JPS5889960A - Spark preventing device for high voltage power source for electrostatic coating - Google Patents

Abstract

PURPOSE:To prevent the generation of sparks securely by providing a band stop filter which removes an AC component having an integrally multiplied frequency of a commercial power source frequency on the input side of a comparing circuit. CONSTITUTION:A resistor 20 for current-voltage conversion is provided between a connection terminal 19 and the ground. The input side of a voltage follower 21 only for input and output impedance conversion is connected to the high potential side of the resistor 20, and the output terminal is connected to the input side of a low-pass filter 22. On the output side of the low-pass filter 22, a band stop filter 23 is provided. This band stop filter 23 removes frequency components which are integrally multiplied frequency of a commercial power source. Then, the input side of a comparing circuit 24 is connected to the output terminal of the band stop filter 23. A signal waveform having high frequency componenets removed through the low-pass filter 22 is passed through the filter 23 to remove the frequency components which are integrally multiplied frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spark prevention device for a high voltage power supply equipped with an electrostatic 1#.

Traditionally, high-voltage power supplies for electrostatic painting have been equipped with spark prevention devices to prevent the generation of sparks that can cause fires and other disasters. The spark prevention device for the power supply will be explained based on Figure 1 and Figure 2. 1 is the high voltage power supply, 2 is the electrostatic fj equipment, and 3 is the high voltage power supply.
1 is a workpiece to be coated, and a spark prevention device 4 and a high voltage generation circuit 5 are incorporated in an internal pressure power source 1.

The spark prevention device 4 has an input disconnection switch 6 and an output grounding switch 7, and these switches 6.7 are controlled by an abnormality detection circuit 8.

The structure and operation of this abnormality detection circuit 8 will be described later. The high voltage generation circuit 5 has a converter 9 and an inverter lO
, a step-up transformer 11 , and a step-up rectifier circuit 12 .

When the input connection/disconnection switch 6 is closed, the commercial power supply voltage is input to the converter 9, converted to direct current, and then input to the inverter 10. Therefore, the inverter 10 oscillates at a frequency of 30-1-kHz, which is less than 1 kilohertz,
The output is boosted by the step-up transistor 11, converted to I& by the step-up rectifier circuit 12, and applied as a DC high voltage to the electrostatic flI equipment 2. When a DC high voltage is applied to the electrostatic type fi-Ia 2, , #W
#II A corona discharge path is formed between the machine 2 and the object 3 to be coated, and just before a spark occurs, a load current l flows through the circuit including the high voltage power supply 1, the electrostatic III machine 2, and the object 3. S is known to increase.

The abnormality detection circuit 8 is configured to detect this increase in the load current 1. In other words, as shown in the second case, the normal detection circuit 8 is a voltage follower 1 that only performs input/output impedance conversion.
3, a low-pass filter 14 that attenuates and outputs the high frequency component superimposed on the load current 1, and a signal of the load current from which the high frequency component has been removed is compared with a reference value to generate a spark precursor signal. It is generally composed of a comparison circuit 15 that outputs an output, and a control transistor 16 that is controlled to be turned on or off by this spark precursor signal. 2. In FIG. 2, the reference numeral 17 indicates a resistor for converting current into voltage, and the reference numeral 18 indicates a connection terminal.

By the way, the magnitude of the load I flowing through the circuit including the high-voltage power supply 1, the electrostatic shield *2, and the object to be coated 3 is on the order of 10 or 100,000 yen, and is weak. , since the amount of increase in this load current 1 is also about several percent of the magnitude of the load W current l that flows steadily, the amount of increase in the load current l is due to the alternating current component superimposed on this load current l. It may be canceled out. As shown in FIG. 3, as one hour t elapses, the output signal of the voltage-converted load current l increases while still containing an alternating current component.

While passing through the low-pass filter 14, its high-frequency components are removed, resulting in a tentative signal shown in figure m4. This signal shaping is input to the comparator circuit 15, where it is compared with a reference value E, and the signal waveform is converted to this reference value. Although the control transistor 16 is activated when the value E is exceeded, the signal of the load current fILi that has passed through the 20-bus filter 414 has a fourth
As shown in the figure, an AC component remains and from the viewpoint of controlling the spark generation prevention device to 'iii*, it is desirable to remove this remaining AC component to N%.

In other words, if this alternating current component is superimposed on the signal waveform of load current 1, it is difficult to distinguish whether the signal is an increase in load current I or an alternating current component signal, and the amount of load current has increased. In order to make a 1 determination, the reference value must be set larger than the peak value of the AC component.
However, if the reference value is set high in this way, the time between detecting a sign of spark generation and before spark generation becomes extremely short. There are cases where sparks occur before spark generation prevention is done.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spar-preventing device for a high-voltage power supply for static painting, which is capable of preventing the occurrence of spar.

The reason for this is that a band-rejection filter is provided on the input side of the comparator circuit to remove AC components having a frequency that is an integral multiple of the frequency of the commercial power supply.

An embodiment of the present invention will be described below with reference to FIGS. 5 and 6.

2 in FIG. 5, the reference numeral 19 is a connection terminal, and the reference numeral 19
A resistor 20 for current/voltage conversion is provided between and ground, and the load current l is ! ! Connecting terminal 19 to resistor 2
0 and flows to ground. resistance s
The input side of a voltage follower 21 that performs only input/output impedance conversion is connected to the high potential side of 20, and its output end is connected to the input side of a low-pass filter 22. The load current I flowing through the resistor 20 has an alternating current component superimposed on it, and the load current 1 passes through the voltage follower 21 and is input into the high-pass filter 22.
The signal waveform includes a cross-R component as shown in @3[i21, and the high frequency component is removed while this signal waveform passes through the low-pass filter 22, resulting in a signal as shown in FIG. It becomes a waveform. On the output side of the low-pass filter 422, a band-removal filter 23 specified by a formula described below is provided. It has a 1% characteristic expressed by this band removal.

2 in this upper order formula.

GO: Any constant Q other than 0: A constant indicating the ability to select a specific frequency.

ω is defined as ω==gNX2gfo, and N is
O is an integer determined by the parameter 9, and fO is the frequency of the commercial power supply.

To summarize, this band-rejection filter 23 has a load current l
The input side of a comparator circuit 24 is connected to the output terminal of the filter 23, and the input side of a comparator circuit 24 is connected to the output terminal of the filter 23.
The signal waveform of the load current I, from which high frequency components have been removed, has frequency components that are integral multiples of the frequency of the commercial power source removed while passing through this band elimination filter 23, and becomes pure direct current as shown in FIG. Only the components will be input to the comparator circuit 24. This comparison circuit 24 has a reference voltage signal generation circuit 25 as a reference value E. Here,
This reference value E can be adjusted using a volume 26.

The comparison circuit 24 compares the signal waveform input thereto with the reference value E.
When the magnitude of the signal waveform exceeds the reference value E, a signal is output, and this signal is input to the control torque switch 27 as a precursor signal of spark generation. An output signal output from the output terminal 28 of the control transistor 27 controls the input a-off switch 6 and the output grounding switch 7.

According to the high positive high voltage power supply park prevention device for electrostatic MII according to the present invention, among the AC components superimposed on the load current 1,
AC components caused by external conduction disturbances such as noise during corona discharge of the electrostatic wP8 machine 2 (so-called 1,000 pulses) and AC components caused by the oscillation of the inverter 10 are filtered by a low-pass filter 22. The AC component that is removed and attributed to the converter 9, that is, the AC component having a frequency that is an integral multiple of the frequency of the commercial 1m source, is passed through the band-removal filter 23.
Therefore, an increase in the load current l can be detected at ii*.

Although the dormitory example has been described above, the present invention is not limited to this, but also includes the following.

In the dormitory example 2, a low-pass filter 22 and a comparison circuit 2 are used.
Although the IN band removal filter 23 is provided between the comparison circuit 24 and the comparison circuit 24, the present invention is not limited to this, for example.

It is also possible to provide a configuration in which this band-rejection filter 23 is provided between the converter 9 and the inverter IO. Also 1
In the present invention, the determination is made based on whether or not the load current 1 exceeds the reference value E, but there is also a configuration in which the determination is made by differentiating the load current I, and an increase in the load current 1 per unit time. The present invention can also be applied to a device configured to calculate and judge a quantity digitally.

Since the present invention is constructed as described above, it has the following effects.

(11) Since the alternating current component superimposed on the load current is removed as much as possible, the reference value can be made as low as possible, and the generation of sparks can be greatly prevented.

(2) It is possible to prevent the spark prevention device from malfunctioning due to the influence of the alternating current component superimposed on the load current, and it is possible to reduce the interruption of the aS operation due to one operation of the spark prevention device.

[Brief explanation of drawings]

Figure 1 shows a conventional spark prevention device for high-voltage power supplies for electrostatic painting. Figure 11112 is a circuit diagram of an abnormality detection circuit of a spark prevention device for a conventional high-voltage power supply for electrostatic painting. Figures # & 3 are load current characteristic diagrams. Figure 11IA4 is a characteristic diagram for removing the high frequency component superimposed on the load current to clarify the situation. FIG. 5 is a circuit diagram of an abnormality detection circuit of a spark prevention device for a high-voltage power supply for electrostatic painting according to the present invention. FIG. 6 is a characteristic diagram showing the characteristics of load current with AC components completely removed. l...High voltage power supply 2...Electrostatic 1jl Eel machine 3...Covering 4...Spark prevention device 22...Low pass filter 23-・Band rejection filter 24...Comparison circuit 1...・Load current patent applicant Toyota Motor Corporation (1 other person)

Claims (1)

[Claims] (11) A low-pass filter is used to remove high-frequency components of a load current flowing through a circuit including a high-voltage power supply, a coating machine, and an object to be coated, and the load current from which the high-frequency components have been removed is used as a reference. The spark prevention device for high-voltage power supplies for silencers is designed to prevent sparks by outputting a spark precursor signal when the load current exceeds a certain value.゛A band-removal filter is provided at the input of the circuit that outputs the spark precursor signal to remove the frequency fHL number component, which is an integral multiple of the frequency of the commercial power source, from among the AC components superimposed on the load current. Spark prevention device for high voltage power supply for electrostatic scissors