JP5785740B2 - Laser output and return light detection method in fiber laser processing machine and processing head of fiber laser processing machine - Google Patents

Description

  The present invention relates to a laser output and return light detection method in a fiber laser processing machine and a processing head of the fiber laser processing machine.

  The fiber laser processing machine is easier to maintain than the carbon dioxide laser processing machine. In addition, fiber lasers are being applied to metal materials and other laser cutting fields because of their many advantages such as excellent beam quality, high absorption rate for metal materials, high oscillation efficiency, and long distance propagation.

  In particular, since laser light can be transmitted from an oscillator to a processing head using an optical fiber, it is a great advantage of a fiber laser processing machine that bend mirrors and other optical components can be minimized.

  However, misalignment or fiber damage in fiber lasers causes a reduction in output, which is a factor that adversely affects processing accuracy and safety. Therefore, in order to avoid these adverse effects, it is best to monitor the output light in the vicinity of the processed portion as much as possible to detect and deal with these factors.

  FIG. 4 schematically shows the outline of the fiber laser processing machine. The laser light output from the fiber laser oscillator 101 of the fiber laser processing machine 100 propagates through the process fiber 103 and the laser processing head 105. The collimating lens 107 is incident on the collimating lens 107, and the collimating lens 107 enters the collimating lens 111 via the bend mirror 109 as a collimated beam, and is focused on the workpiece W.

  A device that monitors the output near the processing part and the reflected light (return light) from the processing point (workpiece upper surface), as shown in FIG. 5, photodiodes are arranged behind and above the bend mirror, respectively. A method of measuring transmitted light that has passed through a mirror is known (for example, Patent Document 1).

The outline of the monitoring apparatus 200 for laser processing described in Patent Document 1 is that a laser light detector 203 made of a photodiode is provided on the back side or the rear side of a vent mirror 202 when viewed from the fiber emitting unit 201 side, and collimated light is collimated by a collimating lens CR. the laser beam LB that is incident on the bent mirror 202, the leaking light M _LB from the bent mirror 202 and receives the laser beam detector 203, emitted from the end face of the optical fiber 204 from the intensity of the leakage light M _LB The light intensity of the laser beam LB immediately after being obtained is obtained.

Above the bent mirror 202, a reflected light detector 206 having a focusing lens 205 and a photodiode for detecting the reflected light R _LB is provided. The reflected light detector 206 allows the focusing lens 207 and the bent mirror to be reflected. 202 receives the reflected light R _LB from the processing point WP of the workpiece W which has passed through the laser output is obtained at the processing point WP from the light intensity.

  Further, as shown in FIG. 6, the direction of the laser beam LB leaked rearward from the rear mirror (not shown) of the laser oscillator is changed by the bend mirror 301, and a plurality of (eight) light diffusion plates 302 (1, 1, There is also a laser output detection device 300 that passes through the ND filter 303 and the infrared transmission filter 304 in order, and then enters the photoelectric conversion element 305 to detect the laser output (for example, Patent Document 2).

JP 2006-247681 A JP-A-11-277259

  Since the fiber laser oscillator 101 shown in FIG. 4 has a monolithic structure including the fiber laser oscillator 101 and the process fiber 103, detection is performed by monitoring output light in the fiber laser oscillator 101 or in the process fiber 103. It is difficult to provide a device.

  Although it is possible to monitor the output light by providing an optical component or an output detection device for monitoring the output light in the laser processing head 105, the weight and volume of the laser processing head 105 increase, There is a problem that accuracy deteriorates.

  Therefore, it is a problem how to build a space-saving, lightweight, and highly reliable output detection device in the laser processing head 105. In addition, in the fiber laser, the return light from the processing point (work upper surface) may damage a laser diode (not shown) used as an excitation light source in the fiber laser oscillator 101. Establishing is also an issue.

As in the monitoring device described in Patent Document 1, the laser light detector 203 receives a part of the transmitted light that has been collimated by the collimator lens CR and transmitted through the vent mirror 202 as leakage light _MLB , and this leakage light M _{In the} method of obtaining the laser output from the light intensity of the laser light LB immediately after being emitted from the end face of the optical fiber 204 from the intensity of _LB , the laser output is transmitted light M _LB indicated by a solid line as shown in FIG. The spatial intensity distribution changes according to time and output, and the transmitted light _MLB having this changing spatial intensity distribution propagates.

Since the laser light detector of the above-described monitoring apparatus measures the transmitted light _MLB that has changed temporally and spatially as described above, the measurement value fluctuates and an accurate laser output cannot be measured. There is.

  In the laser output detection device described in Patent Document 2, since the photoelectric conversion element 305 is provided on the optical axis of leakage light from a rear mirror (not shown), a plurality of light diffusion plates 302, an ND filter 303, and an infrared transmission filter Optical components such as 304 are required, resulting in an increase in the weight of the processing head, a decrease in processing accuracy and a high cost.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to detect a laser output and return light in a fiber laser processing machine that is lightweight and has high processing accuracy without requiring many optical components. And providing a processing head for a fiber laser processing machine.

The laser output and return light detection method in the fiber laser processing machine according to claim 1 as means for solving the above-described problem includes a bend mirror capable of transmitting a part of laser light emitted from a process fiber, and the bend mirror. In a processing head of a fiber laser processing machine provided with a condensing lens for condensing and irradiating reflected light from a processing part of a workpiece, the bend mirror transmitted light of the laser light emitted from the process fiber and the processing The return light from the bend mirror and the transmitted light from the bend mirror are incident on an absorber made of carbon graphite , and the scattered light from the absorber is detected by a light detection means made of a photodiode, and the laser output of the processing portion and the processing portion The gist is to detect the return light from.

The processing head of the fiber laser processing machine according to claim 2, a bend mirror capable of transmitting a part of the laser light emitted from the process fiber, and the reflected light from the bend mirror are collected in a processing portion of the workpiece. In a processing head of a fiber laser processing machine provided with a condensing lens for irradiating light, at least a first absorber made of carbon graphite that absorbs light transmitted through the bend mirror of laser light emitted from the process fiber, and the processing One of the second absorbers made of carbon graphite that absorbs the bend mirror transmitted light of the return light from the section is provided, and scattered light scattered from at least one of the first absorber and the second absorber is provided. The gist of the invention is that it is provided with light detection means including a photodiode to be detected.

  According to the present invention, variation in the spatial intensity distribution of the laser light that the transmitted light of the bend mirror has is averaged in the scattered light from the absorber, so that it is not affected by the change in the spatial intensity distribution of the laser light. A light intensity proportional to the output of the oscillator is always obtained. Therefore, by measuring the amount of such scattered light with a photoelectric conversion element such as a photodiode, the laser output and return light in the vicinity of the processed portion can be accurately detected.

  Further, since the transmitted light of the bend mirror is used, measurement can be performed without losing the laser output. In addition, since no optical component is disposed on the optical axis, the machining head can be manufactured in a compact and low-cost manner.

Explanatory drawing of the laser processing head in the fiber laser processing machine concerning this invention. The graph which showed the relationship between the laser output which concerns on this invention, and a photodiode (PD) light-receiving voltage. Explanatory drawing of distribution of the light intensity of the transmitted light or reflected light which permeate | transmitted the bend mirror, and the spreading | diffusion situation. The figure which demonstrated the outline | summary of the fiber laser processing machine typically. Explanatory drawing of the prior art example (patent document 1) of the apparatus which monitors the output of the process part vicinity, and the reflected light from a process point. A conventional example of a laser output detection device that detects laser output by inputting laser light leaked rearward from a rear mirror to a photoelectric conversion element through a plurality of light diffusion plates, an ND filter, and an infrared transmission filter (Patent Document 2) Illustration. The figure explaining that the spatial intensity | strength of the transmitted light from a bend mirror is changing according to time or a laser output.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a detailed explanatory view of a processing head portion of a fiber laser processing machine according to the present invention. Since the fiber laser processing machine main body and the fiber laser oscillator part are known, the description is omitted.

Referring to FIG. 1, a condensing lens 3 for condensing and irradiating a workpiece W with laser light LB is provided inside a laser processing head 1 that is generally shown. This is a position above the condenser lens 3 reflects 99% of the return light L _M from the incident light Li or processing unit WP, the bend mirror 5 having a property of transmitting the residual, the reflecting surface to incident light Li In contrast, it is inclined at approximately 45 degrees.

  The laser processing head 1 is fixed with an emission end 7t of a process fiber 7 whose other end is connected to a fiber laser oscillator (not shown), and a laser beam LB emitted from the emission end 7t of the process fiber. Is a collimator lens 9 for making the incident light Li of a parallel light beam.

Located on the back side of the bend mirror 5, it passes through the bend mirror 5 at an appropriate position on the extension line of the optical axis of the incident light Li emitted from the process fiber 7 and converted into a parallel light beam by the collimator lens 9. the first absorbent body 11 having the property of absorbing most of the transmitted light LT ₁ is provided by inclining approximately 45 degrees from the first transmitted light LT ₁ of the optical axis. In this embodiment, the inclination is approximately 45 degrees, but an appropriate inclination angle may be used as long as the angle reflects.

  The material of the first absorber 11 is a carbon graphite plate (for example, 50 mm × 60 mm) that absorbs the laser beam LB made of infrared rays well. Carbon graphite has properties such as high heat resistance and high thermal conductivity (2 to 3 times that of steel, 1/2 to 1/3 of copper).

The transmitted light LT ₁ incident on the first absorber 11 reflects the weak reflected light L _R1 upward with respect to the transmitted light LT ₁ , approximately 90 degrees in the embodiment, and generates weak scattered light. To do.

In the laser processing head 1, the first photoelectric conversion element 13 made of a photodiode for detecting a part of the scattered light L _S1 of the weak scattered light is located at an appropriate position facing the first absorber 11. It is provided.

Further, in order to absorb the transmitted light LT ₂ that is behind the bend mirror 5 and transmitted through the bend mirror 5 on the extension line of the optical axis of the condenser lens 3, the same material as the first absorber 11 is used. comprising second absorber 15 is provided so as to face is inclined approximately 45 degrees with respect to the optical axis of the transmitted light LT _2. In the present embodiment, the inclination is approximately 45 degrees, but an appropriate angle may be used as long as the angle reflects.

In the transmitted light LT ₂ incident on the second absorber 15, the weak reflected light LR ₂ is reflected approximately 90 degrees to the right in the embodiment with respect to the transmitted light LT ₂ and generates weak scattered light. .

An appropriate position at which the second photoelectric conversion element 17 made of a photodiode for detecting a part of the scattered light L _S2 of the weak scattered light from the second absorber 15 faces the second absorber 15. Is provided.

When the first photoelectric conversion element 13 or the second photoelectric conversion element 17 made of the photodiode receives the scattered light L _S1 or the scattered light L _S2 from the first absorber 11 and the second absorber 15, the received light is received. A light receiving voltage [V] proportional to the light intensity [W] is generated.

  The relationship between the light receiving voltage [V] and the light intensity [W] of the first and second photoelectric conversion elements (13, 17) made of photodiodes is an approximately linear proportional relationship as shown in FIG. Therefore, it is possible to determine the laser output or the intensity of the return light from the processed portion from this received light voltage.

FIG. 3 shows the light transmitted through the bend mirror (LT ₁ , LT ₂ ), the reflected light (L _R1 , L _R2 ) and the scattered light (L _S1 , L _S2 ) from the absorber (11, 15) made of carbon graphite. The transmitted light (LT ₁ , LT ₂ ) and the reflected light (L _R1 , L _R2 ) have a small beam divergence angle and a high intensity distribution. The light intensity changes randomly due to the change of.

In FIG. 3, the transmitted light (LT ₁ , LT ₂ ) and the reflected light (L _R1 , L _R2 ) are shown together. However, in practice, the light intensity level of the reflected light (L _R1 , L _R2 ) is naturally shown. 3 is considerably reduced, and FIG. 3 merely represents variations in light intensity.

On the other hand, the scattered light (L _S1 , L _S2 ) has a low light intensity but a large beam divergence angle, and the spatial mode is random like transmitted light (LT ₁ , LT ₂ ) or reflected light (L _R1 , L _R2 ). It has a certain intensity distribution without changing. Accordingly, it is possible to quantitatively measure the light intensity by measuring only the scattered light (L _S1 , L _S2 ), and it is possible to accurately detect the laser output and the return light from the processing portion.

At the time of laser processing using the processing head of the fiber laser processing machine having the above-described configuration, the laser beam LB emitted from the exit end 7t of the process fiber 7 is converted into a parallel light beam by the collimator lens 9 and becomes incident light Li to bend mirror 5. The reflected light L _H reflected by the laser beam is directed to the condenser lens 3, and the laser light LB collected by the condenser lens 3 is condensed and irradiated on the workpiece W to perform laser processing.

A part of the incident light Li described above is transmitted through the bend mirror 5 to become transmitted light LT ₁ , and most of the light is absorbed by the first absorber 11, but scattered light L _S1 from the first absorber 11 is absorbed. The laser output at the position immediately before being received by the first photoelectric conversion element 13 and incident on the condenser lens can be accurately detected.

Similarly, the return light L _M from the processing unit WP, next transmitted light LT ₂ passes through the bend mirror 5, but for the most part to the second absorber 15 is absorbed, scattered from the second absorber 15 light L _S2 is received by the second photoelectric conversion element 15, the laser output of the return light L _M from the processing unit WP can be accurately detected.

DESCRIPTION OF SYMBOLS 1 Laser processing head 3 Condensing lens 5 Bend mirror 7 Process fiber 7t Output end part of process fiber 9 Collimator lens 11 1st absorber 13 1st photoelectric conversion element 15 2nd absorber 17 2nd photoelectric conversion element Li Incident light L _M return light L _R1 , reflected light from L _R2 absorber L reflected light directed to condenser lens by L _H bend mirror L _S1 , scattered light from L _S2 absorber LT ₁ , transmitted light at LT ₂ bend mirror LB Laser beam W Work WP Processing part

Claims (2)

A fiber laser processing machine comprising a bend mirror capable of transmitting a part of laser light emitted from a process fiber, and a condensing lens for condensing and irradiating reflected light from the bend mirror onto a processing portion of a workpiece. In the processing head, the bend mirror transmission light of the laser light emitted from the process fiber and the bend mirror transmission light of the return light from the processing portion are incident on an absorber made of carbon graphite , A laser output and return light detection method in a fiber laser processing machine, wherein scattered light is detected by a light detection means comprising a photodiode to detect a laser output of a processing portion and return light from the processing portion. A fiber laser processing machine comprising a bend mirror capable of transmitting a part of laser light emitted from a process fiber, and a condensing lens for condensing and irradiating reflected light from the bend mirror onto a processing portion of a workpiece. in the machining head, the carbon to absorb a first absorber made of carbon graphite which absorbs at least the bend mirror transmitted light of the laser light emitted from the process fibers, the bend mirror transmitted light of the return light from the processing unit One of the second absorbers made of graphite is provided, and light detection means comprising a photodiode for detecting scattered light scattered from both or one of the first absorber and the second absorber is provided. A processing head of a fiber laser processing machine characterized by

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