Surveillance arrangement for a laser system and laser system with the surveillance arrangement

Description

[0001] The invention relates to a monitoring arrangement for a laser system, wherein the laser system is configured to implement a laser processing process, with the features of the preamble of claim 1. Furthermore, the invention relates to a laser system with the monitoring arrangement.

[0002] In laser material processing, a focused laser beam is directed at a workpiece to, for example, cut or weld it. Like any system in industrial manufacturing, laser systems must also meet all occupational safety requirements.

[0003] The laser beam deserves special attention because, in most applications, its wavelength is invisible to the human eye, making it impossible for operators to detect the hazards posed by the laser beam. For this reason, laser systems are typically enclosed in laser-tight housings, designed to prevent penetration even after prolonged exposure to the laser beam. Such housings are often double-walled. Alternatively, the housings may be equipped with large sensors that detect the heat generated by the laser beam, and the laser system is switched off upon detection.

[0004] During laser material processing, characteristic optical process emissions occur, caused by an interaction between the laser beam and the workpiece material. These process emissions are used to control the laser processing process.

[0005] German patent application DE 100 60 176 A1 describes a laser processing head with integrated sensors, wherein the sensor beam path is coaxial with the laser beam path used for material processing. The sensor serves to monitor the processing process during laser beam welding.

[0006] From DE 10 2012 007 304 A1 a method for controlling the weld penetration depth when welding two workpieces is known.

[0007] From DE 10 2012 207 835 A1 a method for monitoring a laser processing process is known, wherein at least one image acquisition device and an associated evaluation unit are provided.

[0008] German patent DE 10 2013 010 200 A1 discloses a method for the precise cutting, drilling, scoring, and notching of materials, as well as for the removal of thin layers with sharp edges and precise depth control. The distance between the imaging optics and the sample, which produces a local minimum in the intensity of the laser-induced plasma emission, is selected as optimal for this purpose. The method also takes material dependencies into account and can therefore be used both for adjusting the process parameters during processing and for the desired shutdown during laser microablation on workpieces, components, and layer systems consisting of multiple materials.

[0009] From DE 689 12 321 T2, a laser beam processing device is known for processing a workpiece with a laser beam incident on a surface of the workpiece, comprising: reflection light detector means for detecting a power level of a laser beam reflected back to a laser oscillator as a result of a reflection of the laser beam at the workpiece surface, and anomaly detector means for stopping operation of the laser oscillator and movement of the workpiece or an aperture part and for an alarm indication on a display device when the power level of the reflected laser beam becomes higher than a predetermined value, wherein the predetermined value is a maximum output value estimated for a range of normal processing operation.

[0010] From US 9,114,477 B1, which is the closest prior art, a method and a device for joining workpieces using a laser beam are known, wherein the device comprises: a scanner optic for guiding the laser beam; a pressing element that is pressed onto at least one of the workpieces along a pressing direction during the joining process; and a housing that encloses the scanner optic and the laser beam extending from the scanner optic to the workpieces, wherein the pressing element forms part of the housing and is movable relative to the rest of the housing by at least one degree of freedom.

[0011] The object of the present invention is to propose a monitoring arrangement and a laser system comprising the monitoring arrangement, which provides further functions. This object is achieved by a monitoring system with the features of claim 1 and by a laser system with the features of claim 3. Preferred or advantageous embodiments of the invention are described in the dependent claims, the following description, and the accompanying figures.

[0012] The invention relates to a monitoring arrangement suitable and / or configured for a laser system. The laser system is configured for implementing a laser processing process. The laser system preferably comprises at least one processing laser for generating a laser beam, in particular a processing laser beam for the laser processing process. The processing laser can be, for example, a gas laser or a solid-state laser, in particular a CO₂ laser or an Nd:YAG laser. Preferably, the processing laser has an output power greater than 500 watts, in particular greater than 1000 watts. The laser system preferably includes a handling device, such as a robot.The laser processing process is in particular a cutting process, a welding process, a hardening process or a soldering process. In the laser processing process, a workpiece is processed, the workpiece being preferably made of metal.

[0013] The monitoring system includes an evaluation unit. This evaluation unit can be a separate component. Alternatively, it can be implemented as a component of the laser system control system. The evaluation unit can be digital or analog, and implemented using hardware or software. In particular, the evaluation unit can be implemented as a computer.

[0014] The evaluation unit has an input interface for receiving at least one sensor signal. The input interface can be wired or wireless. The sensor signal can be transmitted analogously or digitally. It is also possible for the sensor signal to be a pre-processed signal. The sensor signal describes a light emission in the form of a process emission from the laser processing operation. The sensor signal is detected by a sensor device whose detection range is directed towards the laser processing operation and which is designed to detect light emissions from the laser processing operation with respect to wavelength.

[0015] Furthermore, the evaluation unit has an output interface for sending an emergency signal to initiate an emergency response for the laser system. The output interface can be wireless or wired. The emergency signal can be an analog or digital signal. According to the invention, the emergency response leads to the deactivation of the laser beam in the laser processing process.

[0016] Within the scope of the invention, it is proposed that the evaluation unit be configured to examine the sensor signal for deviations in the laser processing process, particularly during the course of the laser processing process. For example, the sensor signal can be compared with a reference sensor signal. Alternatively, it can be checked whether the sensor signal lies within or exceeds certain limit values. The evaluation unit is further configured to trigger the output of the emergency signal upon detection of such a deviation.

[0017] According to the invention, the detection of light emissions in the form of process emissions from the laser processing process determines whether the laser beam is intended to hit the workpiece or whether, due to a disturbance such as misalignment, collision of the handling device, absence of a workpiece, selection of an incorrect processing program, or other errors, the laser beam is not directed onto the workpiece as intended.

[0018] Estimates have shown, for example, that for a kilowatt laser, the light emission intensity due to plasma generated during the laser processing process in the focal spot of the laser beam on the workpiece is approximately 14 kW / mm². Even with an increase in distance of just 30 cm, this value drops to approximately 8 kW / mm². Thus, a significant difference in light emission is noticeable, and consequently, a significant deviation in the sensor signal can be detected. This allows such a misalignment to be detected as a potential fault in a simple and highly reliable manner via the sensor signal. If the sensor signal changes significantly as described, a misalignment of the laser beam relative to the workpiece can be assumed, and an emergency signal can be triggered.

[0019] Optionally, an additional sensor signal or power monitoring signal is fed into the monitoring system, indicating when the processing laser is activated. This allows the monitoring system to determine whether (1) the processing laser is activated and (2) a sensor signal corresponding to the laser processing process is present, based on the light emission of the laser processing process. If the second condition is not met, an emergency signal can be issued to initiate an emergency response for the laser system.

[0020] In principle, the sensor signal could describe light emission from the laser processing process based on a heated workpiece material, particularly thermal radiation. However, it is preferred that the sensor signal describe light emission emanating from a laser plasma. Unlike thermal radiation, the laser plasma emits a higher proportion of UV radiation, so the absence of the laser plasma can be detected particularly accurately by the sensor signal.

[0021] The sensor signal describes a spectrum and / or intensity of a plasma during the laser processing process. Regarding the spectrum, a complete spectrum can be acquired, for example, using a spectrometer. However, it may be sufficient to acquire at least two data points positioned at different wavelengths or wavelength ranges and relate them, for example, by calculating a ratio.

[0022] The deviation manifests itself, among other things, as a weakening or a complete loss of light emission. This occurs precisely when the laser beam is misaligned or misses the workpiece. In both cases, an unplanned laser processing operation must be assumed, and the evaluation unit issues an emergency signal to initiate the emergency response.

[0023] In a preferred embodiment of the invention, the monitoring arrangement includes an aperture device for glare control of the laser beam. The aperture device can be integrated into the laser system so that the laser processing beam can be glare-controlled or blocked by the aperture device. The aperture device is connected to the evaluation unit via a signal. Preferably, this connection is made without access to the laser system's control unit. The emergency signal activates the aperture device, causing the laser beam to be glare-controlled or interrupted. The advantage of the aperture device as an additional component is that it can be activated immediately, allowing the laser beam to be glare-controlled and thus deactivated very quickly upon detection of a deviation, particularly within a time of less than 0.5 seconds, and specifically less than 0.1 seconds.

[0024] A further aspect of the invention relates to a laser system, as previously described, for implementing the laser processing process, wherein the laser system comprises a monitoring arrangement, as previously described or according to one of the preceding claims. The laser system and the monitoring arrangement comprise a sensor device for recording the light emission of the laser processing process and for outputting the sensor signal.

[0025] The sensor device has a detection direction, which is preferably aligned coaxially with the laser beam. In particular, the sensor device is designed as a coaxial sensor device. This means that the sensor device faces the same direction as the laser processing beam, so that any light emissions, especially process emissions, from the laser processing process are reliably detected. For example, the sensor device is integrated into a laser processing head. Depending on the processing laser, a coupling mirror or a bore may be provided, for example, to extract the light emissions from the laser processing process from the beam path.

[0026] In the case that the light emission originates from a plasma, it is preferred that the sensor device for detecting light radiation with a wavelength in the UV range, i.e., in particular less than 350 nm. Alternatively, the sensor device can be designed as a ratio sensor, which detects light radiation in two different wavelength ranges and relates the detected values.

[0027] It is preferably provided that the laser system has an emergency stop device, wherein the emergency stop device is connected to the evaluation unit via a signal connection, and wherein the emergency stop device is controlled by the emergency signal, causing the laser system to enter an emergency stop state. In particular, the processing laser is switched off or deactivated in the emergency stop state. Most preferably, the laser system simultaneously enters an emergency stop, whereby the handling device is stopped.

[0028] In an advantageous embodiment of the invention, the emergency stop device must be manually reset from the emergency stop state to the operating state, in particular by an operator. This ensures that the laser system cannot reactivate automatically and potentially continue running after a processing error, but is first checked by an operator.

[0029] Preferably, the laser system features a work cell enclosure surrounding the laser processing area. This work cell enclosure is designed as a lightweight structure that does not fully comply with current laser safety regulations. The possibility of using a less powerful work cell enclosure arises from the monitoring system, which replaces or supplements the work cell enclosure with regard to laser safety.

[0030] Further features, advantages, and effects of the invention will become apparent from the following description of a preferred embodiment of the invention and the accompanying figures. These figures show: Figure 1 in a highly schematic representation a laser system with a monitoring arrangement in an operating state as a first embodiment of the invention, Figure 2 the laser system in Figure 1 in the same representation in an emergency shutdown state.

[0031] The Figure 1 Figure 1 shows a highly schematic representation of a laser system 1 as an embodiment of the invention. The laser system 1 serves to carry out a laser processing process on a workpiece 2.

[0032] The laser system 1 includes a processing laser 3 for generating a laser beam 4 for processing the workpiece 2. The laser beam 2 is guided by the processing laser 3 over a handling device 5. The handling device can be, for example, a robot, in particular a Cartesian robot or an articulated robot, which carries a beam guide for the laser beam 4. The laser beam 4 is guided via the handling device 5 to a processing head 6, exits there, and reaches the workpiece 2. The workpiece 2 is, for example, made of metal.

[0033] The laser system 1 also features a monitoring arrangement 16 with several components, some of which are partially integrated into the laser system 1.

[0034] Due to the laser processing process, a plasma 7 is generated on the workpiece 2. The plasma 7 emits light, at least partially in the UV range. A coupling mirror 8 is arranged in the processing head 6, which couples the light emission from the plasma 7 against the direction of propagation of the laser beam 4 and directs it to a sensor device 9. The sensor device 9 forms a first possible component of the monitoring arrangement 16. The coupling mirror 8 and the sensor device 9 can be arranged as shown in the Figure 1 This is indicated. However, it is also possible that the output coupler mirror 8 is located closer to the processing laser 3. It is advantageous, however, if the observation of the processing location and / or the laser processing process and / or the plasma 7 is coaxial with the laser beam 4. The observation direction of the sensor device 9 is aligned coaxially with the laser beam 4.

[0035] The sensor device 9 generates a sensor signal, which is forwarded to an evaluation unit 10 and processed there. The evaluation unit 10 is a key component of the monitoring arrangement 16. The evaluation unit 10 receives the sensor signal via an input interface 11. The evaluation unit 10 has at least one, preferably several, output interfaces 12, which are capable of outputting an emergency stop signal or a control signal for generating an emergency stop. It is possible for the emergency stop signal to be routed to an emergency stop device 17 of a controller 13 of the laser system 1, so that an emergency stop is performed centrally. However, it is also possible for the emergency stop signal to be routed to the processing laser 3, so that it is switched off.Another possibility is that the emergency stop signal is routed to an aperture device 14, which can cover the beam path of the laser beam 4 and thus deactivate the laser beam 4. The aperture device 14 forms another possible component of the monitoring arrangement 16.

[0036] During normal operation of the laser system 1, the laser beam 4 is always directed at the workpiece 2 or deactivated. However, it cannot be ruled out during operation that the laser beam 4 might not hit the workpiece 2, for example, because the handling device 5 is deactivated, the workpiece 2 is missing, an incorrect program has been selected for processing, etc. While such malfunctions are, in principle, mitigated by multiple safeguards, laser safety regulations stipulate that the risk of a freely exiting laser beam 4 must be intercepted.

[0037] As already explained, the processing of workpiece 2 generates process emissions, particularly light emissions, due to the plasma 7. Sample calculations have shown that a misalignment between the processing head 6 and workpiece 2 results in a significant change in the intensity of the light emission, which is reflected back in the processing head 6, coupled out via the output mirror 8, and then falls onto the sensor device 9.

[0038] The evaluation unit 10 monitors whether deviations occur in the sensor signal of the sensor device 9 that are attributable to a disturbance in the laser processing process. In the present embodiment of the invention, such deviations are a significant reduction in the intensity of the detected light emission or a change in the spectral distribution of the detected light emission. The evaluation unit 10 is thus configured to examine the sensor signal for deviations in the laser processing process and, in the event of deviations, to transmit an emergency stop signal to the laser system 1 and, in particular, to the emergency stop device 17 via the output interface 12.

[0039] The emergency stop functionality is designed in such a way that the emergency stop can only be reset manually, so that the laser system 1 cannot automatically reset itself to the active state.

[0040] The laser system 1 also has a work cell enclosure 15, which shields the processing area in which the free laser beam 4 is arranged or runs from an environment.

[0041] In the Figure 2 is laser system 1 of the Figure 1The diagram shows that the workpiece 2 deviates in position such that the laser beam 4 shines against a wall of the work cell enclosure 15. When the workpiece 2 is moved, the plasma 7 immediately ceases and the light emission stops. This change in light emission can be detected by the sensor 9 and the evaluation unit 10. Such a change represents a significant deviation from the normal sensor signal. In response to the deviation, the evaluation unit 10 outputs one or more emergency stop signals. Firstly, the laser system 1 is completely deactivated via the control unit 13. Alternatively or additionally, the processing laser 3 can also be deactivated. Another possibility is that the evaluation unit 10 directly controls the aperture 14, closing it and blocking the laser beam 4's path through the aperture 14.

[0042] With this functionality, laser safety for the laser system 1 can be achieved via the monitoring arrangement 16, so that the work cell enclosure 15 can be designed in a lightweight construction. Reference symbol list:

[0043] 1 Laser system 2 Workpiece 3 Processing laser 4 Laser beam 5 Handling device 6 Processing head 7 Plasma 8 Output coupling mirror 9 Sensor device 10 Evaluation device 11 Input interface 12 Output interface 13 Control unit 14 Shutter device 15 Work cell enclosure 16 Monitoring device 17 Emergency stop device

Claims

1. A monitoring arrangement (16) for a laser system (1) for implementing a laser machining process, - having an evaluation device (10), and - having a sensor device (9) the sensing area of which is directed towards the laser machining process and which is configured to be able to receive process light emissions in the form of process emissions of the laser machining process with respect to the wavelength, wherein the evaluation device (10) - has an input interface (11) for accepting at least one sensor signal, wherein the sensor signal is received by the sensor device (9), wherein the sensor signal describes the process light emission of the laser machining process starting from a plasma, - and has an output interface (12) for outputting an emergency signal in the form of a control signal for initiating an emergency reaction for the laser system (1), which leads to a deactivation of the laser beam in the laser machining process, characterized in that the evaluation device (10) is configured to examine and to monitor the sensor signal for deviations of the process light emission in the laser machining process in the form of both a weakening of the process light emission and a failure of the process light emission as well as a change in the spectral distribution of the sensed process light emission, wherein it can be detected, by the detection of the process light emissions, whether the laser beam strikes the workpiece as intended or whether the laser beam is not conducted onto the workpiece as intended due to a disturbance, and, in the event of a deviation being detected, if the laser beam is not conducted onto the workpiece as intended due to the disturbance, to output the emergency signal, wherein the sensor signal describes a spectrum and / or an intensity of a plasma during the laser machining process.

2. The monitoring arrangement (16) according to any one of the preceding claims, characterized by a diaphragm device (14) for integration into the laser system (1) for dimming a laser beam (4), wherein the diaphragm device (14) is connected for signaling purposes to the evaluation device (10) and wherein the diaphragm device (14) is actuated by the emergency signal in order to dim the laser beam (4).

3. A laser system (1) for implementing a laser machining process, characterized by a monitoring arrangement (16) according to any one of the preceding claims.

4. The laser system (1) according to Claim 3, characterized by an emergency stop device (17), wherein the emergency stop device (17) is connected for signaling purposes to the evaluation device (10) and wherein the emergency stop device (17) is actuated by the emergency signal to switch from an operating state into an emergency stop state.

5. The laser system (1) according to Claim 4, characterized in that the emergency stop device (17) has to be manually switched from the emergency stop state into the operating state.

6. The laser system (1) according to any one of Claims 3 to 5, characterized by the sensor device (9) for receiving the light emission of the laser machining process and for outputting the sensor signal to the evaluation device, wherein the sensor device (9) has a sensing direction, wherein the sensing direction is aligned coaxially with the laser beam (4).

7. The laser system (1) according to any one of Claims 3 to 6, characterized by a working cell housing (15) for encompassing the laser machining process, wherein the working cell housing (15) is configured as a light housing with no laser protection function or with a reduced laser protection function.