JP6856833B2 - High voltage controller - Google Patents

Description

The present invention relates to a high voltage control device that controls a high voltage.

In general, an electrostatic coating device generates a negative high voltage to form an electrostatic field with an object to be coated having a ground potential, and coats charged paint particles on the object to be coated. Therefore, the electrostatic coating device includes a high voltage generator that generates a high voltage. The high voltage generator boosts the supplied low voltage power to a high voltage. Therefore, a high-voltage control device that controls high-voltage power using low-voltage power is connected to the high-voltage generator (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-246189

By the way, the high voltage generator includes a flyback transformer and a Cockcroft-Walton circuit (multi-stage voltage doubler rectifier circuit), and generates a high DC voltage from a low voltage composed of a pulse waveform (rectangular wave shape) generated from the DC voltage. Therefore, the high-voltage controller supplies the low-voltage power of the set optimum frequency to the high-voltage generator. However, if the high voltage generator continuously outputs a high voltage, the high voltage generator may self-heat, and humidity changes, load fluctuations, and the like may occur. Due to these effects, the frequency of the low voltage power shifts from the optimum value, the power loss increases, and problems such as not being able to obtain the desired high voltage occur.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a high voltage control device capable of reducing power loss.

In order to solve the above-mentioned problems, the invention of claim 1 is a high voltage control device that supplies low voltage power of a set frequency to a transformer of a high voltage generator and controls a high voltage generated by the high voltage generator. A power supply unit that supplies low-voltage power of the set frequency to the primary side of the transformer, a current detector that detects the peak value of the transformer drive current flowing through the primary side of the transformer, and the current detector. the peak value of the transformer driving current detected is such that a minimum, are Bei Ete a frequency control unit for controlling the set frequency of the low-voltage power supplied from the power supply unit by.

In the invention of claim 1, the frequency control unit has a first frequency which is the same as the current set frequency, a second frequency which is higher than the current set frequency, and a frequency lower than the current set frequency. For each of the third frequencies, the power supply unit generates low voltage power, the current detector detects the peak value of the transformer drive current, and the frequency control unit takes 10 seconds or more and 5 minutes or less. At regular intervals set to values within the range, the frequency at which the peak value of the transformer drive current is the smallest among the first frequency, the second frequency, and the third frequency is set as a new set frequency. It is characterized by that.

In the invention of claim 2, and a storage unit for storing the initial value before Symbol set frequency, and a display unit that displays the initial value and the set frequency in each of the constant period, and further comprising a.

The invention of claim 3 is characterized in that the initial value is updated to the value of the set frequency when the high voltage generator is stopped.

In the invention of claim 4, when the frequency control unit changes the value of the high voltage output from the high voltage generator, the frequency control unit does not set a new set frequency for a predetermined period from the start of the change. It is characterized by that.

According to the invention of claim 1, the high voltage control device includes a power supply unit, a current detector, and a frequency control unit. Here, when the power loss increases due to self-heating of the high voltage generator, humidity change, load fluctuation, etc., the peak value of the transformer drive current increases. That is, when the set frequency deviates from the resonance frequency of the transformer to the low frequency side or the high frequency side, the waveform of the transformer drive current tends to be distorted and the peak value of the transformer drive current tends to increase. Therefore, by detecting the peak value of the transformer drive current, it is possible to grasp that the set frequency deviates from the resonance frequency of the transformer.

In addition to this, in the invention of claim 1 , the frequency control unit has the same first frequency as the current set frequency, the second frequency higher than the current set frequency, and the frequency lower than the current set frequency. For each of the third frequencies, the power supply unit generates low-voltage power, and the current detector detects the peak value of the transformer drive current. Then, the frequency control unit sets the frequency when the peak value of the transformer drive current is the smallest among the first frequency, the second frequency, and the third frequency as a new set frequency. As a result, the currently set frequency can be adjusted so that the peak value of the transformer drive current becomes small.
Further, since the constant cycle is set to a value within the range of 5 minutes or less in 10 seconds or more, the set frequency can be updated in a state where the high voltage output and the transformer drive current are stable.

According to the invention of claim 2 , since the display displays the initial value and the set frequency at regular intervals, the operator can grasp the difference between the initial value and the current set frequency by visually observing the display. can do. Therefore, for example, when the device is stopped, by checking the difference between the initial value and the currently set frequency, whether this difference is in the normal state due to the temperature change of the high voltage generator or an abnormality due to some trouble. It is possible to grasp whether it depends on the state.

According to the invention of claim 3 , the initial value is updated to the value of the set frequency when the high voltage generator is stopped. Therefore, for example, when the change of the optimum set frequency due to the aging is dominant, the change over time The initial value can be changed according to. Therefore, it is possible to shorten the time from the initial value to the adjustment to the optimum set frequency.

According to the invention of claim 4 , when changing the value of the high voltage output from the high voltage generator, the frequency control unit does not set a new set frequency for a predetermined time from the start of the change. For example, immediately after changing the set value of high voltage, the high voltage and transformer drive current are in an unstable state, the set frequency cannot be adjusted based on the transformer drive current, and the set frequency may deviate from the optimum value. There is sex. On the other hand, the current set frequency can be maintained without setting a new set frequency for a predetermined time after changing the high voltage value. Therefore, it is possible to prevent the set frequency from deviating from the optimum value.

It is a block diagram which shows the high voltage control apparatus and the coating machine by embodiment of this invention. It is a flow chart which shows the frequency control processing by a high voltage control device. It is a time chart which shows the transformer drive voltage and the transformer drive current when a set frequency becomes an optimum value. It is a time chart which shows the transformer drive voltage and the transformer drive current when the set frequency becomes a frequency lower than the optimum value. It is a time chart which shows the transformer drive voltage and the transformer drive current when the set frequency becomes a frequency higher than the optimum value. It is a flow chart which shows the frequency control processing by the high voltage control device of the modification.

Hereinafter, as the high voltage control device according to the embodiment of the present invention, a device used for electrostatic coating will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a high voltage control device 11 according to an embodiment of the present invention. The high voltage control device 11 is connected to the coating machine 1 for electrostatic coating.

First, the coating machine 1 to which the high voltage control device 11 is applied will be described. The coating machine 1 includes a sprayer 2 for spraying paint and a high voltage generator (cascade) 3 for generating a high voltage Vh. The sprayer 2 is composed of various atomizing means for performing, for example, air atomization, hydraulic atomization, rotary atomization, etc., atomizes the supplied paint, and sprays it toward an object to be coated (not shown). To do.

The high voltage generator 3 is built in the coating machine 1. The high voltage generator 3 includes a step-up transformer 4 and a multi-stage voltage doubler rectifier circuit 5. As shown in FIG. 1, a high voltage control device 11 is connected to the primary coil of the step-up transformer 4, and a pulse wave (square wave) primary voltage having a frequency (set frequency F) of, for example, several tens of kHz is generated. Entered. This primary voltage corresponds to the transformer drive voltage Vt that drives the step-up transformer 4. The step-up transformer 4 excites a secondary voltage having a voltage higher than the primary voltage in the secondary side coil by inputting the primary voltage to the primary side coil of the step-up transformer 4.

The multi-stage voltage doubler rectifier circuit 5 is composed of a so-called Cockcroft-Walton circuit composed of a plurality of capacitors and diodes (none of which are shown). The multi-stage voltage doubler rectifier circuit 5 further boosts the secondary voltage supplied from the step-up transformer 4 to generate a negative electrode high voltage Vh (for example, Vh = 0 kV to −90 kV).

Then, the coating machine 1 directly or indirectly charges the paint particles sprayed from the sprayer 2 by using the high voltage Vh output from the high voltage generator 3. In addition to this, the coating machine 1 forms an electrostatic field with an object to be coated (not shown) having a ground potential. As a result, the coating machine 1 makes the charged paint particles fly along the electrostatic field and coats the object to be coated.

Next, the high voltage control device 11 will be described. The high voltage control device 11 includes a transformer drive circuit 12, a power supply current detection circuit 13, a tip voltage / current detection circuit 14, and a signal control device 15.

The transformer drive circuit 12 constitutes a power supply unit that supplies low-voltage power at a set frequency F to the primary side of the step-up transformer 4. The transformer drive circuit 12 includes a power supply converter 12A, a switching drive circuit 12B, and an oscillation circuit 12C. The input side of the transformer drive circuit 12 is connected to a commercial power source. The output side of the transformer drive circuit 12 is connected to the primary coil of the step-up transformer 4.

The power converter 12A is composed of, for example, a rectifier circuit, converts an AC voltage supplied from a commercial power supply into a DC voltage, and outputs this DC voltage to the switching drive circuit 12B. The switching drive circuit 12B steps down the DC voltage output from the power supply converter 12A to a voltage corresponding to the voltage command signal Cv from the signal control device 15. The oscillation circuit 12C controls a switching element (not shown) such as a transistor in response to the frequency command signal Cf from the signal control device 15. As a result, the oscillation circuit 12C outputs a pulse signal corresponding to the frequency command signal Cf. The transformer drive circuit 12 converts the DC power output from the switching drive circuit 12B into power corresponding to the pulse signal output from the oscillation circuit 12C, and supplies the DC power to the primary coil of the step-up transformer 4. As a result, a transformer drive voltage Vt having an amplitude corresponding to the DC voltage output from the switching drive circuit 12B and having a frequency of the pulse signal of the oscillation circuit 12C is supplied to the primary coil of the step-up transformer 4. ..

The power supply current detection circuit 13 constitutes a current detector and detects a transformer drive current It as a power supply current flowing through the primary coil of the step-up transformer 4. The power supply current detection circuit 13 outputs the detection signal Sit of the transformer drive current It toward the signal control device 15. Here, the power supply current detection circuit 13 includes a peak current detection circuit (not shown) that detects the peak value of the transformer drive current It. Therefore, the detection signal Sit by the power supply current detection circuit 13 corresponds to the peak value of the transformer drive current It.

Depending on the drive frequency of the transformer drive circuit 12, the waveform of the transformer drive current It changes and the peak value changes. If the drive frequency is an appropriate frequency, the peak value of the transformer drive current It becomes small. On the other hand, when the drive frequency deviates from the appropriate frequency, the peak value of the transformer drive current It increases and the efficiency decreases. In the state where the efficiency is lowered, the unmatched electric power becomes heat in the transformer drive circuit 12 and the high voltage generator 3, and there is a possibility that the circuit parts are deteriorated by long-term operation.

The tip voltage / current detection circuit 14 detects the tip voltage (high voltage Vh) output from the high voltage generator 3 and also detects the current flowing through the secondary coil of the step-up transformer 4. The advanced voltage / current detection circuit 14 outputs the high voltage Vh detection signal Sv output from the high voltage generator 3 and the current detection signal Si flowing through the secondary coil toward the signal control device 15.

The signal control device 15 is composed of a microprocessor or the like and constitutes a frequency control unit. The signal control device 15 generates a voltage command signal Cv and a frequency command signal Cf to be transformer control signals based on the detection signals Sit, Sv, and Si from the power supply current detection circuit 13 and the tip voltage / current detection circuit 14. The signal control device 15 controls the transformer drive circuit 12 by these command signals Cv and Cf so that the high voltage Vh output from the high voltage generator 3 becomes a desired value. Specifically, the signal control device 15 generates a voltage command signal Cv based on the value of the high voltage Vh, and controls the switching drive circuit 12B so that the high voltage Vh becomes a desired value (target value). .. As a result, the switching drive circuit 12B increases or decreases the amplitude of the transformer drive voltage Vt and adjusts the value of the high voltage Vh.

The target value of the high voltage Vh may be stored in the signal control device 15 in advance, or may be input from, for example, a coating machine control device (not shown) that controls the coating machine 1. Therefore, the target value of the high voltage Vh does not have to be a constant value, and may be a value that changes based on various conditions.

Further, the signal control device 15 controls the set frequency F of the pulse signal output from the oscillation circuit 12C based on the detection signal Sit from the power supply current detection circuit 13. Specifically, the signal control device 15 is driven according to the frequency control processing program shown in FIG. As a result, the signal control device 15 generates the frequency command signal Cf based on the peak value of the transformer drive current It, and the transformer drive circuit 12 minimizes the transformer drive current It detected by the power supply current detection circuit 13. Controls the set frequency F of the low voltage power supplied from.

By using the peak value of the transformer drive current It, the rate of change of the detected value of the power supply current detection circuit 13 due to the rate of change of the set frequency F becomes larger than the case of using the average value or the effective value. Further, although it depends on the high voltage generator 3 to be used, in the configuration in which the detection signal Sv of the tip voltage can be used, the signal control device 15 may perform control to keep the high voltage Vh constant while switching and controlling the set frequency F. Good.

Further, the signal control device 15 is connected to a non-volatile memory 16 as a storage unit and an operation / display 17 as a display. The non-volatile memory 16 stores the initial value F0 of the set frequency F. At this time, the initial value F0 can be changed by the operator inputting and operating the operation / display 17. Further, the operation / display 17 is configured by, for example, a touch panel or the like, displays various information, and allows the operator to perform various input operations. At this time, the operation / display 17 displays the initial value F0 and the current set frequency F at regular cycle τ.

Next, a method of controlling the set frequency F by the signal control device 15 will be described with reference to FIG.

In step 1, the set frequency F is set to a predetermined initial value F0. In addition to this, the set voltage that is the target value of the high voltage Vh is also set to a predetermined initial value. In the following step 2, the transformer drive circuit 12 is driven based on the set voltage and the set frequency F. As a result, the high voltage generator 3 generates and outputs a high voltage Vh corresponding to the set voltage based on the low voltage power supplied from the transformer drive circuit 12.

In the following step 3, for example, a timer is used to determine whether or not a preset constant period τ has elapsed. At this time, the constant period τ is set based on the time required for the output of the high voltage Vh and the transformer drive current It to stabilize according to the set voltage and the set frequency F. Specifically, the constant period τ is set to a value within the range of, for example, 10 seconds or more and 5 minutes or less.

In the following step 4, the peak value Ip1 of the transformer drive current It at the same first frequency F1 as the currently set frequency F is measured. At this time, the transformer drive circuit 12 supplies the low voltage power to the high voltage generator 3 while maintaining the current set frequency F. The power supply current detection circuit 13 measures the peak value Ip1 of the transformer drive current It at this time, and outputs the detection signal Sit corresponding to the peak value Ip1 toward the signal control device 15.

As will be described in the following steps 5 and 6, the signal control device 15 measures the peak value Ip1 after a certain switching time elapses for each frequency (F1, F2, F3) switching. This switching time is set to a value of, for example, about 0.1 second to 1 second after setting the frequency (for example, setting the set frequency F to the first frequency F1). The reason for this is that the delay time of the step-up transformer 4 and the multi-stage voltage doubler rectifier circuit 5 used in the high voltage generator 3 has an effect. Therefore, when the set frequency is changed and the measurement is performed immediately, the set frequency is originally set. This is because there is a possibility that the value to be measured by F cannot be measured.

Further, during painting, the peak value of the transformer drive current It changes depending on the load state of the high voltage generator 3. The rate of this change is generally 2-5 Hz or less, depending on the distance between the high voltage generator 3 and the object to be coated. The values of about 0.1 second to 1 second, which are specific examples of the switching time described above, are set to a sufficiently short interval with respect to the rate of change of the peak value of the transformer drive current It due to these loads. When the measurement of the peak value Ip1 is completed, the process proceeds to step 5.

In step 5, the peak value Ip2 of the transformer drive current It at the second frequency F2, which is higher than the currently set frequency F, is measured. At this time, the second frequency F2 is set to a frequency higher than the current set frequency F by a predetermined frequency difference ΔF (F2 = F + ΔF). The frequency difference ΔF is a value at which a detectable change appears in the peak value of the transformer drive current It based on the difference between the first frequency F1 and the second frequency F2, for example, with respect to the maximum value of the set frequency F. It is set to a value of about one hundredth. Specifically, when the set frequency F is in the range of 10 kHz to 30 kHz, the frequency difference ΔF is set to, for example, 0.1 kHz.

Further, this frequency difference ΔF is a frequency difference that does not affect the coating quality. When the frequency difference is larger, it affects the control for keeping the high voltage Vh constant. Specifically, if the frequency difference is made too large, the output of the high voltage generator 3 may be affected, and the coating quality may be affected by the occurrence of an unintended abnormal output or the output fluctuation. This is because the signal control device 15 has a relatively large time constant of the step-up transformer 4 and the multi-stage voltage doubler rectifier circuit 5 used in the high voltage generator 3, and the negative voltage Vh is constant. This is because feedback control (generation of voltage command signal Cv and frequency command signal Cf as transformer control signals based on the detection signals Sit, Sv, and Si) is performed. However, when the set frequency F is switched (when the frequency difference is large), the transformer supply power changes, and the feedback control signals (detection signals Sit, Sv, Si) become discontinuous inputs. In this case, since the amount of energy supplied per unit time changes due to the change in the drive frequency, fluctuations such as overshoot of the negative high voltage Vh occur at the time of switching. Although it depends on the high voltage generator 3 used, a value of about 0.1 kHz is generally used for the frequency difference ΔF so that the fluctuation amount of the high voltage Vh is within ± 1 kV.

Then, when measuring the peak value Ip2, the transformer drive circuit 12 supplies the low voltage power to the high voltage generator 3 in a state where the current set frequency F is changed to the second frequency F2. The power supply current detection circuit 13 measures the peak value Ip2 of the transformer drive current It at this time, and outputs the detection signal Sit corresponding to the peak value Ip2 toward the signal control device 15. When the measurement of the peak value Ip2 is completed, the process proceeds to step 6.

In step 6, the peak value Ip3 of the transformer drive current at the third frequency F3, which is lower than the currently set frequency F, is measured. At this time, the third frequency F3 is set to a frequency lower than the current set frequency F by a predetermined frequency difference ΔF (F2 = F−ΔF). Even if the frequency difference ΔF between the currently set frequency F (first frequency F1) and the third frequency F3 is set to the same value as the frequency difference ΔF between the currently set frequency F and the second frequency F2. Often, they may be set to different values.

Then, when measuring the peak value Ip3, the transformer drive circuit 12 supplies the low voltage power to the high voltage generator 3 in a state where the current set frequency F is changed to the third frequency F3. The power supply current detection circuit 13 measures the peak value Ip3 of the transformer drive current It at this time, and outputs the detection signal Sit corresponding to the peak value Ip3 toward the signal control device 15. When the measurement of the peak value Ip3 is completed, the process proceeds to step 7.

In step 7, the peak values Ip1, Ip2, and Ip3 are compared, and the smallest value is determined. When it is determined in step 7 that the peak value Ip1 is the minimum value, the process proceeds to step 8 and the set frequency F is set to the first frequency F1. As a result, the new set frequency F is maintained at the same value as the current set frequency F. When the process of step 8 is completed, step 2 and subsequent steps are repeated.

By measuring the peak values Ip1, Ip2, and Ip3 using the frequencies F1, F2, and F3 in steps 4, 5, and 6, even if a relatively long-time value is used for the constant period τ in step 3, it is erroneous. The set frequency F corresponding to the minimum peak current value can be obtained without making a determination. In the generally known steepest descent method, when the decrease in the observable is reversed to the increase, the frequency is switched (for example, starting from the frequency F1 and using the frequency F2 for a certain period of time, depending on the observed amount at this time. , Frequency F3, etc.). On the other hand, for example, the internal temperature of the high voltage generator 3 is also affected by the ambient temperature, so it is not necessarily a monotonous increase. When these conventional methods are used, a long-term fluctuation such as a temperature change is erroneously determined, and the minimum peak value cannot be obtained. Therefore, the drive frequency (set frequency F) does not move toward the minimum peak value when the drive frequency is several times as large as the frequency difference ΔF from the optimum frequency, or when the ambient temperature or load fluctuates. The result is that.

When it is determined in step 7 that the peak value Ip2 is the minimum value, the process proceeds to step 9 and the set frequency F is set to the second frequency F2. As a result, the new set frequency F is changed to the second frequency F2, which is higher than the current set frequency F. When the process of step 9 is completed, step 2 and subsequent steps are repeated.

When it is determined in step 7 that the peak value Ip3 is the minimum value, the process proceeds to step 10 and the set frequency F is set to the third frequency F3. As a result, the new set frequency F is changed to the third frequency F3, which is lower than the current set frequency F. When the process of step 10 is completed, step 2 and subsequent steps are repeated.

The high voltage control device according to the present embodiment operates based on the frequency control process as described above.

However, when a pulse wave (rectangular wave) drive voltage (transformer drive voltage Vt) based on the set frequency F is input to the high voltage generator 3, a substantially rectangular wave transformer drive current It is generated according to the transformer drive voltage Vt. It flows. Here, when the set frequency F is set to a value close to the resonance frequency of the step-up transformer 4, the transformer drive current It becomes a waveform having two peaks on the rising side and the falling side (see FIG. 3). However, these two peaks have values close to each other, and the fluctuation in the magnitude of the transformer drive current It becomes small while the transformer drive current It is flowing. Therefore, the waveform of the transformer drive current It is balanced (balanced) between the rising side and the falling side.

However, the resonance frequency of the step-up transformer 4 changes depending on the type of the coating machine 1, the load condition, the number of years of installation, the continuous output time, and the like. On the other hand, when the set frequency F is a fixed value, the set frequency F deviates from the resonance frequency of the step-up transformer 4 according to various conditions.

For example, when the set frequency F becomes a value lower than the resonance frequency of the step-up transformer 4, the transformer drive current It increases as a whole as compared with the case shown in FIG. 3 (see FIG. 4). In addition to this, the transformer drive current It has a waveform that is biased toward the falling side due to the imbalance of the waveform between the rising side and the falling side. At this time, the transformer drive current It has a waveform having a large peak on the falling side.

On the other hand, when the set frequency F becomes a value higher than the resonance frequency of the step-up transformer 4, the transformer drive current It increases as a whole as compared with the case shown in FIG. 3 (see FIG. 5). In addition to this, the transformer drive current It has a waveform that is biased toward the rising side due to the imbalance of the waveform between the rising side and the falling side. At this time, the transformer drive current It has a waveform having a large peak on the rising side.

In this way, when the set frequency F deviates from the value (optimal value) near the resonance frequency of the step-up transformer 4, the magnitude of the transformer drive current It increases as a whole and the waveform also changes. At this time, for example, magnetic saturation occurs in the step-up transformer 4, and the power loss increases, so that the self-heating of the high voltage generator 3 further increases. As a result, there is a problem that the set frequency F deviates from the optimum frequency as the operation of the coating machine 1 is continued.

On the other hand, the high voltage control device 11 according to the present embodiment includes a signal control device 15 that controls a set frequency F of low voltage power supplied from the transformer drive circuit 12 so that the transformer drive current It is minimized. I have. Therefore, for example, when the power loss increases due to self-heating of the high voltage generator 3, humidity change, load fluctuation, etc., the signal control device 15 sets the frequency F so that the transformer drive current It is minimized. To rise or fall. As a result, the set frequency F can be automatically adjusted to approach the optimum value, and the power loss can be reduced.

Depending on the high voltage generator 3, the optimum set frequency F may fluctuate by about 1 to 5% depending on the load fluctuation and the coating condition. In order to cope with the fluctuation of the optimum value of the set frequency F due to the load, a time of about 0.5 seconds to 3 seconds is used for the constant cycle τ in step 3. However, the fluctuation of the load differs depending on the shape of the object to be coated, and the change time of the optimum value of the set frequency F is short in the object to be coated with unevenness, and the optimum value may not be able to follow in the constant period τ. In this case, the coating quality is better when the center value of the optimum value of the set frequency F, which changes depending on the load, is used. Therefore, the set frequency F may be updated at a constant period τ that is sufficiently larger than the load fluctuation as described in step 3.

Further, this constant period τ is set to a value that is less affected by control when switching the set voltage of the high voltage Vh. Generally, painting is performed with the tip voltage constant. When boosting the voltage at the start of high voltage generation, or when switching the tip voltage value from, for example, -90 kV to -70 kV according to the object to be coated (painted object), a transition period of 2 seconds or less is usually provided. During this period, the transformer drive current It changes, but it is extra for calculating the optimum set frequency F. By setting the value of the constant period τ illustrated in step 3 to a value 5 to 10 times larger than such a transition period, the influence of the control of switching the high voltage value can be extremely reduced.

In order to obtain this effect, the following simple process may be added as in the modified example shown in FIG. Specifically, the processes of steps 11 and 12 are added between step 2 and step 3. At this time, the set voltage of the high voltage Vh is changed by the signal control device 15. Therefore, in step 11, it is determined whether or not the set voltage of the high voltage Vh has been changed. When it is determined as "NO" in step 11, the set voltage of the high voltage Vh has not been changed, so the process proceeds to step 3. On the other hand, when it is determined as "YES" in step 11, since the set voltage of the high voltage Vh has been changed, the process proceeds to step 12. In step 12, as a predetermined period from the start of the change, the timer is reset to cancel the time measurement state (measurement of the time in step 3) during the transition period in which the high voltage Vh changes. After that, the process proceeds to step 3. Therefore, during the transition period when the high voltage Vh is changing toward the set voltage, the elapsed time of the constant cycle τ is not measured, but after the high voltage Vh stabilizes near the set voltage, the elapsed time of the constant cycle τ should be measured. Can be done.

The frequency control process in steps 1 to 7 may be a simpler method in consideration of the characteristics of the high voltage generator 3 and the operation method. For example, in the case of the high voltage generator 3 having a characteristic that the optimum drive frequency (optimal value of the set frequency F) decreases as the temperature rises, it is approximated by a gradual monotonous decrease of the set frequency F when the painting equipment is operated all day. This is because a sufficient effect can be obtained even if it is used. In this case, the frequency comparison may be limited to the comparison between the value obtained by subtracting the frequency difference ΔF from the value of the current set frequency F (for example, the initial value F0) and the value of the current set frequency F. As described above, in the present invention, it is effective to make the temporal speed of the frequency change of the high voltage generator 3 and the constant period τ in step 3 about the same.

Next, a method of holding the optimum frequency obtained by the frequency control processing in steps 1 to 7 will be described. Although it depends on the characteristics of the high voltage generator 3, for example, when the change of the optimum set frequency due to aging is dominant, the value of the optimum set frequency F obtained in steps 1 to 7 is periodically set to the non-volatile memory 16 Save to. Then, when the device is used next time, the value of the optimum set frequency F stored in the non-volatile memory 16 may be set as the initial value F0 in step 1.

Alternatively, when the change in the optimum set frequency due to the temperature change is dominant, the value is returned to the initial value F0 preset in the signal control device 15. When painting is performed all day, the temperature of the high voltage generator 3 rises. However, when the painting process for one day is completed and the high voltage generator 3 is stopped for a certain period of time, the temperature of the high voltage generator 3 drops to near room temperature when the operation is performed the next day. Therefore, instead of using the optimum set frequency F value obtained on the previous day, the preset initial value F0 is set to the set frequency F at startup in step 1 by turning on the power of the signal control device 15.

Next, a function of displaying the set frequency F updated in steps 1 to 7 to the operator will be described. The operation / display 17 of the high voltage control device 11 simultaneously displays the initial value F0 of step 1 input by the operator and the current set frequency F (updated value of the set frequency F) obtained in step 7. .. Further, the operation / display 17 is provided with an adjustment start button 17A for adjusting the set frequency F in a short period of time such as 30 seconds to 2 minutes.

When the painting work of one day is completed, the operator can refer to the set frequency F at that time and confirm the difference from the initial value F0. Since the difference due to the temperature rise of the high voltage generator 3 depends on the coating time per day, the difference from the initial value F0 is almost the same difference, for example, 2 kHz. Further, if the voltage is 4 kHz after one year due to aging, for example, by readjusting the initial value F0, it is possible to operate with less loss and extend the life of the high voltage generator 3. it can.

At the start of operation on the next day, the operator can press the adjustment start button 17A to update the initial value F0 and reduce the frequency deviation due to aging. The adjustment of the set frequency F in this short period can be realized by temporarily setting the constant period τ in step 3 to, for example, 0.5 seconds to 1 second.

Furthermore, if the initial value F0 and the current set frequency F value are significantly different, for example, if the difference in several days becomes 5 kHz, there is a possibility that some abnormality has occurred in the high voltage generator 3 or the painting system. , Can be useful for finding abnormalities.

Thus, the high voltage control device 11 according to the present embodiment includes a transformer drive circuit 12, a power supply current detection circuit 13, and a signal control device 15, and the signal control device 15 has a transformer so that the transformer drive current It is minimized. The set frequency F of the low voltage power supplied from the drive circuit 12 is controlled. As a result, the set frequency F of the low-voltage power can be adjusted to the optimum value, so that the power loss can be reduced and the efficiency of the power output can be improved. As a result, the load of the coating machine 1 and the self-heating of the high voltage generator 3 can be suppressed, so that the durability of the high voltage generator 3 can be improved and the life of the high voltage generator 3 can be extended. be able to.

Further, the signal control device 15 compares the magnitude of the current (transformer drive current It) flowing in the primary coil of the step-up transformer 4 with the magnitude of the current flowing in the secondary coil. Then, in the signal control device 15, when the current flowing in the primary coil becomes larger than the permissible range as compared with the current flowing in the secondary coil, it is assumed that an abnormality has occurred in the high voltage generator 3 or the like, and the high voltage Vh Occurrence may stop. If the generation of high voltage Vh is stopped in the middle of coating in this way, electrostatic coating cannot be continued, which may lead to deterioration of coating quality.

On the other hand, the signal control device 15 controls the set frequency F of the low voltage power so that the transformer drive current It is minimized. Therefore, the current flowing through the primary coil (transformer drive current It) can be kept as small as possible, so that the difference between the current flowing through the primary coil and the current flowing through the secondary coil can be reduced. it can. As a result, electrostatic coating can be continuously performed, and coating quality and coating productivity can be improved.

Further, the signal control device 15 has a first frequency F1 which is the same as the current set frequency F, a second frequency F2 which is higher than the current set frequency F, and a third frequency F3 which is lower than the current set frequency F. For each of the above, the transformer drive circuit 12 generates low-frequency power to detect the transformer drive current It. Then, the signal control device 15 sets the frequency when the transformer drive current It is the smallest among the first frequency F1, the second frequency F2, and the third frequency F3 to the new set frequency F. As a result, the currently set frequency F can be increased or decreased so that the transformer drive current It becomes smaller.

Further, the power supply current detection circuit 13 detects the peak value of the transformer drive current It. At this time, when the set frequency F deviates from the resonance frequency of the step-up transformer 4 and the waveform of the transformer drive current It is distorted, the peak value of the transformer drive current It tends to increase. Therefore, by detecting the peak value of the transformer drive current It, it can be grasped that the set frequency F deviates from the resonance frequency of the step-up transformer 4. Therefore, the signal control device 15 can automatically adjust the set frequency F to the resonance frequency of the step-up transformer 4 by controlling the set frequency F so that the peak value of the transformer drive current It is minimized.

Further, in the above-described embodiment, the signal control device 15 controls the set frequency F based on the transformer drive current It detected by the power supply current detection circuit 13. The present invention is not limited to this, and the signal control device 15 may control the set frequency F in consideration of the current of the secondary coil of the step-up transformer 4 in addition to the transformer drive current It. Specifically, the signal control device 15 controls the set frequency F so that the current of the primary coil (transformer drive current It) is minimized with reference to the current of the secondary coil of the step-up transformer 4. May be good. In this case, the signal control device 15 compares the current of the primary coil of the step-up transformer 4 (transformer drive current It) with the current of the secondary coil, and sets the set frequency F so that the difference between the two becomes small. Control.

Further, in the above-described embodiment, the operator has a preset initial value F0 and a current set frequency F updated in step 7, and the operator presets the high voltage control device 11 by turning on the power again. The initial value F0 is set to the set frequency F at startup in step 1. As a result, the temperature change due to the operation and stop state of the high voltage control device 11 can be adjusted to the optimum set frequency F in a short time from the start of operation.

Further, in the above embodiment, the initial value F0 and the current set frequency F can be displayed on the operation / display 17 of the high voltage control device 11. If the initial value F0 and the current set frequency F deviate from each other, the operator (user) can see it and optimize the initial value F0, regardless of the secular change of the high voltage generator 11. , It is possible to operate with high efficiency at any time.

Further, when the current set frequency F is significantly different from the difference due to normal operation, an abnormality in the high voltage control device 11 or the high voltage generator 3 can be detected, and the abnormal product is promptly replaced. Therefore, the quality of the coating can be maintained.

In the above embodiment, the case where the signal control device 15 performs control to keep the high voltage Vh constant while switching and controlling the set frequency F is described as an example, but the output is increased from the structure of the high voltage generator 3. High voltage Vh cannot be observed in some cases. In this case, a high voltage that is approximately proportional to the primary voltage is generated, but the output high voltage may fluctuate depending on the load condition. On the other hand, the present invention controls based on the drive current common to the high voltage generator 3, and the efficiency can be improved regardless of the structure of the high voltage generator 3.

Further, in the above embodiment, the high voltage control device 11 is used for electrostatic coating. The present invention is not limited to this, and can be used for various devices that generate high voltage.

1 Painting machine 3 High voltage generator 4 Step-up transformer (transformer)
11 High voltage controller 12 Transformer drive circuit (power supply unit)
13 Power supply current detection circuit (current detector)
14 Advanced voltage / current detection circuit 15 Signal control device (frequency control unit)
16 Non-volatile memory (storage unit)
17 Operation / Display (Display)

Claims (4)

A high-voltage control device that supplies low-voltage power of a set frequency to the transformer of a high-voltage generator and controls the high voltage generated by the high-voltage generator.
A power supply unit that supplies low-voltage power of the set frequency to the primary side of the transformer, and
A current detector that detects the peak value of the transformer drive current flowing on the primary side of the transformer, and
A frequency control unit that controls the set frequency of the low voltage power supplied from the power supply unit is provided so that the peak value of the transformer drive current detected by the current detector is minimized.
The frequency control unit has a first frequency that is the same as the current set frequency, a second frequency that is higher than the current set frequency, and a third frequency that is lower than the current set frequency. , The power supply unit generates low-voltage power, and the current detector detects the peak value of the transformer drive current.
The frequency control unit has a peak value of the transformer drive current among the first frequency, the second frequency, and the third frequency at regular intervals set to a value within the range of 5 minutes or less in 10 seconds or more. A high voltage control device characterized in that the frequency when is the smallest is set to the new set frequency. A storage unit for storing the initial value before Symbol set frequency,
The high voltage control device according to claim 1 , further comprising a display for displaying the initial value and the set frequency at regular intervals. The high voltage control device according to claim 2 , wherein the initial value is updated to a value of the set frequency when the high voltage generator is stopped. The claim is characterized in that when the high voltage value output from the high voltage generator is changed, the frequency control unit does not set a new set frequency for a predetermined period from the start of the change. high voltage control device according to 1.

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