JP4245761B2 - Pulse superposition type high voltage generator for electrostatic application equipment and electrostatic application equipment - Google Patents

Description

[0001]
[Industrial application fields]
The present invention supplies a pulse superposition type high voltage in which a high voltage pulse is superimposed on a normal DC voltage to a charging electrode of an electrostatic application device with a small current such as an electrostatic coating machine, an air cleaner, or an electrostatic classifier. The present invention relates to a high voltage generator.
[0002]
[Prior art]
Electrostatic coating is applied by adsorbing paint to a workpiece with electrostatic force, and has the advantage of relatively high coating efficiency. However, in recent years, it has increased from the viewpoint of environmental protection. It has been demanded to reduce the amount of power energy, the amount of paint used, and the processing cost of unattached paint, and further improvement in coating efficiency is an urgent issue.
[0003]
As one of the measures, one of the applicants in the patent application of Japanese Patent Application No. 11-279141 is a pulse superposition type high voltage in which a high voltage pulse is superimposed on a normal DC high voltage (herein referred to as a base voltage) at a substantially constant level. A method of charging a voltage to a charging electrode of an electrostatic coating apparatus has been proposed. In the case of such a pulse superposition type high voltage, the pulse voltage peak value can be made higher than the conventional charge voltage at a substantially constant level, so that the charging efficiency can be improved, and the width of the pulse voltage is 200 microseconds. There is an advantage that it does not shift to a spark if it restricts to the following. In particular, if a spark is generated by electrostatic coating, the coating operation is interrupted and there is a risk of ignition of the paint, so it is said that no spark should occur.
[0004]
[Problems to be solved by the invention]
Therefore, the present invention can increase the painting or collection efficiency, and can realize the generation of a pulse superimposed high voltage having a steep rise and fall that can suppress the occurrence of spark with a low cost and simple circuit configuration. It is an object of the present invention to provide a pulse superposition type high voltage generator.
[0005]
[Means for Solving the Problems]
[0006]
According to a first aspect of the present invention, in order to solve the above-described problem, the first and the second stages of a multi-stage vertical voltage doubler rectifier circuit in which a plurality of capacitors and a plurality of diodes are cascade-connected are provided The second high voltage switch circuit is connected in series, and the connection point thereof is connected to a high voltage output terminal connected to the charging electrode of the electrostatic application device through a resistor, and the first and second high voltage switch circuits are connected. By alternately operating the voltage switch circuit, when the second high voltage switch circuit connected to the intermediate stage is on, a base voltage corresponding to the voltage of the intermediate stage is output from the high voltage output terminal, and the final stage When the connected first high voltage switch circuit is on, a pulse superposition type high voltage in which a pulse voltage corresponding to the difference between the voltage of the final stage and the intermediate stage is superimposed on the base voltage is output to the high voltage output terminal Pal for electrostatic application equipment In the superposition type high voltage generator, the high voltage switch circuit, which are connected in series a plurality of FET or IGBT, the control voltages of the high voltage switch is supplied through a plurality of isolation transformers in cascade, and the plurality There is provided a pulse superposition type high voltage generator for electrostatic application equipment, in which each of the potentials of the isolation transformers is fixed in stages to the intermediate stage potential of the multistage vertical voltage doubler rectifier circuit.
[0007]
For a second aspect of the present invention is to solve the above problems, according to claim 1, wherein the first ON period of the high voltage switch circuit is set to be shorter than the on period of the second high voltage switch circuit It proposes a pulse superposition type high voltage generator for electrostatic application equipment.
[0008]
According to a third aspect of the present invention, in order to solve the above-mentioned problem, in the first or second aspect , the pulse signal generator is arranged on the high voltage side, and the pulse signal generator is connected to the plurality of insulations connected in cascade. The present invention proposes a pulse superposition type high voltage generator for electrostatic application equipment that operates with the control voltage supplied through a transformer.
[0009]
According to a fourth aspect of the present invention, in order to solve the above problem, a charged electrode connected to the high voltage output terminal of the pulse superposition type high voltage generator for electrostatic application apparatus according to any one of the first to third aspects is provided. The present invention proposes an electrostatic application device characterized by having the above.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The basic idea of the present invention is that a pair of high voltage switch circuits that alternately perform switching operations at high speed are connected to the final stage and the intermediate stage of a multistage cascaded voltage doubler rectifier circuit, and the high voltage switch circuit connected to the final stage The high-voltage pulse is generated by turning on, and then the high-voltage switch circuit connected to the intermediate stage is turned on to thereby charge the floating capacitance formed between the electrostatic application device and the grounded object. Discharge and suddenly drop from a voltage corresponding to the high voltage pulse to a DC constant high voltage (herein referred to as a base voltage) corresponding to a normal charging voltage, and the base voltage is reduced until the next cycle. By holding a pulse superimposed high voltage that periodically superimposes a high voltage pulse with a narrow pulse width with sharp rising and falling edges, the charging electrode of electrostatic application equipment Since it can be supplied, the charging rate of particles is increased and the coating or collection efficiency is improved without generating a spark between the charged electrode of an electrostatic application device such as an electrostatic coating machine and a grounded workpiece. It is to improve.
[0013]
FIG. 1 shows an embodiment of the present invention. Reference numeral 1 denotes an ordinary multi-stage cascaded voltage doubler rectifier circuit such as a Cockcroft-Walton (hereinafter referred to as CW) circuit or a Shunkel circuit having a negative output formed by cascading a plurality of capacitors and diodes. Reference numeral 2 denotes a high-frequency, high-voltage transformer that drives the multistage cascaded voltage doubler rectifier circuit 1, and the secondary high voltage winding 3 is connected to the input of the multistage cascaded voltage doubler rectifier circuit 1, and the winding start is grounded. The The primary winding 4 is connected to the output of the high frequency inverter 5. The first and second high voltage switch circuits 8 between the first output point X of the final stage 7 and the second output point Y of the intermediate stage 6 and the common output point Z of the multistage cascaded voltage doubler rectifier circuit 1. , 9 are connected in series.
[0014]
As will be described in detail later, in the case of the first high-voltage switch circuit 8, its cathode K is connected to the first output point X and its anode A is connected to the common output point Z. In the case of the voltage switch circuit 9, its anode A is connected to the second output point Y, and its cathode K is connected to the common output point Z. The high voltage switch circuits 8 and 9 are connected to the charging electrode 11 of the electrostatic coating machine through the common output point Z and the discharge prevention resistor 10. A workpiece 11 ′, which is an object to be coated that acts as the other electrode for the charged electrode 11, is grounded. The optical pulse generation circuit 12 transmits optical drive signals A and B for driving the high voltage switch circuits 8 and 9 on and off through the optical fibers 13 and 14. The optical drive signals A and B turn on the high voltage switch circuits 8 and 9 alternately with a predetermined pulse width and frequency, but not simultaneously.
[0015]
Next, before describing the operation, an example of a specific configuration of the high-voltage switch circuits 8 and 9 capable of high-speed switching operation that rises and falls in a short time of several microseconds or less will be described with reference to FIG. In this example, the high-voltage switch circuits 8 and 9 have almost the same configuration, and a dependent firing circuit configuration is possible in which the necessary number of FET switches are connected in series and the FET can be driven without using a control power supply. ing. According to this circuit, not only high speed operation but also control of the FET switch on the high voltage side can be realized at low cost.
[0016]
N FETs 21 </ b> A to 21 </ b> N are connected in series between the anode A and the cathode K. Protective Zener diodes 22A-22N are connected between the gate and source electrodes of each FET. Adjacent gates of the FETs 21A to 21N are connected to each other by a voltage balance resistor 23A-23M, and a voltage balance resistor 23N is connected between the gate and drain of the final stage FET 21N located closest to the anode A. Further, the collector and emitter electrodes of the phototransistor 24 are connected between the gate and source electrodes of the first stage FET 21A located closest to the cathode K. It is known that each of the FETs 21A to 21N has a body diode having a polarity indicated by a chain line.
[0017]
These high voltage switch circuits 8 and 9 are generally known dependent firing circuits and will not be described in detail. However, when the optical drive signal A or B is received through the optical fiber 13 or 14, the phototransistor 24 is turned on. Since it is turned on and the gate-source electrode of the FET 21A is short-circuited, the FET 21A is turned off, and the other FETs 21B-21N are also turned off. Next, when the optical drive signal A or B disappears, the phototransistor 24 is turned off, and a voltage is applied between the anode and cathode of each of the FETs 21A to 21N, so that the gate electrode of the FET 21A has an anode voltage through the resistors 23A to 23N. Forward-biased and turns on at high speed. The other FETs 21B-21N also follow and turn on at high speed.
[0018]
Returning to FIG. 1 again, the operation will be described. FIG. 3 shows the waveforms Q of the optical drive signals a and b and the output voltage Q at the common output point Z in this embodiment. The second output point Y of the intermediate stage 6 of the multistage cascaded voltage doubler rectifier circuit 1 generates, for example, a base voltage of −90 kV. The first output point X of the final stage 7 generates a voltage necessary for the superimposed pulse voltage, for example, −120 kV obtained by adding −30 kV to the base voltage. When the optical drive signal A is at a low level and the optical drive signal B is at a high level, the first high voltage switch circuit 8 is turned on at high speed, and the second high voltage switch circuit 9 is turned off. Accordingly, the charging electrode 11 of the electrostatic coating machine has a DC high voltage substantially equal to −120 kV obtained by adding −30 kV to the base voltage −90 kV through the first high-voltage switch circuit 8, the common output point Z, and the resistor 10. A voltage is applied.
[0019]
Next, after about 100 microseconds, when the optical drive signals A and B are inverted and the optical drive signal A becomes high level and the optical drive signal B becomes low level, the first high voltage switch circuit 8 is turned off at high speed, The high voltage switch circuit 9 is turned on at high speed. Here, as indicated by a chain line in FIG. 1, there is a stray capacitance C between the charged electrode 11 of the electrostatic coating machine and the grounded work 11 ′, and the stray capacitance C is the first high-voltage switch circuit. Immediately before 8 is turned off, it is charged to approximately −120 kV, but as the second high voltage switch circuit 9 is turned on, the charge of the stray capacitance C is instantaneously discharged through the second high voltage switch circuit 9. The voltage of the charging electrode 11 drops to the base voltage of −90 kV in a short time of several microseconds or less. That is, the second high-voltage switch circuit 9 performs the action of discharging the charge of the stray capacitance C between the charging electrode 11 of the electrostatic coating machine and the ground. After discharging to -90 kV, the optical drive signal B is set to the high level. The second high voltage switch circuit 9 may be turned off.
[0020]
This is because the anode A of the second high-voltage switch circuit 9 is connected to the second output point Y and the cathode K is connected to the common output point Z as described above. This is because each body diode (indicated by a chain line) included in each FET 21A-21N of the voltage switch circuit 9 becomes conductive, so that the common output point Z is maintained at -90 kV that is the voltage of the second output point Y. Needless to say, the second high voltage switch circuit 9 may be turned on just before the first high voltage switch circuit 8 is turned on, as indicated by the chain line of the optical drive signal a in FIG.
[0021]
Accordingly, by repeating the state in which the first high voltage switch circuit 8 is on and the second high voltage switch circuit 9 is off at a predetermined pulse width t, for example, 100 microseconds, for example, at 1 kHz, the base voltage A small pulse width having a short rise and fall of a few microseconds or less at −90 kV, for example, a pulse superposition type high voltage Q in which a pulse voltage of −30 kV of 100 μs is superposed at 1 kHz can be applied to the charging electrode 11.
[0022]
In this embodiment, the ratio of the time width of the base voltage and the superimposed pulse voltage is 9: 1, and the peak voltage is increased to -120 kV to improve the charging of particles in a short pulse voltage period. Since the voltage is lowered to −90 kV in the next long base voltage period, it is difficult for sparks to occur even though the charging efficiency is improved. Thus, in order not to generate a spark despite the improvement in charging efficiency, it is necessary to make the time width of the base voltage longer than the time width of the pulse voltage superimposed in each cycle. This time width ratio is such that, by applying a pulse voltage, the amount of ions between the charged electrode 11 of the electrostatic coating machine and the workpiece 11 ′, which is the object to be coated, increases, and the amount of ions hardly generates a spark during the base voltage application period. A value that decreases to the level is selected. Note that the ratio of the time widths does not need to be constant, and may be controlled according to a change in conductivity between the charging electrode 11 and the workpiece 11 ′.
[0023]
FIG. 4 shows a second embodiment of the present invention. In this example, the control power supply 40 is provided on the high voltage side. The same reference symbols as those in FIGS. 1 and 2 indicate the corresponding members. The primary windings and secondary windings of the insulating transformers 41A to 41D for supplying the control power supply voltage are connected in cascade. The primary winding of the first-stage transformer 41A located at the lowest stage is connected to the control power source inverter 42 and is substantially at the ground potential. The output high-frequency voltage of the control power inverter 42 is transmitted to the high voltage side via the isolation transformers 41A to 41D. Here, the secondary winding of the first-stage transformer 41A and the primary winding of the second-stage transformer 41B are connected to the second stage of the multi-stage cascaded voltage doubler rectifier circuit 1, for example, the point 1a of −30 kV.
[0024]
Similarly, the secondary winding of the second-stage transformer 41B and the primary winding of the third-stage transformer 41C are connected to the fourth stage −60 kV point 1b of the multi-stage cascaded voltage doubler rectifier circuit 1. The primary winding of the fourth-stage transformer 41D and the secondary winding of the third-stage transformer 41C are connected to the sixth stage −90 kV point 1c of the multi-stage cascaded voltage doubler rectifier circuit 1. In this way, the primary and secondary windings of each of the isolation transformers 41A to 41D are sequentially connected from the ground side to the intermediate stage of the multistage cascaded voltage doubler rectifier circuit 1, and their potentials are multistage cascaded voltage doubler rectifier circuits. It is fixed to a stable voltage for every two stages that rise in steps of one.
[0025]
As a result, each transformer is equally shared with a withstand voltage of two stages, for example, with a withstand voltage of −30 kV. Of course, it is also possible to use a single isolation transformer having a withstand voltage of -120 kV. However, such a low withstand voltage transformer is more reliable than one transformer with a withstand voltage of −120 kV and is easy to miniaturize. Only the transformer 41D becomes the potential of the charged electrode 11 through the rectifier circuits 45 and 46, and fluctuates with a pulse voltage of −30 kV. A low voltage VL of about 5 to 15 V rectified by the rectifier circuit 45 becomes the control power supply voltage of the optical pulse light receiving circuit 47.
[0026]
The optical drive signals A and B from the optical pulse generation circuit 12 are photoelectrically converted by the optical pulse light receiving circuit 47 to become an electrical pulse drive signal, and the electrical pulse drive signal is supplied to the first high voltage switch circuit 8. At the same time, the signal is inverted by the inverting circuit 48 and supplied to the semiconductor switch 49 such as an FET. Here, 50 and 51 are short-circuit current limiting resistors when a simultaneous ON period occurs when the high-voltage switch circuits 8 and 9 are switched.
[0027]
In this embodiment, the first high-voltage switch circuit 8 has a dependent point arc configuration as shown in FIG. 2, but the second high-voltage switch circuit 9 is not a dependent point arc circuit, and each has a primary order. A pulse transformer drive system is used which is driven through pulse transformers 52A, 52B,... 52N having windings and secondary windings. The gates and sources of the FETs 21A to 21N connected in series of the first high voltage switch circuit 8 are connected to the secondary windings of the pulse transformers 52A to 52N. The gate-source resistors 53A to 53N are for pulse shaping. Resistances 54A to 54N between the drain and source of each FET are for voltage balancing.
[0028]
The primary windings of the pulse transformers 52A to 52N are connected in series, and when the semiconductor switch 49 is turned on by the inverted pulse drive signal from the inverting circuit 48 as described above, the multistage cascaded voltage doubler rectifier circuit The voltage of the difference between the final stage voltage Vx and the voltage Vh is applied. Accordingly, a drive voltage is induced in the pulse transformers 52A to 52N, the FET 21A-21N is turned on instantaneously, and the second high voltage switch circuit 9 is turned on. The on period of the second high voltage switch circuit 9 is an off period of the first high voltage switch circuit 8 due to the inversion action of the inversion circuit 48.
[0029]
In this embodiment, since the control power supply 40 is provided on the high voltage side, the degree of freedom in designing the drive circuit for the high voltage side FET is increased, enabling faster switching, and the width of the superimposed pulse is easily on the order of microseconds. Narrow pulse width.
[0030]
The third embodiment shown in FIG. 5 is similar to the embodiment of FIG. 4 except that a control pulse generator 52 for supplying an electric drive pulse voltage to a semiconductor switch 49 such as an FET is placed on the high voltage side. . That is, when the optimum pulse width and frequency are determined by an actual electrostatic application device and there is no need to change them, there is no need to transmit a pulse signal from the ground side, so no optical fiber is required, and the structure The above merit is great. Further, when the conventional constant DC high voltage is used without using the pulse superposition type high voltage, if the control power supply inverter 42 is stopped, the high-voltage side control power supply voltage disappears and the semiconductor Since the switch 49 is turned off at high speed, the high voltage switch circuit 8 is turned off at high speed, and the high voltage switch circuit 9 is turned on at high speed at the same time, only the base voltage appears at the high voltage output terminal OT.
[0031]
Here, when the control pulse generator 52 generates a high level signal, the high voltage switch circuit 8 is turned on. At the same time, the high level signal is converted into a low level signal by the inverting circuit 48 and the semiconductor switch 49 is turned off at high speed. To. Therefore, the high voltage switch circuit 9 is off. Next, when the control pulse generator 52 generates a low level signal, the high voltage switch circuit 8 is turned off, and the high level signal inverted by the inverting circuit 48 turns on the semiconductor switch 49, and the primary winding of the pulse transformer 53 is turned on. The high voltage switch circuit 9 is turned on via the line L1 and the secondary winding L2. The other parts are the same as those in FIG.
[0032]
In the embodiment described above, the case of the electrostatic coating apparatus has been described. However, the pulse superposition type high voltage generator according to the present invention can be applied to other electrostatic application equipment having a relatively small current capacity, such as an air cleaner, a static cleaner. It can be similarly applied to an electric classifier and an electrostatic flocking device.
[0033]
【The invention's effect】
As described above, according to the present invention, the high-voltage switch circuit is connected in series between the final stage, the intermediate stage and the high-voltage output terminal of the multi-stage cascaded voltage doubler rectifier circuit, so that they do not overlap each other at high speed. Since the pulse superposition type high voltage is generated by the ON operation, the time required for the rise and fall of the pulse superposition type high voltage is very short, so the pulse width Narrow high voltage pulses can be easily obtained, and the charging efficiency of the particles can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first embodiment of a pulse superposition type high voltage generator according to the present invention.
FIG. 2 is a diagram showing an example of a high voltage switch circuit used in the device of the present invention.
FIG. 3 is a diagram showing waveforms for explaining the operation of the apparatus shown in FIG. 1;
FIG. 4 is a diagram showing a second embodiment according to the present invention.
FIG. 5 is a diagram showing a third embodiment according to the present invention.
[Explanation of symbols]
1. ・ Multi-stage cascaded voltage doubler rectifier circuit 2. ・ High frequency high voltage transformer 5 ・ ・ High frequency inverter 5 8. ・ First high voltage switch circuit 9 ・ ・ Second high voltage switch circuit 10 ・ ・ Discharge prevention resistor 11 ・・ Charged electrode 11 ′ ・ ・ Other electrode or load 12 ・ ・ Optical pulse generation circuit 13, 14 ・ ・ Optical fiber 21A-21N ・ ・ FET
22A-22N ... Zener diode 23A-23M ... Voltage balance resistor 17
40 .. Control power supply 41A-41D .. Cascaded insulation transformer 42 .. Control power supply inverters 45, 46..Rectifier circuit 47..Optical pulse light receiving circuit 48..Invert circuit 49..Invert circuit 50, 51.・ ・ Short-circuit current limiting resistor 52 ・ ・ Control pulse generator 53 ・ ・ Pulse transformer

Claims (4)

The first and second high-voltage switch circuits are connected in series between the final stage and the intermediate stage of the multistage longitudinal voltage doubler rectifier circuit formed by cascade-connecting a plurality of capacitors and a plurality of diodes, By connecting these connection points to a high voltage output terminal connected to a charging electrode of an electrostatic application device through a resistor, and operating the first and second high voltage switch circuits alternately, When the connected second high voltage switch circuit is on, a base voltage corresponding to the voltage of the intermediate stage is output from the high voltage output terminal, and the first high voltage switch circuit connected to the final stage is on. in the pulse superposition type electrostatic application pulse superposition type high voltage generator equipment for a high voltage output to the high voltage output terminal of the pulse voltage is superimposed on the base voltage corresponding to a difference between the voltage of the final stage and the intermediate stage when ,
The high voltage switch circuit is a circuit in which a plurality of FETs or IGBTs are connected in series, and the control voltage of these high voltage switches is supplied through a plurality of cascaded isolation transformers, and each of the potentials of the plurality of isolation transformers is supplied. A pulse superposition type high voltage generator for electrostatic application equipment, wherein the multistage longitudinal voltage doubler rectifier circuit is fixed stepwise to an intermediate stage potential. In claim 1 ,
The pulse superposition type high voltage generator for electrostatic applied equipment, wherein the on period of the first high voltage switch circuit is set shorter than the on period of the second high voltage switch circuit . In claim 1 or claim 2 ,
A pulse signal generator for electrostatic application equipment, wherein a pulse signal generator is disposed on a high voltage side and the pulse signal generator is operated with the control voltage supplied through the plurality of cascaded insulating transformers. Type high voltage generator. An electrostatic application device comprising a charged electrode connected to the high voltage output terminal of the pulse superposition type high voltage generator for electrostatic application device according to any one of claims 1 to 3 .

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