JPS6334425Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electrostatic coating device that is capable of reliably preventing spark discharge even when a grounded article to be coated comes very close to or comes into contact with a high-voltage charged electrode. .

Conventional electrostatic coating devices of this type equipped with a spark avoidance function are described in Japanese Patent Publication No. 55-35989 and Japanese Patent Application Laid-Open No. 53-21240, etc. Since all electrostatic coating apparatuses use mechanical switches as short-circuit switches for high voltage output, various problems arise due to the delay time of the operation response. For example, if a mechanical switch has an operation delay time of several tens of milliseconds, it is necessary to determine whether or not the amount of increase in load current will cause spark discharge in a region where the amount of increase in load current is quite small. Therefore, even though complex detection is performed, false detections inevitably increase. In order to reduce this false detection, it is necessary to prepare a large number of setting levels and select the appropriate setting level according to the shape of the object to be coated, but this work requires sufficient consideration of electrostatic painting. A major drawback is that only an operator with experience can select an appropriate setting level. Further, if the article to be coated approaches the high voltage electrode at a speed greater than the speed corresponding to the operating response time of the shorting switch, no amount of detection can avoid the occurrence of spark discharge. Therefore, in order to eliminate these conventional drawbacks, it is preferable to use a semiconductor switch device formed by connecting a large number of semiconductor switch devices in series, such as silicon-controlled rectifier devices, which operate at extremely high speeds.

First, in FIG. 1, a conventional electrostatic coating apparatus using such a semiconductor switch device is shown. In the figure, 1 is an AC power source such as a high frequency inverter;
2 is a step-up transformer, 3 is a DC high voltage generating circuit such as a Kotsukucroft Walton circuit, 4 is the negative output terminal of the circuit, 5 and 6 are current limiting resistors, 7 is a discharge diode, and 8 is for painting. High voltage electrode shown as gun, 9 grounded workpiece, 10
11 is a current detection circuit, 11 is a spark discharge occurrence prediction circuit that predicts the occurrence of spark discharge based on the state of change in the detected current detection signal, and 12 is a pulse generator that generates a pulse when receiving an output signal from the circuit. The circuit includes a pulse transformer 13, a semiconductor switch device 14 in which a large number of thyristors S ₁ , S ₂ , . . . , _So , which are semiconductor switch elements, are connected in series, and R a current limiting resistor.

In the electrostatic coating device with such a configuration, under normal operating conditions, a negative number +KV is applied to output terminal 4.
DC high voltages of around -100KV have appeared,
The load current flows to the output terminal 4 via the current detection circuit 10, ground, the object to be painted 9, the high voltage electrode 8, and the current limiting resistors 6 and 5.

If the object to be painted 9 abnormally approaches the high voltage electrode 8 or the human body abnormally approaches the high voltage electrode 8 in such a state, the state of the current flowing through the current detection circuit 10 changes. Spark discharge occurrence prediction circuit 1
1 outputs a spark discharge occurrence prediction signal when it is determined that the change state of the current detection signal from the current detection circuit 10 is a precursor phenomenon of spark discharge occurrence. In response to this signal, the pulse generator 12 generates a pulse signal, which is transmitted through the pulse transformer 13 to the thyristor S ₁ ,
Turn on S ₂ , ..., S _o at the same time. Along with this, from the grounding point to the current limiting resistor R, each thyristor S ₁ ,
A discharge current flows to the ground point through the semiconductor switch device 14 consisting of a series connection of S ₂ , ..., S _o , the point X, the discharge diode 7, the high voltage electrode 8 and the object to be coated 9, The point Therefore, the occurrence of spark discharge can be almost certainly prevented. However, in this circuit, there is a large distributed capacitance C _R between the current limiting resistor R and the ground, and there is also a large distributed capacitance C R between each of the secondary windings N ₁ , N ₂ , ..., _No of the pulse transformer 13 and the ground. Due to the capacitances C ₁ , C _{2 ,} . Ta.

Furthermore, when the semiconductor switch device is turned on, the high voltage at point It had drawbacks such as having an adverse effect on other electronic circuits in the surrounding area.

The present invention provides a novel electrostatic coating device that eliminates all of the above drawbacks.

FIG. 2 is a diagram showing an embodiment of the present invention.

In the same figure, R ₁ , R ₂ , ..., _Ro are the first
A current limiting resistor having a resistance value r approximately 1/n of the current limiting resistor R in the figure, and the current limiting resistor is alternately connected in series with each thyristor S ₁ , S ₂ , ..., S _o . Assuming that _the voltage of each thyristor S ₁ , S _{2 , .} ,..., the voltage charged in C _o is C ₁ = V/n, C ₂ = 2n/V,..., C _{o-1, respectively.}
=(n-1)V/n, C _o =v.

In such a state, if the object to be painted 9 approaches the high voltage electrode 8 abnormally or the human body approaches the high voltage electrode 8 abnormally, the spark discharge occurrence prediction circuit 11 detects a change in the current detection signal from the current detection circuit 10. When the condition is determined to be a precursor to spark discharge, the thyristor operates in the same manner as described in the explanation of Figure 1.
S ₁ , S ₂ , ..., S _o are turned on at the same time.

By the way, when the thyristors S ₁ , S ₂ , ..., S _o are turned on, the current limiting resistors R ₁ , R ₂ , R ₃ , ..., _Ro equally share the voltage at point X, so the distribution is capacity
The voltages charged in C ₁ , C ₂ , C ₃ , ...C _{o -1} , and Co hardly change. Therefore, thyristor S ₁ ,
During the operation of S ₂ , ..., S _o , large currents no longer flow through these distributed capacitances, and the thyristor
Currents i ₁ , i ₂ , ..., flowing through S ₁ , S ₂ , ..., S _o , respectively
i _o is i ₁ = i ₂ = ... = i _o = v/nr, which limits the current flowing to the semiconductor switch device via the distributed capacitance formed by the structure of the high potential side and the low potential side. be able to. This makes it possible to rationally select the current ratings of the semiconductor switch elements S ₁ , S ₂ , ..., S _o , and the current limiting resistors R ₁ , R ₂ , ...,
The breakdown voltage of R _o is determined by the semiconductor switch elements S ₁ , S ₂ , ...,
It is very economical because it can withstand a pressure of about the same level as _So.

Next, FIG. 3 is a diagram showing another embodiment of the present invention. In the same figure, R′ ₁ , R′ ₂ ..., R′ _o and
C′ ₁ , C′ ₂ , ..., C′ _o are resistors and capacitors that are alternately connected in series between the current limiting resistor R ₁ and the cathode of the thyristor S _o , respectively, and the thyristors S ₁ , S ₂ , ...
..., each gate of S _o-1 is connected to a connection point between a predetermined resistor and a capacitor. In this embodiment, the pulse transformer 13 has only one secondary winding N, which is connected to the thyristor S _o at a high potential.
connected to the gate.

When point X is at a negative high potential, capacitor C′ ₁ ,
C′ ₂ , ..., C′ _o are charged to the polarity shown.

When the pulse generator 12 generates a pulse signal in the same manner as in the above embodiment, the signal turns on the thyristor S _o via the pulse transformer 13.

When the thyristor S _o turns on, the capacitor
The charge on C′ _o is transferred to the resistor R′ _o and the gate of thyristor S _o-1 .
It is discharged through the cathode, the anode/cathode of the resistor R _o and the thyristor S _o . Therefore, thyristor S _o-1 is triggered to turn on, and the turn-on of thyristor S _o-1 discharges the charge of capacitor C' _o-1 to the gate of thyristor S _o-2, turning it on, as before. . Thereafter, the thyristors are turned on one after another in the same manner.

In this way, the semiconductor switch device is turned on and the high potential point X is lowered to a low potential within an extremely short time of several tens of microseconds to _{100 microseconds} . ,...,When turning on S _o , the current limiting resistor is applied as before turning on.
Since R ₁ , R ₂ , ..., _Ro equally share the voltage at point can be significantly restricted.

FIG. 4 is a diagram showing another embodiment of the present invention. In the figure, 15 is an optical pulse generator;
LG ₁ , LG ₂ , ..., LG _o is a light guide, S ₁ , S ₂ ,
..., S _o is a light controlled thyristor. In this embodiment as well, when the optical pulse generator 15 generates an optical pulse signal in the same manner as in the above embodiment, the signal is transmitted to the optically controlled thyristor S ₁ via the light guides LG ₁ , LG ₂ , ..., LG _o . , S ₂ , ..., S _o are turned on at the same time. The following is the same as the example described above,
A similar effect can be obtained. In the above embodiment, resistors R ₁ , R ₂ , ..., are used as current limiting members.
Although R _o is used, an inductance element or a series connection body of an inductance element and a resistor may be used. Further, in the above embodiment, a thyristor or an optically controlled thyristor was used as the semiconductor switch element, but of course other semiconductor devices with control signal electrodes may be used.

As described above, the present invention provides a high-voltage power supply, a high-voltage electrode charged by the high-voltage power supply, a high-voltage line between the high-voltage power supply and the high-voltage electrode, and a low-voltage terminal connected in series. An electrostatic coating device comprising at least a semiconductor switch device comprising a plurality of semiconductor switch devices, characterized in that a current limiting impedance is inserted between each semiconductor switch device of the semiconductor switch device. be. Since the present invention has such characteristics, when the semiconductor switch device is turned on, the current limiting impedance equally shares the high voltage, so that the current limiting impedance is distributed through the distributed capacitance formed by the structure of the high potential side and the low potential side. The current flowing through the semiconductor switch device can be significantly limited. Therefore, the current rating of the semiconductor switch element can be selected rationally, and the withstand voltage of the current limiting impedance can be set to the same level as the withstand voltage of the semiconductor switch element, which is very economical.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional electrostatic coating device, and FIGS. 2 to 4 are diagrams showing different embodiments of the electrostatic coating device according to the present invention. 1... AC power supply, 2... Step-up transformer, 3...
...DC high voltage generation circuit, 5, 6...Current limiting resistor, 7
...Discharge diode, 8...High voltage electrode, 9...
... object to be painted, 10 ... current detection circuit, 11 ... spark discharge occurrence prediction circuit, 12 ... pulse generation circuit,
13...Pulse transformer, 14...Semiconductor switch device, 15...Optical pulse generator, S1 _{~ So} ...Semiconductor switch element, R, _R1 ~ _Ro ...Current limiting resistor,
C ₁ ~C _o ……distributed capacitance, C′ ₁ ~C′ _o ……capacitor,
R′ ₁ ~ R′ _o ……Resistor, LG ₁ ~ LG _o ……Light guide.

Claims (1)

[Scope of utility model registration request] A semiconductor switch consisting of a high voltage power supply, a high voltage electrode charged by the high voltage power supply, and a plurality of semiconductor switch elements connected in series between the high voltage line between the high voltage power supply and the high voltage electrode and the low voltage terminal. What is claimed is: 1. An electrostatic coating device comprising at least an electrostatic coating device, characterized in that a current limiting impedance is inserted between each semiconductor switch element of the semiconductor switch device.