JP3133895B2 - Corona discharge device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corona discharge device used for charging a photosensitive member or transferring toner from a photosensitive member to paper in an electrophotographic copying machine.
The present invention relates to a device for supplying electric power from a single high-voltage transformer to a plurality of corona dischargers.

[0002]

2. Description of the Related Art As a configuration example of a conventional corona discharger,
For example, Japanese Patent Publication No. 5-27858, Japanese Patent Publication No. 5-27
No. 859 and JP-A-61-151554. The configuration of the corona discharge device disclosed in these publications will be described.

A single high-voltage transformer supplies power to a plurality of corona dischargers in parallel, detects a shield current of a corona discharger (charging device) for charging a photoconductor, and detects the shield current. Control the primary output of the transformer to keep it constant.

A single high-voltage transformer supplies power to a plurality of corona dischargers in parallel, detects a shield current of the charger, and controls an output of a primary side of the transformer so as to keep the shield current constant. At the same time, a shield current of another corona discharger (transfer device or the like) is detected, and when the shield current exceeds a predetermined value, supply power (primary output) is cut off.

Power is supplied from a single high-voltage power supply to both the corona discharger of the charger and the transfer device. At this time, the current flowing through the power supply unit is detected, and the output of the power supply unit is controlled so that the current value becomes constant. Further, the corona discharge of the transfer unit can be switched on / off, thereby preventing the problem such as deterioration of the photoconductor due to extra corona discharge.

Japanese Patent Publication No. 5-46547 discloses a structure in which a corona current is made variable by providing a variable impedance between a grid and ground in a scorotron charger.

[0007]

However, the conventional structures shown in the above (1) to (5) have the following problems.

In the configuration (1), if the shield current is increased due to a paper jam or the like in a corona discharger in which the shield current is not detected, for example, a transfer device, the sheet may be ignited or the like. Although an abnormal situation such as the ignition of the paper can be prevented, the shield current detecting means and the power cutoff means of the other corona discharger must be separately provided, which increases the cost.

In the configuration of (1), since the current is detected in the power supply section, there is no distinction between the charging current and the shield current. Therefore, for example, when the paper jam causes the impedance between the shield case and the wire to decrease and the shield current to rise at the position of the transfer device, and the balance with the charging current is lost, the state cannot be detected. May ignite.

In the configuration of (1), in order to make the grid voltage variable, it is necessary to use a bipolar transistor, FET, phototransistor, CdS, etc. as variable impedance means, and a control circuit for variable impedance control is required. Costly.

In view of the above problems, an object of the present invention is to provide a corona discharge device which is inexpensive and can prevent ignition of jammed paper.

[0012]

According to a first aspect of the present invention, there are provided a plurality of corona dischargers connected in parallel to one high-voltage transformer, and two or more corona dischargers in the plurality of corona dischargers. Shield current calculating means for detecting the shield current flowing between the discharge body of the corona discharger and the shield case, and adding the detected shield current of each corona discharger, based on the added value obtained by the shield current calculation means. Means for controlling the input to the high-voltage transformer so that the added value becomes a constant value.

[0013] According to a second aspect of the invention, between the detection portion of the shield case and the shield current, characterized in that a fixed impedance.

According to a third aspect of the present invention, in the corona discharger, a change in impedance between the discharger and the shield case over time is small between the shield case of the corona discharger and a shield current detection unit . A fixed impedance is provided.

According to a fourth aspect of the present invention, there is provided the corona discharge device regulated in any one of the first to third aspects, wherein the corona discharger comprises a discharge body made of a saw-toothed metal plate satisfying the following conditions. H> h + 1 (tan θ / 2), where H: length from the bottom surface of the shield case to the opening surface h: height of the saw-toothed metal plate from the bottom plate θ: Angle of the tip of the saw-tooth electrode l: Length of the shield case in the horizontal direction.

[0016]

According to the present invention, the individual shield currents of the plurality of corona dischargers are detected and added, and the input to the high-voltage transformer is controlled so that the added value becomes a constant value. You. The shield current of each corona discharger fluctuates according to the impedance between the discharger of the corona discharger and the shield case, but in a normal state, since the impedance is constant, the addition value is also constant, and the input to the high-voltage transformer is also reduced. It will be constant. On the other hand, it is assumed that an abnormality in the shield current has occurred in one of the plurality of corona dischargers. Specifically, it is a leak state due to paper jam in the transfer device. Then, the shield current in the one corona discharger abnormally increases, and as a result, the added value increases. Then, in order to keep this added value constant,
As the input to the high-voltage transformer is set smaller, the voltage applied to the corona discharger in which the abnormality has occurred becomes smaller. This avoids problems such as ignition in the corona discharger in which the abnormality has occurred.

According to the second aspect of the present invention, a fixed impedance is arranged between the shield case and the shield current detecting section. The shield current of the corona discharger is
Corresponding to the impedance between the discharger and the shield case, the shield current decreases as the impedance increases, and the shield current increases as the impedance decreases. Here, considering a corona discharger provided for each image forming apparatus, there is a variation in the impedance of each corona discharger due to a dimensional error or an assembly error in manufacturing. However, a fixed value having a large value for this variation is connected between the shield case and the detection part of the shield current, and due to the action of the fixed impedance, the shield due to the variation in the impedance of each corona discharger. Current fluctuations are prevented.

According to the third aspect of the present invention, a fixed impedance is provided to the corona discharger having a small impedance change with time. In the corona discharger, when the impedance between the discharge body and the shield case changes with time, the shield current changes. For example, in the case of a transfer device, the impedance increases due to contamination such as toner adhesion and the shield current decreases. When the shield current of one corona discharger decreases, the sum of the shield currents decreases, so that the input of the high-voltage transformer is controlled to increase, and as a result, the shield current of the corona discharger that has changed over time is kept constant. Dripping.

On the other hand, in a corona discharger whose change with time is small, an unnecessarily high voltage is applied by the above control, and the shield current increases. However, at this time, if the shield current of the corona discharger whose change with time is small is reduced in advance, the fluctuation of the shield current due to the above control is reduced, and the influence of the above control is suppressed. The shield current can be reduced by increasing the impedance between the discharge body and the shield case. At this time,
In a corona discharger having a small change over time, the larger the change over time of a corona discharger having a large change over time, the larger the fixed impedance of the corona discharger having a small change over time, the smaller the change over time. The amount of change with time of a corona discharger having a large change can be absorbed.

According to the invention described in claim 4, when the discharger of the corona discharger is constituted by a saw-toothed metal plate,
The shield current flowing from the discharge body into the shield case can be stabilized. In the case of a wire-shaped discharge body, the discharge is performed in the 360 ° direction around the entire circumference of the wire, so that the size of the shield case does not significantly affect the shield current. However, in the case of the saw-toothed discharge body, since the discharge is performed along the edge of the tip of the saw-toothed discharge body, a stable shield current cannot be obtained depending on the shape of the shield case. Input control based on However, “H> h + 1 (tan
θ / 2) ”, a stable shield current can be obtained even when the discharger is formed of a saw-toothed metal plate.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the invention shown in claim 1, and is a block diagram of a main part of an electrophotographic copying machine.

The photoreceptor 1 is made of a drum tube made of aluminum or the like, and a photosensitive material is uniformly coated on the surface of the drum tube. The drum tube is grounded. Around the photoreceptor 1, a charger 2, a developing unit 3, a transfer unit 4, and the like are arranged. The charger 2 and the transfer device 4 correspond to the corona discharger of the present invention. In addition, as the corona discharger, there may be provided a paper static eliminator, a stripper and the like in addition to the above.

The charger 2 is for uniformly charging the surface of the photoreceptor 1 and comprises a scorotron type corona discharger having a grid electrode 5 for controlling the surface potential of the photoreceptor 1 at a constant level. Have been. The charger 2 is
A wire 2b for performing discharge is stretched in the vertical direction in the drawing in a metal rectangular parallelepiped shield case 2a, and a grid electrode 5 is arranged between the wire 2b and the photoconductor 1. A high voltage power supply is applied to the wire 2b by the power supply unit 10. The grid electrode 5 is controlled by a control / drive circuit 51. The shield case 2a is grounded via the shield current detector 6.

The transfer unit 4 is for transferring the toner image formed on the photoreceptor 1 to a sheet. Transfer device 4
Is a metal rectangular parallelepiped shield case 4a in which a wire 4b is stretched in the vertical direction in the figure, and a high-voltage power is applied to the wire 4b by the power supply unit 10.
Further, the shield case 4a is grounded via the shield current detector 7.

The two corona dischargers provided in the copying machine, namely, the charger 2 and the transfer unit 4, have one power supply unit 1
Power is supplied from 0 in parallel. The power supply unit 10 includes a high-voltage transformer 10a, a rectifier diode 10b, a smoothing capacitor 10c, and the like. When a corona discharger such as a static eliminator and a stripper is further provided in the copying machine, power is also supplied from the power supply unit 10 to these corona dischargers in parallel.

The shield current detectors 6 and 7 detect the shield currents I _FB1 and I _FB2 of the charger 2 and the transfer unit 4, respectively. The detected shield current is added by the adder 8 and then input to the control / drive circuit 9.
The control / drive circuit 9 controls the primary-side input of the high-voltage transformer 10a of the power supply unit 10 based on the input addition result so that the added value of the input shield current becomes constant. If a corona discharger such as a static eliminator or a stripper is provided, the corona discharger also detects a shield current and controls the primary-side input of the high-voltage transformer 10a based on the result of adding all of them. May be.

Here, the shield current I of the charger 2
_If the impedance between the wire 2b of the charger 2 and the shield case 2a is Z ₁ , and the output voltage of the power supply unit 10 is V, _FB1 becomes I _FB1 = V / Z ₁ . Also, the transfer device 4
The shield current I _FB2 becomes I _FB2 = V / Z ₂ , where Z ₂ is the impedance between the wire 4b of the transfer unit 4 and the shield case 4a. On the other hand, as mentioned above,
In the apparatus of this embodiment, as described above, "I _FB1 + I _FB2
= Constant ", the input of the high-voltage transformer 10a is controlled. That is, I _FB1 + I _FB2 = V / Z ₁ + V / Z ₂ = V (1 / Z ₁ +
1 / Z ₂ ) = constant. Therefore, if the impedances Z ₁ and Z ₂ between the wires of the charger 2 and the transfer device 4 and the shield case are kept constant, the output voltage V of the power supply unit 10 becomes a constant value. However, for example, when a paper jam occurs in the transfer device 4, the wire 4 b of the transfer device 4 and the shield case 4 a
Impedance Z ₂ is reduced between the shield current I _FB2 of the transfer device 4 becomes leakage state is increased. Therefore, in order to keep I _FB1 + I _FB2 constant, the control / drive circuit 9 lowers the input voltage of the power supply 10 = the output voltage V of the power supply 10. As a result, an abnormal increase in the shield current of the transfer device 4 is prevented, and a danger such as ignition of jammed paper is avoided.

As described above, in this embodiment, since the shield currents of a plurality of corona dischargers are added and control is performed so that the added value becomes constant, the shield current is reduced in any one of the corona dischargers. When a problem such as an increase occurs, the applied voltage is reduced, and danger such as ignition can be avoided.

An embodiment according to claim 2 will be described. FIG. 2 is a view showing an embodiment of the invention shown in claim 2, and is a block diagram of a main part of an electrophotographic copying machine. In the figure, the same parts as those in FIG. 1 are indicated by the same numbers.

In the copying machine, the wire 2b-
Impedance Z ₁ between the shield case 2a, and a transfer device impedance Z ₂ between the wires 4b- shield case 4a of 4, the shield case 2a, 4a of the dimensional error and the wire 2b, 4b individual copying by variations in the mounting positions of the There is some variation between machines. Thus, the impedance Z ₁ , Z ₂
Are different from each other, a variation occurs with respect to a set value (ratio of each shield current). Therefore, in this embodiment, variations in the impedances Z ₁ and Z ₂ of each copying machine are corrected.

As shown in FIG. 2, an impedance correction resistor 11 is provided between the shield case 2a of the charger 2 and the current detection circuit 6, and an impedance is provided between the shield case 4a of the transfer unit 4 and the current detection circuit 7. Correction resistors 12 are connected to each other. As the impedance correction resistors 11 and 12, for example, one or a plurality of fixed resistors are connected in series between the shield case and the current detection circuit. When a resistor with a low withstand voltage is used, a plurality of fixed resistors are connected in series.

The charger 2 will be described as an example.

_Assuming that the output voltage of the power supply unit 10 is V, the impedance between the wire and the shield case of the charger 2 is Z ₁ , and the impedance of the impedance correction resistor 11 is Z ₁₁ , represented by _{FB1 = V / (Z 1 +} Z 11). Now comparing the case where the Z _11> 0 of Z ₁₁ = 0, in the case of Z _11> 0 to I _FB1 is smaller than that of Z ₁₁ = 0, the variation of I _FB1 It can also be seen that also becomes smaller. Therefore, the detection accuracy of I _FB1 is improved. At this time, the variation in Z ₁₁ is required to be sufficiently smaller than the variation of Z _1, as compared to the mounting accuracy of dimensional accuracy and the wire 2b of the shield case 2a, the resistance value for impedance compensation resistor 11 It is needless to say that the accuracy can be set higher, and it is easy to satisfy the above condition.

On the other hand, in the transfer unit 4 as well, by arranging the impedance correction resistor 12, variations in the shield current I _FB2 can be suppressed.

As described above, if the shield current does not vary between copying machines, it is not necessary to change the added value to be controlled to be constant for each copying machine, and the manufacturing cost can be reduced.

An embodiment according to claim 3 will be described. FIG. 3 is a view showing an embodiment of the invention shown in claim 3, and is a block diagram of a main part of an electrophotographic copying machine. In the figure, the same parts as those in FIG. 1 are indicated by the same numbers.

In an electrophotographic copying machine, a corona discharger (transfer device) 4 for transfer transfers toner with a change over time.
Dirt easily occurs due to the adhesion of paper powder and the like. On the other hand, the corona discharger (charger) 2 for charging is less likely to be stained.

[0039] If dirt adheres to the transfer unit 4 increases the impedance Z ₂ between the shield case 4a- wire 4b, the shield current I _FB2 of the transfer unit 4 is reduced. If the shield current I _FB2 of the transfer unit 4 becomes small,
The output voltage V of 0 is raised, and the shield current I _FB2 returns to the normal state.

On the other hand, if the output voltage of the power supply unit 10 increases, the shield current I _FB1 of the charger 2 also increases, which affects the charging performance. Therefore, as shown in FIG. 3, a corona discharger (charger) 2 having a small variation in impedance is provided.
To the charging device 2
Of the shield current I _FB1 is reduced. The operation of the impedance correction resistor 11 will be described.

The control / drive circuit 9 is, as described above,
The input voltage of the power supply unit 10 is controlled based on I _FB1 + I _FB2 , whereby the output voltage V of the control unit 10 is determined. Here, since the impedance Z ₂ of the transfer device 4 changes with time, the shield current I _{FB2 of the} transfer device 4 is changed.
Varies with time. Therefore, as described above, the input voltage V is varied (increased) in accordance with the temporal variation of the shield current I _FB2 .

On the other hand, the shield current I _FB1 of the charger 2 is obtained by I _FB1 = V / (Z ₁ + Z ₁₁ ). At this time, the keep increasing the value of Z ₁₁ to some extent, the shield current I _FB1 becomes relatively small,
Even if the input voltage V fluctuates, the influence on the shield current I _FB1 is small. In other words, the smaller the amount of variation in the shield current I _FB1 even when the input voltage V varies due to aging of the impedance Z ₂ of the transfer device 4, it is less charging performance is affected.

Since I _FB1 has a small value in advance, a value (I _FB1) for controlling the input voltage of the power supply unit 10 is required.
+ I _FB2 ), the shield current I _FB2 of the transfer unit 4 occupies a large ratio, and the shield current I
The responsiveness of the input voltage V to the fluctuation of _FB1 is improved.

In this embodiment, the impedance correcting means 11 is connected only to the charger 2. However, in a copying machine having a plurality of corona dischargers, the impedance correcting means 11 is arranged according to the connection. .

An embodiment according to claim 4 will be described.

FIG. 4 is a sectional view showing the structure of a corona discharge device provided with the saw-tooth electrode 21. The saw-tooth electrode 21 has a mountain-shaped edge formed at the tip of a metal plate and generates corona discharge from the edge tip. Saw tooth electrode 21
Are arranged in the shield case 22 in the same manner as a wire of a normal corona discharger, and a voltage required for charging is applied to both ends thereof. In the cross section of the shield case 22, the tip of the saw-tooth electrode 21 is arranged at the center of the shield case 22 in the lateral direction (l = 1). The tip of the saw-tooth electrode 21 is located at a position h from the bottom surface of the box-shaped shield case 22 toward the opening surface, and the edge angle of the tip of the saw-tooth electrode 21 is θ. Then, the discharge angle of the corona discharger falls within the range of θ as shown in the figure. In this configuration, the length H from the bottom surface of the shield case 22 to the opening surface is set to H> h + 1 / tan θ. In the case of a configuration that does not satisfy the above expression, a current (shield current) flowing from the saw-tooth electrode 21 to the shield case 22 hardly occurs, and the shield current becomes unstable. On the other hand, by adopting a configuration that satisfies the above equation, a stable shield current can be obtained, and control can be performed based on the shield current in the above embodiment.

[0047]

According to the first aspect of the present invention, both the constant voltage control of the high-voltage transformer during normal operation and the control for preventing a fire or the like during abnormal operation can be performed by one control system. With such a configuration, it is possible to obtain the effect of preventing ignition in the event of an abnormality.

According to the second aspect of the present invention, the fixed impedance disposed between the shield case and the shield current detection unit reduces the variation in impedance of each corona discharger and reduces the detected value of the shield current. The individual difference can be reduced, and the manufacturing cost can be reduced. Further, since the impedance to be arranged may be a fixed impedance, it can be configured at a low cost.

According to the third aspect of the present invention, it is possible to correct a change in shield current due to a change with time in a corona discharger having a large change with time, and to correct a change in a shield current due to a change with time in a corona discharger having a small change with time. Thus, it is possible to prevent the shield current from being affected by the corona discharger, which changes greatly with time.
Thereby, a plurality of corona dischargers can be controlled stably.

According to the fourth aspect of the present invention, a stable shield current can be obtained even when a saw-tooth discharger is used, and the input of the high-voltage transformer is controlled by detecting the shield current. Control accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram according to the first embodiment of the present invention, and is a block diagram illustrating a configuration of a corona discharge device.

FIG. 2 is a diagram according to the invention as set forth in claim 2, and is a block diagram showing a configuration of a corona discharge device.

FIG. 3 is a diagram related to the invention as set forth in claim 3, and is a block diagram showing a configuration of a corona discharge device.

FIG. 4 is a view according to the invention described in claim 4, and is a view showing a cross-sectional configuration of a corona discharger.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 4 Transfer device 2a, 4a, Shield case 2b, 4b Wire (discharge body) 6,7 Current detection part 8 Comparator 9 Control and drive circuit 10 Power supply part 10a High voltage transformer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 15/02 G03G 15/16 102

Claims (4)

(57) [Claims] 1. A plurality of corona dischargers connected in parallel to one high-voltage transformer, and a shield flowing between a discharge body of two or more corona dischargers of the plurality of corona dischargers and a shield case. A shield current calculating means for detecting a current and adding the detected shield current of each corona discharger; and the high voltage so that the added value becomes a constant value based on the added value obtained by the shield current calculating means. A corona discharge device, comprising: means for controlling an input to a transformer. 2. The corona discharge device according to claim 1 , wherein a fixed impedance is disposed between the shield case and a shield current detection unit. During wherein the corona discharger, between the discharge member and the detection portion of the shield case and the shield current changes over time is small corona discharger impedance between the shield case it was arranged fixed impedance The corona discharge device according to claim 1, characterized in that: 4. The corona discharger according to claim 1, wherein the corona discharger comprises a discharge body made of a saw-toothed metal plate satisfying the following conditions, and a shield case. H> h + 1 (tan θ / 2) where H: length from the bottom surface of the shield case to the opening surface h: height from the bottom plate of saw-toothed metal plate θ: tip of saw-tooth electrode Angle l: lateral length of the shield case.