Disconnection detection method and laser machining device

Abstract

To provide a disconnection detection method and a laser machining device which can be constituted of a simple system and can detect disconnection of a signal line.SOLUTION: A disconnection detection method according to the present invention is a disconnection detection method for detecting disconnection of a signal line that transmits a measurement signal output from a sensor 3 that measures return light obtained when a laser beam LB emitted in accordance with an output command signal is reflected by a machining target W, and determines that the signal line is disconnected when the output command signal is close to 0 and the measurement signal is equal to or greater than a predetermined threshold value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a disconnection detection method and a laser processing apparatus.

Background Art

[0002] A laser processing apparatus performs laser processing such as welding, cutting, and drilling of a processing target by irradiating the processing target with laser light. The laser processing apparatus is provided with a protective glass in order to prevent spatter, which is melted and scattered from the processing target by laser processing, from adhering to the optical system. However, even if the protective glass can prevent spatter from adhering to the optical system, spatter may adhere to the protective glass itself. When spatter adheres to the protective glass, the laser light is blocked by the spatter adhering to the protective glass, and the laser light cannot be irradiated onto the processing target with a desired intensity, leading to a deterioration in processing quality. Therefore, techniques for detecting the degree of contamination of the protective glass have been studied. In one such technique, a sensor for measuring the return light of the laser light reflected from the processing target is provided in the laser processing apparatus. By providing such a sensor, based on the intensity of the detected return light, not only the degree of contamination of the protective glass but also a decrease in the output of the laser light itself can be determined.

[0003] For the stabilization of processing quality, high reliability is required for the sensor that measures the return light. For example, when the signal line that transmits the measurement signal output from the sensor that measures the return light is disconnected, the degree of contamination of the protective glass and the decrease in the output of the laser light itself cannot be accurately determined. For this reason, methods for detecting disconnection of the signal line that transmits the measurement signal output from the sensor have been studied. For example, a disconnection detection method for a signal line is proposed in Patent Document 1. Patent Document 1 discloses a method using a sample-and-hold circuit that holds an analog signal selected by a multiplexer for a certain period of time. In this method, disconnection of the analog signal switched by the multiplexer can be determined based on the voltage held by the sample-and-hold circuit.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-244813 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] Regarding the method for detecting a disconnection of a signal line disclosed in Patent Document 1, the inventors have found the following problems. In the method for detecting a disconnection of a signal line disclosed in Patent Document 1, it is necessary to incorporate a multiplexer and a sample-and-hold circuit into a laser processing machine, which complicates the system. Furthermore, the detection of the disconnection of the sensor is required not only before laser processing but also during laser processing.

[0006] The present invention has been made to solve such problems, and provides a disconnection detection method and a laser processing apparatus that can be configured with a simple system and can detect a disconnection of a signal line. [Means for Solving the Problems]

[0007] The disconnection detection method according to the present invention is a disconnection detection method for detecting a disconnection of a signal line that transmits a measurement signal output from a sensor that measures return light reflected by a laser beam emitted in response to an output command signal in a processing target, wherein when the output command signal is near 0 and the measurement signal is equal to or greater than a predetermined threshold value, it is determined that the signal line is disconnected.

[0008] Further, being near 0 for the output command signal preferably means that it is less than or equal to (maximum output value of the laser oscillator ÷ 10) × 0.9.

[0009] Also, it is preferable to execute the determination process for disconnection of the signal line in the laser processing stage where the laser beam is irradiated onto the processing target. In the laser processing stage, if the output of the sensor is not transmitted due to disconnection of the signal line, the desired laser processing cannot be achieved, leading to product defects. Therefore, if the above-described disconnection detection method is executed in the laser processing stage, the occurrence of product defects can be suppressed.

[0010] The laser processing apparatus according to the present invention includes a laser oscillator that oscillates a laser beam in response to an output command signal, a laser processing head that emits the laser beam onto a processing target, a sensor that measures the return light reflected from the processing target by the laser beam, a signal monitoring unit that is connected to the laser oscillator and the sensor by signal lines and monitors the output command signal and the measurement signal of the return light, and a disconnection detection unit that detects disconnection of the signal line connecting the signal monitoring unit and the sensor. The disconnection detection unit determines that the signal line is disconnected when the output command signal is near 0 and the measurement signal of the return light is equal to or greater than a predetermined threshold value.

[0011] Also, it is preferable that the output command signal being near 0 means that it is equal to or less than (the maximum output value of the laser oscillator ÷ 10) × 0.9.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a disconnection detection method and a laser processing apparatus that can be configured with a simple system and can detect disconnection of a signal line.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

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Figure 5

Figure 6

Mode for Carrying Out the Invention

[0014] Embodiment 1 Hereinafter, with reference to the drawings, the disconnection detection method according to Embodiment 1 will be described. The disconnection detection method according to this embodiment detects the disconnection of the signal line in the laser processing apparatus. More specifically, in the laser processing stage of irradiating the processing target with laser light, the disconnection of the signal line that transmits the measurement signal output from the sensor that measures the return light is detected.

[0015] <Configuration of the Laser Processing Apparatus> First, with reference to FIG. 1, the configuration of a laser processing apparatus (laser processing system) for realizing the disconnection detection method according to Embodiment 1 will be described. As shown in FIG. 1, the laser processing apparatus 100 is an apparatus for performing laser processing such as welding, cutting, drilling, and engraving on the processing target W, and includes a laser processing head 1, a laser oscillator 2, a sensor 3, a signal monitoring unit 4, an optical fiber cable 5, a signal line 6 for the laser oscillator, and a signal line 7 for the sensor.

[0016] The laser processing head 1 irradiates the workpiece W with the laser beam LB. The laser processing head 1 includes an optical system (not shown) and a protective glass. The optical system is for condensing, refracting, etc. the laser beam transmitted from the laser oscillator 2 through the optical fiber cable 5 in order to irradiate the workpiece W. The optical system is, for example, a lens, a mirror, a filter, etc. The protective glass is provided in the laser processing head 1 to prevent the spatter generated when the workpiece W melts and scatters due to laser processing from adhering to the optical system. Also, the laser processing head 1 may be attached to a robot. For example, the laser processing head 1 can change its position relative to the workpiece W by operating the robot.

[0017] The laser oscillator 2 emits the laser beam LB into the optical fiber cable 5 by oscillation. In response to an output command signal for commanding the output, etc. of the laser beam LB input by a laser oscillator control unit (not shown), the laser oscillator 2 emits the laser beam LB. More specifically, the output command signal can control the intensity of the laser beam LB output from the laser oscillator 2 to an arbitrary value. Also, the laser oscillator 2 transmits the input output command signal to the signal monitoring unit 4 via the signal line 6 for the laser oscillator. As the light source of the laser oscillator 2, for example, a solid laser light source, a gas laser light source, a fiber laser light source, etc. can be used.

[0018] The optical fiber cable 5 transmits the laser beam LB emitted by the laser oscillator 2 to the laser processing head 1. The optical fiber cable 5 has an optical fiber inside the cable.

[0019] The sensor 3 monitors the state of laser processing for detecting contamination of the protective glass, output reduction of the laser light itself, etc. The sensor 3 is an optical sensor including a light receiving element such as a photodiode or a phototransistor, and generates a signal based on the amount of received light by utilizing the property of the light receiving element whose electrical resistance changes according to the amount of received light. The sensor 3 is provided in the laser processing head 1 and measures the return light reflected by the laser light LB emitted from the laser processing head 1 on the processing target W. The sensor 3 converts the amount of received return light into a signal and transmits it to the signal monitoring unit 4 as a measurement signal via the sensor signal line 7. In the present embodiment, an optical sensor is used as the sensor 3, but it is not limited thereto. The sensor 3 may be, for example, a temperature sensor.

[0020] The signal monitoring unit 4 measures and monitors the output command signal input to the laser oscillator 2 and the measurement signal of the return light measured by the sensor 3. The signal monitoring unit 4 is connected to the laser oscillator 2 and the sensor 3 via the laser oscillator signal line 6 and the sensor signal line 7. In the present embodiment, the signal monitoring unit 4 monitors the output command signal and the measurement signal of the return light, specifically, the voltage change over time as a waveform, but it is not limited thereto. The signal monitoring unit 4 outputs the waveforms of the output command signal and the measurement signal of the return light to a notification unit such as a display (not shown). The signal monitoring unit 4 includes a disconnection detection unit 41. The disconnection detection unit 41 detects the disconnection of the sensor signal line 7 based on the waveforms of the output command signal and the measurement signal of the return light. The disconnection detection unit 41 outputs the detection result to a notification unit such as a display (not shown).

[0021] <Disconnection Detection Method> Next, the wire break detection method according to Embodiment 1 will be described. In this embodiment, the laser processing apparatus 100 welds the workpiece W. FIG. 2 is a flowchart until the end of laser processing according to Embodiment 1, and is composed of three steps: wire break inspection (step S101), dot inspection (step S102), and laser processing (step S103). Usually, before executing laser processing, a wire break inspection of the communication line (step S101) is executed. However, in the wire break inspection of the communication line (step S101) before executing laser processing, a wire break during laser processing (step S103) cannot be detected. Therefore, this embodiment executes a determination process for a wire break of the communication line during laser processing (step S103).

[0022] First, the wire break detection unit 41 executes a wire break inspection of the sensor signal line 7 before executing laser processing (step S101). The wire break detection unit 41 checks whether the measurement signal of the return light is within the range of 0V ± the standard value, and determines that the sensor signal line 7 is normal if it is within this range, and that the sensor signal line 7 is broken if it is outside this range. In this embodiment, the wire break detection unit 41 executes step S101, but the user may also make a determination based on the measurement signal of the return light output by the signal monitoring unit 4 to a notification unit such as a display.

[0023] Next, the user executes a dot inspection (step S102). The laser processing apparatus 100 emits a laser to the workpiece W or a sample different from the workpiece W. Then, the user checks the formed dots to confirm the state of the laser output.

[0024] If there is no abnormality in the inspections of steps S101 and S102, the laser processing apparatus 100 executes laser processing on the workpiece W (step S103). In this embodiment, a determination process for a wire break of the sensor signal line 7 is also executed in this step S103.

[0025] Here, a method for detecting disconnection of the signal line 7 for the sensor in this step S103 will be described. The disconnection detection method in this step S103 is that the disconnection detection unit 41 detects the disconnection of the signal line 7 for the sensor based on the waveforms of the output command signal and the measurement signal of the return light.

[0026] First, the difference in the waveforms of the output command signal and the measurement signal of the return light received by the signal monitoring unit 4 when the signal line 7 for the sensor is disconnected and when it is normal will be described. As shown in FIG. 3, during the laser processing (step S103) when the signal line 7 for the sensor is normal, the measurement signal of the return light changes in response to the change in the output command signal. For example, when the output command signal is near 0V, in other words, when the laser light LB is not emitted, the measurement signal of the return light is also near 0V. On the other hand, as shown in FIG. 4, during the laser processing (step S103) when the signal line 7 for the sensor is disconnected, when the output command signal is near 0V, the measurement signal of the return light does not become near 0V and hardly changes, and becomes a desired value.

[0027] When the signal line 7 for the sensor is disconnected, the reason why the measurement signal of the return light does not become near 0V and hardly changes is considered as follows. As shown in FIG. 5, the sensor 3 includes a light receiving element 31 whose electrical resistance changes according to the amount of received light, a power supply 32, and an internal resistance 33. The signal monitoring unit 4 is connected to the sensor 3 by the signal line 7 for the sensor and receives the voltage of the light receiving element 31 from the sensor 3 as the measurement signal of the return light. When the signal line 7 for the sensor is disconnected, the electrical resistance of the light receiving element 31 becomes infinite regardless of the amount of received light, and the measurement signal of the return light measured by the signal monitoring unit 4 becomes almost the same as the voltage of the power supply 32. Therefore, even if the amount of return light changes due to the change in the output command signal, the measurement signal of the return light received by the signal monitoring unit 4 does not become near 0V and hardly changes.

[0028] Therefore, in this step S103, the disconnection detection unit 41 detects the disconnection of the sensor signal line 7 based on the measurement signal of the return light when the output command signal is near 0. More specifically, the disconnection detection unit 41 determines that the sensor signal line 7 is disconnected when the output command signal is near 0 and the measurement signal of the return light is equal to or greater than a predetermined threshold value. In the present embodiment, the output command signal being near 0 means that the output command signal is less than or equal to (maximum output value of the laser oscillator 2÷10)×0.9. Also, the threshold value of the measurement signal of the return light is preferably within the range of 1 to 100% of the measurement range of the sensor 3.

[0029] <Example> An example of the disconnection detection method according to the present embodiment will be described below. However, the disconnection detection method according to the embodiment is not limited to the following examples.

[0030] In this example, a laser oscillator 2 with a maximum output of 10V was used. Therefore, the output command signal being near 0 in this example means that the output command signal is 0.9V when it is less than (maximum output value of the laser oscillator 2÷10)×0.9. Therefore, in step S103, the disconnection detection unit 41 detects the disconnection of the sensor signal line 7 based on the measurement signal of the return light when the output command signal is 0.9V. Also, the threshold value of the measurement signal of the return light was set to 7% of the measurement range of the sensor 3. Since the maximum output of the sensor 3 used in this example as the measurement range is 10V, the predetermined threshold value of the measurement signal of the return light is 0.7V. In other words, when the output command signal is 0.9V and the measurement signal of the return light is 0.7V or more, the disconnection detection unit 41 determines that the sensor signal line 7 is disconnected.

[0031] FIG. 6 shows the measurement results of the output command signal and the measurement signal of the return light measured by the signal monitoring unit 4 when step S103 is executed using the disconnected sensor signal line 7 in this example. When the output command signal is 0.9V, the measurement signal of the return light is 5V. Therefore, when the output command signal is 0.9V and the measurement signal of the return light is 0.7V or more, the disconnection detection unit 41 determines that the sensor signal line 7 is disconnected.

[0032] As described above, according to the disconnection detection method according to the present embodiment, it is possible to detect a disconnection of a communication line even in the laser processing stage of irradiating a processing target with a laser beam. Conventionally, it has been difficult to detect a disconnection of a communication line in the laser processing stage. Therefore, it has been difficult to prevent contamination detection of a protective glass and defects in quality inspection of a processing target in the laser processing stage. However, if it is possible to detect a disconnection of a communication line even in the laser processing stage by the disconnection detection method according to the present embodiment, these defects can be prevented.

[0033] Note that the present invention is not limited to the above-described embodiment, and can be appropriately modified without departing from the gist thereof.

[0034] In the present disclosure, it is also possible for a user to execute the determination of the disconnection of the signal line 7 for the sensor by the disconnection detection unit 41 in step S103. For example, the waveforms of the output command signal measured by the signal monitoring unit 4 and the return light measurement signal are output to a notification unit such as a display (not shown), and based on the waveforms of the output command signal and the return light measurement signal displayed on the notification unit, the user may determine the disconnection of the signal line 7 for the sensor.

Description of Reference Numerals

[0035] 1 Laser processing head 2 Laser oscillator 3 Sensor 4 Signal monitoring unit 5 Optical fiber cable 6 Signal line for laser oscillator 7 Signal line for sensor 31 Light receiving element 32 Power supply 33 Internal resistance 41 Disconnection detection unit 100 Laser processing apparatus LB Laser beam W Processing target

Claims

1. A wire break detection method for detecting a break in a signal line that transmits a measurement signal output from a sensor that measures return light reflected by a processing target from laser light emitted in response to an output command signal, when the output command signal is near 0 and the measurement signal is equal to or greater than a predetermined threshold value, it is determined that the signal line is broken. Wire break detection method.

2. The output command signal being near 0 means that it is less than or equal to (maximum output value of the laser oscillator ÷ 10) × 0.

9. The wire break detection method according to Claim 1.

3. The determination process for the break in the signal line is executed in the laser processing stage of irradiating the processing target with the laser light. The wire break detection method according to Claim 1 or 2.

4. A laser oscillator that oscillates laser light in response to an output command signal, a laser processing head that emits the laser light to a processing target, and a sensor that measures return light reflected from the processing target by the laser light, a signal monitoring unit connected to the laser oscillator and the sensor by a signal line, which monitors the output command signal and the measurement signal of the return light, a laser processing apparatus comprising a wire break detection unit that detects a break in the signal line connecting the signal monitoring unit and the sensor, wherein the wire break detection unit determines that the signal line is broken when the output command signal is near 0 and the measurement signal of the return light is equal to or greater than a predetermined threshold value. Laser processing apparatus.

5. The output command signal being near 0 means that it is less than or equal to (maximum output value of the laser oscillator ÷ 10) × 0.

9. The laser processing apparatus according to Claim 4.

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