Abstract:
A conventional gas laser oscillation apparatus cannot appropriately deal with an amount of laser gas introduced greater than normal use and can generate a turbulent flow around the total reflective mirror and the partial reflective mirror. This causes unstable discharge, resulting in unstable output of laser beams. The gas laser oscillation apparatus of the present disclosure has a laser oscillator, a first laser-gas inlet, a laser-gas outlet, a first laser-gas introducing port, a laser-gas circulation passage, and a second laser-gas introducing port. Disposed between a first discharge tube and any one of the total reflective mirror and a partial reflective mirror, the first laser-gas introducing port introduces laser gas into the laser oscillator. Disposed in the laser-gas circulation passage, the second laser-gas introducing port introduces laser gas into the laser-gas circulation passage. A laser-gas introducing section is connected to the first and the second laser-gas introducing ports.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a kilowatt-class axial-flow type gas laser oscillation apparatus, a gas laser oscillation method, and a gas laser processing machine, which are mainly used for sheet-metal cutting. 
       BACKGROUND ART 
       [0002]    Conventional axial-flow type gas laser oscillation apparatus  900  described in Patent Literature 1 will be described with reference to  FIG. 6 . 
         [0003]    Gas laser oscillation apparatus  900  shown in  FIG. 6  has discharge tube  901 , electrodes  902  and  903  disposed in the periphery of discharge tube  901 , and power source  904  connected to electrodes  902 ,  903 . 
         [0004]    Discharge space  905  is a space formed in discharge tube  901  and is sandwiched between electrode  902  and electrode  903 . Total reflective mirror  906  and partial reflective mirror  907 , which are disposed at the outside of both ends of discharge tube  901  respectively, form an optical resonator. Laser beam  908  is supplied from partial reflective mirror  907 . 
         [0005]    Laser-gas flow passage  909  is connected to discharge tube  901 . Heat exchangers  910 ,  911  and blower  912  are disposed in laser-gas flow passage  909 . Blower  912  circulates laser gas in a direction shown by arrow  913  in discharge tube  901  and laser-gas flow passage  909 . 
         [0006]    Total reflective mirror  906  is held by total-reflective-mirror holder  914   a  and is connected to the left end of a discharge area via non-discharge tube  915  and copper ring  916 . Partial reflective mirror  907  is held by partial-reflective-mirror holder  914   b  and is connected to the right end of the discharge area via non-discharge tube  915  and copper ring  916 . 
         [0007]    Copper ring  916  has laser-gas inlet  917  opened like a slit. A section connecting between non-discharge tube  915  and copper ring  916  is covered with joint tube  918 . Each joint tube  918 —one is disposed on the side of total reflective mirror  906  and the other is disposed on the side of partial reflective mirror  907 —is connected to laser-gas supply device  919 . According to gas laser oscillation apparatus  900 , laser gas is supplied from laser-gas supply device  919  to discharge tube  901  via joint tube  918 , laser-gas inlet  917  of copper ring  916 , and non-discharge tube  915 . By virtue of its shape of a slit, laser-gas inlet  917  prevents laser gas from generating a turbulent flow around total reflective mirror  906  and partial reflective mirror  907 . This allows gas laser oscillation apparatus  900  to output laser beam  908  with stability. 
         [0008]    When a gas laser oscillation apparatus is left unused for a long time, impurities, particularly water molecules attach to the discharge tube and the laser-gas flow passage of the gas laser oscillation apparatus. Restarting the gas laser oscillation apparatus under the condition above fails to offer stable discharge, decreasing output of laser beams. According to a known method to address the matter described above, the decrease in laser beam output is prevented by, for a predetermined period of time from the start of discharge, supplying the discharge tube and the laser-gas flow passage with an amount of laser gas greater than that used for normal operation. 
       CITATION LIST 
     Patent Literature 
       [0009]    PTL 1: Japanese Unexamined Patent Application Publication No. 2003-110171 
       SUMMARY OF THE INVENTION 
       [0010]    Such a slit-like laser gas inlet of the conventional laser gas oscillation apparatus nevertheless cannot deal appropriately with an amount of laser gas introduced greater than normal use and fails to prevent generation of a turbulent flow around the total reflective mirror and the partial reflective mirror. The turbulent flow of laser gas causes unstable discharge, resulting in unstable output of laser beams. 
         [0011]    To address the problem above, the gas laser oscillation apparatus of the present disclosure has a laser oscillator, a first laser-gas inlet, a laser-gas outlet, a first laser-gas introducing port, a laser-gas circulation passage, and a second laser-gas introducing port. The laser oscillator has one of the total reflective mirror and the partial reflective mirror disposed at a first end, the other of the total reflective mirror and the partial reflective mirror disposed at a second end that is opposite to the first end, and a first discharge tube for exciting laser gas. The first laser-gas inlet, which is disposed between the partial reflective mirror and the first discharge tube, supplies the laser oscillator with laser gas. The laser gas outlet, which is disposed between the total reflective mirror and the first discharge tube, emits laser gas from the laser oscillator. The first laser-gas introducing port, which is disposed between the partial reflective mirror and the first discharge tube, introduces laser gas into the laser oscillator. The laser-gas circulation passage connects the first laser-gas inlet to the laser-gas outlet. The second laser-gas introducing port, which is disposed in the laser-gas circulation passage, introduces laser gas into the laser-gas circulation passage. A laser-gas introducing section is connected to the first laser-gas introducing port and the second laser-gas introducing port. 
         [0012]    The gas laser oscillation method of the present disclosure has a first laser-gas introducing step, a circulating step, a laser oscillating step, and a second laser-gas introducing step. In the first laser-gas introducing step, laser gas is introduced into the laser oscillator. In the circulating step, the laser-gas circulation passage connected to the laser oscillator circulates the laser gas in the laser oscillator. In the laser oscillating step, voltage is applied to the laser oscillator to excite the laser gas. In the second laser-gas introducing step, laser gas is introduced into the laser-gas circulation passage. Upon detecting laser oscillation in the laser oscillating step, the second laser-gas introducing step starts, and after a lapse of a predetermined period, the second laser-gas introducing step ends. 
         [0013]    The gas laser processing machine of the present disclosure has the gas laser oscillation apparatus described previously, a reflective mirror, a torch, and a table. The reflective mirror reflects off laser beams supplied from the gas laser oscillation apparatus. The torch has a condensing lens that collects the laser beams reflected off the reflective mirror. The table holds a workpiece to be radiated with the laser beams collected by the condensing lens. 
         [0014]    The gas laser oscillation apparatus, the gas laser oscillation method, and the gas laser processing machine of the present disclosure increase the amount of laser gas in the laser oscillator with no need for increasing an amount of laser gas introduced in the periphery of the total reflective mirror and the partial reflective mirror of the laser oscillator. This allows the gas laser oscillation apparatus to quickly output stable laser beams even at restarting the apparatus. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a block diagram of a gas laser oscillation apparatus in accordance with a first exemplary embodiment. 
           [0016]      FIG. 2  is a flowchart showing the operation procedures of a laser-gas supply device in accordance with the first exemplary embodiment. 
           [0017]      FIG. 3  is a block diagram of a gas laser processing machine using the gas laser oscillation apparatus of the first exemplary embodiment. 
           [0018]      FIG. 4  is a block diagram of a gas laser oscillation apparatus in accordance with a second exemplary embodiment. 
           [0019]      FIG. 5  is a block diagram of a gas laser oscillation apparatus in accordance with the second exemplary embodiment. 
           [0020]      FIG. 6  is a block diagram of a conventional gas laser oscillation apparatus. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    The exemplary embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. 
       Exemplary Embodiment 1 
       [0022]    First, the gas laser oscillation apparatus of the first exemplary embodiment will be described below. 
         [0023]      FIG. 1  is a block diagram of axial-flow type gas laser oscillation apparatus  100  of the embodiment. As shown in  FIG. 1 , axial-flow type gas laser oscillation apparatus  100  is formed of laser oscillator  110 , laser-gas circulation section  130 , and laser-gas introducing section  140 . 
         [0024]    Laser oscillator  110  has discharge tube  111  formed of dielectric material such as glass. The inside of discharge tube  111  forms discharge section  112 . Laser oscillator  110  has discharge section  112 , laser-gas inlet  113  (as a first laser-gas inlet), laser-gas outlet  114  (as a first laser-gas outlet), and laser-gas introducing port  115  (as a first laser-gas introducing port). 
         [0025]    In discharge section  112 , discharge is generated by electrode  116  (as a first electrode) and electrode  117  (as a second electrode) disposed outside discharge tube  111 . Power source  118  applies high voltage between electrode  116  and electrode  117 , generating discharge in discharge section  112 . The discharge excites laser gas in discharge section  112 , causing laser oscillation. Laser oscillator  110  has total reflective mirror  119  at one end (first end) and partial reflective mirror  120  at the other end (second end). Laser-gas inlet  113  is disposed between discharge section  112  and partial reflective mirror  120 , while laser-gas outlet  114  is disposed between discharge section  112  and total reflective mirror  119 . Laser-gas introducing port  115  is disposed closer to partial reflective mirror  120  than laser-gas inlet  113  is. 
         [0026]    The laser oscillated in discharge section  112  resonates between total reflective mirror  119  and partial reflective mirror  120 . Upon exceeding a predetermined amount of energy, the laser goes outside laser oscillator  110  as laser beam  121  through partial reflective mirror  120 . Laser beam  121  is used, for example, for laser processing. 
         [0027]    Laser-gas circulation section  130  is connected to laser oscillator  110  so as to supply it with laser gas via laser-gas inlet  113  and so as to emit laser gas from it via laser-gas outlet  114 . 
         [0028]    Laser-gas circulation section  130  has laser-gas circulation passage  131 , heat exchangers  132 ,  133 , blower  134 , laser-gas introducing port  135  (as a second laser-gas introducing port), laser-gas exhaust port  136 , and exhaust pump  137 . 
         [0029]    Laser-gas circulation passage  131  includes the total structure from laser-gas inlet  113  to laser-gas outlet  114 . The following components are disposed on laser-gas circulation passage  131  in the order named from the side of laser-gas outlet  114 : heat exchanger  132 , laser-gas exhaust port  136 , blower  134 , heat exchanger  133 , laser-gas introducing port  135 . Laser gas heated by discharge in laser oscillator  110  and operation of blower  134  is cooled down by heat exchangers  132 ,  133 . Blower  134  circulates laser gas from laser-gas outlet  114  toward laser-gas inlet  113 , allowing the laser gas to flow at a speed of approximately  100  m/sec in discharge section  112 . 
         [0030]    Laser-gas introducing section  140  has laser-gas introducing passage  141 , laser-gas introducing passage  142 , and laser-gas introducing device  143 . Laser-gas introducing passage  141  is connected to laser-gas introducing port  115 , while laser-gas passage  142  is connected to laser-gas introducing port  135 . Laser-gas introducing device  143  has timer  144 , controller  145 , laser-gas tank  146 , and valves  147 ,  148 . Laser-gas introducing passage  141  is connected to laser-gas tank  146  through valve  147  (as a first valve); similarly, laser-gas introducing passage  142  is connected to laser-gas tank  146  through valve  148  (as a second valve). Controller  145  is connected to timer  144 , valves  147 ,  148 , power source  118 , and exhaust pump  137  so as to control them. 
         [0031]    As described above, the gas laser oscillation apparatus of the embodiment has laser-gas introducing port  135  through which laser gas is introduced into laser-gas circulation passage  131 , in addition to laser-gas introducing port  115  through which laser gas is introduced into laser oscillator  110 . At a restart operation of a gas laser oscillation apparatus (even after long-term no operation), the aforementioned structure allows to increase the flow volume of laser gas in laser oscillator  110  more than that used in normal operation, while maintaining the amount of laser gas introduced into laser oscillator  110  the same as that used in normal operation. With the structure above, gas laser oscillation apparatus  100  of the embodiment provides output of laser beams with stability shortly after restart of the apparatus. 
         [0032]    Next, a gas laser oscillation method of the embodiment will be described below. 
         [0033]    During the normal operation of gas laser oscillation apparatus  100 , laser oscillator  110 , laser-gas circulation section  130 , and laser-gas introducing section  140  work as follows. 
         [0034]    In laser oscillator  110 , power source  118  applies high voltage to first electrode  116  and second electrode  117 . The application of voltage excites laser gas in discharge section  112 , causing laser oscillation. The laser oscillated in discharge section  112  has resonance between total reflective mirror  119  and partial reflective mirror  120 . Upon exceeding a predetermined amount of energy, the laser goes outside laser oscillator  110  as laser beam  121  through partial reflective mirror  120 . 
         [0035]    Laser-gas introducing section  140  opens valve  147  and closes valve  148 , so that fresh laser gas is supplied, through laser-gas introducing port  115  only, to laser oscillator  110 . 
         [0036]    Laser-gas circulation section  130  opens laser-gas exhaust port  136  to exhaust degraded laser gas outside laser-gas circulation passage  131 . The laser gas to be exhausted at that time is as much as the newly introduced laser gas supplied from laser-gas introducing port  115 . In this way, degraded laser gas is replaced with fresh one with no changes in internal pressure of laser oscillator  110 . Besides, operating heat exchangers  132 ,  133  and blower  134  allows cooled laser gas to be supplied into the laser oscillator at a constant speed. 
         [0037]    In normal operation, as described above, laser oscillator  110  has laser oscillation with stability by cooling laser gas and replacing degraded gas with fresh one, so that gas laser oscillation apparatus  100  outputs laser beam  121  with stability. 
         [0038]    Next, the description below is on a gas laser oscillation method for restarting gas laser oscillation apparatus  100  after long-term no use. The method is described with reference to  FIG. 2 . 
         [0039]    If gas laser oscillation apparatus  100  has no operation for a long time, impurities including water molecules build up in laser oscillator  110 , causing instable discharge. Therefore, at the restart of gas laser oscillation apparatus  100 , until the impurities are removed, the flow volume of laser gas in laser oscillator  110  has to be increased more than that used in normal operation. The structure of the embodiment determines that, at the restart of operation, the flow volume of laser gas in laser oscillator  110  is more than five times as much as that in normal operation, and the increased flow volume is maintained for five minutes. 
         [0040]    First, as shown in step Si of  FIG. 2 , laser-gas introducing section  140  opens valve  147  so that laser gas flows through laser-gas introducing port  115  into laser oscillator  110 . Meanwhile, like in the normal operation, in laser-gas circulation section  130 , heat exchangers  132 ,  133 , blower  134 , and exhaust pump  137  start the operation, and laser-gas exhaust port  136  opens. 
         [0041]    Next, as shown in step S 2  of  FIG. 2 , controller  145  controls power source  118  of laser oscillator  110  to apply high voltage between first electrode  116  and second electrode  117 . Power source  118  sends a discharge start signal—it shows presence or absence of discharge in discharge section  112 —to controller  145 . Until detecting the start of discharge, controller  145  introduces laser gas through laser-gas introducing port  115  into laser oscillator  110 ; at the same time, laser-gas circulation section  130  circulates laser gas. 
         [0042]    Upon a discharge starts in discharge section  112 , as shown in step S 3  of  FIG. 2 , controller  145  opens valve  148  to introduce laser gas through laser-gas introducing port  135  into laser-gas circulation passage  131 . At the same time, controller  145  increases the rotation speed of exhaust pump  137  so as to increase the amount of laser gas exhausted through laser-gas exhaust port  136 . 
         [0043]    Through the control above, an increased volume of laser gas more than that in normal operation is supplied to discharge section  112  and laser-gas circulation passage  131 , so that the flow volume of laser gas in discharge section  112  increases. Specifically, the laser gas introduced through laser-gas introducing port  135  is increased to four times as much volume as that introduced through laser-gas introducing port  115 . At approximately the same time, the laser gas to be exhausted through laser-gas exhaust port  136  is increased to five times as much volume as that in normal operation. This allows discharge section  112  and laser-gas circulation passage  131  to have laser gas five times as much volume as that in normal operation. During the procedures above, the internal pressure of laser gas in discharge section  112  has almost no increase. 
         [0044]    As shown in step S 4  of  FIG. 2 , upon opening valve  148 , controller  145  resets timer  144 . As shown in step S 5  of  FIG. 2 , timer  144  restarts and measures time from the reset moment, thereby sending the measured time to controller  145 . As shown in step S 6  of  FIG. 2 , if the measured time from timer  144  is smaller than five minutes, controller  145  maintains valve  148  open. 
         [0045]    As shown in step S 7  of  FIG. 2 , upon the measured time from timer  144  reaches five minutes, controller  145  closes valve  148 , and gas laser oscillation apparatus  100  returns to normal operation (with control procedures described previously). 
         [0046]    As described above, at restart of a gas laser oscillation apparatus after long-time no use, the gas laser oscillation method of the embodiment increases the laser gas in laser oscillator  110  to about five times as much volume as that used in normal operation, while maintaining the amount of laser gas introduced into laser oscillator  110  the same as that used in normal operation. With the gas laser oscillation method described above, a gas laser oscillation apparatus—even after long-term no use—outputs laser beams with quickly recovered stability. 
         [0047]    Next, the gas laser processing machine of the embodiment will be described. 
         [0048]    As shown in  FIG. 3 , gas laser processing machine  300  of the embodiment has gas laser oscillation apparatus  100 , reflective mirror  301 , torch  302 , condensing lens  303  in torch  302 , table  304 , X-axis motor  305 , and Y-axis motor  306 . With the structure above, gas laser processing machine  300  processes, i.e., performs welding or cutting on workpiece  307  mounted on table  304 . 
         [0049]    The processing by gas laser processing machine  300  will be described. Laser beams supplied from gas laser oscillation apparatus  100  reflects off reflective mirror  301  and travels toward condensing lens  303  disposed in torch  302 . Condensing lens  303  collects the incident laser beams and sends them onto workpiece  307 . Torch  302  is moved by X-axis motor  305  and Y-axis motor  306  to a position according to an intended shape of workpiece  307  to be processed. Instead of moving torch  302 , table  304  may be moved to a position according to an intended shape of workpiece  307  to be processed. 
       Exemplary Embodiment 2 
       [0050]    Next, a gas laser oscillation apparatus of the second exemplary embodiment will be described. 
         [0051]      FIG. 4  is a block diagram of axial-flow type gas laser oscillation apparatus  400  in accordance with the second exemplary embodiment.  FIG. 5  is a block diagram of another axial-flow type gas laser oscillation apparatus  500  of the exemplary embodiment. In the figures above, like parts similar to the structure of gas laser oscillation apparatus  100  of the first exemplary embodiment have the same reference marks and the descriptions thereof will be omitted. 
         [0052]    Gas laser oscillation apparatus  400  differs from gas laser oscillation apparatus  100  in the following respects. 
         [0053]    As shown in  FIG. 4 , laser oscillator  410  of gas laser oscillation apparatus  400  has the structure of laser oscillator  110  of gas laser oscillation apparatus  100 , plus the following components: discharge tube  411  (as a second discharge tube); discharge section  412  (as a second discharge section); laser-gas inlet  413  (as a second laser-gas inlet); laser-gas introducing port  415  (as a third laser-gas introducing port); electrode  416  (as a third electrode); electrode  417  (as a fourth electrode); and power source  418  (as a second power source). Controller  145  controls power sources  118  and  418 . Laser-gas outlet  114  is disposed between discharge tube  111  and discharge tube  411 . The structure on the side of discharge tube  111  and the structure on the side of discharge tube  411  are symmetrically arranged with respect to laser-gas outlet  114 . 
         [0054]    In laser-gas circulation section  430 , laser-gas circulation passage  431  is separated into two lines at a downstream part of heat exchanger  133 , and the separated two lines are each connected to laser-gas inlets  113  and  413 . Similarly, in laser-gas introducing section  440 , laser-gas introducing passage  441  is separated into two lines at a downstream part of valve  147 , and the separated two lines are each connected to laser-gas introducing ports  115  and  415 . 
         [0055]    Gas laser oscillation apparatus  400  has discharge sections  112 ,  412  in its right and left, and two laser-gas inlets  113 ,  413  and two laser-gas introducing ports  115 ,  415 . With the structure above, the amount of laser gas passing through each port decreases, which suppresses a turbulent flow of laser gas. 
         [0056]    Gas laser oscillation apparatus  500  differs from gas laser oscillation apparatus  400  in the following respects. 
         [0057]    According to laser-gas introducing section  540  of gas laser oscillation apparatus  500 , as shown in  FIG. 5 , laser-gas introducing passage  542  is separated into two lines. The two lines of laser-gas introducing passage  542  are connected to laser-gas introducing port  135  and laser-gas introducing port  535  (as a fourth laser-gas introducing port) disposed in laser-gas circulation passage  431  that is also separated into two. With the structure above, fresh laser gas uniformly introduced into the right and the left of the structure, with no influence of the gas flow from heat exchanger  133 . 
         [0058]    Instead of gas laser oscillation apparatus  100 , gas laser oscillation apparatuses  400  and  500  can be used for the gas laser processing machine shown in  FIG. 3 . 
         [0059]    In the structures described in the first and the second exemplary embodiments, laser-gas introducing ports  115  and  415  may be a slit formed along a side surface of laser oscillator  110 . Such a slit-like port allows laser gas to flow along the entire side surface into the inside of laser oscillator  110 , suppressing a turbulent flow of laser gas introduced through laser-gas introducing ports  115  and  415 . 
       INDUSTRIAL APPLICABILITY 
       [0060]    According to the gas laser oscillation apparatus, the gas laser oscillation method, and the gas laser processing machine of the present disclosure, the apparatus outputs quickly stabilized laser beams, even at its restart operation, which is useful for cutting and welding. 
       REFERENCE MARKS IN THE DRAWINGS 
       [0061]      100 ,  400 ,  500 ,  900  gas laser oscillation apparatus 
         [0062]      110 ,  410  laser oscillator 
         [0063]      111 ,  411 ,  901  discharge tube 
         [0064]      112 ,  412  discharge section 
         [0065]      113 ,  413  laser-gas inlet 
         [0066]      114 ,  414  laser-gas outlet 
         [0067]      115 ,  135 ,  415 ,  535  laser-gas introducing port 
         [0068]      116 ,  117 ,  416 ,  417 ,  902 ,  903  electrode 
         [0069]      118 ,  418 ,  904  power source 
         [0070]      119 ,  906  total reflective mirror 
         [0071]      120 ,  907  partial reflective mirror 
         [0072]      121  laser beam 
         [0073]      130 ,  430  laser-gas circulation section 
         [0074]      131 ,  431  laser-gas circulation passage 
         [0075]      132 ,  133 ,  910 ,  911  heat exchanger 
         [0076]      134 ,  912  blower 
         [0077]      136  laser-gas exhaust port 
         [0078]      137  exhaust pump 
         [0079]      140 ,  440 ,  540  laser-gas introducing section 
         [0080]      141 ,  142 ,  441 ,  542  laser-gas introducing passage 
         [0081]      143  laser-gas introducing device 
         [0082]      144  timer 
         [0083]      145  controller 
         [0084]      146  laser-gas tank 
         [0085]      147 ,  148  valve 
         [0086]      300  gas laser processing machine 
         [0087]      301  reflective mirror 
         [0088]      302  torch 
         [0089]      303  condensing lens 
         [0090]      304  table 
         [0091]      305  X-axis motor 
         [0092]      306  Y-axis motor 
         [0093]      307  workpiece 
         [0094]      905  discharge space 
         [0095]      908  laser beam 
         [0096]      909  laser-gas passage 
         [0097]      913  arrow 
         [0098]      914   a  total-reflective-mirror holder 
         [0099]      914   b  partial-reflective-mirror holder 
         [0100]      915  non-discharge tube 
         [0101]      916  copper ring 
         [0102]      917  laser-gas introducing section 
         [0103]      918  joint tube 
         [0104]      919  laser-gas supply device