JPH05224508A - Driving method and driving circuit for corona discharger - Google Patents

Abstract

(57) [Summary] [Object] A driving method and a driving circuit for a corona discharger that corona-discharges an image carrier such as a photosensitive drum in an image forming apparatus such as an electrophotographic system. Intended to discharge at a frequency. According to a method of driving a corona discharger for driving a corona discharger 11, 15 for corona-discharging an image carrier 10 with a superposition signal in which an alternating current is superposed on a direct current bias, the direct current bias current is detected, The DC bias voltage is controlled so that the DC bias current value is constant.

Description

Detailed Description of the Invention

(Table of Contents) Industrial Application Field of the Prior Art (FIGS. 3 to 4) Problem to be Solved by the Invention Means for Solving the Problem (FIG. 1) Action Example (a) Description of One Example (FIG. 2) (b) Description of another embodiment Effect of the invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method and a driving circuit of a corona discharger for corona discharging to an image carrier such as a photosensitive drum in an image forming apparatus such as an electrophotographic system.

In a latent image forming type image forming apparatus such as an electrophotographic system, a corona discharger is used for an image bearing member such as a photosensitive drum in each step of charging, transferring and separating, and a corona discharge is generated on the photosensitive drum. Then, charging, transfer, and charge removal are performed.

It is desired that such a corona discharger can be driven at a low voltage, generate no ozone, and realize a predetermined operation.

[0005]

2. Description of the Related Art FIGS. 3 and 4 are explanatory views (1) and (2) of a conventional technique. As shown in FIG. 3A, in the electrophotographic apparatus, the rotating photosensitive drum 10 is charged by the charger 11 and then the optical image is exposed by the optical unit to form a latent image. After toner development, the transfer unit 14 transfers the toner image onto the sheet PP fed from the sheet hopper 13, and the static eliminator 15 transfers the sheet PP and the photosensitive drum 1.
The electrostatic attraction force of 0 is weakened, the paper PP is separated, and the paper PP
Is thermally fixed by the heat fixing device 17, discharged to the stacker 18, and the photosensitive drum 10 is cleaned by the cleaner 16.

In such an electrophotographic apparatus, the charger 1
1, a corona discharger is used for the transfer device 14 and the static eliminator 15. Here, for example, the static eliminator 15 applies a charge having a polarity opposite to that of the back surface of the paper PP to the back surface of the paper PP to reduce the potential difference between the surface of the photosensitive drum 10 and the back surface of the paper PP, and to reduce the stiffness of the paper PP. The paper PP is separated from the photosensitive drum 10.

At this time, the amount of electric charge applied to the back surface of the sheet PP is
It is represented by the amount of discharge current flowing from the electrode of the static eliminator 15, and if the amount of charge on the back surface of the sheet PP is always constant, the amount of discharge current needs to be always constant regardless of the ambient humidity.

As a driving method for discharging from the electrodes of this corona discharger, an AC bias method as shown in FIG. 3B is known. The static elimination separation method using only AC has the advantages that the discharge amount is stable and it is strong against changes in the humidity environment, but it requires the application of a high-voltage AC voltage. Since a high voltage and a high frequency AC voltage are used, a high concentration of ozone is generated around the electrodes.

On the other hand, as shown in FIG. 3C, in the DC bias method, although the ozone generation is small, the discharge is unstable, and the surface of the photosensitive drum 10 and the electrode position due to the eccentricity of the photosensitive drum 10 or the like. If it is misaligned, a spark will fly from the electrode to the photosensitive drum 10 and the back surface of the sheet PP cannot be discharged, and the life of the photosensitive drum 10 will be shortened.
As a result, it cannot be used at a high voltage and therefore the amount of discharge current cannot be increased. Therefore, when the strength of the paper PP is extremely weak, the separation of the paper PP by static elimination is not performed well. There are drawbacks.

For this reason, conventionally, the method of AC + DC in which an alternating current is superimposed on a direct current bias as shown in FIG. 4 (A) reduces high voltage application, which is a drawback of the alternating current method, and stabilizes the discharge amount and the humidity environment. It has been proposed to take advantage of the advantage of being strong against changes (for example, Japanese Patent Laid-Open No. 62-24427).
No. 2, etc.).

[0011]

However, the prior art has the following problems. When the voltage of the DC component is increased, the same problem as in the case where only the DC component is applied occurs, the discharge becomes unstable, and the discharge effect becomes insufficient.

Therefore, the discharge effect is obtained by increasing the direct current component, and as a result, the same problem as in the case of discharging only by alternating current occurs, requiring high voltage and high frequency, and ozone Often occurs.

Therefore, an object of the present invention is to provide a driving method and a driving circuit for a corona discharger, which discharge is stable and can be discharged at a low voltage and a low frequency.

[0014]

FIG. 1 shows the principle of the present invention. According to claim 1 of the present invention, in the corona discharger driving method of driving the corona dischargers 11 and 15 for performing corona discharge on the image carrier 10 with a superposition signal in which alternating current is superposed on direct current bias, the direct current bias current is It is characterized by detecting and controlling the DC bias voltage so that the DC bias current value becomes constant.

According to claim 2 of the present invention, in claim 1,
The corona dischargers 11 and 15 are static eliminators 15 for statically separating a sheet from the image carrier 10.

A third aspect of the present invention is based on the first aspect.
The corona dischargers 11 and 15 are chargers 11 that charge the image carrier 10. A fourth aspect of the present invention is characterized in that, in the first, second or third aspect, the corona dischargers 11 and 15 are brush type dischargers.

According to a fifth aspect of the present invention, in the drive circuit of the corona discharger for driving the corona dischargers 11 and 15 for performing the corona discharge on the image carrier 10 with the superposition signal in which the alternating current is superposed on the direct current bias, A DC power supply 2 that generates a bias voltage and an AC power supply 1 that generates an AC voltage are connected in series, the DC bias current of the DC power supply 2 is detected, and the DC bias current value is kept constant. It is characterized by controlling the DC bias voltage.

According to a sixth aspect of the present invention, in the fifth aspect,
The corona dischargers 11 and 15 are static eliminators 15 for statically separating a sheet from the image carrier 10.

According to claim 7 of the present invention, in claim 5
The corona dischargers 11 and 15 are chargers 11 that charge the image carrier 10. An eighth aspect of the present invention is characterized in that, in the fifth, sixth or seventh aspect, the corona dischargers 11 and 15 are brush type dischargers.

[0020]

In the present invention, an AC + DC bias is applied, but the DC voltage and frequency are reduced to such an extent that ozone generation does not pose a problem, the AC voltage is lowered, and the DC voltage is superimposed to provide a stable discharge. Is possible.

By doing so, as shown in FIG. 4 (B), the discharge current changes even if the voltage is constant due to a change in the environment around the electrodes. Therefore, in claims 1 and 5 of the present invention, FIG. As shown in A), by detecting the DC bias current,
The DC bias voltage is controlled so that the DC bias current value is constant, and the discharge current amount due to the DC component is controlled to be constant.

In the second and sixth aspects of the present invention, since the corona discharger is the static eliminator 15, the separation of the sheet PP by the static eliminator can be favorably performed. According to the third and seventh aspects of the present invention, since the corona discharger is the charger 11, the charging by corona discharge can be improved.

In claims 4 and 8 of the present invention, since the corona discharger is a brush type discharger, it can be driven at a lower voltage.

[0024]

【Example】

(a) Description of an Embodiment FIG. 2 is an illustration of an embodiment of the present invention, showing an electrophotographic apparatus.

In FIG. 2, the same components as those shown in FIGS. 1 and 3 are designated by the same symbols, and the static eliminator 15 is used.
Is composed of a brush type discharger. An AC (alternating current) power source 1 is one in which a primary winding T1 is connected to an alternating current source AC1 (for example, 2 KV, 800 Hz), and an output is obtained from a secondary winding T2, and as shown in FIG. Amplitude 2 · Va
(Va = Vd ₁ −Vd) voltage, amplitude 2 · Ia (Ia =
A current of (Id ₂ −Id) is generated.

In the DC (direct current) power supply 2, a primary winding T3 and a switching transistor Tr are connected in series to an alternating current source AC2, and a DC voltage of Vd is obtained from a secondary winding T4 by a rectifying diode D1 and a smoothing capacitor C1. This is supplied to the secondary winding T2 of the AC power supply 1 to obtain a DC superimposed AC voltage, and the other end of the secondary winding T4 is connected to the ground, to which the photosensitive drum 10 is connected. To do.

Further, the DC power source 2 has a current detecting resistor R.
1 and R2, a current detection circuit 20 that detects a detection current of the resistors R1 and R2, and a stabilization circuit 21 that controls the switching transistor Tr by the output of the current detection circuit 20 to keep the output current constant. It is provided.

Explaining with reference to FIG. 1 (B) and FIG. 4 (B), Vd ≧ 2Va and Id ≧ 2I in order to reduce the AC voltage.
Since the direct current voltage is set to a and is intended to assist the discharge, it is necessary to stabilize the discharge by the direct current voltage.

Here, when the ambient environment such as the distance between the electrode of the static eliminator 15 and the paper PP changes between times t ₁ and t ₃ and the discharge becomes difficult, the conventional example shown in FIG.
As in (B), since the applied bias is constant, the discharge current amount of the DC component remains reduced during that time, and the separation of the sheet PP becomes insufficient.

On the other hand, in the present invention, as shown in FIG. 1 (B), the discharge current amount of the DC component is I between the times t ₁ and t _2.
The current detection circuit 20 indicates that the voltage has decreased from d to Id _1.
Is detected by the stabilization circuit 21, and the transistor Tr
The on-time of is increased and the applied bias voltage is changed from Vd to Vd.
_It is increased to ₁ and is corrected so that the discharge current amount of the DC component becomes Id.

Then, between the times t ₃ and t ₄ , the current detecting circuit 20 detects that the discharge current amount of the DC component is increasing from Id to Id ₂ , and the stabilizing circuit 21 The ON time of the transistor Tr is reduced, the applied bias voltage is lowered from Vd ₁ to Vd, and the discharge current amount of the DC component is corrected to Id.

In this way, in the AC + DC system, the voltage and frequency of the AC component are lowered to the extent that ozone generation does not pose a problem, the amount of that is assisted by the DC component, and the DC current is stabilized. AC component voltage,
The frequency can be lowered and the generation of ozone can be prevented, while the cost of the AC power supply unit can be greatly reduced.

(B) Description of Other Embodiments In addition to the above embodiments, the present invention can be modified as follows. Although the static eliminator has been described as an example of the corona discharger, it can be applied to a charger and a transfer device.

The corona discharger has been described as a brush type, but other types of dischargers such as a wire type and a needle electrode type can be used. Although the electrophotographic apparatus using the photosensitive drum has been described, it can be applied to other latent image forming apparatuses such as an electrostatic recording apparatus using a dielectric drum.

The present invention has been described above with reference to the embodiments.
Various modifications are possible within the scope of the invention, and these modifications are not excluded from the scope of the invention.

[0036]

As described above, according to the present invention,
It has the following effects. In the AC + DC method, lower the voltage and frequency of the AC component to the extent that ozone generation is not a problem,
Since it is assisted by the C component and the DC current is stabilized, the voltage and frequency of the AC component can be lowered, and stable discharge is possible even when DC is superimposed while preventing ozone generation.

Since the voltage and frequency of the AC component can be lowered, the cost of the AC power supply section can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is an explanatory diagram of an embodiment of the present invention.

FIG. 3 is an explanatory diagram (1) of a conventional technique.

FIG. 4 is an explanatory diagram (part 2) of the conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 DC power supply 10 Photosensitive drum (image carrier) 11 Charging device 12 Developing device 13 Paper hopper 14 Transfer device 15 Static eliminator 16 Cleaner 20 Current detection circuit 21 Stabilization circuit Tr switching transistor

Claims (8)

[Claims] 1. A method of driving a corona discharger for driving a corona discharger (11, 15) for corona discharge on an image carrier (10) with a superposition signal in which an alternating current is superposed on a direct current bias. Is detected and the DC bias voltage is controlled so that the DC bias current value becomes constant, and a method of driving a corona discharger. 2. The driving of a corona discharger according to claim 1, wherein the corona discharger (11, 15) is a static eliminator (15) for statically separating a sheet from the image carrier (10). Method. 3. The method of driving a corona discharger according to claim 1, wherein the corona discharger (11, 15) is a charger (11) that charges the image carrier (10). 4. The method for driving a corona discharger according to claim 1, 2 or 3, wherein the corona discharger (11, 15) is a brush type discharger. 5. A drive circuit of a corona discharger for driving a corona discharger (11, 15) for performing a corona discharge on an image carrier (10) with a superposition signal in which an alternating current is superposed on a direct current bias. Is connected in series with an AC power supply (1) that generates an AC voltage, the DC bias current of the DC power supply (2) is detected, and the DC bias current value is constant. The corona discharger drive circuit is characterized in that the DC bias voltage is controlled so that 6. The corona discharger drive according to claim 5, wherein the corona discharger (11, 15) is a static eliminator (15) for statically separating a sheet from the image carrier (10). circuit. 7. The drive circuit for the corona discharger according to claim 5, wherein the corona discharger (11, 15) is a charger (11) for charging the image carrier (10). 8. The corona discharger drive circuit according to claim 5, wherein the corona discharger (11, 15) is a brush type discharger.