ABNORMAL CONDITION DETECTOR IN A LASER OSCILLATOR CONDUIT SYSTEM

Abstract: The conduit system of a laser oscillator (1) includes pipes (211,212,213,214) for circulating a medium gas to a laser discharge tube (11). A medium gas circulation pump (23) is provided in the pipes which are coupled to medium gas supply pipes (217,218). A pump (24) driven by a unit discharges the medium gas from the laser discharge tube and the medium gas circulation pipes. A controller (7) for the operation of the conduit system generates signals for the pump drive unit and a display device (6). When a switch valve (26) in the medium gas pipe is closed and the discharge pump (24) is driven, any abnormal condition in the conduit system may be detected and displayed based upon whether the operation signal of a pressure sensor (3) is generated within a predetermined period of time or not.

Description: The present invention relates to an abnormality detection device for a laser oscillator piping system used, for example, for precision processing and the like. In general, when a laser discharge tube of a laser oscillator is actuated, the laser discharge tube is filled with a medium gas such as a mixture of carbon dioxide, nitrogen gas, and helium gas. In this case, used and deteriorated remaining medium gas must be exhausted from the laser discharge tube as well as the piping system connected with the laser discharge tube, and subsequently, the laser discharge tube and the related piping system thereof must be filled with new medium gas, but if an abnormality such as a penetration of outside air or leakage of inside gas exists in the piping system, an unnecessarily long time is required to exhaust the remaining medium gas, and further, it becomes difficult to determine when the exhausting operation will end, resulting in a problem of an inconvenient practice. To carry out the operation described above, a simple and reliable structure for a predetermined procedure for operating the structure should be prepared, but a satisfactorily appropriate prior art structure is not known. An object of the present invention is to provide an improved abnormality detection device for a laser oscillator piping system to cope with the aspect of the problem described above. JP-A-60-52081 discloses a laser comprising a laser discharge tube for generating laser oscillation in medium gas filled therein; a medium gas supply pipe for supplying a medium gas to the discharge tube; a switching valve arranged in the medium gas supply pipe; a pressure sensor connected with the medium gas supply pipe; a medium gas exhaust pump arranged in a medium gas exhaust pipe and driven by a drive device for exhausting the medium gas in the discharge tube; and a control device; and, according to the invention, such a laser is characterised by medium gas circulating pipes connected with the discharge tube for circulating the medium gas therethrough, and a medium gas circulating pump arranged in the medium gas circulating pipes; and by the control device having signal receiving means for receiving a signal from the pressure sensor, means for detecting the output signal of the pressure sensor for a predetermined length of time and for detecting whether or not the gas pressure indicates the existence or non-existence of an abnormality of the piping system, means for supplying a pump control signal to the drive device for the medium gas exhaust pump, and means for supplying an abnormality signal to a display device. In the accompanying drawings: Fig. 1 shows an arrangement of an abnormality detection device for laser oscillator piping system as an embodiment of the present invention; Fig. 2 is a flow chart showing an example of the operation of the device shown in Fig.1. In Fig. 1, the laser oscillator 1 includes a laser discharge tube 11, a total reflection mirror 12, an output coupling mirror 13, electrodes 141 and 142 on one side, and electrodes 143 and 144 on the other side. The electrodes 141 and 142 on one side are connected with one side of the output terminal of the power source 15, and the electrodes 143 and 144 on the other side are connected with the other side of the output terminal of the power source 15. The gas piping connected with the laser discharge tube 11, includes the gas circulating pipes 211, 212, 213 and 214, the gas supply pipes 217 and 218, the gas exhaust pipe 215, and the gas circulation portion exhaust pipe 216. In the gas circulating pipes, a circulating pump 23, for example, a Roots type, and coolers 221 and 222 are arranged. By the operation of the gas circulating pump, the medium gas exhausted from the laser discharge tube 11 through the pipe 213 flows through the cooler 221, the circulating pump 23, the pipe 214, and the cooler 222, then branches to the pipes 211 and 212, and returns to the laser discharge tube. When a switching valve 26 is opened, a medium gas, for example, a mixture of carbon dioxide, nitrogen gas, and helium gas, stored in a gas source is supplied through pipes 217 and 218 to the laser discharge tube. The medium gas in the laser discharge tube 11 and the gas circulating pipes 211, 212, 213, and 214 is exhausted through the pipe 215 by the operation of the gas exhaust pump 24. The exhaust pump 24 is driven by a drive device 4. The gas supply pipe is equipped with a pressure sensor 3, and the gas circulating pipe 211 is equipped with a gas circulating portion exhaust pipe 216 including a needle valve type control valve 25. To control the laser oscillator piping system, a control device is arranged. The control device includes a CPU 71, clock portion 711, bus 72, ROM 73, RAM 74, latch portion 75, keyboard signal receiving portion 76, display control portion 77, and pressure sensor signal receiving portion 78. The output signal of the latch portion 75 is delivered to the exhaust pump drive portion 4; the signal from the keyboard is delivered to the keyboard signal receiving portion; the signal from the display control portion 77 is delivered to the display portion 6 of cathode ray tube or the like; and the output signal of the pressure sensor 3 is delivered to the pressure sensor signal receiving portion 78. In the device shown in Fig. 1, before the laser discharge tube 11 is actuated, the laser discharge tube 11 must be filled with a medium gas, for example, a mixture of carbon dioxide, nitrogen gas and helium gas. In this case, after the switching valve 26 in the gas supply pipe is closed, the gas exhaust pump 24 is driven, and accordingly, used and deteriorated medium gas remaining in the laser discharge tube 11 and piping system is removed from the device. In a process of a gradual failure of the pressure of the medium gas in the piping system, the value of the gas pressure corresponding to a predetermined length of time such as 15 sec. is monitored, and when the predetermined length of time has elapsed, if the value of gas pressure in the piping system is less than 2 Torr, for example, it is determined that an abnormality does not exist, and thus the operation of the gas exhaust pump is stopped and, subsequently, an operation under the normal procedure is carried out, but if the gas pressure does not drop to the predetermined value of pressure, it is determined that an abnormality such as a penetration of outside air or leakage of inside gas exists, and thus an alarm is indicated at the display portion 6. The flow chart in Fig. 2 describes an example of an operation of an abnormality detection device for the laser oscillator piping system shown in Fig. 1. In step S0, when a power source is turned on, an exhaust pump 24 is started in step S1 with the switching valve 26 closed, a timer function of the control device 7 is started in step S2, and a determination of whether or not an output signal of the pressure sensor is ON is carried out in step S3. If the result of the determination is YES, this indicates a non-existence of an abnormality in the laser oscillator piping system, and thus the exhaust pump 24 operation is stopped in step S5, switching valve 26 is opened step S6, a control valve 25 is operated in step 7, and a gas circulating pump 23 is started in step S8. If the result of the determination is NO, a determination of whether or not a time has expired is carried out in step 4. If the result of the determination is NO, step 3 is repeated. If the result of the determination is YES, this indicates the existence of an abnormality such as a penetration of outside air or a leakage of inside gas, and thus an alarm is indicated at the display portion 6. Subsequently, a power source is turned off in step 10, and the operation proceeds to the next steps, i.e., checking of the device, etc. Further, in the example mentioned above, the laser discharge tube is described as a single piece, but this is not limited to this case, and a plurality of the laser discharge tubes may be used in a parallel arrangement. In the device of Fig. 1, after the switching valve in the medium gas supply pipes is closed and the medium gas exhaust pump is driven, the existence or non-existence of an abnormality of the laser oscillator piping system is detected and displayed based on a determination of whether or not an operation signal of the pressure sensor is generated within a predetermined length of time, and thus the detection and display of the existence or non-existence of an abnormality in the piping system can be appropriately carried out by a relatively simple construction.

Claims: 1. A laser comprising a laser discharge tube (11) for generating laser oscillation in medium gas filled therein; a medium gas supply pipe (217, 218) for supplying a medium gas to the discharge tube (11); a switching valve (26) arranged in the medium gas supply pipe; a pressure sensor (3) connected with the medium gas supply pipe; a medium gas exhaust pump (24) arranged in a medium gas exhaust pipe (215) and driven by a drive device (4) for exhausting the medium gas in the discharge tube; and a control device (7) for controlling the operation of the piping system; characterised by medium gas circulating pipes (211-214) connected with the discharge tube (11) for circulating the medium gas therethrough, and a medium gas circulating pump (23) arranged in the medium gas circulating pipes; and by the control device having signal receiving means (78) for receiving a signal from the pressure sensor, means for detecting the output signal of the pressure sensor for a predetermined length of time and for detecting whether or not the gas pressure indicates the existence or non-existence of an abnormality of the piping system, means (75) for supplying a pump control signal to the drive device (4) for the medium gas exhaust pump, and means (77) for supplying an abnormality signal to a display device (6).

Inventors: IEHISA, NOBUAKI, YAMAZAKI, ETSUO
Applicants: FANUC LTD.
Application year: 1988
Main classification: H01S3
IPC codes: H01S3