Submerged plasma generator

Abstract

The present invention provides a liquid-immersion plasma generator that can accurately grasp the state of the plasma in the liquid and adjust the distance between electrodes accordingly. [Solution] The liquid-submerged plasma generator comprises a power supply unit (pulse power supply for continuous plasma generation) 1 that generates plasma between electrodes A and B by applying a high-voltage pulse between a pair of electrodes A and B provided opposite each other in a liquid-submerged container X that is kept liquid-tight, and an electrode distance adjustment mechanism unit 2 that adjusts the distance between the pair of electrodes A and B via the power supply unit 1.

Description

Technical Field

[0001] The present invention relates to an in-liquid plasma generating apparatus that generates plasma between electrodes by applying a high-voltage pulse between a pair of electrodes disposed to face each other in a liquid container kept liquid-tight.

Background Art

[0002] Conventionally, as this type of in-liquid plasma generating apparatus, as shown in Patent Document 1 below, an in-liquid plasma electrode for generating plasma in a liquid is composed of a conductive wire and an insulating member covering the outer periphery of the conductive wire, the insulating member is formed such that the tip end surface of the insulating member protrudes further toward the tip side than the tip end surface of the conductive wire, and the conductive wire is configured to be slidable relative to the insulating member, which is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] According to the conventional in-liquid plasma electrode, since the conductive wire is arranged inside the insulating member, the plasma is stabilized, and since the conductive wire is slidable relative to the insulating member, even when the conductive wire is worn and the inter-electrode distance fluctuates, the inter-electrode distance can be corrected, but in the first place, in in-liquid plasma, there is a problem that it is difficult to judge whether the inter-electrode distance should be adjusted.

[0005] In view of the above problems, an object of the present invention is to provide an in-liquid plasma generating apparatus capable of accurately grasping the state of in-liquid plasma and adjusting the inter-electrode distance.

Means for Solving the Problem

[0006] The liquid-submerged plasma generator of the first invention generates plasma between electrodes by applying a high-voltage pulse between a pair of electrodes placed facing each other in a liquid-submerged container that is kept liquid-tight, A high-voltage pulse generating unit that applies a high-voltage pulse between the pair of electrodes, A power supply unit that supplies power to the high-voltage pulse generating unit, A plasma state detection unit for detecting the state of the plasma generated between the pair of electrodes, An electrode distance adjustment mechanism adjusts the distance between the pair of electrodes according to the plasma state detected by the plasma state detection unit. Equipped with, The plasma state detection unit is characterized by detecting the plasma generation state from a processed waveform obtained by filtering the current detection waveform from a current detection unit provided between the high-voltage pulse generation unit and the power supply unit so as to distinguish between a leakage current state and a plasma generation state.

[0007] According to the liquid-immersed plasma generator of the first invention, the plasma state detection unit uses a current detection waveform from a current detection unit provided between the high-voltage pulse generation unit and the power supply unit to filter the current detection waveform so as to distinguish between a leakage current state and a plasma generation state, and detects the plasma generation state from the resulting processed waveform.

[0008] Here, by using the current detection waveform from the current detection unit installed between the high-voltage pulse generation unit and the power supply unit, it is possible to detect the plasma state from the output vibration wave detectable between the high-voltage pulse generation unit and the power supply unit, while deliberately avoiding current detection on the pair of electrodes in the high-voltage state.

[0009] Furthermore, by filtering the current detection waveform obtained from detecting vibration waves to distinguish between leakage current conditions and plasma generation conditions, the plasma generation condition can be reliably detected from the processed waveform.

[0010] Thus, the liquid-immersed plasma generator of the first invention makes it possible to accurately grasp the state of the liquid-immersed plasma and adjust the distance between electrodes.

[0011] The liquid-immersion plasma generator of the second invention is, in the first invention, The plasma state detection unit is characterized in that, when a plasma generation state is detected, it generates a plasma detection signal corresponding to the processing waveform, thereby detecting a plasma deterioration state in which the plasma detection signal is not generated for a certain period of time, and generates an electrode adjustment signal to adjust the distance between the pair of electrodes of the electrode distance adjustment mechanism.

[0012] According to the liquid-immersed plasma generator of the second invention, when a plasma generation state is detected by the plasma state detection unit, a plasma detection signal corresponding to the processing waveform is generated. Then, using this plasma generation signal as an indicator, if the plasma detection signal is not generated for a certain period of time, it is detected that the plasma state has deteriorated.

[0013] As a result, the liquid-immersed plasma generator of the second invention makes it possible to accurately grasp the state of the liquid-immersed plasma and convert it into an indicator called a plasma detection signal, thereby actually adjusting the distance between electrodes.

[0014] The liquid-immersion plasma generator of the third invention is, in the second invention, The plasma state detection unit is characterized by detecting a plasma deterioration state when the mono-multi-plasma signal detected by the mono-multi-plasma detection unit is OFF and the switch drive signal is ON, by comparing the mono-multi-plasma signal detected by the mono-multi-plasma detection unit with the switch drive signal of the high-voltage pulse generation unit.

[0015] According to the liquid-immersed plasma generator of the third invention, deterioration of the plasma state can be actually detected when the plasma state is deteriorating, by converting the plasma detection signal into a mono-multi-plasma signal detected by mono-multi, while the mono-multi-plasma signal is OFF and the switch drive signal is ON.

[0016] As described above, according to the in-liquid plasma generator of the third invention, it becomes possible to actually grasp the deterioration of the in-liquid plasma state and adjust the inter-electrode distance.

[0017] The in-liquid plasma generator of the fourth invention is, in any one of the first to third inventions, in the case where the high-voltage pulse generation unit is constituted by an inverter connected to the power supply unit, and a pulse transformer provided between the inverter and the pair of electrodes, the current detection unit is provided between the pulse transformer and the power supply unit.

[0018] According to the in-liquid plasma generator of the fourth invention, when the high-voltage pulse generation unit is constituted by an inverter connected to the power supply unit and a pulse transformer provided between the inverter and the pair of electrodes, the current detection unit can be provided between the pulse transformer and the power supply unit, that is, between the pulse transformer and the inverter, or between the inverter and the power supply unit.

[0019] Thereby, according to the in-liquid plasma generator of the fourth invention, it is possible to provide the current detection unit at a position where the state of in-liquid plasma can be grasped according to the circuit configuration, to actually grasp the plasma state and adjust the inter-electrode distance.

[0020] The in-liquid plasma generator of the fifth invention is, in any one of the first to third inventions, in the case where the high-voltage pulse generation unit is constituted by an inverter provided between the power supply unit and the pair of electrodes, the current detection unit is provided between the inverter and the power supply unit.

[0021] According to the in-liquid plasma generator of the fifth invention, when the high-voltage pulse generation unit is constituted by an inverter provided between the power supply unit and the pair of electrodes, the current detection unit can be provided between the inverter and the power supply unit.

[0022] Thereby, according to the in-liquid plasma generating apparatus of the fifth invention, it is possible to provide a current detection unit at a position where the state of in-liquid plasma can be grasped according to the circuit configuration, actually grasp the plasma state, and adjust the inter-electrode distance.

[0023] The in-liquid plasma generating apparatus of the sixth invention is, in any one of the first to third inventions, The inter-electrode distance adjustment mechanism unit is configured to be capable of adjusting the distance between the electrodes by an advancing / retreating mechanism that advances or retreats one or both of the pair of electrodes into or from the in-liquid container.

[0024] According to the in-liquid plasma generating apparatus of the sixth invention, by configuring the inter-electrode distance adjustment mechanism unit with the advancing / retreating mechanism that advances or retreats one or both of the pair of electrodes into or from the in-liquid container, the distance between the electrodes can be actually adjusted.

[0025] As described above, according to the in-liquid plasma generating apparatus of the sixth invention, it is possible to accurately grasp the state of in-liquid plasma and actually adjust the inter-electrode distance. [Brief Description of the Drawings]

[0026] [Figure 1] An explanatory view showing the overall configuration of the in-liquid plasma generating apparatus of the present invention. [Figure 2] An explanatory view showing the configuration of the inter-electrode distance adjustment mechanism unit in Figure 1. [Figure 3A] An explanatory view showing the configuration of the pulse power source for continuous plasma generation in Figure 1. [Figure 3B] An explanatory view showing another configuration of the pulse power source for continuous plasma generation in Figure 1. [Figure 4A] An explanatory view showing the processing contents of the plasma state detection circuit in Figure 3A. [Figure 4B] An explanatory view showing the processing contents of the plasma state detection circuit in Figure 3A. [Mode for Carrying Out the Invention]

[0027] A liquid-submerged plasma generator as one embodiment of the present invention will be described with reference to Figures 1 to 4.

[0028] First, as shown in Figure 1, the liquid-submerged plasma generator includes a power supply (pulse power supply for continuous plasma generation) 1 that generates plasma between electrodes A and B by applying a high-voltage pulse between a pair of electrodes A and B placed facing each other in a liquid-submerged container X that is kept liquid-tight (including when targeting a bubbling liquid), and an electrode distance adjustment mechanism 2 that adjusts the distance between the pair of electrodes A and B via the power supply 1.

[0029] The liquid container X is connected, for example, via a resin hose to a tank Y in which the processing liquid to be processed by the plasma generator is stored, and a flow path is formed so that the processing liquid from tank Y flows into the liquid container X via a pump P and returns to tank Y.

[0030] In this configuration, the processing liquid is arranged to flow in from the bottom of the liquid container X and out from the top. Additionally, a bubbling device Z may be provided to introduce a reaction gas (such as oxygen or argon) into the flow path below the liquid container X, if necessary, so that the reaction gas is mixed into the processing liquid within the liquid container X, particularly between a pair of electrodes A and B.

[0031] In this configuration, by grounding the tank Y and part of the flow path (for example, via a metal joint W), it is possible to apply a high voltage between electrodes A and B while avoiding the high voltage applied between the pair of electrodes A and B flowing into the ground, as would occur if one of the two electrodes A and B were grounded.

[0032] Next, we will postpone a detailed explanation of the power supply unit 1 and first describe the configuration of the electrode distance adjustment mechanism unit 2.

[0033] The electrode distance adjustment mechanism 2 includes, for example, electrode wires 20A and 20B, each having one end tip forming a pair of electrodes A and B; a plurality of rollers 21A, 22A, 21B, and 22B that feed the one end tips out into the liquid container X facing each other; and loop portions 23A and 23B, each with a winding at the other end of the electrode wires 20A and 20B.

[0034] The high-frequency, high-voltage pulses applied to the pair of electrodes A and B are supplied from the power supply unit 1 via the connecting pieces 24A and 24B at the other ends (loop sections 23A and 23B) of the electrode wires 20A and 20B, respectively.

[0035] Some of the multiple rollers 21A, 22A, 21B, and 22B (in this embodiment, rollers 21A and 21B) are configured to be rotatable via a drive means such as a stepping motor. The rollers 21A and 21B are rotated by the drive means according to the number of steps in response to the electrode feed signal (corresponding to the electrode adjustment signal of the present invention) from the power supply device 1, which will be described later, causing the electrode wires 20A and 20B to move forward (and backward if necessary).

[0036] Furthermore, rollers 22A and 22B, which are not connected to the drive mechanism, function as guides (together with rollers 21A and 21B) to ensure that the tips of the electrode wires 20A and 20B move straight toward each other. For this reason, grooves corresponding to the electrode wires 20A and 20B may be formed in rollers 21A, 22A, 21B, and 22B as needed.

[0037] Furthermore, the electrode distance adjustment mechanism 2 is configured to be insulated as a whole, except for the electrical contact parts such as the connecting pieces 24A and 24B. Specifically, the rollers 21A, 22A, 21B, and 22B are made of insulating resin material, as are the bobbin portions of the loop sections 23A and 23B, which are also made of insulating resin material.

[0038] Next, I will explain power supply unit 1, which I postponed explaining earlier.

[0039] As shown in Figure 3A, in a first embodiment of the power supply device 1, from left to right in the figure, it comprises a DC power supply 10 (corresponding to the power supply unit of the present invention) connected to a commercial power supply such as three-phase 200V and converting the commercial power supply into a DC power supply of a predetermined voltage; a SiC inverter 11 (corresponding to the high-voltage pulse generation unit of the present invention) connected to the DC power supply 10; a pulse transformer 12 (corresponding to the high-voltage pulse generation unit of the present invention) connected to the SiC inverter; a control circuit 15 that controls the overall operation of the power supply device 1; a Gate signal generation circuit 16 provided between the control circuit 15 and the SiC inverter 11; and a plasma state detection circuit 17 (corresponding to the plasma state detection unit of the present invention) that detects the state of the plasma.

[0040] In this first embodiment, the SiC inverter 11, which is a switching element, is operated by a Gate signal from the Gate signal generation circuit 16 (which is converted and generated by the Gate signal generation circuit 16 based on a control signal from the control circuit 15 (Gate output _EN signal)) based on a DC power supply boosted to a low voltage of about 600V by the DC power supply 10 (compared to the second embodiment described later).

[0041] Then, the full-bridge output from the SiC inverter 11 is increased in voltage by the pulse transformer 12, generating a high-frequency, high-voltage pulse on the output side, which is then applied between a pair of electrodes A and B.

[0042] On the other hand, the second embodiment of the power supply device 1 shown in Figure 3B includes, from left to right in the figure, a high-voltage DC power supply 10' (corresponding to the power supply unit of the present invention) connected to a commercial power supply such as three-phase 200V and converting the commercial power supply into a DC power supply of a predetermined voltage (higher voltage than the first embodiment described above), a SiC inverter 11' (corresponding to the high-voltage pulse generation unit of the present invention) connected to the high-voltage DC power supply 10', a control circuit 15 that controls the overall operation of the power supply device 1, a Gate signal generation circuit 16 provided between the control circuit 15 and the SiC inverter 11', and a plasma state detection circuit 17 that detects the state of the plasma. In the second embodiment, components identical to those in the first embodiment are denoted by the same reference numerals and their descriptions are omitted.

[0043] In this second embodiment, a SiC inverter 11', which is a switching element, is operated by a Gate signal from a Gate signal generation circuit 16 (which is converted and generated by the Gate signal generation circuit 16 based on a control signal from the control circuit 15 (Gate output _EN signal)) based on a high-voltage DC power supply 10' which has been boosted to a high voltage of about 10kV (compared to the first embodiment described above) by a DC power supply.

[0044] In this case, the SiC inverter 11' directly switches the DC power supply, which has already been boosted to a high voltage by the high-voltage DC power supply 10', so (eliminating the need for a pulse transformer or the like to boost its output), a high-frequency, high-voltage pulse is generated directly on the output side and can be applied directly between the pair of electrodes A and B.

[0045] Next, with reference to Figure 4, the details of the plasma state detection circuit 17 (corresponding to the plasma state detection unit of the present invention), which is common to both the first and second embodiments, will be described.

[0046] In the first embodiment, the plasma state detection circuit 17 detects the plasma generation state between a pair of electrodes A and B based on the current detection waveform from the current detection unit CT that detects the current waveform between the SiC inverter 11 and the pulse transformer 12, and in the second embodiment, based on the current detection waveform from the current detection unit CT that detects the current waveform between the high-voltage DC power supply 10' and the SiC inverter 11', as follows.

[0047] In other words, the plasma generation state is detected from a processed waveform obtained by filtering the current detection waveform detected by the current detection unit CT in order to distinguish between a leakage current state and a plasma generation state.

[0048] While it is conceivable to place the current detection unit CT on the output side to electrodes A and B, this would require extensive insulation treatment for high-voltage pulses, and the current detection waveform measured by the current detection unit CT itself would contain a lot of noise. Therefore, it is desirable to place the current detection unit CT one block before the output side (before the pulse transformer 12 in the first embodiment, and before the SiC inverter 11' in the second embodiment), so that the plasma generation state can be detected from the processed waveform obtained by filtering the current detection waveform.

[0049] Figure 4A shows the actual processing waveform (lower plasma current detection waveform) on the left. In this processing waveform, in region I on the left, the plasma generation is insufficient and a leakage current state is occurring (the downward-convex peak shape is broken and partially pulsed). On the other hand, in region II on the right, plasma is being generated (a clean downward-convex peak shape).

[0050] The plasma state detection circuit 17 generates a plasma detection signal (upper side in the figure) corresponding to the plasma shape (a nice, downward-convex mountain shape) when plasma is generated. When it detects a plasma deterioration state in which no plasma detection signal is generated for a certain period of time, it generates an electrode feed signal (electrode adjustment signal) and outputs it to the electrode distance adjustment mechanism 2.

[0051] Specifically, the plasma state detection circuit 17 generates a mono-multi-plasma signal by detecting the plasma detection signal using a mono-multi (monostable multivibrator), as shown on the right side of Figure 4A.

[0052] A mono-multiplex is a circuit that captures the rising or falling edge of an input logic signal and extracts an output pulse with the required time width.

[0053] In this case, with monomulti, each time a plasma detection signal is detected, the monomulti plasma signal remains in a Hi state for a certain period of time (e.g., 1 sec).

[0054] The plasma state detection circuit 17 then detects the plasma deterioration state by comparing the mono-multi-plasma signal with the Gate output_EN signal (switch drive signal of the high-voltage pulse generation unit of the present invention) sent from the control circuit 15 to the Gate signal generation circuit 16, as follows.

[0055] In other words, as shown in Figure 4B, the plasma state detection circuit 17 detects a normal plasma state when the mono-multi-plasma signal is in a Hi state (ON state) and the Gate output _EN signal is in a Hi state (ON state), and a deteriorated plasma state when the mono-multi-plasma signal is in a Low state (OFF state) and the Gate output _EN signal is in a Hi state (ON state).

[0056] In this way, when the plasma state detection circuit 17 detects a plasma deterioration state, it generates a single-pulse electrode feed signal in response and outputs it to the electrode distance adjustment mechanism 2. The plasma state detection circuit 17 continues to generate a single-pulse electrode feed signal at regular intervals (for example, every 1 second) as long as the plasma deterioration state continues to be detected.

[0057] Each single pulse of electrode feed signal corresponds to one step in the aforementioned number of steps. The drive means rotates the rollers 21A and 21B, causing the electrode wires 20A and 20B to advance, for example, by 0.1 mm, and adjusting the distance between electrodes so that the distance between electrodes A and B decreases. This allows the system to automatically adjust the distance between electrodes and continue plasma generation even if one or both electrodes A and B become worn out due to the continuation of the plasma generation state, causing the distance between electrodes to increase.

[0058] As explained in detail above, the liquid-immersed plasma generator of this embodiment addresses the problem that in liquid-immersed plasma, it is difficult to determine the state of the plasma and therefore difficult to decide whether or not to adjust the inter-electrode distance. This is achieved by accurately grasping the state of the liquid-immersed plasma and adjusting the inter-electrode distance accordingly.

[0059] In this embodiment, although the current detection unit CT is provided between the SiC inverter 11 and the pulse transformer 12 in the first embodiment described above (Figure 3A), it is not limited to this and may be provided between the DC power supply 10 and the SiC inverter 11.

[0060] Alternatively, the plasma state detection circuit 17 may detect the plasma deterioration state by comparing the Gate signal output from the Gate signal generation circuit 16, which corresponds to the Gate output _EN signal, with the mono-multi-plasma signal, instead of using the Gate output _EN signal.

[0061] Furthermore, although this embodiment describes a case in which a pair of electrodes A and B are provided in a liquid-submerged container X to generate plasma, the invention is not limited to this, and multiple pairs of electrodes may be provided in the liquid-submerged container X. In this case, multiple SiC inverters (and pulse transformers) can be provided for one DC power supply in the power supply device 1, and plasma can be generated between pairs of electrodes corresponding to the output of each inverter. This makes it possible to generate plasma simultaneously and continuously between multiple pairs of electrodes in a single liquid-submerged container X, enabling highly efficient processing of large quantities of processing liquid. [Explanation of Symbols]

[0062] 1...Power supply unit (pulse power supply for continuous plasma generation), 2...Electrode distance adjustment mechanism, 10...DC power supply (power supply unit), 10'...High voltage DC power supply (power supply unit), 11,11'...SiC inverter, 12...Pulse transformer, 15...Control circuit, 16...Gate signal generation circuit, 17...Plasma state detection circuit, X...Liquid container, Y...Tank, Z...Bubbling device, W...Metal fitting.

Claims

1. In a liquid-submerged plasma generator that generates plasma between electrodes by applying a high-voltage pulse between a pair of electrodes placed opposite each other in a liquid-tight container, A high-voltage pulse generating unit that applies a high-voltage pulse between the pair of electrodes, A power supply unit that supplies power to the high-voltage pulse generating unit, A plasma state detection unit for detecting the state of the plasma generated between the pair of electrodes, An electrode distance adjustment mechanism adjusts the distance between the pair of electrodes according to the plasma state detected by the plasma state detection unit. Equipped with, The plasma state detection unit is characterized in that it detects the plasma generation state from a processed waveform obtained by filtering the current detection waveform from a current detection unit provided between the high-voltage pulse generation unit and the power supply unit so as to distinguish between a leakage current state and a plasma generation state.

2. In the liquid plasma generator according to claim 1, The plasma state detection unit generates a plasma detection signal corresponding to the processing waveform when a plasma generation state is detected, thereby detecting a plasma deterioration state in which the plasma detection signal is not generated for a certain period of time, and generates an electrode adjustment signal to adjust the distance between the pair of electrodes of the electrode distance adjustment mechanism.

3. In the liquid-submerged plasma generator according to claim 2, The plasma state detection unit is characterized in that it detects a plasma deterioration state when the mono-multi-plasma signal detected by the mono-multi-plasma detection unit is in the OFF state and the switch drive signal is in the ON state, by comparing the mono-multi-plasma signal detected by the mono-multi-plasma detection unit with the switch drive signal of the high-voltage pulse generation unit.

4. In a liquid-immersion plasma generator according to any one of claims 1 to 3, When the high-voltage pulse generating unit is composed of an inverter connected to the power supply unit and a pulse transformer provided between the inverter and the pair of electrodes, A liquid-immersion plasma generator characterized in that the current detection unit is provided between the pulse transformer and the power supply unit.

5. In a liquid-immersion plasma generator according to any one of claims 1 to 3, When the high-voltage pulse generation unit is configured by an inverter provided between the power supply unit and the pair of electrodes, A liquid-immersion plasma generator characterized in that the current detection unit is provided between the inverter and the power supply unit.

6. In a liquid-immersion plasma generator according to any one of claims 1 to 3, The inter-electrode distance adjustment mechanism is configured to allow adjustment of the distance between electrodes by an inter-electrode movement mechanism that moves one or both of the pair of electrodes into and out of the liquid-filled container, thereby enabling adjustment of the distance between the electrodes.

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