Laser welding device and focus shift detection method

Abstract

This laser welding device comprises: a laser oscillator; a machining head that condenses a laser beam generated from the laser oscillator and irradiates a workpiece with the laser beam; and a controller that detects the presence of a focus shift of the laser beam. The machining head has at least one optical element, a protective glass, a laser light source which emits guide light having a wavelength different from that of the laser beam, and a sensor array which is disposed symmetrically with the laser light source, having at least the protective glass therebetween. The controller detects the presence of the focus shift and corrects the focus shift, on the basis of the position of receiving the guide light in the sensor array.

Description

Laser welding device and focus shift detection method

[0001] The present disclosure relates to a laser welding apparatus and a method for detecting focus shift.

[0002] Patent Literature 1 discloses an apparatus for determining a focal position of a laser beam in a laser processing system, which comprises an optical element configured to separate a first sub-beam of the laser beam by reflecting a portion of the laser beam, a spatially resolved sensor for detecting an intensity distribution of the first sub-beam, and an evaluation unit configured to determine an actual diameter of the first sub-beam based on the detected intensity distribution, and to determine an actual focal position of the laser beam from the actual diameter, the laser beam power, and calibration data (e.g., beam diameter measured as a function of the laser beam power).

[0003] Japanese Patent No. 6963680

[0004] The present disclosure has been devised in consideration of conventional circumstances, and provides a laser welding device and a focus shift detection method that detect the presence or absence of a focus shift of a laser beam irradiated from a processing head toward a workpiece, correct the focus shift, and obtain stable processing quality for the workpiece.

[0005] The present disclosure provides a laser welding device comprising: a laser oscillator; a processing head that focuses laser light generated from the laser oscillator and irradiates the laser light onto a workpiece; and a controller that detects whether or not a focus shift has occurred in the laser light, wherein the processing head has at least one optical element, a protective glass, a laser light source that emits guide light having a wavelength different from that of the laser light, and a sensor array that is arranged symmetrically with the laser light source across at least the protective glass, and the controller detects whether or not a focus shift has occurred based on the light receiving position of the guide light by the sensor array, and corrects the focus shift.

[0006] The present disclosure also provides a focus shift detection method that is performed by a laser welding apparatus that includes at least a laser oscillator, a processing head, and a controller, and includes the steps of: focusing laser light generated from the laser oscillator with the processing head and irradiating the laser light onto a workpiece; and detecting whether or not a focus shift has occurred in the laser light, wherein the processing head includes at least one optical element, a protective glass, a laser light source that emits guide light having a wavelength different from that of the laser light, and a sensor array that is arranged symmetrically with the laser light source across at least the protective glass, and in the step of detecting whether or not a focus shift has occurred, the focus shift detection method detects whether or not a focus shift has occurred based on the light receiving position of the guide light by the sensor array, and corrects the focus shift.

[0007] According to the present disclosure, it is possible to detect whether or not there is a focus shift in the laser beam irradiated from the processing head toward the workpiece, and correct the focus shift, thereby obtaining stable processing quality for the workpiece.

[0008] FIG. 1 shows an example of the general configuration of a laser welding device according to each embodiment. FIG. 2 shows an example of the configuration of a processing head according to embodiment 1. FIG. 3 shows an example of the effect on light passing through a lens when a focus shift occurs. FIG. 4 shows an example of the effect on light passing through a protective glass when a focus shift occurs. FIG. 5 shows an example of thermal deformation of a lens when the temperature rises. FIG. 6 shows an example of thermal deformation of a protective glass when the temperature rises. Graph showing an example of the temperature characteristics of glass constituting a lens or protective glass when the temperature rises. Graph showing an example of the relationship between the movement amount on the Z axis of a sensor array and the focus shift amount. Flowchart showing an example of the operation procedure for detecting the presence or absence of a focus shift according to embodiment 1 in chronological order. FIG. 1 shows an example of the first configuration of a processing head according to embodiment 2. FIG. 2 shows an example of the second configuration of a processing head according to embodiment 2. FIG. 3 shows an example of the first configuration of a processing head according to embodiment 3.

[0009] (Background to the present disclosure) Laser light has a high power density, is capable of performing high-speed, high-quality welding, and is applied to welding a variety of workpieces. Various types of processing heads are used for laser welding. For example, they range from simple ones consisting of a collimator lens and a condenser lens with a fixed optical axis to highly functional ones such as galvanometer heads that can scan laser light (in other words, a laser beam) toward a welding point on a workpiece at high speed.

[0010] However, in actual laser processing, optical components inside the processing head may absorb the laser beam guided from the optical fiber, or processing products (e.g., spatter, fumes) adhering to optical components exposed to the outside may absorb more of the laser beam, resulting in a significant rise in the temperature of the optical components. When the temperature of the optical components rises, the focal position of the laser beam changes, posing a problem of a high possibility of causing a focus shift.

[0011] To address this issue, approaches such as optical system design and cooling have generally been taken to address the absorption of the laser beam guided from the optical fiber by optical components inside the processing head. On the other hand, optical system design alone is insufficient to address the issue of greater absorption of the laser beam by processing products (e.g., spatter, fumes) adhering to exposed optical components. Therefore, approaches have been taken to sense and correct focus shift during laser processing. Patent Document 2 proposes this approach. However, the configuration of Patent Document 2 requires the insertion of a reflective element in the path through which the main laser beam passes during processing to reflect the main beam required for sensing. Because the light from this reflective element varies depending on the intensity of the main laser beam, there is a high possibility that it will affect sensing accuracy. Furthermore, because a beam in the same wavelength band as the main laser beam is used for sensing, there is a risk of light scattering within the processing head, which may potentially degrade sensing accuracy.

[0012] Therefore, in the following embodiments, an example of a laser welding device and a focus shift detection method will be described that can detect whether or not there is a focus shift in the laser beam irradiated from the processing head toward the workpiece, correct the focus shift, and obtain stable processing quality for the workpiece.

[0013] Hereinafter, with reference to the accompanying drawings, a detailed description of embodiments specifically disclosing a laser welding apparatus and a focus shift detection method according to the present disclosure will be provided. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters or redundant description of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter recited in the claims.

[0014] (Embodiment 1) In embodiment 1, the laser welding device uses a laser light source provided in the processing head and a sensor array arranged symmetrically to the laser light source across at least a protective glass (more specifically, a protective glass, a focusing lens, and a collimating lens) to detect whether or not there is a focus shift (i.e., a deviation of the focus in the Z direction (see below)) of the laser light irradiated from the processing head, correct the focus shift, and output the detection result.

[0015] 1. Configuration of the Laser Welding Apparatus Fig. 1 is a diagram showing a schematic configuration example of a laser welding apparatus 100 according to each embodiment. The laser welding apparatus 100 includes a laser oscillator 10, an optical fiber 20, a processing head 30, a manipulator 40, and a controller 50. A display DP1 may be connected to the controller 50 so as to be able to display various data (e.g., screen data, etc.) from the controller 50.

[0016] In the following description, the direction in which the laser light LB is irradiated from the machining head 30 to the workpiece 200 is referred to as the Z direction, and the two orthogonal directions constituting the planar direction perpendicular to the Z direction are referred to as the X direction and the Y direction.

[0017] The laser oscillator 10 is a laser light source that receives power from a laser drive power supply (not shown) and generates laser light LB. The laser oscillator 10 may be composed of a single laser light source or may be composed of multiple laser modules.

[0018] The laser light source or laser module used in the laser oscillator 10 is appropriately selected depending on the material of the workpiece 200 to be welded, the shape of the welded portion, etc. For example, a fiber laser, a disk laser, or a yttrium aluminum garnet (YAG) laser can be used as the laser light source. In this case, the wavelength of the laser light LB is set in the range of 1000 nm to 1100 nm. A semiconductor laser can also be used as the laser light source or laser module. In this case, the wavelength of the laser light LB is set in the range of 800 nm to 1000 nm. A visible light laser can also be used as the laser light source or laser module. In this case, the wavelength of the laser light LB is set in the range of the blue wavelength band of 400 nm to 500 nm or the visible light wavelength band of 500 nm to 700 nm.

[0019] The optical fiber 20 has one end (incoming end) optically coupled to the laser oscillator 10 and the other end (outgoing end) optically coupled to the machining head 30. The optical fiber has a core (not shown) at its center, and a cladding (not shown) that is in contact with the outer circumferential surface of the core and coaxial with the core. The core and cladding are each primarily composed of quartz, and the refractive index of the core is higher than the refractive index of the cladding. Therefore, the laser light LB generated by the laser oscillator 10 is incident on the incoming end of the optical fiber 20 and is transmitted through the core toward the outgoing end while repeatedly reflecting, etc. In addition, a coating (not shown) or a resin-based protective layer (not shown) that mechanically protects the optical fiber 20 is provided on the outer circumferential surface of the cladding.

[0020] The machining head 30 is attached to the output end of the optical fiber 20 and houses at least one optical element, a protective glass 34, and a sensor array 36. An example of the internal configuration of the machining head 30 according to the first embodiment will be described in detail with reference to FIG. 2 . The machining head 30 first collimates the laser light (in other words, a laser beam) transmitted and spread through the optical fiber 20 into parallel light, and then focuses the collimated parallel light to irradiate the laser light LB that passes through the protective glass 34 toward the workpiece 200. This enables the workpiece 200 to be machined by laser welding. Data on the detection results of the sensor array 36 is input to the controller 50 via wiring 37.

[0021] As will be described in detail in an embodiment below, the processing head 30 may be configured to two-dimensionally scan the laser beam LB to irradiate it toward any position (e.g., a desired welding point) on the surface of the workpiece 200. In this case, the processing head has an optical scanning mechanism (e.g., a scanner unit such as a galvanometer scanner) that scans the laser beam LB.

[0022] The manipulator 40 is, for example, a known vertical six-axis robot having six joint axes. The sixth joint axis is provided at the tip of a robot arm included in the manipulator 40. The manipulator 40 can grasp the machining head 30 via a gripping part (not shown) attached to the sixth joint axis, and controls the position of the machining head 30 so that it can be moved in response to a command signal from the controller 50.

[0023] The controller 50 has a control unit 51 including a processor and the like, and a memory 52 including a memory and the like. The controller 50 controls the timing, output, start, end, etc. of laser oscillation of the laser oscillator 10. Specifically, the controller 50 controls the laser oscillation and laser output in the control unit 51 by supplying control signals such as output current and on / off time to a laser drive power supply (not shown) connected to the laser oscillator 10. The controller 50 also controls the laser irradiation position of the processing head 30 in accordance with the contents of a processing program for laser welding (processing) the workpiece 200, which is stored in the memory 52. ​​The controller 50 also generates command signals for controlling the operation of the manipulator 40 and sends them to the manipulator 40.

[0024] The memory 52 stores a processing program for laser welding. The memory 52 may be provided inside the controller 50 as shown in Fig. 1, or may be provided outside the controller 50 and configured to be able to exchange data with the controller 50.

[0025] The display DP1 is configured using, for example, a Liquid Crystal Display (LCD) or an organic electroluminescence (EL) display, and is connected to the controller 50 so as to allow input and output of data signals. The display DP1 displays a screen showing the processing results by the control unit 51 (for example, a message indicating that laser welding (processing) will be stopped because the amount of focus shift is outside the allowable range).

[0026] 2. Configuration Example of Processing Head Next, with reference to FIG. 2, a configuration example of the processing head 30 according to the first embodiment will be described. FIG. 2 is a diagram schematically illustrating a configuration example of the processing head 30 according to the first embodiment. In FIG. 2, a-a' indicates the optical axis of the laser light LB incident on the processing head 30. The processing head 30 has a substantially cylindrical housing. The processing head 30 accommodates a fiber coupling unit 31, a sensor array 36, a collimating lens 32, a condensing lens 33, a protective glass 34, and a laser light source 35 in the housing along the Z direction.

[0027] The fiber coupling unit 31 is connected to the other end of the optical fiber 20 (see above), and causes the laser light LB guided through the optical fiber 20 to enter (be guided into) the housing of the processing head 30. In the description of FIG. 2 , the laser light LB that enters the processing head 30 may be referred to as laser light LB1. The laser light LB1 diffuses when it enters the processing head 30.

[0028] The collimating lens 32 is configured to be drivable in the Z direction or the −Z direction, for example, based on drive control by a controller 50 of a motor (not shown) arranged in the processing head 30. The collimating lens 32 is an example of an optical element, and collimates the laser light LB1 that spreads from the fiber coupling portion 31. The collimated laser light LB1 travels toward the condenser lens 33.

[0029] The condenser lens 33 is an example of an optical element, and condenses the laser beam LB1 collimated by the collimator lens 32 toward a predetermined welding point on the workpiece 200. The laser beam LB1 transmitted through the condenser lens 33 travels toward the protective glass 34. The condenser lens 33 may be configured as a single lens or may be configured with multiple lenses.

[0030] The protective glass 34 prevents contamination inside the processing head 30 due to the intrusion of scattered deposits (e.g., spatter and fumes) that are generated when the laser beam LB1 is irradiated onto the workpiece 200 to perform welding. The protective glass 34 transmits the laser beam LB1 that has passed through the condenser lens 33. The laser beam LB1 that has passed through the protective glass 34 proceeds toward a predetermined welding point on the workpiece 200.

[0031] The laser light source 35 emits a guide laser beam LB2 used for detecting (sensing) whether or not a focus shift of the laser beam LB1 has occurred based on a command from the control unit 51 of the controller 50. The guide laser beam LB2 has a different wavelength band from the laser beam LB1 used in laser welding (processing). For example, when the laser beam LB1 has a wavelength band of 1000 to 1100 nm, the guide laser beam LB2 may have a red light wavelength band of 630 to 780 nm, a green light wavelength band of 480 to 560 nm, or a blue light wavelength band of 420 to 500 nm. As a result, the wavelength bands of the laser beam LB1 and the guide laser beam LB2 are different within the housing of the processing head 30, so that the detection accuracy of the light receiving position (imaging position) of the guide laser beam LB2 is not reduced, and the accuracy of detecting (sensing) whether or not a focus shift of the laser beam LB1 has occurred is less likely to deteriorate. The laser light source 35 is disposed, for example, at the bottom inside the housing of the machining head 30. In this embodiment, the guide laser beam LB2 from the laser light source 35 passes through the protective glass 34, the condenser lens 33, and the collimator lens 32 in this order, and is received by the sensor array 36. Note that the wavelength band of the guide laser beam LB2 and the wavelength band of the laser beam LB1 may be the same.

[0032] The sensor array 36 is configured by, for example, a position sensitive detector (PSD) in which a plurality of light receiving elements such as photodiodes are arranged one-dimensionally (i.e., in the Z direction). The sensor array 36 can detect the light receiving position (imaging position) of the incident guide laser beam LB2 in the Z direction. The sensor array 36 receives the guide laser beam LB2 transmitted through the protective glass 34, the condenser lens 33, and the collimator lens 32 in this order. By receiving the light, the sensor array 36 can detect the imaging position, which is the position where the guide laser beam LB2 transmitted through the protective glass 34, the condenser lens 33, and the collimator lens 32 in this order is irradiated. The sensor array 36 outputs detection result data of the imaging position of the guide laser beam LB2 to the controller 50 via wiring 37. 2, an optical system for collimating and focusing the guide laser beam LB2 from the laser light source 35 is omitted, and the same applies to the following embodiments. In order to increase the resolution of the irradiation position of the guide laser beam LB2 on the sensor array 36, it is desirable to make the image of the guide laser beam LB2 on the surface of the sensor array 36 as small as possible.

[0033] 3. Causes of Focal Shift and Effects of Focal Shift Next, with reference to Figures 3A, 3B, 4A, 4B, 5, and 6, the causes of focal shift of laser light LB1 and the effects of focal shift will be described. Figure 3A is a diagram showing an example of the effects on light passing through a lens when a focal shift occurs. Figure 3B is a diagram showing an example of the effects on light passing through a protective glass when a focal shift occurs. Figure 4A is a diagram showing an example of thermal deformation of a lens when the temperature rises. Figure 4B is a diagram showing an example of thermal deformation of a protective glass when the temperature rises. Figure 5 is a graph showing an example of the temperature characteristics of the glass constituting the lens or protective glass when the temperature rises. Figure 6 is a graph showing an example of the relationship between the amount of movement of the sensor array on the Z axis and the amount of focus shift.

[0034] 3A, 3B, 4A, and 4B, the characteristic indicated by T0 is the temperature distribution of the lens LN0 at room temperature, which is approximately uniform regardless of position. On the other hand, the characteristic indicated by T1 is the temperature distribution of the lens LN0 when the temperature rises from room temperature, with the temperature rise being more noticeable at the center of the lens LN0 than at either end.

[0035] As shown in Figure 3A, when the temperature of lens LN0 is generally about the same as room temperature T0, incident beam LBin (in other words, laser light incident on lens LN0) passes through lens LN0 to become solid-line output beam LBout1, which is then focused on focal plane FPL1. In Figure 3A, bb' indicates the optical axis of incident beam LBin incident on lens LN0. Typically, the optical system (optical elements) within the processing head is set to this state (i.e., the incident beam LBin is focused into output beam LBout1). Focal plane FPL1 is the design focal plane of the optical system.

[0036] Here, let's assume that slight absorption of the laser beam in the lens LN0 itself (although often present in an actual machining head, the amount is small) or absorption of the laser beam by dirt adhering to the surface of the lens LN0 results in a higher temperature distribution in the center of the lens LN0 than at either end, as shown by temperature T1. In this case, the incident beam LBin passes through the lens LN0 and becomes the dashed exit beam LBout2, which is focused on the focal plane FPL2. In other words, a focal shift Δf (i.e., the focus of the incident beam LBin moves in the -Z direction) occurs relative to the designed focal plane FPL1. As a result, for example, the power density of the laser beam irradiated on the surface of the workpiece 200 located on the designed focal plane FPL1 is lower than the power density assumed during the design of the optical system. In actual laser welding (processing), a focal shift within a certain tolerance range is often permitted depending on the workpiece and welding conditions, etc.

[0037] In the case of a clean lens LN0, the absorption of the laser beam on the lens surface is small, and even if a focal shift Δf occurs, it is kept within the allowable range and does not pose a major problem. However, if the lens LN0 becomes dirty, the amount of laser beam absorption increases significantly, resulting in a significant rise in the temperature of the lens LN0. Therefore, the focal shift Δf also increases significantly. In other words, the quality of the laser welding (processing) deteriorates. In some cases, the optical components may even be damaged.

[0038] As shown in Figure 3B, when the temperature of the protective glass SG0 is generally approximately the same as room temperature T0, the solid incident beam LBin (in other words, the laser light incident on the protective glass SG0) passes through the protective glass SG0 and becomes the solid outgoing beam LBout3, and the laser beam travels in a straight line (in other words, the focal length can be considered to be infinite).

[0039] Here, let's assume that slight absorption of the laser beam in the protective glass SG0 itself (although this amount is often small in an actual processing head), or absorption of the laser beam by dirt adhering to the surface of the protective glass SG0, results in a temperature distribution, such as temperature T1, in which only the center portion of the protective glass SG0 is higher than the two ends. In this case, the incident beam LBin passes through the protective glass SG0 and becomes the dashed exit beam LBout4, which no longer travels in a straight line. As a result, the protective glass SG0 acts as a lens with a finite focal length. Therefore, if the protective glass SG0 in this state is incorporated and used with the optical elements of the processing head, the amount of focus shift Δf shown in FIG. 3A will be further increased.

[0040] As shown in Figure 4A, when the temperature rises from room temperature T0 to temperature T1, lens LN0 is affected by the temperature distribution and deforms non-uniformly. Specifically, lens LN0 deforms into lens LN1. In other words, the central portion of lens LN0 deforms more than the ends, resulting in a shorter focal length. cc' in each of Figures 4A and 4B indicates the central axis of lens LN0.

[0041] 4B , when the temperature rises from room temperature T0 to temperature T1, the protective glass SG0 is affected by the temperature distribution and deforms non-uniformly. Specifically, the protective glass SG0 deforms into the protective glass SG1. In other words, the central portion of the protective glass SG0 deforms more than the ends, causing it to function as a lens with a very long focal length.

[0042] The horizontal axis of FIG. 5 represents temperature, e.g., from -100°C to +100°C. The vertical axis of FIG. 5 represents dn / dT (i.e., the rate of change of refractive index with respect to temperature). The temperature change of dn / dT indicated by characteristic N1 is positive, and the refractive index of the vitreous material (e.g., glass) constituting the lens or protective glass increases with increasing temperature. Therefore, the higher the temperature, the more significant the increase in refractive index. For example, in FIGS. 3A and 3B or 4A and 4B, when the temperature is T1, the overall refractive index of the lens and protective glass increases. Also, when the temperature is T1, the temperature at the center of each of the lens and protective glass is higher than at the ends, further increasing the refractive index. Therefore, in the case of a lens, the focal length becomes shorter, but in the case of a protective glass, it behaves as a lens with a long focal length.

[0043] The horizontal axis in Fig. 6 represents the amount of focus shift Δf. The vertical axis in Fig. 6 represents the movement amount (absolute value) of the imaging position of the guide laser beam LB2 on the sensor array 36 on the Z axis. When the amount of focus shift Δf is 0 (zero), the imaging position of the guide laser beam LB2 on the sensor array 36 on the Z axis is set to 0 (zero). In Fig. 6, this corresponds to the coordinate (0, 0).

[0044] During laser welding (processing), if any of the protective glass 34, the condenser lens 33, or the collimator lens 32 absorbs the laser light (laser beam) in the processing head 30, or if the surface of any of these lenses becomes dirty with scattered deposits (e.g., sputters or fumes) generated during processing and absorbs the laser beam, the focal length of the lens shortens, and the protective glass begins to function as a lens. The imaging position on the Z axis of the guide laser beam LB2 that has passed through these lenses also moves on the sensor array 36. The control unit 51 of the controller 50 can recognize the amount of focus shift Δf by sensing the amount of this movement.

[0045] 6 conceptually illustrates the relationship between the amount of the focal shift Δf and the movement amount of the imaging position of the guide laser beam LB2 on the sensor array 36 on the Z axis. The quantitative correlation changes depending on the configuration of the optical elements (optical system) housed in the machining head 30 and the configuration of the optical elements (optical system) for appropriately focusing the light on the sensor array 36. Once the optical system is determined, the relationship between the two (i.e., the relationship between the amount of the focal shift Δf and the movement amount of the imaging position of the guide laser beam LB2 on the sensor array 36 on the Z axis) may be measured in advance and stored as a database. This enables the control unit 51 to efficiently calculate the amount of the focal shift Δf.

[0046] The optical elements and protective glass housed in the processing head 30 have the following characteristics that require attention. (1) Protective glass 34: Since it is closest to the processing point of the workpiece 200 and is easily soiled, contamination by sputters or fumes can be a major cause of focus shift. (2) Condenser lens 33: Although it is often located near the protective glass 34, it is prone to temperature rise due to the influence of thermal radiation from the protective glass 34, increasing the likelihood of focus shift. (3) Collimator lens 32: Since it is located farthest from the processing point of the workpiece 200 compared to the protective glass 34 and the condenser lens 33, it is less likely to cause focus shift due to the influence of sputters, fumes, etc. during normal laser welding (processing). However, if the collimator lens 32 becomes contaminated for some reason, focus shift is more likely to occur.

[0047] 4. Focal Shift Detection Operation Procedure Next, a focal shift detection operation procedure performed by the laser welding apparatus 100 according to the first embodiment will be described with reference to Fig. 7. Fig. 7 is a flowchart showing an example of a chronological order of the operation procedure for detecting whether or not a focus shift has occurred according to the first embodiment. The various processes shown in Fig. 7 are mainly executed by the control unit 51 of the controller 50. As a prerequisite for starting the process of Fig. 7, it is assumed that the laser welding apparatus 100 has already been set up.

[0048] 7 , the control unit 51 sends a command to the laser light source 35 to emit a guide laser beam LB2 for detecting (sensing) whether or not a focus shift of the laser beam emitted from the machining head 30 has occurred. The laser light source 35 emits the guide laser beam LB2 based on the command from the control unit 51 (step St1). When the guide laser beam LB2 is emitted from the laser light source 35 in step St1, the guide laser beam LB2 passes through the protective glass 34, the condenser lens 33, and the collimator lens 32 in this order, and is imaged (received) by the sensor array 36. That is, in a state where there is no focus shift before welding is started in step St4 (described later), the image position of the guide laser beam LB2 on the sensor array 36 on the Z axis is detected and input to the control unit 51 (step St2). That is, the processes of steps St1 and St2 are performed before laser welding (machining) is performed on the workpiece 200, and the processes from step St3 onward are performed during laser welding (machining). However, the irradiation of the guide laser beam LB2 in step St1 is continued during each process from step St3 onwards.

[0049] The control unit 51 reads out a processing program for laser welding (processing) stored in the memory 52 or the like, and moves the processing head 30 in accordance with the processing program so as to irradiate the laser beam toward a desired welding point on the workpiece 200 (step St3). After step St3, the control unit 51 causes the laser oscillator 10 to generate laser beam, and performs laser welding (processing) by irradiating the laser beam toward the desired welding point on the workpiece 200 via the optical fiber 20 and the processing head 30 (step St4).

[0050] The control unit 51 acquires data on the detection result of the imaging position on the Z axis of the sensor array 36 of the guide laser beam LB2 irradiated in step St1 from the sensor array 36 via the wiring 37. The control unit 51 calculates the focal shift Δf of the laser beam irradiated from the processing head 30 during welding based on the data on the detection result of the imaging position on the Z axis of the sensor array 36 in a state without focus shift detected in step St2 and the data on the detection result of the imaging position on the Z axis of the sensor array 36 acquired after the start of welding in step St4 (step St5). For example, if the imaging position on the Z axis of the sensor array 36 in a state without focus shift detected in step St2 is 0 (zero) and the imaging position on the Z axis of the sensor array 36 acquired after the start of welding in step St4 is 3, the control unit 51 calculates that the focal shift Δf is "3" (= 3 - 0).

[0051] The control unit 51 determines whether the value of the focus shift Δf (in other words, the correction amount) calculated in step St5 is outside the tolerance range stored in the memory 52 (step St6). If the control unit 51 determines that the value of the focus shift Δf is within the tolerance range (NO in step St6), the control unit 51 performs control to correct the focus shift Δf (step St7). For example, the control unit 51 moves the collimator lens 32 in the machining head 30 by a predetermined amount along the Z direction. Alternatively, the control unit 51 may move the machining head 30 by a predetermined amount along the Z direction. This predetermined movement amount of the collimator lens 32 or the machining head 30 may be, as a first example, a fixed value stored in advance in the memory 52. ​​Alternatively, as a second example, it may be one of the set values ​​that are set in stages in advance according to the value of the focus shift Δf and stored in the memory 52.

[0052] After step St7, if the laser welding (processing) started in step St4 is completed (step St8, YES), the process of the control unit 51 shown in Fig. 7 is completed. If the laser welding (processing) started in step St4 is not completed (step St8, NO), the process of the control unit 51 returns to step St4, and the laser welding (processing) is continued.

[0053] On the other hand, if the control unit 51 determines that the value of the focus shift Δf is outside the allowable range (step St7, YES), it generates a warning signal to stop laser welding (processing) the workpiece 200 and outputs and displays it on the display DP1 (step St9). Note that this warning signal is not limited to a warning to stop laser welding (processing) the workpiece 200, but may also be a warning to clean the protective glass 34 and / or to prompt maintenance of the processing head 30, for example. After step St9, the processing of the control unit 51 shown in FIG. 7 ends.

[0054] As described above, in the first embodiment, the guide laser beam LB2 from the laser light source 35 in the processing head 30 passes through the protective glass 34, the condenser lens 33, and the collimator lens 32, and is then received (imaged) by the sensor array 36. The laser welding device 100 detects the presence or absence of a focus shift of the laser beam based on the difference between the image position of the guide laser beam LB2 on the Z axis on the sensor array 36 during welding and the image position of the guide laser beam LB2 on the sensor array 36 when no focus shift occurs before the start of welding, and corrects the focus shift. When the amount of focus shift Δf is outside the allowable range, it can be detected that any of the protective glass 34, the condenser lens 33, and the collimator lens 32 is dirty or has a high temperature, and it is possible to prompt an operator or the like to take appropriate measures.

[0055] (Embodiment 2) In embodiment 2, the laser welding device uses a laser light source provided in the processing head and a sensor array arranged symmetrically to the laser light source across at least a protective glass (more specifically, the protective glass and a condenser lens, or only the protective glass) to detect whether or not there is a focus shift of the laser light irradiated from the processing head (i.e., a deviation of the focus in the Z direction (see below)), corrects this, and outputs the detection result.

[0056] Except for the configuration example of the processing head, the configuration of the laser welding apparatus according to embodiment 2 is the same as that of the laser welding apparatus 100 according to embodiment 1. Therefore, the following will mainly describe the configuration example of the processing head according to embodiment 2, focusing on the differences from the configuration of the laser welding apparatus 100 according to embodiment 1.

[0057] 5. Configuration Examples of Machining Heads First, configuration examples of the machining heads 30a and 30b according to embodiment 2 will be described with reference to Figures 8A and 8B. Figure 8A is a diagram schematically showing a first configuration example of the machining head according to embodiment 2. Figure 8B is a diagram schematically showing a second configuration example of the machining head according to embodiment 2. In Figures 8A and 8B, aa' indicates the optical axis of the laser beam LB1 incident on the machining heads 30a and 30b.

[0058] As shown in FIG. 8A , the processing head 30a has a substantially cylindrical housing. The processing head 30a accommodates a fiber coupling unit 31, a collimating lens 32, a sensor array 36a, a condensing lens 33, a protective glass 34, and a laser light source 35 in the housing along the Z direction. The processing head 30a in FIG. 8A differs from the processing head 30 in FIG. 2 in the arrangement of the sensor array 36a within the processing head 30a. Specifically, the sensor array 36a is arranged between the collimating lens 32 and the condensing lens 33. This arrangement of the sensor array 36a is assumed, for example, when the distance between the collimating lens 32 and the fiber coupling unit 31 is physically limited, or when it is determined in advance that the collimating lens 32 is unlikely to cause focus shift.

[0059] The sensor array 36a is configured by a position sensitive detector (PSD) in which a plurality of light receiving elements such as photodiodes are arranged one-dimensionally (i.e., in the Z direction), and can detect the light receiving position (imaging position) of the incident guide laser beam LB2 in the Z direction.

[0060] 8A , the sensor array 36a receives the guide laser beam LB2 that has been transmitted through the protective glass 34 and the condenser lens 33 in this order. By receiving the light, the sensor array 36a can detect the imaging position, which is the position where the guide laser beam LB2 that has been transmitted through the protective glass 34 and the condenser lens 33 in this order is irradiated. The sensor array 36a outputs data of the detection result of the imaging position of the guide laser beam LB2 to the controller 50 via the wiring 37.

[0061] As described above, in the second embodiment, the guide laser beam LB2 from the laser light source 35 in the processing head 30a passes through both the protective glass 34 and the condenser lens 33 before being received (imaged) by the sensor array 36a. The laser welding apparatus 100 detects the presence or absence of a focus shift of the laser beam based on the difference between the image position of the guide laser beam LB2 on the Z axis on the sensor array 36a during welding and the image position of the guide laser beam LB2 on the Z axis on the sensor array 36a when no focus shift occurs before welding starts. Therefore, when the amount of focus shift Δf is outside the allowable range, the laser welding apparatus 100 can detect that either the protective glass 34 or the condenser lens 33 is dirty or has a high temperature, and can prompt an operator or the like to take appropriate measures. Note that, as in the first embodiment, the control unit 51 may drive the collimator lens 32 in the processing head 30a along the Z direction when a focus shift Δf occurs.

[0062] As shown in FIG. 8B , the processing head 30b has a substantially cylindrical housing. The processing head 30b accommodates, in the housing, a fiber coupling unit 31, a collimating lens 32, a condensing lens 33, a sensor array 36b, a protective glass 34, and a laser light source 35 along the Z direction. The processing head 30b in FIG. 8B differs from the processing head 30 in FIG. 2 in the arrangement of the sensor array 36b within the processing head 30b. Specifically, the sensor array 36b is arranged between the condensing lens 33 and the protective glass 34. This arrangement of the sensor array 36b is assumed when narrowing down the causes of focal shift caused by the protective glass 34, which is most susceptible to contamination due to the effects of laser welding (processing).

[0063] The sensor array 36b is configured by a position sensitive detector (PSD) in which a plurality of light receiving elements such as photodiodes are arranged one-dimensionally (i.e., in the Z direction). The sensor array 36a can detect the light receiving position (imaging position) of the incident guide laser beam LB2 in the Z direction.

[0064] 8B , the sensor array 36b receives the guide laser beam LB2 that has passed only through the protective glass 34. By receiving the light, the sensor array 36b can detect the imaging position, which is the position irradiated with the guide laser beam LB2 that has passed only through the protective glass 34. The sensor array 36a outputs data of the detection result of the imaging position of the guide laser beam LB2 to the controller 50 via the wiring 37.

[0065] In the second embodiment, the guide laser beam LB2 from the laser light source 35 in the processing head 30b passes only through the protective glass 34 before being received (imaged) by the sensor array 36b. The laser welding device 100 detects the presence or absence of a focus shift of the laser beam based on the difference between the image position of the guide laser beam LB2 on the Z axis on the sensor array 36b during welding and the image position of the guide laser beam LB2 on the Z axis on the sensor array 36b when no focus shift occurs before welding starts, and corrects the focus shift. If the amount of focus shift Δf is outside the allowable range, it can be detected that the protective glass 34 is dirty or its temperature has risen, and the operator or the like can be prompted to take appropriate measures. As in the first embodiment, the control unit 51 may drive the collimator lens 32 in the processing head 30a along the Z direction when a focus shift Δf occurs.

[0066] (Embodiment 3) In embodiment 3, the laser welding device further accommodates one more sensor array in the processing head according to embodiment 2. Using the laser light source and two sensor arrays provided in the processing head, the laser welding device detects whether or not there is a focus shift of the laser light irradiated from the processing head (i.e., a deviation of the focus in the Z direction (see below)), corrects the focus shift, and outputs the detection result.

[0067] The configuration of the laser welding apparatus according to embodiment 3 is the same as that of the laser welding apparatus 100 according to embodiment 2, except for the configuration example of the processing head. Therefore, the following will mainly describe the configuration example of the processing head according to embodiment 3, and only the differences from the configuration of the laser welding apparatus 100 according to embodiment 2.

[0068] 6. Configuration Examples of Processing Heads First, configuration examples of processing heads 30c and 30d according to embodiment 3 will be described with reference to Figures 9A and 9B. Figure 9A is a diagram schematically showing a first configuration example of a processing head according to embodiment 3. Figure 9B is a diagram schematically showing a second configuration example of a processing head according to embodiment 3. In Figures 9A and 9B, aa' indicates the optical axis of laser light LB1 incident on processing heads 30c and 30d.

[0069] As shown in Fig. 9A, the processing head 30c has a substantially cylindrical housing. The processing head 30c accommodates, in the housing, a fiber coupling unit 31, a sensor array 36c, a collimating lens 32, a sensor array 36a, a condensing lens 33, a protective glass 34, and a laser light source 35 along the Z direction. The processing head 30c in Fig. 9A differs from the processing head 30a in Fig. 8A in that a sensor array 36c is further added within the processing head 30c. Specifically, the sensor array 36c is disposed on the opposite side of the collimating lens 32 from the sensor array 36a.

[0070] The sensor array 36c is configured by a position sensitive detector (PSD) in which a plurality of light receiving elements such as photodiodes are arranged one-dimensionally (i.e., in the Z direction). The sensor array 36a can detect the light receiving position (imaging position) in the Z direction of the guide laser beam LB3 that is reflected by the sensor array 36a, passes through the collimator lens 32, and enters the sensor array 36a.

[0071] 9A , the sensor array 36a receives the guide laser beam LB2 transmitted through the protective glass 34 and the condenser lens 33 in this order. This reception allows the sensor array 36a to detect an imaging position, which is a position where the guide laser beam LB2 transmitted through the protective glass 34 and the condenser lens 33 in this order is irradiated. The sensor array 36c receives the guide laser beam LB3, which is a part of the reflected light from the surface of the sensor array 36a, through the collimator lens 32. This reception allows the sensor array 36c to detect an imaging position, which is a position where the guide laser beam LB3 transmitted through the collimator lens 32 is irradiated. Each of the sensor arrays 36a and 36c outputs data of the detection results of the imaging positions of the guide laser beams LB2 and LB3 to the controller 50 via the wiring 37.

[0072] As described above, in the third embodiment, the guide laser beam LB2 from the laser light source 35 in the processing head 30c passes through both the protective glass 34 and the condenser lens 33 and is received (imaged) by the sensor array 36a, and further, the guide laser beam LB3 obtained by the guide laser beam LB2 being reflected by the sensor array 36a passes through the collimator lens 32 and is received (imaged) by the sensor array 36c. The laser welding apparatus 100 detects the presence or absence of a focus shift of the laser beam based on the difference between the image positions on the Z axis of the guide laser beams LB2 and LB3 on the sensor arrays 36a and 36c during welding and the image positions on the Z axis of the guide laser beams LB2 and LB3 on the sensor arrays 36a and 36c when no focus shift has occurred before the start of welding. Therefore, when the amount of the focal shift Δf is outside the allowable range, the laser welding device 100 can identify and detect without exception that any of the protective glass 34, the condenser lens 33, and the collimator lens 32 is dirty or has a temperature rise, and can prompt an operator to take appropriate measures. Note that, similar to the first embodiment, when the focal shift Δf occurs, the control unit 51 may drive the collimator lens 32 in the machining head 30a along the Z direction.

[0073] As shown in Figure 9B, the processing head 30d has a substantially cylindrical housing. The processing head 30d accommodates, in the housing, a fiber coupling unit 31, a sensor array 36d, a collimating lens 32, a condensing lens 33, a sensor array 36b, a protective glass 34, and a laser light source 35 along the Z direction. The processing head 30d in Figure 9B differs from the processing head 30b in Figure 8B in that a sensor array 36d is further added within the processing head 30d. Specifically, the sensor array 36d is disposed on the opposite side of the sensor array 36b across the condensing lens 33 and the collimating lens 32.

[0074] The sensor array 36d is configured by a position sensitive detector (PSD) in which a plurality of light receiving elements such as photodiodes are arranged one-dimensionally (i.e., in the Z direction). The sensor array 36a can detect the light receiving position (imaging position) in the Z direction of the guide laser beam LB3 that is reflected by the sensor array 36b and passes through the condenser lens 33 and the collimator lens 32 and enters the sensor array 36b.

[0075] 9B , the sensor array 36b receives the guide laser beam LB2 transmitted only through the protective glass 34. This reception allows the sensor array 36b to detect an imaging position, which is a position where the guide laser beam LB2 transmitted only through the protective glass 34 is irradiated. The sensor array 36d also receives the guide laser beam LB3, which is a part of the reflected light from the surface of the sensor array 36b, via the condenser lens 33 and the collimator lens 32. This reception allows the sensor array 36d to detect an imaging position, which is a position where the guide laser beam LB2 transmitted through the condenser lens 33 and the collimator lens 32 is irradiated. Each of the sensor arrays 36b and 36d outputs data of the detection results of the imaging positions of the guide laser beams LB2 and LB3 to the controller 50 via the wiring 37.

[0076] In the third embodiment, the guide laser beam LB2 from the laser light source 35 in the processing head 30d passes only through the protective glass 34 and is received (imaged) by the sensor array 36b, and further, the guide laser beam LB3 obtained by the guide laser beam LB2 being reflected by the sensor array 36b passes through the condenser lens 33 and the collimator lens 32 and is received (imaged) by the sensor array 36d. The laser welding device 100 detects the presence or absence of a focus shift of the laser beam based on a difference between the image positions on the Z axis of the guide laser beams LB2 and LB3 on the sensor arrays 36b and 36d during welding and the image positions on the Z axis of the guide laser beams LB2 and LB3 on the sensor arrays 36b and 36d when no focus shift has occurred before the start of welding, and corrects the focus shift. When the amount of the focal shift Δf is outside the allowable range, it is possible to identify and detect without exception whether any of the protective glass 34, the condenser lens 33, or the collimator lens 32 is dirty or has a temperature rise, and to prompt an operator to take appropriate measures. Note that, similar to the first embodiment, when a focal shift Δf occurs, the control unit 51 may drive the collimator lens 32 in the machining head 30a along the Z direction.

[0077] Although the above has not gone into detail about the surface reflection of the sensor array 36a, when light is incident on the sensor array at an angle, a portion of the light is usually reflected. This reflected light may be incident on the sensor array 36b, but if the amount of reflected light is small and needs to be increased, a coating that has a strong reflection for oblique incidence may be used, or instead of a coating, an optical component that has a strong reflection for oblique incidence may be provided in front of the sensor array 36a.

[0078] <Technology of the Present Disclosure> As described above, the present disclosure discloses the following technical ideas.

[0079] <Technology 1> A laser welding device comprising: a laser oscillator (10); a processing head (30) that collects a laser beam (LB1) generated from the laser oscillator and irradiates the laser beam onto a workpiece (200); and a controller (50) that detects whether or not a focus shift of the laser beam has occurred, wherein the processing head has at least one optical element (a collimating lens 32, a collecting lens 33), a protective glass (34), a laser light source (35) that emits a guide beam (guide laser beam LB2) having a wavelength different from that of the laser beam, and a sensor array (36) that is disposed symmetrically with the laser light source across at least the protective glass, and the controller detects whether or not a focus shift has occurred based on a light-receiving position (imaging position) of the sensor array of the guide beam, and corrects the focus shift. This allows the laser welding device to detect whether or not there is a focus shift (in other words, a deviation from the focus) in the Z direction of the laser light (in other words, the laser beam) irradiated from the processing head 30 toward the workpiece 200, and correct the focus shift. Therefore, the laser welding device can detect whether or not a laser beam having an appropriate power density is being irradiated onto the workpiece 200, which is the object of laser welding (processing), and correct the focus shift, making it possible to obtain stable processing quality for the workpiece 200, similar to when no focus shift occurs.

[0080] <Technology 2> The laser welding device according to Technology 1, wherein the controller moves the optical element along the direction in which the laser beam is emitted to the workpiece when it detects that the focus shift is within an allowable range (for example, a range of −f1 to +f1 registered in memory 52). As a result, since the focus shift detected during laser welding (processing) is within the allowable range, the laser welding device can appropriately correct the focus shift of the laser beam LB1 by moving the optical element (for example, collimator lens 32) of the processing head 30 along the Z direction, thereby suppressing deterioration in the processing quality of the workpiece 200.

[0081] <Technology 3> The laser welding device according to Technology 1 or Technology 2, wherein the controller outputs a warning signal to the display (DP1) to indicate that laser processing of the workpiece will be stopped when the controller detects the focus shift that is outside the allowable range (for example, outside the range of -f1 to +f1 registered in the memory 52). As a result, the laser welding device displays on the display DP1 a message to the effect that laser welding (processing) of the workpiece 200 should be stopped immediately because the focus shift detected during laser welding (processing) is not within the allowable range, thereby urging the operator to check for maintenance of the processing head 30, etc.

[0082] <Technology 4> The laser welding device according to any one of Technologies 1 to 3, wherein the optical elements are a collimating lens (32) and a condensing lens (33), and the sensor array receives light that is the guide light from the laser light source and has passed through the protective glass, the condensing lens, and the collimating lens. This allows the laser welding device to determine whether any one of the collimating lens 32, the condensing lens 33, and the protective glass 34 housed in the processing head 30 is causing the focus shift, and can prompt the operator to check the inside of the processing head 30.

[0083] <Technology 5> The laser welding device according to any one of Technologies 1 to 3, wherein the optical elements are a collimating lens (32) and a condensing lens (33), and the sensor array receives light that is the guide light from the laser light source and has passed through the protective glass and the condensing lens. This allows the laser welding device to determine whether either the collimating lens 32 or the condensing lens 33 housed in the processing head 30 is causing the focus shift, and can prompt the operator to check the inside of the processing head 30.

[0084] <Technology 6> The laser welding device according to any one of Technologies 1 to 3, wherein the sensor array receives the guide light from the laser light source that has passed only through the protective glass. This allows the laser welding device to determine that the protective glass 34, which is easily soiled by the influence of reflected light from the workpiece 200 among the contents contained in the processing head 30, is the cause of the focus shift, and can prompt the operator to replace the protective glass 34, etc.

[0085] <Technology 7> The laser welding device according to any one of Technologies 1 to 3, wherein the optical element is a collimating lens (32) and a condensing lens (33), the sensor array has a first sensor array (sensor array 36a) and a second sensor array (sensor array 36c), the first sensor array receives light of the guide light from the laser light source that has passed through the protective glass and the condensing lens, and the second sensor array receives light of the guide light that has been reflected by the first sensor array and passed through the collimating lens. Thus, the laser welding device can determine which optical element or protective glass is causing the focus shift by using the sensor array 36a that receives the guide laser beam LB2 that has passed through the protective glass 34 and the condensing lens 33 and the sensor array 36c that receives the guide laser beam LB3 that has passed through the collimating lens 32.

[0086] <Technology 8> The laser welding device according to any one of Technologies 1 to 3, wherein the optical element is a collimating lens (32) and a condensing lens (33), the sensor array has a first sensor array (sensor array 36b) and a second sensor array (sensor array 36d), the first sensor array receives light of the guide light from the laser light source that has passed through the protective glass, and the second sensor array receives light of the guide light reflected by the first sensor array that has passed through the condensing lens and the collimating lens. Thus, the laser welding device can determine which optical element or protective glass is causing the focus shift by using the sensor array 36b that receives the guide laser beam LB2 that has passed through the protective glass 34 and the sensor array 36d that receives the guide laser beam LB3 that has passed through the condensing lens 33 and the collimating lens 32.

[0087] <Technology 9> A focus shift detection method that is performed by a laser welding apparatus including at least a laser oscillator, a processing head, and a controller, and includes the steps of: focusing laser light generated from the laser oscillator with the processing head and irradiating the laser light onto a workpiece; and detecting and correcting the presence or absence of focus shift of the laser light, wherein the processing head includes at least one optical element, a protective glass, a laser light source that emits guide light having a wavelength different from that of the laser light, and a sensor array that is arranged symmetrically with the laser light source across at least the protective glass, and in the step of detecting the presence or absence of focus shift, the presence or absence of focus shift is detected and corrected based on the light receiving position of the sensor array for the guide light. Thus, the focus shift detection method by a laser welding apparatus can detect and correct the presence or absence of focus shift (in other words, defocus) in the Z direction of laser light (in other words, laser beam) irradiated from the processing head 30 toward the workpiece 200. Therefore, according to this focus shift detection method, the laser welding device can detect and correct whether a laser beam with appropriate power is being irradiated onto the workpiece 200, which is the object of laser welding (processing), and it is possible to obtain stable processing quality for the workpiece 200, similar to when a focus shift does not occur.

[0088] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications, alterations, substitutions, additions, deletions, and equivalents within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. Furthermore, the components of the various embodiments described above may be combined in any manner without departing from the spirit of the invention.

[0089] This application is based on a Japanese patent application (Patent Application No. 2023-116129) filed on July 14, 2023, the contents of which are incorporated herein by reference.

[0090] The present disclosure is useful as a laser welding device and a laser welding method that detect the presence or absence of a focus shift of a laser beam irradiated from a processing head toward a workpiece, correct the focus shift, and obtain stable processing quality for the workpiece.

[0091] REFERENCE SIGNS LIST 10 Laser oscillator 20 Optical fiber 30, 30a, 30b, 30c, 30d Processing head 31 Fiber coupling section 32 Collimating lens 33 Condenser lens 34 Protective glass 35 Laser light source 36, 36a, 36b, 36c, 36d Sensor array 40 Manipulator 50 Controller 51 Control section 52 Memory 100 Laser welding device 200 Work LB1 Laser light LB2, LB3 Guide laser light

Claims

1. A laser welding device comprising: a laser oscillator; a processing head which focuses the laser light generated from the laser oscillator and irradiates the laser light onto a workpiece; and a controller which detects whether or not a focus shift has occurred in the laser light, wherein the processing head has at least one optical element, a protective glass, a laser light source which emits guide light having a wavelength different from that of the laser light, and a sensor array which is arranged symmetrically with the laser light source across at least the protective glass, and the controller detects whether or not the focus shift has occurred based on the light receiving position of the guide light by the sensor array.

2. The laser welding device according to claim 1, wherein the controller moves the optical element along the direction in which the laser light is emitted to the workpiece when the controller detects the focus shift being within an acceptable range.

3. The laser welding device according to claim 1, wherein the controller outputs a warning signal to a display to stop laser processing of the workpiece when the controller detects the focus shift falling outside an allowable range.

4. The laser welding device according to claim 1, wherein the optical elements are a collimating lens and a condensing lens, and the sensor array receives the guide light from the laser light source that has passed through the protective glass, the condensing lens and the collimating lens.

5. The laser welding device according to claim 1, wherein the optical elements are a collimating lens and a condensing lens, and the sensor array receives the guide light from the laser light source that has passed through the protective glass and the condensing lens.

6. The laser welding device according to claim 1, wherein the sensor array receives the guide light from the laser light source that has passed only through the protective glass.

7. The laser welding device according to claim 1, wherein the optical elements are a collimating lens and a condensing lens, the sensor array has a first sensor array and a second sensor array, the first sensor array receives light that is the guide light from the laser light source that has passed through the protective glass and the condensing lens, and the second sensor array receives light that is the guide light reflected by the first sensor array that has passed through the collimating lens.

8. The laser welding device according to claim 1, wherein the optical elements are a collimating lens and a condensing lens, the sensor array has a first sensor array and a second sensor array, the first sensor array receives light that is the guide light from the laser light source that has passed through the protective glass, and the second sensor array receives light that is the guide light reflected by the first sensor array that has passed through the condensing lens and the collimating lens.

9. A focus shift detection method which is executed by a laser welding device having at least a laser oscillator, a processing head, and a controller, and which comprises the steps of: focusing laser light generated from the laser oscillator with the processing head and irradiating the workpiece with the laser light; and detecting whether or not there is a focus shift of the laser light, wherein the processing head comprises: at least one optical element; a protective glass; a laser light source which emits guide light having a wavelength different from that of the laser light; and a sensor array which is arranged symmetrically with the laser light source across at least the protective glass, and wherein in the step of detecting whether or not there is a focus shift, the presence or absence of the focus shift is detected based on the light receiving position of the guide light by the sensor array.

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