JPH01292369A - Corona discharge device - Google Patents

Abstract

PURPOSE:To reduce an electric voltage between peaks and to make a corona discharge device suitable for high speed operation and for miniaturization without accompanying abnormal discharge by impressing an electric voltage having sine alternate current wave form alone. CONSTITUTION:A DC power source 7, a sine AC power source 6, having (f) frequency, and a sine AC power source 5 having (mf) frequency (wherein m is 2n+1; n is an integer) are connected to a charging line 3 of a corona discharge device. Thus, an electric voltage resulted by the superposition of said two ACs on DC is impressed to the charging line 3. A mark 1 means a sum current of a positive and a negative component conducted to the charging line 3. By this constitution, a desired discharge current can be maintained by a low voltage between peaks without causing abnormal discharge.

Description

Detailed Description of the Invention (1) Purpose of the Invention (Field of Industrial Application) The present invention is particularly suitable for use in image forming apparatuses that utilize an electrostatic recording process, such as electrostatic copying machines and printers. This invention relates to a corona discharge device.

(Prior art and problems to be solved) After uniformly charging a photoreceptor as an image carrier, a light image is irradiated onto it to form an electrostatic latent image, and then a developer is applied to the latent image. A sheet-like transfer material such as paper is brought into contact with this, and the developed image is transferred to the transfer material by imparting an appropriate polar charge to this transfer material. Image forming apparatuses configured to apply charges of opposite polarity to separate the charge from the image carrier are conventionally well known.

In such an apparatus, corona discharge is performed by the charger when uniformly charging the photosensitive layer, transferring the developed image, and separating the transfer material as described above. As a means for applying voltage to the discharge electrode for
Means such as applying a voltage that is a superimposition of alternating current and direct current are widely used.

The charge removal and charge functions of this type of charger depend on the magnitude of the peak-to-peak voltage of the applied voltage, and the higher the value, the greater the charge or charge removal function tends to be.

Therefore, in view of the recent trend towards higher speeds in this type of apparatus, it is desirable to increase the peak dark value of the applied voltage in order to quickly and reliably charge and remove static electricity from the image carrier, transfer material, etc. On the other hand, if it is set too high, the risk of abnormal discharges such as spark discharges and creeping discharges inevitably increases.

On the other hand, in this type of image forming apparatus, smaller and lighter ones are gradually being used, and people from all walks of life are starting to use them easily. It is desirable that the desired charging and static eliminating functions can be obtained at peak-to-peak voltage.

Therefore, as a means to suppress the peak value of the applied voltage and increase the effective current amount, for example, a method using a rectangular wave as the applied voltage waveform, as seen in Japanese Patent Application Laid-open No. 52-15328 and Japanese Patent Publication No. 52-42218, etc. , Japanese Patent Publication No. 54-1397
As seen in Publication No. 36, etc., a device has been proposed in which a predetermined peak value is obtained by slicing the vicinity of the positive and negative peaks of a sinusoidal alternating current.

If the frequency and maximum voltage value of the square wave and sine wave are the same,
The area surrounded by the waveform between the discharge starting voltage and the maximum voltage is larger for the rectangular wave, and the amount of charge supplied is larger, but
In an actual device, it is common to amplify a rectangular wave signal of several volts to several tens of volts to several kV to several tens of kV using a transformer, so for example, the input waveform shown in FIG. The output waveform should be as shown by the dotted line in the figure, but as shown by the solid line in the figure, it is distorted and it is difficult to reduce the peak-to-peak voltage and flatten the peak portion, making it impractical.

Also, number 1! The figure schematically shows the latter case, but in this case, it goes without saying that the power loss (symbol 2
4) occurs, which is undesirable. Note that reference numeral 14 in the figure indicates the discharge starting voltage value.

Figure 12 shows how to maintain a current amount equal to the discharge current when corona discharge is performed with a sinusoidal alternating current of 13.6 kV (peak-to-peak voltage), and apply the maximum voltage (represented by reference numeral 21 in the figure) in the manner shown in Figure 11. 12 is a graph showing how much loss occurs by increasing the peak-to-peak voltage before slicing when decreasing the value shown in FIG.

In the figure, the horizontal axis represents the peak-to-peak voltage of the sinusoidal alternating current before slicing.

The change in the previous maximum voltage 21 when the peak-to-peak voltage is increased is shown by e, and the increase in loss is shown by f.
It can be seen that a small reduction in the peak-to-peak voltage results in a large loss.

The present invention has been made to deal with such a situation, and by applying only a voltage with a sinusoidal AC waveform, the peak-to-peak voltage of the applied voltage can be reduced, without the risk of abnormal discharge. Speeding up this type of image forming device,
The object of the present invention is to provide a corona discharge device that can be adapted to miniaturization.

(2) Structure of the invention (technical means for solving the problem and its operation) In order to achieve the above object, the present invention provides a corona discharge device that charges or removes electricity from a surface to be discharged by corona discharge. In order to obtain a corona discharge electrode, a sinusoidal alternating current with a frequency f and a frequency (2n+1; n is a positive integer)×f
The present invention is characterized in that among the sine wave alternating currents, priority is given to one having a small frequency, and a voltage in which at least one sine wave alternating current is superimposed is applied.

With this configuration, a desired discharge current can be maintained with a low peak-to-peak voltage without fear of abnormal discharge.

(Description of an Embodiment) FIG. 1 is a side view of a main part of an embodiment in which the present invention is applied to an image forming apparatus equipped with a rotating cylindrical photoreceptor. A charger 2 consisting of a charging wire 3 and a shield case 4 disposed to surround the charging wire 3 is disposed in parallel with the photoreceptor 1 which rotates.

The surface of the photoreceptor 1 is uniformly charged by the charger 2, and an electrostatic latent image is formed thereon in a well-known manner.Toner is applied to this to form a toner image, and the toner image is After being transferred to a transfer material such as paper while being in contact with it, this transfer material is separated from the photoreceptor, and a developing device, transfer charger, and separation static eliminator are used to carry out these operations. , a cleaning device, and other members are provided, but they are all omitted.

In the above configuration, in the present invention, the charging line 3 of the discharge device is connected to a DC power source 79, a sine wave AC power source 6 of frequency f, and a sine wave of frequency mf (m=2n+1; n is a positive integer). An AC power supply 5 is connected, thereby applying a voltage that is a superimposition of these two alternating currents and direct current to the charging wire 3.6 The symbol I in the figure indicates both positive and negative components flowing into the charging wire. is the sum current of

The relationship between the peak-to-peak voltage ratio of the power source 5.6 and the current I is shown in FIG.

The horizontal axis represents the ratio A of the peak-to-peak voltage of the power source 5 to the peak-to-peak voltage of the power source 6, and the vertical axis represents the current I. As can be seen, the appropriate ratio A is 1/10 to 1/3.

In FIG. 3, a waveform 8 of frequency f (illustrated point yj
) and a waveform 9 (shown as a chain line) of frequency 3f from the power source 5 superimposed on a waveform 10 (shown as a solid line). In this case, the ratio A is 0.175.

As shown in the figure, when the voltage at frequency f is Ov, the voltage at frequency 3f is also synchronized so that it becomes Ov, and when the former waveform peaks, the peak value of the latter waveform cancels out this. Make it.

As shown in FIG. 4, it can be seen that the applied voltage waveform 10 according to the present invention is effectively better than the sine waveform 8'' having the same peak value.

FIG. 5 shows a sine wave (curve a) and a waveform according to the present invention (curve a).
This is a graph showing the relationship between peak-to-peak voltage and sum current I in the practical range (peak-to-peak voltage 8 to 14 kV) when applying curve b) and a complete rectangular wave (curve C), with approximately the same amount. According to the present invention, compared to the case of a simple sine wave, the peak-to-peak voltage is 100
It can be seen that the voltage can be lowered by 0 to 1500V.

FIG. 6 is a graph showing changes in the differential current i (positive component current - positive component current) when the voltage of the DC power supply 7 in the device shown in FIG. 1 is changed.

In the graph, a is the peak-to-peak voltage 11k of the superimposed alternating current.
When using a sine wave of V, b is the peak-to-peak voltage 9. 5
kV using an alternating current waveform according to the invention as described above.

As can be seen from the figure, according to the present invention, less DC bias is required to obtain the same current,
The DC power supply can be downsized.

Specifically, when negatively charging an organic semiconductor device (PC) as a photoreceptor, in order to charge it to -700V, it is necessary to flow a current of approximately -600 pA through the photoreceptor. In the above a in the graph, -6
Although a DC bias of kV is required, it can be seen that only 14 kV is required for b.

FIG. 7 shows an embodiment in which the present invention is applied to a transfer charger.

As shown in the figure, a DC power source 79, an AC power source 6 with a frequency f, and an AC power source 5 with a frequency (2n+4)×f are connected to the transfer charger 11, as in the device shown in the first figure. It is assumed that the voltages are applied to the transfer charger ll in a superimposed manner.

In an image forming apparatus using a positive polarity developer and an oPC photoreceptor, a DC bias (0 to 8 kV) is applied.

A sine wave alternating current with a frequency of 500 Hz and a peak-to-peak voltage of 10 kV and a frequency of 1500 Hz and a peak-to-peak voltage of 1. 8kV
When a superimposed sinusoidal alternating current was applied, good transfer was achieved.

In this type of device, during transfer, the fog toner on the photoreceptor surface is not transferred or retransfer occurs, so the peak value of the positive component of the superimposed waveform is the discharge as shown schematically in Figure 8. The whole is biased in the negative direction so as not to exceed the starting voltage (value indicated by reference numeral 14).
In such a case, an effective bias can be obtained with a low peak-to-peak voltage, so even if the above operation is performed, the peak value of the negative component can be suppressed within a range that does not pose the risk of abnormal discharge.

FIG. 9 is a side view of a main part showing an embodiment in which the present invention is applied to a static eliminator that removes residual charges.

As shown in the figure, the charging wire 19 of the static eliminator 20 is connected to the DC 1 frequency f, (2n+1
)×f bias power supplies 7, 6.5 are arranged to apply these biases in a superimposed manner. An amorphous silicon photoreceptor is used as the photoreceptor, and this is 440 a in the direction of the arrow shown in the figure.
Jumping was performed by rotating at rm/sec and using toner having a triboelectric charge of -8 JLc/gr as a developer.

A sine wave alternating current with a frequency of 500 Hz and a peak-to-peak voltage of 10 kV was applied to the power source 6, and a sine wave alternating current with a frequency of 1500 Hz and a peak-to-peak voltage of 1.8 kV was superimposed on the power source 5 to give a combined peak-to-peak voltage of 9 kV.

When a solid ring is copied under these conditions, an electrostatic latent image with a photoreceptor potential of approximately 450 V is formed, and when this passes through the image exposure area with no light intensity and reaches the development area, the latent image potential is approximately Attenuates to 400V.

Toner is supplied to this to form a toner image, and the toner image is further transferred to a transfer material at a transfer site equipped with a transfer charger 11. Thereafter, the transfer material is separated from the photoreceptor by the action of a separation static eliminator 12. It is assumed that the image is transported to a fixing site (not shown).

The surface potential of the photoreceptor after the above separation process is approximately +3
After 0 separation, which is 00V, the residual toner is removed and the static electricity is removed by the static eliminator 20. When the DC component of the bias by the static eliminator 20 is -500V,
After neutralization, the surface potential of the photoreceptor dropped to +50V, which was sufficient for use.

As a sinusoidal AC voltage applied to each charger, a first waveform of frequency f, a second waveform of frequency 3f, and a further waveform of frequency 5f are applied.
The peak-to-peak voltage of the second waveform is 0.24 times that of the first waveform, and the peak-to-peak voltage of the third waveform is
The first result is the composite waveform when it is 0.07 times that of the waveform.
It is schematically shown in Figure 3.

In the figure, numerals 8, 9, and 26 represent the first, second, and third waveforms, respectively, and numeral 27 represents the composite waveform.

It has been found that when such a bias waveform is applied to the device shown in FIG. 1, a characteristic curve such as curve d in FIG. 5 can be obtained, and better effects can be obtained.

FIG. 14 also shows the peak-to-peak voltage and the ratio of the second waveform and third waveform to the first waveform, respectively, at 0. 22,
The composite waveform in the case of 0.05 is schematically shown by a solid line 27. In this way, it is also possible to further flatten the area near the peak of the applied bias.

As mentioned above, although the waveform can be made more suitable by superimposing higher-order harmonics, it is natural that problems such as increased cost due to the increase in the number of transformers and leakage of high-frequency components may occur. If these problems are solved by the progress of the present invention, the effectiveness of the present invention will be even more significant.

(3) As described in detail, the present invention uses a sine wave, which has been widely used in practice and is easy to handle, in a corona discharge device used in an image forming apparatus that performs electrostatic image processing. By using only alternating current, it is possible to reduce the peak-to-peak voltage of the applied bias while maintaining the desired discharge current, thereby suppressing the occurrence of abnormal discharges, eliminating the need for special incidental mechanisms for waveform formation and reducing the complexity of the entire device. Since it is possible to avoid increasing the size and size of the image forming apparatus, it can be well adapted to speeding up and downsizing the image forming apparatus.

[Brief explanation of the drawing]

Fig. 1 is a side view of a main part showing an embodiment in which the present invention is applied to a primary charger of an image forming apparatus equipped with a rotating cylindrical photoreceptor, and Fig. 2 shows peak-to-peak voltages of two types of applied AC voltages. A graph showing the relationship between the ratio and the sum current. Figures 3 and 4 are diagrams showing two types of applied AC voltages and their combined waveforms. Figure 5 is the peak-to-peak voltage of various applied AC voltages and the resulting sum current. FIG. 6 is a graph showing the relationship between applied DC voltage and differential current. FIG. 7 is a side view of the main part of an embodiment in which the present invention is applied to a transfer charger. FIG. 8 is a graph showing the relationship between applied DC voltage and differential current. FIG. 9 is a side view of a main part showing an embodiment in which the present invention is applied to a static eliminator; FIGS. 10A and 10B are diagrams showing input waveforms and output waveforms of rectangular waves, respectively; FIG. 11 is an explanatory diagram of loss when the peak part of a sine wave is sliced into a flat shape, Figure 12 is a graph showing changes in loss as above, Figures 13 and 14 are waveforms that synthesize three sine wave alternating currents. FIG. 1 φ fist/photoreceptor, 2... - charger, 5... AC power supply with frequency (2n+1) x f, 6... AC power supply with frequency f, 7... φ DC power supply, 8.9. Φ・Applied voltage waveform by AC power supply, 10...Synthetic waveform of 8 and 9, 11・$
・Transfer charger, 12・Red・Separate static eliminator, 14...Discharge starting voltage, 20 Red...Static eliminator. Figure 1 Engineering Figure 2 Figure 3 Figure 4 Vpp (kV) 71 Figure 8 μ Figure 9 Figure 10A Figure IOS Figure 11

Claims (2)

[Claims] (1) In a corona discharge device that charges or neutralizes a surface to be discharged by corona discharge, in order to obtain the desired corona discharge, a sinusoidal alternating current of frequency f is applied to the corona discharge electrode, and a frequency (2n+1; n is a positive integer) is applied to the corona discharge electrode.
A corona discharge device characterized by applying a voltage superimposed with at least one sine wave alternating current, giving priority to one having a small frequency among xf sine wave alternating currents. (2) The corona discharge device according to claim 1, wherein the peak-to-peak voltage of the sinusoidal alternating current of frequency (2n+1)×f is 1/10 to 1/3 of the alternating current of frequency f.