. This selection can reduce the number of process levels or value ranges with which measured values ​​from the monitoring period are compared.

[0064] Preferably, the comparison of measured values ​​from the monitoring period is performed only with those value ranges that have been selected or that are available through the selection. Non-selected value ranges are preferably not used for the comparison of measured values ​​from the monitoring period with value ranges.

[0065] In general, a process level can be based on at least one of the following information: information about the laser processing system, information about the laser processing process, information about the temperature of the laser processing system, information about the operating time of the laser processing system, information about the pressure in and / or outside the laser processing system, information about a user of the laser processing system, information about aging and / or wear of at least one component of the laser processing system, a component tolerance of one or more components of the laser processing system, a batch of workpieces to be processed in the laser processing process and / or a scan field position.

[0066] Different process levels may differ in at least one characteristic or configuration of the laser processing system and / or laser processing process.

[0067] The measured variable can be at least one of the following: a temperature, a thermal radiation, and an intensity of at least one process emission, in particular an optical process emission. The process emission can include laser light reflected from a workpiece, plasma radiation generated by the laser processing process, light in the visible spectral range generated by the laser processing process, and / or light in the infrared spectral range generated by the laser processing process.

[0068] The measured variable can be detected by a sensor unit or a sensor. The sensor or sensor unit can comprise at least one, in particular several, photodiodes that are sensitive to different wavelength ranges. Alternatively or additionally, the sensor or sensor unit can comprise at least one two-zone photodiode configured to detect two different wavelength ranges separately.

[0069] The sensor or sensor unit can have a first photodiode configured to detect process radiation in at least a first predetermined wavelength range, in particular in the visible wavelength range. The sensor unit can further have a second photodiode configured to detect process radiation in at least a second predetermined wavelength range, in particular in the ultraviolet wavelength range. Preferably, the sensor unit can have a third photodiode configured to detect process radiation in at least a third predetermined wavelength range, in particular in the infrared wavelength range. Preferably, the first, second, and third wavelength ranges do not intersect or overlap, or at least do not overlap completely.

[0070] The different photodiodes can be configured to detect different types or wavelength ranges of process radiation, such as thermal radiation, a back reflection of the processing laser beam, scattered light, or plasma radiation. Thermal radiation or thermal radiation can be in the infrared and / or near-infrared wavelength range, whereas plasma radiation can be in the visible wavelength range. The use of multiple photodiodes, i.e. at least two photodiodes that can detect process radiation in different wavelength ranges, has the advantage that different components of the process radiation can be detected and evaluated separately. For example, one processing error may be primarily reflected in the thermal radiation, while another processing error can be best detected in the plasma radiation signal.This allows the laser processing process to be monitored across a wide range of the spectrum and for various processing errors or artifacts, and therefore leads to particularly comprehensive and reliable monitoring of laser processing processes.

[0071] For each measured variable or for each sensor or for each of the photodiodes, there can be a separate value range per process level.

[0072] The laser processing process may be or include a laser welding process, a laser cladding process, a laser cutting process, a laser engraving process, or a laser hardening process.

[0073] Brief description of the drawings

[0074] The invention is described in detail below with reference to figures.

[0075] Figs. 1a and 1b each show a laser processing system 400;

[0076] Fig. 2 shows measured values ​​for different process levels 601, 602, 603, 604;

[0077] Fig. 3 shows measured values ​​501, 502, 503 for different process levels 601, 602, 603;

[0078] Fig. 4 shows value ranges 701, 702, 703 for different process levels 601, 602, 603; and

[0079] Figs. 5 and 6 show measured values ​​801, 802, 803 in different monitoring periods tU.

[0080] Detailed description of the drawings

[0081] The laser processing system 400 shown in Figs. 1a and 1b includes a laser processing head 100 and a control device 300. The laser processing system 500 may include a laser source 200.

[0082] The laser source 200 can generate a processing laser beam L (laser beam). The laser source 200 can be configured as a single-mode laser, a solid-state laser, or a fiber laser. The processing laser beam L generated by the laser source 200 can be transmitted from the laser source 200 to the laser processing head 100 via an optical fiber. The processing laser beam L can be coupled into the laser processing head 100 via a fiber coupler 140. The fiber coupler 140 can be arranged on a housing 110 of the laser processing head 100.

[0083] The laser processing head 100 may include collimation optics 121 (collimating optics). The collimation optics 121 may be arranged and configured in the laser processing head 100 such that the processing laser beam L entering the laser processing head 100 divergently is collimated. The collimation optics 121 may be arranged in the housing 110 of the laser processing head 100.

[0084] The collimation optics 121 can comprise at least one lens or two or more lenses. The distance between the two or more lenses can be adjustable, in particular by an electric motor. The collimation optics 121 can define an optical axis.

[0085] The laser processing head 100 can include at least one aperture 125. The aperture 125 can be arranged between the fiber coupler 140 and the collimation optics 121. The aperture 125 can shape the processing laser beam L so that it strikes the collimation optics 121 with a defined diameter.

[0086] Furthermore, the laser processing head 100 can include focusing optics 122. The focusing optics 122 can be arranged and configured in the laser processing head 100 such that the collimated processing laser beam L is focused. The focusing optics 122 can be arranged in the housing 110 of the laser processing head 100.

[0087] The focusing optics 122 can comprise at least one lens or two or more lenses. A distance between the two or more lenses can be adjustable, in particular by an electric motor. An optical axis can be defined by the focusing optics 122. The focusing optics 131 can be an F-theta lens. The F-theta lens can be arranged telecentrically. The focused processing laser beam L can be emitted from the laser processing head 100 and irradiated onto a workpiece W in order to process the workpiece W. The housing 110 preferably comprises a nozzle 171 from which the processing laser beam L is emitted.

[0088] For example, the workpiece W can be welded. Two workpieces W can be welded together, or a component can be welded to the workpiece W. Likewise, the workpiece W can be cut, engraved, or hardened.

[0089] The laser processing head 100 may be a laser welding head, a laser cutting head, a laser engraving head, a laser hardening head, or a laser cladding head.

[0090] The laser processing head 100 can include at least one protective glass 123. The protective glass 123 can be arranged at one end of the housing 110. In particular, the protective glass 123 is replaceable. The protective glass 123 can protect an interior of the laser processing head 100 against contaminants, particles, smoke, fumes, splashes, etc. The processing laser beam L can exit the laser processing head 100 through the protective glass 123, in particular to be irradiated onto the workpiece W.

[0091] Furthermore, the laser processing head 100 may comprise a lens, a transmissive element, a reflective element, a radiation shaping element, a beam splitter and / or an optical wedge.

[0092] An optical path for the processing laser beam L through the laser processing head 100 can be defined by optical elements of the laser processing head 100.

[0093] The laser processing head 100 can comprise a sensor unit 130 (also referred to as "sensor" for short). The sensor unit 130 can be configured to detect measured values ​​of a measurand, in particular a measurand of the laser processing process and / or the laser processing system 400. The sensor unit 130 can be arranged at least partially, in particular completely, within the housing 110 of the laser processing head 100. Such a configuration is shown in Fig. 1a. The sensor unit 130 can comprise a temperature sensor and be configured to detect a temperature, in particular a temperature of a component of the laser processing system and / or a temperature of the laser processing process. Alternatively, the sensor unit 130 can comprise a radiation sensor or a photodiode for detecting scattered radiation and / or process emissions.

[0094] The sensor unit 130 can be arranged at least partially, in particular completely, outside the housing 110 of the laser processing head 100. Such a sensor unit 130 is shown in Fig. 1b. In particular, the sensor unit 130 is configured to detect a process emission E that arises during the laser processing process. The process emission E is, for example, plasma radiation, light generated by the laser processing process in the visible spectral range, and / or light generated by the laser processing process in the infrared spectral range. The process emission E can radiate into the laser processing head 100 and be coupled out of the laser processing head 100 by an optical element, for example, by a semi-transparent mirror E, and coupled into the sensor unit 130. The sensor unit 130 can be an optical sensor unit 130.

[0095] The control device 300 can control the operation of the laser processing head 100. In particular, the control device 300 can control the laser power and / or the position and / or attitude of at least one optical element.

[0096] To monitor the laser processing process, i.e. during a monitoring phase, the control device 300 can be configured to record measured values ​​801, 802, 803 and to automatically examine them in real time for predetermined or previously learned process levels. For this purpose, the measured values ​​801, 802, 803 can be compared with (predetermined) value ranges of these process levels. If the measured values ​​801, 802, 803 are not within a value range of one of the known process levels, the process can be marked as faulty. If a process level is detected, i.e. if the measured values ​​801, 802, 803 are within a value range of one of the known process levels, this process level is set for process monitoring and the laser processing process is monitored based on one or more parameters assigned to this process level.For process monitoring, the measured values ​​801, 802, and 803 can be compared with the parameters for the set process level, and a process evaluation can be performed. This eliminates the need for manual intervention and switching to the corresponding parameters.

[0097] In particular, the control device 300 is configured to compare measured values ​​801, 802, 803 during a monitoring phase or during a monitoring period tU with value ranges 701, 702, 703 of different process levels 601, 602, 603, 604. The control device 300 is further configured to determine whether the measured values ​​801, 802, 803 lie within one of the value ranges 701, 702, 703 of the process levels 601, 602, 603, 604. The control device 300 is further configured, if the measured values ​​801, 802, 803 lie within one of the value ranges 701, 702, 703 of the process levels 601, 602, 603, 604, to set the process level 601, 602, 603, 604 for process monitoring, in whose value range 701, 702, 703 the measured values ​​801, 802, 803 lie. In this way, process monitoring can also be carried out for laser processing processes with changing process levels.

[0098] Fig. 2 shows actual measured values ​​of process emissions with different process levels 601, 602, 603, 604, which were recorded by an optical sensor, e.g., a photodiode. The intensity of the measured signal is plotted against time. Four process levels 601, 602, 603, 604 are shown as examples for this measured variable; however, fewer or more process levels can be considered. The measured value curves from several stable, i.e., defect-free, laser processing processes were superimposed to illustrate the process levels 601, 602, 603, 604. The measured values ​​lie in different value ranges and correspond to different process levels 601, 602, 603, 604. As can be seen in Fig. 2, the measured value curves differ considerably. The process levels can be automatically detected in an initial phase and the corresponding parameters for process monitoring can be statistically calculated or determined for each process level.

[0099] During the learning phase, the process levels and at least one process monitoring parameter can be determined for each process level. Process monitoring can be deactivated during this time. As shown in Fig. 3, measured values ​​are recorded during a (non-monitored or exemplary) machining process; no external process evaluation or monitoring takes place. Ideally, all commonly occurring process levels are represented in the measured values. The recorded or acquired measured values ​​can then be examined for different process levels (process windows), and one or more process monitoring parameters can be automatically calculated for each process level using statistical methods. Process monitoring can then be activated by the operator.

[0100] Fig. 3 schematically shows three curves of measured values ​​501, 502, and 503, again plotting the intensity of the measured signal against time. The curves of measured values ​​501, 502, and 503 can be mean value curves, median value curves, or raw data. In particular, the curves of measured values ​​501, 502, and 503 are determined using a statistical method.

[0101] The measured values ​​501, 502, and 503 were recorded during a recording period tE. Each of the measured value curves 501, 502, and 503 corresponds to error-free or stable operation of a laser processing process at different process levels 601, 602, and 603.

[0102] As shown in Fig. 4, an upper envelope 511, 521, 531 and a lower envelope 512, 522, 532 can be formed for each of the measured value curves 501, 502, 503. The distance between the measured value curves 501, 502, 503 and the corresponding upper envelopes 511, 521, 531 and lower envelopes 512, 522, 532 can be an absolute or relative value. The distance can be a fixed value or selected by a user. The distance between a curve of measured values ​​501, 502, 503 and an upper envelope 511, 521, 531 and the distance between a curve of measured values ​​501, 502, 503 and a lower envelope 512, 522, 532 can be the same or different. The distance between a curve of measured values ​​501, 502, 503 and an upper envelope 511, 521, 531 and / or a lower envelope 521, 522, 532 can be constant or varying along the respective curve.

[0103] A value range 701, 702, 703 can be formed by an upper envelope curve 511, 521, 531 and a lower envelope curve 512, 522, 532. Each of the value ranges 701, 702, 703 can be assigned to or linked to a process level 601, 602, 603. At least one parameter for process monitoring is assigned to each of the process levels 601, 602, 603. The parameter can be used to monitor the laser processing process. The parameters of the process levels 601, 602, 603 can (all) be the same or (all) different. Likewise, the parameters of the process levels 601, 602, 603 can be at most partially or at least partially different. Different types of parameters or different parameter values ​​can be used.

[0104] In Figs. 5 and 6, in addition to the value ranges 701, 702, 703 of the process levels 601, 602, 603, measured values ​​801, 802, 803 are shown in a respective monitoring period tU.

[0105] During the monitoring period tU, measured values ​​801, 802, 803 of a measured variable of a laser processing process are recorded. The measured variable is preferably the same measured variable for which measured values ​​501, 502, 503 were recorded during the recording period tE.

[0106] Preferably, the measured values ​​501, 502, 503 of the measured variable are recorded in the recording period tE before measured values ​​801, 802, 803 of the measured variable are recorded in the monitoring period tU. Further measured values ​​501, 502, 503 in a recording period tE can be recorded after measured values ​​801, 802, 803 have been recorded in at least one monitoring period tU. In other words, the value ranges 701, 702, 703 of the process levels 601, 602, 603 can initially be defined in an embedding phase, for example, within the scope of a test or calibration laser processing process, but also within the scope of a real laser processing process. Further value ranges of process levels can be added, or existing process levels can be removed. In particular, value ranges of process levels are added or removed after the laser processing process has been changed, e.g.by changing a setting of the laser processing process, or after the laser processing system has been modified, e.g. by replacing a component or part of the laser processing system.

[0107] The measured values ​​801, 802, 803 in the monitoring period tU are compared with the value ranges 701, 702, 703 of the process levels 601, 602, 603, and it is determined whether the measured values ​​801, 802, 803 lie within one of the value ranges 701, 702, 703. If the measured values ​​801, 802, 803 lie within one of the process levels, the (detected) process level 601, 602, 603 is used for process monitoring, in whose value range 701, 702, 703 the measured values ​​801, 802, 803 lie.

[0108] The measured values ​​801, 802, 803 can be compared with all value ranges 701, 702, 703 or only or at most with a portion of the value ranges 701, 702, 703. A selection of the value ranges 701, 702, 703 with which the measured values ​​801, 802, 803 are compared can be made by a user or can be made based on information about the laser processing process and / or information about the laser processing system. For example, the operating time of the laser processing process can be known. Based on the operating time, a selection of value ranges 701, 702, 703 with which the measured values ​​801, 802, 803 are compared can be made.

[0109] Preferably, the measured values ​​801, 802, 803 are compared with at least two value ranges 701, 702, 703.

[0110] In the example of Fig. 5, the measured values ​​801 in the monitoring period tU lie entirely within the value range 701 of the process level 601. Based on this, the process level 601 can be identified as the currently applicable process level. The laser processing process can be monitored based on the parameter assigned to the identified process level 601.

[0111] In the first example of Fig. 6, measured values ​​802 in a monitoring period tU lie completely outside all value ranges 701, 702, 703 of the considered process levels 601, 602, 603. This makes it possible to detect that an error is present or that the laser processing process is faulty.

[0112] In the second example of Fig. 6, measured values ​​803 in a monitoring period tU only partially lie within the value range 703 of a process level 603. In this case, it can be determined over which period tA measured values ​​lie outside the value range. If the period lies above a limit value, it can be recognized that an error is present. If the period lies below the limit value, the process level 603 can be recognized as the currently applicable process level. Based on the at least one parameter for process monitoring of this process level 603, the laser processing process can be monitored. Alternatively, it can be determined over which period the measured values ​​lie within the value range. If the period lies above a limit value, the process level 603 can be recognized as the currently applicable process level. If the period lies below the limit value, it can be recognized that an error is present.

[0113] Alternatively or additionally, the amount by which the measured values ​​lie outside the value range can be determined. If a limit value for the amount is exceeded, it can be detected that an error has occurred. If the limit value for the amount is undershot, process level 603 can be identified as the currently applicable process level. After detecting a process level, any method disclosed herein for monitoring the laser processing process can be applied.

[0114] In general, a limit or each of the limit values ​​can be an absolute or relative value. The limit or each of the limit values ​​can be user-specified or fixed.

[0115] According to the present disclosure, during process monitoring, the measured values ​​recorded or acquired by a sensor can be automatically analyzed in real time for previously learned process levels. If the measured values ​​do not fall within a known process level, the process can be marked as faulty. If a process level is detected, the measured values ​​can be compared with the previously determined parameters for this process level, and a process evaluation can be performed (process monitoring).

Claims

Patent claims 1. A method for monitoring a laser processing process based on at least one measured variable of the laser processing process, the method comprising the following steps for each measured variable: Recording, in a monitoring period (tU), measured values ​​(801, 802, 803) of the measured variable of the laser processing process; Comparing the measured values ​​(801, 802, 803) with value ranges (701, 702, 703) of several process levels (601, 602, 603, 604); Determining whether the measured values ​​(801, 802, 803) are within one of the value ranges (701, 702, 703) of the process levels (601, 602, 603, 604); if the measured values ​​(801, 802, 803) are within one of the value ranges (701, 702, 703) of the process levels (601, 602, 603, 604), setting the process level (601, 602, 603, 604) for process monitoring, in whose value range (701, 702, 703) the measured values ​​(801, 802, 803) are; and Monitoring the laser processing process based on at least one parameter associated with the set process level (601, 602, 603, 604).

2. The method according to claim 1, wherein the method further comprises for each measured variable, if the measured values ​​(801, 802, 803) are not in any of the value ranges (701, 702, 703) of the process levels (601, 602, 603, 604): Detect that an unknown process level (601, 602, 603, 604) exists; or Detect that there is an error in the laser processing process.

3. Method according to one of the preceding claims, wherein each of the value ranges (701, 702, 703) is defined by fixed limit values ​​and / or by two curves (511, 512; 521, 522; 531, 532).

4. Method according to one of the preceding claims, wherein the method further comprises for each measured variable: Recording, in a recording period (tE), measured values ​​(501, 502, 503) of the measured quantity; Determining a value range (701, 702, 703) for at least one process level (601, 602, 603, 604) based on the measured values ​​(501, 502, 503) in the acquisition period (tE); and Determining at least one parameter for monitoring the laser processing process for the process level (601, 602, 603, 604).

5. The method according to claim 4, wherein the acquisition of measured values ​​(501, 502, 503) in the acquisition period (tE), the determination of a value range (701, 702, 703) and the determination of at least one parameter are carried out for a plurality of process levels (601, 602, 603, 604).

6. The method according to claim 4 or 5, wherein the acquisition of measured values ​​(501, 502, 503) in the acquisition period (tE), the determination of value ranges (701, 702, 703) and the determination of at least one parameter is carried out before commissioning of the laser processing system (400) and / or in a learning phase.

7. The method according to one of claims 4 to 6, wherein a further recording of measured values ​​(501, 502, 503) in a recording period (tE), a further determination of value ranges (701, 702, 703) and a further determination of at least one parameter is carried out after the recording of measured values ​​in a monitoring period (tU), in particular after a change in the laser processing system (400) and / or a change in the laser processing process.

8. The method according to any one of claims 4 to 7, wherein the determination of the value ranges (701, 702, 703) and / or the parameter for monitoring the laser processing process is carried out by one or more statistical methods.

9. Method according to one of the preceding claims, wherein before comparing the measured values ​​(801, 802, 803) with the value ranges (701, 702, 703) of the process levels (601, 602, 603, 604), a selection of process levels (601, 602, 603, 604) is made and the measured values ​​(801, 802, 803) are compared with the value ranges (701, 702, 703) of the selected process levels (601, 602, 603, 604), in particular wherein the selection is based on at least one of the following information: information about the laser processing system, information about the laser processing process, information about the temperature of the laser processing system, information about the operating time of the laser processing system, information about the pressure in and / or outside the laser processing system, information about a user of the laser processing system, information about an aging of at least one component of the laser processing system,information about a component tolerance of one or more components of the laser processing system, Information about a tolerance of a clamping device, information about a batch of workpieces to be machined in the laser machining process and / or a scan field position.

10. The method according to any one of the preceding claims, wherein a process level (601, 602, 603, 604) is based on at least one of the following information: information about the laser processing system, information about the laser processing process, information about the temperature of the laser processing system, information about the operating time of the laser processing system, information about the pressure in and / or outside the laser processing system, information about a user of the laser processing system, information about an aging of at least one component of the laser processing system, information about a component tolerance of one or more components of the laser processing system, information about a tolerance of a clamping device, information about a batch of workpieces to be processed in the laser processing process and / or information about a scan field position.

11. Method according to one of the preceding claims, wherein the at least one measured variable is at least one of the following: a temperature, a temperature radiation and an intensity of at least one process emission, in particular an optical process emission, wherein the process emission in particular comprises laser light reflected from a workpiece (W), plasma radiation generated by the laser processing process, light generated by the laser processing process in the visible spectral range and / or light generated by the laser processing process in the infrared spectral range.

12. The method according to any one of the preceding claims, wherein the laser processing process is or comprises a laser welding process, a laser cladding process, a laser cutting process, a laser engraving process or a laser hardening process.

13. Laser processing system (400) for carrying out a laser processing process, the laser processing system (400) comprising: a laser processing head (100) with at least one sensor unit (130), wherein the sensor unit (130) is configured to record measured values ​​(801, 802, 803) of a measured variable of the laser processing process in a monitoring period (tU); and a control device (300) which is configured to compare the measured values ​​(801, 802, 803) with value ranges (701, 702, 703) of a plurality of process levels (601, 602, 603, 604) and to determine whether the measured values ​​(801, 802, 803) are in one of the value ranges (701, 702, 703) of the process levels (601, 602, 603, 604), and if the measured values ​​(801, 802, 803) are in one of the value ranges (701, 702, 703) of the process levels (601, 602, 603, 604), to set the process level (601, 602, 603, 604) for process monitoring, in whose value range (701, 702, 703) the measured values ​​(801, 802, 803) lie, and to monitor the laser processing process based on at least one parameter associated with the set process level (601, 602, 603, 604).

14. The laser processing system (400) of claim 13, wherein the sensor (130) comprises at least one of the following: a first photodiode configured to detect electromagnetic radiation in the visible wavelength range, a second photodiode configured to detect electromagnetic radiation in the ultraviolet wavelength range, and a third photodiode configured to detect electromagnetic radiation in the infrared wavelength range.

15. A computer program product comprising instructions that cause a laser processing system to carry out the method according to any one of claims 1 to 12.

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