JPH0125639Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a safety device for preventing spark discharge during electrostatic painting of an electrostatic atomizer having a high voltage cable. This is a safety device that detects the proximity of an electrostatic gun to a grounded object and prevents spark discharge.

Conventionally, this type of spark discharge prevention device that has been generally used has a configuration as shown in FIG. 1, which simply detects the output current of a high voltage power supply, that is, the current flowing to the ground (load current). For this reason, a complicated arithmetic circuit is required, and a long processing time is required, making quick detection impossible.

In view of the above-mentioned circumstances, the present invention provides a safety device for preventing spark discharge in electrostatic painting, which detects changes in current at an early stage, cuts off high voltage, and reliably prevents spark discharge.

That is, the present invention provides an electrostatic coating machine with a high-voltage cable, and a transient current detection circuit of opposite polarity is provided between the shield wire of the high-voltage cable and the ground electrode.
This output is input to two comparators, and a danger signal (caution signal, cutoff signal) is output by comparing it with a value set in advance in the comparator, and based on this output, static electricity is removed from a grounded object. This is to release the gun or cut off the high voltage.

Hereinafter, the present invention will be explained based on the drawings of embodiments.

1 is a high voltage cable having a high voltage generator 2 at one end and an electrostatic gun 4 facing a grounding object 3 at the other end, and a shielded current detection circuit 6 connected to a shielded wire 5 of the high voltage cable 1. and connect the detection circuit 6
The output of the comparator 7a is connected in parallel to two comparators 7a and 7b, and a setting device 8a is connected to the comparator 7a, which gives the lower set value.A caution alarm 9 is connected to the comparator 7a, which also gives the higher set value. A high voltage cutoff alarm 10 is connected to a comparator 7b to which a setting device 8b is connected. This detection means detects the shield current of the high voltage cable 1, and the current in this case is a transient current with a polarity opposite to that of the normal current.

Next, to explain this effect, the current flowing through the shield wire 5 of the high voltage cable 1 is as shown in FIG. When the voltage cable 1 is filled with electric charge, no current flows (only leakage current occurs).

Here, when the charging switch is turned off, a transient discharge current Ic of opposite polarity flows, but the absolute value is
It is not as large as Ia and Ib. Also, when the grounding object 3 approaches the electrode part of the electrostatic gun 4 during charging, the transient discharge current a, b,
A transient current of opposite polarity flows as shown in c. In this case, the magnitude of the approach speed is c>b>a (see FIG. 3). This reverse polarity transient current is detected to detect the approaching speed, and the output of the comparator 7b is used to activate the high voltage cutoff alarm 10 to perform high voltage cutoff.
However, the setting of the critical speed can be arbitrarily selected by making the setting devices 8a and 8b facing the comparators 7a and 7b variable.

As mentioned above, the spark discharge prevention safety device for electrostatic coating of the present invention is provided with two comparators in the reverse polarity transient current detection circuit connected to the shielded wire part of the high voltage cable, and a set value is input to the comparators. High, low 2
The configuration is such that the output of the comparator set to a low value is used as a caution signal, and the output of the comparator set to a high value is used as a cutoff signal for high voltage cutoff, stoppage of the paint sprayer, etc. , the approach speed is converted into the peak value of the pulse, so the objective is achieved with a set of comparators and setters. Further, complicated arithmetic circuits and the like are not required. Therefore, the processing time is shortened, and as a result, rapid detection is possible, reliable high voltage interruption is possible, and the occurrence of spark discharge can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional device, FIG. 2 is a block diagram of the present invention, and FIG. 3 is a graph showing discharge current. 1...High voltage cable, 2...High voltage generator,
3... Grounding object, 4... Electrostatic gun, 5... Shield wire, 6... Reverse polarity transient current detection circuit, 7a, 7
b...Comparator, 8a, 8b...Setter, 9...Caution alarm, 10...High voltage cutoff alarm.

Claims (1)

[Scope of utility model registration request] A high-voltage power supply, an electrostatic coating gun with a charged electrode, and an output terminal of the high-voltage power supply and the electrostatic coating gun are electrically connected using a high-voltage cable, and electrostatic coating is applied to a grounded workpiece. In the device for performing this, a transient current detection circuit of opposite polarity is provided between the shield wire sheathed on the high voltage cable and the ground electrode, and the output of the transient current detection circuit of opposite polarity is input to two comparators, Electrostatic coating with a configuration in which the comparator set to the lower value outputs a caution signal and the comparator set to the higher value outputs a cutoff signal by comparing with two preset high and low comparison values. Spark discharge prevention safety device.