JPS61177119A - High voltage apparatus with spark preventing function - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to high voltage equipment having a spark prevention function, such as electrostatic coating equipment and static eliminators.

[Conventional technology]

For example, in the case of electrostatic painting, when atomized paint is applied to an object to be painted at a distance from the gun using an electrostatic painting gun charged with high voltage, the object to be painted or other A conductive object may come abnormally close to a high-voltage charged electrostatic painting gun. In this case, there is a risk of inducing a spark discharge and igniting the solvent, so it is necessary to detect a sign of spark generation and promptly activate a protective function before a spark occurs.

The first conventional protection method is to obtain a detection signal corresponding to the magnitude of the load current, and when this detection signal exceeds a predetermined reference level, close the high voltage switch and lower the high voltage line. There is a method of shorting the voltage terminals and dropping the high voltage line to a low voltage within a very short time. Although this method is relatively simple and convenient, it is rarely compatible with the operating speed of the high voltage switch when the article to be coated or conductive object approaches the electrostatic spray gun at high speed. The disadvantage is that sparks are generated.

As a method to compensate for the shortcomings of the first protection method, the detection signal corresponding to the load current is substantially differentiated to the first or second order, and when this differentiated signal exceeds a predetermined reference value, a high voltage is detected. A second protection method is to close the switch and short the high voltage line to the low voltage terminal.

However, this method cannot prevent the generation of sparks in cases where sparks are generated as a result of a relatively gradual increase in the load current.

[Problems to be solved by the present invention]

The present invention is a high voltage device that can achieve a method in which the first and second protection methods are combined so as to mutually compensate for the drawbacks of the first and second protection methods. In this case, it is unclear which of the first protection function and the second protection function worked to provide spark protection;
Tamashi any protection! ! Not knowing whether the function has worked and spark protection has been performed is extremely inconvenient in discovering the cause of spark generation and taking countermeasures.

[Means for solving problems]

a first comparison circuit that compares the magnitude of a current detection signal corresponding to the load current with a reference level; a differentiation circuit that differentiates the detection signal; a second comparison circuit that compares the differential value with the reference value; The high-voltage device includes a drive circuit that operates when the first and second comparison circuits generate an abnormal signal indicating a sign of spark generation, and a high-voltage switch that is driven by the drive circuit to prevent spark generation. The spark factor identification circuit includes a first and second identification circuit that receives the abnormal signal from the first or second comparison circuit, respectively, and the first and second identification circuits receive the abnormal signal from the first or second comparison circuit. The one received earlier prohibits the other from operating and simultaneously operates to activate the indicator.

[For production]

According to the present invention, it is possible to detect a sign of spark occurrence from both the magnitude of a current detection signal corresponding to the load current and the magnitude of the differential value of the detection signal, and as a result, it is possible to detect a precursor of spark occurrence. It is possible to display whether this is due to the cause of the problem.

Therefore, for example, if protective operations are frequently performed due to the magnitude of the detection signal itself, the distance between the electrostatic coating gun and the article to be coated may be changed, or the current detection settings may be changed. Alternatively, it is possible to do both of these.

In addition, if the protection operation is frequent due to the magnitude of the differential value of the detection signal, the conveyance speed of the article to be coated or its fluctuation is too large, or the shape Km of the article to be coated is not suitable for the transport method. If this is the cause, you can quickly take countermeasures by changing the conveying speed, changing the conveying method, or changing the current detection settings.

〔Example〕

Referring to FIGS. 1 and 2, a case will be described in which an embodiment of the present invention is applied to an electrostatic coating device.

In FIG. 1, 1 is a normal high voltage power supply consisting of a high frequency inverter, a step-up transformer, a multi-stage voltage doubler rectifier circuit, etc.
2 is a current-limiting resistor connected to a high voltage line 6; 4 is a high-voltage charged electrode of an electrostatic coating gun; 5 is an article to be painted; 6 is grounded from the positive terminal of the high-voltage power supply 1; A current detection circuit that detects the current flowing to the negative terminal of the high voltage power supply 1 via the high voltage charged electrode 4 and the high voltage line 3, 7 is a circuit 6
9 is a unit of the detection signal from the current detection circuit 6; 9 is a unit of the detection signal from the current detection circuit 6; A differentiating circuit 10 performs differentiation to obtain voltage changes per time, and 10 compares the differentiated signal from the differentiating circuit with the reference value of the reference source 8', and outputs an abnormal signal S2 when the former is larger than the latter. 2 comparison circuit, 11 the first and second comparison circuit 7.10
This is a spark factor identification circuit that is activated when an abnormal signal is received from the engine.It consists of a circuit as shown in Figure 2 in detail.

Further, 12 is a display device that displays the identification result of the circuit 11 by light or sound, and 16 is a first and second comparison circuit 7.1.
A drive circuit 14 is a high-speed high-voltage switch driven by a drive circuit 16, which is activated when any of the signals 0 and 0 outputs an abnormal signal.

Next, the operation of an embodiment of the high voltage device according to the present invention will be explained while explaining an embodiment of the spark factor identification circuit with reference to FIG.

The spark factor identification circuit 11 includes first and second identification circuits 11.
A and 11B are provided. First and second identification circuits 11A, 1
1B has a similar circuit configuration, the first identification circuit 11A operates upon receiving the abnormal signal Sl from the first comparison circuit 7, and the second identification circuit 11B operates upon receiving the abnormal signal Sl from the second comparison circuit 10. It operates in response to S2.

The following description will focus on the first identification circuit 11A.

Resistors R1 and R2 divide the constant DC voltage +V into the circuit
give to Circuit X consists of comparator circuit C1 and feedback diode D
1, and when receiving the abnormal signal S1 from the first comparator circuit 7 at its inverting terminal, it outputs a high level signal. This high level signal is maintained until a reset signal is applied, which causes the Zener diode ZD to break down and create a voltage drop across resistor R3. Due to this voltage drop? ) The transistor Tr is turned on, and current flows through the resistor R4, the light emitting diode LD, and the relay coil RL connected in parallel with them. Here, the light emitting diode LD is an indicator light on the circuit board, and the contacts (not shown) of the relay coil RL are related to a normal circuit (not shown) including an indicator lamp installed in a housing etc. It is related to the drive circuit 13.

Furthermore, when the transistor Tr is turned on, its collector potential drops to almost zero potential, so the diode D2
becomes conductive, and latches the output of circuit X' in the second identification circuit 11B to a potential approximately equal to the voltage drop of diode D2. Therefore, while the first identification circuit 11A is operating, the second identification circuit 11B never performs the identification operation.

By operating the first identification circuit 11A in this manner, it can be determined that the protection function has been activated due to the magnitude of the current detection signal corresponding to the load current exceeding the set level. If the protective function is activated frequently due to this cause, you can adjust the distance between the charged electrode 4 of the electrostatic coating gun and the article 5 to be coated, or adjust the current detection settings. Optimal protection operation can be performed.

The second identification circuit 11B also operates in the same manner as the circuit 11A, and latches the potential at the output point of the circuit X in the circuit 11A to a very low voltage via the diode D≦ while this circuit is operating. .

If the second identification circuit 11B is activated frequently, the article 5 to be coated, or a portion thereof, or other conductive object may come too close to the high-voltage charged electrode 4 of the electrostatic coating gun. Since this is the main cause, it is possible to perform optimal protection by taking measures such as changing the conveyance speed and method of the article to be coated or adjusting the current detection settings.

Here, when one of the first and second identification circuits 11A, 11B operates, it is necessary to prohibit the other from operating. When the high voltage switch 14 closes, the A large current due to the charge stored in the stray capacitor between them flows in a pulsed manner through the high voltage switch 14, causing large noise, and this large noise causes the other identification circuit that is not operating to malfunction. This is because it is not possible to determine which cause caused the protection function to work.

Further, in this embodiment, an integrated circuit c2 having a signal terminal T1t, resistors R5, R6, Rヮ, and a diode D
3, etc., is provided with an operation restriction circuit 15.

An output on-off signal and a reset signal, which are substantially synchronized with turning on and turning off the high voltage power supply 1, are applied to the signal terminal T1 of the circuit C2. An off signal 1 is applied to the signal terminal T1 in synchronization with turning off the high voltage power supply 1, and the output voltage of the circuit C2 drops to a low level, so that the identification operation of the first identification circuit 11A is prohibited. Therefore, even if the high voltage switch 14 is closed to discharge the electric charge of the device when the high voltage power supply 1 is turned off, the spark cause identification circuit 11 will not operate and display an abnormality display. Furthermore, when the high voltage power supply 1 is turned on, an on signal is applied to the control terminal T1 so that the first identification circuit 11A can normally perform the identification operation from the time the high voltage power supply 1 is turned on. Even if there is an article to be coated near or in contact with 4, generation of sparks can be reliably prevented.

Further, once the output of the circuit X in the first identification circuit 11A becomes a high level, the high level state is maintained, so it is necessary to perform a reset. This reset signal is also applied to the signal terminal T at the time of reset. When the reset signal is applied to the signal terminal T1, the output voltage of the circuit 15 drops to a low level, thus causing the output voltage of the circuit 11A is reset.

Furthermore, this embodiment has a second signal terminal T2f that receives a reset signal that resets the operation of the second identification circuit 11B and a restriction signal that limits the operation of the second identification circuit 11B. This signal terminal T2 is connected to the second
It is connected to the connection point between the output point of circuit X' and the Zener diode ZD' in the identification circuit 11B of descend to.

Here, the limit signal is to prohibit the discrimination operation of the second discrimination circuit 11B until the high voltage output is stabilized, and spark generation is performed using the differential value of the detection signal of the current complementary to the output current. This is to prevent malfunctions caused by predicting the signs of failure.

Incidentally, in the embodiment shown in FIG.
Of course, the display device 12 may also be configured as an accessory device.

In addition, although the above embodiments described electrostatic coating equipment,
Any high-voltage device that poses a risk of generating sparks and dislikes generation of sparks, such as static eliminators, electrostatic printing devices, and various electrostatic sorting devices, may be used.

〔Effect of the invention〕

As described above, according to the present invention, a sign of spark generation is detected from both the magnitude of the detection signal of the current corresponding to the output current and the magnitude of the first or second derivative of the detection signal. Since the protection function is activated by the spark, it is possible to prevent sparks with high certainty, and at the same time, it is possible to reliably identify which cause caused the protection function to activate, so the cause of spark generation can be easily removed. This makes it possible to prevent sparks even more reliably.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams for explaining one embodiment of the present invention. 1...High voltage power supply 4...High voltage charged electrode 6...
・Current detection circuit

Claims (1)

[Claims] a current detection circuit that detects a current flowing through a circuit including a high-voltage power source, a high-voltage charged electrode, and a load; a first comparison circuit that compares a value corresponding to the magnitude of a detection signal from the circuit with a reference level; A differentiation circuit that obtains a differential signal corresponding to a change per unit time in the detection signal from the current detection circuit, a second comparison circuit that compares the differential value with a reference value, and the first or second comparison circuit. A high voltage device comprising: a drive circuit that is activated when the spark generator generates an abnormal signal indicating a sign of spark generation; and a high voltage switch that is driven by the drive circuit to prevent spark generation; A spark factor identification circuit is provided that includes first and second identification circuits that each receive the abnormal signal from a comparison circuit, and one of the first and second identification circuits receives the abnormal signal first, and the other operates. A high-voltage device with a spark prevention function, characterized in that it operates to prohibit sparking and at the same time activate an indicator.