Method and control unit for operating a plasma generation apparatus

Abstract

The invention relates to a method and to a control unit for operating the plasma generation apparatus. The invention is based on a method and a control unit in which a voltage is applied as an ignition voltage between an anode and a cathode for ignition of a plasma. In order to enable a gentle operation of the plasma generation apparatus it is provided in accordance with the invention that a check is continuously carried out during the ignition process whether the ignition of the plasma has been effected. Additionally, the ignition voltage (U.sub.Z) is increased starting from an initial ignition voltage (U.sub.ZA) and after recognizing an effected ignition (at the point in time t.sub.Z) of the plasma, the voltage is reduced between the anode and the cathode to a maintenance voltage (U.sub.A).

Claims

1. A method of initiating plasma in an apparatus comprising an anode and a cathode, the method comprising: applying a maintenance voltage between an anode and a cathode; applying an igniting voltage between the anode and the cathode in order to cause ignition of plasma; increasing the igniting voltage; continuously checking to determine whether the ignition of the plasma has occurred; and when ignition of the plasma is determined to have occurred, reducing or stopping the igniting voltage so that the voltage between the anode and the cathode is reduced to the maintenance voltage.

2. The method of claim 1, wherein the igniting voltage increases from a start igniting voltage.

3. The method of claim 2, wherein the start igniting voltage is zero volts.

4. The method of claim 1, wherein the continuously checking comprises measuring a current flow between the anode and the cathode.

5. The method of claim 1, wherein the igniting voltage increases monotonically from a start igniting voltage.

6. The method of claim 1, wherein the ignition voltage increases at a constant rate from a start igniting voltage.

7. The method of claim 1, wherein the applying the igniting voltage comprises applying an increasing igniting voltage via an ignition device.

8. The method of claim 7, wherein, when ignition of the plasma is determined to have occurred, the ignition device is disconnected from the anode and/or the cathode.

9. The method of claim 1, further comprising identifying the anode and the cathode prior to the ignition of the plasma.

10. The method of claim 1, further comprising reading an identification parameter associated with the anode and the cathode prior to the ignition of the plasma.

11. The method of claim 1, further comprising detecting and storing at least one parameter of the anode and the cathode.

12. The method of claim 1, further comprising detecting and storing the igniting voltage associated with the cathode and the anode.

13. The method of claim 1, further comprising at least one of: storing and evaluating an end igniting voltage that is reached upon the ignition of the plasma; and detecting an end igniting voltage that is reached upon the ignition of the plasma.

14. The method of claim 1, further comprising: prior to the ignition of the plasma, comparing a stored parameter associated with the anode and the cathode.

15. The method of claim 1, further comprising: comparing a stored parameter associated with the anode and the cathode; and controlling the maintenance voltage and/or the igniting voltage.

16. The method of claim 1, further comprising: identifying the anode and the cathode; comparing a stored parameter associated with the anode and the cathode; and controlling the maintenance voltage and/or the igniting voltage.

17. A plasma initiation control system comprising: a maintenance voltage source connected to and supplying to a maintenance voltage to an anode and a cathode of a plasma generating apparatus; an ignition voltage source connected to and supplying an igniting voltage to the anode and the cathode; a control unit structured and arranged to continuously check to determine whether ignition of a plasma has occurred, increase the igniting voltage starting from an initial ignition voltage, and detect the ignition of the plasma and stop or reduce the igniting voltage.

18. The plasma initiation control system of claim 17, wherein the maintenance voltage source and an ignition voltage source are separate voltage sources.

19. A plasma initiation control system comprising: a voltage source connected to an anode and a cathode of a plasma generating apparatus; an ignition voltage source connected to the anode and the cathode; a control unit connected to the ignition voltage source and being structured and arranged to each of: continuously check to determine whether ignition of a plasma has occurred, and control the ignition voltage source such that upon detecting the ignition of the plasma, an igniting voltage supplied by the ignition voltage source is reduced or stopped.

20. A method of initiating plasma using a plasma initiation control system comprising a voltage source connected to an anode and a cathode of a plasma generating apparatus, an ignition voltage source connected to the anode and the cathode, and a control unit connected to the ignition voltage source, the method comprising: maintaining a voltage between an anode and a cathode; during the maintaining, applying an increasing igniting voltage between the anode and the cathode; during the applying, continuously checking to determine whether the ignition of the plasma has occurred; and when ignition of the plasma is determined to have occurred, reducing the igniting voltage while maintaining the voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In this connection there is shown:

(2) FIG. 1 shows a schematic illustration of a plasma generation unit; and

(3) FIG. 2 shows an illustration of voltage extents on igniting a plasma generation apparatus in accordance with FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(4) In accordance with FIG. 1, a plasma generation apparatus 10, which can, for example, be configured as a part of a plasma torch of a plant for the plasma coating of substrates, includes an anode-cathode-pair 11 having an anode 12 and a cathode 13 between which a plasma should be formed. On the use of the plasma generation apparatus 10 in a plasma torch a gas flows between the anode 12 and the cathode 13, for example, argon, helium, hydrogen, nitrogen or a mixture thereof, which gas is ionized on the formation of the plasma. For the formation of the plasma either argon or nitrogen is used. Only after an effected ignition other gases are admixed if required.

(5) The anode 12 and the cathode 13 are electrically connected both to a maintenance voltage source 14 and also to an ignition voltage source 15. The maintenance voltage source 14 and the ignition voltage source 15 are controlled by a control unit 16 of the plasma generation apparatus 10. The anode-cathode-pair 11 further has a torch control unit 17 in which, amongst other things an identification parameter in the form of a serial number of the anode-cathode-pair 11 is stored. The torch control unit 17 is in signal communication with the control unit 16, so that the control unit 16 can read out the said serial number and can carry out the control of the maintenance voltage source 14 and/or of the ignition voltage source 15 in dependence of the serial number.

(6) A first switch 18 is arranged between the ignition voltage source 15 and the anode 12 and a second switch 19 is arranged between the ignition voltage source 15 and the cathode 13 by way of which switches the connections between the anode 12 and/or the cathode 13 and the ignition voltage source 15 can be interrupted. The switches 18 and 19 are likewise controlled by the control unit 16.

(7) The extents of an ignition voltage U.sub.Z generated by the ignition voltage source 15 and a maintenance voltage U.sub.A generated by the maintenance voltage source 14 are illustrated on ignition of the plasma in the plasma generation apparatus 10 over time in FIG. 2, wherein the extents are only illustrated qualitatively and not true to scale.

(8) Before the start of the ignition process, the control unit 16 reads the serial number of the anode-cathode-pair 11, this means an identification parameter of the anode-cathode-pair 11, from the torch control unit 17. This information is required, on the one hand, in order to match the course of the ignition process to the currently actually present anode-cathode-pair 11, on the other hand, a parameter of the course of the ignition voltage U.sub.Z is detected up to the effected ignition of the plasma and stored in association with the serial number.

(9) As a preparation of the actual ignition process the constant maintenance voltage U.sub.A is generated at the point in time t0 by the maintenance voltage source 14 which constant maintenance voltage U.sub.A is applied at the anode-cathode-pair 11 and in this way is applied between the anode and the cathode. The maintenance voltage U.sub.A amounts, for example, to approximately 100 V. In as far as the switches 18 and 19 are opened, they are controlled at the point in time t0 such that they are closed and such that the anode-cathode-pair 11 is electrically connected to the ignition voltage source 15.

(10) At the point in time t1, the ignition voltage source 15 starts starting from an initial ignition voltage U.sub.ZA of 0 V to generate the ignition voltage U.sub.Z, which is applied in addition to the maintenance voltage U.sub.A at the anode-cathode-pair 11 and in this way is applied between the anode and the cathode. The ignition voltage U.sub.Z is increased along a straight line having a constant gradient and in this way is increased increasing in a strongly monotonous manner. The used gradient is, in particular selected in dependence on the above-mentioned serial number of the anode-cathode-pair 11. For this purpose, a table is stored in the control unit 16 in which table the gradient of the ignition voltages are associated with the serial numbers.

(11) Starting from the point in time t1, it is furthermore continuously checked whether the ignition of the plasma has been effected. For this purpose a current flowing over the ignition voltage source 15, a so-called ignition current is measured by way of a, not separately illustrated, current measurement device integrated into the ignition voltage source 15. As soon as the ignition current exceeds a pre-determinable current threshold which likewise can depend on the above-mentioned serial number of the anode-cathode-pair 11 it is concluded that the ignition of the plasma has been effected. This is the case at the point of time t.sub.Z in the FIG. 2. As a consequence thereof, the ignition voltage U.sub.Z is abruptly reduced to 0 V so that then only the maintenance voltage U.sub.A is present between the anode 12 and the cathode 13. Moreover, the switches 18 and 19 are controlled, such that they are electrically separated from the ignition voltage source 15.

(12) The final ignition voltage U.sub.ZE is detected by the ignition voltage source 15 and is provided to the control unit 16 which final ignition voltage is generated at the point in time t.sub.Z by the ignition voltage source 15 and in this way is applied between the anode 12 and the cathode 13. The final ignition voltage U.sub.ZE, for example, amounts to between 6 kV and 21 kV. In this connection it can viewed as a parameter of the extent of the ignition voltage UZ up to the effected ignition of the plasma. The final ignition voltage U.sub.ZE is stored in the control unit 16 together with the above-mentioned serial number of the anode-cathode-pair 11.

(13) After the effected ignition of the plasma the control unit 16 evaluates the timely extent of the final ignition voltage U.sub.ZE. For this purpose, the current end ignition voltage U.sub.ZE is compared to a comparison value. When the current end ignition voltage U.sub.ZE deviates by a pre-determinable difference value, for example, amounting to between approximately 5 kV and 30 kV, a conclusion is drawn that a problem exists at the current anode-cathode-pair 11, for example, that too strong a wear is present and a corresponding note is illustrated at a non-separately illustrated screen of the control unit 16.

(14) The said comparison value can be fixedly predefined, for example, for a certain type of anode-cathode-pair. The comparison value can also be configured as the first final ignition voltage determined after the first taking into operation of the current anode-cathode-pair or of the plasma generation apparatus. However, it is also possible to use, as a comparison value, a mean value of a pre-determinable number of final ignition voltages after taking into operation of the current anode-cathode-pair or of the plasma generation apparatus.