DE102022101118A1 - Operating method for a laser processing machine and laser protection device - Google Patents

Abstract

The invention relates to an operating method (82) for a laser processing machine (12) to protect against laser radiation (42) escaping into an environment (40) of the laser processing machine (12), wherein at least one process variable is measured continuously in a processing area (52) of a laser beam (22), the measured process variable is compared with at least one predetermined error value of at least one predetermined error event and a safety measure is initiated if the environment (40) is endangered by the error event. The invention also relates to a laser radiation protection device.

Description

Background of the Invention

The invention relates to an operating method for a laser processing machine to protect against laser radiation escaping into the surroundings of the laser processing machine. The invention also relates to a laser radiation protection device.

When a workpiece is processed by a laser beam of a laser processing machine, the processing radiation emitted by the laser beam is not completely absorbed by the workpiece to be processed, which can result in direct or diffuse reflection of the laser beam. In addition, the laser beam can penetrate the workpiece to be processed during processing or be directed unhindered into the environment as a result of incorrect positioning of the laser optics or the workpiece to be processed. In the aforementioned cases, laser radiation can escape into the area surrounding the laser processing machine. As a result, people and objects located there can be endangered and possibly significantly damaged.

Laser processing machines therefore usually have passive laser protection in the form of at least one laser protection wall and/or a laser protection cabin in order to hold back misdirected or reflected laser radiation.

The increasing performance of laser processing machines and the increasing brilliance of the laser beams represent a constantly growing challenge for passive laser protection. This must have an ever increasing protective effect in order to prevent the misdirected or reflected laser radiation from penetrating the laser protective wall and/or the laser protective cabin . An increase in the protective effect through increased use of materials is technically and economically limited, which is why passive laser protection is often expanded to include active laser protection.

In such a combined laser protection, the active laser protection is designed for sensory monitoring of the passive laser protection. If the passive laser protection is penetrated by the laser beam, this can be recognized by the active laser protection and the laser beam can be interrupted. If necessary, the laser processing machine can be switched off. The passive laser protection can thus have a reduced protective effect with the laser protection combined in this way, which only has to withstand a short maximum exposure to the laser beam until the laser beam is interrupted and/or the laser processing machine is switched off. As a result, the provision costs for passive laser protection can be reduced.

However, with this combined laser protection, the laser protection wall and/or the laser protection cabin must be monitored over the full area by the active laser protection using appropriate sensors in order to ensure a sufficiently high level of protection against laser radiation with a random beam angle. This requires a great deal of design effort in the design of the active laser protection, as a result of which considerable costs arise even when the active laser protection is provided. In addition, in the event of damage to the passive laser protection, the sensors used in the active laser protection often have to be repaired at great expense, which results in additional costs.

Conventional passive, active and/or combined laser protection must also be conceptually adapted to the laser processing machine to be shielded and the laser processing carried out by means of the laser processing machine, or its laser processing parameters. In order to maintain the protective effect of the laser protection when the laser processing machine is modified, for example by increasing the power and/or changing the laser processing, it is therefore usually necessary to carry out a complex and costly revision of the laser protection.

object of the invention

It is an object of the invention to propose laser protection that can be easily adapted to a change in the laser processing machine and is also inexpensive to provide and maintain.

Description of the invention

This object is achieved according to the invention by an operating method and a laser radiation protection device of the type mentioned at the beginning with the further inventive features according to claim 1 and according to claim 11.

In other words, the object is achieved by an operating method for a laser processing machine to protect against laser radiation escaping into the surroundings of the laser processing machine, in which at least one process variable is continuously measured in a processing area of a laser beam, the measured process variable is compared with at least one predetermined error value of at least one predetermined error event compared and a safety measure is initiated if the environment is endangered by the error event.

Escaping laser radiation is to be understood here and in the following in particular as the laser radiation reflected from the workpiece into the surroundings, the laser radiation directed through the workpiece and/or the laser radiation directed past a workpiece.

In other words, the operating method according to the invention can protect against laser radiation directed away from the workpiece.

Here and in the following, the error event according to the invention is to be understood in particular as a process event that deviates from a predetermined course of the laser processing, in particular an undesired process event. In other words, the error event represents a process event that does not occur during proper laser processing. The inventors have found that laser radiation, which is unusually high for laser processing and directed into the area surrounding the laser processing machine, is largely dependent on proper laser processing. With proper laser processing, only the usual scattered radiation occurs, which can be held back using conventional passive laser protection. On the other hand, in the event of a fault, laser radiation escapes into the environment at a level that is unusual for the process, or is greatly increased compared to the scattered radiation that is usual for the process, which means that the passive laser protection of the laser processing machine can be penetrated or overcome.

• Freistrahl: Das Auftreten eines Freistrahls ist durch ein ungehindertes oder durch ein direkt spiegelndes reflektiertes Austreten des Laserstrahls in die Umgebung der Laserbearbeitungsmaschine charakterisiert. Mit anderen Worten kann sich der Laserstrahl ungehindert im Raum ausbreiten. Die Gefährdung der Umgebung durch die Laserstrahlung ist in diesem Fall maximal, jedoch auf einen geringen Winkelbereich beschränkt.
• Strahldurchtritt: Beim Auftreten eines Strahldurchtritts durchdringt der Laserstrahl das Werkstück. Mit anderen Worten tritt der Laserstrahl auf einer einem Laserbearbeitungskopf zugewandten Seite in das Werkstück ein und auf einer dem Laserbearbeitungskopf abgewandten Seite wieder aus. Die Gefährdung der Umgebung nähert sich dabei mit der Dauer des Strahldurchtritts und der zunehmenden Aufweitung der Laserstrahlausnehmung der Gefährdung durch den Freistrahl an.
• Fehlerhaftes Einkoppeln und/oder Laserstrahlabriss: Das Auftreten von Fehlerhaftem Einkoppeln und/oder einem Laserstrahlabriss ist durch erhebliche Reflexion der Laserstrahlung an dem Werkstück charakterisiert. Das Werkstück bzw. ein Schmelzbad des Werkstücks kann in diesem Fall starke Temperaturschwankungen aufweisen und/oder vermindert ausgebildet sein. Fehlerhaftes Einkoppeln kann beispielsweise durch ein unzureichendes und/oder verzögertes bzw. verspätetes Einkoppeln des Laserstrahls in das Werkstück eintreten. Fehlerhaftes Einkoppeln kann zu Beginn einer Laserbearbeitung auftreten, wohingegen ein Laserstrahlabriss meistens bei fortgeschrittener Laserbearbeitung auftritt.
• Falsche Fokuslage: Eine Falsche Fokuslage kann das Fehlerhafte Einkoppeln und/oder den Laserstrahlabriss bewirken, wobei das Auftreten der Falschen Fokuslage ebenfalls durch erhebliche Reflexionen der Laserstrahlung in die Umgebung charakterisiert ist.

The error event means, for example, the occurrence of one or more events as listed below:

• Free beam: The occurrence of a free beam is characterized by an unimpeded or by a directly specular reflected exit of the laser beam into the environment of the laser processing machine. In other words, the laser beam can spread unhindered in space. In this case, the danger to the environment from the laser radiation is maximum, but limited to a small angle range.
• Beam penetration: When a beam penetration occurs, the laser beam penetrates the workpiece. In other words, the laser beam enters the workpiece on a side facing a laser processing head and exits again on a side facing away from the laser processing head. The hazard to the environment approaches the hazard posed by the free jet with the duration of the beam passage and the increasing widening of the laser beam recess.
• Incorrect coupling and/or laser beam break: The occurrence of incorrect coupling and/or a laser beam break is characterized by significant reflection of the laser radiation on the workpiece. In this case, the workpiece or a molten pool of the workpiece can exhibit strong temperature fluctuations and/or be of reduced design. Incorrect coupling can occur, for example, due to insufficient and/or delayed or late coupling of the laser beam into the workpiece. Incorrect coupling can occur at the beginning of a laser processing, whereas a laser beam break occurs mostly with advanced laser processing.
• Incorrect focus position: An incorrect focus position can cause faulty coupling and/or the laser beam to break off, with the occurrence of the incorrect focus position also being characterized by significant reflections of the laser radiation into the environment.

The inventors have also established that, in the event of an error event, at least one process variable in the processing area of the laser beam on the workpiece deviates from values of the process variable that are typical for the process. According to the invention, the at least one process variable is therefore measured in the processing area of the laser beam on the workpiece. Depending on the process variable to be measured, the operating procedure can provide for the use of various types of measuring equipment.

The process variable is a measurable physical variable that can be changed as a result of the impact of the laser beam on the workpiece. Process variables in the sense of the invention can be, for example, the distance between the workpiece and the laser processing head; the spatially and/or temporally resolved thermal radiation; the punctiform thermal radiation of the workpiece; and/or the radiation intensity of the workpiece.

The processing area of the laser beam on the workpiece includes the partial areas on the workpiece that are either irradiated by the laser beam or in which the direct effect of the irradiation continues.

For example, in the case of laser welding processing of the workpiece, the processing area can be understood as the area in which the beam penetrates into the workpiece, as well as the weld pool caused by the laser beam. the first A welded seam, on the other hand, is not understood as a processing area in the sense of the invention.

The processing area can change during laser processing. For example, the processing area can shift along a surface of the workpiece and/or into the workpiece. In addition, the processing area can increase or decrease depending on the direction.

The measured process variable is then compared with at least one predetermined error value of the process variable. The error value represents a limit value of the process variable that is only present when an error event occurs. On the other hand, with proper laser processing, the process variable in the processing area does not assume the error value. In other words, an error event and consequently the emergence of laser radiation at a level that is unusual for the process or is impermissible can be determined using at least one symptomatic error value of the process variable. The environment is therefore endangered by the laser radiation when the process variable measured on the workpiece in the processing area of the laser beam is below or above (depending on the type of process variable) the error value.

The error value can be determined analytically and/or empirically. The error value was preferably predetermined empirically by measuring the process variable during the laser processing and then evaluating the laser processing as correct or incorrect. The evaluation can be carried out, for example, by measuring the laser radiation emitted during laser processing, assessing the laser processing process, evaluating process parameters of the laser processing machine and/or assessing the result of the laser processing. The assessment can be carried out manually and/or visually, in particular by a person skilled in the art, or by machine, in particular using a neural network. More preferably, the predetermined error value is based on at least ten, in particular one hundred, particularly preferably one thousand, correct and/or faulty laser processing operations.

According to the invention, it is provided that a safety measure is initiated if the environment is endangered by escaping laser radiation. A safety measure serves to protect the environment and is intended to prevent further escape of the laser radiation and/or a further increase in the laser radiation. The safety measure is preferably dependent on the degree of risk of the laser radiation emerging in the event of a fault event, with the safety measure introducing a more drastic intervention in the laser processing as the risk increases.

A security measure can be, for example, changing process parameters; in breaking the laser beam; and/or the laser processing machine being switched off. Changing the process parameters can consist, for example, in changing the focus position, the feed rate and/or the position of the processing head over the workpiece. For example, it can be provided that when the laser radiation emitted is only slightly increased, process parameters are first changed and the laser beam of the laser processing machine is only interrupted when the laser radiation emitted increases further.

Furthermore, it can be provided that the process variable is compared with two or more predetermined error values. The error values are preferably staggered and can indicate an increasing degree of danger to the environment from the exiting laser radiation. As a result, the safety measure can also consist of an increasing intervention in the laser processing machine, with the laser processing machine being switched off when the highest degree of danger occurs.

In summary, the present operating method according to the invention ensures laser radiation protection for the environment through the targeted monitoring of the at least one process variable in the processing area of the laser beam on the workpiece. The detection of erroneous events is controlled by predetermining the at least one error value for the monitored or continuously measured process variable, and the associated emergence of laser radiation that is not typical for the process into the environment is counteracted. This enables the active laser protection to be provided in a particularly simple manner.

It is also advantageously possible to adapt the operating method to a modified laser processing strategy in a particularly simple manner. In this case, the adaptation of the operating method can be limited to changing the predetermined error values quickly and inexpensively, which means that downtimes in processing and costs for the planning effort that is no longer required can be saved.

A laser processing strategy in the sense of the invention can at least one vorbe appropriate combination, in particular a plurality of predetermined combinations, of laser processing parameters. Alternatively or additionally, a laser processing strategy can include one or more laser processing processes of the laser processing machine. In other words, within a laser processing strategy, differently designed workpieces can be processed in different ways by the laser processing machine. For example, two pipes can be welded together and/or a plate can be cut. Furthermore, the laser processing strategy can be subsequently expanded or reduced.

Laser processing parameters are to be understood as meaning, for example, the laser power, focus position, feed rate, processing geometry and/or beam orientation.

In a preferred embodiment of the operating method, at least two process variables are measured and the at least two measured process variables are compared with at least two error values of the at least one error event, with a risk being determined as a function of both comparisons. In other words, two symptomatic error values of two different process variables are compared for two-channel determination of a hazard. In this way, a more reliable determination of the fault event and consequently of the hazard from escaping laser radiation can be determined.

Also preferred is an embodiment of the operating method in which the at least one process variable is measured with at least two, in particular identical, measuring devices and the measured process variable of the at least two measuring devices is compared with the at least one error value of the at least one error event, with a risk depending on both comparisons is determined. In other words, a redundant or two-channel measurement of the at least one process variable is carried out, as a result of which there can be a risk from escaping laser radiation even if a measuring device fails.

The embodiments described above for the two-channel measurement of the at least one process variable and/or the determination of the error event can thus meet the safety requirements of relevant standards, as specified in particular in EN ISO 13849-1 be demanded.

Also preferred is an operating method in which the process variable “distance between the workpiece and a processing head of the laser processing machine” is measured along a laser beam axis. By measuring this process variable and comparing it with the error value, the error events laser free beam, beam penetration and/or the incorrect focus position can be determined, for example. If too great a distance is measured, for example the focus position may have been set incorrectly and/or a measurement may have taken place past the workpiece or through the workpiece. In the latter cases, this can lead to a free jet and/or a jet penetration, as a result of which there is a significant risk to the environment.

In a preferred operating method, it is provided that heat radiation emitted by the workpiece, in particular infrared heat radiation, is measured in a locally resolved manner. A locally resolved measurement of the heat radiation is to be understood in particular as creating a temperature image of the workpiece surface in at least a partial area of the processing area of the laser beam. The temperature map can then be evaluated, in particular by an image evaluation, with characteristic temperature ranges being able to be used to determine an error event. By measuring the heat dissipation, for example, the error events beam penetration; Incorrect coupling; and/or a laser beam break can be determined. A laser beam break-off and incorrect coupling can be determined, for example, by evaluating an expansion of the melt pool from the temperature image.

In a preferred development of the operating method, it is provided that the heat radiation emitted by the workpiece coaxially to the laser beam is measured. As a result, the processing area can be measured particularly precisely, since scattered radiation obliquely to the laser beam, for example from an adjacent area of the workpiece, can go unnoticed.

In a preferred embodiment of the operating method, heat radiation emitted by the workpiece, in particular infrared heat radiation, is evaluated in a time-resolved manner. In this case, the continuously measured process variable is stored for the purpose of displaying the process variable over time. By evaluating the course of the heat radiation over time, for example, the fault events of laser beam breakage and/or faulty coupling can be determined particularly reliably.

Also preferred is an embodiment of the operating method in which a laser beam is emitted from the workpiece in a laser machining center Heat dissipation is measured. In this way, for example, the error event beam passage can be determined. When the beam passes through, only a small amount of heat radiation is measured in the laser processing center compared to the adjacent edge area, since the workpiece was removed in the said area as a result of the beam passing through.

In a preferred embodiment of the operating method, heat radiation emitted by the melt pool on the workpiece is measured. The heat radiation is preferably measured at points in the molten bath and evaluated at a point in time and/or over time. A temporal evaluation of the heat radiation can be used particularly effectively to determine the error event incorrect coupling.

Also preferred is an embodiment of the operating method in which heat radiation emitted by the workpiece is locally measured. As a result, the process variable can be measured in an area of the processing area that is characteristic of an error event, and the remaining processing area can be ignored. This promotes rapid evaluation and can increase the accuracy of the measurement.

The underlying object is also achieved by a laser radiation protection device for protecting the environment from the laser radiation of the laser beam of the laser processing machine, which is preferably set up to carry out the operating method according to the invention described above.

According to the invention, the laser radiation protection device has the passive laser protection, which is designed to hold back the laser radiation that is typical for the process and escapes into the environment. Furthermore, the laser radiation protection device has active laser protection.

The active laser protection has a controller, a monitoring sensor system and an evaluation unit. The controller is set up to initiate a safety measure if the permissible laser radiation emitted into the environment is exceeded. According to the invention, the monitoring sensor system is designed to measure the at least one process variable in the processing area of the laser beam and the evaluation unit is set up to determine the at least one error event by comparing the measured process variable with the at least one error value.

Passive laser protection means in particular a barrier that blocks the laser radiation. In other words, the laser radiation is absorbed and/or reflected by the passive laser protection and is thus prevented from escaping into the environment. The passive laser protection can partially surround the laser processing machine, for example in the form of a laser protection wall and/or completely, for example in the form of a laser protection cabin.

According to the invention, active laser protection is to be understood as meaning a device which is designed to detect laser radiation directed into the environment and is set up to counteract the production of the laser radiation. As a result, the passive laser protection can have a lower protective effect, which means that the deployment costs can be reduced.

The monitoring sensor system is designed to measure the process variable in the processing area of the laser beam. For this purpose, a measuring device is permanently aimed at the processing area of the laser beam. This allows a continuous measurement to take place.

The monitoring sensor system is preferably set up for direct data transmission with the monitoring sensor system. A particularly fast exchange of data can thereby take place.

According to the invention, the controller is set up to initiate the safety measure. For example, the controller can be set up to issue a warning and/or to trigger an alarm. The controller is preferably connected to a machine controller of the laser processing machine. As a result, a security measure can be initiated particularly quickly. More preferably, the controller is set up to access the machine controller of the laser processing machine and to change the process parameters. As a result, the security measure can be initiated particularly effectively and without any loss of time worth mentioning. In a particularly preferred manner, the controller is set up to switch off the laser processing machine and/or to interrupt an energy supply to the laser processing machine.

According to the invention, the active laser protection is set up to detect the laser radiation directed into the environment using the monitoring sensor system to measure the at least one process variable directly in the processing area on the workpiece. In this case, active laser protection can take place particularly advantageously at an early stage, in particular preventively, as a result of which considerable damage to the passive laser protection can be avoided.

The active laser protection can be adapted to different laser processing machines and laser processing strategies by selecting the process variable to be measured and predetermining the at least one error value. Laser protection can thus be provided in a cost-effective manner, which can be adapted particularly easily to different laser processing machines. A full-area monitoring of the passive laser protection by means of expensive monitoring sensors can be omitted, which avoids costs with regard to provision and repair.

In a preferred embodiment of the laser radiation protection device, the monitoring sensor system is designed to measure at least two process variables and the evaluation unit is set up to determine the at least one fault event by evaluating the at least two process variables. As a result, the error event can be determined particularly reliably. Furthermore, the redundant determination of the error event can be ensured by the monitoring sensor system in the event of insufficient measurement of one of the process variables. This can improve the reliability of the active laser protection.

An embodiment of the laser radiation protection device is particularly preferred in which the monitoring sensor system has at least two measuring devices for measuring the at least one process variable and wherein the evaluation unit is set up to determine the at least one error event by evaluating the measured process variable of the two measuring devices. In this way, the proper functioning of the measuring equipment can be ensured and the reliability of the active laser protection can be further improved.

In addition, an embodiment of the laser radiation protection device is preferred in which the monitoring sensor system has a coherence tomograph for optical distance measurement and/or a thermal imaging camera and/or a pyrometer for thermal radiation measurement. As a result, the active laser radiation protection can be configured particularly cost-effectively using measurement means that are customary in the process.

In a preferred embodiment of the laser radiation protection device, the monitoring sensor system is arranged at least partially, in particular completely, on and/or in a processing head of the laser cutting machine. This favors the simple entrainment of the monitoring sensor system on a movable processing head and the unimpeded measurement of the at least one process variable in the processing area of the laser beam.

The laser radiation protection device according to the invention and the operating method according to the invention are explained in more detail below with reference to preferred modes of operation of the exemplary measuring means.

An optical coherence tomograph implements an interferometric measuring method for optical distance measurement. Polychromatic light from a superluminescence diode with a short coherence length is guided into a reference arm and a measuring arm using a beam splitter. The measuring arm has a reflecting mirror at its end, which directs the light through the beam splitter onto a spectrometer assembly. The workpiece, which scatters the measuring light, is located at an open end of the measuring arm. The backscattered light passes the measuring arm in the opposite direction, is guided via the beam splitter to the spectrometer and here interferes with the light component from the reference arm. A one-dimensional tomographic image can be determined from the resulting interference pattern and imaged by the spectrometer using inverse Fourier transformation, the depth information of which extends along the optical axis of the measuring arm. The measuring range of an optical coherence tomograph used in laser processing can be in the low two-digit millimeter range, the temporal resolution for generating a tomographic image can reach up to a few 100 kHz, the spatial resolution can be a few 10 µm. The measuring light of the optical coherence tomograph is coupled coaxially to the laser beam into focusing optics or processing optics. Since a single measurement of an optical coherence tomograph generates a sectional image that is orthogonal to the optical axis at a defined distance, the measuring arm of the optical coherence tomograph can be deflected by a mirror scanner, for example, to generate a surface profile.

The optical coherence tomograph can be used to determine the risk from a free beam, to detect the focus position and/or to indirectly determine the risk from a beam penetration by comparing the distance measurement with the predetermined error value of the respective error event.

The zero point of the measuring range of the optical coherence tomograph is preferably congruent with a focus of the laser beam over the entire processing field of the scanning optics or is related to the focus by calculation or is tracked to the focus.

To determine the risk of a free jet, the optical coherence tomograph generates at least one, in particular multiple, tomographic images along the optical axis of the processing laser beam. If no workpiece can be detected within the entire axial measuring range of the optical coherence tomograph, the laser processing is prevented by the control. Alternatively or additionally, a line profile or any other pattern can be scanned. The same consideration can take place during laser processing. In this case, it can be provided that the laser processing is aborted by the controller if no workpiece is recognizable in the at least one tomographic image for a predetermined period of time, for example 100 milliseconds.

In order to ensure that the measuring range of the optical coherence tomograph does not unintentionally cover a component of the laser processing machine or the passive laser protection, which could result in the workpiece being misinterpreted as correctly positioned, the movement space of the scanning optics of the optical coherence tomograph can be restricted.

The determination of the hazard due to an incorrect focus position can take place essentially analogously, but with the difference that the workpiece must be located within a predetermined distance range within the measuring range of the optical coherence tomograph.

The optical coherence tomograph can measure the depth of processing by the laser beam on the workpiece to determine the risk of a beam passing through. For this purpose, several tomographic images are preferably generated along the laser beam axis in each focal position. If a predetermined error value of the maximum machining depth, for example 80% of a depth of the workpiece, is exceeded for a period of time to be predetermined, for example 100 milliseconds, the laser machining can be interrupted and/or aborted. Likewise, the laser processing can be interrupted and/or aborted if a through-hole in the workpiece, i.e. an opening on the rear side of the workpiece facing away from the processing head, is determined from one of the tomographic images.

With the thermal imaging camera, an optical image of the heat radiation of the processing area can be generated on a sensor level by means of a matrix sensor. The processing area of the workpiece can be irradiated by a heat source and reflect this in the direction of the matrix sensor, or the processing area itself can emit heat radiation. The heat radiation emitted is preferably measured in the near infrared or infrared wavelength range.

The thermographic camera can be placed coaxially in the beam path of the laser processing optics and aligned with the processing area. The thermal radiation emitted by the workpiece during laser processing can be measured using the thermal imaging camera. The thermal imaging camera can have, for example, an InGaAs image chip with a measuring range for wavelengths of more than 1000 nanometers or a Si image chip with a measuring range for wavelengths of more than 500 nanometers. In the latter case in particular, provision can be made for interfering portions of the thermal radiation to be masked out by using a bandpass filter. For example, a red glow up to approx. 650nm in ferrous materials or a processing radiation of the laser beam as disturbing components in the measurement of heat radiation can be masked out by a bandpass filter.

The thermal imaging camera can be used, for example, to determine the risk from the error events beam passage, faulty coupling and/or beam breakage and is explained in more detail below.

To determine the risk from the error event of beam passage, the thermal radiation in a center of the laser processing area can be measured by the thermal imaging camera. In order to reduce motion blur, in particular due to keyhole dynamics, short exposure times in the microsecond range, for example five to twenty microseconds, can be provided in this case. In the case of the error event of beam passage, the workpiece has a through-hole formed up to the rear side of the metal sheet, which is shown in a thermographic image as an, in particular circular, imaging area with reduced heat emission. For example, it can be provided that the laser processing is interrupted and/or aborted if this imaging area is visible for a predetermined period of time and/or in a predetermined number of consecutive thermographic images.

To determine the risk of incorrect coupling, the evaluation unit can evaluate the thermographic images of the thermographic camera with reference to a chronological development of the heat radiation from the molten pool after activation of the laser beam. If, for example, at a defined point in time, for example ten milliseconds after the start of the laser processing, there is insufficient thermal radiation or radiation intensity of a sufficiently large area visible on the workpiece, the laser processing can be aborted.

To determine the risk of beam breakage, the evaluation unit can evaluate the thermographic images of the thermographic camera with regard to a time course of the heat radiation during the laser processing. If, for example, decreasing and/or insufficient heat emission or radiation intensity is detected in the molten bath once and/or repeatedly for a predetermined period of time, preferably 50 milliseconds, the laser processing can be interrupted and/or aborted.

The pyrometer can be used to measure the thermal radiation emitted or reflected by the workpiece without spatial resolution, but with the option of locally limiting the measuring range on the workpiece, for example by means of a so-called measuring spot and/or measuring ring.

In order to locally limit the measurement area, imaging optics can be provided, which conduct the heat radiation recorded by the measurement area to a photodiode arrangement with a high dynamic range for evaluation using fiber optics.

The thermal radiation emitted by the workpiece can vary in any spectral range and is in particular proportional to the fourth power of the temperature. In order to cover as large an intensity or temperature range as possible, the photodiode arrangement preferably has a high dynamic range. The spectral ranges to be considered can vary in their width, their position (VIS for high temperatures, NIR & FIR for low temperatures) and in number (single-color pyrometer, quotient pyrometer or multi-color pyrometer for temperature determination). In the simplest case, the measurement can be carried out using a pyrometer by forming a photodiode with a downstream amplifier, the photodiode being arranged in the laser beam in order to receive the heat radiation emitted by the processing area via the optical fiber of the processing laser. An opening of the optical fiber can be used in conjunction with the imaging (focusing) optics as a confocal spatial filter, in which case advantageously only the heat radiation emitted at or near the focus of the laser beam is directed to the photodiode.

The pyrometer can be used, for example, to determine the risk from the fault events of faulty coupling, beam breakage and/or laser free beam.

Preferably, the principle of single-color pyrometry is used in an analogous procedure to thermography to determine the risk of incorrect coupling and/or jet breakage. For example, the laser processing can be interrupted and/or aborted if the evaluation unit measures reduced heat radiation in the processing area compared to proper laser processing at a predetermined point in time, for example ten milliseconds after the start of the laser processing.

More preferably, the laser processing can be interrupted and/or aborted when the error event beam breakage is determined if the thermal radiation or radiation intensity emanating from the processing area falls below an error value predetermined as a minimum once or repeatedly for a certain period of time.

As an alternative or in addition to the previously described application of the principle of single-color pyrometry, multi-color pyrometry provided for temperature determination can be used. For example, when using multicolor pyrometry, the temperature of the workpiece measured as a function of time can be compared with a temperature of the molten pool on the workpiece. The error events described above can be determined by the evaluation unit when the workpiece is heated above the error value predetermined as the melting temperature of the workpiece. Otherwise the laser processing can be interrupted and/or aborted.

Further features and advantages of the invention result from the description, the claims and the drawing. According to the invention, the features mentioned above and those detailed below can each be used individually or collectively in any desired, expedient combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather have an exemplary character for the description of the invention.

character list

• 1 shows a laser processing machine and a laser radiation protection device with a passive and an active laser protection in a schematic, perspective view.
• 2 shows a schematic measurement setup of a monitoring sensor system of the active laser protection at the laser processing machine off 1 for measuring a process variable.
• 3 shows a schematic view of a laser beam beam path and a measuring beam beam path.
• 4 shows a schematic sequence of the method according to the invention.

1 shows an arrangement 10 with a laser processing machine 12 and a metal workpiece 14 arranged on the laser cutting machine 12 for laser processing. The laser processing machine 12 preferably has a CO ₂ laser, a solid-state laser or a diode laser as the laser beam generator 16, a movable processing head 18 and a workpiece support 20 , on which the metallic workpiece 14 is arranged. A laser beam 22 is generated in the laser beam generator 16 and is directed by means of a fiber optic cable (not shown) or deflection mirrors 24 (see 2 ) is guided from the laser beam generator 16 to the processing head 18. The laser beam 22 is arranged in the processing head 18 by means of focusing optics 26 (see 2 until 5 ) directed to the metallic workpiece 14. According to the exemplary representation, the laser processing machine 12 is supplied with a working gas 28 . The working gas 28 is supplied to the processing head 18--preferably under pressure control--from which it emerges together with the laser beam 22. The laser processing machine 12 also includes a machine control 30 which is programmed, among other things, to move the processing head 18 along a processing line 32 relative to the metallic workpiece 14 .

The arrangement 10 also has a laser radiation protection device with a passive laser protection 34 and an active laser protection 36 . The passive laser protection 34 has, for example, a radiation protection wall 38 . Provision can also be made for the passive laser protection 34 to have further radiation protection walls 38 or a laser protection cabin (not shown) as an alternative or in addition. The passive laser protection 34 is designed to block laser radiation 42 escaping into an environment 40 of the laser processing machine 12 . This can prevent an object (not shown) and/or a person (not shown) located in the surroundings 40 from being endangered.

The active laser protection 36 has a monitoring sensor system 44 , an evaluation unit 46 and a controller 48 . The monitoring sensor system 44 is shown in FIG 1 arranged on the processing head 18 or integrated in the processing head 18 . The evaluation unit 46 and the controller 48 are arranged here in a common housing. The active laser protection 36 is set up to detect laser radiation 42 escaping into the surroundings 40 .

2 shows a schematic measurement setup 50 for measuring a process variable in a processing area 52 of the laser beam 22. The measurement setup 50 has the monitoring sensor system 44, which is arranged on the processing head 18 of the laser cutting machine 12. The processing head 18 has a processing nozzle 54 , the focusing optics 26 for focusing the laser beam 22 and the deflection mirror 24 . The deflection mirror 24 can be part of a deflection system that has, in particular, a plurality of deflection mirrors 24 . In the present case, the deflection mirror 24 is designed to be partially transparent and therefore forms an entry-side component of the monitoring sensor system 44 .

The laser beam 22 - shown here by dashed lines - is generated by the laser beam generator 16 (see 1 ) coming by means of the deflection mirror 24 onto the focusing optics 26 - a converging lens of the focusing optics 26 is shown here by way of example - directed.

The deflection mirror 24 reflects the incident laser beam 22 and transmits measurement radiation 56, which is relevant for the measurement of the process variable and comes from the processing area 52.

A further deflection mirror 58 is arranged in the monitoring sensor system 44 behind the partially transparent deflection mirror 24 and deflects the measuring radiation 56 onto a measuring means 60 . The measuring means 60 can be, for example, an optical coherence tomograph, a thermal imaging camera or a pyrometer. Furthermore, the parallel use of several measuring means 60 can be provided. The measuring means 60 can be aligned coaxially to a laser beam axis 62 or to the extension 62a of the laser beam axis 60 and thus independent of direction by the additional deflection mirror 58 .

For an improved recording, according to the illustration shown, an in 2 imaging, focusing optical system 64 shown as a lens can be provided, which focuses measuring radiation 56 onto measuring means 60 . An aspheric design of the imaging optical system 64—here a lens—for focusing can prevent or at least reduce spherical aberrations during imaging.

In addition, according to in 2 shown example, a filter 66 in front of the measuring means 60 angeord not be. This is particularly advantageous if certain radiation or wavelength components are to be excluded from the detection with the measuring device 60 . The filter 66 can be embodied, for example, as a narrow-band bandpass filter with a small half-width in order to avoid or reduce chromatic aberrations. The position of the measuring means 60 and the imaging optical element 64 present in the present example and/or the filter 66 along the extension 62a of the laser beam axis 62 can be adjusted and, if necessary, changed using a positioning system 68 known to those skilled in the art and, for the sake of simplicity, represented by a double arrow.

The measuring device 60 is according to in 2 example shown for measuring a process variable set up coaxially to the laser beam 22. In other words, process variables that can be detected predominantly coaxially to the laser beam 22 are measured with the measuring means 60 . Provision can also be made for alternative or additional measuring means 60 to be set up to measure process variables at an angle to the laser beam axis 62 . As a result, further process variables can be measured and the active laser protection 36 can be improved.

For a better understanding of the active laser protection 36, the mode of operation is explained in more detail below using an example. For example, the measuring device 60 is designed as a thermographic camera. In this case, the measuring radiation 56 is heat radiation emitted by the workpiece 14 in the processing area 52 of the laser beam 22. The thermal imaging camera converts the measured heat radiation into thermal radiation of the processing area 52 is generated. The thermal is then evaluated by the evaluation unit 46 . In the example, two temperature ranges 72a, 72b are determined by the evaluation unit 46, with the inner temperature range 72a having a significantly lower temperature than the outer temperature range 72b. With proper laser processing, however, the inner temperature area 72a would have a significantly higher temperature than the temperature area 72b. The evaluation unit 46 then determines that a beam passage error event has occurred, in which there is a significant risk from the to the environment 40 (see 1 ) emerging laser beam 22 is given. The controller 48 then accesses the machine controller 30 (see 1 ) and the laser processing machine 12 (see 1 ) switch off.

3 shows schematically a beam path through the focusing optics 26 and the processing nozzle 54 of the processing head 18 2 to the back of the workpiece 14. The measuring radiation 56 is directed in a direction opposite to the laser beam 22, coaxially to the laser beam axis 62, by means of the further deflection mirror 58 (see 2 ) on the measuring device 60 (see 2 ) directed.

In 3 the beam path of the laser beam 22 is also shown, which, starting from the deflection mirror 24, is directed onto the workpiece 14 by means of the focusing optics 26 for laser processing. For this purpose, the focusing optics 26 bundle the laser beam 22 in a focus point or focus 74 of the laser beam 22 . According to the illustration, the laser beam 22 has a focus 74 which is arranged in a focus position 76 below the workpiece 14 . Consequently, the laser beam 22 passes through the workpiece 14 in the illustration shown.

The workpiece 14 also has a molten pool 78 which is formed asymmetrically around a laser machining center formed by the laser beam 22 . The machining area 52 therefore has a planar extension 80 on a side of the workpiece 14 facing the machining head 18, which includes an extension of the molten bath 38 and the laser machining center.

4 shows a schematic representation of an operating method 82 according to the invention, which with reference to FIG 2 and 3 and should be explained in more detail using exemplary training and values.

In a first method step "measurement of a process variable" 84, the at least one process variable in the processing area 52 (see 2 and 3 ) measured on the workpiece 14.

For example, a measuring device 60 can be in the form of an optical coherence tomograph, the optical coherence tomograph being set up to measure a distance between the machining head 18 and the workpiece 14 . The optical coherence tomograph is preferably designed to create a large number of tomographic images along the laser beam axis 62 , each tomographic image representing a cross-sectional image of the processing region 52 orthogonal to the laser beam axis 62 . The tomographic images are recorded by the processing head 18 with a known spacing. The tomographic images can then be evaluated graphically in the evaluation unit 46, the spacing of those tomographic images being important for measuring the distance between the processing head 18 and the workpiece 14 at which the tomographic images reveal the workpiece 14. In this way, the distance between the workpiece 14 and the machining head 18 can be determined.

In a further method step “comparing the process variable with an error value” 86, the measured process variable is compared with at least one predetermined error value.

According to the example, the measured distance between the machining head 18 and the workpiece 14 can thus be compared with at least one predetermined distance value that is symptomatic of an error event. For example, different distance values can be predetermined for the free beam error event and the wrong focus position error event. While in the case of the free beam error event it is checked whether the workpiece 14 is within a production distance provided by the laser processing machine, when the incorrect focus position error event is determined, it is checked whether the workpiece 14 is in the focus position 76 .

In a subsequent method step “determining an error event” 88, the evaluation unit 46 determines whether an error event has occurred.

According to the illustration in 3 the workpiece 14 is located, for example, within the production area provided by the laser processing machine 12, so that the free beam error event did not occur. In contrast, the error event incorrect focus position is determined as having occurred, since the focus position 76 is at a greater distance than the workpiece 14 . Furthermore, it can be provided that the error event beam penetration is determined by evaluating the tomographic images in relation to an opening that has occurred on the workpiece 14 .

In a further method step “initiating a security measure” 90, a security measure is then initiated if a faulty event was detected in step 88. In this case, the controller 48 can be set up to intervene in the machine controller 30 of the laser processing machine 12 . It should be noted that the controller 48 and the machine controller 30 may be integral with each other. The evaluation unit 48 can also be integrated.

The type of safety measure introduced can depend on the error event that has been determined. For example, it can be provided that only the focus position 76 on the machine controller 30 is changed by the controller 48 when the error event wrong focus position is determined. On the other hand, in the event of a beam passage error event, an interruption of the laser beam 22 and/or an interruption of the energy supply can be provided by the controller 48 .

Reference List

10

arrangement

12

laser processing machine

14

workpiece

16

laser beam generator

18

processing head

20

workpiece support

22

laser beam

24

deflection mirror

26

focusing optics

28

working gas

30

machine control

32

editing line

34

Passive laser protection

36

Active laser protection

38

radiation protection wall

40

Vicinity

42

laser radiation

44

monitoring sensors

46

evaluation unit

48

steering

50

measurement setup

52

editing area

54

processing nozzle

56

measuring beams

58

Another deflection mirror

60

measuring equipment

62

laser beam axis

62a

extension of the laser beam axis 62;

64

Focusing optical system

66

filter

68

positioning system

70

Thermal mapping

72a

internal temperature range

72b

External temperature range

74

focus

76

focal position

78

melt pool

80

Planar extent of the machining area 52;

82

operating procedures

84

Method step "Measurement of a process variable"

86

Method step "Comparing the process variable with an error value"

88

Method step "Determining an error event"

90

Process step "Initiating a security measure"

QUOTES INCLUDED IN DESCRIPTION

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

Non-patent Literature Cited

• DIN EN ISO 13849-1 [0031]

Claims (15)

Operating method (82) for a laser processing machine (12) for protection against laser radiation (42) escaping into an environment (40) of the laser processing machine (12); wherein at least one process variable in a processing area (52) of a laser beam (22) is measured continuously; wherein the measured process variable is compared to at least one predetermined error value of at least one predetermined error event; wherein in the case of the error event, the laser radiation (42) escapes into the environment (40) in an impermissible manner; and a security measure being initiated if the environment (40) is endangered by the error event. Operating procedure (82) according to claim 1 , wherein at least two process variables are measured and the at least two measured process variables are compared with at least two error values of the at least one error event, with a risk being determined as a function of both comparisons. Operating procedure (82) according to claim 1 or 2 , wherein the at least one process variable is measured with at least two measuring devices (60) and the measured process variable of the at least two measuring devices (60) is compared with the at least one error value of the at least one error event, with a risk being determined as a function of both comparisons. Operating method (82) according to any one of Claims 1 until 3 , wherein a distance between the workpiece (14) and a laser processing head (18) of the laser cutting machine (12) along a laser beam axis (62) is measured. Operating method (82) according to any one of Claims 1 until 4 , wherein a heat radiation emitted by the workpiece (14) is measured in a locally resolved manner. Method of operation (82) according to one of Claims 1 until 5 , wherein a heat radiation reflected from the workpiece (14) coaxially to the laser beam (22) is measured. Operating method (82) according to any one of Claims 1 until 6 , wherein a heat radiation emitted by the workpiece (14) is evaluated in a time-resolved manner. Operating method (82) according to any one of Claims 1 until 7 , wherein a heat radiation emitted by the workpiece (14) in a laser machining center is measured. Method of operation (82) according to one of Claims 1 until 8th , wherein a heat radiation emitted by a molten pool (78) on the workpiece (14) is measured. Operating method (82) according to any one of Claims 1 until 9 , wherein a heat radiation emitted by the workpiece (14) is locally measured. Laser radiation protection device for protecting the surroundings (40) from the laser radiation (42) of the laser beam (22) of the laser processing machine (12), having passive laser protection (34) and active laser protection (36), wherein the passive laser protection (34) is designed to hold back laser radiation (42) that is typical for the process and escapes into the environment (40); and wherein the active laser protection (36) has a controller (48), a monitoring sensor system (44) and an evaluation unit (46); wherein the monitoring sensor system (44) is designed to measure the at least one process variable in the processing area (52) of the laser beam (22); wherein the evaluation unit (46) is set up to determine the at least one error event by comparing the measured process variable with the at least one error value; and wherein the controller (48) is set up to initiate a safety measure if the permissible laser radiation emitted into the environment is exceeded. Laser radiation protection device according to one of Claims 11 , wherein the monitoring sensor system (44) is designed to measure at least two process variables and wherein the evaluation unit (46) is set up to determine the at least one error event by evaluating the at least two process variables. Laser radiation protection device claim 11 or 12 , wherein the monitoring sensor system (44) has at least two measuring devices (60) for measuring the at least one process variable and wherein the evaluation unit (46) is set up to determine the at least one error event by evaluating the measured process variable of the two measuring devices (60). Laser radiation protection device according to one of Claims 11 until 13 , wherein the monitoring sensor system (44) has a coherence tomograph for optical distance measurement and/or a thermal imaging camera and/or a pyrometer for thermal radiation measurement. Laser radiation protection device according to one of Claims 11 until 14 , The monitoring sensor system (44) being arranged at least partially on and/or in a processing head (18) of the laser cutting machine (12).

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