Method for analysing a sound, method for training artificial intelligence, and method for determining a cut break position

Abstract

The invention relates to a method for analysing a sound which occurs during the laser cutting of a workpiece (1) as a result of a cut break (8), in which a cutting operation (A) is carried out in which the workpiece (1) is cut by means of a laser cutting head (4) which is guided in a cutting device along a cutting line and provides the laser beam (5). In addition, a testing operation (B) is carried out in which the laser cutting head (4) is again guided along at least portions of the cutting line. In addition, a locally resolved sound, recorded during the cutting operation, at a cut break position of the laser cutting head (4) determined during the testing operation (B) is analysed, and based on the analysis, a characteristic (19) of the sound is determined (C), said characteristic being allocated to the cut break (8).

Description

[0001] Method for analyzing a sound, method for training an artificial intelligence, and method for determining a cutting position

[0002] The invention relates to a method for analyzing a noise, a method for training an artificial intelligence and a method for determining a cut-off position of a laser cutting head along a cutting line during a cut-off.

[0003] During laser cutting, especially during fusion and flame cutting, a cut can break. This means that a cut is no longer separated satisfactorily. If the cut break is detected and its position can be determined, the cut can be subsequently overcut. This can prevent waste.

[0004] JP 2014 113 597 A discloses a laser processing device with a condensing device that condenses laser beams and a torch comprising the condensing device. Auxiliary gas is directed onto a workpiece simultaneously with the condensed laser beams, whereby the workpiece is cut by the laser beams. The laser processing device further comprises a device for detecting sound generated during cutting of the workpiece and a control device for analyzing a sound signal obtained from the sound detecting device. Based on the sound signal, it is determined whether the cut performed is satisfactory.

[0005] Furthermore, US 11 224 938 B2 discloses a method for monitoring laser cutting processes and automatic quality control after interruption and / or termination of a cutting process carried out with predefined cutting parameters. The cutting process can be interrupted after a first partial processing step, whereupon a partial section of a processing path is scanned. Based on a scan result, at least one quality characteristic of the machined workpiece is automatically determined and compared with predefined quality specifications. Depending on the result of the comparison, an error message can then be issued, processing can be interrupted, rework can be performed on a defect location, and the cutting process can be continued with the modified cutting parameter set.

[0006] It is the object of the invention to create a solution which enables a particularly reliable determination of a cut break during a laser cutting process.

[0007] The problem is solved by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the subclaims, the description, and the drawings. Features, advantages, and possible embodiments presented in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims.

[0008] The invention relates to a method for analyzing a noise that occurs during laser cutting of a workpiece as a result of a cut break. The workpiece is, in particular, a sheet metal. Laser cutting refers to the severing of solids using continuous or pulsed laser radiation through material ablation. In physics, ablation refers to the removal of material by heating, for example by a laser. In the case of a cut break, the energy introduced into the workpiece by a laser beam is not sufficient to melt the entire cutting gap volume. During thermal cutting of a workpiece with a high-energy beam, in particular with a laser beam, a cut break can occur. This means that the high-energy beam no longer cuts completely through the workpiece, especially if it is a metal.When the cut occurs, a kerf or cutting gap is not defined over the entire thickness of the workpiece, so that the high-energy beam only cuts a furrow into the workpiece.

[0009] The method for analyzing noise involves performing a cutting process followed by a testing process. During the cutting process, the workpiece is cut using a laser cutting head that is guided in a cutting direction along a cutting line and provides the laser beam. The cutting line along which the laser cutting head is guided to cut the workpiece is predetermined depending on the geometry of the cut to be made on the workpiece. During the cutting process, the position of the laser cutting head along the cutting line is continuously recorded. It is thus known when and where along the cutting line the laser cutting head is located.Furthermore, during the cutting process, it is provided that a sound that changes during cutting of the workpiece due to the cut break is recorded using an acoustic sensor, wherein the sound is stored in a spatially resolved manner and assigned to the respective positions of the laser cutting head along the cutting line. In other words, a respective frequency and amplitude curve of the recorded sound is plotted against the positions of the laser cutting head along the cutting line that were recorded at the same time as the noise. This stores the frequency and amplitude of the sound when the laser cutting head is arranged at respective positions along the cutting line. This stores how the sound behaves when the laser cutting head is moved along the cutting line during the cutting process.

[0010] During the testing process carried out following the cutting process, the laser cutting head is again guided at least sectionally along the cutting line. During the testing process, the position of the laser cutting head along the cutting line is continuously recorded. This means that the testing process also records at what point in time the laser cutting head is at which position along the cutting line. During the testing process, it is further provided that the laser beam is provided by means of the laser cutting head at a lower power than during the cutting process and / or (if necessary only) a process gas jet is provided by means of the laser cutting head. During the testing process, it is therefore provided that either the laser beam with the lower power is provided alone or together with the process gas jet by means of the laser cutting head, or only the process gas jet is provided by means of the laser cutting head.During the inspection process, the laser power is reduced so much that the workpiece is not cut again. For example, the laser beam power can be set to 200 watts during the inspection process.

[0011] By guiding the laser cutting head at least partially along the cutting line, the laser beam or process gas jet is guided through the kerf or cutting gap, in particular through the area where the cut is located. During the testing process, at least one measured value is recorded continuously or repeatedly and at regular intervals using a detection device. If the detection device determines, based on a measured value changing at the cut, that the laser beam or process gas impinges on the location of the cut on the workpiece, the assigned position of the laser cutting head is determined as the cut position.This means that the measured value is continuously recorded by the recording device during the test process. As soon as a characteristic change in the measured value is detected, it is determined that the laser beam or the process gas has reached the cut point. For this point in the cutting gap, for which it has been determined that the laser beam or the process gas has reached the cut point, the assigned position of the laser cutting head is determined as the cut point position. If the laser cutting head is positioned at the cut point position, the laser beam or the process gas beam provided by the laser cutting head strikes the cut point, which is determined based on the change in the measured value.

[0012] The method further provides for the spatially resolved noise at the determined cut-off position of the laser cutting head to be analyzed. Based on the analysis, a characteristic of the noise associated with the cut-off is determined. In other words, the noise determined during the cutting process and resolved for the respective positions of the laser cutting head along the cutting line is examined to determine how it is characterized at the determined cut-off position. The characteristic of the noise can be analyzed in particular based on a frequency and / or a phase and / or an amplitude of the noise. The method makes it possible to determine how a noise occurring during cutting of the workpiece behaves in the event of a cut-off. Based on the determined characteristic, a cut-off can thus be detected particularly easily, quickly and simply during subsequent cutting processes.

[0013] In a possible development of the invention, it is provided that the detection device determines, during the testing process, on the basis of a further noise and / or structure-borne sound of the workpiece and / or a luminous intensity of the laser beam and / or a luminous intensity of the inherent glow of the material of the workpiece glowing due to the laser exposure, that the point of the cut break on the workpiece has been reached. The further noise is, in particular, a noise resulting from the process gas jet impinging on the cut break. If the cutting gap is completely severed, the noise resulting from the process gas jet impinging on the cutting gap is different from that resulting from an incomplete cutting gap. The incomplete cutting gap occurs at a transition between the completely severed cutting gap and the incompletely severed cutting gap.During the test process, it is therefore possible to determine the position of the cut break purely based on acoustics. This is due to the fact that the cutting gap is not yet present during the cutting process, but is already present during the test run. The position of the cut break can be determined particularly easily and reliably during the test process based on the changing additional noise. In particular, the same sensor can be used to record the noise during the cutting process and the additional noise during the test process.

[0014] To measure the structure-borne sound of the workpiece, a sensor can be placed on the workpiece. For this purpose, the sensor can be arranged, for example, in clamping jaws that hold the workpiece during the testing process.

[0015] Using a camera device of the detection device, images of the workpiece can be recorded during the inspection process. These images are assigned to respective positions of the laser cutting head along the cutting line. The cut break can be identified in the images based on a change in the optical properties of the recorded laser beam and / or the glowing material. Since the images are assigned to respective positions of the laser cutting head along the cutting line at which the laser cutting head was located when the respective image was captured, the assigned cut break position of the laser cutting head can be determined based on the image in which the cut break was identified based on the optical properties of the laser beam or the glowing material of the workpiece.As an alternative to the camera device, the detection device can comprise at least one photodiode configured to record the respective luminous intensity, wherein the respective recorded luminous intensity is stored associated with respective positions of the laser cutting head along the cutting line. The respective detected luminous intensities are associated with those positions of the laser cutting head at which the laser cutting head was located at the time the respective luminous intensity was recorded. A microphone can be arranged on the laser cutting head, which is configured to record the noise during the cutting process and / or to record the additional noise during the testing process.By arranging the microphone on the laser cutting head, the microphone is guided along the cutting line together with the laser cutting head, whereby a relative position between the microphone and the point at which the laser beam hits the workpiece can be kept constant during the entire cutting process or during the entire testing process, provided that the distance between the laser cutting head and the workpiece is constant.

[0016] Based on the additional noise, the position of the cut can be determined particularly easily using a microphone. Based on the structure-borne noise of the workpiece, the position of the cut can also be determined particularly easily using a structure-borne noise sensor. Based on the respective images, the position of the cut can be determined very precisely using the luminous intensity of the laser beam or the luminous intensity of the molten material.

[0017] In a further possible embodiment of the invention, it is provided that the determined characteristic is made available to an electronic computing device. This electronic computing device is configured to determine, on the basis of a noise determined during a further cutting process, whether a cut has been torn by checking the recorded noise with regard to the characteristic. It is thus provided that the determined characteristic of the noise is made available as a reference for the electronic computing device. The electronic computing device can thus be used during further cutting processes to determine respective cut breaks in further cutting processes. For this purpose, the electronic computing device examines whether the determined characteristic can be detected in the respective recorded noises for the respective further cutting processes to be analyzed.If the electronic computer determines the characteristic in the recorded noise during a subsequent cutting process, the electronic computer determines that a cut has been torn off during this cutting process. This makes it possible for the characteristic determined within the framework of the method to be particularly well-used for the analysis of subsequent cutting processes. In a further possible embodiment of the invention, it is provided that the laser cutting head is guided along the cutting line for the testing process, opposite to the cutting direction. In other words, the laser cutting head is guided forward along the cutting line during the cutting process and backward along the cutting line during the testing process.If it is suspected that a cut break may have occurred, or if it is determined, for example, based on a visual inspection of the workpiece that a cut break has actually occurred, the cutting process is halted and the laser cutting head is stopped in its movement along the cutting line. The laser cutting head is then moved back against the cutting direction and thus backwards. As part of the inspection process, a kerf or cutting gap created by the laser cutting of the workpiece can be examined for the position of the cut break. In particular, the laser cutting head can only be moved back along the cutting line against the cutting direction until the position of the cut break has been determined by the detection device based on the changing measured value at the cut break.This method thus makes it possible for the laser cutting head to be guided along the cutting line only over a particularly short distance during the testing process in order to determine the position of the cut break.

[0018] In an alternative possible embodiment of the invention, it is provided that for the testing process, the laser cutting head is moved back by a predetermined offset along the cutting line, opposite to the cutting direction, and then guided in the cutting direction along the cutting line. This means that if a cut break is suspected or detected, the cutting process is stopped and the laser cutting head is thus held in its position along the cutting line. The laser cutting head is then moved back by the predetermined offset along the cutting line and guided again in the cutting direction along the cutting line for the testing process. It is thus provided that the laser cutting head is guided in the cutting direction along the cutting line during both the cutting process and the testing process.

[0019] The invention further relates to a method for training artificial intelligence. This artificial intelligence can in particular be software that is executed on hardware. In particular, the artificial intelligence is an artificial neural network. In the method for training the artificial intelligence, at least one characteristic of a recorded sound that is assigned to the cut break and determined in a method as has already been described in connection with the method according to the invention for analyzing a sound is fed to the artificial intelligence as training data. In this way, the artificial intelligence is trained to recognize a cut break based on a recorded sound, in particular when the artificial intelligence recognizes the characteristic assigned to the cut break in the recorded sound.The training data can be fed to at least one input interface or at least one input layer of the artificial intelligence. Training the artificial intelligence enables the trained artificial intelligence to determine the cut break particularly reliably based on the respective recorded sounds.

[0020] The invention further relates to a method for determining a cut-off position of a laser cutting head along the cutting line in the event of a cut-off that occurs during a cutting process. During this cutting process, a workpiece is cut using a laser beam. The laser beam is provided by the laser cutting head and directed onto the workpiece. The method provides that during the cutting process, a sensor records a noise that changes as the laser beam is guided over the workpiece due to a cut-off. The sensor is, in particular, a microphone. The recorded noise is stored in a spatially resolved manner and assigned to respective positions of the laser cutting head along the cutting line. The assignment is made in each case over time.This means that the temporal progression of the noise is overlaid with the temporal progression of the respective position of the laser cutting head along the cutting line. This makes it possible to determine how the noise behaves while the laser cutting head is at various positions along the cutting line. Using a characteristic of the noise assigned to the cut break, the cut break position of the laser cutting head assigned to the cut break can be determined via the spatial resolution of the noise. This means that the recorded noise is examined for the occurrence of the characteristic, whereby the characteristic characterizes the presence of the cut break. If it is determined that the noise has the characteristic, then the position of the laser cutting head is examined when the characteristic of the noise occurred.This determined position of the laser cutting head is the cut-off position at which the laser cutting head was located along the cutting line when the cut-off occurred during the cutting process. The cut-off position of the laser cutting head can be used to determine particularly well where on the workpiece the cut-off is located, as well as what the respective laser cutting parameters of the cutting process were when the laser cutting head was located at the cut-off position along the cutting line. This allows the cause of the cut-off to be investigated particularly well. This, in turn, makes it possible to avoid the cause of the cut-off in subsequent cutting processes.

[0021] In a possible development of the invention, the noise is recorded using a microphone arranged on or in the laser cutting head as a sensor. This allows for particularly good reproducibility of the recorded noise, since the relative position between the microphone and the laser cutting head is fixed. An acoustic sensor arranged in the laser cutting head (in particular the microphone) can be arranged, in particular, in a cutting nozzle of the laser cutting head. The microphone, and in particular an arrangement of the microphone in the laser cutting head, enables particularly precise recording of sound waves representing the noise.

[0022] In a further possible embodiment of the invention, it is provided that the characteristic represents a reduction in the volume of the noise and / or a change in the frequency of the noise and / or the characteristic is represented by the occurrence of a specific subsequence of an acoustic signal representing the noise. This specific subsequence can in particular be a so-called shapelet. Shapelets are distinctive subsequences of time series that best predict a characteristic to be determined. The characteristic to be determined is the presence of the cut break. If the distinctive subsequence is thus determined as a characteristic of the noise in the acoustic signal, it is determined that the laser cutting head was arranged at the cut break position when this specific subsequence of the acoustic signal occurred.If the characteristic represents a reduction in the volume of the noise, then, in the case of a reduction in amplitudes, in particular a constriction of the acoustic signal relative to the respective amplitude levels, it can be determined that the laser cutting head is positioned at the cut-off position at the time these reduced amplitudes of the noise are detected. If the characteristic is represented by the frequency change of the noise, then, based on the frequency curve occurring in the acoustic signal representing the noise, the cut-off position of the laser cutting head can be determined for the time at which the frequency change was detected in the acoustic signal.

[0023] In this context, a possible development of the invention can provide for the specific subsequence to be a periodic oscillation sequence. Thus, the acoustic signal representing the noise can be an iterative signal, at least over the specific subsequence. In this case, the acoustic signal has a specific amplitude sequence that repeats, such as an ECG signal. If the specific subsequence is the periodic oscillation sequence, then the specific subsequence can be particularly well identified in the acoustic signal representing the noise.

[0024] In a further possible embodiment of the invention, it is provided that the characteristic of the noise assigned to the cut break has been determined using a method as already described in connection with the method according to the invention for analyzing a noise. The characteristic of the noise assigned to the cut break has thus been determined based on the noise recorded during the cutting process at the cut break position of the laser cutting head determined during the testing process. Within the scope of the described method, the characteristic assigned to the cut break can be determined particularly precisely, which in turn allows the cut break to be detected particularly reliably and with particularly precise positioning during the further cutting process.

[0025] In a further possible embodiment of the method, it is provided that the cut-off position of the laser cutting head is determined based on the recorded noise by means of an artificial intelligence that has been trained in a method as already described in connection with the inventive method for training an artificial intelligence. Using artificial intelligence to determine the cut-off position of the laser cutting head enables the cut to be detected particularly reliably based on the respective recorded noises, even if the characteristics of the noise are not identical but merely similar, for example, with a lower or higher amplitude or lower or higher frequency, or with a phase shift.Using the trained artificial intelligence to determine the cut break position of the laser cutting head thus enables the cut break to be detected particularly reliably in a particularly large number of different cutting processes.

[0026] In a further possible embodiment of the invention, the cutting process is stopped in response to the detected cut interruption. This means that when the cut interruption has been detected, the laser cutting head is stopped at its position along the cutting line. In addition, the provision of the laser beam by means of the laser cutting head can be terminated. Consequently, the cutting process is terminated and no further cutting of the workpiece takes place by means of the laser cutting head for the time being. This can prevent the incomplete cutting kerf from being drawn further across the workpiece by means of the laser cutting head after the cut interruption has occurred. Instead, the cutting process is stopped, whereby the cut interruption or the incomplete cutting kerf can be corrected.This means that the risk of the workpiece having to be disposed of as scrap can be kept particularly low.

[0027] In a further possible embodiment of the invention, it is provided that the laser cutting head, in response to the detected cut break, is moved back to a position on the cutting line that lies a defined distance ahead of the cut break position, counter to the cutting direction. Furthermore, it is provided that a further cut is made using the laser cutting head along the cutting line in the cutting direction. This means that the laser cutting head is moved back along the cutting line beyond the cut break position. Subsequently, the laser cutting head cuts again in the original cutting gap or kerf. This results in a clean separation of the workpiece and the correction of the cut break.To ensure that the cutting gap is reliably severed across its entire length, the laser cutting head is moved back a defined offset along the cutting line, starting from the determined cut-off position. This guides the laser beam section by section through the completely severed cutting gap, then reaches the cut-off point, and from there, completely separates the workpiece for a clean cut. In response to the detected cut-off point, the cutting process is stopped, and the cut of the workpiece is subsequently corrected, thus significantly reducing the risk of the workpiece becoming scrap.

[0028] In this context, a further embodiment of the invention can provide that during the further cut, a speed of the laser cutting head as it moves along the cutting line and / or a gas pressure of the process gas used during cutting and / or a focus position of the laser beam provided by the laser cutting head are adjusted compared to the cutting process. This means that the aforementioned parameters are adjusted during the second cut. In particular, a cutting speed and / or the gas pressure and / or the focus position of the laser beam are adjusted during cutting. By making these adjustments during the further cut, the risk of a further cut being interrupted can be kept particularly low. The method thus enables correction of the cut that is faulty due to the cut being interrupted and allows the workpiece to be reused and not having to be sorted out as scrap.

[0029] Further features of the invention can be derived from the following description of the figures and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures alone, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0030] The drawing shows:

[0031] Fig. 1 is a process diagram for a method for analyzing a noise that occurs during laser cutting of a workpiece as a result of a cut break;

[0032] Fig. 2 is a schematic perspective view of a laser cutting machine by means of which a workpiece is cut;

[0033] Fig. 3 is a plan view of a cut made on the workpiece by means of a laser beam; Fig. 4 is a schematic perspective view of a laser cutting head of the laser cutting machine by means of which the workpiece is cut;

[0034] Fig. 5 shows a time-resolved curve of an audio signal which characterises a noise occurring during cutting of the workpiece in the event of a cut break;

[0035] Fig. 6 shows a time-resolved curve of an audio signal characterizing a noise resulting from cutting the workpiece, where no cut break occurs; and

[0036] Fig. 7 a process diagram for a control system of a laser cutting machine.

[0037] Identical or functionally equivalent elements are provided with the same reference numerals in the figures.

[0038] Fig. 1 shows a process diagram for a method for analyzing a noise that occurs during laser cutting 20 of a workpiece 1 as a result of a cut break 8. Fig. 2 shows a laser cutting machine 3, by means of which the workpiece 1 can be cut. The laser cutting machine 3 comprises a laser cutting head 4. The laser cutting head 4 is configured to provide a laser beam 5, in this case a laser cutting beam, by means of which the workpiece 1 is cut. As a result of the cutting of the workpiece 1 by means of the laser beam 5, a cutting gap 6 results in the workpiece 1. An exemplary cutting gap 6 is shown in Fig. 3. If the cutting gap 6 is completely severed, then this is a so-called good cut 7. If the cutting gap 6 no longer extends continuously through the entire thickness of the workpiece 1, then a cut break 8 has occurred. Slag 9 escapes as part of the cut break 8.Furthermore, the cut break 8 can result in the material of the workpiece 1 no longer being melted, as can be seen in area 10. The cut break 8 is a defect that can lead to the workpiece 1 being discarded as scrap. To avoid the workpiece 1 being discarded as scrap, the cut break 8 can be corrected by cutting again. For this purpose, it is advantageous if the exact position of the cut break 8 is known. The laser cutting machine 3 shown in Fig. 2 further comprises a laser source 11, a beam guide 12, and a workpiece support 13.Although the laser cutting machine 3 according to Figure 2 shows a beam guide 12 with mirrors as deflection elements, which are particularly required for use in CC>2 lasers, it is understood that solid-state lasers such as fiber lasers or disk lasers, or even diode lasers, can also be used as the laser beam source 11, and that the beam guide can in particular comprise one or more optical fibers. The workpiece support 13 comprises a plurality of support webs 14 on which the workpiece 1 is placed during laser cutting 20. In order to be able to move the laser cutting head 4 particularly flexibly, the laser cutting machine 3 comprises a gantry 15. The laser cutting head 4 is held on the gantry 15 so that it can be moved relative to the gantry 15. The gantry 15, in turn, is arranged so that it can be displaced relative to the workpiece support 13. Fig. 2 also shows cutting gas containers 16 of the laser cutting machine 3 and an extraction device 17 of the laser cutting machine 3.

[0039] To record the noise to be analyzed, the laser cutting machine 3 comprises at least one acoustic sensor 18, in this case several acoustic sensors 18. The acoustic sensors 18 are designed as microphones. Alternatively, at least one of the acoustic sensors 18 can be designed as a structure-borne sound sensor, by means of which the structure-borne sound resulting from the laser cutting process 20 in the workpiece 1 can be detected.

[0040] The intention is to determine the cut break 8 based on the noise resulting from the laser cutting 20 of the workpiece 1. For this purpose, a characteristic 19 of the noise associated with the cut break 8 must be determined. In order to determine the characteristic 19 of the noise associated with the cut break 8, the method shown in Fig. 1 is carried out.

[0041] The method for analyzing the noise comprises three method steps A, B and C. In the first method step A, the workpiece 1 is cut, during which the cutting gap 6 is generated in the workpiece 1 by means of the laser beam 5. In the second method step B, a testing process takes place, during which the cutting gap 6 generated during the cutting process is checked. In the third method step C, a characteristic 19 of the noise associated with the cut break 8 is determined. During the cutting process of the first method step A, the workpiece 1 is cut by means of the laser cutting head 4, which provides the laser beam 5 and is guided in a cutting direction along a cutting line. During the cutting process, a position of the laser cutting head 4 along the cutting line is continuously recorded in a first step S1 of the first method step A.At the same time, in a second step S2 of the first method step A, the noise changing during cutting of the workpiece 1 due to the cut break 8 is recorded by means of the at least one acoustic sensor 18. The noise is stored in a spatially resolved manner associated with the respective positions of the laser cutting head 4 along the cutting line.

[0042] During the testing process of the second method step B, the laser cutting head 4 is guided at least partially along the cutting line. In the first step S3 of the second method step B, a position of the laser cutting head 4 along the cutting line is continuously recorded. At the same time, in a second step S4 of the testing process, the laser beam 5 is provided by the laser cutting head 4 with a lower power compared to the cutting process. Alternatively, the laser beam 5 can not be provided by the laser cutting head 4 in the second step S4 of the testing process and instead only a process gas jet can be provided. In a third step S5 of the testing process, a measured value is continuously and repeatedly recorded using a recording device. The first step S3, the second step S4 and the third step S5 of the testing process take place, in particular, simultaneously.In a fourth step S6 of the testing process, the cut break position of the laser cutting head 4 is determined. If the detection device determines, based on the changing measured value at the cut break 8, that the laser beam 5 impinges on the location of the cut break 8 on the workpiece 1, the associated position of the laser cutting head 4 is defined as the cut break position. The detection device can determine, based on an additional noise recorded by the acoustic sensors 18 and / or based on structure-borne sound of the workpiece 1 recorded by a structure-borne sound sensor and / or based on a luminous intensity of the laser beam 5 and / or based on a luminous intensity of an inherent glow of the material of the workpiece 1 glowing due to the laser exposure, that the location of the cut break 8 on the workpiece 1 has been reached.In the third method step C, the spatially resolved noise at the determined cut break position of the laser cutting head 4 is analyzed. Based on the analysis, a characteristic 19 of the noise associated with the cut break 8 is determined. This determined characteristic 19 can, in turn, be provided to an electronic computing device, which, during subsequent cutting processes, uses the respective determined noises to determine whether a cut break 8 is present in the respective subsequent cutting process by checking the respective recorded noise for the presence of the characteristic 19.

[0043] In Fig. 4, the laser cutting head 4 is shown at different positions along the cutting line. Furthermore, in Fig. 4, the workpiece 1 can be recognized, which is cut by means of the laser cutting head 4. In the first method step A and thus during the cutting process, the workpiece 1 is cut by moving the laser cutting head 4 in the cutting direction along the cutting line. During the testing process in the second method step B, the laser cutting head 4 is moved in the cutting direction or against the cutting direction along the cutting line. In other words, if it has been determined that the cut break 8 is present, the laser cutting head 4 can be moved backward and thus against the cutting direction along the cutting line for the testing process, starting from a position in which the laser cutting head 4 was located when it was determined that the cut break 8 was present.Alternatively, the laser cutting head 4 is moved back by a predetermined offset along the cutting line, counter to the cutting direction, for the inspection process and then guided in the cutting direction along the cutting line, in particular over a position at which the cut break 8 is suspected. During the inspection process, the laser beam 5 is provided by the laser cutting head 4 with a reduced laser power compared to the cutting process, so that no further cutting of the workpiece 1 occurs during the inspection process.

[0044] In Figs. 5 and 6, the noise recorded by the respective acoustic sensors 18 during the cutting process, as well as the additional noise recorded during the testing process, are plotted as a sound pressure level in Pascal over time in seconds. Due to the temporal recording of the respective positions of the laser cutting head 4 along the cutting line, the course of the acoustic signal recorded by the acoustic sensors 18, which characterizes the noise or the additional noise, can be assigned to the respective positions of the laser cutting head 4 by temporal assignment.

[0045] Here, the acoustic signal 21 in Fig. 5 is shown for a cutting process in which a cut break 8 occurred, whereas in the cutting process shown in Fig. 6 no cut break 8 occurred. Based on the additional noise recorded during the test process, the cut break position of the laser cutting head 4 can be determined via the spatial assignment to the respective positions of the laser cutting head 4 along the cutting line. Based on the cut break position of the laser cutting head 4, it can in turn be determined what the acoustic signal 21 looked like during the cutting process when the cut break 8 occurred and thus the laser cutting head 4 was arranged at the cut break position. This cut break 8 is characterized in the acoustic signal 21 for the cutting process by a characteristic expression and thus the characteristic 19 of the acoustic signal 21.

[0046] Respective characteristics 19 determined during multiple cutting processes in the respective methods explained in connection with Fig. 1 can be fed as training data 28 to an artificial intelligence, in particular an artificial neural network. Based on the training data 28, this artificial intelligence can be trained to detect the presence and, in particular, the position of a cut break 8 based on a noise recorded during laser cutting 20 of a workpiece 1.

[0047] The detected characteristic 19 assigned to the cut break 8 makes it possible, in further cutting processes in which a workpiece 1 is cut using a laser beam 5, to detect whether and where a cut break 8 is present based on a noise recorded by the at least one acoustic sensor 18, which changes during the cutting process when the laser beam 5 is guided over the workpiece 1 due to a cut break 8. In the method, the noise is stored with spatial resolution assigned to the respective positions of the laser cutting head 4 along the cutting line, and based on the characteristic 19 of the noise assigned to the cut break 8, the cut break position of the laser cutting head 4 assigned to the cut break 8 can be determined via the spatial resolution of the noise. The cut break position of the laser cutting head 4 can be determined from the noise using the trained artificial intelligence.As can be seen in Figures 2 and 4, at least one acoustic sensor 18 can be arranged at different positions within the laser cutting machine 3. In particular, at least one acoustic sensor 18 is arranged on the laser cutting head 4, in particular fastened and fixed thereto. Another acoustic sensor 18 can be arranged on the workpiece support 13. It can be advantageous if at least one acoustic sensor is arranged in the laser cutting head 4, in particular in a cutting nozzle of the laser cutting head 4 (not shown in the figures).

[0048] As shown in Fig. 5, characteristic 19 may be a reduction in the volume of the noise. Alternatively or additionally, characteristic 19 may represent a change in the frequency of the noise. Alternatively or additionally, characteristic 19 may be represented by the occurrence of a specific subsequence, in particular a periodic oscillation sequence, in the acoustic signal 21 characterizing the noise.

[0049] If the cut break 8 is detected, in particular based on the characteristic 19 of the recorded noise, the cutting process can be stopped. Additionally, in response to the detected cut break 8, the laser cutting head 4 can be moved back to a position along the cutting line that lies a defined distance ahead of the cut break position, counter to the cutting direction. Subsequently, a further cut of the workpiece 1 can be performed using the laser cutting head 4 along the cutting line in the cutting direction to ensure complete severance of the cutting gap 6 over its entire length.In order to avoid a further cut break 8 when cutting the workpiece 1 again and thus during the correction, a speed of the laser cutting head 4 during its movement along the cutting line and / or a gas pressure of the process gas used during cutting and / or a focus position of the laser beam 5 provided by the laser cutting head 4 can be adjusted in comparison to respective settings of the laser cutting machine 3 during the cutting process.

[0050] Fig. 7 shows a process diagram for linking the method for determining the cut-off position of the laser cutting head 4 along a cutting line during a cut-off 8 with the method for training the artificial intelligence. In this case, a laser cut 20 of the workpiece 1 takes place according to the cutting process. An acoustic signal 21 recorded during the laser cutting 20 is transmitted to a process controller 22. The acoustic signal 21 represents the noise recorded during the laser cutting 20 by means of the at least one acoustic sensor 18. By means of the process controller 22, the acoustic signal 21 is transmitted to an evaluation device 23, which is configured to evaluate the acoustic signal 21 in real time. In particular, the evaluation device 23 examines the acoustic signal 21 for the presence of the characteristic 19 specific to the cut-off 8.If the presence of characteristic 19 in the acoustic signal 21 is determined by the evaluation device 23, the evaluation device 23 transmits a cut-break detection signal 24 to the process control 22. This cut-break detection signal 24 characterizes that the cut break 8 has been detected and at which cut break position the laser cutting head 4 was located when the cut break 8 occurred. Upon receipt of the cut break detection signal 24, the process control 22 transmits a recutting signal 25, which triggers the laser cutting machine 3 to correct the cut by recutting over the determined position of the cut break 8.The evaluation device 23 further provides a cut-off training signal 26 representing the acoustic signal 21 and the cut-off position of the laser cutting head 4 to a labeling device 27, which creates training data 28 by linking the acoustic signal 21 to the cut-off position of the laser cutting head 4 via the temporal assignment. The labeling device 27 provides the training data 28 for the artificial intelligence training 29.

[0051] In the laser cutting machine 3, one or more acoustic sensors 18 are mounted in the machine room or on (or in) the laser cutting head 4. If a cut break 8 occurs, this can be detected in real time using the sensor data recorded by the acoustic sensors 18. If the laser moves over the cutting gap 6 again with lower laser power, the position of the cut break 8 can be determined using the sensor data. This means that if the cut break 8 is detected by the audio signal analysis, the laser cutting head 4 moves over the already cut cutting gap 6 again during the inspection process with a lower laser power compared to the cutting process until the position of the cut break 8 is found by means of audio signal analysis.In this case, either immediately after detection of the cut break 8, the laser cutting head 4 can be moved back in the opposite direction to the cutting direction and the cutting gap 6 can be analyzed, or the laser cutting head 4 is moved back by a defined offset along the cutting line and then moves again over the cutting gap 6 in the cutting direction. The position determination of the cut break 8 can be used to subsequently label recorded sensor signals, which represent the recorded noise, and to train the artificial intelligence with this labeled data as training data 28.

[0052] The cut break can be detected optically during the test process. For this purpose, images are recorded by the detection device, based on which the position of the cut break 8 can be determined. Determining the cut break position during the test run based on the additional noise is particularly cost-effective due to the use of at least one acoustic sensor 18, particularly compared to determining the cut break position based on the images recorded by the camera. During the test run, the cutting process can be monitored by a camera integrated in the laser cutting head 4. A first step towards autonomous or unmanned laser cutting 20 is the automatic detection of a cut break 8, which can be carried out using the described method based on the recorded noise.

[0053] Using machine learning methods, the images recorded by the camera device during the inspection process can be classified as either OK or showing the cut 8. Thus, using the machine learning method, the cut 8 can be detected based on the images recorded by the camera device during the inspection process. The images are only required to determine the characteristic 19 for creating the training data 28. In the method for detecting the cut 8 using the trained artificial intelligence, the cut 8 is determined solely based on the recorded noise. Recording images is not necessary for the specific use of the trained artificial intelligence.

[0054] Overall, the invention shows how acoustic cut break detection can be implemented.

[0055] I Workpiece

[0056] 3 laser cutting machines

[0057] 4 laser cutting head

[0058] 5 Laser beam

[0059] 6 Cutting gap

[0060] 7 Good cut

[0061] 8 Sectional outline

[0062] 9 escaping slag

[0063] 10 Area

[0064] II Laser source

[0065] 12 Beam guidance

[0066] 13 Workpiece support

[0067] 14 landing stage

[0068] 15 Portal

[0069] 16 cutting gas containers

[0070] 17 Extraction device

[0071] 18 acoustic sensor

[0072] 19 Characteristics

[0073] 20 laser cutting

[0074] 21 acoustic signal

[0075] 22 Process control

[0076] 23 Evaluation device

[0077] 24 Cut break detection signal

[0078] 25 Re-grooving signal

[0079] 26 Cut break training signal

[0080] 27 Label setup

[0081] 28 training data

[0082] 29 trainings

[0083] AC respective procedural steps

[0084] S1-S5 respective steps

Claims

PATENT CLAIMS 1. A method for analyzing a noise that occurs during laser cutting (20) of a workpiece (1) as a result of a cut break (8), in which, during a cutting process (A), in which the workpiece (1) is cut by means of a laser cutting head (4) guided in a cutting direction along a cutting line and providing the laser beam (5): o a position of the laser cutting head (5) along the cutting line is continuously recorded (S1), and o a noise that changes during cutting of the workpiece (1) due to the cut break (8) is recorded by means of an acoustic sensor (18), wherein the noise is stored in a spatially resolved manner associated with respective positions of the laser cutting head (4) along the cutting line (S2), during a testing process (B),in which the laser cutting head (4) is again guided at least partially along the cutting line: o a position of the laser cutting head (4) along the cutting line is continuously recorded (S3), o the laser beam (5) is provided by means of the laser cutting head (4) with a lower power compared to the cutting process (A) and / or a process gas jet is provided (S4), and o when it is determined by means of a detection device based on a measured value (S5) changing at the cut break (8) that the laser beam (5) or the process gas impinges on the location of the cut break (8) on the workpiece (1), the associated position of the laser cutting head (4) is determined as the cut break position (S6), the spatially resolved noise at the determined cut break position of the laser cutting head (4) is analyzed, and based on the analysis, a characteristic (19) of the noise associated with the cut break (8) is determined (C).

2. Method according to claim 1, wherein by means of the detection device on the basis of a further noise and / or on the basis of structure-borne noise of the workpiece (1) and / or based on a luminous intensity of the laser beam (5) and / or based on a luminous intensity of a self-luminous emittance of the material of the workpiece (1) glowing due to the laser exposure, it is determined that the point of the cut break (8) on the workpiece (1) has been reached.

3. Method according to claim 1 or 2, wherein the determined characteristic (19) is provided for an electronic computing device which is configured to determine, on the basis of a noise determined during a further cutting process (A), whether a cut break (8) is present by checking the recorded noise with regard to the characteristic (19).

4. Method according to one of the preceding claims, wherein the laser cutting head (4) for the test process (B) is guided along the cutting line against the cutting direction.

5. Method according to one of claims 1 to 4, wherein for the testing process (B) the laser cutting head (4) is moved back by a predetermined offset along the cutting line opposite to the cutting direction and is then guided in the cutting direction along the cutting line.

6. A method for training an artificial intelligence, in which at least one characteristic (19) of a recorded noise, determined in a method according to one of the preceding claims and associated with the cut (8), is supplied to the artificial intelligence as training data (28), whereby the artificial intelligence is trained to recognize a cut (8) on the basis of a recorded noise.

7. Method for determining a cutting break position of a laser cutting head (4) along a cutting line in the case of a cutting break (8) which occurs during a cutting process (A) in which a workpiece (1) is cut by means of a laser beam (5) is cut, wherein in the method during the cutting process (A) by means of a sensor (18) a noise which changes when the laser beam (5) is guided over the workpiece (1) due to a cut break (8) is recorded, wherein the noise is stored in a spatially resolved manner associated with the respective positions of the laser cutting head (5) along the cutting line, and wherein the cutting break position of the laser cutting head (4) associated with the cutting break (8) is determined on the basis of a characteristic (19) of the noise associated with the cutting break (8) via the spatial resolution of the noise.

8. The method according to claim 7, wherein the noise is detected by means of a microphone arranged on or in the laser cutting head (4) as a sensor (18).

9. The method according to claim 7 or 8, wherein the characteristic (19) represents a reduction in volume of the noise and / or a change in frequency of the noise and / or the characteristic (19) is represented by the occurrence of a specific subsequence of an acoustic signal (21) representing the noise.

10. The method of claim 9, wherein the specific subsequence is a periodic oscillation sequence.

11. Method according to one of claims 7 to 10, wherein the characteristic (19) of the noise associated with the cut (8) has been determined in a method according to one of claims 1 to 5.

12. Method according to one of claims 7 to 11, wherein the cutting break position of the laser cutting head (4) is determined from the recorded noise by means of an artificial intelligence which has been trained in a method according to claim 6.

13. Method according to one of claims 7 to 12, wherein the cutting process (A) is stopped in response to the detected cut break (8).

14. The method according to claim 13, wherein the laser cutting head (4) is moved back to a position on the cutting line in response to the detected cut break (8) which is located a defined distance in front of the cut break position, opposite to the cutting direction, and a further cut is carried out by means of the laser cutting head (4) along the cutting line in the cutting direction.

15. The method according to claim 14, wherein during the further cut, a speed of the laser cutting head (4) during its movement along the cutting line and / or a gas pressure of process gas used during cutting and / or a focus position of the laser beam (5) provided by the laser cutting head (4) are adjusted in comparison to the cutting process (A).

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