JP2006292424A - Optical fiber monitoring system and laser beam machining system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber monitoring device capable of detecting a damage of an optical fiber like chipping off, breaking off, or the like in real time, when the damage occurs in an end face of the optical fiber or inside it, and a high-reliability laser beam machining system equipped with the monitoring device. <P>SOLUTION: This monitoring device is constituted, by providing a laser oscillator 1 for emitting a laser beam 2 of a specific frequency, an optical condensing system 8 for condensing rays of reflected light 6 from the optical fiber 4 on which the laser beam 2 is incident, and a photodetector 5 which measures the quality of the reflected light 6 made to impinge on itself from the optical system 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical fiber monitoring device that detects damage on an end face and an inner surface of an optical fiber that transmits laser light, and a laser processing system that includes the device to laser process an article.

  In general, in a processing system such as cutting or welding using a YAG laser, an optical fiber is used for transmitting laser light. Quartz is generally used as the optical fiber for YAG laser, and the core diameter of the optical fiber is generally φ0.4 to 1.0mm. Depending on the application, there is an optical fiber whose core diameter exceeds φ2.0mm. Sometimes used.

  The YAG laser used for industrial use is generally of the 1 to 4 kW class as the laser output, and the incident position is shifted or the return light from the laser processing head returns directly to the optical fiber. In some cases, the optical fiber may be instantly melted and damaged.

  As an apparatus for monitoring optical fiber damage, an apparatus as shown in Patent Document 1 below is used. In this device, an optical fiber and a conductive wire are inserted in a protective tube, and when the optical fiber is damaged, the laser beam emitted from the damaged part or the laser beam that reverses from the damaged part is detected at a high temperature. Is opened, and the detection device detects it and sends a signal to the laser oscillator to stop the oscillation.

  Similarly, as shown in FIG. 10, a conductive wire (thermocouple) 26 for sensing heat coaxially with the optical fiber 4 is provided, and a change in the current flowing through the conductive wire 26 is detected by a detection device 27. An apparatus for monitoring the state of the optical fiber 4 is used. In this device, for example, when heat is generated on the end face of the optical fiber 4 due to an incident abnormality or the like, the heat is transmitted to the conductive wire 26 to change the resistance value of the conductive wire 26, and the change is detected by the detection device 27. Thus, the occurrence of damage is prevented in advance by applying a feedback to the laser oscillator itself.

On the other hand, in construction such as laser ablation and laser peening using a giant pulse YAG laser, the damage to the optical fiber does not melt the end face, but damage such as chipping occurs and the chip expands. Damage progresses in shape. In this case, almost no heat is generated when the damage occurs, and a defect caused by microscopic impact is the main cause of the damage. Therefore, in the case of such a damage form, the above-described heat-sensing optical fiber damage detection system cannot detect the occurrence of damage.
JP 2003-279444 A

  In the above-described conventional optical fiber monitoring device, it is not possible to detect defective damage that occurs on the end face or inside of the optical fiber due to the microscopic impact of the pulse laser emitted from a giant pulse YAG laser oscillator or the like.

  Accordingly, the present invention provides an optical fiber monitoring device capable of detecting the occurrence of damage in real time when defective damage occurs on the end face or inside of the optical fiber, and a highly reliable laser processing system including the device. The purpose is to provide.

  An optical fiber monitoring device of the present invention includes a laser oscillator that emits laser light of a specific frequency, a condensing optical system that condenses reflected light from an optical fiber on which the laser light is incident, and the condensing optical system And a photodetector that measures the amount of the reflected light when the reflected light is incident.

  A laser beam processing system according to the present invention is an optical fiber monitor device according to claim 1, a processing laser oscillator that emits a processing laser beam to be irradiated on a workpiece, and guides the laser beam and the processing laser beam. It is set as the structure provided with an optical fiber.

  According to the present invention, an optical fiber monitoring device capable of detecting the occurrence of damage in real time when defective damage occurs in the end face or inside of the optical fiber, and a highly reliable laser processing system including the device. Can be provided.

  Embodiments of an optical fiber monitoring device and a laser processing system according to the present invention will be described below with reference to the drawings.

(First embodiment)
As shown in FIG. 1, the optical fiber monitoring device according to the present embodiment includes a laser oscillator 1, a partial reflection mirror 7, condensing optical systems 3 and 8, and a photodetector 5. The laser beam 2 irradiated from the laser oscillator 1 passes through the partial reflection mirror 7, is condensed by the condensing optical system 3, and enters the optical fiber 4. The laser reflected light 6 reflected from the end face or inside of the optical fiber 4 is condensed by the condensing optical system 3, reflected by the partial reflection mirror 7, condensed by the condensing optical system 8, and enters the photodetector 5.

  The surface of the partial reflection mirror 7 is coated with a coating corresponding to the oscillation wavelength of the laser oscillator 1 so that only a specific wavelength is transmitted and reflected. For example, when the laser oscillator 1 is a blue laser having a wavelength of 488 nm, a coating that transmits only light having a wavelength of 488 nm is applied to the surface on the laser oscillator 1 side, and 488 nm light is applied to the surface on the optical fiber 4 side. Apply a reflective coating. As a result, the laser reflected light 6 reflected from the end face or inside of the optical fiber 4 is reflected by the partial reflection mirror 7 and enters the photodetector 5 through the condensing optical system 8. The configuration of the partial reflection mirror 7 is not limited to this, and when a sufficient amount of the laser reflected light 6 can be expected, the partial reflection mirror 7 may be provided with a hole through which the laser light 2 passes.

  Most of the laser light 2 incident on the optical fiber 4 propagates through the optical fiber 4 to reach the exit end of the optical fiber 4, but a part of the laser light 2 enters the optical fiber 4 and the inside of the optical fiber 4. When there is damage, the light is reflected by the damage and becomes laser reflected light 6 and returns to the laser oscillator 1 side. The laser reflected light 6 is preferably configured as shown in FIG. 1 because the amount of light is maximized when the laser light 2 is perpendicularly incident on the incident end face 4a of the optical fiber 4, but the laser reflected light 6 is detected by light. If it is incident on the vessel 5, the laser beam 2 may be incident obliquely as shown in FIG. 2. Although not shown in FIGS. 1 and 2, an image processing device that displays an image of the incident end face 4 a of the optical fiber 4 may be provided.

  The laser beam 2 used for damage detection may be any laser beam that can propagate through the optical fiber 4, but it is desirable to use laser beams having different wavelengths when used together with the processing laser beam. When visible laser light is used as the laser light 2, not only alignment of the optical fiber 4 but also adjustment of incidence on the photodetector 5 is facilitated. Further, if the laser beam 2 in the infrared wavelength region is used, the laser beam 2 is absorbed by water when performing underwater processing, so even if the surface of the workpiece is glossy, There is no change in the amount of light and it is not affected by the reflection of the workpiece surface.

  The laser reflected light 6 guided to the detector 5 is converted into an electric signal after the light amount is measured by a laser power meter, a piezoelectric element, or the like in the light detector 5, and is taken into a data processing device (not shown). . As a data processing device, a data signal is processed using an oscilloscope, a boxcar integrator, or the like.

  The amount of the laser reflected light 6 was measured using the detector 5 in the case where the optical fiber end surface 21 as shown in FIGS. 3A, 3B, and 3C was irradiated with the laser beam 2 for inspection. However, as shown in FIG. 4, it was recognized that the amount of the laser reflected light 6 tended to decrease as the area ratio of the damages 22, 23, and 24 on the optical fiber end face 21 increased. This is because the amount of laser reflected light 6 is reduced because the surface area of the optical fiber end face 21 that reflects the laser light 2 becomes smaller as damage increases. Therefore, the damage state of the end face of the optical fiber can be grasped by measuring the light quantity of the laser reflected light 6. The damage inside the optical fiber 4 can be grasped similarly.

  As described above, the optical fiber monitoring device according to the present embodiment can detect the presence or absence and the size of the optical fiber end face or the internal damage based on the amount of the reflected light of the laser light 2. Further, by using a visible light laser as the light source of the laser light 2, the optical axis can be easily adjusted, and the wavelength is different from the fundamental wave (wavelength: 1064 nm) of a YAG laser generally used for processing with an optical fiber. Therefore, it becomes easy to detect the reflected light emitted from the end face of the optical fiber or inside.

  Furthermore, by using laser light of infrared wavelength as the laser light source, it is not affected by the reflection of the surface of the workpiece when laser irradiation such as underwater laser processing is performed in water. Monitoring is possible.

(Second Embodiment)
When a pulse laser is used as the laser beam 2 in FIG. 1, a laser beam having a specific period and amplitude is incident on the optical fiber 4 according to the characteristics of the laser beam 2. The speed at which the laser light propagates through the optical fiber is 200 mm / ns. When the total length of the optical fiber 4 is 40 m, the tip of the optical fiber is reached in 200 ns. A part of the light that reaches the tip of the optical fiber is reflected by the tip of the optical fiber and returns to the optical fiber entrance end surface over the same time. As a result, 400 ns after the laser light enters the optical fiber. Later, the laser reflected light returns to the incident end face.

  In the optical fiber monitoring apparatus shown in FIG. 1, the photodetector 5 captures the reflected light at the optical fiber exit end face in addition to the laser reflected light reflected at the incident end face 4a of the optical fiber 4. By measuring the waveform continuously with a measuring instrument such as an oscilloscope, the amount of reflected light 6 from the incident end face 4a and the outgoing end face of the optical fiber 4 can be measured. As an example, FIGS. 5, 6 and 7 show the results of plotting the monitor values in which the inspection laser beam 2 is incident on the optical fiber 4 having a total length of 40 m and the amount of the reflected light 6 is measured by the photodetector 5.

  When the optical fiber incident end face 4a is damaged, the monitor value of the incident end face is lower than that when the optical fiber incident end face is healthy as shown in FIG. 5, so that the optical fiber incident end face is damaged. Recognize. When the optical fiber exit end face is damaged, the monitor value at the exit end face is low as shown in FIG. 6, so that it can be determined that the optical fiber exit end face is damaged. In addition, when the optical fiber 4 is disconnected in the middle, the reflected light returns from the middle (20 m) where the reflected light should not return as shown in FIG. It can be determined that it occurred.

  As described above, in the optical fiber monitor device of the present embodiment, since the pulsed laser beam is used as the laser beam 2, the pulse width is shortened and the photodetector 5 is adjusted. Damage detection with high resolution becomes possible.

(Third embodiment)
The present embodiment is a laser processing system. As shown in FIG. 8, a processing laser oscillator 15, a total reflection mirror 9a and a partial reflection mirror 9b for transmitting the processing laser light 16, and a monitoring laser oscillator 1 are provided. A partial reflection mirror 9c and 9d for transmitting the monitoring laser beam 2, a condensing optical system 3 for condensing the laser beams 2 and 16, an optical fiber 4, and a photodetector for detecting the laser reflected beam 6. 5, a tapered fiber 11 in which the core diameter of the optical fiber continuously changes, a connector 10 that connects the optical fiber 4 and the tapered fiber 11, an irradiation head 12 for performing laser irradiation on the workpiece, an optical fiber It comprises a CCD camera 18 and an image processing device 19 for observing the state of the end face.

  The processing laser light 16 emitted from the processing laser oscillator 15 is reflected by the total reflection mirror 9 a and the partial reflection mirror 9 b, collected by the condensing optical system 3, and incident on the optical fiber 4. As the processing laser oscillator 15, a giant pulse YAG laser is used for ablation processing and laser peening.

  Processing processes such as laser ablation and laser peening, when a pulse laser with a high peak energy is irradiated onto a solid, if the intensity of the laser beam irradiation exceeds a certain level, thermal, photochemical and mechanical energy is applied to the solid surface. This is a process of etching or improving stress on the solid surface by utilizing the phenomenon that neutral atoms, molecules, ions, clusters, electrons, photons (photons) are explosively emitted. In such a process, when an optical fiber is used as means for transmitting laser light to the irradiation head, damage such as chipping is likely to occur on the end face of the optical fiber. As for the damage, the area becomes larger with the damage generated as shown in FIGS. 3 (a), (b), and (c).

  Although the output of the giant pulse YAG laser is as low as about 10 W, the pulse energy is as high as 100 mW. Therefore, when the light is incident on the optical fiber 4 as it is, end face damage occurs instantaneously. Therefore, 4 can be incident on the optical fiber by using the homogenizer 20 for making the intensity distribution of the processing laser beam 16 uniform. As a laser oscillator used for laser peening, a YAG laser oscillator having a wavelength of 532 nm, a repetition frequency of 60 Hz, and an average output of 10 W or more is preferable, but not limited thereto. The processing laser light 16 incident on the optical fiber 4 propagates through the optical fiber, enters the tapered fiber 11 via the connector 10, enters the irradiation head 12, and then irradiates a workpiece (not shown). Is done.

  On the other hand, the laser beam 2 emitted from the damage detecting laser oscillator 1 is incident on the end face of the optical fiber 4 through the mirrors 9c, 9d, 9b and the condensing optical system 3 along the laser beam optical path. The laser reflected light 6 reflected by the end face of the optical fiber 4 returns along the same optical path as the laser light 2 and is introduced into the photodetector 5. If a laser oscillator having a wavelength different from that of the laser oscillator 15 used for laser processing is used as the laser oscillator 1 for monitoring, the laser reflected light 6 can be easily detected by the photodetector 5.

  Furthermore, by taking an image of the end face of the optical fiber with the CCD camera 18 and observing the state of the end face of the optical fiber with the image processing device 19, it is possible to identify the site of damage on the end face of the optical fiber 4, and to detect light. By combining with the monitor value of the device 5, it is possible to grasp the finer damage state of the optical fiber. If a CCD camera having a time resolution function is used as the CCD camera 18, the position of damage in the optical fiber 4 can be specified by time from the speed at which the monitoring laser light 2 propagates in the optical fiber 4. By using together with the monitor value of the photodetector 5, it is possible to monitor the optical fiber with higher accuracy.

  In the case of a system in which an optical fiber is connected using the connector 10 as in the present embodiment, the laser light incident on the optical fiber 4 is reflected from three points: the optical fiber incident end face, the end face inside the connector, and the outgoing end face. Light is taken into the photodetector 5. FIG. 9 shows the result of continuously measuring the waveform of the laser reflected light 6 taken into the photodetector 5 using an oscilloscope. Since the laser reflected light 6 returns from the incident end face, the connector, and the outgoing end face of the optical fiber 4, three peaks occur in the monitor value curve as shown in FIG. As described above, when damage has occurred on the end face of the optical fiber, it is possible to discriminate by reducing these peaks. Furthermore, if an interference filter is provided inside the photodetector 5, only the wavelength to be detected can be taken into the photodetector, so that the detection performance is improved.

  Further, if a photodetector that detects light having a wavelength of 532 nm used in laser peening is used, it is possible to detect laser reflected light during laser peening. Here, the laser reflected light from the emission end face can be handled as the intensity data of the laser light by integrating the obtained waveform. For example, when the peak value shown in FIG. 9 is the standard laser irradiation output, the peak value is lowered when the optical fiber emitting end face is damaged, and the integrated value is also lowered. As described above, the damage that occurs during the laser peening operation proceeds over a relatively long time as described above. Therefore, even if the damage occurs, the laser peening operation can be continued for a while. However, if the optical fiber is damaged, the laser output that is actually irradiated onto the workpiece is reduced. Therefore, by defining the integral value of the peak at the laser emission end in FIG. 9 as the necessary laser output, if the peak value is made the same as the integral value by increasing the output of the processing laser oscillator 15, the optical fiber Laser peening can be continued even if damaged.

  Further, if a shutter is provided on the optical path between the laser oscillator 15 and the optical fiber 4, the damage to the optical fiber proceeds and the laser output necessary for laser peening cannot be secured. By issuing a blocking command, the optical path can be blocked, and the influence on the workpiece and the degree of damage to the optical fiber can be minimized.

  As described above, in the laser processing system of the present embodiment, the state of the end face of the optical fiber 4 is observed using the image processing device 19, so that the damage of the optical fiber 4 can be monitored more accurately. Further, since the end face state of the optical fiber 4 can be monitored while performing the laser processing using the processing laser oscillator 15, the laser processing can be continuously performed under a certain threshold value.

  Furthermore, a giant pulse YAG laser is provided as the processing laser oscillator 15, and laser ablation processing and laser peening can be performed while monitoring the state of the end face of the optical fiber in real time. Problems can be reduced.

  Furthermore, by providing a laser beam blocking shutter on the optical path of the processing laser beam, when an abnormality occurs in the optical fiber during laser processing, the laser beam can be blocked by closing the shutter. Damage to the optical fiber can be prevented.

  Further, by providing an interference filter in the photodetector 5, only reflected light having a specific wavelength from the monitoring laser oscillator 1 can be taken in, and more accurate measurement can be performed.

  Furthermore, the amount of laser reflected light at the optical fiber output end is read by the detector 5, and the read waveform can be integrated to be handled as a laser output at the output end, and feedback is provided to the processing laser oscillator 15 side. The output control can be performed by applying.

The figure which shows the structure of the optical fiber monitor apparatus of the 1st Embodiment of this invention. The figure which shows the structure of the optical fiber monitor apparatus of the modification of the 1st Embodiment of this invention. The figure which shows notionally the damage state of an optical fiber end surface, and demonstrates the effect | action of the optical fiber monitor apparatus of the 1st Embodiment of this invention. The graph which shows the relationship between the damage area ratio of an optical fiber end surface, and a laser reflected light light quantity relative value, and demonstrates the effect | action of the optical fiber monitor apparatus of the 1st Embodiment of this invention. The graph which shows the relationship between the distance from an incident end surface when an optical fiber incident end surface is damaged, and a monitor value, and demonstrates the effect | action of the optical fiber monitor apparatus of the 1st Embodiment of this invention. The graph which shows the relationship between the distance from an incident end surface when an optical fiber output end is damaged, and a monitor value, and demonstrates the effect | action of the optical fiber monitor apparatus of the 1st Embodiment of this invention. The graph which shows the relationship between the distance from an incident end surface when an optical fiber has a disconnection, and a monitor value, and demonstrates the effect | action of the optical fiber monitor apparatus of the 1st Embodiment of this invention. The figure which shows the structure of the laser processing system of the 3rd Embodiment of this invention. The graph which shows the relationship between the distance from an optical fiber entrance end surface, and a monitor value, and demonstrates the effect | action of the optical fiber monitor apparatus of the 3rd Embodiment of this invention. The figure which shows the conventional optical fiber monitor apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser oscillator, 2 ... Laser beam, 3 ... Condensing optical system, 4 ... Optical fiber, 4a ... Incident end surface, 5 ... Photodetector, 6 ... Laser reflected light, 7 ... Partial reflection mirror, 8 ... Condensing optics System: 9a ... Total reflection mirror, 9b, 9c, 9d ... Partial reflection mirror, 10 ... Connector, 11 ... Tapered fiber, 12 ... Irradiation head, 15 ... Processing laser oscillator, 16 ... Processing laser beam, 18 ... CCD camera , 19 ... Image processing device, 20 ... Homogenizer, 21 ... Optical fiber end face, 22 ... Damage (area ratio 5%), 23 ... Damage (area ratio 10%), 24 ... Damage (area ratio 20%), 26 ... Conductivity Line 27 ... Detection device.

Claims (9)

  A laser oscillator that emits laser light of a specific frequency; a condensing optical system that condenses reflected light from an optical fiber on which the laser light is incident; and the reflected light is incident from the condensing optical system. An optical fiber monitor device comprising a photodetector for measuring the amount of reflected light.   2. The optical fiber monitor device according to claim 1, wherein the laser light is laser light in a visible light region or laser light in an infrared wavelength region.   2. The optical fiber monitoring device according to claim 1, wherein the laser beam is a pulse laser.   The optical fiber monitor apparatus according to claim 1, further comprising an image processing apparatus that displays an image of an end face state of the optical fiber.   The optical fiber monitor device according to claim 1, a processing laser oscillator that emits a processing laser beam irradiated to a workpiece, and an optical fiber that guides the laser beam and the processing laser beam. A featured laser processing system.   6. The laser processing system according to claim 5, wherein the processing laser beam is a giant pulse YAG laser beam.   The laser processing system according to claim 5, further comprising a shutter that blocks the processing laser light when an abnormality occurs in the optical fiber on an optical path of the processing laser light.   The laser processing system according to claim 5, wherein the photodetector includes an interference filter that blocks light other than the wavelength to be detected. 6. The laser processing system according to claim 5, wherein a laser output at an output end of the optical fiber is measured by the photodetector and output control of the processing laser oscillator is performed.

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