JPS5811056A - Electrostatic coating device - Google Patents

Abstract

PURPOSE:To exactly prevent generation of spark discharge, providing a residual voltage cutting-off element for substantially cutting off a main circuit automatically when voltage between a high voltage charge electrode and an object to be coated has dropped to a value of residual voltage or so, in series to the main circuit. CONSTITUTION:This device is provided with a DC high voltage power source 2, a high voltage electrode 4 charged by the power source 2, and a short-circuiting device 9 connected between a high voltage line 5 connecting the power source 2 and the electrode 4, and a low voltage terminal. In its DC high voltage device, a residual voltage cutting-off element 10 for executing main conduction by residual voltage or so in the device 9 or voltage exceeding said voltage is provided on a main current path extending from the positive terminal of the power source 2 to its negative terminal through the low voltage side terminal, a load 6 and the electrode 4. That is to say, conduction start voltage of the element 10 is selected to voltage being slightly larger than the residual voltage of the device 9, therefore, when the device 9 conducts and the potential of the voltage line 5 becomes the residual voltage or so, the element 10 becomes non-conducting automatically.

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 disclosed in Japanese Patent Publication No. 55-35989 and Japanese Patent Application Laid-open No. 56-21.
The electrostatic coating devices described in these publications all use a mechanical switch as a short-circuit switch for high voltage output, so the operational response is The delay time causes various problems. For example, if a mechanical switch has an operation delay time of tens of 817 seconds, it is determined whether the increase in load current would cause spark discharge in a region where the increase in load current is very small. In order to minimize the amount of static electricity that must be applied, it is necessary to prepare a large number of setting levels and select the appropriate setting level depending on the shape of the object to be coated. A major drawback is that only an operator with experience in painting can select an appropriate setting level. Furthermore, if the object to be coated approaches the high voltage electrode at a speed greater than the speed corresponding to the operational 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 necessary to use a short-circuit switch element that has an extremely high operating speed, such as a short-circuit switch element formed by connecting a large number of silicon-controlled rectifiers in series, or a gap-type switch that has a discharge gap between electrodes. It is preferable to use a short-circuiting switch element, or a short-circuiting switch element formed by appropriately connecting both of these in series. It was found that the resulting voltage appeared as a residual voltage, and that this voltage could not be ignored. Depending on the form and structure of the switch element, this residual voltage may be in the hundreds of sevens.
Even after the short-circuit switch element has become conductive, if the object to be coated comes into contact with or comes close to contacting the high-voltage charged electrode, there is a sufficient risk that spark discharge will occur due to the residual voltage. It is in.

Based on this knowledge, the present invention provides a residual voltage interrupting element that automatically cuts off the main circuit when the voltage between the high-voltage charged electrode and the article to be coated drops to a value similar to the residual voltage. It is characterized by being installed in series with the main circuit through which the current flows.

First, an embodiment of the present invention will be explained with reference to FIG.

In this figure, 1 is a step-up transformer having a low voltage winding N and a high voltage winding N2 to which a high frequency oscillator (not shown) is connected, and 2 is a step-up transformer with a positive output terminal connected to the high voltage winding N2. Connected DC high voltage power supply, 6 is DC high voltage power supply 2
A high voltage resistor for current control is connected in the middle of a high voltage line 5 from the negative output terminal to a high voltage electrode 4 shown as a painting gun, 6 is a grounded article to be painted, 7 is a DC high voltage It consists of a current detection circuit connected between the positive output terminal of the power supply 2 and the ground terminal, 8 a spark discharge occurrence prediction circuit, 9 a short-circuit switch element formed by connecting a number of thyristors in series, and its ignition circuit, etc. The short-circuit device 10 is a normal diode or Zener having avalanche characteristics connected in series to the main circuit through which the main current IL flows so that the polarity is opposite to the direction in which the main current 5 flows. It is a residual voltage cutoff element like a diode.

Next, the operation of the circuit with such a configuration will be described. From the positive output terminal of the DC high voltage power supply 2 to the current detection circuit 7, the grounded low voltage terminal, the article to be painted 6, the high voltage electrode 4, and the current limiting resistor 6 When the main current (1) flowing through the main circuit leading to the negative output terminal via the residual voltage cutoff element 10 is normal, the spark discharge prediction circuit 8 does not operate, and the short circuit device 9 opens. in a state. In this state, the output voltage of the DC high voltage power supply 2 is much larger than the breakdown voltage ψ◆ of the residual voltage cutoff element 10, so the residual voltage cutoff element 10 is conducting in the opposite direction. The main current ■L is flowing in the opposite direction. Since this main current (1) is normally very small, ranging from several tens of μA to several hundred μA, there is no problem in using the residual voltage cutoff element 10.

Next, due to the increase in the main current IL, the spark discharge occurrence prediction circuit 8
When a spark discharge notification signal is generated from the spark discharge notification signal, the short circuit device 9 is energized and the short circuit switch portion thereof becomes conductive. Accordingly, the potential of the negative high voltage line 5 rapidly rises toward the ground potential, but becomes lower than the ground potential by a voltage approximately equivalent to the residual voltage v5 of the short circuit device 9. In other words, even after the short-circuiting device 9 has become conductive, a voltage approximately equal to the residual voltage v5 remains applied between the high-voltage charged electrode 4 of the coating gun and the grounded article 6 to be coated. However, since the conduction start voltage of the residual voltage interrupting element 10 is selected to be slightly larger than the residual voltage V5, the shorting device 9 is conductive and the high voltage distribution line 5
When the potential of the residual voltage reaches about 5, the residual voltage cutoff element automatically becomes non-conductive. Even if the article 6 to be coated further approaches and contacts the high-voltage charged electrode 4 after that, only a voltage of about the residual voltage v6 is applied to both ends of the residual voltage cut-off element 100, so that the residual voltage cut-off element 100 1
0 remains non-conducting and no short circuit current flows through this element 10. Here, in a normal diode, a leakage current of less than 1 μA flows at a voltage of about 80% of the avalanche voltage.

Therefore, even if the article 6 to be coated comes into contact with the high-voltage charged electrode 4 of the coating gun, no spark discharge will occur between them. Incidentally, it is preferable that the residual voltage interrupting element 10 be provided within the painting gun in order to minimize the adverse effects of stray capacitance.

Next, another embodiment will be explained with reference to FIG.

In this embodiment, the short-circuiting device 9 is completely equipped with trigger electrodes 9B and 90 and a main discharge electrode 9D, which are arranged at predetermined intervals in a bulb 9A which is filled with a specific insulating gas. A gap-type discharge switch 9' is used, and a nonlinear element made of sintered zinc oxide or the like is used as the residual voltage cutoff element 10, which has a voltage approximately equal to the residual voltage of the gap-type discharge switch 9'. , or has a voltage-current characteristic such that the flowing current increases rapidly at a voltage greater than or equal to . The cutout 11 is a high impedance element, such as a high voltage resistor, or a series connection of a high voltage resistor and an inductor.

Next, the operation of such a circuit will be explained.

When the voltage across the high impedance element 11 rises above the trigger voltage of the switch 9' due to a change in the load current IL flowing through the high impedance element 11, a discharge occurs between the trigger electrodes 9B and 9C of the switch 9'. , this discharge causes a main discharge to occur between these trigger electrodes and the main discharge electrodes 9D. As a result, the high-voltage line 5 is connected to the ground terminal via the switch 9', but the gap-type discharge switch 9' is turned off when the voltage across it drops below the voltage. This voltage reaches the residual voltage 5 of the switch 9', and a voltage approximately equal to the residual voltage V is applied to the high voltage line 5 even after the switch 9' is turned on. However, according to this embodiment, the short circuit device 9 is provided with a residual voltage cutoff element 10 in series with the main current path, which does not conduct main conduction unless an operating voltage equal to or higher than the residual voltage v5 of the switch 9' is applied. After electrically connecting the high voltage line 5 and the ground terminal, the residual voltage interrupting element 10 becomes substantially non-conductive and substantially interrupts the main current path.

Therefore, even if the article 6 to be coated comes into contact with the high-voltage charged electrode 4 of the coating gun, no spark discharge will flow, and no spark discharge will occur.

Next, another embodiment of the present invention will be described with reference to FIG.
In this embodiment, a thyrisk switch 91 and a gap-type discharge switch 92 connected in series are used as the short circuit device 9, and the residual voltage cutoff element 10 is used at a voltage higher than the residual voltage V of the short circuit device 9. A discharge tube that starts discharging or lighting is used. This discharge tube 10
The function of this device is almost the same as that of the residual voltage interrupting element of the previous embodiment, and the effect obtained is also the same, so a complete explanation will be omitted, and the short circuit device 9 will be briefly explained.

First, the negative DC high voltage of the high voltage line 5 is set to V. Then, when the short-circuiting device 9 is in a non-conducting state, the thyrisk switch 91
A high DC voltage V is applied across the gap type discharge switch 92 and the gap type discharge switch 92.
. is applied. Approximately V is applied to both ends of the thyrisk switch 91. /4 is applied, and a voltage of approximately V/4 is also applied between each of the electrodes E1 and E2, E2 and E3, and E6 and E4 of the gap type discharge switch 92.

The gap type discharge switch 92 has approximately V between each electrode. Various types have been selected that will surely lead to a discharge state and a conductive state when a voltage corresponding to /6 is applied. Therefore, when the thyristor switch 91 is instantaneously closed by applying a prediction signal from the spark discharge occurrence prediction circuit rNS8 to the thyristor switch 91 of the short-circuiting device 9, the voltage that has been applied to both ends of the thyristor switch 91 until now becomes
. /4 is also applied to the gap type discharge switch 92, so the voltage Vo/4 applied between each electrode of the switch 92 rises to Vo/3. In the process of this voltage increase, a discharge occurs between the electrodes of the switch 92,
The entire switch 92 enters the discharge state, connecting the high voltage line 5 to the ground terminal, ie the low voltage terminal. According to the short circuit device 9 having such a configuration, it is possible to use a thyristor switch having a withstand voltage of about 174 DC high voltage Vo, and it is also possible to use an optical thyristor switch.

It goes without saying that a plurality of gap type discharge switches having a single structure may be connected in series.

As described above, according to the present invention, when a voltage equal to or lower than the residual voltage of the switch section of the short-circuiting device is applied, a residual voltage interrupting element is provided which substantially interrupts the main circuit in the main current flow direction. Since it is provided in series with the main circuit, even if the article to be coated collides with the high-voltage charged electrodes of the coating gun, the generation of spark discharge can be almost completely prevented. Therefore, explosion accidents and electric shock accidents during painting work can be reliably prevented, and the efficiency of painting work can also be improved.

[Brief explanation of drawings]

1 to 3 are circuits showing different embodiments of the present invention. 1 is a step-up transformer, 2 is a DC high-voltage power supply, the filter is a current-limiting resistor, 4 is a high-voltage charged electrode of a painting gun, 5 is a high-voltage line,
6 is an article to be painted, 7 is a current detection circuit, 8 is a spark discharge occurrence prediction circuit, 9 is a short circuit device, 10 is a residual voltage cutoff element, 11 is a high impedance element Patent applicant Origin Electric Co., Ltd. Procedural Amendments Showa June 11, 1957, Mr. Commissioner of the Japan Patent Office 1, Indication of the case: 1981 Patent Application No. 109153, 2, Title of the invention: DC high voltage device 3, Relationship with the amended person case: Patent applicant Address: 1-18-1-4 Takada, Toshima-ku, Tokyo; Date of amendment order: Vol. 5; Subject of amendment: ``Title of the invention,'' ``Scope of claims,'' and ``Detailed description of the invention'' in the specification. Column 6, Contents of amendment ■ The scope of claims is corrected as shown in the attached sheet. 6) Details of this case? The following 9 corrections have been made to lines 15 to 18 on page 1-1, "Relating to the present invention." [The present invention is a high-voltage device equipped with a short-circuit device, for example, a static device with a function that can reliably prevent spark discharge even when a grounded article to be coated comes very close to or comes into contact with a high-voltage charged electrode.] This invention relates to a DC high voltage device used in electrocoating equipment. "0) Ibid., page 3, line 18 F - Between articles to be coated..." is corrected to "Between loads such as articles to be coated." 6) Fang, page 11, line 7 [...Improve. ' shall be corrected as follows. ``...Improved.''Although all of the above embodiments have been described with respect to electrostatic coating, it is clear that the present invention can be similarly applied to other electrostatic application equipment as required. ” “Claims

Claims (1)

[Claims] It comprises at least a high voltage power supply, a high voltage electrode charged by the high voltage power supply, and a shorting device connected between the high voltage line between the high voltage power supply and the high voltage electrode and the low voltage terminal. In the electrostatic coating device, the main current path from the positive terminal of the high voltage power supply to the low voltage side terminal, the article and the high voltage electrode to its negative terminal includes a residual voltage level in the shorting device; 1. An electrostatic coating device characterized by comprising a residual voltage cutoff element that performs main conduction at a voltage of 1.5 or higher.