Plasma generating device

Abstract

This plasma generating device comprises a power supply device, a load, a measurement circuit, and a determination unit. The power supply device comprises a resonance circuit. The load is a member connected to the power supply device, and power output from the power supply device is supplied to an electrode of a plasma head that generates plasma. The measurement circuit measures the output voltage of the resonance circuit. The determination unit causes the power supply device to apply power at a voltage level at which discharge does not occur between the electrodes to the load for a predetermined time, and determines whether or not the output voltage measured by the measurement circuit falls within an allowable range indicating that the load is normal.

Description

Plasma generator

[0001] This specification discloses a technology related to a plasma generator.

[0002] The plasma generator described in Patent Document 1 includes a determination processing unit and a tuning processing unit. The determination processing unit determines a power abnormality based on a detected power value detected by a detection device and a reference power value when generating plasma. The tuning processing unit executes an operation of generating plasma by discharging an electrode, and determines a reference power value based on the executed result.

[0003] International Publication No. 2021 / 214876

[0004] A resonance circuit is used in the power supply device of the plasma generator, and the voltage applied to the electrodes of the plasma head is likely to fluctuate due to the load connected to the power supply device. When the voltage applied to the electrodes of the plasma head is lower than the allowable range, discharge does not start at the electrodes, and it may be difficult to generate plasma. Conversely, when the voltage applied to the electrodes of the plasma head is higher than the allowable range, an overvoltage state occurs, and there is a possibility of equipment failure. The latter can be solved by increasing the withstand voltage of the equipment, but there is a possibility of increasing the size and cost of the equipment to ensure insulation.

[0005] In view of such circumstances, this specification discloses a plasma generator capable of determining the presence or absence of an abnormality in a load connected to a power supply device.

[0006] This specification discloses a plasma generator including a power supply device, a load, a measurement circuit, and a determination unit. The power supply device includes a resonance circuit. The load is a member connected to the power supply device and supplies the power output from the power supply device to the electrodes of a plasma head that generates plasma. The measurement circuit measures the output voltage of the resonance circuit. The determination unit applies the power at a voltage level at which no discharge occurs between the electrodes from the power supply device to the load for a predetermined time, and determines whether the output voltage measured by the measurement circuit is included in an allowable range indicating that the load is normal.

[0007] Furthermore, this specification discloses a technical concept in which, in claim 5 of the claims initially attached to the application (hereinafter referred to as the "original claims"), "the plasma generator described in claim 1" is changed to "the plasma generator described in any one of claims 1 to 4". In addition, in claim 10 of the original claims, a technical concept is disclosed in which "the plasma generator described in claim 9" is changed to "the plasma generator described in any one of claims 1 to 9".

[0008] According to the plasma generator described above, by applying power to the load at a voltage level that does not cause a discharge between the electrodes of the plasma head, it is possible to determine whether or not there is an abnormality in the load connected to the power supply unit.

[0009] This is a schematic diagram showing an example configuration of a plasma generator. This is a schematic diagram showing an example electrical configuration of a plasma generator. This is a block diagram showing an example control block of a plasma generator. This is a flowchart showing an example control flow by a plasma generator. This is a block diagram showing an example control block including a measurement circuit. This is a circuit diagram showing an example measurement circuit. This is a schematic diagram showing an example voltage level. This is a flowchart showing an example of derivation of a specific range. This is a schematic diagram showing an example of output adjustment of a power supply.

[0010] 1. Embodiment 1-1. Example of Plasma Generator 1 Configuration The plasma generator 1 of this embodiment is an atmospheric pressure plasma generator that generates plasma at atmospheric pressure. As shown in Figure 1, the plasma generator 1 comprises a plasma head 10, a power supply unit 20, a gas supply unit 30, gas piping 31, a control device 40, a robot 50, a housing 60, a cover 70, and a power cable 80.

[0011] The plasma generator 1 supplies power to the plasma head 10 from the power supply unit 20 via the power cable 80. The plasma generator 1 also supplies the process gas to be plasma-generated from the gas supply unit 30 via the gas piping 31. As a result, the plasma generator 1 can irradiate the plasma head 10 with plasma gas.

[0012] The power supply unit 20 supplies power to the plasma head 10, which generates plasma. The power supply unit 20 can use a high-frequency power supply capable of generating plasma. As shown in Figure 2, the power supply unit 20 includes a converter 21, an inverter 22, a resonant circuit 23, a boost converter 24, and a terminal block 25. The converter 21 converts AC power, such as commercial power, into DC power. The inverter 22 converts the DC power output from the converter 21 into AC power. The resonant circuit 23 smooths the AC power output from the inverter 22. The boost converter 24 boosts the AC power smoothed by the resonant circuit 23 to generate power to supply to the plasma head 10.

[0013] The power supply unit 20 only needs to be able to supply power to the plasma head 10, and any known power equipment can be used. For example, the inverter 22 can be an inverter having multiple (e.g., four) bridged switching elements. The resonant circuit 23 can be a resonant circuit having an inductor and a capacitor. The boost converter 24 can be a transformer. As shown in Figure 2, the transformer has a primary winding 24a and a secondary winding 24b.

[0014] The transformer boosts the AC power input to the primary winding 24a (AC power smoothed by the resonant circuit 23) and outputs the boosted AC power from the secondary winding 24b. For example, the output voltage of the AC power output from the secondary winding 24b is approximately 15kV at most. The output voltage at the start of discharge is approximately 10kV to 12kV (RMS). When the output voltage exceeds the above voltage at the start of discharge, continuous discharge occurs between the electrodes, and the output voltage decreases to approximately 2kV to 4kV (RMS) during plasma generation. Note that even if the output voltage does not exceed the above voltage at the start of discharge and an output voltage of approximately 2kV to 4kV (RMS) is maintained, discharge will not start. In this way, the power supply 20 can output AC power ranging from several thousand volts to tens of thousands of volts. The power supply 20 can also output AC power with frequencies ranging from several kilohertz to tens of kilohertz.

[0015] As shown in Figure 2, the terminal block 25 includes an input terminal section 25a, an input terminal section 25b, an output terminal section 25c, and an output terminal section 25d. One end of the secondary winding 24b, the output end 24b1, is connected to the input terminal section 25a. The other end of the secondary winding 24b, the output end 24b2, is connected to the input terminal section 25b.

[0016] Furthermore, one end 80a of the power cable 80 in the axial direction is connected to the output terminals 25c and 25d. The other end 80b of the power cable 80 in the axial direction is connected to electrodes 10a and 10b provided on the plasma head 10. The housing 10h of the plasma head 10, which is electrode 10b, is formed in a cylindrical shape and is arranged to surround electrode 10a, which is provided inside electrode 10b.

[0017] The gas supply device 30 pumps and supplies a process gas containing at least one of an inert gas (e.g., nitrogen) and an active gas (e.g., oxygen) (e.g., air, dry air, etc.). For this reason, the gas supply device 30 is equipped with a tank for storing the process gas. The gas supply device 30 may also be equipped with a heater to heat the process gas supplied to the plasma head 10 as needed.

[0018] In this case, the gas supply device 30 can, for example, supply process gas heated by a heater to the plasma head 10. Alternatively, the gas supply device 30 can also mix unheated process gas supplied from a tank with process gas heated by a heater and supply the mixture to the plasma head 10.

[0019] The control device 40 drives and controls the plasma generator 1. As shown in Figure 1, the power cable 80 and gas piping 31 are mounted along the robot arm 51 of the robot 50. The plasma head 10 is attached to the tip of the robot arm 51. The robot arm 51 has multiple (two in the figure) arm sections 51a connected in one direction. In other words, the robot 50 is a multi-joint robot. The robot 50 is driven and controlled by the control device 40. Specifically, the robot 50 drives the robot arm 51 based on commands from the control device 40 to move the plasma head 10 and irradiate the workpiece W0 supported on the worktable D0 with plasma gas.

[0020] As shown in Figure 1, the plasma head 10 is fixed to the housing 60 at its base end and covered by a cover 70 at its tip end. An opening 71 is provided at the tip of the cover 70 for irradiating the plasma gas generated by the plasma head 10. The plasma head 10 generates plasma gas by plasmaizing a process gas using power supplied from the power supply unit 20. The plasma head 10 irradiates the surface of the workpiece W0 with the generated plasma gas. The plasma gas irradiated onto the surface of the workpiece W0 can be used for various surface treatments of the workpiece W0, such as a modification treatment that changes the surface of the workpiece W0 from hydrophobic to hydrophilic.

[0021] 1-2. The abnormal load 90 connected to the power supply unit 20 is a component connected to the power supply unit 20 that supplies power output from the power supply unit 20 to the electrodes 10a and 10b of the plasma head 10 that generates plasma. The load 90 only needs to be connected to the power supply unit 20 and be able to supply power as described above, and can include various components. As shown in Figure 2, the load 90 includes a power cable 80 that transmits power from the power supply unit 20 to the electrodes 10a and 10b of the plasma head 10.

[0022] The power cable 80 has multiple (two) wires 81, which transmit power output from the power supply unit 20 to the electrodes 10a and 10b of the plasma head 10. One of the multiple (two) wires 81 is designated as wire 81f, and the other wire 81 is designated as wire 81s. Electrode 10a, one of the wires 81f of the power cable 80, and one output end 24b1 of the booster 24 are electrically connected. Also, electrode 10b, the other wire 81s of the power cable 80, the other output end 24b2 of the booster 24, and the housing 20a of the power supply unit 20 are electrically connected and grounded. In the figure, the grounded state is indicated by the symbol E0 (the same applies in Figure 1).

[0023] As shown in Figure 2, a resonant circuit 23 is used in the power supply unit 20 of the plasma generator 1, and the voltage applied to the electrodes 10a and 10b of the plasma head 10 is prone to fluctuations depending on the load 90 connected to the power supply unit 20. If the voltage applied to the electrodes 10a and 10b of the plasma head 10 is lower than the allowable range, discharge may not start at the electrodes 10a and 10b, making plasma generation difficult. Conversely, if the voltage applied to the electrodes 10a and 10b of the plasma head 10 is higher than the allowable range, an overvoltage condition may occur, potentially causing equipment failure. The latter can be solved by increasing the voltage withstand capability of the equipment, but this may result in larger equipment and increased costs in order to ensure insulation.

[0024] Therefore, the plasma generator 1 applies power to the load 90 at a voltage level that does not cause a discharge between electrodes 10a and 10b, and determines whether or not there is an abnormality in the load 90 connected to the power supply unit 20. Specifically, as shown in Figures 2 and 3, the plasma generator 1 comprises a power supply unit 20, a load 90, a measurement circuit 100, and a determination unit 200. The plasma generator 1 may also include a specific unit 300. The plasma generator 1 may also include an adjustment unit 400. The plasma generator 1 of this embodiment comprises a power supply unit 20, a load 90, a measurement circuit 100, a determination unit 200, a specific unit 300, and an adjustment unit 400.

[0025] The determination unit 200, the identification unit 300, and the adjustment unit 400 can be provided in various control devices, management devices, computing devices, etc. For example, at least one of the determination unit 200, the identification unit 300, and the adjustment unit 400 can be provided in the control device 40. At least one of the determination unit 200, the identification unit 300, and the adjustment unit 400 can also be provided in a control device, management device, computing device, etc. outside the plasma generator 1. At least one of the determination unit 200, the identification unit 300, and the adjustment unit 400 can also be formed on the cloud. As shown in Figure 3, in this embodiment, the determination unit 200, the identification unit 300, and the adjustment unit 400 are provided in the control device 40.

[0026] Furthermore, the plasma generator 1 performs control according to the flowchart shown in Figure 4. The measurement circuit 100 performs the process shown in step S11. The determination unit 200 performs the determination and processing shown in steps S12 and S13. The identification unit 300 performs the process shown in step S14. The adjustment unit 400 performs the process shown in step S15. Note that the matters described in this specification can be selected and applied as appropriate. Also, the matters described in this specification can be combined as appropriate.

[0027] 1-2-1. Measurement Circuit 100 and Judgment Unit 200 The measurement circuit 100 measures the output voltage V0 of the resonant circuit 23. The measurement circuit 100 can also measure both the output voltage V0 and the output current I0 of the resonant circuit 23 (step S11 shown in Figure 4). The measurement circuit 100 only needs to be able to measure the output voltage V0 of the resonant circuit 23 and can take various forms. For example, as shown in Figure 5, the measurement circuit 100 is provided between the resonant circuit 23 and the boost converter 24 and can include a voltage measurement circuit 101 and a current measurement circuit 102. The voltage measurement circuit 101 measures the output voltage V0 of the resonant circuit 23. The current measurement circuit 102 measures the output current I0 of the resonant circuit 23.

[0028] As previously described, the resonant circuit 23 is provided in the power supply unit 20 and smooths the AC power output from the inverter 22. The resonant circuit 23 can take various forms. For example, as shown in Figure 6, the resonant circuit 23 can include an inductor 23a and a capacitor 23b. Specifically, one end of the inductor 23a is connected to one output end of the inverter 22, and the other end of the inductor 23a is connected to one end of the capacitor 23b. The other end of the capacitor 23b is connected to another output end of the inverter 22.

[0029] As shown in Figure 6, in this embodiment, the voltage measurement circuit 101 and the current measurement circuit 102 are formed in a known integrated circuit capable of measuring the output voltage V0 and output current I0. The other end of the inductor 23a and one end of the capacitor 23b are connected to one input terminal of the integrated circuit, and the other end of the capacitor 23b is connected to another input terminal of the integrated circuit. As a result, the measurement circuit 100 can measure the output voltage V0, which corresponds to the terminal voltage of the capacitor 23b, and the output current I0, which corresponds to the current flowing through the inductor 23a. One output terminal of the integrated circuit is connected to one end of the primary winding 24a of the boost converter 24. The other output terminal of the integrated circuit is connected to the other end of the primary winding 24a of the boost converter 24.

[0030] As previously described, if the voltage applied to the electrodes 10a and 10b of the plasma head 10 becomes overvoltage, equipment failure may occur. Therefore, the determination unit 200 applies power from the power supply unit 20 to the load 90 for a predetermined time at a voltage level that does not cause discharge between the electrodes 10a and 10b. The determination unit 200 then determines whether the output voltage V0 measured by the measurement circuit 100 falls within the allowable range TR0 that indicates the load 90 is normal. The determination unit 200 can also determine whether at least the output voltage V0 among the output voltage V0 and output current I0 measured by the measurement circuit 100 falls within the allowable range TR0 that indicates the load 90 is normal (step S12 shown in Figure 4).

[0031] The determination unit 200 only needs to be able to apply power to the load 90 at a voltage level that does not cause discharge between electrodes 10a and 10b, and the voltage level is not limited. However, if the voltage level becomes extremely low, the error in the pulse width of the pulse control (e.g., PWM control) by the inverter 22 will increase, which may adversely affect the output power of the power supply unit 20. Therefore, for example, if the voltage level at which discharge occurs between electrodes 10a and 10b is about 10 to 12 kV (effective value), it is preferable to set the voltage level at which discharge does not occur between electrodes 10a and 10b to about 2 to 4 kV (effective value).

[0032] Similarly, the predetermined time for applying power to the load 90 at a voltage level that does not cause discharge between electrodes 10a and 10b is not limited. However, if the predetermined time is extremely short, the measurement accuracy of the output voltage V0 and output current I0 may decrease. Therefore, for example, the predetermined time should be about 100 ms. The measurement of the output voltage V0 and output current I0 when deriving the specific range SR0 described later is also similar, and for example, the predetermined time should be about 100 ms. In other words, the predetermined time for applying power to the load 90 at a voltage level that does not cause discharge between electrodes 10a and 10b should be about 200 ms in total, for example.

[0033] The determination unit 200 can determine that the load 90 is abnormal and stop the output of the power supply unit 20 if the output voltage V0 is not included in the allowable range TR0. In other words, the determination unit 200 can determine that the load 90 is normal and allow the output of the power supply unit 20 if the output voltage V0 is included in the allowable range TR0. Furthermore, the determination unit 200 can also determine that the load 90 is abnormal and stop the output of the power supply unit 20 if at least the output voltage V0 of the output voltage V0 and output current I0 is not included in the allowable range TR0 (if the answer is No in step S12 shown in Figure 4) (step S13). In other words, the determination unit 200 can also determine that the load 90 is normal and allow the output of the power supply unit 20 if at least the output voltage V0 of the output voltage V0 and output current I0 is included in the allowable range TR0 (if the answer is Yes in step S12).

[0034] The tolerance range TR0 only needs to be able to determine whether or not there is an abnormality in the load 90, and can be set arbitrarily. For example, Figure 7 shows an example of the voltage level of the output voltage V0. When the output voltage V0 is smaller than the lower limit VD0 of the tolerance range TR0, the output voltage V0 has dropped to a voltage level where discharge is not possible. Conversely, when the output voltage V0 is larger than the upper limit VU0 of the tolerance range TR0, if power at a voltage level that causes discharge between electrodes 10a and 10b is applied to the load 90, an overvoltage condition occurs, and the output voltage V0 rises to a voltage level equivalent to the overvoltage.

[0035] In either case, the power supply unit 20 is functioning normally, and the problem is caused by an abnormality in the load 90. Thus, the determination unit 200 can determine whether or not there is an abnormality in the load 90 by applying power to the load 90 at a voltage level that does not cause discharge between electrodes 10a and 10b, before applying power to the load 90 at a voltage level that causes discharge between electrodes 10a and 10b. Therefore, the determination unit 200 can stop the output of the power supply unit 20 before an overvoltage is applied between electrodes 10a and 10b of the plasma head 10.

[0036] Furthermore, the determination unit 200 can stop the output of the power supply unit 20 and notify the operator of an abnormality in the load 90 (step S13). For example, the determination unit 200 can notify the operator of an abnormality in the load 90 on the operation panel of the plasma generator 1 operated by the operator. This allows the operator to become aware of the abnormality in the load 90 and take action to address it. The abnormality in the load 90 is not limited to, but examples of abnormalities in the load 90 include short circuits, open circuits, and disconnections of the power cable 80. When an abnormality in the load 90 is notified, the operator can check the condition and connection status of the power cable 80 and take action such as replacing the power cable 80 or making appropriate connections.

[0037] 1-2-2. Identification Unit 300 and Adjustment Unit 400 As previously described, the determination unit 200 can determine whether or not there is an abnormality in the load 90 by applying power to the load 90 at a voltage level that does not cause discharge between electrodes 10a and 10b. However, when the load 90 is normal, it is difficult for the determination unit 200 to grasp the range of variation (variation) for each load 90 within the allowable range TR0 of the output voltage V0.

[0038] Therefore, the identification unit 300 derives a specific range SR0 (step S14) when the determination unit 200 determines that at least the output voltage V0 is included in the allowable range TR0 and the load 90 is normal (when the result is Yes in step S12 shown in Figure 4). The specific range SR0 is a predetermined range within the allowable range TR0 of the output voltage V0 that includes the output voltage V0 measured by the measurement circuit 100. The identification unit 300 only needs to be able to derive a specific range SR0 and can take various forms.

[0039] For example, as shown in Figure 7, the specific unit 300 can divide the allowable range TR0 of the output voltage V0 into multiple ranges and derive the divided range that includes the output voltage V0 measured by the measurement circuit 100 as the specific range SR0. In the example shown in the figure, the allowable range TR0 of the output voltage V0 is divided into n equal parts (where n is any natural number greater than or equal to 2), and is divided into multiple (n) ranges. In the figure, for example, the output voltage V0 measured by the measurement circuit 100 is greater than the first threshold TH(1) and less than or equal to the second threshold TH(2), and the second range from the lower limit VD0 of the allowable range TR0 is shown as the specific range SR0.

[0040] The specific unit 300 only needs to be able to derive a specific range SR0, and can take various forms. For example, the specific unit 300 can derive a specific range SR0 by searching through the divided ranges in order from the lower limit range DR0 which includes the lower limit value VD0 of the allowable range TR0 of the output voltage V0. Figure 8 shows an example of the derivation of the specific range SR0 in this case.

[0041] First, the specifying unit 300 determines whether the output voltage V0 measured by the measuring circuit 100 is greater than the first threshold TH(1) shown in FIG. 7 (step S14a). When the output voltage V0 measured by the measuring circuit 100 is less than or equal to the first threshold TH(1) (No in step S14a), the specifying unit 300 sets the output of the power supply device 20 to the first setting (step S14b).

[0042] When the output voltage V0 measured by the measuring circuit 100 is greater than the first threshold TH(1) (Yes in step S14a), the specifying unit 300 determines whether the output voltage V0 measured by the measuring circuit 100 is greater than the second threshold TH(2) shown in FIG. 7 (step S14c). When the output voltage V0 measured by the measuring circuit 100 is less than or equal to the second threshold TH(2) (No in step S14c), the specifying unit 300 sets the output of the power supply device 20 to the second setting (step S14d).

[0043] Hereinafter, similarly, the specifying unit 300 determines whether the output voltage V0 measured by the measuring circuit 100 is greater than the (n - 2)-th threshold TH(n - 2) shown in FIG. 7 (step S14e). When the output voltage V0 measured by the measuring circuit 100 is less than or equal to the (n - 2)-th threshold TH(n - 2) (No in step S14e), the specifying unit 300 sets the output of the power supply device 20 to the (n - 2)-th setting (step S14f).

[0044] When the output voltage V0 measured by the measuring circuit 100 is greater than the (n - 2)-th threshold TH(n - 2) (Yes in step S14e), the specifying unit 300 determines whether the output voltage V0 measured by the measuring circuit 100 is greater than the (n - 1)-th threshold TH(n - 1) shown in FIG. 7 (step S14g). When the output voltage V0 measured by the measuring circuit 100 is less than or equal to the (n - 1)-th threshold TH(n - 1) (No in step S14g), the specifying unit 300 sets the output of the power supply device 20 to the (n - 1)-th setting (step S14h).

[0045] When the output voltage V0 measured by the measurement circuit 100 is greater than the (n - 1)-th threshold TH(n - 1) (Yes in step S14g), the output voltage V0 measured by the measurement circuit 100 is not more than the n-th threshold TH(n) shown in FIG. 7. The n-th threshold TH(n) corresponds to the upper limit value VU0 of the aforementioned allowable range TR0. Then, the specifying unit 300 sets the output of the power supply device 20 to the n-th setting (step S14i).

[0046] In the example shown in FIG. 7, the output voltage V0 measured by the measurement circuit 100 is greater than the first threshold TH(1) and not more than the second threshold TH(2), and the specifying unit 300 sets the output of the power supply device 20 to the second setting (step S14d). Also, the output setting of the power supply device 20 defines the voltage level of the power output from the power supply device 20 to the load 90 when power at a voltage level at which discharge occurs between the electrodes 10a and 10b is applied to the load 90. Similarly, the specifying unit 300 can also derive the specific range SR0 by searching in order the divided ranges from the upper limit range UR0 including the upper limit value VU0 of the allowable range TR0 of the output voltage V0.

[0047] As described above, the specifying unit 300 can derive the specific range SR0 by searching in order the divided ranges from the upper limit range UR0 including the upper limit value VU0 of the allowable range TR0 of the output voltage V0 or from the lower limit range DR0 including the lower limit value VD0 of the allowable range TR0 of the output voltage V0. Also, the specifying unit 300 can also derive the specific range SR0 by performing a binary search on the divided ranges from the central range including the median value of the allowable range TR0 of the output voltage V0 toward the upper limit range UR0 side or the lower limit range DR0 side.

[0048] As described above, for example, when the voltage level at which discharge occurs between the electrodes 10a and 10b is about 10 to 12 kV (effective value), the voltage level at which no discharge occurs between the electrodes 10a and 10b can be about 2 to 4 kV (effective value). For the sake of simplicity of explanation, for convenience of explanation, the voltage level at which no discharge occurs between the electrodes 10a and 10b is set to 1 / k of the voltage level at which discharge occurs between the electrodes 10a and 10b (k is a real number).

[0049] For example, the specific unit 300 sets the output of the power supply unit 20 to generate an output voltage V0 obtained by multiplying the voltage in the lower limit range DR0, which includes the lower limit value VD0, by k (hereinafter referred to as the voltage coefficient as appropriate). This applies a voltage to the load 90 at a voltage level that causes discharge between electrodes 10a and 10b. The same applies to other divided ranges (second setting to nth setting).

[0050] Furthermore, the electrical and magnetic characteristics of the actual boost converter 24 have nonlinear components. Therefore, it is advisable to obtain the above-mentioned voltage coefficients for each defined range in advance through simulation or verification using the actual device, and then set the output of the power supply unit 20. Also, as shown in Figure 9, the voltage level of the output power of the power supply unit 20 described above is smallest in the first setting, and increases gradually from the first setting to the nth setting, reaching the maximum in the nth setting. Thus, there is a range of variation (variation) in the voltage of the output power of the power supply unit 20.

[0051] Therefore, when the adjustment unit 400 applies power at a voltage level that generates a discharge between electrodes 10a and 10b from the power supply unit 20 to the load 90, it is preferable to adjust the output of the power supply unit 20 based on the specific range SR0 derived by the specific unit 300 (step S15 shown in Figure 4). This allows the adjustment unit 400 to reduce the voltage fluctuation range (variation) of the output power of the power supply unit 20.

[0052] Specifically, when the specific range SR0 derived by the specific unit 300 is included in the lower limit range DR0, the adjustment unit 400 sets the output of the power supply unit 20 so that an output voltage V0 is generated which is the voltage of the lower limit range DR0 multiplied by k (first setting). Also, when the specific range SR0 derived by the specific unit 300 is included in the upper limit range UR0, the adjustment unit 400 sets the output of the power supply unit 20 so that an output voltage V0 is generated which is the voltage of the upper limit range UR0 multiplied by k (nth setting). The same applies to other divided ranges, and the adjustment unit 400 sets the output of the power supply unit 20 so that an output voltage V0 is generated which is the voltage of the corresponding range multiplied by k.

[0053] In the example shown in Figure 9, the specific range SR0 derived by the specific unit 300 is one range above the lower limit range DR0. Therefore, the adjustment unit 400 sets the output of the power supply unit 20 so that an output voltage V0 is generated which is the voltage in the range one range above the lower limit range DR0 multiplied by k (second setting). As a result, the adjustment unit 400 can limit the output range of the output voltage of the power supply unit 20, and the voltage fluctuation range (variation) of the output power of the power supply unit 20 is reduced.

[0054] Furthermore, for example, the greater the variation (tolerance) in the electrical characteristics of the inductor 23a of the resonant circuit 23, the more likely the voltage fluctuation range of the output power of the power supply unit 20 will increase. Similarly, the greater the variation (tolerance) in the processing dimensions (for example, the length of the power cable 80) of the power cable 80 included in the load 90, the greater the variation (tolerance) in the electrical characteristics of the power cable 80, and the more likely the voltage fluctuation range of the output power of the power supply unit 20 will increase. In this way, the voltage fluctuation range of the output power of the power supply unit 20 is likely to increase due to variations in the electrical characteristics of at least one of the resonant circuit 23 and the load 90. In this case, reducing the above-mentioned tolerances can reduce the voltage fluctuation range of the output power of the power supply unit 20, but this may lead to increased costs.

[0055] Therefore, the adjustment unit 400 can adjust the output to reduce the voltage fluctuation range of the output power of the power supply unit 20 caused by variations in the electrical characteristics of at least one of the resonant circuit 23 and the load 90. In other words, as shown in Figure 9, the voltage fluctuation range (variation) of the output power of the power supply unit 20 is caused by variations in the electrical characteristics of at least one of the resonant circuit 23 and the load 90. In this case, the adjustment unit 400 is better able to adjust the output of the power supply unit 20 as described above, based on the specific range SR0 derived by the specific unit 300.

[0056] As previously described, the load 90 includes a power cable 80 that transmits power from the power supply unit 20 to the electrodes 10a and 10b of the plasma head 10. As shown in Figure 1, the power cable 80 is mounted along the robot arm 51 of the robot 50. Therefore, the power cable 80 may bend as the robot arm 51 moves. For this reason, it is preferable that the power cable 80 be a flexible cable that can be bent.

[0057] In this case, the capacitance of the power cable 80 is less stable compared to a fixed cable. Therefore, when the power cable 80 is a flexible cable that can be bent, the adjustment unit 400 should adjust the output to reduce the voltage fluctuation range of the output power of the power supply unit 20 caused at least by variations in the electrical characteristics of the power cable 80.

[0058] 2. An example of the effects of the embodiment According to the plasma generator 1, power at a voltage level that does not cause a discharge between the electrodes 10a and 10b of the plasma head 10 can be applied to the load 90, and it is possible to determine whether or not there is an abnormality in the load 90 connected to the power supply unit 20.

[0059] 1: Plasma generator, 10: Plasma head, 10a, 10b: Electrodes, 20: Power supply unit, 23: Resonant circuit, 80: Power cable, 90: Load, 100: Measurement circuit, 200: Judgment unit, 300: Specification unit, 400: Adjustment unit, V0: Output voltage, I0: Output current, TR0: Allowable range, SR0: Specification range, VU0: Upper limit, UR0: Upper limit range, VD0: Lower limit, DR0: Lower limit range.

Claims

1. A plasma generator comprising: a power supply unit equipped with a resonant circuit; a load connected to the power supply unit, which supplies power output from the power supply unit to electrodes of a plasma head that generates plasma; a measurement circuit for measuring the output voltage of the resonant circuit; and a determination unit that applies the power from the power supply unit to the load for a predetermined time at a voltage level that does not cause discharge between the electrodes, and determines whether the output voltage measured by the measurement circuit falls within an acceptable range indicating that the load is normal.

2. The plasma generator according to claim 1, wherein the determination unit determines that the load is abnormal when the output voltage is not within the allowable range and stops the output of the power supply unit.

3. The plasma generator according to claim 1, wherein the measurement circuit measures the output current of the resonant circuit, and the determination unit determines that the load is abnormal and stops the output of the power supply unit if at least the output voltage among the output voltage and the output current is not within the allowable range.

4. The plasma generator according to claim 2 or 3, wherein the determination unit stops the output of the power supply and notifies of the abnormality of the load.

5. The plasma generator according to claim 1, further comprising a determination unit that, when the determination unit determines that at least the output voltage is within the allowable range and the load is normal, derives a specific range which is a predetermined range within the allowable range of the output voltage and which includes the output voltage measured by the measurement circuit.

6. The plasma generator according to claim 5, wherein the specific unit divides the allowable range of the output voltage into a plurality of ranges, and derives the divided range that includes the output voltage measured by the measurement circuit as the specific range.

7. The plasma generator according to claim 6, wherein the identifying unit searches for the defined ranges in order from the upper limit range which includes the upper limit of the allowable range of the output voltage, or the lower limit range which includes the lower limit of the allowable range of the output voltage, and derives the identified range.

8. A plasma generator according to any one of claims 5 to 7, further comprising an adjustment unit that adjusts the output of the power supply unit based on the specific range derived by the specific unit when applying the power, which is at a voltage level that generates a discharge between the electrodes, from the power supply unit to the load.

9. The plasma generator according to claim 8, wherein the adjustment unit adjusts the output to reduce the voltage fluctuation range of the output power of the power supply unit caused by variations in the electrical characteristics of at least one of the resonant circuit and the load.

10. The plasma generator according to claim 9, wherein the load includes a power cable that transmits power from the power supply unit to the electrodes of the plasma head.

11. The plasma generator according to claim 10, wherein the power cable is a flexible cable.

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