JPH0673045B2 - Corona discharge device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a corona discharge device for generating a corona discharge by applying a high voltage to a corona discharge electrode, and more specifically, an electrophotographic apparatus such as an electrophotographic copying machine or a laser beam printer. The present invention relates to a corona discharge device that is used in a device and that charges a photoreceptor.

(Background Art) Corona discharge devices that generate a corona discharge by applying a high voltage to a corona discharge electrode are roughly classified into the following three cases according to the type of the applied voltage.

The first is the case where a DC voltage is applied to the corona discharge electrode. This is because corona discharge is generated by applying a positive DC high voltage to the corona discharge electrode, and a negative DC
Corona discharge is generated by applying a high voltage.

On the other hand, the second is the case where an AC voltage is applied to the corona discharge electrode.
Bipolar corona discharge is generated.

Furthermore, the third is a case where a superimposed voltage of an AC voltage and a DC voltage is applied to the corona discharge electrode. This is mainly due to the bipolar corona discharge due to the AC voltage, and the surface of the body to be discharged is neutralized by the difference in the bipolar corona discharge charge amount (current amount). Here, the DC voltage is auxiliary, and serves to adjust the difference in the amount of corona discharge current between the polarities due to the AC voltage or to keep the difference constant.

By the way, in the case of charging an object to be charged, for example, a photoconductor to a desired potential by using a corona discharge device, the first one is most commonly used. However, DC
When negative corona discharge is performed by applying a voltage to the corona discharge electrode, there is a drawback that uneven discharge occurs unless the amount of corona discharge current flowing from the corona discharge electrode is increased. Therefore, in order to increase the amount of corona discharge current, it is necessary to increase the output and capacity of the high-voltage power supply, which causes a problem of increasing the size of the high-voltage power supply. Further, there is also a problem that the amount of corona products such as ozone and nitrogen oxides increases as the amount of discharge current increases. Incidentally, these things are not the same as those of the negative corona discharge, but the same tendency is observed when the positive corona discharge is performed.

Further, although it is possible to perform charging by using the corona discharge device as described above, in the case of this corona discharge device, charging is performed by the difference in the corona discharge current amount of both positive polarity and negative polarity. Therefore, when the surface of the body to be charged is charged in one polarity, the charging efficiency is low.

(Object of the Invention) It is an object of the present invention to provide a corona discharge device capable of obtaining stable corona discharge with little discharge unevenness even at a low corona discharge current without increasing the output or capacity of a high voltage power supply. .

Another object of the present invention is to provide a corona discharge device in which generation of corona products such as ozone and nitrogen oxides is reduced.

(Summary of the Invention) The present invention has a corona discharge electrode and a power source for applying a voltage to the corona discharge electrode, wherein the voltage is a DC voltage and an AC voltage superposed, and has the same polarity as the DC voltage. When the corona discharge current is a voltage at which only the DC voltage is applied to the corona discharge electrode in order to bring the charged body to a desired potential, the charged body is The corona discharge device is characterized in that the maximum value of the corona discharge current when the superimposed voltage is applied to the corona discharge electrode so as to obtain a desired potential is set to be substantially 2 · I or more. Further, the present invention has a corona discharge electrode and a power supply for applying a voltage to the corona discharge electrode, wherein the voltage is a DC voltage and an AC voltage superimposed, and only a component having the same polarity as the polarity of the DC voltage. The DC voltage is a voltage at which a corona discharge current flows, and the DC voltage is set to a voltage value V near the corona discharge start voltage, and the AC voltage has its peak.
The corona discharge device is characterized in that a voltage at which a to peak value is substantially 1 to 2 times V is set. Thereby, stable corona discharge without uneven discharge can be performed.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIG. 1 schematically shows an electrophotographic copying machine to which the corona discharge device of the present invention can be applied. Reference numeral 1 denotes a photosensitive drum as a member to be charged, which is rotationally driven in a direction indicated by an arrow at a predetermined peripheral speed.
2 uniformly charges the surface of the photosensitive drum 1 uniformly. 1 is a corona discharge device according to the present invention. The uniformly charged photosensitive drum 1 is subjected to optical image exposure 3 corresponding to a document (not shown) to form an electrostatic latent image. This electrostatic latent image is developed by the developing device 4 and visualized. The developed image is transferred by the transfer charging device 5 onto the transfer material P that is conveyed in the direction of the arrow by a conveying system (not shown). After the transfer, the transfer material P is guided to a fixing device (not shown), where the image is fixed, and then the transfer material P is discharged outside the machine. On the other hand, after the transfer is completed, the developer remaining on the photosensitive drum 1 is removed by the cleaning device 6, and the photosensitive drum 1 is repeatedly used for image formation. In this way, the required process steps are performed on the photosensitive drum to form an image.

Here, the corona discharge device 2 will be described.

In FIG. 1, 20 is a corona discharge wire as a corona discharge electrode of the corona discharge device 2, and 21 is a shield plate.
The corona discharge line 20 is connected to an AC high voltage power supply 22 and a DC high voltage power supply 23 which are connected in series with each other. Both power supplies 2
2,23 A to DC high voltage V _DC for corona discharge 20.
C. Voltage V _PP is applied. In this embodiment, the shield plate 21 is grounded.

In this example, the distance between the side surface of the shield plate 21 of the corona discharge device 2 and the corona discharge wire 20 is about 7 mm, the distance between the back surface of the shield plate 21 and the corona discharge wire 20 is about 8 mm, and the corona discharge wire 20 is The distance from the surface of the photoconductor 1 is about 10 mm, the diameter of the corona discharge wire 20 is about 60 μ, and the peripheral speed of the photoconductor 1 is about 66 mm / sec. As the photoconductor 1, an opc (organic photoconductor) photoconductor is used. did.
The voltage applied to the corona discharge line 20 is the AC high voltage power supply 22
Output V _PP frequency about 400Hz (sin wave), voltage about 6KV _PP (pr
ak to peak), the output voltage V _DC of the DC voltage power supply 23 is approximately −3.5 KV
The superimposed voltage of By operating the corona discharge device 2 under these conditions, a negative corona discharge current I ₂ flows from the corona discharge line 20 to the photoconductor 1 and the surface of the photoconductor 1 is negatively charged. As a result, the photoconductor 1 is charged to about -800V. I ₁
Is the total corona current.

FIG. 2 shows the voltage applied to the corona discharge line 20 and the photoreceptor 1.
The relationship between the amount of corona discharge current I ₂ flowing in is shown. V ₀ is the corona discharge inception voltage (about −3.5 KV). The output voltage V _DC of the DC voltage power supply 23 is approximately equal to V ₀ . In addition, the peak value of the sin waveform AC voltage V _PP side of the AC high-voltage power supply 22 is + 3.0K.
Since the peak value on the V side is −3.0 KV, AC discharge does not start with the AC voltage power supply alone (since the discharge start voltage on the side is higher than that on the side, discharge does not start). In this embodiment, since the surface of the photosensitive member 1 is charged to −800V, the corona discharge current amount I ₂ flowing in the drum direction is about 500 μA, and the DC voltage V _DC and the AC voltage V _PP superposed on the DC voltage V _DC. Gives this value.

Next, referring to FIGS. 3A and 3B, the difference in discharge unevenness between the case of the corona discharge device as in the present embodiment and the case of the corona discharge device in which only the DC voltage is applied to the corona discharge line will be described. .

FIG. 3A can be placed when the applied voltage to the corona discharge line 20 is the superimposed voltage of DC-3.5KV and AC6KV _PP as described above.
6 is a graph showing a variation distribution of a discharge current I ₂ with respect to each part of the surface of the photoconductor 1 immediately below the corona discharge device 2 along the length of the corona discharge line 20. As a comparative example, FIG. 3B is a graph showing the variation distribution of the same discharge current I ₂ when corona discharge is performed with the applied voltage to the corona discharge line 20 being only the DC voltage V _{DC of} −5.2 KV (note that , DC-5.2KV DC voltage applied, I
A corona discharge current amount of ₂ = 50 μA can be obtained.

In both FIGS. 3A and 3B, the total corona discharge current amount I ₁ was about 500 μA. Thus, the ripple R of the discharge current distribution (that is, showing discharge unevenness) of the former is about 6%, while the ripple R of the discharge current distribution of the latter is about 15%. That better to voltage V _DC + V _PP to the voltage applied to the corona discharge wire 20 to a DC voltage V _DC by superimposing an AC voltage V _PP is, discharge current with respect to the corona discharge wire longitudinally than when only a DC voltage V _DC It can be seen that the distribution is stable.

The ripple R (%) is calculated by (B / A) × 100 (%) where A is the maximum value of the discharge current distribution and B is the maximum fluctuation range. When the ripple R is 10% or less, there is no particular problem in practical use and almost no unevenness occurs on the image.

Here, in order to keep the corona discharge current constant (-50 μA in the present embodiment), including the above-described embodiment, various combinations of the voltage values of the DC high voltage V _DC and the AC voltage V _PP that are superimposed on each other are used. The following Table 1 shows the measurement results of the ripple R of the discharge current distribution along the longitudinal direction of the corona discharge line and the unevenness on the image when the image was actually printed when the image was changed.

Further, FIGS. 4A to 4G show the waveform of the applied voltage and the waveform of the discharge current in the cases of Tables 1 (a) to (g). 4A, 4B,
4C, 4E, 4F, 4G figures are (a), (b), and
It corresponds to (c), (d), (e), (f) and (g).

As is clear from the table, the AC voltage V _PP superimposed on the DC voltage V _DC has an effect as a practical image from about 3 KV,
At 4KV or higher, the unevenness hardly appears in the image. In order to increase the AC voltage V _PP more than necessary, it must be avoided to prevent spark discharge. In this example, 7KV is set as a temporary upper limit and 7KV
We conducted experiments up to V _PP , but on the image, there was almost no difference up to 4 KV _PP .

Further, as is clear from FIGS. 4A to 4G, the DC voltage V _DC
Maximum value of corona discharge current I ₂ compared to
The higher I ₂ max |, the smaller the ripple R,
It can be seen that the image unevenness is reduced and the image quality is improved.

By the way, as a measure of the voltage to be superimposed, the voltage values of V _DC and V _PP are set so that I ₂ max that is about twice or more the discharge current I ₂ (-50 μA in this embodiment) when only V _DC is obtained. By setting, it is possible to further reduce the uneven discharge.
From another point of view, the discharge start voltage V _DC as V _DC
By selecting a value close to ₀ (about −3.5 KV in this embodiment), and further superimposing an AC voltage V _PP (about 4 to 7 KV in this embodiment) that is about 1 to 2 times the discharge start voltage V _0. Discharge unevenness can be further reduced.

As described above, in the present invention, the corona discharge current amount flowing in the photoconductor by applying the superposed voltage to the corona discharge line is obtained by applying only the DC voltage to the corona discharge line to obtain the desired charging potential. The voltage value of the DC component of the superimposed voltage is set so as to be equal to the discharge current amount (including an error of about ± 5% with respect to the current amount when only the DC voltage is used). In the present invention, the spark discharge starting voltage (about 7 KV in this embodiment) determined by the configuration of the corona discharge device.
The peak value of the waveform of the superimposed voltage is made smaller. Further, according to the present invention, the corona discharge current having only the same polarity as that of the DC voltage flows. This allows
The present invention can reduce the discharge unevenness as compared with the case where only the DC voltage is applied to the corona discharge line.

By the way, it can be considered that the stabilization of the discharge due to the superimposed voltage of the DC high voltage and the AC voltage is due to the following phenomenon. That is, especially in corona discharge, the ripple R indicating the unevenness of the corona discharge distribution is inversely proportional to the amount of corona discharge current. R × I ₂ = C between the ripple R and the corona discharge current I ₂ flowing in the drum direction.
There is a relationship. C changes depending on the state of the corona discharge wire (surface property, stain condition, wire diameter, etc.), but is a constant determined for a specific corona discharge wire. Therefore, it can be seen that R increases as I ₂ increases.

By the way, the above-mentioned I ₂ is not a steady current obtained in the case of only a DC high voltage, but is determined by the maximum value I ₂ max of the current obtained when an AC voltage is superimposed on the DC high voltage as in the present invention. It is something. This state is shown in FIG. The curve here is for a clean discharge line, the curve for a clean discharge line, and the curve for a clean discharge line in between. The constant C is determined by each discharge line and becomes | C ₁ | <| C ₂ | <| C ₃ |, and for a given I ₂ max, the smaller | C | is, the smaller R is, that is, stable. A discharge is obtained. Further, if C is specified and considered, R becomes smaller as | I ₂ max | becomes larger, and stable discharge can be obtained.

That is, in the present invention, by superimposing an AC voltage, I ₂ max is necessarily increased in order to effectively obtain a corona discharge current equivalent to the case of only a DC voltage (in the integrated value of the current). Become. This is considered to stabilize the corona discharge.

FIG. 6 is a corona discharge device showing another embodiment of the present invention. This example has the same polarity as the DC high voltage power supply 23 of the shield plate 21 of the corona discharge device 2 for the purpose of reducing the total corona current amount I _1. The bias voltage V _B is applied from the bias power source 24 for use. The configuration of the other corona discharge device is the same as that of the first illustrated example. The above bias voltage V _B
May be applied by a linear or non-linear voltage element (varistor, constant voltage diode, etc.). Further, in the illustrated example, it is omitted in each process step.

The applied voltage to the corona discharge line 20 was V _DC (−3.5 KV) and V _PP (6 KV _PP , about 400 Hz, Sin wave), and the bias voltage V _B was −1 KV, as in the above embodiment. As a result, the total corona current I ₁ can be reduced to 200 μA,
Moreover, I ₂ was set to 50 μA ', which was the same as that in the above-mentioned embodiment, and the same photoreceptor potential as that in the above-mentioned embodiment was obtained.

FIG. 7 is a graph showing the relationship between the voltage applied to the corona discharge line 20 and the corona discharge current amount I ₂ flowing through the photoconductor 1 in this example. In addition, FIG. 8A shows the corona discharge line 20 just below the corona discharge device 2 under the above voltage conditions.
5 is a graph showing a variation distribution of the discharge current I ₂ with respect to each part of the surface of the photoreceptor 1 along the longitudinal direction of FIG. As a comparative example, FIG. 8B shows a case where the voltage applied to the corona discharge line 20 is only a DC voltage V _DC of -5.2 KV and a bias voltage V _{B of} -1 KV is applied to the shield plate 21 to perform corona discharge ( In this case I ₁ is 200μ
A and I ₂ are 50 μA. 4) is a graph showing the variation distribution of the same discharge current I ₂ in FIG. Thus, the ripple R of the discharge current distribution in the former FIG. 8A is about 9%, which is within the practical level, whereas that in the latter FIG. 8B is 22%, which is below the practical level.

Thus, the total corona current can be reduced by applying a bias voltage to the shield plate, and
By applying a superposed voltage of DC high voltage and AC voltage to the corona discharge line, it is possible to reduce discharge unevenness.

FIG. 9 shows a further embodiment of the present invention. In this embodiment, a voltage as shown in FIG. 10 is applied to the corona discharge wire 20.
That is, a DC voltage V _{DC of} about −3.5 KV is applied with a rectangular wave voltage having a frequency of about 400 Hz and a voltage (peak to peak) of 6 KV _PP as the AC voltage V _PP . Further, a control circuit 25 for varying a duty ratio of a rectangular wave (which will be described later) is connected to the AC high-voltage power supply 22, and a control signal generation source for inputting a control signal to the control circuit 25 is connected to the control circuit 25. 26 is connected. The control signal from the control signal generation source 26 is, for example, a control signal from the corona discharge current detection circuit when the corona discharge current is constant (that is, constant current),
Alternatively, when performing potential control, it is a potential control signal or the like generated by calculating a detection signal of the potential sensor.

Here, the duty ratio is defined by b / a. In this embodiment, d
We will show the uty ratio in%. In Figure 10, about 50%
Is. FIG. 11 shows the change of the current I ₂ when the duty ratio is changed. As is clear from this figure, to increase the total corona current I ₁ or the current I ₂ flowing through the drum, du
It is sufficient to increase the ty ratio, and conversely, to decrease I ₁ and I ₂ , d
The uty ratio should be reduced. In this embodiment, the peak voltage value of the voltage applied to the corona discharge line is -6.5KV.
Is constant, the discharge unevenness hardly changes even if the duty ratio is reduced.

In this way, by keeping the voltage values of the DC high voltage and the AC high voltage constant and changing the duty ratio of the rectangular wave, it is possible to adjust the corona discharge current while reducing discharge unevenness.

Although the present embodiment has been described based on the case of performing corona discharge, the present invention is not limited to this and the present invention can be applied to the case of performing corona discharge. However, the present invention is particularly effective when performing corona discharge.

Further, in the above-mentioned embodiment, the sin waveform as the waveform of the AC voltage,
Although the rectangular wave has been described, a triangular wave or a pulse wave can be selected as the waveform of the AC voltage.

Further, in order to maintain the maximum value I ₂ max of the corona discharge current, it is better that the top of the voltage waveform is flat rather than the needle end shape.

Also. The bias voltage V _B applied to the shield plate 4 is not limited to DC / AC, and the present invention can be applied to a charger further provided with a grid electrode.

(Effects of the Invention) As described above, when a desired photoconductor potential is obtained, that is, when a desired corona current flowing in the drum direction is obtained, an AC is applied to a DC high voltage rather than a corona discharge using only a DC high voltage. It was possible to reduce the ripple R of the discharge current by superimposing the voltage and effectively generating a corona current equivalent to that in the case of only the high DC voltage.

And, even with a low corona discharge current that was difficult to put into practical use in the conventional corona discharge by applying only a high DC voltage, a corona discharge current with only a desired charging polarity can be obtained by the corona discharge due to the superimposed voltage of the high DC voltage and the AC voltage. By flowing it, stable corona discharge without discharge unevenness could be performed.

Furthermore, because of the low-current corona discharge, the amount of ozone, nitrogen oxides, and other corona products generated by corona discharge can be greatly reduced, and the photoreceptor and other components can be prevented from deteriorating due to corona products. It was

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electrophotographic copying machine to which the corona discharge device of the first embodiment of the present invention is applied, FIG. 2 is a graph of applied voltage-discharge current characteristics of the corona discharge device of FIG. 1, and FIG. Fig. 1 is a graph of the discharge current distribution of the corona discharge device, Fig. 3B is a graph of the discharge current distribution of the corona discharge device when only DC high voltage is applied, and Figs. 4A to 4G are time t. 5 is a graph showing the waveform of the discharge current, and FIG. 5 is a graph showing the relationship between the ripple R of the discharge current distribution and the maximum value I ₂ max of the discharge current. FIG. 6 is the second embodiment of the present invention. FIG. 7 is a schematic diagram of an example corona discharge device, FIG. 7 is a graph of applied voltage-discharge current characteristics of the corona discharge device of FIG. 6, and FIG. 8A is a graph of discharge current distribution of the corona discharge device of FIG. Figure 8B shows the discharge current of the corona discharger when only DC high voltage is applied. 9 is a schematic diagram of the corona discharge device of the third embodiment of the present invention, FIG. 10 is a graph showing the applied voltage waveform in the case of FIG. 9, and FIG. 11 is a corona discharge current and duty. The graph which shows the relationship with a ratio. 1 ... Photosensitive drum 2 ... Corona discharge device 20 ... Corona discharge wire 22 ... AC voltage power supply 23 ... DC voltage power supply

Claims (2)

[Claims] 1. A corona discharge electrode, and a power supply for applying a voltage to the corona discharge electrode, wherein the voltage is a DC voltage and an AC voltage superposed, and only a component having the same polarity as the polarity of the DC voltage. When the corona discharge current is a voltage at which a discharge current flows and only a DC voltage is applied to the corona discharge electrode to set the charged body to a desired potential, the charged body is set to the desired potential. Therefore, the maximum value of the corona discharge current when the superimposed voltage is applied to the corona discharge electrode is set to be substantially 2 · I or more. 2. A corona discharge electrode, and a power source for applying a voltage to the corona discharge electrode, wherein the voltage is a DC voltage and an AC voltage superposed, and a corona having only a component having the same polarity as the DC voltage. The discharge current is a voltage at which the DC voltage is set to a voltage value V near the corona discharge start voltage, and the AC voltage has a peak to peak value of substantially 1 to 2 of V.
A corona discharge device characterized in that a doubled voltage value is set.