Laser processing machine and processing failure detection method

Abstract

A laser processing machine (1) is provided with: a camera (5) that captures light emitted from a processing point of sheet metal (W) when the sheet metal (W) is irradiated with a laser beam and cut; and a control unit (7) that detects a processing failure of the sheet metal (W) on the basis of the emitted light captured by the camera (5). The control unit (7) measures a degree of spread of the emitted light in a direction perpendicular to the traveling direction of the laser beam, and determines the presence or absence of any processing failure in the sheet metal (W) on the basis of the measured degree of spread of the emitted light.

Description

Laser processing machine and processing defect detection method

[0001] The present disclosure relates to a laser processing machine and a processing defect detection method.

[0002] Patent Document 1 describes a laser processing machine that determines whether or not a burning defect has occurred. The laser processing machine in Patent Document 1 detects reflected light when a laser beam is irradiated onto a metal plate to cut it, and determines whether or not a burning defect has occurred by calculating a standard deviation from the detection level of the reflected light at a predetermined calculation cycle.

[0003] Japanese Patent Application Laid-Open No. 2021-45779

[0004] However, since the detection level of reflected light changes due to factors other than processing defects, the conventional laser processing machine described above has the problem that it may erroneously detect a processing defect when there is no processing defect.

[0005] A laser processing machine according to one aspect of the present disclosure includes a camera that captures radiation light emitted from a processing point on a metal sheet when the metal sheet is cut by irradiating it with a laser beam, and a control unit that detects processing defects on the metal sheet based on the radiation light captured by the camera. The control unit measures the degree to which the radiation light spreads in a direction perpendicular to the direction of travel of the laser beam, and determines whether the metal sheet is processed defectively based on the measured degree of spread of the radiation light.

[0006] A method for detecting processing defects according to another aspect of the present disclosure involves using a camera to capture an image of the radiation light emitted from the processing point of a metal sheet when a laser processing machine irradiates the metal sheet with a laser beam to cut it, measuring the extent to which the captured radiation light spreads in a direction perpendicular to the direction of travel of the laser beam, and determining whether the metal sheet has processing defects based on the measured extent to which the radiation light spreads.

[0007] According to a laser processing machine and a processing defect detection method according to an aspect of the present disclosure, it is determined whether or not a sheet metal has been processed defectively based on the degree of spread of radiated light. Since the degree of spread of radiated light correlates with the state of the cut surface when laser cutting, by determining whether or not the sheet metal has been processed defectively based on the degree of spread of radiated light, it is possible to accurately determine the processing defect.

[0008] According to one aspect of the present disclosure, processing defects during laser cutting can be accurately determined, and erroneous detection of processing defects can be prevented.

[0009] FIG. 1 is a diagram showing the configuration of a laser processing machine according to the first embodiment. FIG. 2 is a diagram showing an example of an image captured by a camera provided in the laser processing machine according to the first embodiment. FIG. 3A is a diagram showing an example of an image captured showing a change in the spread of radiated light when there is no processing defect. FIG. 3B is a diagram showing an example of the state of a cut surface of a metal sheet when there is no processing defect. FIG. 4A is a diagram showing an example of an image captured showing a change in the spread of radiated light when there is a processing defect. FIG. 4B is a diagram showing an example of the state of a cut surface of a metal sheet when there is a processing defect. FIG. 4C is a diagram showing the depth and period of scratches formed on the cut surface of a metal sheet when there is a processing defect. FIG. 5 is a flowchart showing the processing defect detection process performed by the laser processing machine according to the first embodiment. FIG. 6 is a diagram for explaining a method of measuring an angle using the laser processing machine according to the first embodiment. FIG. 7 is a diagram showing the distribution of angles measured by the laser processing machine according to the first embodiment. FIG. 8 is a diagram for explaining the spread width of radiated light measured by the laser processing machine according to the second embodiment.

[0010] [First embodiment] [Configuration of laser processing machine] A laser processing machine and a processing defect detection method therefor according to a first embodiment will be described below with reference to the drawings. Fig. 1 is a diagram showing the configuration of the laser processing machine. As shown in Fig. 1, the laser processing machine 1 includes a processing head 3, a camera 5, a control unit 7, a laser oscillator 9, and an illumination device 11. The laser processing machine 1 is a device that emits a laser beam from the laser oscillator 9 to perform laser cutting on a metal sheet metal W.

[0011] The laser processing machine 1 includes a camera 5 that captures an image of radiant light emitted from a processing point on the metal sheet W when the metal sheet W is irradiated with a laser beam to cut it, and a control unit 7 that detects processing defects on the metal sheet W based on the radiant light captured by the camera 5. The control unit 7 measures the degree to which the radiant light spreads in a direction perpendicular to the traveling direction of the laser beam, and determines whether or not the metal sheet W has been processed defectively based on the measured degree of spread of the radiant light.

[0012] The processing head 3 is connected to a laser oscillator 9 via a transmission fiber, and irradiates the laser beam emitted from the laser oscillator 9 toward the metal plate W. Inside the processing head 3, a camera 5, a bandpass filter 13, an eyepiece 15, collimating lenses 17 and 19, a beam splitter 21, a bend mirror 23, and a focusing lens 25 are provided.

[0013] The camera 5 is disposed at the upper end inside the processing head 3, and captures an image of the radiation emitted from the processing point of the metal sheet W. When the laser beam is irradiated onto the metal sheet W and radiation is emitted from the processing point, the radiation enters the camera 5 via the eyepiece 15 and the bandpass filter 13. At this time, the bandpass filter 13 transmits light in a specific wavelength band, and the eyepiece 15 is moved vertically to adjust the focus of the camera 5. The image captured in this manner is output to the control unit 7.

[0014] Fig. 2 is a diagram showing an example of an image captured by the camera 5. As shown in Fig. 2, the camera 5 captures an image of a processing point where the metal sheet W is irradiated with a laser beam, and the captured image captures the metal sheet W reflecting light from the lighting device 11 and radiant light 31 emitted when the metal sheet W is heated by the laser beam and reaches a high temperature.

[0015] The center 31A of the emitted light corresponds to the center of the laser beam, and since the upward direction in FIG. 2 is the traveling direction F of the laser beam, the area above the center 31A of the emitted light is the front part 31B of the emitted light, and the area below the center 31A of the emitted light is the rear part 31C of the emitted light.

[0016] The front part 31B of the emitted light is a part in front of the center 31A of the emitted light in the traveling direction F, and has a semicircular shape corresponding to the shape of the laser beam, with a kerf 33 formed around its periphery.

[0017] The rear portion 31C of the emitted light is a portion rearward of the center 31A of the emitted light in the direction of travel F, and is a portion where the emitted light emitted when the metal plate W is heated spreads rearward in the direction of travel F as the laser beam travels.

[0018] The control unit 7 executes a process for detecting defects in the processing of the metal sheet W based on the radiation imaged by the camera 5. Specifically, the control unit 7 measures the degree of spread of the radiation in a direction perpendicular to the traveling direction F of the laser beam, and determines whether or not the metal sheet W has defects in processing based on the measured degree of spread of the radiation.

[0019] Fig. 3A is a diagram showing an example of an image captured showing a change in the spread of radiated light when there are no processing defects, and Fig. 3B is a diagram showing an example of the state of the cut surface of the metal sheet W when there are no processing defects. Fig. 3B shows a case where the metal sheet W is cut normally and the cut surface is smooth. Fig. 3A shows multiple frames from consecutive times t1 to t6 when the cut surface is smooth as shown in Fig. 3B, and the traveling direction F of the laser beam is from left to right in Fig. 3A.

[0020] 3A, the degree of spreading of the rear part 31C of the emitted light is almost constant and does not spread in a direction perpendicular to the laser beam propagation direction F. Moreover, the degree of spreading of the rear part 31C of the emitted light is stable and does not change among multiple frames from time t1 to t6.

[0021] On the other hand, Fig. 4A is a diagram showing an example of an image captured showing a change in the spread of the emitted light when there is a processing defect, and Fig. 4B is a diagram showing an example of the state of the cut surface of the metal sheet W when there is a processing defect. Fig. 4B shows a case where the metal sheet W is abnormally cut and the cut surface is rough. Fig. 4A shows multiple frames from consecutive times t1 to t6 when the cut surface is rough as shown in Fig. 4B, and the traveling direction F of the laser beam is from left to right in Fig. 4A.

[0022] 4A, the extent to which the rear portion 31C of the radiation spreads by a width h in a direction perpendicular to the traveling direction F. This width h is approximately 137 μm. Furthermore, between frames at times t1 to t6, the extent to which the rear portion 31C of the radiation spreads repeats increasing by the width h and decreasing from the width h, with a fluctuation period of 904 μm.

[0023] Here, Figure 4C is a diagram showing measurements of the scratches formed on the cut surface of Figure 4B. As shown in Figure 4C, the scratch depth is 140 µm and the scratch period is 950 µm. The spread width h of the rear portion 31C of the synchrotron radiation is 137 µm and the fluctuation period is 904 µm, so the scratch depth and spread width h are approximately the same, and the scratch period and the fluctuation period of the spread width h are also approximately the same. As can be seen, there is a correlation between the scratches formed on the cut surface and the spread width h. Therefore, by measuring the spread of the rear portion 31C of the synchrotron radiation, processing defects on the cut surface of the sheet metal W can be detected.

[0024] Therefore, the control unit 7 determines that the metal sheet W has been poorly machined when the change in the degree of spread of the radiated light within a predetermined time is equal to or greater than a predetermined value. For example, the control unit 7 measures the angle at which the radiated light spreads in a direction perpendicular to the traveling direction of the laser beam as the degree of spread of the radiated light, calculates a variance value from multiple angles measured within a predetermined time, and determines that the metal sheet W has been poorly machined when the calculated variance value is equal to or greater than a predetermined value. The variance value may be a standard deviation, or may be a rate of change per unit time or a difference between previous and next frames. Furthermore, a machine learning algorithm using the angle and variance value as learning data may be used to determine poor machining.

[0025] The control unit 7 is configured by a computer having a memory, a processor such as a CPU (Central Processing Unit), and various interfaces. The memory and various interfaces are connected to the processor via a bus. The control unit 7 executes a processing defect detection process to detect processing defects in the metal sheet W by having the processor execute a program stored in the memory. The control unit 7 may be provided in an NC (Numerical Control) device that controls the entire laser processing machine 1.

[0026] The laser oscillator 9 is a fiber laser oscillator, a YAG laser oscillator, or the like, and oscillates a laser beam and supplies it to the processing head 3. The laser beam supplied from the laser oscillator 9 is converted into parallel light (collimated light) by a collimating lens 19, reflected by a bend mirror 23 and bent 90 degrees in its traveling direction, and focused by a focusing lens 25 to be irradiated onto the metal sheet W.

[0027] The lighting device 11 is composed of a plurality of light-emitting diodes (LEDs) and irradiates illumination light onto the metal sheet W. The illumination light irradiated from the lighting device 11 is converted into parallel light (collimated light) by a collimating lens 17, reflected by a beam splitter 21 and bent by 90 degrees in its traveling direction, and then passes through a focusing lens 25 to be irradiated onto the metal sheet W. Note that the lighting device 11 need not be provided.

[0028] [Processing Defect Detection Processing] Next, the processing defect detection processing by the laser processing machine 1 according to the first embodiment will be described. Fig. 5 is a flowchart showing the processing procedure of the processing defect detection processing. The processing defect detection processing starts when the laser processing by the laser processing machine 1 is started.

[0029] 5, in step S101, the control unit 7 acquires an image captured by the camera 5. When a laser beam is emitted from the laser oscillator 9, the camera 5 captures an image of the radiant light emitted from the processing point of the metal sheet W. The control unit 7 acquires the captured image output from the camera 5. Note that the captured image may be temporarily stored in a memory (not shown) and then acquired by the control unit 7 from the memory.

[0030] In step S103, the control unit 7 measures the degree of spread of the emitted light in a direction perpendicular to the traveling direction of the laser beam. Specifically, in the first embodiment, the angle at which the emitted light spreads in the direction perpendicular to the traveling direction of the laser beam is measured as the degree of spread of the emitted light.

[0031] A specific method for measuring the angles will be described with reference to Fig. 6. As shown in Fig. 6, the control unit 7 binarizes the acquired image 61 and converts it into a binarized image 62. Next, the control unit 7 detects the center 31A of the radiated light from the binarized image 62 and extracts contours 63A and 63B located behind the center 31A of the radiated light with respect to the traveling direction of the laser beam. The control unit 7 performs linear estimation on the extracted contours 63A and 63B to detect straight lines 64A and 64B, and measures the angles θL and θR that the straight lines 64A and 64B form with a direction perpendicular to the traveling direction of the laser beam. These angles θL and θR are the angles at which the radiated light spreads in the direction perpendicular to the traveling direction of the laser beam.

[0032] In step S105, the control unit 7 calculates the variance value of the angles measured in step S103. Specifically, the control unit 7 acquires angles for the past N frames and calculates the variance value from multiple angles measured within a predetermined time period.

[0033] In step S107, the control unit 7 determines whether the dispersion value calculated in step S105 is equal to or greater than a predetermined value. If there is no processing defect, the emitted light does not spread in a direction perpendicular to the traveling direction of the laser beam and remains stable without changing. On the other hand, if there is a processing defect, the emitted light spreads in a direction perpendicular to the traveling direction of the laser beam and is not stable, repeatedly expanding and contracting by the same amount. Therefore, when the dispersion value is calculated, if there is no processing defect, it will be a small value, and if there is a processing defect, it will be a large value.

[0034] For example, as shown in FIG. 7, when the distribution of angles measured in step S103 is created, it can be seen that the angle distribution 71 in the case of a good cut without processing defects is concentrated near 90 degrees, and therefore the variance value is small.

[0035] On the other hand, the angle distribution 72 when cross-section roughness, a processing defect, occurs is mostly near 90 degrees, but is widely distributed from 70 degrees to 110 degrees, so it can be seen that the variance value is large.Furthermore, the angle distribution 73 when burning, a processing defect, occurs, is widely distributed from 80 degrees to 120 degrees without being concentrated and large, so it can be seen that the variance value is large.

[0036] Since the variance value changes depending on whether or not there is a processing defect, a predetermined value is set in advance through experiments or simulations, and by comparing this predetermined value with the variance value, it is possible to determine whether or not there is a processing defect. In this way, in step S107, the variance value is compared with the predetermined value, and if the variance value is equal to or greater than the predetermined value, it is determined that there is a processing defect and the process proceeds to step S109, but if it is less than the predetermined value, it is determined that there is no processing defect and the process proceeds to step S117.

[0037] In step S109, the control unit 7 determines whether the user has set the laser processing to continue if it is determined that the metal sheet W is defective. The control unit 7 is set so that the user can choose whether to continue laser processing or stop laser processing if it is determined that the metal sheet W is defective. A user who believes that processing defects can be addressed with post-processing selects to continue laser processing, while a user who wants to immediately stop processing if a processing defect is detected selects to stop laser processing. Therefore, if the user has set the laser processing to continue, the process proceeds to step S111, and if the user has set the laser processing to stop without continuing, the process proceeds to step S113.

[0038] In step S111, the control unit 7 outputs a machining abnormality alarm indicating that a machining defect has occurred, and notifies the user of the occurrence of a machining defect by an alarm display or a warning sound, and continues machining.

[0039] In step S113, the control unit 7 notifies the NC device to stop laser processing by the laser processing machine 1. In step S115, the control unit 7 outputs a processing abnormality notification indicating that a processing defect has occurred, and notifies the user that laser processing has been stopped due to the processing defect. When the processing abnormality notification is output, the processing defect detection process according to the first embodiment ends.

[0040] In step S117, the control unit 7 determines whether or not laser processing by the laser processing machine 1 has been completed. If not, the process returns to step S101; if completed, the processing defect detection process according to the first embodiment is terminated.

[0041] In the first embodiment, the angle at which the radiated light spreads in the vertical direction is measured, and the variance value of the angle is calculated to determine whether or not the metal sheet W has been machined poorly. However, it is also possible to determine that the metal sheet W has been machined poorly when the angle at which the radiated light spreads in the vertical direction is equal to or greater than a predetermined value, without calculating the variance value.

[0042] That is, the control unit 7 measures the angle at which the radiated light spreads in a direction perpendicular to the traveling direction of the laser beam as the degree of spread of the radiated light, and if the angle is equal to or greater than a predetermined value, determines that there is a processing defect in the metal sheet W. In this case, in the flowchart of Fig. 5, the step of calculating the variance value in step S105 may be deleted, and step S107 may be modified to determine whether or not the angle is equal to or greater than a predetermined value.

[0043] [Effects of the First Embodiment] As described above in detail, the laser processing machine 1 according to the first embodiment measures the degree of spread of the radiant light in the direction perpendicular to the traveling direction of the laser beam, and determines whether or not the metal sheet W has been processed defectively based on the measured degree of spread of the radiant light. Since the degree of spread of the radiant light correlates with the state of the cut surface when laser cutting, determining whether or not the metal sheet W has been processed defectively can accurately determine the processing defect by determining the degree of spread of the radiant light. Therefore, the laser processing machine 1 according to the first embodiment can accurately determine whether or not the processing defect has occurred during laser cutting, thereby preventing erroneous detection of the processing defect.

[0044] Furthermore, the laser processing machine 1 according to the first embodiment measures the angle at which the radiated light spreads in a direction perpendicular to the traveling direction of the laser beam as the degree of spread of the radiated light, calculates a dispersion value from a plurality of angles measured within a predetermined time, and if the calculated dispersion value is equal to or greater than a predetermined value, determines that there is a processing defect in the metal sheet W. By measuring the angle in this way, it is possible to accurately measure the degree of spread of the radiated light, and by calculating the dispersion value, it is possible to accurately determine a processing defect even if the radiated light changes periodically.

[0045] Furthermore, the laser processing machine 1 according to the first embodiment measures the angle at which the radiant light spreads in a direction perpendicular to the traveling direction of the laser beam as the degree of spread of the radiant light, and if the angle is equal to or greater than a predetermined value, determines that there is a processing defect in the metal sheet W. By measuring the angle in this way, it is possible to accurately measure the degree of spread of the radiant light, and by determining the processing defect based on the angle, it is possible to easily determine the processing defect.

[0046] Furthermore, the laser processing machine 1 according to the first embodiment is configured so that the user can select whether to continue or stop laser processing when it is determined that the metal sheet W has been processed poorly. This allows the user to set how to deal with the occurrence of a processing defect according to their wishes.

[0047] [Second embodiment] A laser processing machine and a processing defect detection method therefor according to a second embodiment will be described below with reference to the drawings. Note that the configuration of the laser processing machine 1 according to the second embodiment is the same as the configuration of the first embodiment shown in Figure 1, so detailed description will be omitted.

[0048] In the first embodiment, the degree of spread of the emitted light is measured as the angle at which the emitted light spreads in a direction perpendicular to the direction of propagation of the laser beam, whereas in the second embodiment, the degree of spread of the emitted light is measured as the width at which the emitted light spreads in a direction perpendicular to the direction of propagation of the laser beam, which is different from the first embodiment.

[0049] That is, the control unit 7 measures the width of the radiation light that spreads in a direction perpendicular to the direction of travel of the laser beam as the degree of spread of the radiation light, calculates a dispersion value from multiple widths measured within a specified time, and if the calculated dispersion value is greater than or equal to a specified value, determines that the sheet metal W has been poorly processed.

[0050] As shown in Figure 8, the control unit 7 measures a width L1 in a direction perpendicular to the traveling direction F of the laser beam at the position of the center 31A of the emitted light, and a width L2 in a direction perpendicular to the traveling direction F of the laser beam at the position of the rear part 31C of the emitted light.

[0051] The control unit 7 calculates the difference (L2-L1) between the measured widths L1 and L2. As a result, this difference is measured as the width L of the radiation spread in the direction perpendicular to the laser beam propagation direction F, which represents the spread of the radiation. After the width L is measured in this manner, the control unit 7 calculates a dispersion value from the multiple widths L measured within a predetermined time, and if the calculated dispersion value is equal to or greater than a predetermined value, it determines that the metal sheet W is defectively machined. Note that the spread width h shown in FIG. 4A may be used instead of the width L.

[0052] Therefore, in the second embodiment, step S103 of the flowchart shown in FIG. 5 may be modified to calculate the width L of the radiation spread in the vertical direction as the degree of spread of the radiation.

[0053] In the second embodiment, the width L of the emitted light in the vertical direction is measured, and the dispersion value of the width L is calculated to determine whether or not the metal sheet W is defectively machined. However, it is also possible to determine that the metal sheet W is defectively machined when the width L is equal to or greater than a predetermined value without calculating the dispersion value.

[0054] That is, the control unit 7 measures the width of the radiation in the direction perpendicular to the traveling direction of the laser beam as the degree of spread of the radiation, and if the width is equal to or greater than a predetermined value, determines that the metal sheet W is defectively machined. In this case, the flow chart of Fig. 5 may be modified such that the step of calculating the variance value in step S105 is deleted and step S107 is modified to determine whether the width is equal to or greater than a predetermined value.

[0055] [Effects of the Second Embodiment] As described above in detail, the laser processing machine 1 according to the second embodiment measures the width by which the radiated light spreads in the direction perpendicular to the traveling direction of the laser beam as the degree of spread of the radiated light, calculates a dispersion value from multiple widths measured within a predetermined time, and if the calculated dispersion value is equal to or greater than a predetermined value, determines that there is a processing defect in the metal sheet W. By measuring the width by which the radiated light spreads in this way, it is possible to accurately measure the degree of spread of the radiated light, and by calculating the dispersion value, it is possible to accurately determine a processing defect even if the radiated light changes periodically.

[0056] Furthermore, the laser processing machine 1 according to the second embodiment measures the width of the radiation light that spreads in a direction perpendicular to the direction of travel of the laser beam as the degree of spread of the radiation light, and if the width is equal to or greater than a predetermined value, determines that there is a processing defect in the metal sheet W. By measuring the width in this way, it is possible to accurately measure the degree of spread of the radiation light, and by determining the processing defect based on the width, it is possible to easily determine the processing defect.

[0057] Although the embodiments of the present disclosure have been described above, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure.

[0058] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-158148, filed on September 22, 2023, the entire disclosure of which is incorporated herein by reference.

Claims

1. A laser processing machine comprising: a camera that captures an image of radiation light emitted from a processing point on a metal sheet when the metal sheet is cut by irradiating the metal sheet with a laser beam; and a control unit that detects defects in the processing of the metal sheet based on the radiation light captured by the camera, wherein the control unit measures the degree to which the radiation light spreads in a direction perpendicular to the direction of travel of the laser beam, and determines whether or not the metal sheet has been processed defectively based on the measured degree of spread of the radiation light.

2. The laser processing machine according to claim 1, wherein the control unit measures the angle at which the radiated light spreads in a direction perpendicular to the traveling direction of the laser beam as the degree of spread of the radiated light, calculates a dispersion value from a plurality of the angles measured within a specified time, and determines that the sheet metal has been defectively processed if the calculated dispersion value is equal to or greater than a specified value.

3. The laser processing machine according to claim 1, wherein the control unit measures the width by which the radiated light spreads in a direction perpendicular to the traveling direction of the laser beam as the degree of spread of the radiated light, calculates a dispersion value from multiple widths measured within a specified time, and determines that the sheet metal has been defectively processed if the calculated dispersion value is equal to or greater than a specified value.

4. The laser processing machine according to claim 1, wherein the control unit measures the angle at which the radiated light spreads in a direction perpendicular to the traveling direction of the laser beam as the degree of spread of the radiated light, and if the angle is equal to or greater than a predetermined value, determines that the sheet metal has been defectively processed.

5. The laser processing machine according to claim 1, wherein the control unit measures the width by which the radiated light spreads in a direction perpendicular to the traveling direction of the laser beam as the degree of spread of the radiated light, and if the width is equal to or greater than a predetermined value, determines that the sheet metal has been defectively processed.

6. A laser processing machine according to any one of claims 1 to 5, wherein the control unit is configured to allow a user to select whether to continue laser processing or to stop laser processing when it is determined that the sheet metal has been defectively processed.

7. A method for detecting processing defects, comprising: capturing an image of radiation light emitted from a processing point on a metal sheet when a laser processing machine irradiates the metal sheet with a laser beam to cut the metal sheet; measuring a degree to which the captured radiation light spreads in a direction perpendicular to the traveling direction of the laser beam; and determining whether or not the metal sheet has been processed defectively based on the measured degree of spread of the radiation light.

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