JPH0415337Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to an electrostatic coating device with a self-protection function that is extremely simple in construction.

[Conventional technology]

Generally, in an electrostatic coating apparatus, a high current-limiting resistor is inserted into a high-voltage cable extending from the high-voltage power source to the high-voltage charged electrodes in order to limit the current flowing from the high-voltage power source to the load side. This method is very simple and economical, and is effective from the point of view of limiting the current, but it has the drawbacks of a large steady voltage drop due to the high resistance inserted, and the fact that the object to be coated is a high-voltage electrically charged object. The disadvantage is that spark discharge occurs when the poles are very close to each other.

Therefore, as a device for suppressing the occurrence of such spark discharge, a device as shown in FIG. 1 has already been proposed.

In Figure 1, 1 is a DC high voltage power supply that can variably output DC voltage in the range of several tens of kilovolts to about 100 kilovolts, and the output is supplied to the high voltage charged electrodes of the electrostatic coating device via a current limiting resistor 2. 3 and the object to be painted 4 which is in a grounded state, and the coating current I _P is applied from the positive side of the DC high voltage power supply 1 to the current detection resistor 5, the ground, the object to be painted 4, the high voltage charged electrode 3, the high voltage The voltage flows to the negative side of the DC high voltage power supply 1 via the voltage cable 6 and the current limiting resistor 2. The spark discharge prediction/drive circuit 7 predicts the occurrence of a spark discharge based on the state of the current flowing through the current detection resistor 5, and applies a drive signal to the normally open switch 8 to close it. switch 8
By closing, the high voltage cable 6 is connected to the ground point via the switch 8 and the protective resistor 9, so that the high voltage cable 6 and the high voltage charged electrode 3 suddenly drop to a low potential.

[The problem that the idea aims to solve]

In this way, the occurrence of spark discharge is prevented, but the drawbacks of this circuit are that it is complicated and expensive, and that switch 8 may malfunction due to noise or may have a delay in operation. There is a drawback that spark discharge cannot necessarily be prevented when the object to be coated approaches the high-voltage charged electrode at high speed.

[Means to solve the problem]

In order to eliminate all such drawbacks of the conventional technology, the present invention aims to prevent voltage drops that are outside the constant current range in the normal load current range in the middle of high voltage cables or in close proximity to high voltage charged electrodes of electrostatic coating equipment. A high-voltage uncontrolled constant-current element that operates in a small region of current, operates in a constant current region when exceeding the normal load current range, and has a breakdown voltage value higher than the maximum voltage value of the DC high-voltage power supply. It is connected at a relatively close location.

〔Example〕

First, a case in which an embodiment of the present invention is applied to an electrostatic coating machine will be described with reference to FIGS. 2 and 3.

A high voltage uncontrolled constant current element 10 connected in the middle of the high voltage cable 6 between the DC high voltage power supply 1 and the high voltage charged electrodes 3 of the electrostatic coating device exhibits a forward characteristic as shown in FIG. It is.

In the normal load current range, the current I _P flowing through the high voltage uncontrolled constant current element 10 is in a range lower than the current I _H corresponding to the bending point a of the characteristic curve shown in FIG. Therefore, the voltage drop of the high voltage uncontrolled constant current element 10 during painting is small, and the painting voltage is hardly lowered.

When the object 4 to be coated abnormally approaches the high voltage charged electrode 3, the current I _P flowing through the high voltage uncontrolled constant current element 10 exceeds I _H and enters the constant current region X. Along with this, due to a slight increase in the current I _P , the voltage drop across the high voltage uncontrolled constant current element 10 rapidly increases according to its characteristic curve, and almost all of the output voltage of the DC high voltage power supply 1 is taken up. In other words, in the characteristic curve of FIG. 3, the voltage V _H corresponding to the voltage at the bending point b transitioning from the constant current region When no other impedance is connected in series to the cable 6, the high voltage uncontrolled constant current element 10 is selected so that _VH is equal to or higher than the maximum DC output voltage of the DC high voltage power supply 1. Therefore, when the high-voltage charging electrode 3 is about to come into contact with the object to be coated 4, the load current increases and moves from point a to point b in FIG. 3, resulting in a state of X.

At this time, the output voltage/current characteristics move on the curve shown in FIG. That is, when a normal coating current is flowing, it is on the line W between points o and a in FIG. 4, and is moving in a range slightly lower than the supply voltage of the high voltage power supply 1. and high voltage charging electrode 3
When the load current is about to come into contact with the object 4 to be coated, the load current increases and moves from point a to point b in FIG. 4, and finally the output voltage quietly drops to zero. This moving state X from point a to point b utilizes the unique characteristics of the uncontrolled constant current element 10, so it is fast and reliable.

In other words, the present invention utilizes the low voltage drop in the small current region of the uncontrolled constant current element to effectively supply voltage to the charging electrode, and limits the output current in the constant current region of the uncontrolled constant current element. At the same time, since the uncontrolled constant current element is disposed relatively close to the charging electrode and the energy stored in its capacitance is small, spark discharge is prevented.
In the conventional method using a series resistor, the voltage supplied to the charging electrode decreases at a slope because the voltage moves on the line R in Fig. 4, whereas in the present invention, spark discharge is reliably prevented and an effective charging action is performed. .

In this embodiment, if the high voltage cable 6 is coated with insulation, the high voltage cable 6
Depending on the length, the capacitance formed between this and the ground may become quite large, and when the high voltage charged electrode 3 and the object to be coated 4 come into contact, the charge of this capacitance will be Since the discharge occurs via the high-voltage charged electrode 3 and the object to be coated 4, spark discharge may occur. Therefore, in such a case, the high voltage uncontrolled constant current element 10 should be connected in close proximity to the high voltage charged electrode 3, or the high voltage uncontrolled constant current element 10 should be connected between the high voltage charged electrode 3 and the high voltage uncontrolled constant current element 10. It is best to connect them with short bare cables.

The high voltage uncontrolled constant current element used in the present invention has a small resistance in the opposite direction, or may be large. Depending on the output current capacity, high voltage uncontrolled constant current elements may be connected in parallel. May be used.

[Effect of idea]

Since the present invention has the above-mentioned characteristics,
It exhibits the effects shown below.

(1) The voltage drop of the uncontrolled constant current element during normal electrostatic painting work is smaller than that of a resistor, and the effective voltage of the charging electrode is increased, improving painting efficiency.

(2) The voltage drop of the uncontrolled constant current element during normal electrostatic painting work is smaller than that of a resistor, the power loss is reduced, and the ability to prevent paint, which is a flammable substance, from catching fire is improved.

(3) When an abnormal load current flows, the uncontrolled constant current element carries a voltage corresponding to the output voltage of the DC high voltage power supply. Since this action is uncontrolled and almost instantaneous, protection is ensured and the occurrence of spark discharges, which could pose a risk of fire or explosion, can be avoided.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining an example of a conventional electrostatic coating device, Fig. 2 is a diagram showing an embodiment of an electrostatic coating device according to the present invention, and Fig. 3 is a diagram showing a high voltage uncontrolled constant current element. FIG. 4 is an output characteristic diagram for explaining the present invention. 1...High voltage power supply, 3...High voltage charged electrode, 6...
...High voltage cable, 10...High voltage uncontrolled constant current element.

Claims (1)

[Scope of utility model registration request] Between the DC high-voltage power supply and the high-voltage charged electrode in series with these, it operates in a region with small voltage drop outside the constant current region in the normal load current range, and in the constant current region when exceeding the normal load current range. an electrostatic coating device, characterized in that a high voltage uncontrolled constant current element that operates at 100 volts and has a breakdown voltage value higher than the highest voltage value of the DC high voltage power source is connected to a position relatively close to the high voltage charging electrode. .