STATIC ELIMINATOR

TECHNICAL FIELD

The present invention relates to a static eliminator (ionizer) having a function for outputting an alarm for signaling the arrival of cleaning time of a discharge electrode.

BACKGROUND

A static eliminator (ionizer) for ionizing air by a corona discharge and for eliminating static electricity by blowing the ionized air over a charged object is disclosed, for example, in Japanese Unexamined Patent Publication No. 2002-75589.

In this type of static eliminator, if a high- voltage power supply or a discharge electrode is contaminated, the corona discharge performance drops and static electricity cannot be eliminated sufficiently within a prescribed time. Here, the high- voltage in the static eliminator means a voltage more than 1 kV and up to ten and several kV. Generally, it is not easy to know firsthand how much the corona discharge performance has degraded due to contamination, and therefore, it has traditionally been practiced to periodically perform cleaning, irrespective of the degree of contamination, in order to maintain the required static elimination performance.

Japanese Unexamined Patent Publication No. 2003-17293 cited below discloses a device for displaying the arrival of cleaning time based on an ion balance control value in a static eliminator that performs ion balance control of positive and negative ions. This ion balance control is performed based on minuscule currents of pico-ampere order that flow between ground and the positive and negative ion current detecting electrodes placed in an ionized air flow. The control is therefore susceptible to noise voltages induced at the electrodes as well as noise due to the operating environment, and it is difficult to accurately determine the degree of performance degradation. It is an object of at least one embodiment of the present invention to provide a static eliminator equipped with an alarm output function that can accurately determine the arrival of cleaning time in accordance with a predetermined reference.

SUMMARY

According to at least one embodiment of the present invention, there is provided a static eliminator comprising: a high-voltage generating circuit generating a high voltage

which is applied to a discharge electrode; a voltage comparator circuit comparing the voltage applied to the discharge electrode with a reference voltage value based on which to determine the arrival of cleaning time of the discharge electrode; and an alarm output section outputting an alarm when the voltage applied to the discharge electrode is smaller than the reference voltage value.

The reference voltage value is determined, for example, based on a required static elimination time,

According to at least one embodiment of the present invention, by noting that the insulation resistance between electrode and ground degrades due to contamination, causing a decrease in discharge electrode voltage, and that there is a certain relationship between the decrease of the electrode voltage and the static elimination time (the time required to achieve the necessary static elimination effect), provisions are made to compare the electrode voltage with a reference value and to output an alarm for signaling the arrival of the cleaning time; the invention can thus determine the arrival of the cleaning time with good accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a block diagram showing in simplified form the configuration of a static eliminator according to one embodiment of the present invention.

Figure 2 is a circuit diagram showing one example of the detailed circuit configuration of a voltage comparator 16.

Figure 3 is a circuit diagram showing one modification of the circuit of Figure 2.

DETAILED DESCRIPTION

Figure 1 shows in simplified form the configuration of a static eliminator having an alarm function according to one embodiment of the present invention. In Figure 1, a high- voltage generator 10 generates positive and negative high voltages +HV and -HV of several thousand volts from a DC power supply and supplies the respective voltages to positive and negative discharge electrodes 12 and 14 to produce a corona discharge with respect to ground. A voltage comparator 16 compares the voltage produced between ground and the respective electrodes 12 and 14 with a predetermined reference value and, when the absolute value of the voltage becomes smaller than the reference value, causes an LED 18 to light or a buzzer 30 to sound to signal the arrival of the cleaning time.

Table 1 shows by way of example the results of the measurements made to obtain the relationship between the electrode voltage and the static elimination time, i.e., the time that the voltage of a metal plate charged to +1000 V at a distance of 30 cm from the front of the static eliminator takes to decay to +100 V.

Table 1. Relationship between electrode voltage and static elimination time (example)

From Table 1, if it is desired to maintain the static elimination time at 0.5 second or shorter, the above reference value should be set to 4 kV, and the cleaning should be performed when the alarm is produced. Compared with the case of measuring ion currents of pico-ampere order, the electrode voltage can be measured much more accurately as it is unaffected by noise, and the arrival of the cleaning time can thus be determined with higher accuracy.

Figure 2 is a diagram showing one example of the detailed circuit configuration of the voltage comparator 16. In Figure 2, resistors 20 and 22 are provided to divide the high- voltage of several thousand volts therebetween to obtain a voltage of about 1 volt. The voltage thus obtained by dividing between the resistors 20 and 22 is fed to the non- inverting input terminal of an OP amplifier 24 used as a comparator, while a voltage corresponding to the above reference voltage is supplied to the inverting input terminal of the OP amplifier 24. When the voltage obtained by dividing between the resistors 20 and 22 becomes lower than the reference voltage, the output of the OP amplifier 24 changes from an H level to a L level, causing the LED 18 to light.

In the circuit of Figure 2, only the positive voltage is evaluated, but two circuits similar to the one shown may be used so that an alarm can be produced for each of the positive and negative electrodes. Alternatively, the positive and negative alarm outputs may be ORed together and then the LED may be lit based on the result. Figure 3 shows one modification of the circuit of Figure 2. In the example of

Figure 3, a constant voltage from a constant current source 26 is resistively divided and supplied as the reference voltage to the inverting input terminal of the OP amplifier 24. One end of the resistive divider is selectable by a switch so that the level of the alarm, that is, the level of the static elimination time to be maintained, can be selected by this switch.

It should be noted that although the above embodiments are described with respect to static eliminators having direct current high- voltage generators, the present invention is not limited to these, but can also be applied to static eliminators having alternate current high-voltage generators.