JP6890978B2 - High voltage power supply for electrostatic coating equipment - Google Patents

Description

The present invention relates to a high voltage power supply device used in an electrostatic coating device that sprays electrostatically charged coating material particles.

A high-voltage power supply device in a conventional electrostatic coating device switches a high-voltage module including a high-voltage transformer and a voltage booster circuit (for example, a voltage doubler rectifier circuit) on the secondary side thereof with a current flowing on the primary side of the high-voltage transformer. It includes a drive circuit and a high voltage controller that includes a controller that supplies drive signals to it. As the coating material, a liquid paint material or the like is used.

The controller supplies a drive signal to the drive circuit and generates a periodic or oscillating drive voltage on the primary side of the high voltage transformer via the drive circuit. As a result, a high voltage is generated on the secondary side of the high-voltage transformer, which is applied to the voltage booster circuit, and the output high voltage of the voltage booster circuit is used for coating equipment using electrostatic potential (injector that sprays charged coating material particles). ) Is to be supplied.

The secondary voltage of the high-voltage transformer and the output voltage of the high-voltage module change in approximately proportion to the amplitude of the drive voltage on the primary side of the high-voltage transformer. In a controller composed of a microcomputer or the like, the operating DC power supply is composed of a variable output power supply such as a DC-DC converter so that the efficiency and safety are within the desired range, and the internal voltage (DC) on the primary side of the high voltage transformer is used. Supply voltage) is controlled. Typical internal voltages are in the range of about 5V to 21V. The internal voltage is switched by a switching element such as a FET to generate a periodic or oscillating drive voltage on the primary side of the high voltage transformer.

FIG. 5 shows a general electrostatic coating device, and is a current waveform of a power source when a pulse voltage 3 is supplied from a power source in the high voltage control device 2 to the primary side of a high voltage transformer of a coating machine 1 having a built-in high voltage module. 4 (current waveform on the primary side of the high voltage transformer) is shown. A high voltage module is generally a resonant high voltage power supply with a center frequency with the highest output efficiency. This center frequency is not constant and fluctuates depending on load conditions, temperature conditions and aging. Therefore, if the pulse voltage 3 has an appropriate frequency, the effective current value is small and the peak current is small, but if the pulse voltage 3 deviates from the appropriate frequency, the effective current value is large and the peak current is large, and the efficiency is lowered.

Therefore, conventionally, the feedback signal of the load current flowing through the load (coating device) and the feedback signal of the output high voltage are used to adjust the drive signal applied to the drive circuit. For example, there is a technique for manually adjusting or automatically adjusting the frequency of the drive signal, that is, the drive frequency on the primary side of the high-voltage transformer so that the high-voltage module operates efficiently with respect to the target load. ..

The following is an example of how to adjust the drive frequency.
-Under the condition that the high voltage output of the high voltage module and the load current are constant, the variable voltage on the primary side of the high voltage transformer is minimized (Patent Document 1 below).
-Detect the phase on the secondary side of the high-voltage transformer (Patent Document 1 below).
-Minimize the average current on the primary side of the high-voltage transformer under the condition that the high-voltage output and load current of the high-voltage module are constant (references are not presented, but it is common).
-Maximize the efficiency from the high voltage output, load current, internal voltage, and average current on the primary side of the high voltage transformer under the condition that the high voltage output and load current of the high voltage module are constant (references are not presented, but general). ).

With the method of minimizing the average current on the primary side of the transformer under the condition that the high voltage output and load current of a conventional general high voltage module are constant, the change in the detected amount with respect to the frequency change is small near the center frequency, and the accuracy is high. The circuit was required, and a configuration was required to improve the reading accuracy by averaging the software using an A / D converter of 10 bits or more. Even when the center frequency is obtained by the program, if the unit of the frequency to be changed is made small, the change in the detected amount is small, so that an error occurs between the drive frequency obtained by the program and the center frequency, or a high-voltage transformer or high-voltage module. It was sometimes affected by waveform distortion due to the length of the cable connecting the cables. When an algorithm that searches for the minimum value is used by the program, it may not quickly converge to the optimum value due to disturbance noise, so the number of trials may be increased and it may take time to determine the optimum point. Further, even if the primary current becomes an abnormal value due to an abnormal state such as magnetic flux saturation due to a failure of the high voltage transformer, if the frequency range at the time of adjusting the drive frequency is narrow, the change that the abnormal current gives to the detected amount is still obtained. Because there are few, I sometimes overlooked the state of failure.

In addition, since it is difficult to observe the secondary side high voltage signal of 5 kV to 20 kV by the method of detecting the phase of the secondary side voltage and current of the high voltage transformer, a winding for detection is added to the high voltage transformer. This is done and the structure of the high voltage transformer is complicated. In addition, a comparator and an integrator circuit are required for phase detection, and there is also a problem that the waveform distortion is easily affected.

Japanese Unexamined Patent Publication No. 10-202151

The present invention has been made in recognition of such a situation, and an object of the present invention is an electrostatic coating device capable of accurately and easily finding the frequency of a drive signal in which a coating device using an electrostatic potential operates efficiently. To provide a high voltage power supply for use.

One embodiment of the present invention is a high voltage power supply device for an electrostatic coating device. This high-voltage power supply device for an electrostatic coating device is used in an electrostatic coating device that sprays electrostatically charged coating material particles.
It has a high-voltage transformer having a primary winding and a secondary winding, and a high-voltage rectifier that rectifies the induced voltage of the secondary winding, and transfers the output voltage of the high-voltage rectifier to a coating device using an electrostatic potential. The high voltage generator to supply and
A drive circuit that switches the current flowing through the primary winding,
A peak detection unit that detects the peak value of the current of the primary winding, and
It is equipped with a controller that generates a drive signal and supplies it to the drive circuit.
It is characterized in that the frequency of the drive signal is variably controlled by the controller so that the peak value of the peak detection unit is minimized.
In the above embodiment, a circuit for detecting the average value of the current of the primary winding may be further provided.

In the above aspect, the peak detection unit has a first time constant for acquiring the peak value and a second time constant for holding the peak value.
The first time constant is in the range of 5,000 to 30,000 times the noise pulse width mixed in the peak detection unit.
The second time constant is preferably equal to or longer than the period of the drive signal.

In the above embodiment, the first time constant is in the range of 250 to 1500 times the cycle of the drive signal, and the second time constant is in the range of 100 to 3000 times the cycle of the drive signal. Moreover, the second time constant is preferably in the range of 100 times to 500 times the determination time of the detected value corresponding to the amount of frequency change when adjusting the drive signal cycle.

In the above embodiment, a smoothing circuit for detecting the average current of the primary winding, an operating means for increasing or decreasing a drive frequency which is a frequency of the drive signal by a unit frequency, a means for displaying the drive frequency, and the primary winding. A display means for displaying the peak value of the current of the line and a display means for displaying the average current value are provided, and the current peak value and the average current value are updated with respect to the increase / decrease of the drive frequency by the operation means. It is preferable that the configuration is such that

Any combination of the above components and a conversion of the expression of the present invention between methods, systems and the like are also effective as aspects of the present invention.

According to the present invention, in a high-voltage power supply device used for an electrostatic coating device that sprays electrostatically charged coating material particles, a high-voltage transformer detects a current peak value on the primary side of the high-voltage transformer with a peak detection unit. By variably controlling the drive frequency (drive signal frequency) on the primary side, the drive frequency is controlled with higher accuracy than the conventional control method using average current and efficiency, and the operation of the high voltage generator is optimized. Things will be possible. Further, when adjusting the drive frequency of the high-voltage transformer, it becomes possible to detect a current waveform abnormality due to a failure of the high-voltage transformer with higher sensitivity.

The block diagram which shows the embodiment of the high voltage power supply device for an electrostatic coating device which concerns on this invention. The circuit diagram which shows the peak detection part in embodiment. The explanatory view which shows the drive frequency-detection value curve in the case of an embodiment (when the current peak value is used) in comparison with the conventional drive frequency-detection value curve by a current average value or an efficiency value. The current waveform diagram of the high-voltage transformer primary side when the drive frequency of the high-voltage transformer primary side is the center frequency and when it deviates from the center frequency. Explanatory drawing which shows the current waveform when the drive frequency is appropriate, and when it deviates from the high voltage power supply device for an electrostatic coating device. Explanatory drawing which shows an abnormal current waveform in a high voltage power supply device for an electrostatic coating device. The current waveform diagram of the high-voltage transformer primary side when the drive frequency of the high-voltage transformer primary side is the center frequency, and when the drive frequency deviates from the center frequency and an abnormal current is generated.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The same or equivalent components, members, processes, etc. shown in the drawings are designated by the same reference numerals, and redundant description will be omitted as appropriate. Moreover, the embodiment is not limited to the invention but is an example, and all the features and combinations thereof described in the embodiment are not necessarily essential to the invention.

1 to 4 show an embodiment of a high voltage power supply device for an electrostatic coating device according to the present invention. The high-voltage power supply device for an electrostatic coating device shown in FIG. 1 controls a high-voltage module 20 as a high-voltage generating unit that generates a high voltage and supplies it to the injector (gun) 10 and the output of the high-voltage module 20. It also has a high voltage control unit 30 for optimizing efficiency and a cable connecting both. The injector 10 is a coating device that utilizes an electrostatic potential, and sprays charged coating material particles on an object. Since the high voltage module 20 is usually housed in the casing of the injector 10, a cable is used. Is electrically connected to the high voltage control unit 30.

The high voltage module 20 has a high voltage transformer 21 having a primary winding 21a and a secondary winding 21b, and a voltage multiplying circuit 22 for rectifying and multiplying the induced voltage of the secondary winding 21b. The high voltage output of 22 is supplied to the injector 10. The voltage multiplying circuit 22 is, for example, a voltage doubler rectifier circuit or the like.

The high voltage control unit 30 includes a variable control stabilized power supply 40 as an operating DC power supply, a drive circuit 50 that switches the current flowing from the variable control stabilized power supply 40 to the primary winding 21a of the high voltage transformer 21, and a primary winding 21a. The current detection unit 60 that detects the current, the smoothing circuit 65 that smoothes the voltage value proportional to the current value of the current detection unit 60 and detects the average current value of the primary winding 21a, and the current value of the current detection unit 60. It has a peak detection unit 70 that detects the peak value of the current of the primary winding 21a from a proportional voltage value, a microcontroller (abbreviation: microcomputer) 80, and a display operation unit 85. The variable control stabilized power supply 40 is, for example, a switching regulator or the like, and can change the output voltage in the range of about 5V to 21V in response to the voltage setting signal 81 from the microcomputer 80. The drive circuit 50 receives the drive signal 82 from the microcomputer 80 and switches the current flowing through the primary winding 21a of the high voltage transformer 21. Since the current of the primary winding 21a is switched at the frequency of the drive signal 82, the frequency of the drive signal and the switching frequency (drive frequency) match. A voltage value proportional to the peak value of the current of the primary winding 21a from the peak detection unit 70 is applied to the A / D conversion input terminal of the microcomputer 80, and a smoothing circuit 65 is applied to another A / D conversion input terminal. A voltage value proportional to the average current value of the primary winding 21a is applied.

FIG. 2 specifically shows the configurations of the drive circuit 50, the current detection unit 60, and the peak detection unit 70. The drive circuit 50 includes a FET drive circuit 51 that receives a drive signal 82 from the microcomputer 80, an FET 52 that is switched by an output signal of the FET drive circuit 51, and a snubber circuit 53 that is connected between the drain and the source of the FET 52. The current detection unit 60 has a current detection resistor R1, and a series connection of the FET 52 and the current detection resistor R1 is inserted in series with the primary winding 21a of the high voltage transformer 21 that receives the DC voltage supply from the variable control stabilized power supply 40. Is connected to the ground (GND). As a result, a voltage value proportional to the current value of the primary winding 21a can be obtained at both ends of the current detection resistor R1.

The peak detection unit 70 includes voltage amplifiers A1 and A2, diodes D1, resistors R2, R3, R4, R5, R6, and capacitors C1, C2, and C3. The resistors R2 and R3 (10Ω each) and the capacitor C1 (0.01 μF) inserted between the current detection resistor R1 and the input side of the voltage amplifier A1 are low-pass filters with a cutoff frequency of 796 kHz and are used for removing high-frequency noise. (For removing noise caused by parasitic inductors in FET packages) and for protecting electrostatic noise. If this cutoff frequency is lowered, the peak waveform becomes dull and the characteristics of the peak detection unit 70 are affected. Therefore, the value is set to a sufficiently large value with respect to the drive frequency. The cutoff frequency of 796 kHz of this low-pass filter is an example, and it is sufficient to have a time constant in the range of 1/30 to 1/100 of the period of the drive signal in order to reduce the frequency of about 1 MHz.

As the diode D1 having a rectifying function, a diode having a small capacitance component such as a Schottky diode and a reverse recovery time is used. The voltage from which high-frequency noise is removed from the voltage across the current detection resistor R1 is amplified by the voltage amplifier A1, and the resistor R4 (2 kΩ), resistor R5 (1.5 kΩ), and capacitors C2 and C3 (each 0) are amplified via the diode D1. It is added to the peak value holding time constant circuit consisting of .1 μF). The output voltage of the peak value holding time constant circuit is supplied to the A / D conversion input terminal of the microcomputer 80 via the voltage amplifier A2 (for example, a buffer having an amplification degree of 1). Capacitors C2 and C3 are used for the purpose of holding voltage, and the charging speed is determined by the rectifying action of the diode D1 and the resistors R4 and R5. The output voltage of the peak detection unit 70 output converges to a detection value proportional to the peak current while the input waveform is repeated. For example, in contrast to the input waveform of a square wave, in the input waveform of a triangular wave, the charging time becomes shorter as it approaches the end of the triangular wave, so that the time for approaching the detection level or the saturation value becomes longer. In the circuit configuration of FIG. 2, assuming that the lower limit frequency of 20 kHz is adjusted with respect to the center frequency of 23 kHz, the frequency of the drive signal (that is, the drive frequency) is 20 msec for a triangular wave having a duty ratio of about 25%. It is determined so that the peak detection value is obtained from the waveforms of ~ 30 msec and 400 to 600 (the first time constant for acquiring the peak value is set).

The high-voltage power supply device for an electrostatic coating device shown in FIG. 1 is installed in a factory, and noise is induced from a cable connecting the high-voltage module 20 and the high-voltage control unit 30, and pulse-shaped noise peaks. It may be mixed in the part 70. For example, the pulse width is 1 μsec, the current noise is 30 A, and the like. This pulse width is about 1 / 43.5 of the drive cycle assuming a center frequency of 23 kHz, and the peak detection unit 70 is adjusted so as to reach the detected value with 400 to 600 waveforms as described above. Therefore, assuming that the minimum value of the peak current is 0.5A,
30A ÷ 0.5A ÷ 43.5 ÷ 400 = 0.0043
Therefore, the influence of this noise on the peak detection unit 70 can be 1% or less even with the minimum peak value as a reference. At this time, the time 20 msec for the peak detection unit 70 to reach the detected value is 20000 times the noise pulse width of 1 μsec. Considering the minimum value of the peak current and the fluctuation width of the noise pulse width, the first time constant for acquiring the peak value is in the range of 5000 to 30,000 times the noise pulse width mixed in the peak detection unit 70. It can be said that there is preferable. Further, a range of 250 to 1500 times the cycle of the drive signal is more preferable.

On the other hand, the holding characteristic of the peak value in the peak detection unit 70 is determined in consideration of the ripple of the output voltage. Since the electric charge of the capacitors C2 and C3 is discharged by the resistor R6, the second time constant for holding the peak value is determined by the capacitors C2 and C3 and the resistor R6. In order to keep the ripple of the output voltage within 1%, the sum of the capacitors C2 and C3 and the second time constant due to the resistor R6 are set to 100 times or more the period of the drive signal. In addition to the resistor R6, the current is discharged by the leakage current of the diode D1 and the input bias current of the A / D converter of the microcomputer 80 to be connected. This size is about 1 to 5 μA in consideration of the ambient temperature, and when a capacitor of about 0.1 μF is used for the capacitors C2 and C3, the resistor R6 is not connected, and the capacitor capacity and the leakage current of the above device are measured. It may be decided in consideration. For example, if the voltage of the capacitors C1 and C2 corresponding to the lowest current peak is 0.05V, the discharge time due to the leakage current is the minimum value: (0.1μF × 2 × 0.05V) ÷ 5μA = 2msec,
Maximum value: (0.1 μF × 2 × 0.05 V) ÷ 1 μA = 10 msec
Therefore, the waveform is in the range of 100 to 500 with respect to the minimum frequency of 20 kHz.
The above describes the lowest current peak, but this peak value changes depending on the load of the high-voltage power supply, that is, the shape of the electrostatic coating device and the object to be coated, the distance to the object to be coated, etc., and usually the best coating quality is obtained. Assuming that the voltages of the capacitors C1 and C2 corresponding to the current peaks in the obtained load state are 0.3V, the voltage is in the range of 600 to 3000 waveforms with respect to the minimum frequency of 20 kHz by the same calculation.
Further, when the optimum frequency is determined by the program of the microcomputer 80, for example, if the voltage change of the maximum capacitors C1 and C2 due to the change of 0.1 Hz is 0.1 V, the voltage is determined by this frequency change. , 0.1 μF × 2 × 0.1 V) ÷ 1 μA = 20 msec or more is required. The program observes the voltage of the peak detection unit 70 after a lapse of time such as 0.05 seconds to 0.1 seconds or more, which is a cycle of this time or more.

In consideration of the above, the second time constant is preferably in the range of 100 to 3000 times the period of the drive signal, and further, the second time constant is a frequency change when adjusting the drive signal period. It is desirable that the determination time of the detection value corresponding to the quantity is in the range of 100 to 500 times the cycle of the drive signal.

In the actual circuit, it is restricted by the components. This is because ripples occur in the output due to the ratio of the capacitance component of the diode D1 to the capacitors C2 and C3 that realize the holding characteristics. As the diode having a rectifying function, a diode having a small capacitance component and reverse recovery time such as a Schottky type is used. Generally, when the filter is composed of a resistor and a capacitor, the capacitor capacity is set to 10,000 pF or more in consideration of the capacitor capacity of the above diode, and the range of 10,000 pF to 470,000 pF is suitable.

Further, the high voltage control unit 30 includes a display / operation unit 85, a drive frequency display unit 851 for displaying the drive frequency, an average current value display unit 852 for displaying the average current value, and a peak current value display for displaying the peak current value. It has a part 853. The average current value of the average current value display unit 852 is a value obtained from the A / D conversion input terminal of the microcomputer 80 by connecting the output of the current detection unit 60 to the smoothing circuit 65. The peak current value of the peak current value display unit 853 is a value obtained by acquiring the output of the peak detection unit 70 from the A / D conversion input terminal of the microcomputer 80. The drive frequency can be increased by, for example, 0.1 Hz from the current value by the frequency adjustment button 854 of the display / operation unit 85, and can be decreased by 0.1 Hz by the frequency adjustment button 855. The display / operation unit 85 may be composed of a 7-segment LED or a switch attached to the high voltage control unit 30, or may realize an equivalent function by software of a PC connected to the high voltage control unit 30. ..

The operation of the above embodiment will be described. The variable control stabilized power supply 40 of the high voltage control unit 30 generates an internal voltage according to the voltage setting instruction of the voltage setting signal 81 from the microcomputer 80. The internal voltage output is supplied to one end of the primary winding 21a of the high voltage transformer 21 in the high voltage module 20 via a cable of 5 m to 30 m. The other end of the primary winding 21a of the high-voltage transformer 21 returns to the high-voltage control unit 30 via a cable, and is switched at the drive frequency by the drive circuit 50. This switching frequency is performed by the FET 52 of FIG. 2 by the drive signal 82 from the microcomputer 80.

The range of the drive frequency varies depending on the internal circuit configuration of the high voltage module 20, but for example, the center frequency is 23 kHz, the adjustment range is 21 kHz to 25 kHz, and the frequency range suitable for operation is 22.5 kHz to 23.5 kHz. The high voltage control unit 30 may have specifications that can be adjusted in the range of 10 kHz to 50 kHz so as to be compatible with various high voltage modules 20.

In the present embodiment, in order to keep the efficiency of the high voltage module 20 good, the current detection unit 60 that detects the current on the primary side of the high voltage transformer 21 and converts it into a voltage, and the voltage output from the current detection unit 60. A peak detection unit 70 is used that inputs a signal and detects the peak voltage of the signal. As shown in FIG. 3, when the drive frequency-detection value curve 71 in the case of the embodiment (when the current peak value is used) is compared with the conventional drive frequency-detection value curve 72 based on the current average value or the efficiency value. The curves of, 71 _{have a narrower and more sensitive characteristic with respect to the center frequency f 0} (resonance frequency of the power supply in the high voltage module 20). Therefore, the drive frequency can be adjusted to the _{center frequency f 0} with relatively high accuracy by controlling the detection value proportional to the current peak value to the minimum. Further, the frequency change range when obtaining the optimum value of the drive frequency may be narrow (in the case of automatic adjustment, the adjustment time can be shortened).

Further, the effectiveness when the drive frequency is controlled by the current peak value will be described with reference to FIG. FIG. 4 shows an example of the primary side current of _{the high voltage transformer 21 at the center frequency f 0} and the primary side current when the drive frequency _{deviates from the center frequency f 0.} FIG. 4 (a) shows when the drive frequency is _{100% (frequency matching) of the center frequency f 0} , FIG. 4 (b) shows 101% (high frequency), and FIG. 4 (c) shows 99% (frequency match). When (low), the figure (d) is 109%, and the figure (e) is 91%. In the high-voltage transformer of the high-voltage power supply device for electrostatic coating equipment, the winding number ratio on the primary side and the secondary side is significantly different. It is generally known that the waveform becomes.

For example, in FIG. 4A, the peak current is 3A and the average current is 1.2A. In FIGS. 4 (b) and 4 (c), the peak current is 3.24 A, which is an increase of 8%, whereas the average current is a resonance type current waveform, so that the g portion is convex and the h portion is concave. Therefore, it is clear that there is almost no change. As an example from the actual measurement, at a frequency of 99%, the output voltage of the peak detection unit 70 is about + 8%, the average value is about + 2%, the efficiency value is + 3 to 4%, and the resonance type high voltage module 20. The detection of the peak value is effective in the power supply device including.

Further, FIGS. 4 (d) and 4 (e) show a case where the drive frequency deviates significantly from the center frequency. Especially when the drive frequency in FIG. 4 (e) is significantly low, the peak current is 9 A, and the shape is close to a triangular wave having a duty ratio of 25% to 30%. Due to this shape, the average value is not larger than expected and is 1.5A. The effective value in FIG. 4 (e) is 2.7 Arms, and the unmatched power is the high voltage control unit 30 and the high voltage module as compared with the current waveform at the _{center frequency f 0 in FIG. 4 (a).} It becomes heat at 21, and there is a possibility that the circuit parts may deteriorate due to long-term operation. In the configuration for detecting the current peak value of the present embodiment, 9A / 3A = 3 times the current value at the center frequency in FIG. 4A, whereas the conventional current average value is FIG. 4 1.5A / 1.2A = 1.25 times the current value at the center frequency of (a), and in the case of peak value detection, the increase is on the order of almost the effective value of the current. Therefore, even in a waveform having a shape different from that of a sine wave, such as a transformer primary side current waveform, it is possible to remarkably discriminate inconsistency in drive frequencies.

According to the embodiment of the present invention, even when the primary current of the high voltage transformer 21 becomes abnormal when adjusting the drive frequency, it becomes easy to detect. FIG. 6 is a drive waveform when an abnormality occurs in the high voltage transformer 21. For example, when the high-voltage transformer 21 is overheated, magnetic saturation of the high-voltage transformer 21 may occur due to the primary side current, and the current may increase. In the magnetic saturation phenomenon, when the current value exceeds a certain value, the inductance of the transformer decreases and a large current flows. Since the current change due to the abnormality of the high-voltage transformer 21 occurs every cycle, it can be detected as an increase in the current peak.

FIG. 7 is a current waveform diagram of the primary side of the high-voltage transformer when the drive frequency on the primary side of the high-voltage transformer is the center frequency and when the drive frequency deviates from the center frequency. The case where a large current is generated is shown. Since the current increases abnormally in a part of the drive waveform from a certain frequency, a discontinuous portion occurs with respect to the normal increase / decrease curves 71 and 72. Since the pulse current is detected, the slope of the detection value change becomes remarkable in the discontinuity portion 74 due to the pulse current with respect to the discontinuity portion 73 due to the average current.

The button 854 of the display / operation unit 85 can be used to increase the drive frequency by, for example, 0.1 Hz, and the button 855 can be used to decrease the drive frequency by 0.1 Hz, so that the drive frequency can be adjusted. The optimum frequency is determined by pressing the buttons 854 and 855 so that the peak current value of the peak current value display unit 853 is minimized from the vicinity of the center frequency f _0. At this time, if an abnormal current is generated, the peak current value changes significantly by the button operation, so that the operator can notice the abnormality.

For example, when the button 855 is pressed to reduce the drive frequency by 0.1 Hz from a certain frequency point, the peak current value changes from 3 A to 3.1 A and the average current value changes from 1.2 A to 1.21 A. Subsequently, when the button 855 is pressed to reduce the drive frequency by 0.1 Hz, the peak current value and the average current value increase as 3.24A and 1.22A, respectively. If the button 855 is continuously pressed and a magnetic flux saturation phenomenon occurs in a part of the waveform and an abnormal current is generated, the peak current value is 3.24A to 4.0A based on the ratio of the peak current detection sensitivity described above. The average current value is about 1.22A to 1.3A (6% increase in the center frequency) with respect to (23% increase in the value of the previous frequency). In this way, it is easy to feel that there was a discontinuous change with respect to the manual operation. By displaying the average current value and the peak current value of the display units 852 and 853 in the shape of an indicator such as a bar graph instead of a numerical value, it becomes easier to discriminate. The average current value is displayed as a guide for the load status. This is, in the vicinity of the drive frequency is the center frequency f _0, because the average current substantially proportional to the output current of the high-voltage module 20 increases. It is possible to determine whether or not the change in current due to the load state is related to the increase in the peak current value.

According to this embodiment, the following effects can be obtained.

(1) In a high-voltage power supply device having resonance-type characteristics used in an electrostatic coating device that disperses electrostatically charged coating material particles, it is proportional to the current peak value of the primary winding 21a of the high-voltage transformer 21. By variably controlling the drive frequency on the primary side of the high-voltage transformer so that the output voltage of the peak detector 70 is minimized, the drive frequency is controlled and optimized with higher accuracy than the conventional control method using average current and efficiency. It becomes possible to do.

(2) Since the detection sensitivity to the frequency deviation from the center frequency is excellent, a high-precision detection circuit is not required, and even when the drive frequency is automatically adjusted by software, the deviation from the center frequency is relatively small. The optimum value can be reached in a short period of time even from the initial state. As a result, not only the efficiency of the high voltage module 20 can be optimized, but also the life of the high voltage module 20 can be extended by lowering the effective value of the current of the high voltage transformer 21.

(3) The drive frequency can be adjusted without erroneous detection so that the noise mixed from the connection cable of the electrostatic coating device is less affected and the current peak becomes the minimum value.

(4) During the operation of the high voltage control unit, it is possible to appropriately display abnormalities such as damage or deterioration of elements such as the high voltage transformer 21, which are difficult to understand from the average current.

Although the present invention has been described above by taking the embodiment as an example, it will be understood by those skilled in the art that various modifications can be made to each component and each processing process of the embodiment within the scope of the claims. By the way. Hereinafter, a modified example will be touched upon.

In the above embodiment, a circuit configuration in which one drive circuit for switching the primary side of the high-voltage transformer is illustrated. However, a center tap is provided in the primary winding of the high-voltage transformer, and two phases having 90 ° phases different from each other are provided. The present invention can be applied even when two drive circuits are used as the method.

The circuit configurations of the drive circuit, the current detection unit, and the peak detection unit in FIG. 2 are examples, and can be changed as appropriate, and it is clear that the switching element in the drive circuit is not limited to the FET.

10 Injector 20 High voltage module 21 High voltage transformer 22 Voltage booster circuit 30 High voltage control unit 40 Variable control stabilized power supply 50 Drive circuit 51 FET drive circuit 52 FET
53 Snubber circuit 60 Current detection unit 65 Smoothing circuit 70 Peak detection unit 80 Microcomputer 85 Display / operation unit 851 Drive frequency display unit 852 Average current value display unit 853 Peak current value display unit 854,855 Frequency adjustment buttons A1, A2 Voltage amplifier C1, C2, C3 Capacitor D1 Diode R1, R2, R3, R4, R5, R6 Resistor

Claims (5)

A high-voltage power supply used in an electrostatic coating device that sprays electrostatically charged coating material particles.
It has a high-voltage transformer having a primary winding and a secondary winding, and a high-voltage rectifier that rectifies the induced voltage of the secondary winding, and transfers the output voltage of the high-voltage rectifier to a coating device using an electrostatic potential. The high voltage generator to supply and
A drive circuit that switches the current flowing through the primary winding,
A peak detection unit that detects the peak value of the current of the primary winding, and
It is equipped with a controller that generates a drive signal and supplies it to the drive circuit.
A high-voltage power supply device for an electrostatic coating device, characterized in that the frequency of the drive signal is variably controlled by the controller so that the peak value of the peak detection unit is minimized. The high-voltage power supply device for an electrostatic coating device according to claim 1, further comprising a circuit for detecting an average value of the current of the primary winding. The peak detection unit has a first time constant for acquiring the peak value and a second time constant for holding the peak value.
The first time constant is in the range of 5,000 to 30,000 times the noise pulse width mixed in the peak detection unit.
The high-voltage power supply device for an electrostatic coating device according to claim 1 or 2 , wherein the second time constant is equal to or longer than the period of the drive signal. The first time constant is in the range of 250 to 1500 times the cycle of the drive signal, the second time constant is in the range of 100 to 3000 times the cycle of the drive signal, and the second time constant is in the range of 100 to 3000 times. The time constant of the above is for the electrostatic coating apparatus according to claim 3 , wherein the determination time of the detected value corresponding to the amount of frequency change when adjusting the drive signal cycle is in the range of 100 times to 500 times. High voltage power supply. A smoothing circuit that detects the average current of the primary winding, an operating means that increases or decreases the drive frequency, which is the frequency of the drive signal, in a unit frequency, a means for displaying the drive frequency, and a current of the primary winding. A display means for displaying a peak value and a display means for displaying the average current value are provided, and the current peak value and the average current value are updated with respect to an increase or decrease in the drive frequency by the operating means. The high-voltage power supply device for an electrostatic coating device according to claim 1.

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