JP2000284643A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device capable of minimizing toner consumption at the time of starting the rotation of a photoreceptor drum and at the time of stopping the rotation thereof. SOLUTION: In the two-component reversal developing type image forming device using the photoreceptor drum 12, a developing sleeve 15 and the drum 12 are started to be driven and rotated in a state where developing bias voltage having a reverse polarity is applied to a developing sleeve 15 in the case of starting image-forming. Thus, the fogging of toner at the time of starting image- forming is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a two-component reversal developing system, such as an electrophotographic copying machine, a printer, a facsimile, and the like.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus of a reversal developing system using a two-component developer, as shown in FIG.
After the surface of the photosensitive drum 2 is positively charged by the charger 1, for example, exposure is performed.
Is the developing unit position G facing the developing sleeve 3 in the developing device.
, And the positively charged toner T of the two-component developer is supplied from the developing device to the exposed region 4 on the surface of the photosensitive drum.
a and developed.

[0003]

Incidentally, it is preferable that the positive developing bias voltage to the developing sleeve 3 is applied at the same time when the charging area 4 reaches the developing section position G facing the developing sleeve 3. However, it is not easy to control the timing, and the application timing of the developing bias voltage may be shifted.

When the rotation of the photosensitive drum is started, the timing at which a positive developing bias voltage V _Bias of, for example, +560 volts is applied to the developing sleeve 3 is, for example, +740.
If the electrostatic charge portion S of the photosensitive drum 2 charged with the volt is later than the time when it reaches the developing portion position G, the electrostatic charge portion S may reach the developing portion position G during that time.
Since the developing bias voltage V _Bias is not applied to the developing sleeve 3, the negatively charged carrier E is attracted to the surface of the photosensitive drum 2 due to the presence of the electrostatic charge portion S, as shown in FIG. That is, at the start of rotation of the photosensitive drum,
If the timing of the developing bias voltage V _Bias applied to the developing sleeve 3 is shifted with respect to the photosensitive drum 2 that has reached the developing unit position G, where the surface potential has already been applied, carrier jump occurs.

The _reason is that the relative difference ΔV between the surface potential V _SP and the developing bias voltage V _Bias (= the surface potential V _{SP −the} developing bias voltage V _Bias ) is the maximum potential difference (the carrier potential does not occur). it is from exceed the carrier jump occurrence limit maximum potential difference) V _max (see FIG. 5).

Conventionally, in order to prevent the carrier jump, the timing at which a positive developing bias voltage V _Bias of, for example, +560 volts is applied to the developing sleeve 3 at the start of the rotation of the photosensitive drum is set to, for example, +740 volts. The electrostatic charge portion S of the body drum 2 is set to be earlier than the time when it reaches the developing portion position G.
A large amount of toner T adheres to the surface of the photosensitive drum 2 (solid black state) (see FIG. 6).

The _reason is that the relative difference ΔV between the surface potential V _SP and the developing bias voltage V _Bias is the toner adhesion amount minimum potential difference V _min at which the toner adhesion amount is the minimum (the fog state indicated by K in FIG. 3). (See FIG. 7). The above situation is the same when the rotation of the photosensitive drum 2 is stopped.

In short, in the conventional control method, when the rotation of the photosensitive drum is started or stopped, wasteful toner is consumed every time the rotation of the photosensitive drum is started or stopped in order to avoid carrier jump. . Further, since all the toner is collected, the amount of toner collected increases along with the amount of toner consumption.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to form an image forming apparatus capable of minimizing the amount of toner consumed when the rotation of the photosensitive drum starts and when the rotation of the photosensitive drum stops. It is to provide a device.

[0010]

An image forming apparatus according to the present invention is a two-component reversal developing type image forming apparatus using a photosensitive drum. When an image is started, a developing sleeve having a reverse polarity is formed on a developing sleeve. The driving of the developing sleeve and the photosensitive drum is started with the bias voltage applied.

In another aspect, the present invention is directed to a two-component reversal developing type image forming apparatus using a photosensitive drum, wherein a developing bias voltage having a reverse polarity is applied to a developing sleeve when image formation is completed. In this state, the developing sleeve and the photosensitive drum are stopped from rotating.

According to the present invention, V _min ≦ ΔV ≦ V in order to prevent the carrier from jumping at the start and stop of the rotation of the photosensitive drum and to suppress the toner adhesion amount to the fog level.
surface potential V _SP and developing bias voltage V that satisfy _max
The relative difference ΔV from _Bias is maintained.

The value of the toner adhesion amount minimum potential difference V _min at which the toner adhesion amount is about fogging and the maximum potential difference V _max at the potential difference at which carrier jump does not occur are appropriately set according to the image forming apparatus to be used. You.

In the present invention, when the rotation of the photosensitive drum is started, first, a developing bias voltage having a reverse polarity is applied to the developing sleeve. That is, until the charging start portion of the photosensitive drum moves to the developing unit position G (see FIG. 2),
The surface potential V _{S. P} of the photosensitive drum is 0 volt (see FIG. 1)
While the surface of the uncharged drum rubs against the developer on the surface of the developing sleeve, a developing bias voltage of the opposite polarity is applied to the developing sleeve. Thereafter, the charge amount and the developing bias voltage are controlled by gradually changing the charge amount on the photosensitive drum surface from zero (the 0 volt) to a predetermined value, and gradually changing the developing bias voltage to a predetermined voltage value. In any ascending stage up to the copying operation, the relative potential difference ΔV between the surface potential V _SP of the photosensitive drum and the developing bias voltage V _Bias at the developing unit position is V _min and V
_It is within the range of _max .

In short, the developing bias voltage V _Bias and the surface potential V _SP are controlled with each other at each stage, and the relative potential difference Δ
By preventing V from _exceeding Vmax, it is possible to avoid the occurrence of carrier jump, and to reduce the relative potential difference ΔV to V
A large amount of toner can be avoided so as not to exceed _min .

Further, even when the rotation of the photosensitive drum is stopped, the carrier jump and the adhesion of a large amount of toner can be avoided in the same manner as when the rotation of the photosensitive drum is started.

[0017]

Embodiments of the present invention will be described below. It should be noted that the present invention is not limited thereby. Figure 1 illustrates an embodiment of the present invention which is adapted to stepwise controlled by the surface potential V _SP of photoreceptor drum 12 at the start and stop the photosensitive drum rotation, changing the charger grid voltage V _Grid a diagram for a timing chart of control of the surface potential V _SP and the developing bias voltage V _{Bi the as} at the developing portion position G when the photosensitive drum rotation start and stop.

In this embodiment, as shown in FIG. 1, a two-component developer consisting of a toner T and a carrier E is used, and a developing bias voltage V _Bias is applied to a developing sleeve 15 to transfer the toner T to the photosensitive drum. an image forming apparatus for attaching to 12, at the start and stop the photosensitive drum rotation surface potential V _SP of the photosensitive drum a developing bias voltage V
The relative difference ΔV between _Bias, are controlled stepwise within the carrier jump occurrence limit maximum potential difference V _max and the toner adhesion amount minimum potential V _min.

FIG. 2 shows a reversal developing type copying machine. In FIG. 2, the photosensitive drum 12 is rotating counterclockwise. Grid voltage of charger 11 (grid is indicated by symbol R)
When the surface potential sensor 16 measures the surface potential of the photosensitive drum 12 and performs exposure for image formation, the charge of the charger 11 is controlled. When the electrostatically charged portion of the photoconductor drum charged at the position (2) reaches the position of the exposure unit, it is exposed by the LED array 13 to form a latent image. In addition, rotate
When the toner reaches the developing device 14, the toner T is skipped and developed.
Thereafter, the developed portion is transferred, and the remaining toner is removed by the cleaning device L. The charger 11 is connected to a high-voltage power supply circuit 20 for charging the photosensitive drum 12 to about +850 volts (controlling the grid voltage to about +920 volts). Also,
A control circuit 19 for controlling the magnitude of the voltage generated by the high-voltage power supply circuit 20 is connected to the high-voltage power supply circuit 20. On the other hand, the high-voltage power supply circuit 21
And a control circuit 22 for controlling the magnitude of the voltage generated by the high-voltage power supply circuit 21 is connected to the control circuit 22. Furthermore, a control circuit 24 for controlling the amount of exposure light is connected to the LED array 13. And these control circuits 1
CPU 23 for instructing control contents of 9, 22, and 24
Is provided, and the output signal of the surface potential sensor 16 is input thereto. The CPU 23 instructs the charge amount to gradually change from 0 to a predetermined value by the grid voltage V _Grid of the charger 11 and also instructs the developing device 14 to gradually change the developing bias voltage to the predetermined voltage value. It is supposed to.

[0020] The following describes the development bias voltage V _Bias application timing and the surface potential V _SP of the photosensitive drum at the start of the photosensitive drum rotation. In this embodiment, FIG.
At the start of rotation, first, a developing bias voltage V _Bias (−200 volts) of the opposite polarity is applied to the developing sleeve 15, and then, at the time A before the polarity switching of the developing bias voltage V _Bias , the surface potential V _SP (+150 volts) is applied to the photoconductor, and at time B, the bias voltage V _Bias is first controlled to be in the OFF state.

The relative potential difference ΔV at the time point B is ΔV (time point B) = 150 volts−0 volts = 150 volts. Therefore, even if the developing bias voltage V _Bias is 0 volt, the surface potential V _SP is 150 volts and the relative potential difference ΔV is V _max (3
50 volts), so that carrier jump does not occur.

Subsequently, the surface potential V _SP is increased by 150 at time C.
In the ascending phase of controlling from 300 volts to 300 volts,
The relative potential difference [Delta] V at the time C is, [Delta] V (point C) = 300 volts -0 volts = 300 volts, and the the relative potential difference [Delta] V does not exceed the V _max value, never again jumping carriers are generated.

Then, the developing bias voltage is set to 0 vol.
During the ascending phase of controlling to +150 volts from
The relative potential difference ΔV at point D is: ΔV (time D) = 300 volts−150 volts = 150
Volts, and the relative potential difference Δ
V is V_maxSince the value does not exceed the value,
Does not occur. Further, when the relative potential difference ΔV is V _minvalue
As it does not protrude, the amount of toner adhered is suppressed to fog level
Can be

As described above, when the rotation of the photosensitive drum is started, the charge amount on the surface of the photosensitive drum is changed from zero to a predetermined value (+85).
0 volts) and the developing bias voltage is gradually changed to a predetermined voltage value (+650 volts) to control the charge amount and the developing bias voltage. The relative potential difference ΔV between the surface potential V _SP of the photosensitive drum 12 and the developing bias voltage V _Bias at the developing unit position G is represented by V _max and V _min
Within the range.

That is, when the relative potential difference ΔV is _Vmax-
While maintaining without protruding the range of V _min, the surface potential V _SP and the development bias voltage V _bias is respectively 850
Volts, until the developing bias voltage V reaches 650 volts.
_{Both the bias} and the surface potential V _SP are controlled stepwise.

The same control is performed when the rotation of the photosensitive drum is stopped after the copying operation.

As described above, in the embodiment, the developing bias voltage V _Bias and the surface potential V _SP are mutually controlled at each stage,
Since the relative voltage difference ΔV that does not exceed V _max,
With jumping carrier can be avoided from occurring, because the relative difference ΔV that does not exceed V _min, avoiding a large amount of toner adhesion.

In this embodiment, the surface potential V_SP
Is the grid voltage V of the charger. _GridChange
And step-by-step control method.
Controlled stepwise by changing charger output
To change the output of the laser or the LED to change the photosensitive drum 1
So that it is controlled step by step by changing the amount of exposure
May be.

Then, in setting the surface potential V _SP ,
If the method of changing the grid voltage V _Grid or changing the charger output is adopted, the surface potential rises and falls only linearly, and therefore, the rise and fall of the surface potential become only gentle. When used, the time width can be narrowed, so that time management is possible, and furthermore, a sharp edge can be provided and the setting of the surface potential V _SP can be further improved.

Furthermore, the value of the maximum potential difference V _max and the minimum potential V _min is set appropriately according to the apparatus.

[0031]

As described above, according to the image forming apparatus of the two-component reversal developing system using the photosensitive drum of the present invention, when the developing bias voltage of the opposite polarity is applied to the developing sleeve when starting the image formation. Since the rotation drive of the developing sleeve and the photosensitive drum is started, toner fogging at the start of image formation can be reduced.

Also, in the present invention, the rotation of the developing sleeve and the photosensitive drum is stopped with the developing bias voltage of the opposite polarity applied to the developing sleeve even when the image formation is completed. It is possible to reduce the fogging of the toner at the end of the image formation.

Therefore, it is possible to avoid a large amount of toner from adhering, and to minimize the consumption of toner not used for image formation.

As described above, since the amount of toner not used for image formation before and after image formation is reduced, the size of the collection container can be reduced.

[Brief description of the drawings]

FIG. 1 is a timing chart for explaining an embodiment of the present invention.

FIG. 2 is an overall configuration explanatory diagram showing a reversal developing type image forming apparatus applied to the embodiment.

FIG. 3 is a diagram for explaining a reversal developing method using a two-component developer.

FIG. 4 is a diagram for explaining occurrence of carrier jump in a conventional example.

FIG. 5 is a diagram showing a relative difference ΔV between a surface potential V _SP and a developing bias voltage V _Bias used to explain occurrence of carrier jump in the conventional example.

FIG. 6 is a view for explaining a large amount of toner adhesion in a conventional example.

FIG. 7 is a diagram showing a relative difference ΔV between a surface potential V _SP and a developing bias voltage V _Bias used for explaining a large amount of toner adhesion in a conventional example.

[Explanation of symbols]

12 photoreceptor, 15 developing sleeve, T toner, E ...
Career, V _SP ... surface potential, V _Bias ... developing bias voltage.

Claims (4)

[Claims] 1. An image forming apparatus of a two-component reversal developing method using a photosensitive drum, wherein a developing bias voltage having a reverse polarity is applied to a developing sleeve when image formation is started. An image forming apparatus, wherein rotation driving of the photosensitive drum is started. 2. The developing sleeve according to claim 1, wherein the developing bias voltage of the opposite polarity is continuously applied to the developing sleeve until a charging start portion of the photosensitive drum moves to a developing unit position. Image forming device. 3. An image forming apparatus of a two-component reversal developing system using a photosensitive drum, wherein a developing bias voltage having a reverse polarity is applied to the developing sleeve when image formation is completed. An image forming apparatus, wherein rotation of the photosensitive drum is stopped. 4. The developing bias voltage of the opposite polarity is applied to the developing sleeve from a point in time when the charging end portion of the photosensitive drum has passed the developing unit position to a point in time when the photosensitive drum and the developing sleeve stop. The image forming apparatus according to claim 3, wherein the voltage is continuously applied.