DE3532977A1 - Method for stabilizing the output power of a gas laser - Google Patents

Abstract

The invention relates to a method for stabilizing the output power of a laser, especially of a fast-flow CO2 gas-transport laser (10) having laser gas-pressure regulation with a switching difference. In order to compensate for the power fluctuations of a laser having laser gas-pressure regulation, the fluctuations in the laser gas pressure ( DELTA p) are supplied to an adjuster (42) in order to correct the discharge current (i0) (Fig. 1). <IMAGE>

Description

The invention relates to a method for keeping constant the output power of a glass laser according to the generic term of claim 1.

In order to process especially when welding, cutting, Hardening, perforating and drilling workpieces with to achieve a constant quality of work with a gas laser, the output power of the laser during the Machining process to be almost constant.

From DE-OS 19 12 292 a control device for Regulation of the output power of a gas continuous wave laser known to determine the output power Coupled part of the laser beam power and with one Sensor measures. The sensor generates an actual value signal  that is compared with a target value and the one obtained from it Control value for changing the plasma voltage and / or used to change the gas composition.

However, it is necessary in the beam path of the laser To arrange decoupling devices and / or sensors, which on the one hand is expensive to manufacture and assemble are and on the other hand to reduce the Lead laser power.

This interferes with the output power of the laser according to DE-PS 19 50 043 by the simultaneous use a discharge current and sidelight control avoided. The side light signal can also be used Control of the gas pressure can be used.

The invention is based, the performance fluctuations the task a laser with laser gas pressure control compensate.

This task is carried out in a generic method by the characterizing features of claim 1 and in the generic device for implementation of the procedure by the characteristic features of the Claim 5 solved.

Further developments of the invention are in the subclaims specified.

The advantages achieved with the invention are in particular in that a cheap and simple structure Gas pressure regulator with a large switching differential such as a two-point pressure regulator for power control a gas laser can be used. By compensation the switching difference of the laser gas pressure control through a simple and cheap discharge current correction is it possible to have a constant output power or an almost constant output power in a particularly simple manner to achieve the gas laser. In the laser beam arranged sensors or decoupling devices can advantageously eliminated.

An embodiment of the invention is in the drawing shown and is described in more detail below.

Show it

Fig. 1 is a schematic illustration of a gas laser with laser gas pressure control and compensation circuit,

Fig. 2 is a simplified circuit for compensating reduction of the laser output power fluctuations.

In FIG. 1, the schematic construction of a designated 10, axial flow gas transport CO ₂ laser is shown. The laser 10 essentially consists of two laser discharge tubes 11 which are mounted in two end heads 12 and are connected to one another via a connecting head 20 . The end heads 12 and the connection head 20 are connected to a high voltage supply 13 . The positive pole of the high voltage supply 13 is connected to the interior 14 of the end heads 12 and the negative pole of the high voltage supply to the interior 15 of the connecting head 20 .

The laser mirrors arranged in the end heads 12 are denoted by 16 and 17 .

The 100% reflecting mirror 16 and the partially transmissive mirror 17 form the optical resonator. The laser beam 9 emerges from the resonator as light of small divergence through the partially transparent mirror 17 . The laser beam 9 is directed onto a workpiece (not shown) to be machined via deflecting mirrors 8 arranged in the machining head 7 and further optical devices.

A laser gas inlet opening 18, 19 is provided in each of the end heads 12 , via which laser gas is supplied to the discharge tubes 11 in the direction of the arrow 21 . The connection head 20 has a laser gas outlet opening 22 . Gas inlet openings 18 and 19 and the gas outlet opening 22 are connected via lines 23, 24, 25 to a unit 26 for cooling and transporting the laser gas. The cooling / transport unit 26 has a heat exchanger 27 and a gas blower 28 , which is preferably designed as a roots blower. Due to the tangential inflow of the laser gas at the end heads 12 and the suction at the connection head 20 of the preferably self-contained gas circuit, a flow direction against the laser mirror arrangement 16, 17 is achieved and the risk of contamination of the decoupling plate and mirror 16, 17 is thus reduced.

In order to maintain an average pressure within the discharge tubes 11 of approximately 70 mbar, a vacuum pump 29 is connected to the laser gas circuit 30 .

A small amount of laser gas from the gas supply 32 is continuously fed to the gas laser 10 via a line 31 . The laser gas is preferably a helium-nitrogen-carbon dioxide mixture. A throttle 33 (shown schematically in FIG. 1) is arranged within the line 31 and is used to determine the laser gas throughput.

Of course, it is also possible to provide an orifice in line 31 instead of throttle 33 .

A solenoid valve 34 is arranged in line 31 between gas supply 32 and throttle 33 . Of course, it is also possible to arrange the throttle 13 within the solenoid valve 34 or the solenoid valve 34 after the throttle in the line 31 .

Furthermore, a pressure or vacuum measuring cell 35 is connected to the laser gas circuit 30 , which detects the laser gas actual pressure ( p ) and supplies it as an analog value via line 36 to a preferably electronic evaluation device 37 . A measuring transducer is arranged in the evaluation device, by means of which the laser gas pressure ( p ) is converted into an electrical signal corresponding to this pressure. The evaluation device 37 has a minimum and a maximum setpoint adjuster 38, 39 , at which two threshold values are specified as comparison variables. A threshold value P ₂ ≦ λτ p _{o is} predefined on the minimum setpoint adjuster, p _o corresponding to the laser gas target pressure.

The totalizer or the setpoint adjuster with the two positions (minimum, maximum) opens and closes the solenoid valve 34 via control line 40 , so that the laser gas pressure always fluctuates between the minimum setpoint and the maximum setpoint, so that p ₁ p p ₂ is always , ie p _o cannot be reached exactly due to the switching difference / hysteresis.

The greater the switching difference (difference between the top and bottom laser gas pressure values) of the laser gas pressure control 35, 37, 40, 34, 31 , the greater the fluctuations in the output power of the laser beam 9 .

To compensate for the resulting difference by the switching of the processing unit 37 fluctuations of the laser output power, the pressure or Vakuummeßzelle 35 with interposition of a compensating circuit 4 is preferably connected to the phaser of the high voltage power supply. 13 Via the adjuster 42 , which is not shown in any more detail, the discharge current is changed as a function of the laser gas actual pressure ( p ) by means of a manipulated variable generated in the compensation circuit 14 .

The compensation circuit 41 according to one embodiment of the invention consists of a summer 43 connected to the pressure or vacuum measuring cell 35 , the non-inverting input 44 of which is connected to the measuring cell 35 with the interposition of a measuring transducer 47 and the inverting input 45 of which is connected to an adjuster 46 . A current signal corresponding to the target laser gas pressure ( p _o ) is set on the adjuster 46 and fed to the summer 43 .

The summer 43 is preferably designed as a voltage summer and a voltage signal corresponding to the desired laser gas pressure ( p _o ) is set on the adjuster 46 . This voltage signal can be generated by the evaluation device 37 instead of by the adjuster 46 , corresponding to the set pressure p _o .

In the summer 43 , the target laser gas pressure voltage is compared with the actual laser gas pressure voltage and an output signal corresponding to the differential pressure of the laser gas is formed. The output signal is fed via the output 48 to the input 49 of a computing element 50, preferably a multiplier.

Of course, it is also possible to connect the computing element 50 directly to the evaluation device 37 . This advantageously makes it possible to carry out the comparison between the pressure setpoint and the actual pressure value in the evaluation device 37 and to supply an output signal corresponding to the pressure difference to the input 49 .

The computing element 50 is connected via the input 51 to an adjuster 53 for the discharge current setpoint and via the input 52 to an adjuster 54 for the reciprocal input of a voltage value corresponding to the laser gas setpoint pressure (1 / p _o ). Instead of the adjuster 54 , a computing element (diode) can also be used, which generates the signal 1 / p _o from the pressure setpoint present in the evaluation device 37 . The discharge current setpoint is preferably entered as a voltage value u _o on the adjuster 53 . This adjuster 53 can be the same adjuster that specifies the discharge current value when the method of high-voltage supply 13 described here is not used.

In the arithmetic unit 50, the values input according to the arithmetic operation are - u _o / p _o × Δ p linked, preferably multiplied, so that at the output 55 of the arithmetic device 50 - Δ u is present. The output 55 of the arithmetic element 50 is connected to the inverting input 57 of a summer 56 , the non-inverting input 58 of which is connected to the adjuster 53 for the discharge current setpoint. In the summer 56 - Δ u and u _o are compared with one another, so that u is present at the output 59 of the summer 56 . The output 59 is connected to the adjuster of the high voltage with the interposition of an amplifier 60 which has the amplification factor c _i . The high voltage supply can be designed as a direct or alternating current supply.

The measured pressure deviation is compensated for via the adjuster 42 with the aid of an adapted discharge current correction. The method can advantageously be used both in continuous wave (CW) operation and in pulse operation. Of course, the method can also be used for any other pressure control and in addition to any other line control or compensation device. The device described above for compensating the switching difference of a laser gas pressure control is based on the consideration that the laser power is a function of the laser gas pressure and discharge current according to the equation

P _L = f ( p, i )

is.

This function can be approximated in other areas are considered as

P _L ∼ c · i

If you consider small deviations from the nominal value ₀ (see above), the following results:

dP = c · p · di · + c · i · dp

For

I.e. small corrections of the discharge current value largely compensate for the laser gas pressure fluctuations that arise due to the switching difference of the laser gas pressure regulator. As already mentioned above, the discharge current is set via a voltage specification, so that is.

If it is not necessary to fully compensate for the error, the compensation circuit 41 is simplified in accordance with FIG. 2. In FIG. 2, the same reference numbers have been used for the same components as in FIG. 1. Different from the embodiment according to Fig. 1 54, an amplifier 61 having the gain k, is connected between the summing unit 43, 56 rather than the computing element 50 with adjusters 53. The input 62 of the amplifier 61 is connected to the output 48 of the summer 43 and the output 63 of the amplifier 61 to the inverting input 47 of the summer 56 .

The compensation circuit 41 according to FIG. 2 is based on the following arithmetic operation.

If you choose k so that it holds

u _{o 1 O}  =p _O  ·k  u _{o 2},in whichu _{o 1} andu _{o 2}

the limits of the adjustment range (a laser of the described Type can usually be within a setting range of 10% operated up to 100% of its maximum output. It However, there are often applications where the performance is only in a restricted area, e.g. B. 50% to 100% is varied), the accuracy corresponds to _O  =p _O  ·k that of the 1st circuit. So it does increase proportionally with the distanceu _O  - _O  but gives up to certain  Limits still an improvement in the overall result. The limit is reached when throughΔ u one in amount same, but signed reverse deterioration as byΔ p arises. If one looks at this approximately, it results yourself

In the following, these limits and the improvements made by the simplified compensation circuit 41 are explained by examples.

1st example

Comparisons of the change in performance result in the following values

a) only pressure change results in a change in performance of

b) Power change with current correction at Δ p = 10 mbar, Δ u = -0.2 and u _o = 1V Δ P _L is 0.1 · p _o in both cases _, ie there is no improvement in the lowest setting range.
With u _o = 2 K we get and at u _o = 10 V

This shows that over a very large range improvements can be achieved with this method. By the adaptation of _O  atu _O  can the deviations for the be optimized for the respective application.

The closer the relationshipu _{o 1}/u _{o 2} is 1 and the smaller the Pressure fluctuations are, the more precise the simplified Circuit. The more you get from the above specified relationship for _O  come off. This will then change the relationship approach.

2nd example

with u _{o 1} = 5 V, u _{o 2} = 10 V, p _o = 100 mbar and Δ p = +5 mbar

Comparisons of the change in performance now result in the following values:

a) The change in pressure without current correction results in a change in output of

b) With current correction, there is a change in output of u _o = 5 V at and at u _o = 10 V from

With an optimization of _O  can in this case the 5% misprints to about 2% performance errors overall Adjustment range can be reduced, d. H. the simplified Circuit will suffice in most cases.

Claims (12)

1. A method for keeping the output power of a gas laser constant, in particular a fast-flowing CO ₂ gas transport laser with a laser gas pressure control with switching differential, characterized in that the fluctuations in the laser gas pressure ( Δ p ) an adjuster ( 42 ) for correcting the discharge current ( i _o ) are fed. 2. The method according to claim 1, characterized in that the power deviation of the discharge current ( i _o ) caused by the laser gas pressure fluctuations ( Δ p ) according to the condition is compensated for
Δ i = discharge current difference
i _o = discharge current setpoint
p _o = target laser gas pressure
Δ p = laser gas pressure difference 3. The method according to claim 1 or claim 2, characterized in that the discharge current difference ( Δ i ) is set via a voltage specification after termination i _o = c _i · u _o , so that
is. 4. The method according to claim 3, characterized, that the discharge current (i _O ) according to the condition  = -K ·Δ p +u _O  is set.
in whichu _{o 1   O}   u _{o 2} is so that
u _O  the manipulated variable for approx. 10% or more laser power andu _{o 2}  is the manipulated variable for 100% or less laser power. 5. Device for performing the method according to one of claims 1 to 4, characterized in that the laser gas pressure control ( 32, 34, 37 ) has a pressure sensor ( 35 ) which, with the interposition of a compensation circuit ( 41 ) on the adjuster ( 42 ) the high voltage supply ( 13 ) is connected. 6. Device according to claim 5, characterized in that the compensation circuit ( 41 ) has a computing element ( 50 ), the inputs ( 49, 51, 52 ) with adjusters ( 53, 54 ) for u _o and 1 / p _o and with the Output ( 48 ) of a summer ( 43 ) for Δ p and its output ( 55 ) is connected to the inverting input ( 57 ) of a comparator ( 56 ). 7. Device according to claim 5 or claim 6, characterized in that the non-inverting input ( 58 ) of the summer ( 56 ) with the u _o adjuster ( 53 ) and the output ( 59 ) of the summer ( 56 ) with the interposition of an amplifier ( 60 ), which has the gain factor c _i , is connected to the adjuster ( 42 ). 8. Device according to one of claims 3 to 5, characterized in that the compensation circuit ( 41 ) has an amplifier ( 61 ) with the gain factor k , the input ( 62 ) with the output ( 48 ) of a summer ( 43 ) for Δ p and whose output ( 63 ) is connected to the inverting input ( 57 ) of a summer ( 56 ). 9. Device according to claim 8, characterized in that the non-inverting input ( 58 ) of the summer ( 56 ) with the u _o adjuster ( 53 ) and the output ( 59 ) of the summer ( 56 ) with the interposition of an amplifier ( 60 ) which has the gain factor c _i , is connected to the adjuster ( 42 ). 10. Device according to one of claims 1 to 9, characterized in that the adjuster present on a laser for the discharge current or the laser power is used as the u _o adjuster ( 53 ). 11. Device according to one of claims 1 to 10, characterized in that the 1 / p _o adjuster ( 54 ) is a computing element (dioidizer). 12. Device according to one of claims 1 to 11, characterized in that a signal corresponding to the pressure difference is generated in the evaluation device ( 37 ).