Laser processing device that regulates a focal point shift during laser processing depending on the degree of contamination of the optical system.

Abstract

Laser processing device (10) which performs laser processing of a workpiece while correcting a focal point shift due to contamination of an optical system, wherein the laser processing device a laser oscillator (11); an external optical system (12) to guide laser light from the laser oscillator (11) and collect it on the surface of the workpiece; a return light measuring unit (4) that measures the amount of energy of the return light reflected by the workpiece and returning to the laser processing device (10); and a focal point shift control unit (21) that regulates the focal point shift due to contamination of the external optical system (12) during laser processing based on the energy of the return light, includes the focal point shift control unit (21) a first focal point movement magnitude calculation unit (32) which calculates the focal point movement magnitude on the basis of a comparison between a first measurement value, for which several measurement values ​​measured by the return light measuring unit (4) within a first period were averaged, and a second measurement value, for which several measurement values ​​measured by the return light measuring unit (4) within a second period occurring after the first period were averaged, and a focal point position correction unit (33) that corrects the focal point position during laser processing based on the calculated focal point movement extent, exhibits wherein the first period is a period immediately after the start of the laser emission, during which the external optical system (12) is not heated, or a period after a correction of the focal point position, and the second period is a period after the expiry of a certain time during which the external optical system (12) has been heated.

Description

1. Field of the invention

[0001] The present invention relates to a laser processing apparatus, and more particularly to a laser processing apparatus that regulates a focal point shift during laser processing depending on the degree of contamination of the optical system. 2. Description of the state of the art

[0002] A laser processing device that irradiates an object to be processed with laser light and performs laser processing of the object to be processed. It focuses the laser light through a lens at a specific focal position and irradiates the object to be processed with the focused laser light. In such a laser processing device, if an external optical system that guides the laser light from a laser oscillator and converges it onto the surface of a workpiece becomes dirty and absorbs the laser light, the bending rate is changed by the so-called thermal lens effect, and the focal position is moved. Depending on the type of contamination, the transmittance of the external optical system also changes. Since processing defects occur when the focal position and transmittance change, it is necessary to ensure that the external optical system is not dirty.This circumstance affects automatic operation.

[0003] To solve this problem, it is well known to detect contamination of the external optical system by attaching a temperature sensor or a scattered light sensor to the external optical system. Furthermore, Japanese Patent Application Laid-Open No. 2014-117730 A discloses a laser processing apparatus that performs a specific processing multiple times at different focal positions as pre-processing, not during laser processing, but before laser processing. From the relationship between the different focal positions (Fp) and the return light generation periods (T) corresponding to each of these different focal positions, the focal position that results in the smallest value (Tm) for the return light generation period is set as the focal position in actual laser processing.It is described that the adjustment of the focal position of the laser light projected onto the workpiece can be performed with high precision and stability by this laser processing device without using an independent large-scale device.

[0004] Patent Application JP 2015-199113 A discloses a laser device for performing through-hole machining. The device controls a variable beam diameter optical system so that the beam diameter at the laser beam converging point decreases as the through-hole machining progresses. It is described that this laser machining device allows through-hole machining conditions to be selected with an ideal beam intensity in consideration of the material being machined and its thickness during the through-hole machining.

[0005] Furthermore, a laser processing device is known from US 2016 / 0 136 756 A1, for example, which uses a control unit to regulate a focal point shift during laser processing based on the energy quantity of emitted laser light. Other comparable devices are described, for example, in US 2016 / 0 031 038 A1 and DE 10 2015 001 421 A1. Brief description of the invention

[0006] The external optical system deteriorates over time. As a result, a loss of laser power occurs at the focal point. Since the focal point position moves even with slight contamination, this causes a significant deterioration in laser processing quality. In this case, the optical system must be replaced or cleaned quickly. However, when performing maintenance on the optical system after processing defects occur, there is the problem that a large number of defective components will be generated during automatic operation. On the other hand, the method of attaching a temperature sensor or a stray light sensor to the external system requires additional equipment, which makes the device complicated and the external optical system heavy, affecting the machine performance, or there is the problem that retrofitting is not possible.In addition, since not all external optical systems are compatible with sensors that can detect contamination, it also happens that contamination of the optical system becomes apparent after machining defects have occurred.

[0007] In addition, the method that uses return light detection has the problem that the return light cannot be reliably detected depending on the type of laser processing being performed, the material of the workpiece, and the surface condition of the workpiece. For example, in a system that uses laser welding, the surface condition of the workpiece is unstable because the workpiece surface is melted during welding (during cleaning, marking), and the return light is subject to significant noise.

[0008] On the other hand, in a system that performs laser cutting, it is possible to detect the return light during drilling, but the return light cannot be detected during cutting because the laser light passes through the workpiece. Especially in fly cutting, which is used for laser cutting of thin plates, the return light cannot be reliably detected because there is no drilling processing time during which the axis is stopped, and laser cutting is performed only by switching the laser emission on and off while the axis is constantly moving.

[0009] Therefore, a technique is desired that regulates the focal point shift during laser processing under stable detection of the returned light depending on the contamination level of the external optical system.

[0010] One form of the present disclosure provides a laser processing apparatus that performs laser processing of a workpiece while correcting a focal shift due to contamination of an optical system, comprising a laser oscillator; an external optical system for guiding laser light from the laser oscillator and condensing it on the surface of the workpiece; a return light measuring unit that measures the energy amount of the return light reflected by the workpiece and returning to the laser processing apparatus; and a focal shift regulating unit that regulates the focal shift due to contamination of the external optical system during laser processing based on the energy amount of the return light, wherein the focal shift regulating unit includes a first focal movement amount calculating unit,which calculates the focal point movement amount based on a comparison between a first measured value, for which a plurality of measured values ​​measured by the return light measuring unit within a first period were averaged, and a second measured value, for which a plurality of measured values ​​measured by the return light measuring unit within a second period subsequent to the first period were averaged, and a focal point position correction unit that corrects the focal point position during laser processing based on the calculated focal point movement amount, wherein the first period is a period immediately after the start of laser radiation, at which the external optical system is not heated, or a period after a correction of the focal point position, and the second period is a period after the elapse of a certain time during which the external optical system was heated.

[0011] Another form of the present disclosure provides a laser processing apparatus that performs laser processing of a workpiece while correcting a focal shift due to contamination of an optical system, comprising a laser oscillator; an external optical system for guiding laser light from the laser oscillator and condensing it on the surface of the workpiece; a return light measuring unit that measures the energy amount of the return light reflected by the workpiece and returning to the laser processing apparatus; and a focal shift regulating unit that regulates the focal shift due to contamination of the external optical system during laser processing based on the energy amount of the return light, wherein the focal shift regulating unit includes a first focal movement amount calculating unit,which calculates the focal point movement amount based on a comparison between a first measured value measured by the return light measuring unit at a first drilling processing time and a second measured value measured by the return light measuring unit at a second drilling processing time subsequent to the first drilling processing time, and a focal point position correction unit which corrects the focal point position during laser processing based on the calculated focal point movement amount, wherein the first drilling processing time is a time immediately after the start of laser radiation at which the external optical system is not heated or a time after a correction of the focal point position, and the second drilling processing time is a time after the elapse of a certain time during which the external optical system was heated.

[0012] A different form of the present disclosure provides a laser processing apparatus that performs laser processing of a workpiece while correcting a focal shift due to contamination of an optical system, comprising a laser oscillator; an external optical system for guiding laser light from the laser oscillator and condensing it on the surface of the workpiece; a return light measuring unit that measures the energy amount of the return light reflected by the workpiece and returning to the laser processing apparatus; and a focal shift regulating unit that regulates the focal shift due to contamination of the external optical system during laser processing based on the energy amount of the return light, wherein the focal shift regulating unit includes an output command unit,which issues a command to the laser oscillator to emit laser light with a predetermined output power or a command not to emit it, a focal point movement amount calculation unit that calculates the focal point movement amount based on a comparison between a first measured value for which the peak values ​​measured by the return light measuring unit during a first period when switching from the non-emission command to the emission command were averaged, and a second measured value for which the peak values ​​measured by the return light measuring unit during a second period subsequent to the first period when switching from the non-emission command to the emission command were averaged, and a focal point position correction unit that corrects the focal point position during laser processing based on the calculated focal point movement amount,wherein the first period is a period immediately after the start of laser emission, at which the external optical system is not heated, or a period after a correction of the focal point position, and the second period is a period after the lapse of a certain time during which the external optical system has been heated.

[0013] Yet another different form of the present disclosure provides a laser processing apparatus that performs laser processing of a workpiece while correcting a focal shift due to contamination of an optical system, comprising a laser oscillator; an external optical system for guiding laser light from the laser oscillator and condensing it on the surface of the workpiece; a return light measuring unit that measures the energy amount of the return light reflected by the workpiece and returning to the laser processing apparatus; and a focal shift regulating unit that regulates the focal shift due to contamination of the external optical system during laser processing based on the energy amount of the return light, wherein the focal shift regulating unit includes a change amount calculating unit,which calculates the amount of change per unit time of the amount of energy of the return light measured by the return light measuring unit, a focal point movement amount calculation unit which calculates the focal point movement amount based on a comparison between a first measured value for which the peak values ​​measured by the return light measuring unit within a first period of time when the amount of change per unit time calculated by the change amount calculation unit is greater than or equal to a certain value were averaged, and a second measured value for which the peak values ​​measured by the return light measuring unit within a second period of time subsequent to the first period of time when the amount of change per unit time calculated by the change amount calculation unit is greater than or equal to a certain value were averaged, and a focal point position correction unit,which corrects the focal point position during laser processing based on the calculated focal point movement amount, wherein the first period is a period immediately after the start of laser radiation at which the external optical system is not heated, or a period after a correction of the focal point position, and the second period is a period after the elapse of a certain time during which the external optical system was heated. Simple explanation of the drawings Fig. Figure 1 is a schematic view for explaining the types of contamination of an external optical system. Fig. Figure 2 is a graph showing the relationship between the focal point movement amount and the amount of energy of the return light depending on the type of pollution. Fig. 3 is a schematic view showing the schematic structure of a laser processing apparatus according to an embodiment. Fig. 4A is a graph regarding the amount of energy of the return light and the time when laser welding was performed n times (n is an integer of at least 1). Fig. Figure 4B is a graph of the energy amount of the return light and the time after adjusting the focus shift in a 1000th laser welding. Fig. 5 is a block diagram showing the structure of the laser processing apparatus according to the embodiment. Fig. 6 is a flowchart showing the operation of the laser processing apparatus according to the embodiment. Fig. 7 is a view showing machining conditions in the normal state and machining conditions after correction. Fig. 8 is a schematic view showing the schematic structure of a laser processing apparatus according to another embodiment. Fig. 9 is a graph relating the amount of energy of the return light and the time when laser cutting accompanied by drilling was performed n times (n is an integer of at least 1). Fig. 10 is a block diagram showing the structure of the laser processing apparatus according to the other embodiment. Fig. 11 is a flowchart showing the operation of the laser processing apparatus according to the other embodiment. Fig. 12 is a block diagram showing the structure of a laser processing apparatus according to a different embodiment. Fig. 13 is a schematic view showing the schematic structure of a laser processing apparatus according to another different embodiment. Fig. 14 is a graph relating the amount of energy of the return light and the time when laser cutting in which a command to emit laser light and a command not to emit it are repeated n times (n is an integer of at least 1) was performed. Fig. 15 is a block diagram showing the structure of the laser processing apparatus according to the further different embodiment. Fig. 16 is a flowchart showing the operation of the laser processing apparatus according to the further different embodiment. Fig. 17 is a schematic view showing the schematic structure of a laser processing apparatus according to still another embodiment. Fig. 18 is a graph relating the amount of energy of the return light and the time when laser cutting was performed n times (n is an integer of at least 1). Fig. 19 is a block diagram showing the structure of the laser processing apparatus according to the further other embodiment. Fig. 20 is a flowchart showing the operation of the laser processing apparatus according to the further other embodiment. Detailed explanation

[0014] A detailed explanation of embodiments of the present disclosure will be given below with reference to the accompanying drawings. In the individual drawings, identical or similar structural elements are designated by identical or similar reference numerals. Furthermore, the embodiments described below do not limit the technical scope of the invention or the meaning of the terminology in the claims.

[0015] Now, the definition of terminology in this specification will be explained. The term "lens" in this specification means an optical component provided with a surface having a curvature. In other words, a lens used in this specification is an optical component in which the change in curvature due to the so-called thermal lens effect is large in the case of absorption of laser light by a contaminant. The term "window" in this specification means an optical component formed of a generally flat surface. In other words, a window used in this specification is an optical component in which the change in curvature is small even in the case of absorption of laser light by a contaminant.Furthermore, the term "contamination" in the present specification does not simply mean the state of accumulation of dust and dirt, but also includes the state of occasional burning of the accumulated dust and dirt by laser light or the state of deterioration by peeling off of a thin film formed on mirrors or the like.

[0016] Fig. Figure 1 is a schematic diagram for explaining the types of contamination of an external optical system. The external optical system includes, but is not limited to, a lens 1 for collecting laser light from a laser oscillator onto a workpiece surface, and a window 2 located at an outermost side of the external optical system.When the focal point position is set on the surface of a smooth copper reflection plate arranged perpendicularly with respect to the optical axis of the laser light and having a certain reflectance (for example, 98%) with respect to the laser light, and laser light L is emitted from the external optical system with such a low output power (for example, 10 W) that the reflection plate 3 is not melted or deformed, an energy amount of 98% (for example, 9.8 W) is observed in the normal state in which neither the lens 1 nor the window 2 is dirty by a return light measuring unit 4 that measures the energy amount of the return light R reflected by the reflection plate 3 and returning to the laser processing device. In . Fig. For ease of understanding, in Figure 1, the emitted laser light L is shown on the right side of the optical axis of the laser light, and the returned light R reflected by the reflection plate 3 is shown on the left side of the optical axis. In a window fouling situation where only the window 2 is fouled, the energy amount of the returned light R measured by the returned light measuring unit 4 decreases because the window 2 absorbs or scatters the laser light. In a lens fouling situation where only the lens 1 is fouled, the energy amount of the returned light R measured by the returned light measuring unit 4 decreases because the focal point position moves upward (or downward) due to the thermal lens effect of the lens 1. When both the lens 1 and the window 2 are fouled, which is not shown, the energy amount of the returned light R measured by the returned light measuring unit 4 becomes the smallest.

[0017] Fig. Figure 2 is a graph showing the relationship between the amount of focal movement depending on the type of contamination and the amount of energy of the returned light. As mentioned above, in the case of lens contamination shown by the dashed line, the focal position moves and the amount of energy decreases compared to the normal state shown by the solid line. In the case of window contamination shown by the single-dotted-dashed line, although the focal position does not move, the amount of energy decreases. In the case of lens and window contamination shown by the double-dotted-dashed line, the focal position moves and the amount of energy becomes the smallest.However, it should be noted that since the focal position may shift to approach the surface of the reflection plate 3 when laser light is irradiated with the focal position set above or below the surface of the reflection plate 3, an increase in the amount of energy of the returned light may also occur. Furthermore, in a state where the external optical system has been heated by laser light with a high output such as that used for laser processing, thermal lensing and movement of the focal position occur, whereas in a state immediately after the start of laser processing in which the external optical system is not heated, even if the lens becomes dirty, thermal lensing does not occur and the focal position does not move.The laser processing apparatus according to the present embodiment adjusts the processing conditions during laser processing according to the degree of contamination of the external optical system by utilizing this physical phenomenon.

[0018] Fig. 3 is a schematic view showing the schematic structure of a laser processing apparatus 10 according to the present embodiment. The laser processing apparatus 10 is directed to a system that performs laser processing in which continuous detection of returned light is possible, for example, a system that performs laser welding, and includes a laser oscillator 11, an external optical system 12 for guiding laser light from the laser oscillator 11 and condensing it onto the surface of the workpiece, and a numerical control device 13 that controls the entire laser processing apparatus 10. The laser oscillator 11 is a fiber laser oscillator with a wavelength of, for example, 1060 to 1080 nm. The laser processing apparatus 10 further includes a returned light measuring unit 4 that measures the energy amount of the returned light reflected from a workpiece W and returning to the laser processing apparatus 10.The return light measuring unit 4 can utilize an existing power sensor located inside the laser oscillator 11. As a result, the laser processing device 10 does not require an additional sensor. Alternatively, the return light measuring unit 4 can also be a power sensor located inside the processing head.

[0019] Fig. Figure 4A is a graph relating the amount of energy of the return light and the time when laser welding was performed n times (n is an integer of at least 1). As shown in Fig. As shown in Figure 4A, in the system that uses laser welding, the surface condition of the workpiece is unstable because the workpiece surface is melted during welding (during cleaning, marking), and the returned light is subject to considerable noise. Since the external optical system 12 is not heated during the first laser welding immediately after the start of laser emission, even if the lens 1 becomes dirty, no focal point shift due to the thermal lens effect occurs, and the energy amount of the returned light does not change significantly. In contrast, since the external optical system 12 is heated after a certain time from the start of laser emission during the 1,000th laser welding, if the lens 1 becomes dirty, a focal point shift due to the thermal lens effect occurs, and the energy amount of the returned light decreases over time.However, it should be noted that the amount of energy of the returned light may also increase over time because, when laser light is emitted while adjusting the focal point position above or below the surface of the workpiece, the focal point position may shift so that it approaches the surface of the workpiece.

[0020] Fig. Figure 4B is a graph relating the amount of energy of the return light and the time after adjusting the focal point shift in a 1000th laser welding operation. To adjust the focal point shift while taking the noise of the return light into account, it is advisable to adjust the focal point shift as shown in Fig. 4B, based on a comparison between a first measurement value for which a plurality of measurement values ​​measured by the return light measuring unit 4 within a first period were averaged and a second measurement value for which a plurality of measurement values ​​measured by the return light measuring unit 4 within a second period subsequent to the first period were averaged. Furthermore, it is preferable to repeatedly perform the processing for adjusting the focal point shift; and to use the first measurement value for which a plurality of measurement values ​​measured within the first period were averaged as a reference value, the first period must be a period immediately after the start of laser emission (for example, within 1 second) when the external optical system is not heated, or a period after a correction of the focal point position.If the first period is a period after a correction of the focal point position, a first measured value (reference value) is obtained with the same level as with a non-heated external optical system 12. The second period is a period after a certain time has elapsed during which the external optical system 12 was heated. The first period and the second period may be discontinuous, continuous, or overlap.

[0021] Fig. 5 is a block diagram showing the structure of the laser processing system 10 according to the present embodiment. The laser processing system 10 further includes a drive control unit 20 for moving the focal position and the optical axis of the laser light emitted from the external optical system 12; a focal shift adjustment unit 21 configured by a program executable by a semiconductor integrated circuit such as an ASIC, an FPGA, or the like, a processor, or a computer, and adjusting the focal shift due to contamination of the external optical system 12 during laser processing based on the amount of energy of the return light; and a storage unit 22 for storing various data.The focus shift regulating unit 21 further includes a drive command unit 30 that gives the drive control unit 20 a command to set the focus position of the laser light with respect to the workpiece W to a predetermined position, and an output command unit 31 that gives the laser oscillator a command to emit laser light with a predetermined output power (for example, 3000 W).The focal shift adjustment unit 21 further includes a first focal movement amount calculation unit 32 that calculates the focal movement amount based on a comparison between the first measurement value for which a plurality of measurement values ​​measured by the return light measurement unit 4 within the first period were averaged and the second measurement value for which a plurality of measurement values ​​measured by the return light measurement unit 4 within the second period subsequent to the first period were averaged, and a focal position correction unit 33 that corrects the focal position during laser processing based on the calculated focal movement amount.The focal point shift regulating unit 21 may further include a correction amount determining unit 34 that repeats the correction of the focal point position and determines whether the correction amount is correct or not, and a laser power correcting unit 35 that corrects the laser power based on a comparison between the first measured value and the second measured value when the correction amount is not correct.

[0022] Fig. Fig. 6 is a flowchart showing the operation of the laser processing apparatus 10 according to the present embodiment. The following will be described with reference to Fig. 5 and Fig. 6 explains the processing for adjusting the focal shift due to contamination of the external optical system during laser processing based on the amount of energy of the return light. When the focal shift adjusting unit 21 starts adjusting the focal shift during laser processing, in step S10, the drive command unit 30 instructs the drive control unit 20 to set the focal position to the predetermined position, and the output command unit 31 instructs the laser oscillator 10 to emit laser light with the predetermined output power, and the workpiece W is laser welded. In step S11, the first movement amount calculating unit 32 averages the multiple measurement values ​​measured by the return light measuring unit 4 during the first period (first measurement value). In step S12, the storage unit 22 stores the first measurement value.In step S13, the first movement amount calculation unit 32 averages the plurality of measurement values ​​measured by the return light measurement unit 4 during the second period following the first period (second measurement value). In step S14, the storage unit 22 stores the second measurement value. In step S15, the first focal point movement amount calculation unit 32 compares the first measurement value and the second measurement value and calculates the focal point movement amount (for example, +1 mm). In step S16, the focal point position correction unit 33 corrects the focal point position during laser processing (for example, correcting it from 1 mm to 0 mm). In step S17, the correction amount determination unit 34 determines whether the correction amount is correct or not by comparing the correction amount with a margin α.If the correction amount (for example, -1 mm) exceeds the margin α (for example, ±0.85) in step S17, the process returns to step S10 and repeats the focus shift adjustment. Since there is a possibility that the energy amount of the return light decreases not only due to a focus shift caused by contamination of the lens 1 but also due to contamination of the window 2, if the correction amount (for example, -0.9 mm) in step S17 still exceeds the margin α (for example, ±0.85), in step S18, the laser power correction unit 35 corrects the laser power based on a comparison between the first measured value and the second measured value (for example, correcting it from 3000 W to 3500 W).If the correction amount (for example, -0.3 mm) is at most the margin α (for example, ±0.85) in step S17, the laser processing device 10 continues laser processing in step S19 based on the corrected focal position and the corrected laser power. As mentioned above, the processing for adjusting the focal shift is preferably performed repeatedly. By this laser processing device 10, the focal shift can be automatically adjusted according to the degree of contamination during laser processing under stable detection of the return light. Consequently, since the automatic operation can be continued without generating a large number of processing defects, the maintenance period of the external optical system can be extended.

[0023] Fig. Figure 7 is a view showing machining conditions in the normal state and machining conditions (1) to (3) after correction. Although not shown, these machining conditions are all in the Fig. 4. The processing conditions (1) show a case where the focal point position was corrected from 1 mm to 0 mm during laser processing. The processing conditions (2) show a case where the laser power was corrected from 3000 W to 3500 W. The processing conditions (3) show a case where the focal point position and the laser power were corrected to 0 mm and 3500 W, respectively.

[0024] Fig. Fig. 8 is a schematic view showing the schematic structure of a laser processing apparatus 40 according to another embodiment. The laser processing apparatus 40 differs from the laser processing apparatus 10 of Fig. 5 in that it is directed to a system that performs laser cutting accompanied by drilling. For example, the laser processing device 40 repeats laser processing in which a workpiece W is cut into a specific shape after drilling the workpiece W and forming a hole H n times (n is an integer of at least 1).

[0025] Fig. Figure 9 is a graph relating the amount of energy of the return light and the time when laser cutting accompanied by drilling was performed n times (n is an integer of at least 1). As shown in Fig. As shown in Figure 9, the return light can be detected during drilling, but the return light cannot be detected during cutting because the laser light passes through the workpiece. Fig. When the external optical system 12 shown in Figure 8 is dirty, repeated laser cutting results in a focal point shift due to the thermal lens effect, and the amount of energy of the return light decreases over time. However, it should be noted that since the focal point position may shift to approach the surface of the workpiece when laser light is irradiated with the focal point position set above or below the workpiece surface, the amount of energy of the return light may also increase over time.In order to regulate the focal point shift taking into account the timing with which detection of the return light is possible, it is advantageous to regulate the focal point shift on the basis of a comparison between a first measured value measured by the return light measuring unit 4 at a first drilling processing time and a second measured value measured by the return light measuring unit 4 at a second drilling processing time subsequent to the first drilling processing time.Furthermore, it is preferable to repeatedly perform the processing for adjusting the focal shift; and to use the first measured value measured at the first drilling processing time as a reference value, the first drilling processing time must be a time immediately after the start of laser radiation (for example, after 1 second) when the external optical system is not heated, or a time after a correction of the focal position. If the first time is a time after a correction of the focal position, a first measured value (reference value) with the same level as when the external optical system 12 is not heated is obtained. The second time is a time after a certain time has elapsed during which the external optical system 12 has been heated (for example, n = 100,000).

[0026] Fig. 10 is a block diagram showing the structure of the laser processing apparatus 40. The laser processing apparatus 40 includes the drive control unit 20 for moving the focal position and the optical axis of the laser light emitted from the external optical system 12; a focal shift adjustment unit 41 configured by a program executable by a semiconductor integrated circuit such as an ASIC, an FPGA, or the like, a processor, or a computer, and adjusting the focal shift due to contamination of the external optical system 12 during laser processing based on the amount of energy of the return light; and a storage unit 22 for storing various data.The focus shift regulating unit 41 further includes the drive command unit 30 that gives the drive control unit 20 a command to set the focus position of the laser light with respect to the workpiece W to a predetermined position, and the output command unit 31 that gives the laser oscillator a command to emit laser light with a predetermined output power (for example, 3000 W).The focal shift adjustment unit 41 further includes a second focal movement amount calculation unit 42 that calculates the focal movement amount based on a comparison between the first measurement value measured by the return light measurement unit 4 at the first drilling processing time and the second measurement value measured by the return light measurement unit 4 at the second drilling processing time subsequent to the first drilling processing time. The second focal movement amount calculation unit 42 can also distinguish between the drilling processing time and a processing time other than the drilling processing time (for example, the cutting time) based on identification information for identifying the type of laser processing being performed.The identification information is stored in the storage unit 22, and, for example, the G-code used by the numerical control device 13 can be used. This makes it possible to easily detect the peak value of the energy amount of the return light during the drilling processing time. The focal shift control unit 41 may further include the correction amount determination unit 34, which repeats the correction of the focal position and determines whether the correction amount is correct, and the laser power correction unit 35, which corrects the laser power based on a comparison between the first measured value and the second measured value when the correction amount is incorrect.

[0027] Fig. 11 is a flowchart showing the operation of the laser processing apparatus 40. The following will be described with reference to Fig. 10 and Fig. 11 explains the processing for adjusting the focal shift due to contamination of the external optical system during laser processing based on the amount of return light energy. When the focal shift adjusting unit 41 starts adjusting the focal shift during laser processing, in step S20, the drive command unit 30 instructs the drive control unit 20 to set the focal position to the predetermined position, and the output command unit 31 instructs the laser oscillator 11 to emit laser light with the predetermined output power, and laser cutting of the workpiece W is performed. In step S21, the second focal movement amount calculating unit 42 acquires the first measurement value measured by the return light measuring unit 4 at the first drilling processing time. In step S22, the storage unit 22 stores the first measurement value.In step S23, the second focal point movement amount calculation unit 42 acquires the second measurement value measured by the return light measurement unit 4 at the second drilling processing time subsequent to the first drilling processing time. In step S24, the storage unit 22 stores the second measurement value. In step S25, the second focal point movement amount calculation unit 42 calculates the focal point movement amount (for example, +1 mm) by comparing the first measurement value and the second measurement value. In step S26, the focal point position correction unit 33 corrects the focal point position during laser processing (for example, correcting it from 1 mm to 0 mm). In step S27, the correction amount determination unit 34 determines whether the correction amount is correct by comparing the correction amount with a margin α.If the correction amount (for example, -1 mm) exceeds the margin α (for example, ±0.85) in step S27, the process returns to step S20 and repeats the focus shift adjustment. Since there is a possibility that the energy amount of the return light decreases not only due to a focus shift caused by contamination of the lens 1 but also due to contamination of the window 2, if the correction amount (for example, -0.9 mm) in step S27 still exceeds the margin α (for example, ±0.85), in step S28, the laser power correction unit 35 corrects the laser power based on a comparison between the first measured value and the second measured value (for example, correcting it from 3000 W to 3500 W).If the correction amount (for example, -0.3 mm) is at most the margin α (for example, ±0.85) in step S27, the laser processing device 40 continues laser processing in step S29 based on the corrected focal position and the corrected laser power. As mentioned above, the processing for adjusting the focal shift is preferably performed repeatedly. By this laser processing device 40, the focal shift can be automatically adjusted according to the degree of contamination during laser processing under stable detection of the return light. Consequently, since the automatic operation can be continued without generating a large number of processing defects, the maintenance period of the external optical system can be extended.

[0028] Fig. 12 is a block diagram showing the structure of a laser processing apparatus 50 according to a different embodiment. It differs from the laser processing apparatuses 10, 40 discussed above in that a focus shift control unit 51 includes both the first focus movement amount calculation unit 32 and the second focus movement amount calculation unit 42, as well as a switching unit 52 that switches between the first focus movement amount calculation unit 32 and the second focus movement amount calculation unit 42 based on identification information identifying the type of laser processing being performed. The identification information is stored in the storage unit 22, and, for example, the G-code used by the numerical control device 13 can be used.This makes it possible to distinguish between laser processing in which the return light is noisy (for example, laser welding) and laser processing in which the return light can be detected intermittently (for example, laser cutting accompanied by drilling). When the identification information indicates laser processing in which the return light is noisy, the switching unit 52 switches to the first focal point movement amount calculation unit 32, and when the identification information indicates laser processing in which the return light can be detected intermittently, the switching unit 52 switches to the second focal point movement amount calculation unit 42.With this laser processing device 50, the focal point shift during laser processing can be automatically adjusted according to the degree of contamination, regardless of the type of laser processing, while reliably detecting the return light. Consequently, since automatic operation can continue without generating a large number of processing defects, the maintenance period of the external optical system can be extended.

[0029] Fig. Fig. 13 is a schematic view showing the schematic structure of a laser processing apparatus 60 according to another different embodiment. The laser processing apparatus 60 differs from the laser processing apparatus 40 of Fig. 8 in that it is directed to a system that performs laser cutting by fly cutting, which is not accompanied by drilling. For example, the laser processing device 60 repeats laser processing in which a workpiece W is cut into a desired shape while moving the axis with respect to the workpiece W n times (n is an integer of at least 1).

[0030] Fig. Figure 14 is a graph relating the amount of energy of the return light and the time when laser cutting, in which a command to emit laser light (laser ON) and a command to not emit it (laser OFF) are repeated n times (n is an integer of at least 1), was performed. As shown in Fig. As shown in Figure 14, a return light can be detected when switching from laser OFF to laser ON, but after a certain time (for example, 2 milliseconds) has elapsed after switching to laser ON, no return light can be detected because the laser light passes through the workpiece. Fig. When the external optical system 12 shown in Figure 13 is dirty, repeated laser cutting results in a focal point shift due to the thermal lens effect, and the amount of energy of the return light decreases over time. However, it should be noted that since the focal point position may shift to approach the surface of the workpiece when laser light is irradiated with the focal point position adjusted above or below the workpiece surface, the amount of energy of the return light may also increase over time.In order to regulate the focal point shift taking into account the timing with which detection of the return light is possible, it is advantageous to regulate the focal point shift on the basis of a comparison between a first measured value for which the peak values ​​measured by the return light measuring unit 4 during a first period of time when changing from laser OFF to laser ON were averaged, and a second measured value for which the peak values ​​measured by the return light measuring unit 4 during a second period of time after the first period of time when changing from laser OFF to laser ON were averaged.Furthermore, it is preferable to repeatedly perform the processing for adjusting the focal shift; and to use the first measurement value, for which the peak values ​​measured by the return light measuring unit 4 during the first period when switching from laser OFF to laser ON were averaged, as the reference value, the first period must be a period immediately after the start of laser emission (for example, after 1 second) when the external optical system is not heated, or a period after a focal position correction. If the first period is a period after a focal position correction, a first measurement value (reference value) having the same level as when the external optical system 12 is not heated is obtained. The second period is a period after a certain time has elapsed during which the external optical system 12 has been heated (for example, n = 100,000 to 100,003).

[0031] Fig. 15 is a block diagram showing the structure of the laser processing apparatus 60. The laser processing apparatus 60 includes the drive control unit 20 for moving the focal position and the optical axis of the laser light emitted from the external optical system 12; a focal shift adjustment unit 61 configured by a program executable by a semiconductor integrated circuit such as an ASIC, an FPGA, or the like, a processor, or a computer, and adjusting the focal shift due to contamination of the external optical system 12 during laser processing based on the amount of energy of the return light; and a storage unit 22 for storing various data.The focus shift control unit 61 further includes the drive command unit 30 that gives the drive control unit 20 a command to move the focus position of the laser light with respect to the workpiece W to a predetermined position, and an output command unit 62 that gives the laser oscillator 11 a command to emit laser light with a predetermined output power (for example, 3000 W) (laser ON) or a command not to emit it (laser OFF).The focal shift regulating unit 61 further includes a third focal movement amount calculation unit 63 that calculates the focal movement amount based on a comparison between the first measurement value for which the peak values ​​measured by the return light measuring unit 4 during the first period when switching from laser OFF to laser ON were averaged and the second measurement value for which the peak values ​​measured by the return light measuring unit 4 during the second period after the first period when switching from laser OFF to laser ON were averaged, and the focal position correction unit 33 that corrects the focal position during laser processing based on the calculated focal movement amount.That is, the third focal point movement amount calculation unit 63 determines the peak values ​​of the energy amount of the return light based on the laser ON and laser OFF from the output command unit 62. The information regarding laser ON / OFF may also be stored in the storage unit 22. This allows the peak values ​​of the energy amount of the return light to be easily distinguished. The focal point shift adjustment unit 61 may further include the correction amount determination unit 34, which repeats the correction of the focal point position and determines whether the correction amount is correct, and the laser power correction unit 35, which corrects the laser power based on a comparison between the first measured value and the second measured value when the correction amount is incorrect.

[0032] Fig. 16 is a flowchart showing the operation of the laser processing apparatus 60. The following will be described with reference to Fig. 15 and Fig. 16 explains the processing for adjusting the focal shift due to contamination of the external optical system during laser processing based on the amount of energy of the return light. When the focal shift adjusting unit 61 starts adjusting the focal shift during laser processing, in step S30, the drive command unit 30 instructs the drive control unit 20 to set the focal position to the predetermined position, and the output command unit 62 instructs the laser oscillator 11 to emit laser light at the predetermined output power (laser ON) or not (laser OFF), and laser cutting of the workpiece W is performed.In step S31, the third focal point movement amount calculation unit 63 obtains the first measurement value for which the peak values ​​measured by the return light measurement unit 4 during the first period when switching from laser OFF to laser ON were averaged. In step S32, the storage unit 22 stores the first measurement value. In step S33, the third focal point movement amount calculation unit 63 obtains the second measurement value for which the peak values ​​measured by the return light measurement unit 4 during the second period after the first period when switching from laser OFF to laser ON were averaged. In step S34, the storage unit 22 stores the second measurement value. In step S35, the third focal point movement amount calculation unit 63 calculates the focal point movement amount (for example, +1 mm) by comparing the first measurement value and the second measurement value.In step S36, the focal position correction unit 33 corrects the focal position during laser processing (for example, correcting it from 1 mm to 0 mm). In step S37, the correction amount determination unit 34 determines whether the correction amount is correct by comparing the correction amount with a margin α. If the correction amount (for example, -1 mm) exceeds the margin α (for example, ±0.85) in step S37, the process returns to step S30 and repeats the focal shift adjustment once more.Since, when the correction amount (for example, -0.9 mm) in step S37 still exceeds the margin α (for example, ±0.85), there is a possibility that the energy amount of the return light decreases not only due to a focal shift caused by contamination of the lens 1 but also due to contamination of the window 2, the laser power correction unit 35 corrects the laser power based on a comparison between the first measured value and the second measured value (for example, correcting it from 3000 W to 3500 W) in step S38. If the correction amount (for example, -0.3 mm) in step S37 is at most the margin α (for example, ±0.85), the laser processing device 60 continues laser processing based on the corrected focal position and the corrected laser power in step S39. The focal shift adjustment processing is preferably performed repeatedly as mentioned above.With this laser processing device 60, the focal point shift during laser processing can be automatically adjusted according to the degree of contamination while reliably detecting the return light. Consequently, since automatic operation can continue without generating a large number of processing defects, the maintenance period of the external optical system can be extended.

[0033] Fig. Fig. 17 is a schematic view showing the schematic structure of a laser processing apparatus 70 according to another embodiment. The laser processing apparatus 70 is arranged in the same manner as the laser processing apparatus 60 of Fig. 13 refers to a system that performs laser cutting by fly cutting, which is not accompanied by drilling. For example, the laser processing device 70 repeats laser processing in which a workpiece W is cut into a desired shape while moving the axis with respect to the workpiece W n times (n is an integer of at least 1).

[0034] Fig. Figure 18 is a graph relating the amount of energy of the return light and the time when laser cutting was performed n times (n is an integer of at least 1). As shown in Fig. As shown in Figure 18, return light can be detected when the amount of change α per unit time of the energy quantity of the return light (i.e., the slope of the curve) has reached at least a certain value (for example, +1.73), but no return light can be detected when the amount of change α per unit time of the energy quantity of the return light (i.e., the slope of the curve) is 0, since the laser light passes through the workpiece. If the amount of change α per unit time of the energy quantity of the return light (i.e., the slope of the curve) is 0, Fig. When the external optical system 12 shown in Figure 18 is dirty, repeated laser cutting results in a focal point shift due to the thermal lens effect, and the amount of energy of the return light decreases over time. However, it should be noted that since the focal point position may shift to approach the surface of the workpiece when laser light is irradiated with the focal point position set above or below the workpiece surface, the amount of energy of the return light may also increase over time.In order to regulate the focal point shift taking into account the timing with which detection of the return light is possible, it is advantageous to regulate the focal point shift based on a comparison between a first measured value for which the peak values ​​measured by the return light measuring unit 4 within a first period of time when the amount of change per unit time of the amount of energy of the return light reached at least a certain value were averaged, and a second measured value for which the peak values ​​measured by the return light measuring unit 4 within a second period of time subsequent to the first period of time when the amount of change per unit time of the amount of energy of the return light reached at least the certain value were averaged.Furthermore, it is preferable to repeatedly perform the processing for adjusting the focal shift; and to use the first measurement value, for which the peak values ​​averaged by the return light measuring unit 4 within a first period when the amount of change per unit time reached at least a certain value, as a reference value, the first period must be a period immediately after the start of laser radiation (for example, after 1 second) when the external optical system is not heated, or a period after a focal position correction. When the first period is a period after a focal position correction, a first measurement value (reference value) with the same level as that of the external optical system 12 not heated is obtained.The second period is a period after the lapse of a certain time during which the external optical system 12 has been heated (for example, n = 100000 to 100003).

[0035] Fig. 19 is a block diagram showing the structure of the laser processing device 70. The laser processing device 70 includes the drive control unit 20 for moving the focal position and the optical axis of the laser light emitted from the external optical system 12; a focal shift control unit 71 formed by a program executable by a semiconductor integrated circuit such as an ASIC, an FPGA, or the like, a processor, or a computer; and which controls the focal shift due to contamination of the external optical system 12 during laser processing based on the energy amount of the return light; and a storage unit 22 for storing various data. The focal shift control unit 71 further includes the drive command unit 30.which issues a command to the drive control unit 20 to move the focal position of the laser light relative to the workpiece W to a predetermined position, and the output command unit 31 which issues a command to the laser oscillator 11 to emit laser light with a predetermined output power (for example, 3000 W). The focal shift regulating unit 71 further includes a change amount calculation unit 72 which calculates the change amount per unit time of the energy amount of the return light measured by the return light measuring unit 4, a fourth focal movement amount calculation unit 73 which calculates the focal movement amount based on a comparison between the first measured value for which the peak values ​​measured by the return light measuring unit 4 within the first period of time,when the change amount per unit time calculated by the change amount calculation unit 72 reached at least a certain value, and the second measurement value for which the peak values ​​measured by the return light measuring unit 4 within the second period subsequent to the first period when the change amount per unit time calculated by the change amount calculation unit 72 reached at least the certain value were averaged, and the focal point position correction unit 33, which corrects the focal point position during laser processing based on the calculated focal point movement amount. That is,The fourth focal point movement amount calculation unit 73 distinguishes the peak values ​​of the energy amount of the return light based on the change amount per unit time from the change amount calculation unit 72. Information regarding the change amount may be stored in the storage unit 22. This allows the peak values ​​of the energy amount of the return light to be easily distinguished. The focal point shift adjustment unit 71 may further include the correction amount determination unit 34, which repeats the correction of the focal point position and determines whether the correction amount is correct or not, and the laser power correction unit 35, which corrects the laser power based on a comparison between the first measured value and the second measured value when the correction amount is incorrect.

[0036] Fig. 20 is a flowchart showing the operation of the laser processing apparatus 70. The following will be described with reference to Fig. 19 and Fig.20 explains the processing for adjusting the focal shift due to contamination of the external optical system during laser processing based on the amount of energy of the return light. When the focal shift adjusting unit 71 starts adjusting the focal shift during laser processing, in step S40, the drive command unit 30 instructs the drive control unit 20 to set the focal position to the predetermined position, and the output command unit 31 instructs the laser oscillator 11 to emit laser light with the predetermined output power, and laser cutting of the workpiece W is performed. In step S41, the change amount calculating unit 72 calculates the change amount per unit time of the amount of energy of the return light.In step S42, the fourth focal point movement amount calculation unit 73 acquires the first measurement value for which the peak values ​​measured by the return light measurement unit 4 within the first period when the change amount per unit time calculated by the change amount calculation unit 72 reached at least a predetermined value were averaged. In step S43, the storage unit 22 stores the first measurement value. In step S44, the focal point movement amount calculation unit 73 acquires the second measurement value for which the peak values ​​measured by the return light measurement unit 4 within the second period subsequent to the first period when the change amount per unit time calculated by the change amount calculation unit 72 reached at least the predetermined value were averaged. In step S45, the storage unit 22 stores the second measurement value.In step S46, the fourth focal point movement amount calculation unit 73 calculates the focal point movement amount (for example, +1 mm) by comparing the first measurement value and the second measurement value. In step S47, the focal point position correction unit 33 corrects the focal point position during laser processing (for example, correcting it from 1 mm to 0 mm). In step S48, the correction amount determination unit 34 determines whether the correction amount is correct or not by comparing the correction amount with a margin α. If the correction amount (for example, -1 mm) exceeds the margin α (for example, ±0.85) in step S48, the process returns to step S40 and repeats the focal point shift adjustment once more.Since there is a possibility that the energy amount of the return light decreases not only due to a focal shift caused by contamination of the lens 1 but also due to contamination of the window 2 when the correction amount (for example, -0.9 mm) in step S48 still exceeds the margin α (for example, ±0.85), the laser power correction unit 35 corrects the laser power based on a comparison between the first measured value and the second measured value (for example, correcting it from 3000 W to 3500 W) in step S49. If the correction amount (for example, -0.3 mm) is at most the margin α (for example, ±0.85) in step S50, the laser processing device 70 continues laser processing based on the corrected focal position and the corrected laser power. The focal shift adjustment processing is preferably performed repeatedly as mentioned above.With this laser processing device 70, the focal point shift during laser processing can be automatically adjusted according to the degree of contamination while reliably detecting the return light. Consequently, since automatic operation can continue without generating a large number of processing defects, the maintenance period of the external optical system can be extended.

[0037] The computer-executable program in the above-described embodiments may be provided recorded on a computer-readable non-transitory recording medium, a CD-ROM, or the like. Various embodiments have been explained in the present specification, but the present invention is not limited to the above-described embodiments. It should be understood that various modifications may be made within the scope of the appended claims.

Claims

[1] A laser processing apparatus (10) which performs laser processing of a workpiece while correcting a focal point shift due to contamination of an optical system, the laser processing apparatus a laser oscillator (11); an external optical system (12) for guiding laser light from the laser oscillator (11) and collecting it on the surface of the workpiece; a return light measuring unit (4) which measures the amount of energy of the return light reflected by the workpiece and returning to the laser processing device (10); and a focal point shift regulating unit (21) which regulates the focal point shift due to contamination of the external optical system (12) during laser processing based on the amount of energy of the return light, wherein the focus shift regulating unit (21) a first focal point movement amount calculation unit (32) which calculates the focal point movement amount based on a comparison between a first measured value for which a plurality of measured values ​​measured by the return light measuring unit (4) within a first period were averaged and a second measured value for which a plurality of measured values ​​measured by the return light measuring unit (4) within a second period subsequent to the first period were averaged, and a focal position correction unit (33) which corrects the focal position during laser processing on the basis of the calculated focal movement amount, has, wherein the first period is a period immediately after the start of laser emission at which the external optical system (12) is not heated, or a period after a correction of the focal point position, and the second period is a period after the lapse of a certain time during which the external optical system (12) has been heated. [2] The laser machining apparatus according to claim 1, wherein the focal point shift regulating unit (21) further comprises a second focal point movement amount calculation unit (42) that calculates the focal point movement amount based on a comparison between a first measurement value measured by the return light measuring unit (4) at a first drilling machining time and a second measurement value measured by the return light measuring unit (4) at a second drilling machining time subsequent to the first drilling machining time, wherein the first drilling machining time is a time immediately after the start of laser irradiation at which the external optical system (12) is not heated or a time after a correction of the focal point position, and the second drilling machining time is a time after the lapse of a certain time during which the external optical system (12) has been heated. [3] A laser processing apparatus (40) which performs laser processing of a workpiece while correcting a focal point shift due to contamination of an optical system, the laser processing apparatus a laser oscillator (11); an external optical system (12) for guiding laser light from the laser oscillator (11) and collecting it on the surface of the workpiece; a return light measuring unit (4) which measures the amount of energy of the return light reflected by the workpiece and returning to the laser processing device (40); and a focus shift regulating unit (41) which regulates the focus shift due to contamination of the external optical system (12) during laser processing based on the energy amount of the return light, wherein the focus shift regulating unit (41) a first focal point movement amount calculation unit (42) which calculates the focal point movement amount based on a comparison between a first measured value measured by the return light measuring unit at a first drilling processing time and a second measured value measured by the return light measuring unit at a second drilling processing time subsequent to the first drilling processing time, and a focal position correction unit (33) which corrects the focal position during laser processing on the basis of the calculated focal movement amount, has, wherein the first drilling processing time is a time immediately after the start of laser radiation at which the external optical system is not heated or a time after a correction of the focal point position, and the second drilling processing time is a time after the lapse of a certain time during which the external optical system has been heated. [4] The laser processing apparatus according to claim 3, wherein the focal shift correction unit (41) further comprises a second focal movement amount calculation unit (32) that calculates the focal movement amount based on a comparison between a first measurement value for which a plurality of measurement values ​​measured by the return light measuring unit within a first period were averaged and a second measurement value for which a plurality of measurement values ​​measured by the return light measuring unit (4) within a second period subsequent to the first period were averaged. wherein the first period is a period immediately after the start of laser emission at which the external optical system (12) is not heated, or a period after a correction of the focal point position, and the second period is a period after the lapse of a certain time during which the external optical system has been heated. [5] The laser machining apparatus according to claim 2 or 3, wherein the first focal point movement amount calculation unit (32; 42) or the second focal point movement amount calculation unit (42; 32) distinguishes the drilling machining time and a machining time other than the drilling machining time based on identification information identifying the type of laser machining being performed. [6] The laser processing apparatus according to claim 2 or 4, wherein the focus shift regulating unit (51) further comprises a switching unit (52) that switches between the first focus movement amount calculation unit (32; 42) and the second focus movement amount calculation unit (42; 32) based on the identification information identifying the type of laser processing being performed. [7] A laser processing apparatus (60) which performs laser processing of a workpiece while correcting a focal point shift due to contamination of an optical system, the laser processing apparatus a laser oscillator (11); an external optical system (12) for guiding laser light from the laser oscillator (11) and collecting it on the surface of the workpiece; a return light measuring unit (4) which measures the amount of energy of the return light reflected by the workpiece and returning to the laser processing device; and a focal point shift regulating unit (61) which regulates the focal point shift due to contamination of the external optical system (12) during laser processing based on the energy amount of the return light, wherein the focus shift regulating unit (61) an output command unit (62) which gives the laser oscillator (11) a command to emit laser light with a predetermined output power or a command not to emit it, a focal point movement amount calculation unit (63) that calculates the focal point movement amount based on a comparison between a first measurement value for which the peak values ​​measured by the return light measuring unit (4) during a first period when changing from the non-radiation command to the radiation command were averaged, and a second measurement value for which the peak values ​​measured by the return light measuring unit (4) during a second period subsequent to the first period when changing from the non-radiation command to the radiation command were averaged, and a focal position correction unit (33) which corrects the focal position during laser processing on the basis of the calculated focal movement amount, has, wherein the first period is a period immediately after the start of laser emission at which the external optical system (12) is not heated, or a period after a correction of the focal point position, and the second period is a period after the lapse of a certain time during which the external optical system (12) has been heated. [8] A laser processing apparatus (70) which performs laser processing of a workpiece while correcting a focal point shift due to contamination of an optical system, the laser processing apparatus a laser oscillator (11); an external optical system (12) for guiding laser light from the laser oscillator (11) and collecting it on the surface of the workpiece; a return light measuring unit (4) which measures the amount of energy of the return light reflected by the workpiece and returning to the laser processing device (70); and a focal point shift regulating unit (71) which regulates the focal point shift due to contamination of the external optical system (12) during laser processing based on the energy amount of the return light, wherein the focus shift regulating unit (71) a change amount calculation unit (72) which calculates the change amount per unit time of the energy amount of the return light measured by the return light measuring unit (4), a focal point movement amount calculation unit (73) that calculates the focal point movement amount based on a comparison between a first measured value for which the peak values ​​measured by the return light measuring unit (4) within a first period of time when the change amount per unit time calculated by the change amount calculation unit (72) is greater than or equal to a certain value were averaged, and a second measured value for which the peak values ​​measured by the return light measuring unit (4) within a second period of time subsequent to the first period of time when the change amount per unit time calculated by the change amount calculation unit (72) is equal to or greater than a certain value were averaged, and a focal position correction unit (33) which corrects the focal position during laser processing on the basis of the calculated focal movement amount, has, wherein the first period is a period immediately after the start of laser emission at which the external optical system (12) is not heated, or a period after a correction of the focal point position, and the second period is a period after the lapse of a certain time during which the external optical system (12) has been heated. [9] The laser processing apparatus according to any one of claims 1 to 8, wherein the focal point shift regulating unit (71) further comprises a laser power correcting unit (35) that corrects the laser power based on a comparison between the first measured value and the second measured value when the correction amount is not correct despite repetition of the correction of the focal point position.

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