JPH08137202A - Stabilizing method for charging in charging device - Google Patents

Abstract

PURPOSE: To stabilize charging by specifying the total current, process speed, etc., among the sawtooth electrode, grid electrode and image carrier. CONSTITUTION: In a charging device which is provided with a corona discharging electrode (sawtooth electrode) 4 having two or more protrusions in a line and a grid electrode 5 disposed between the electrode 4 and an image carrier 1 so as to charge the surface of the freely rotatable image carrier 1, a condition that It /n>=0.0032PS+0.35 is established to stabilize discharging, where It is the total current supplied to the sawtooth electrode 4; n is the number of protrusions of the sawtooth electrode 4; and PS is the rotational peripheral speed of the image carrier 1. Through this, the surface of the image carrier 1 can be uniformly and stably charged to allow fine representation, such as halftone, of the original image concentration and thereby improved image quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for uniformly charging the surface of an electrostatic electrophotographic image carrier in a copying machine or a printer, and more particularly to a method for performing stable charging.

[0002]

2. Description of the Related Art An electrostatic electrophotographic image forming apparatus comprises process units for charging, exposing, developing, transferring, peeling, cleaning and neutralizing. That is, in the image forming process step, first, the surface of the image carrier that is rotationally driven is uniformly charged by the charging device, and the optical image of the original image is exposed through the exposure optical device to electrostatically charge the surface of the image carrier. Record the latent image. Next, toner is electrostatically attached to the electrostatic latent image on the image carrier to develop it, and a toner image is formed on the surface of the image carrier. Then, the toner image on the image carrier is transferred onto the transfer material by the discharge of the transfer device, and the toner image on the transfer material is fixed by the heat fixing device. Further, the transfer residual toner remaining on the surface of the image carrier is removed by a cleaning device, and is collected in a predetermined collecting unit, and the surface of the image carrier after cleaning is subjected to residual electrification by a charge eliminating device. Prepare for the image forming process step.

The image carrier is, for example, an OPC (Organi).
(c Photo Conductor) A corona discharge electrode is used as a charging device that gives an electric charge to the surface of an image bearing member, such as a sawtooth shape having a plurality of sharp protrusions in a row at a constant pitch. (Hereinafter, referred to as a sawtooth electrode), and the material is stainless steel or the like. Further, a grid electrode having a predetermined potential for controlling the passage amount of the corona current is arranged between the image carrier and the serrated electrode.

There are already some prior arts regarding the charging device having the serrated electrode. U.S. Pat. No. 4,591,713 discloses a discharge device including an insulating shield case, a sawtooth electrode and a grid, and U.S. Pat. No. 4,725,731 discloses a sawtooth electrode, a grid and a sawtooth electrode. Regarding the technique of having a supporting means for supporting and forming a corona-like flow by forming a hole in the supporting means, U.S. Pat. US Pat. No. 4,792,680 uses beryllium copper for the grid and stabilizes discharge due to life. US Pat. No. 3,691,373 discloses discharge by immersing metal plate in etching solution. Each of the techniques for forming electrodes is described. In particular, it is disclosed that the interval between the protrusions of the sawtooth electrode is 0.200 to 0.400 inch and the tip angle is 5 to 30 °. Further, in British Patent 1,388,084, the plate thickness is 0.
There is a description of a sawtooth electrode having a staggered electrode portion, which is an electrode having a 1 mm pitch and a plate thickness of 0.6 mm and a pitch of 6 mm.

FIG. 18 is a view showing a charging device having a saw-toothed electrode, in which the projections 3 are arranged in a staggered manner on a shield case 2 having a front opening facing the image carrier 1. The electrode 4 is internally provided, and the grid electrode 5 stretched by tension is disposed between the saw-tooth electrode 4 and the image carrier 1. The saw-toothed electrode 4 is insulated and fixed to a substantially central portion of the shield case 2 formed of an insulator. In the figure, 6 is a power supply to the sawtooth electrode 4, and 7 is a power supply to the grid electrode 5.

In the charging device 8 configured as described above, a predetermined voltage V is applied to the sawtooth electrode 4 by the power source 6, and the grid electrode 5 has the projections 3 of the sawtooth electrode 4. A grid voltage Vg is applied to control the corona current that acts on the surface of the image carrier 1 discharged from the tip discharge part. At this time, the current flowing through the sawtooth electrode 4 is the total current It, and the current flowing through the grid electrode 5 is the grid current Ig.

[0007]

The charging device 8 gives uniform charge to the surface of the image carrier 1 by corona discharge, but the charging condition of corona discharge changes delicately under all conditions. When the charging conditions change, uneven charging of the surface of the image carrier 1 occurs, and the original image to be formed is affected in terms of image quality.

Further, as a problem in the step of forming the saw-toothed electrode 4, the charging characteristics slightly affect the shape and state of the discharge portion of the electrode.

The manufacturing technique for staggered saw-toothed electrodes described in British Patent 1,388,084 uses polishing to form teeth, is very expensive, and the shape variation between electrodes is large. Was difficult to stabilize.

Further, in the technique described in US Pat. No. 3,691,373, the tip angle of the electrodes is formed steeply when forming the discharge electrode. In such a steep electrode, a plurality of electrodes are arranged in a row. When formed into a shape, there is a problem that the height of the electrode varies greatly. Furthermore, if the tip of the electrode is steep after aging or cleaning, it is worn and deteriorated so much that it cannot withstand actual use.

As shown in FIG. 19, due to variations in the manufacturing process of the saw-toothed electrode 4 and the grid electrode 5, the heights of the tips of the protrusions 3 of the saw-toothed electrode 4 are not uniform. . At this time, the distances l ₁ , l ₂ , l ₃ ... l ₈ between the respective tip portions of the sawtooth electrode 4 and the grid electrode 5 are different from each other. Therefore, the impedance between the tip portion of the sawtooth electrode 4 and the grid electrode 5 is different, and the discharge action from each tip portion with respect to the surface of the image carrier 1 is different, resulting in uneven charging of the surface of the image carrier 1. .

As a simple improvement method for reducing this discharge, a method of increasing the total current flowing through the sawtooth electrode 4 is considered. However, increasing the total current means increasing the voltage applied to the sawtooth electrode 4, and the discharge current increases as the voltage applied to the sawtooth electrode 4 increases. The amount of ozone generated from a portion increases, and the surface of the image bearing member 1 is also affected, resulting in deterioration of the image quality of the original image.

When the amount of ozone generated increases, nitrogen oxides (NO _x ) or silicon oxides (S) are generated due to the combination with various gases and foreign substances in the air floating in the image forming apparatus.
iO ₂ ) and the like are generated. This product adheres to the surfaces of the saw-toothed electrode 4 and the surface of the grid electrode 5 to reduce the discharge ability of the saw-toothed electrode 4 and the charging potential control ability of the grid electrode 5.

Further, in order to prevent the leakage discharge from the tip portion of the saw-toothed electrode 4 to an unnecessary place outside due to the increase of the applied voltage due to the increase of the total current, the saw-toothed electrode 4 is to be prevented. The distance from the discharge part to the shield case 2 must be secured more than necessary. Then, the shield case 2 becomes larger, that is, the charging device itself becomes larger.

Therefore, in view of the above, an object of the present invention is to stabilize the charging of a charging device having a sawtooth electrode.

[0016]

According to the present invention, there is provided a corona discharge electrode (saw-tooth electrode) 4 having a plurality of protrusions 3 in a row, a sawtooth electrode 4 and an image carrier. In the charging device for charging the surface of the rotatable image carrier 1 with the grid electrode 5 arranged between the body 1 and the body 1, the following conditions are set in order to stabilize the charging. .

It ≧ 0.0032PS + 0.35 However, the rotational peripheral speed of the image carrier 1 is PS, and the sawtooth electrode 4
The number of protrusions is n, and the total current supplied to the sawtooth electrode 4 is It, and it = It / n.

1 / m> 1 m> 1 (mm) However, the pitch of the protrusions 3 of the sawtooth electrode 4 is m, and the protrusions 3 are
Let l be the shortest distance between the tip of the grid electrode and the grid electrode 5.

It ≧ 0.69PS + 27.00 However, the rotational peripheral speed of the image carrier 1 is PS, and the sawtooth electrode 4
Let It be the total current supplied to.

0.5 ≦ Id / It ≦ 1 However, the total current supplied to the sawtooth electrode 4 is I
Let t be the current flowing through the image carrier 1.

Id ≧ 0.35PS + 13.39 where PS is the rotational peripheral speed of the image carrier 1 and Id is the current flowing through the image carrier 1.

It ≧ −OP + 140 However, the total current supplied to the sawtooth electrode 4 is I
t and the aperture ratio of the grid electrode 5 is OP.

Id ≧ 0.05 GH + 5.00 where GH is the voltage of the power supply for supplying the current to the grid electrode 5, and Id is the current flowing through the image carrier 1.

The total current supplied to the sawtooth electrode 4 is set to be 2.5 times or more of the minimum total current at which the charging is stable at the beginning of life.

[0025]

In the above means for solving the above-mentioned problems, by setting any of the following conditions, it becomes possible to uniformly and stably charge the surface of the image bearing member 1. By being able to charge at this stable potential, it is possible to obtain halftones and the like. The delicate expression of the density of the image becomes possible, and the image quality can be improved.

Further, by suppressing the voltage applied to the sawtooth discharge electrode to a low level, the amount of ozone generated from the discharge portion can also be suppressed.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram for explaining one embodiment of a charging device 8 according to the present invention.
Sawtooth electrode 4, grid electrode 5, holding piece 10 for holding the sawtooth electrode 4, holding piece 1 for holding the grid electrode 5
1. An electrode holder 12 including the holding pieces 10 and 11 and the like.

The shield case 2 is a shield plate made of a conductive resin or the like and having a length substantially aligned with the width direction of the image carrier 1, and has an opening formed on the side facing the surface of the image carrier 1. The saw-toothed electrode 4 is provided with a plurality of protrusions 3 in a row at predetermined intervals, and is formed by etching a strip-shaped thin plate of stainless steel (for example, SUS304). The saw-toothed electrode 4 is positioned on a holding piece 10 made of an insulating material and attached by screws or by adhesion.

In the grid electrode 5, a mesh-like uniform opening 13 is formed by etching a strip of stainless steel strip. The engaging holes 14 at both ends are stretched by being engaged with the claws 15 of the holding piece 11. In the figure, 16 is a sawtooth electrode 4
Is an electrode plate connected to.

When the charging device 8 is assembled, the saw-toothed electrode 4 is first attached to the holding piece 10 to be held by the holding body 12, and the holding body 12 is held with the saw-toothed electrode 4 held. The shield case 2 is positioned and mounted at a predetermined position. Then, when both ends of the grid electrode 5 are engaged with the holding piece 11, the grid electrode 5 is stretched with an appropriate tension.

FIG. 2 is a block diagram of a printer having a charging device according to the present invention. The printer main body 20 is provided with a drum-shaped image bearing member 1 having a photosensitive layer on its surface, and each unit that constitutes an electrophotographic process is centered around the image bearing member 1 to make the image bearing member 1 uniform. Charging device 8 for charging
And an optical recording unit 21 such as a semiconductor laser that exposes an original image on the surface of the image carrier 1 uniformly charged by the charging device 8.
A developing device 22 for developing the electrostatic latent image formed on the image carrier 1 with toner, and a transfer of the toner image formed on the image carrier 1 sent out by one of the sheet storage cassettes 23 and 24. A transfer device 25 that transfers to the surface of the material S and a cleaning device 26 that removes and collects the residual toner that remains partially because the toner image on the image carrier 1 is not transferred are arranged.

A heat fixing device 27 for fixing the transferred toner image on the transfer material S is arranged above the image carrier 1, and the toner image is fixed on the transfer material S by heat and pressure.
The paper is discharged to the paper discharge tray 29 above the printer body 20 via the paper discharge rollers 28. In the figure, 30 is a paper feed roller, 31 is a transport roller, and 32 is a registration roller.

FIG. 3 is a view showing the vicinity of the charging device of the image carrier 1. The cleaning device 26 and the charging device 8 are arranged in this order from the upstream side in the rotational direction of the image carrier 1, and below the charging device 8. A laser optical path L for guiding the laser light emitted from the optical recording unit 21 to the surface of the image carrier 1 is formed in the.

Here, the corona discharged from the tip discharge portion of the projection 3 of the saw-toothed electrode 4 is discharged toward the surface of the image carrier 1 within the discharge area indicated by the chain double-dashed line. This released corona is a uniform opening 1 of the grid electrode 5.
3 to act on the photosensitive layer of the image carrier 1. The amount acting on the photosensitive layer on the surface of the image carrier 1 at this time is controlled by the grid voltage Vg applied to the grid electrode 5.

Further, the waveform shown by the broken line in FIG. 3 represents the discharge characteristic discharged from the tip discharge portion of the sawtooth electrode 4, and the peak point P of the waveform is the most in the image carrier 1. This shows that the property of charging the photosensitive layer is good. Normally, this waveform has a waveform peak point P in a region directly facing the tip discharge portion of the sawtooth electrode 4, but as shown in FIG. 4, the lower tip of the shield case 2 is bent upward in an L shape. The presence of the portion 35 allows the peak point P of the waveform to be deflected as shown by the broken line. This is because the bent portion 35 of the shield case 2 is closer to the tip portion of the sawtooth electrode 4 than the facing surface 36, and is deflected to the bent portion side due to the difference in impedance. The waveform of the discharge characteristic is obtained.

Here, one side of the shield case 2 is bent into an L shape to change the impedance with the other side. However, as another method of changing the impedance with respect to the tip discharge part, a part of the inner surface of the shield case 2 is used. It is possible to obtain the same effect by applying a coating or by partially changing the material of the shield case 2 itself.

Incidentally, it is desirable that the corona discharged from the tip of the saw-toothed electrode 4 is usually set so as not to affect other process step regions. However, as the image forming apparatus such as a printer is downsized, there is almost no structural arrangement space around the process of the image carrier 1 and each apparatus must be arranged close to each other. Therefore, by configuring a part of the shield case 2 of the charging device 8 to have the above-described configuration, it becomes possible to easily deflect the peak point P of the discharge characteristic to a desired side that does not affect other devices. .

When corona discharge is generated from the sawtooth electrode 4, a flow of air is generated in the corona discharge direction. Since the corona discharge from the tip portion of the saw-toothed electrode 4 also has directional characteristics as shown in FIG. 3, the air flow is also formed in a specific direction. Therefore, by shifting the discharge peak point P by the above-described method according to the arrangement configuration of the device, the air flow can be deflected in any direction.

The arrow a in FIG. 3 indicates the flow of air flowing into the charging device 8 due to the above discharge characteristics, the arrow b indicates the flow of air flowing out of the charging device 8, and the air flow indicated by the arrow b indicates Ozone generated by corona discharge of the sawtooth electrode 4 is discharged from the charging device 8.

As described above, the corona discharge from the tip of the sawtooth electrode 4 has a discharge characteristic in a specific direction,
Unlike the conventional wire corona discharge device, it is not necessary to uniformly shield the periphery with the shield case. Therefore, one auxiliary electrode plate is provided in parallel to the tip end portion of the sawtooth electrode 4 in the longitudinal direction in a region from the tip end portion of the sawtooth electrode 4 to the image carrier 1 side. The same effect can be obtained by arranging the serrated electrode 4 in the discharge region from the tip portion.

FIG. 5 shows a high-voltage applying circuit in the electrophotographic process. The charging voltage V is applied to the sawtooth electrode 4 of the charging device 8 from the output terminal MC of the high-voltage power supply unit 37. The current flowing through the sawtooth electrode 4 is constant current controlled by the total current It. In addition, the shield case 2 includes a high-voltage power supply unit 3
The case voltage Vc is applied from the output terminal CASE of the reference numeral 7 by constant voltage control, and the grid voltage Vg is applied to the grid electrode 5 from the output terminal GRID of the high-voltage power supply unit 37 by constant voltage control. At this time, the case current Ic flows through the shield case 2 and the grid current Ig flows through the grid electrode 5.

Further, the photosensitive layer substrate of the image carrier 1 is grounded, and the drum current Id flows through the substrate. Voltages are applied to the developing device 22 and the transfer device 25 from the output terminals DVB and TC of the high-voltage power supply unit 37, respectively.

In the above structure, the total current It
Are case current Ic, grid current Ig, and drum current I.
d and are represented by the following equation (1).

It = Ic + Ig + Id (1) The high-voltage power supply unit 37 supplies the required high-voltage power supply to each unit in the electrophotographic process, and the charging device 8 also applies a high voltage to the saw-toothed electrode 4. A corona discharge phenomenon is generated, the surface of the image carrier 1 is charged, and a corona current is generated. The corona current generated at this time flows to the shield case 2, the grid electrode 5, and the image carrier 1. The current flowing through each is controlled by controlling the voltage applied to the grid electrode 5.

Here, in order to uniformly charge the image carrier 1, the following conditions are set between the sawtooth electrode 4, the grid electrode 5 and the image carrier 1.

The rotational peripheral speed of the image carrier 1 is PS (mm /
s), the number of projections in a row on the sawtooth electrode 4 is n, and the number of projections is n
When it = It / n with respect to the total current It (μA) supplied to the saw-toothed electrode 4 having the protrusions 3 of the relational expression (2) with the rotational peripheral speed PS of the image carrier 1. When the above condition is satisfied, the image carrier 1 is uniformly charged and the image is stabilized.

It ≧ 0.0032PS + 0.35 (2) In the experiment, the rotational peripheral speed PS of the image carrier 1 was 48 mm / s, 8
The value of the total current at which the charging becomes unstable when changing from 0 mm / s to 120 mm / s was examined. The unstable charging means that black streaks can be visually confirmed on the printed sample as shown in FIG. FIG. 6 shows black streaks that occur when a halftone image is printed.
If there is a fluctuation of V or more, black streaks occur. This fluctuation of the surface potential was used as an objective standard for charging stability.

The experimental results are shown in FIG. This P
A graph of the relationship between S and it is as shown in Fig. 8.
When the formula (2) is satisfied, the charging becomes uniform. In addition, the protrusion 1
Only the lower limit of it, which represents the current flowing per unit, is shown because of low ozone. Then, when the corona current for charging the surface of the image carrier 1 shows a certain constant value, uniform charging is performed, but in the present invention, the total current supplied to the electrodes for corona discharge is Due to the directivity of the serrated electrode 4, it is smaller than the other corona discharge devices, the discharge current is reduced, and the ozone generation amount is reduced.

The upper limit value of the rotational peripheral speed PS of the image carrier 1 was confirmed to be 240 mm / s by performing the same experiment.

As shown in FIG. 9, the pitch of the protrusions 3 of the sawtooth electrode 4 is m, the tip of the protrusion 3 and the grid electrode 5 are arranged.
Let l be the shortest distance from. FIG. 10 is a graph showing the relationship between the pitch m and the shortest distance l. In the following, ◯ indicates that the charging is stable, and x indicates that the charging is unstable. From this graph, the charging becomes stable when the expressions (3) and (4) are satisfied.

L / m> 1 (3) m> 1 (mm) (4) Here, the pitch m of the protrusions 3 of the sawtooth electrode 4 or the shortest distance between the tip of the protrusion 3 and the grid electrode 5. When l becomes large, in order to perform uniform charging, the sawtooth electrode 4
It is necessary to increase the current It supplied to the valve, which increases the amount of ozone generated. Therefore, the pitch m of the protrusions 3
It has been confirmed that the above formula is satisfied within a range of 1 to 5 mm and the shortest distance 1 between the tip of the protrusion 3 and the grid electrode 5 is 2 to 8 mm.

FIG. 11 is a graph showing the relationship between the current It supplied to the sawtooth electrode 4 and the rotational peripheral speed PS of the image carrier 1. From this graph, the charging becomes stable when the expression (5) is satisfied.

It ≧ 0.69PS + 27.00 (5) The upper limit value of the rotational peripheral speed PS of the image carrier 1 is 240 m.
Up to m / s.

FIG. 12 shows the relationship between the current It supplied to the sawtooth electrode 4 and the drum current Id flowing into the conductor electrode attached to the image carrier 1. From this graph, if the formula (6) is satisfied, the charging becomes stable.

0.5 ≦ Id / It ≦ 1 (6) Since the drum current Id flowing into the image carrier 1 is generated by the current It supplied to the sawtooth electrode 4, Id
/ It cannot take a value of 1 or more.

FIG. 13 is a graph showing the relationship between the drum current Id flowing into the conductor electrode attached to the image carrier 1 and the rotational peripheral speed PS of the image carrier 1. From this graph, stable charging can be obtained when the expression (7) is satisfied.

Id ≧ 0.35PS + 13.39 (7) The drum current Id flowing into the image carrier 1 is (6)
As shown in the equation, there is a correlation with the current It supplied to the sawtooth electrode 4, and the upper limit of Id is determined by It.

As shown in FIG. 14, since the openings 13 are arranged at regular intervals in the grid electrode 5, the aperture ratio O
When P is expressed as a percentage of L ₁ / L ₂ , this grid electrode 5
The relationship between the aperture ratio OP and the current It supplied to the sawtooth electrode 4 is as shown in FIG. From this graph,
When the formula (8) is satisfied, the charging becomes stable.

It ≧ −OP + 140 (8) When the aperture ratio OP of the grid electrode 5 is 90% or less,
It is confirmed that this relational expression holds.

The relationship between the voltage of the power supply for supplying the current to the grid electrode 5 to GH and the drum current Id flowing into the image carrier 1 is as shown in FIG. As a result, the charging becomes stable when the expression (9) is satisfied.

Id ≧ 0.05 GH + 5.00 (9) The drum current Id flowing into the image carrier 1 is (6)
As shown in the equation, there is a correlation with the current It supplied to the sawtooth electrode 4, and the upper limit of Id is determined by It. Also,
The voltage GH of the power supply for supplying the current to the grid electrode 5 was confirmed in the range of -700V to -400V by performing the same experiment.

Of the currents supplied to the sawtooth electrode 4, the minimum current value I at which the charging is stable at the beginning of life.
t is −60 μA, and the sawtooth electrode 4 with respect to life.
The charge stability at the end of the life of the current IT supplied to was confirmed. The result is shown in FIG. According to this, when the set current value IT is set within a range of 2.5 to 4 times the minimum current value, it is possible to stabilize the charging throughout the life.

As described above, by setting any one of the above-mentioned conditions, it is possible to uniformly and stably charge the photosensitive layer of the image bearing member, and by this stable potential charging, halftone and other original The delicate expression of the density of the image becomes possible, and the image quality can be improved.

Since the voltage applied to the sawtooth electrode can be suppressed to a low level, the amount of ozone generated from the discharge part can be suppressed. Therefore, the harmful effects of ozone are reduced. That is, the deterioration of the image quality of the original image due to the influence of the image bearing member on the surface of the photosensitive layer is prevented, and nitrogen oxides (NO _x ) generated by combining various gases and foreign matters in the air floating in the image forming apparatus. Alternatively, silicon oxide (SiO ₂ ) or the like adheres to the surface of the sawtooth electrode and the surface of the grid electrode, and the discharge ability of the sawtooth electrode,
It is possible to prevent the deterioration of the image quality of the original image due to the deterioration of the charge potential control capability of the grid electrode, and as a result, it is possible to improve the image quality.

Further, it is possible to reduce the size of the shield case, that is, the size of the charging device itself, without securing an unnecessary distance from the corona discharge portion to the shield case. Therefore, the electrophotographic process section can be compactly assembled, and the size of the image forming apparatus main body can be reduced.

Further, by using the saw-toothed electrode according to the present invention, the long-term stability of discharge is improved against the adhesion of whiskers due to silicon oxide which is generated in proportion to the use time. Further, since it is not easily affected by erosion of the discharge electrode due to nitrogen ions, etc., stable discharge can be maintained even after long-time discharge. Therefore, it is possible to reduce the service cost without requiring the operator to frequently clean the charging device.

Moreover, in the saw-toothed electrode, it is possible to simultaneously form a plurality of projections for discharging on one electrode plate at one position at the same time. Considering the service life, it is possible to realize a much cheaper charging device.

The present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention. For example, the image carrier 1 is not limited to a drum shape, but may be a belt shape. Further, the saw-toothed electrode is not limited to the one shown in FIG. 1 and can be applied to an electrode in which protrusions are arranged in a staggered pattern.

[0069]

As is apparent from the above description, according to the present invention, the total current, the process speed, the grid voltage, the image carrier current, and the projection are provided between the sawtooth electrode, the grid electrode, and the image carrier. Stable charging can be performed by defining the pitch and the like. Therefore,
The uneven charging on the surface of the image carrier is eliminated, and the image quality can be improved. Further, the ozone generated by the discharge is reduced, and the adverse effect on the charging device can be prevented. Further, since leakage discharge from the sawtooth electrode is reduced, the shield case can be downsized, and the charging device can be downsized. Moreover, stable charging can be performed for a long period of time, and long life and maintenance-free can be achieved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a state in which a charging device according to an exemplary embodiment of the present invention is disassembled.

FIG. 2 is a configuration diagram of a printer including the charging device of the present invention.

FIG. 3 is a diagram showing the vicinity of a charging device for an image carrier.

FIG. 4 is a diagram showing discharge characteristics of a charging device.

FIG. 5 is a diagram showing a high voltage application circuit in an electrophotographic process.

FIG. 6 is a diagram showing a print sample regarding charging stability.

FIG. 7 is a diagram showing an experimental result using the total current of the sawtooth electrode and the rotational peripheral speed of the image carrier as parameters.

FIG. 8 is a diagram showing the relationship between the total current of the sawtooth electrode divided by the number of protrusions and the rotational peripheral speed of the image carrier.

FIG. 9 is a diagram for explaining the shortest distance between the pitch of the protrusions of the sawtooth electrode and the grid electrode.

FIG. 10 is a diagram showing the relationship between the pitch of the protrusions of the sawtooth electrode and the shortest distance from the grid electrode.

FIG. 11 is a diagram showing the relationship between the total current of the sawtooth electrode and the rotational peripheral speed of the image carrier.

FIG. 12 is a diagram showing the relationship between the total current of the sawtooth electrode and the current flowing into the image carrier.

FIG. 13 is a diagram showing a relationship between a current flowing into the image carrier and a rotational peripheral speed.

FIG. 14 is a diagram for explaining the aperture ratio of a grid electrode.

FIG. 15 is a diagram showing the relationship between the total current of the sawtooth electrode and the aperture ratio of the grid electrode.

FIG. 16 is a diagram showing a relationship between a voltage of a power supply that supplies a current to a grid electrode and a current flowing into an image carrier.

FIG. 17 is a view showing an experimental result regarding charging stability of a total current of a sawtooth electrode with respect to life.

FIG. 18 is a configuration diagram of a conventional charging device.

FIG. 19 is a view showing a state in which the distance between the projections of the sawtooth electrode and the grid electrode is not constant.

[Explanation of symbols]

 1 image carrier 2 shield case 3 protrusion 4 sawtooth electrode 5 grid electrode 8 charging device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Imagawa 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Inventor Junji Morimoto 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Osaka Incorporated (72) Inventor Kanji Kawato 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (8)

[Claims] 1. A charging device comprising: a corona discharge electrode having a plurality of protrusions in a row; and a grid electrode arranged between the discharge electrode and an image carrier, for charging a rotatable image carrier surface. In the charging device, the rotational peripheral speed of the image carrier is set to P
S, the number of protrusions of the discharge electrode is n, and the total current supplied to the discharge electrode is It, and it = It / n, in order to stabilize the charging, the relation of it ≧ 0.0032PS + 0.35 must be satisfied. A method for stabilizing charging, which is characterized by: 2. A charging device comprising: a corona discharge electrode having a plurality of protrusions in a row; and a grid electrode arranged between the discharge electrode and the image carrier, for charging a rotatable image carrier surface. In the charging device described above, if the pitch of the protrusions of the discharge electrode is m and the shortest distance between the tip of the protrusion and the grid electrode is l, the relationship of 1 / m> 1 m> 1 (mm) is satisfied in order to stabilize the charging. A method for stabilizing charging according to claim 1, wherein: 3. A corona discharge electrode having a plurality of protrusions arranged in a row, and a grid electrode arranged between the discharge electrode and the image carrier, for charging a rotatable image carrier surface. In the charging device, the rotational peripheral speed of the image carrier is set to P
S is the total current supplied to the discharge electrode, and It is a charging stabilization method characterized by satisfying the relationship: It ≧ 0.69PS + 27.00 in order to stabilize charging. 4. A corona discharge electrode having a plurality of protrusions in a row, and a grid electrode arranged between the discharge electrode and the image carrier, for charging the surface of the rotatable image carrier. In the charging device, if the total current supplied to the discharge electrode is It and the current flowing to the image carrier is Id, the relationship of 0.5 ≦ Id / It ≦ 1 must be satisfied in order to stabilize the charging. A method for stabilizing charging, which is characterized by: 5. A corona discharge electrode having a plurality of protrusions in a row, and a grid electrode arranged between the discharge electrode and the image carrier, for charging a rotatable image carrier surface. In the charging device, the rotational peripheral speed of the image carrier is set to P
S, where Id is the current flowing through the image bearing member, the following condition is satisfied: Id ≧ 0.35PS + 13.39 in order to stabilize the charging. 6. A corona discharge electrode having a plurality of protrusions arranged in a row, and a grid electrode arranged between the discharge electrode and the image carrier, for charging a rotatable image carrier surface. In the charging device of No. 3, if the total current supplied to the discharge electrode is It and the aperture ratio of the grid electrode is OP, it is possible to stabilize the charging by satisfying a relation of It ≧ −OP + 140. Method. 7. A corona discharge electrode having a plurality of protrusions in a row, and a grid electrode arranged between the discharge electrode and the image carrier, for charging a rotatable image carrier surface. In the charging device, the voltage of a power source for supplying a current to the grid electrode is GH, and the current flowing through the image carrier is I.
In order to stabilize the charging, let d be: Id ≧ 0.05GH + 5.00, the method of stabilizing charging. 8. A charging device comprising: a corona discharge electrode having a plurality of protrusions in a row; and a grid electrode arranged between the discharge electrode and the image carrier, for charging the surface of the rotatable image carrier. In the charging device, the total current supplied to the discharge electrode is set to 2.5 times or more of the minimum total current at which the charging is stable at the beginning of life.