Beam closure, laser arrangement and operating method for a laser arrangement

Abstract

Beam closure (12) for a laser beam (16) comprising - a reflective optic (20) for deflecting the laser beam (16), and - a holding arm (18) which can be moved into a release position and a closed position and on which the reflective optics (20) are held, characterized by that the beam closure (12) - a sensor circuit (38) with at least one sensor component (50) arranged between the reflective optics (20) and the holding arm (18), and - an evaluation device (34) which interacts with the sensor circuit (38) at least in the closed position of the holding arm (18), and that the evaluation device (34) interacts contactlessly with the sensor circuit (38).

Description

Background of the invention

[0001] The invention relates to a beam shutter for a laser beam, comprising a reflective optic for deflecting the laser beam and a holding arm that can be moved into a release position and a closure position and on which the reflective optic is held. The invention further relates to a laser arrangement with a laser light source for generating a laser beam and with such a beam shutter. Furthermore, the invention relates to an operating method for such a laser arrangement.

[0002] In prior art laser arrangements with a laser light source for generating a laser beam, it is often provided that when a safety circuit is opened (for example, interrupting a light barrier or opening an enclosure), a reflective optic is folded into the beam path of the laser beam. The reflective optic then interrupts the path of the laser beam to an exit opening. The laser beam is deflected by the reflective optic and typically strikes an absorber.

[0003] With such devices, it can sometimes happen that the reflective optics detach from a support arm or lose their reflective properties. The laser beam can then pierce the support arm for the reflective optics. This can result in personal injury and / or property damage.

[0004] To detect a failure of the reflective optics, it is known to place a temperature-sensitive bimetallic component behind the reflective optics. When the laser beam hits the bimetallic component, this can cause it to heat up, especially if the laser light source emits long laser pulses or operates in continuous wave mode. This heating causes the bimetallic component to change shape. This change in shape can be detected by a proximity switch, which then triggers the laser light source to shut down.

[0005] However, especially when using ultrashort pulse lasers as a laser light source, a defect in the reflective optics can cause the laser beam to penetrate the holding arm without significant heating ("cold"). This cannot be reliably detected with temperature-sensitive bimetallic components.

[0006] Furthermore, reference is made to the following publications, which were cited as relevant prior art in the examination proceedings before the German Patent and Trademark Office: US 5 596 590 A, CA 2 389 255 A1, US 2008 / 0 317 077 A1, US 2011 / 0 211 243 A1, US 5 911 319 A. Object of the invention

[0007] It is an object of the invention to improve the operational reliability of laser light sources, in particular to avoid hazards in the event of faults. Description of the invention

[0008] This object is achieved according to the invention by a beam shutter according to claim 1, a laser arrangement according to claim 12, and a method having the features specified in claim 13. The respective subclaims and the description specify advantageous embodiments or variants. Beam closure according to the invention

[0009] According to the invention, a beam closure for a laser beam is provided. The beam closure can also be referred to as a shutter. The beam closure has a reflective optic for deflecting the laser beam. The reflective optic typically has a mirror layer. In particular, the reflective optic can be a mirror.

[0010] The beam shutter also has a holding arm. The reflective optics are held on the holding arm. The holding arm can be moved into a release position and a closed position. In the closed position, the laser beam of a laser arrangement with the beam shutter strikes the reflective optics and is deflected by them. In the release position, the laser beam can pass through the beam shutter without being deflected by the reflective optics.

[0011] According to the invention, the beam shutter comprises a sensor circuit with at least one sensor component arranged between the reflective optics and the support arm. The sensor circuit is an electrical circuit. The sensor component is accordingly a component of this electrical circuit. In special cases, the sensor circuit can consist of the sensor component.

[0012] Further according to the invention, the beam shutter comprises an evaluation device. The evaluation device interacts with the sensor circuit, at least in the closed position of the holding arm. This allows a change in the sensor circuit to be detected by the evaluation device. Preferably, the evaluation device can detect at least one characteristic property of the sensor circuit.

[0013] Since the sensor component of the sensor circuit is arranged between the reflective optics and the holding arm, if the reflective optics are defective, the laser beam strikes the sensor component. This changes the sensor component. In particular, the sensor component can be destroyed by the laser beam, for example if the laser beam pierces the sensor component. The change in the sensor component caused by the laser beam leads to a change in the sensor circuit, in particular at least one characteristic property of the sensor circuit. This change in the sensor circuit can in turn be detected by the evaluation device. If the evaluation device detects such a change in the sensor circuit, a laser light source can be switched off. A dangerous escape of laser radiation can thus be avoided.

[0014] The evaluation unit interacts with the sensor circuit without contact. This simplifies the design of the beam shutter. Furthermore, there is no wear between the evaluation unit and the sensor circuit. Furthermore, no moving wires or conductors are required to connect the evaluation unit and the sensor circuit, eliminating the risk of breakage due to material fatigue.

[0015] The sensor component or one of the sensor components can be a capacitor, a coil, a conductor track, an RFID chip, a thermistor, a diode, preferably a photodiode, a transistor, or a fuse. If multiple sensor components are provided, several of the sensor components or all of the sensor components can each be one of the aforementioned elements; for example, a first sensor component can be a capacitor and a second sensor component a conductor track. In particular, multiple similar sensor components, e.g., two coils, can be provided.

[0016] The capacitor is preferably a film capacitor. Experiments conducted by the inventors have shown that film capacitors are particularly sensitive to laser radiation.

[0017] If the sensor component is an RFID chip, it can have an integrated temperature sensor. This allows for additional temperature monitoring. In particular, if the temperature rises, a laser light source can be switched off before the laser beam destroys the RFID chip. If no heating occurs—for example, when using an ultrashort pulse laser as the laser light source—the laser light source will be switched off if the RFID chip is destroyed.

[0018] The evaluation device can interact directly with the sensor component. In this case, the sensor circuit can be formed by the sensor component. The sensor component or sensor circuit can be an RFID chip.

[0019] The sensor circuit preferably has a coupling component for the evaluation device. The evaluation device then interacts with the sensor circuit via the coupling component. The coupling component and the sensor component are fundamentally separate parts of the sensor circuit. The coupling component can be a coil. In particular, the evaluation device can be designed to induce a voltage in the coil and / or to detect a magnetic field induced by the coil.

[0020] Particularly preferably, the coupling component is arranged next to the reflective optics. This facilitates access by the evaluation device to the coupling component. While the sensor component is concealed by the reflective optics and the holding arm, the coupling component can be freely accessible from at least one direction. The coupling component and the evaluation device can thus be positioned close to one another when the holding arm is in the closed position. In particular, when moving the holding arm from the release position to the closed position, the coupling component can be pivoted over the evaluation device.

[0021] Particularly preferably, the sensor circuit has a capacitor as a sensor component and a coil as a coupling component. The capacitor and the coil form an oscillating circuit. Sections of conductor tracks that connect the capacitor and the coil to one another can extend as additional sensor components between the reflective optics and the holding arm. If the laser beam hits the capacitor and / or sections of the conductor tracks in the event of a defect in the reflective optics, this changes a natural frequency or resonant frequency of the oscillating circuit. In other words, after the laser beam hits the sensor circuit, the current natural frequency or resonant frequency no longer corresponds to the original natural frequency or resonant frequency of the oscillating circuit. When the laser beam hits the capacitor, its capacitance can, in particular, be reduced.When the laser beam hits the sections of the conductor tracks, they can be charred or severed, which increases their electrical resistance.

[0022] The sensor circuit is preferably formed on a printed circuit board. This simplifies the provision of the sensor circuit. The printed circuit board extends at least partially between the reflective optics and the support arm. This allows the sensor circuit to be arranged at least partially between the reflective optics and the support arm. In particular, the partial area of ​​the printed circuit board that carries the sensor component is located between the reflective optics and the support arm. If the sensor circuit has a coupling component, this is typically arranged in a partial area of ​​the printed circuit board that is not concealed by the reflective optics and / or the support arm. In particular, the printed circuit board can protrude laterally beyond the reflective optics.

[0023] The evaluation device can comprise an inductance, in particular an evaluation coil. In particular, if the sensor circuit has a coupling component in the form of a coil (sensor coil), the state of the sensor circuit can be monitored by means of mutual induction.

[0024] Preferably, the evaluation device is a proximity switch. The proximity switch can have the inductance of the evaluation device. In particular, a change in the resonant frequency of an oscillating circuit of the sensor circuit can be detected by means of the proximity switch. The inductive proximity switch can be tuned to the resonant frequency of the intact oscillating circuit.

[0025] It can be provided that a characteristic property of the sensor circuit can be reversibly changed. This makes it possible to test the interaction of the sensor circuit with the evaluation device. For functional testing, the characteristic property is specifically changed. The characteristic property is then determined using the evaluation device, and it is checked whether the evaluation device has detected the change in the characteristic property. After the functional test is completed, the change in the characteristic property is reversed.

[0026] A switch can be provided to change the characteristic property. The switch is preferably a reed switch. The switch can be used to interrupt a conductor path of the sensor circuit or to short-circuit the sensor circuit. This changes a property of the sensor circuit that can be detected by the evaluation device.

[0027] The holding arm can be rotatably mounted on a base body of the beam closure. A pivot bearing can be implemented particularly easily. The holding arm can thus be pivoted between the closed position and the released position. A rotary actuator, in particular a stepper motor, can be provided for rotating or pivoting the holding arm. In particular, the holding arm can be attached to a shaft of the rotary actuator. This results in a particularly simply constructed beam closure.

[0028] Preferably, the retaining arm is pre-tensioned into the closed position. This ensures that the retaining arm automatically moves into the closed position or remains in the closed position unless actively moved into the release position by a drive. This increases safety in the event of a defect or failure of the drive. A spring element can be provided to pre-tension the retaining arm. The spring element can be hinged or attached to the retaining arm and a base body of the steel closure.

[0029] A stop can be provided for the holding arm. The stop can, in particular, define the locked position or prevent the holding arm from moving beyond the locked position. Combined with a preload, the stop can make the transition of the holding arm into the locked position even safer. Alternatively or additionally, the stop can define the release position or prevent the holding arm from moving beyond the release position. Laser arrangement according to the invention

[0030] The invention also encompasses a laser arrangement comprising a laser light source for generating a laser beam and a beam shutter according to the invention described above. The laser light source can be an ultrashort pulse laser, in particular a picosecond laser (pulse duration of less than one nanosecond) or a femtosecond laser (pulse duration of less than one picosecond). Ultrashort pulse lasers enable cold material processing even at moderate to medium power levels (e.g., 10 to 150 watts), with virtually no heat input to the workpiece.

[0031] When the holding arm is in the closed position, the laser beam strikes the reflective optics. The beam shutter is thus positioned in the beam path of the laser beam. The advantages of the beam shutter according to the invention can be utilized in such a laser arrangement. In particular, with ultrashort pulse lasers, it is particularly important to be able to detect a failure of the reflective element without having to rely on measuring a temperature increase, since ultrashort pulse lasers involve cold material processing. The beam shutter according to the invention is capable of achieving this.

[0032] The laser assembly typically also includes an absorber onto which the laser beam is directed by the reflective optics when the holding arm is in the closed position. Operating method according to the invention

[0033] The present invention further includes a method for operating a laser arrangement according to the invention described above. The method comprises the steps a) Move the holding arm into the closed position, b) operating the laser light source and determining at least one characteristic property of the sensor circuit with the evaluation device, c) Switching off the laser light source if the characteristic property of the sensor circuit is outside a permissible range.

[0034] During operation, the laser light source emits a laser beam. Operation of the laser light source may have begun before step a) is performed. Step a) ensures that the laser beam cannot pass through the beam shutter.

[0035] While the holding arm is in the closed position and the laser light source emits the laser beam, the evaluation device determines at least one characteristic property of the sensor circuit. In particular, the evaluation device can determine a resonant frequency of an oscillating circuit of the sensor circuit.

[0036] If the characteristic property lies outside a predefined permissible range, it can be assumed that the reflective optics are defective. The laser light source is therefore switched off. A target value is known for the characteristic property of the sensor circuit. The target value of the characteristic property can be determined mathematically or experimentally using an intact sensor circuit. The permissible range can specify tolerable deviations from the target value. Such deviations can arise, for example, due to manufacturing tolerances or environmental influences. For example, it can be provided that the laser light source is switched off if a resonant frequency of an oscillating circuit of the sensor circuit deviates by at least 10% from its target value.The setpoint value of the resonant frequency of the oscillating circuit can depend, for example, on the capacitance of a capacitor forming the sensor component, the inductance of a coil forming the coupling component and the electrical resistance of the conductor tracks connecting the capacitor and the coil.

[0037] In step b), the sensor component of the sensor circuit can be destroyed by the laser beam emitted by the laser light source. This is particularly the case if the reflective optics are no longer able to deflect the laser beam, causing it to strike the sensor component. The destruction of the sensor component changes at least one characteristic property of the sensor circuit. The change in the characteristic property is detected by the evaluation device. The laser light source is then switched off.

[0038] Further advantages of the invention will become apparent from the description and the drawings. According to the invention, the above-mentioned and further-described features can be used individually or in combination in any convenient way. The embodiments shown and described are not intended to be exhaustive, but rather are exemplary in nature for describing the invention. Detailed description of the invention and drawing

[0039] The invention is illustrated in the drawing and described using exemplary embodiments. They show: Fig. 1 shows a laser arrangement according to the invention with a beam shutter according to the invention, wherein a holding arm with a reflective optic is in a closed position so that a laser beam emitted by a laser light source is deflected onto an absorber, in a schematic perspective view; Fig. 2 the beam shutter of the sensor arrangement of Fig. 1 in a schematic sectional view, wherein an evaluation device interacts contactlessly with a sensor circuit to monitor the functionality of the reflective optics; Fig. 3 the holding arm of the steel shutter of the laser assembly of Fig. 1 in a schematic plan view, wherein it can be seen that a circuit board with the sensor circuit extends between the reflective optics and the holding arm; Fig. 4 an abstract cross-sectional view through the support arm, the reflective optics and the circuit board with the sensor circuit according to the arrangement of Fig. 3; Fig. 5 a schematic flow diagram of an operating method according to the invention for a laser arrangement.

[0040] Fig. 1 shows a laser assembly 10. The laser assembly 10 has a beam shutter 12 and a laser light source 14. The laser light source 14 can be an ultrashort pulse laser. The laser light source 14 emits a laser beam 16. The beam shutter 12 has a holding arm 18. The holding arm 18 carries a reflective optic 20. The reflective optic 20 is a mirror here. The holding arm 18 with the reflective optic 20 can be moved into a release position and a closure position. Fig. 1, the holding arm 18 with the reflective optics 20 is in the closed position. In the closed position, the holding arm 18 can rest against a stop 22. In the closed position, the reflective optics 20 are arranged in the beam path of the laser beam 16. The reflective optics 20 then deflects the laser beam 16. The deflected laser beam 16 strikes an absorber 24 of the sensor arrangement 10. In the release position, the laser beam 16 can pass through the beam shutter 12 without being deflected by the reflective optics 20 (not shown).

[0041] Fig. Figure 2 shows the beam shutter 12 in a sectional view. The holding arm 18 is rotatably mounted on a base body 26 of the beam shutter 12. In this case, the holding arm 18 is attached to a shaft 28 of a rotary actuator 30. The rotary actuator 30 serves to move the holding arm 18 with the reflective optics 20 between the release position and the closed position. In this case, the holding arm 18 is preloaded into the closed position. A spring element 32 can be provided for this purpose. The spring element 32 is attached here to the base body 26 and the holding arm 18.

[0042] The beam shutter 12 has an evaluation device 34. The evaluation device 34 serves to check the functionality of the reflective optics 20. The evaluation device 34 can be a proximity switch, preferably an inductive one. An inductance (evaluation coil) 36 can be arranged at an end of the evaluation device 34 facing the support arm. The evaluation device 34 can have evaluation logic, which can be stored, for example, as software in a control unit (not shown in detail).

[0043] In order to monitor the functionality of the reflective optics 20, the evaluation device 34 interacts with a sensor circuit 38, see Fig. 3, which shows the support arm 18, the reflective optics 20, and the sensor circuit 38 with a view of the reflective optics 20. The sensor circuit 38 can be arranged on a circuit board 40.

[0044] Viewed from the reflective optics 20 behind the support arm 18, a copper sheet 41 (compare Fig. 1). The copper sheet 41 is more resistant to laser radiation than the holding arm 18. In particular, the copper sheet can have a higher ablation threshold or a higher ablation resistance. This extends the time until the laser beam 16 has penetrated the holding arm 18 and the copper sheet 41 in the event of a defect in the reflective optics 20. During the time required for the laser beam 16 to penetrate the holding arm 18 and the copper sheet 41, the sensor circuit 38 can be evaluated and the laser light source 14 can be switched off.

[0045] The sensor circuit 38 is designed here as an electrical resonant circuit. The evaluation device 34 can determine whether a resonant frequency of the resonant circuit is within a predefined permissible range. The sensor circuit 38 has a capacitor 42 and a coil 44. The capacitor 42 can be a film capacitor. The capacitor 40 and the coil 44 are connected to one another via conductor tracks 46. In the illustrated embodiment, the sensor circuit 38 also has a switch 47. The switch 47 can be a reed switch. The switch 47 makes it possible to temporarily short-circuit the conductor tracks 46 in order to change the resonant frequency of the resonant circuit. This makes it possible to check whether the evaluation device 34 is interacting correctly with the sensor circuit 38.

[0046] The capacitor 42 and meandering sections 48 of the conductor tracks 46 form sensor components 50 of the sensor circuit 38. The sensor components 50 are arranged between the reflective optics 20 and the holding arm 18, see also Fig. 4. The circuit board 40 extends, with its portion carrying the capacitor 42 and the meandering sections 48 of the conductor tracks 46, between the reflective optics 20 and the holding arm 18. The holding arm 18 and / or the reflective optics 20 can have recesses 52 to accommodate the sensor components 50 or the circuit board 40. Preferably, the capacitor 42 and the meandering sections 48 are arranged on the circuit board 40 facing the reflective optics 20. If the reflective optics 20 fails and the holding arm 18 is in the closed position, the laser beam 16 strikes the sensor components 50 during operation of the laser light source 14. The sensor components 50 are thereby damaged and ultimately destroyed. This changes at least one characteristic property of the sensor circuit 38, for example, the resonant frequency of the oscillating circuit.

[0047] This change in the sensor circuit 38 is detected by the evaluation device 34. The evaluation device 34 can interact with the sensor circuit 38 without contact, see in particular Fig. 2. In the closed position, the end of the evaluation device 34 facing the holding arm 18 is located close to the coil 44 of the sensor circuit 38. The coil 38 serves here as a coupling component 54 of the sensor circuit 38. Through mutual induction between the inductance 36 of the evaluation device 34 and the coil 44 of the sensor circuit 38, the evaluation device 34 can determine characteristic properties of the sensor circuit 38. The coil 44 or the coupling component 54 of the sensor circuit 38 is arranged next to the reflective optics 20 in the illustrated embodiment, compare in particular Fig. 3. The holding arm 18 also does not cover the coupling component 54. This makes it easier to bring the evaluation device 34, in particular its inactivity 36, close to the sensor circuit 38, in particular its coupling component 54, see Fig. 2. This ensures that the evaluation device 24 and sensor circuit 38 interact reliably.

[0048] Fig. Figure 5 shows a flow chart of an operating method for a laser arrangement. The operating method is illustrated here using the laser arrangement 10 of Fig. 1 explained.

[0049] In a step 102, the holding arm 18 with the reflective optics 20 is moved into the closed position. For this purpose, the rotary actuator 30 can pivot the holding arm 18 relative to the base body 26.

[0050] While the holding arm 18 with the reflective optics 20 is in the closed position, the laser light source 14 is operated in a step 104. A laser beam 16 emitted by the laser light source 14 strikes the reflective optics 20. The operation of the laser light source 14 may have already begun before the execution of step 102.

[0051] While the laser light source 14 is operating and the holding arm 18 is in the closed position, a characteristic property of the sensor circuit 38 is determined in a step 106. For example, the evaluation device 34 can determine the resonant frequency of the oscillating circuit of the sensor circuit 38 at regular intervals or continuously.

[0052] If the reflective optics 20 fail to reflect the laser beam 16, i.e., if the reflective optics 20 are defective, the laser beam 16 strikes the sensor components 50 of the sensor circuit 38. The sensor components 50 can be destroyed as a result. This changes characteristic properties of the sensor circuit 38, for example, the resonant frequency of the oscillating circuit. As soon as the evaluation device 34 determines that a characteristic property of the sensor circuit 38 detected by it lies outside a predefined permissible range, the laser light source 14 is switched off in a step 108.

[0053] In summary, the invention relates to a monitored beam shutter 12. When a holding arm 18 with a reflective optic 20 is in a closed position, an evaluation device 34 determines at least one characteristic property of a sensor circuit 38. At least one element of the sensor circuit 38 serving as a sensor component 50 is arranged between the reflective optic 20 and the holding arm 18. In the event of a defect in the reflective optic 20, a laser beam 16 therefore strikes the sensor components 50. This changes the properties of the sensor circuit 38. An evaluation device 34 preferably interacts with the sensor circuit 38 in a contactless manner. The evaluation device 34 checks whether one or more properties of the sensor circuit 38 are within a permissible range. If this is not the case, this indicates a defect in the reflective optic 20. The laser light source 14 is therefore switched off. List of reference symbols 10 Laser arrangement 12 Beam closure 14 Laser light source 16 laser beam 18 Holding arm 20 reflective optics 22 stop 24 absorbers 26 basic bodies 228 Wave 30 rotary actuator 32 spring element 34 Evaluation device 36 Inductance 38 Sensor circuit 40 circuit board 41 copper sheet 42 Capacitor 44 coil 46 conductor tracks 47 switches 48 sections of the conductor tracks 46 50 sensor components 52 withdrawals 54 coupling component 102 Moving the holding arm 18 into the closed position 104 Operating the laser light source 14 106 Determining a characteristic property of the sensor circuit 38 108 Switching off the laser light source 14

Claims

[1] Beam shutter (12) for a laser beam (16) comprising - a reflective optic (20) for deflecting the laser beam (16), and - a holding arm (18) which can be moved into a release position and a closed position and on which the reflective optics (20) are held, characterized by , that the beam closure (12) - a sensor circuit (38) with at least one sensor component (50) arranged between the reflective optics (20) and the holding arm (18), and - an evaluation device (34) which interacts with the sensor circuit (38) at least in the closed position of the holding arm (18), and that the evaluation device (34) interacts contactlessly with the sensor circuit (38). [2] Beam closure (12) according to claim 1, characterized bythat the sensor component (50) is a capacitor (42), preferably a film capacitor, a coil, a conductor track (46), an RFID chip, a thermistor, a diode, preferably a photodiode, a transistor or a fuse. [3] Beam closure (12) according to one of the preceding claims, characterized by that the sensor circuit (38) has a coupling component (54) for the evaluation device (34). [4] Beam closure (12) according to claim 3, characterized by that the coupling component (54) is arranged next to the reflective optics (20). [5] Beam closure (12) according to one of the preceding claims, characterized by that the sensor circuit (38) is formed on a printed circuit board (40) which extends between the reflective optics (20) and the holding arm (18). [6] Beam closure (12) according to one of the preceding claims, characterized bythat the evaluation device (34) has an inductance (36). [7] Beam closure (12) according to one of the claims, characterized by that the evaluation device (34) is a proximity switch. [8] Beam closure (12) according to one of the preceding claims, characterized by that a characteristic property of the sensor circuit (38) is reversibly changeable. [9] Beam closure (12) according to claim 8, characterized by that a switch (47), preferably a reed switch, is provided for changing the characteristic property of the sensor circuit (38). [10] Beam closure (12) according to one of the preceding claims, characterized by that the holding arm (18) is rotatably mounted on a base body (26), preferably by means of a shaft (28) of a rotary actuator (30). [11] Beam closure (12) according to one of the preceding claims, characterized bythat the holding arm (18) is pre-tensioned in the closed position. [12] Laser arrangement (10) with a laser light source (14) for generating a laser beam (16) and with a beam shutter (12) according to one of the preceding claims, wherein the laser beam (16) strikes a reflective optic (20) in the closed position of a holding arm (18). [13] Method for operating a laser arrangement (10) according to claim 12, comprising the steps a) moving (102) a holding arm (18) into the closed position, b) operating (104) a laser light source (14) and determining (106) at least one characteristic property of a sensor circuit (38) with an evaluation device (34), c) switching off (108) the laser light source (14) if the characteristic property of the sensor circuit (38) is outside a permissible range. [14] Method according to claim 13, characterized bythat in step b) a sensor component (50) of the sensor circuit (38) is destroyed by a laser beam (16) emitted by the laser light source (14).

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