Patent Publication Number: US-2022234145-A1

Title: Method for determining laser irradiation state

Description:
TECHNICAL FIELD 
     The present invention relates to a laser irradiation state determination method (method for determining laser irradiation state) for determining a state of a laser irradiation device in accordance with an output of a laser emitted by the laser irradiation device. 
     BACKGROUND ART 
     JP 6279589 B2 and JP 6021929 B2 disclose techniques for measuring laser output of a laser irradiation device. 
     SUMMARY OF THE INVENTION 
     The techniques disclosed in JP 6279589 B2 and JP 6021929 B2 do not take into account the fact that the output characteristics at the rising edge immediately after the start of laser irradiation differ from one laser irradiation device to another. Therefore, there is a problem in that the accuracy of the obtained laser output is low. 
     The present invention has been made to solve the above-described problem, and an object thereof is to provide a laser irradiation state determination method capable of acquiring an output of a laser with high accuracy. 
     According to an aspect of the present invention, there is provided a laser irradiation state determination method for determining an irradiation state of a laser beam emitted by a laser irradiation device, the method including: an output stabilization time acquisition step of acquiring, as an output stabilization time, a time from when the laser irradiation device starts irradiation of the laser beam to when an output of the laser beam is stabilized; an energy acquisition step of acquiring energy of the laser beam irradiated by the laser irradiation device for a predetermined time period set in advance, after the output stabilization time or more has elapsed since the laser irradiation device started the irradiation of the laser beam; a conversion step of converting the acquired energy into the output of the laser beam irradiated by the laser irradiation device; and a state determination step of determining the irradiation state of the laser beam based on the converted output of the laser beam. 
     According to the present invention, it is possible to obtain output of a laser beam with high accuracy. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view showing how a vehicle body of an automobile is processed by a laser brazing machine; 
         FIG. 2  is a block diagram showing a configuration of a laser irradiation state determination device; 
         FIG. 3  is a graph showing a change in laser output with respect to time of the laser irradiation device; 
         FIG. 4  is a flowchart showing an energy acquisition process performed by an energy acquisition unit; 
         FIG. 5  is a graph showing a change in laser output with respect to time of the laser irradiation device; 
         FIG. 6  is a flowchart showing an output conversion process; 
         FIG. 7  is a flowchart showing a laser irradiation state determination process; 
         FIGS. 8A, 8B, and 8C  are diagrams illustrating conventional methods for obtaining the laser output; 
         FIGS. 9A, 9B, and 9C  are diagrams for explaining a method for obtaining the laser output, according to a first embodiment; 
         FIG. 10  is a block diagram showing a configuration of the laser irradiation state determination device; 
         FIG. 11  is a flowchart showing a laser irradiation state determination process; 
         FIG. 12  is an example of time-series data stored in a time-series data storage unit; 
         FIG. 13  is an example of time-series data stored in the time-series data storage unit; 
         FIG. 14  is an example of time-series data stored in the time-series data storage unit; 
         FIG. 15  is an example of time-series data stored in the time-series data storage unit; and 
         FIG. 16  is an example of time-series data stored in the time-series data storage unit. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     First Embodiment 
     [Configuration of Laser Brazing Machine] 
       FIG. 1  is a schematic view showing how a vehicle body  12  of an automobile is processed by a laser brazing machine  10 . A laser brazing machine  10  joins steel plates to each other by using a brazing material  14  having a melting point lower than that of the steel plates constituting the vehicle body  12 . A laser brazing machine  10  sequentially performs machining on vehicle bodies  12  flowing on a line.  FIG. 1  shows how a laser brazing machine  10  joins a roof panel  16  and a side panel  18  of a vehicle body  12 . 
     The laser brazing machine  10  includes a brazing material supply device  20 , a laser irradiation device  22 , and a transfer robot  24 . 
     The brazing material supply device  20  reels out a wire-shaped brazing material  14  from a reel (not shown), and supplies the brazing material  14  from a guide  26  to a portion to be joined  28  between the roof panel  16  and the side panel  18 . 
     The laser irradiation device  22  irradiates the brazing material  14  supplied to the portion to be joined  28  with a laser beam from an irradiation head  30 . The irradiation head  30  is connected to a laser oscillator (not shown) via a transmission cable. The brazing material  14  is melted by the energy of the laser, and then the brazing material  14  is cooled and solidified to form a bead  32 . The roof panel  16  and the side panel  18  are joined by the bead  32 . A protective glass  31  is provided at a portion, of the irradiation head  30  of the laser irradiation device  22 , from which a laser beam is emitted. 
     The transfer robot  24  is a robot that transfers the brazing material supply device  20  and the laser irradiation device  22 . The transfer robot  24  moves the brazing material supply device  20  and the laser irradiation device  22  along the portion to be joined  28  of the vehicle body  12 . Further, the transfer robot  24  moves the laser irradiation device  22  above a laser output sensor  34 . The laser irradiation device  22  emits a laser beam toward the laser output sensor  34 . The laser output sensor  34  detects the output of the laser beam. Based on the detected laser output, a laser irradiation state determination unit  44  described later determines the laser irradiation state of the laser irradiation device  22 . The measurement of the laser output of the laser irradiation device  22  is performed each time the machining of one vehicle body  12  is completed. The measurement of the laser output of the laser irradiation device  22  may be performed every time before the machining of one vehicle body  12  is started. The laser output sensor  34  is covered with a protective glass  35 . 
     [Configuration of Laser Irradiation State Determination Device] 
       FIG. 2  is a block diagram showing a configuration of a laser irradiation state determination device  36 . A laser brazing machine  10 L and a laser brazing machine  10 R are installed across a line which the vehicle bodies  12  move down. The laser irradiation state determination device  36  according to the present embodiment determines the laser irradiation state of the laser irradiation device  22  included in each of the laser brazing machines  10 L and  10 R. The laser irradiation state determination device  36  includes an output stabilization time acquisition unit  38 , an energy acquisition unit  40 , an output conversion unit  42 , a laser irradiation state determination unit  44 , and a notification control unit  46 . The laser irradiation state determination device  36  may determine the laser irradiation state for the laser irradiation device  22  included in one laser brazing machine  10  or for the laser irradiation device  22  included in each of three or more laser brazing machines  10 . 
     The output stabilization time acquisition unit  38  acquires an output stabilization time from laser output information detected by the laser output sensor  34 . The output stabilization time is a time from the start of laser irradiation by the laser irradiation device  22  to the stabilization of the laser output. The output stabilization time will be described later in detail. 
     The energy acquisition unit  40  acquires the energy of the laser beam emitted by the laser irradiation device  22  for a predetermined time period from the laser output information detected by the laser output sensor  34 . The process of acquiring laser energy will be described later in detail. 
     The output conversion unit  42  converts the laser energy acquired by the energy acquisition unit  40 , into the laser output. An output conversion process for converting the laser energy into the laser output will be described later in detail. 
     The laser irradiation state determination unit  44  determines the laser irradiation state of the laser irradiation device  22  based on the laser output obtained by the output conversion unit  42 . The determination process of the laser irradiation state of the laser irradiation device  22  will be described later in detail. 
     The notification control unit  46  controls a notification unit  48  based on the laser irradiation state of the laser irradiation device  22  determined by the laser irradiation state determination unit  44 , and performs notification to the operator. The notification unit  48  may be a display device that displays characters, images, or the like, or may be an acoustic device that emits sound or the like. 
     The output stabilization time acquisition unit  38 , the energy acquisition unit  40 , the output conversion unit  42 , the laser irradiation state determination unit  44 , and the notification control unit  46  are realized by a processor executing a program stored in a storage medium (not illustrated). 
     [Output Stabilization Time Acquisition Process] 
       FIG. 3  is a graph showing change in laser output with respect to time of the laser irradiation device  22 . The graph of  FIG. 3  shows an example of change in laser output with respect to time, from the start of laser irradiation to the elapse of a set time T 1  [ms], in each of the three laser irradiation devices  22 . Each of the three laser irradiation devices  22  is controlled so as to irradiate a laser beam having a set output W 1  [W]. 
     As shown in  FIG. 3 , immediately after the laser irradiation is started, the characteristics of the laser output are greatly different for each individual laser irradiation device  22 . In addition, immediately after the start of laser irradiation, the amount of change in laser output with respect to time in each laser irradiation device  22  is large. As time elapses from the start of laser irradiation, the difference in laser output characteristics among the individual laser irradiation devices  22  decreases. In addition, as time elapses from the start of laser irradiation, the amount of change in laser output with respect to time in each laser irradiation device  22  decreases. 
     When the change in laser output of the laser irradiation device  22  with respect to time changes as shown in the graph of  FIG. 3 , the output stabilization time is T 0  [ms]. The output stabilization time acquisition unit  38  acquires this output stabilization time. The output stabilization time is measured in advance using a device equivalent to the laser irradiation device  22  which is a determination target of the laser irradiation state. Alternatively, before the determination of the laser irradiation state is performed, the output stabilization time may be measured using the laser irradiation device  22  that is the determination target of the laser irradiation state. 
     [Energy Acquisition Process] 
       FIG. 4  is a flowchart illustrating an energy acquisition process performed by the energy acquisition unit  40 . The energy acquisition process is executed each time the laser irradiation state of the laser irradiation device  22  is determined. For performing the determination of the laser irradiation state of the laser irradiation device  22 , the laser brazing machine  10  is controlled so as to irradiate the laser beam of the set output W 1  [W] from the laser irradiation device  22  toward the laser output sensor  34  for the set time T 1  [ms]. 
     In step S 1 , the energy acquisition unit  40  determines whether or not the output stabilization time or more has elapsed since the laser irradiation device  22  started the laser irradiation. If the output stabilization time or more has elapsed, the process proceeds to step S 2 . If the output stabilization time has not elapsed, the determination of step S 1  is repeated. 
     In step S 2 , the energy acquisition unit  40  acquires, as energy, a value obtained by integrating the laser output detected, by the laser output sensor  34 , for a predetermined time period ΔT 2  [ms] which is set in advance, and ends the energy acquisition process. 
       FIG. 5  is a graph showing an example of change in laser output with respect to time of the laser irradiation device  22  detected by the laser output sensor  34 . The graph of  FIG. 5  shows an example of change in laser output with respect to time from when the laser irradiation device  22  starts irradiation of the laser to when a set time T 1  [ms] elapses. 
     After the output stabilization time T 0  [ms] or more has elapsed from the start of laser irradiation by the laser irradiation device  22 , the energy acquisition unit  40  acquires, as energy, the value obtained by integrating the laser output for a predetermined time period ΔT 2  [ms]. When the laser output varies as shown in  FIG. 5 , the energy acquisition unit  40  acquires E [J] as the laser energy irradiated from the laser irradiation device  22  for a predetermined time period ΔT 2  [ms]. 
     [Output Conversion Process] 
       FIG. 6  is a flowchart showing an output conversion process performed by the output conversion unit  42 . The output conversion process is executed each time the energy acquisition process described above ends. 
     In step S 11 , the output conversion unit  42  inputs the laser energy acquired by the energy acquisition unit  40 , and then the process proceeds to step S 12 . 
     In step S 12 , the output conversion unit  42  converts the laser energy into the laser output, and ends the output conversion process. When the laser output changes as shown in  FIG. 5 , the energy acquisition unit  40  acquires E [J] as the energy for a predetermined time period ΔT 2  [ms]. The output conversion unit  42  converts the laser energy into the laser output by dividing the acquired laser energy E [J] by the predetermined time period ΔT 2 . 
     [Laser Irradiation State Determination Process] 
       FIG. 7  is a flowchart illustrating a laser irradiation state determination process performed by the laser irradiation state determination unit  44  and the notification control unit  46 . 
     In step S 21 , the laser irradiation state determination unit  44  inputs the laser output obtained by the output conversion unit  42 , and the process proceeds to step S 22 . 
     In step S 22 , the laser irradiation state determination unit  44  determines whether the laser output input in step S 21  is less than a preset threshold value or not. When the laser output is less than the threshold value, the process proceeds to step S 23 . When the laser output is equal to or greater than the threshold value, the process proceeds to step S 24 . 
     In step S 23 , the notification control unit  46  controls the notification unit  48  to notify the operator that the output of the laser irradiation device  22  has decreased, and the laser irradiation state determination process is terminated. 
     In step S 24 , the notification control unit  46  controls the notification unit  48  to notify the operator that the output of the laser irradiation device  22  is normal, and the laser irradiation state determination process is terminated. 
     [Operational Effects] 
       FIGS. 8A, 8B, and 8C  are diagrams illustrating conventional methods for obtaining the laser output; The graphs of  FIGS. 8A to 8C  show change in laser output with respect to time from when the laser irradiation starts until the set time T 1  [ms] elapses in each of the three laser irradiation devices  22 . 
     In the conventional laser output acquisition method, the laser output is acquired based on energy obtained by integrating the laser output from immediately after the laser irradiation device  22  starts laser irradiation. The laser output sensor  34  of the present embodiment has high responsiveness, and can detect a change in laser output during laser irradiation of several milliseconds. Therefore, the energy of the laser irradiated for a short period of time can be obtained, and the laser output can be obtained in a short period of time. However, a period during which the laser output is not stable makes up a relatively large proportion of the entire period during which the laser energy is obtained, and there is a problem in that the accuracy of the laser output converted from the obtained laser energy reduces. 
     In a case where the laser output varies as illustrated in  FIGS. 8A to 8C , the energy of the laser beam irradiated during a time period from 0 [ms] to the set time T 1  [ms] after each of the laser irradiation devices  22  starts the irradiation of the laser is Ea [J], Eb [J], and Ec [J] (Eb&gt;Ea&gt;Ec). The laser output converted by dividing each of the energies Ea [J], Eb [J], and Ec [J] by the set time T 1  [ms] has a large variation among the individual laser irradiation devices  22 . Therefore, in a case where the laser irradiation state of the laser irradiation device  22  is determined based on the laser output acquired by the conventional acquisition method, there is a possibility that an erroneous determination is made. 
       FIGS. 9A, 9B, and 9C  are diagrams illustrating a method of obtaining the laser output according to the present embodiment. The graphs of  FIGS. 9A to 9C  show change in laser output with respect to time from when a laser irradiation starts until the set time T 1  [ms] elapses, in each of the three laser irradiation devices  22 . 
     In the case where the laser output changes as shown in  FIGS. 9A to 9C , after the output stabilization time T 0  [ms] elapses from the start of laser irradiation by each of the laser irradiation devices  22 , energy Ed [J], energy Ee [J], and energy Ef [J] of the laser irradiated for a predetermined time period ΔT 2  [ms] from the output stabilization time T 0  [ms] to the set time T 1  [ms] become substantially equal. The laser outputs obtained by dividing the energies Ed [J], Ee [J], and Ef [J] by the predetermined time period ΔT 2  [ms] are substantially equal to each other. 
     In general, when the laser output is obtained based on the energy of the laser irradiated for a time period as long as possible, the obtained laser output has higher accuracy. However, in the present embodiment, in consideration of the characteristics of the laser output sensor  34 , the output is acquired based on the energy of the laser beam irradiated for a short time period excluding a time period during which the laser output is not stable. Accordingly, the laser output can be obtained with high accuracy, and the accuracy of the determination of the laser irradiation state of the laser irradiation device  22  based on the laser output can be improved. 
     Second Embodiment 
     The laser irradiation state determination device  36  according to the present embodiment specifically determines the cause of the decrease in output of the laser irradiated by the laser irradiation device  22  from time-series data of the laser output of the laser irradiation device  22  obtained by the output conversion unit  42 . 
     [Configuration of Laser Irradiation State Determination Device] 
       FIG. 10  is a block diagram showing a configuration of the laser irradiation state determination device  36 . A laser brazing machine  10 L and a laser brazing machine  10 R are installed across a line which the vehicle bodies  12  move down. The laser irradiation state determination device  36  according to the present embodiment determines the laser irradiation state of the laser irradiation device  22  included in each of the laser brazing machines  10 L and  10 R. 
     The laser irradiation state determination device  36  includes an output stabilization time acquisition unit  38 , an energy acquisition unit  40 , an output conversion unit  42 , a time-series data storage unit  50 , a laser irradiation state determination unit  44 , and a notification control unit  46 . Among these components, the output stabilization time acquisition unit  38 , the energy acquisition unit  40 , and the output conversion unit  42  are the same as the output stabilization time acquisition unit  38 , the energy acquisition unit  40 , and the output conversion unit  42  of the first embodiment. The laser irradiation state determination unit  44  and the notification control unit  46  are partially different from the laser irradiation state determination unit  44  and the notification control unit  46  of the first embodiment in the contents of processing to be performed. The time-series data storage unit  50  is a constituent element added in the present embodiment. 
     Each time the laser irradiation state of the laser irradiation device  22  is determined, the time-series data storage unit  50  stores, as time-series data, the laser output obtained by the output conversion unit  42  in association with the time at which the laser irradiation state of the laser irradiation device  22  is determined. 
     The laser irradiation state determination unit  44  determines the laser irradiation state of the laser irradiation device  22  based on the time-series data stored in the time-series data storage unit  50 . The laser irradiation state determination process of the laser irradiation device  22  will be described later in detail. 
     The notification control unit  46  controls the notification unit  48  based on the laser irradiation state of the laser irradiation device  22  determined by the laser irradiation state determination unit  44 , and performs notification to the operator. 
     The output stabilization time acquisition unit  38 , the energy acquisition unit  40 , the output conversion unit  42 , the laser irradiation state determination unit  44 , and the notification control unit  46  are realized by a processor executing a program stored in a storage medium (not illustrated). The time-series data storage unit  50  is realized by a storage medium (not shown). 
     [Laser Irradiation State Determination Process] 
       FIG. 11  is a flowchart illustrating a laser irradiation state determination process performed by the laser irradiation state determination unit  44  and the notification control unit  46 . 
     In step S 31 , the laser irradiation state determination unit  44  inputs the laser output obtained by the output conversion unit  42 , and the process proceeds to step S 32 . 
     In step S 32 , the laser irradiation state determination unit  44  stores the laser output input in step S 31  in the time-series data storage unit  50  as time-series data in association with the sequential order in which the laser output is input, and then the process proceeds to step S 33 . 
     In step S 33 , the laser irradiation state determination unit  44  acquires the time-series data of laser output from the time-series data storage unit  50 , and the process proceeds to step S 34 . 
     In step S 34 , the laser irradiation state determination unit  44  determines the laser irradiation state of the laser irradiation device  22  based on the time-series date, and the process proceeds to step S 35 . The determination process of the laser irradiation state of the laser irradiation device  22  based on the time-series data will be described later in detail. 
     In step S 35 , the notification control unit  46  controls the notification unit  48  to notify the operator of the laser irradiation state of the laser irradiation device  22  determined in step S 34 , and the laser irradiation state determination process ends. 
     [Details of Determination of Laser Irradiation State] 
       FIGS. 12, 13, and 14  are examples of time-series data stored in the time-series data storage unit  50 . As described above, the measurement of the laser output of the laser irradiation device  22  is performed each time the machining of one vehicle body  12  is completed. Accordingly, the time-series data shown in  FIGS. 12 to 14  is represented as a graph showing a change in laser output with respect to the number of vehicle bodies  12  machined by the laser irradiation device  22 . 
     An air knife is provided on the surface of the protective glass  31  of the irradiation head  30  of the laser irradiation device  22 . The air knife prevents spatters and fumes from entering the protective glass  31  side. However, in some cases, spatters or fumes may pass through the air knife to enter the protective glass  31  side and adhere to the protective glass  31 . When the spatter or fume adheres to the protective glass  31 , the laser output irradiated by the laser irradiation device  22  decreases. The change of the time-series data differs depending on whether what is attached to the protective glass  31  is the spatter or the fume, and further depending on the main component of the spatter. 
     The time-series data in  FIG. 12  shows an example of a case where a spatter containing zinc as a main component adheres to the protective glass  31  of the irradiation head  30  of the laser irradiation device  22 . The time-series data in  FIG. 13  shows an example of a case where a spatter containing copper as a main component adheres to the protective glass  31  of the irradiation head  30  of the laser irradiation device  22 . 
     By irradiating the brazing material  14  with the laser, fine particles (spatters) of zinc or copper contained in the brazing material  14  are scattered. Spatters containing zinc as the main component have a relatively low melting point. The spatters containing zinc as the main component adheres to the protective glass  31  and thereafter is burned and spread by heat of the laser. Therefore, the laser output gradually decreases over several tens of vehicle bodies after the spatters containing zinc as the main component have been attached to the protective glass  31 . The laser irradiation state determination unit  44  determines that spatters containing zinc as the main component are attached to the protective glass  31  in a case where the laser output gradually decreases over several tens of vehicle bodies, as shown in the time-series data illustrated in  FIG. 12 . In this case, the notification control unit  46  controls the notification unit  48  to notify the operator that there is a possibility that the protective glass  31  has, adhered thereto, spatters containing zinc as the main component. 
     The size of the spatter containing copper as the main component is larger than the size of the spatter containing zinc as the main component. Therefore, when spatters containing copper as the main component adhere to the protective glass  31 , the output of the laser is greatly reduced. When the output of the laser decreases stepwise as shown in the time-series data in  FIG. 13 , the laser irradiation state determination unit  44  determines that the protective glass  31  has, attached thereto, spatters containing copper as the main component. In this case, the notification control unit  46  controls the notification unit  48  to notify the operator that there is a possibility that the protective glass  31  has, attached thereto, spatters containing copper as the main component. 
     The time-series data of  FIG. 14  shows an example of a case in which fumes adhere to the protective glass  31  of the irradiation head  30  of the laser irradiation device  22 . The amount of fumes adhering to the protective glass  31  increases in accordance with the number of vehicle bodies  12  machined by the laser irradiation device  22 . When the laser irradiation device  22  machines about 5000 vehicle bodies  12 , the output of the laser irradiated by the laser irradiation device  22  is reduced by about 1% to 2%. Although depending on the number of vehicle bodies machined per day, the protective glass  31  needs to be replaced in about one week. The laser irradiation state determination unit  44  determines that the amount of fumes adhering to the protective glass  31  is increasing when the output of the laser decreases by approximately 1% to 2% over approximately 5000 vehicle bodies as shown in the time-series data illustrated in  FIG. 14 . In this case, the notification control unit  46  controls the notification unit  48  to notify the operator that the fumes adhering to the protective glass  31  are increasing. 
       FIGS. 15 and 16  show examples of time-series data stored in the time-series data storage unit  50 . There are cases where decrease in the output of the laser irradiated by the laser irradiation device  22  may be generated by a cause other than adhesion of spatters or fumes to the protective glass  31 . 
     The time series data of  FIG. 15  shows an example of a case where there is a defect in a roller (not shown) of the guide  26  of the brazing material supply device  20  of the laser irradiation device  22 . The guide  26  feeds out the brazing material  14  by rotating the roller. When the output of the laser is to be measured, the guide  26  reversely rotates the roller by a predetermined length (predetermined rotation amount) and rewinds the brazing material  14  to a position where the brazing material  14  does not intercept the laser beam. However, due to wear of the roller, looseness of a position adjustment portion of the roller, or the like, there are cases where the brazing material  14  may not be sufficiently unwound and the brazing material  14  may intercept the laser beam. In this case, only when the brazing material  14  intercepts the laser beam at the time of measurement of the laser, a one-shot decrease in the laser output occurs accordingly. When there is a defect in the guide  26  as shown in the time-series data of  FIG. 15 , an event of the decrease in laser output occurs every several vehicle bodies, and the interval between the occurrences of the events gradually shortens. 
     As shown in the time-series data of  FIG. 15 , the laser irradiation state determination unit  44  determines that a defect has occurred in the roller of the guide  26  in a case where the event of the decrease in laser output occurs every several vehicle bodies and the interval between the occurrences of the events is gradually shortened. In this case, the notification control unit  46  controls the notification unit  48  to notify the operator that a defect has occurred in the roller of the guide  26 . 
     The time-series data of  FIG. 16  shows an example in which the irradiation head  30  of the laser irradiation device  22  interferes with an obstacle during machining and the position or posture of the irradiation head  30  is shifted. In a case where the position or the posture of the irradiation head  30  is deviated, as shown in the time-series data of  FIG. 16 , after the output of the laser decreases, the output is stabilized in the state where the output of the laser decreases. The laser irradiation state determination unit  44  determines that the irradiation head  30  has interfered with an obstacle during machining when the output of the laser is stabilized in the state in which the output of the laser decreases after the output of the laser decreases as in the time-series data of  FIG. 16 . In this case, the notification control unit  46  controls the notification unit  48  to notify the operator that the irradiation head  30  has interfered with an obstacle during machining. 
     In both the time series data ( FIG. 16 ) obtained when the irradiation head  30  of the laser irradiation device  22  interferes with an obstacle during machining and the time series data ( FIG. 13 ) obtained when spatters containing copper as the main component adhere to the protective glass  31  of the irradiation head  30  of the laser irradiation device  22 , the output of the laser decreases stepwise. In a case where the output of the laser decreases stepwise, the laser irradiation state determination unit  44  may determine that the irradiation head  30  has interfered with an obstacle during machining or alternatively that spatters have adhered to the protective glass  31  of the irradiation head  30 . 
     [Operational Effects] 
     In the present embodiment, the laser output of the laser irradiation device  22  acquired by the output conversion unit  42  is stored as time-series data in the time-series data storage unit  50 . Then, the laser irradiation state determination unit  44  determines the laser irradiation state of the laser irradiation device  22  based on the stored time-series data. As a result, it is possible to perform more detailed determination on the laser irradiation state. 
     Invention Obtained from Embodiments 
     The inventions that are capable of being grasped from the above-described embodiments will be mentioned below. 
     There is provided a laser irradiation state determination method for determining an irradiation state of a laser beam emitted by a laser irradiation device ( 22 ), the method including: an output stabilization time acquisition step of acquiring, as an output stabilization time, a time from when the laser irradiation device starts irradiation of the laser beam to when an output of the laser beam is stabilized; an energy acquisition step of acquiring energy of the laser beam irradiated by the laser irradiation device for a predetermined time period set in advance, after the output stabilization time or more has elapsed since the laser irradiation device started the irradiation of the laser beam; a conversion step of converting the acquired energy into the output of the laser beam irradiated by the laser irradiation device; and a state determination step of determining the irradiation state of the laser beam based on the converted output of the laser beam. As a result, it is possible to obtain the output of the laser with high accuracy, and it is possible to improve the accuracy of determination by determining the irradiation state of the laser based on the highly accurately obtained output of the laser. 
     In the laser irradiation state determination method described above, the output stabilization time may be set in advance. As a result, since the process of obtaining the output stabilization time is not performed during machining, a load imposed on the laser irradiation state determination device  36  can be reduced. 
     In the above-described laser irradiation state determination method, the state determination step may determine the irradiation state of the laser beam by comparing the converted output of the laser beam with a preset threshold value. By determining the irradiation state of the laser by comparing the acquired output of the laser with the threshold value, it is possible to easily determine the irradiation state of the laser. 
     The laser irradiation state determination method may further include a time-series data storage step of storing the converted output of the laser beam as time series data, and the state determination step may determine the irradiation state of the laser beam on the basis of the time series data. As a result, it is possible to perform more detailed determination on the laser irradiation state. 
     REFERENCE SIGNS LIST 
     
         
           22 : laser irradiation device