JP2000098705A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a developing device constituted so that the carry-over phenomenon (attachment of carrier) to a latent image carrier is surely evaded at the rising time of AC bias and the various kinds of failure associated with the attachment of the carrier are eliminated while satisfying such request that the cost of a device is reduced. SOLUTION: In the two-component developing system developing device constituted so that developing bias VB obtained by superimposing the AC bias VAC on DC bias VDC is applied to a developing roll 2, a developing bias applying means 3 is provided with a DC bias applying means 4 applying the bias VDC and an AC bias applying means 5 applying the bias VAC whose positive- side waveform VST(+) and negative-side waveform VST(-) are asymmetric at at least the rising time. Besides, a carrier transition suppression means 6 suppressing the waveform component of the side being suddenly changed in the rising waveform of the bias VAC from acting as an electric field moving the carrier on the roll 2 to a latent image carrier 1 side is arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing apparatus applied to an image forming apparatus such as a copying machine or a printer of an electrophotographic system or an electrostatic recording system, and more particularly to a developing system in which an AC bias is superimposed on a DC bias. To a developing device of a two-component developing system in which a developing bias is applied to a developing roll and a two-component developer including a toner and a carrier is used.

[0002]

2. Description of the Related Art Conventionally, as a developing device of this type of a two-component developing system, for example, a developing roll is disposed opposite to a photosensitive drum as a latent image carrier, and the developing roll is composed of a toner and a carrier. A two-component developer is carried and conveyed, and a predetermined developing bias is applied to the developing roll to form a predetermined developing electric field between the developing roll and the photosensitive drum. The upper electrostatic latent image is visualized with toner on a developing roll. Here, as the developing bias,
Although it is possible to use only the DC bias, from the viewpoint of further improving the developing property, by using the DC bias with the AC bias superimposed thereon, the oscillating electric field acts on the developer on the developing roll. In this case, it is preferable to increase the number of times the toner flies between the photosensitive drum and the developing roll, thereby improving the developing property.

[0003]

In such a developing device of the two-component developing system, for example, as shown in FIG. 12, the charging device is turned on almost simultaneously with the rotation of the photosensitive drum, and When the photosensitive drum area charged by the developing device reaches the developing position, the developing device is driven (the developing roll and the like are driven and rotated), and a direct current bias (DC bias) of a developing bias is applied. A control method is adopted in which an AC bias (AC bias) of a developing bias is applied when a (portion where an electrostatic latent image is written by an exposure device) reaches a developing position. However, when such a control method is adopted, a carry-over phenomenon (so-called BCO: Bead Carry) in which carriers are transferred to the photosensitive drum when the AC bias rises (ON timing).
Over occurs), which easily leads to image quality defects such as white spots in image formation, and that the photosensitive drum is liable to be damaged due to carrier adhesion.

[0004] The present inventors have pursued the cause of such a technical problem, and as a result, have found that the waveform shape at the time of rising of the AC bias has an influence. That is, as the AC bias power supply in this type of conventional developing device, a power supply that generates an AC bias by turning on / off a DC power supply at a predetermined frequency is sometimes used, for example, from the viewpoint of cost reduction. . The AC bias VAC generated by this type of AC bias power supply has a positive waveform VST (+) at the time of rising (region A in the figure) and a negative waveform VST (+) as shown in FIG. The waveform VST (-) becomes asymmetric. In FIG. 13, VP-P indicates a peak-to-peak voltage of the AC bias VAC.

At this time, for example, when a reversal developing method (a method of developing an exposed portion as an image portion) is applied to a negative photosensitive drum, as shown in FIG. If the waveform VST (+) rises more rapidly than the negative waveform VST (-), the positive waveform VST (+) and the negative waveform VST, as shown by the hatched portion M in FIG.
(-), A potential difference .DELTA.VST is generated, and the DC bias VDC level of the developing bias is apparently changed by the potential difference .DELTA.VST. Then, a potential difference between the background portion potential VH and the developing bias DC bias VDC (hereinafter referred to as a cleaning potential as required)
Is temporarily increased, and it is assumed that the carry-over phenomenon described above occurs with the increase in the cleaning potential. This type of carry-over phenomenon occurs when a DC bias is applied to perform a normal developing operation, and does not occur when no DC bias is applied.

In order to avoid this kind of carry-over phenomenon, a method may be adopted in which an AC power supply is used as it is without using a method of oscillating a DC bias, but it is difficult to adopt this method under a demand for cost reduction. In addition, when adopting the method of oscillating the AC bias, it is conceivable to oscillate the DC bias at a low level and amplify it with a transformer or the like. However, they do not meet the demand for cost reduction, and none of them is preferable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problem, and a carry-over phenomenon (carrier) to a latent image carrier at the time of rising of an AC bias while satisfying a demand for lowering the cost of an apparatus. It is an object of the present invention to provide a developing device which reliably avoids adhesion and eliminates various adverse effects caused by carrier adhesion.

[0008]

That is, according to the present invention, as shown in FIG.
A two-component developer G composed of a toner and a carrier is carried and conveyed on the developing roll 2, and a developing bias VB in which an AC bias VAC is superimposed on a DC bias VDC is applied to the surface of the developing roll 2. Then, in the developing device in which the electrostatic latent image formed on the latent image carrier 1 is visualized by the developer G, the DC bias VDC for applying the DC bias VDC is applied to the developing bias applying means 3. Applying means 4 and at least a positive-side waveform VST (+) at the time of rising
Bias VAC where the waveform and the negative waveform VST (-) are asymmetric
And an AC bias applying means 5 for applying
A carrier transition suppressing means 6 is provided for suppressing a waveform component on the side of the rising edge of the AC bias VAC, which rapidly changes, from acting as an electric field for moving the carrier on the developing roll 2 to the latent image carrier 1 side. It is characterized by the following.

In such technical means, the developing device according to the present invention uses a two-component developer G and uses a developing bias VB in which an AC bias VAC is superimposed on a DC bias VDC. For example, an embodiment may be such that the developer G is in contact with the latent image carrier 1 in the developing region, or an embodiment in which the developer G is disposed in a non-contact manner. Also, the developing method may be a reversal developing method in which an exposed portion is developed as an image portion, or a regular developing method in which an exposed portion is developed as a background portion and a non-exposed portion is developed as an image portion. Good.

The developing bias applying means 3 includes:
A DC bias applying means 4 and an AC bias applying means 5 are provided, and the AC bias applying means 5 includes at least a positive waveform VST (+) and a negative waveform VST (-) at the time of rising.
It is only necessary that an asymmetric AC bias VAC be applied. Here, a typical example of the AC bias applying means 5 is a mode in which a DC power supply is turned ON / OFF at a predetermined frequency. In this mode, if a positive DC power supply is used, the AC bias Of the rising waveforms of VAC, the positive side waveform VST (+) rises more rapidly than the negative side waveform VST (-). Waveform VST
(-) Rises more rapidly than the positive waveform VST (+).

Further, the carrier transfer suppressing means 6 includes:
Any one may be selected as long as it suppresses carrier transition due to a waveform component on the side that changes rapidly in the rising waveform of the AC bias VAC. As a first mode, the time t0 at which the rising waveform of the AC bias VAC stabilizes is obtained. After passing, the developing area between the latent image carrier 1 and the developing roll 2 is passed through at least the actual latent image forming area of the latent image forming area on the latent image carrier 1 so as to pass therethrough. One that controls the developing bias applying means 3 may be used. At this time, regarding the application timing of the DC bias VDC, the latent image forming area (for example, the initial charging area by the charging unit)
It is necessary to turn on at the timing when the leading end of the image reaches the developing area, so that the background potential and the DC bias VDC are always synchronized in the developing area so that no toner band or BCO is generated in the background area. It is necessary to.
Here, from the viewpoint of reliably avoiding the carry-over phenomenon, the AC bias VAC should be applied at a timing at least a time t0 before the rising waveform of the AC bias VAC stabilizes from the timing of applying the DC bias VDC. In addition, it is preferable to control the developing bias applying means 3. Further, in the first mode of the carrier transfer suppressing means 6, the control of the AC bias applying means 5 is performed in terms of simplifying the configuration and stabilizing the operation. It is preferable to control the application timing of the AC bias VAC by the AC bias application unit 5 in synchronization with the charging start timing.

As a second mode of the carrier transfer suppressing means 6, the waveform component on the side of the rising edge of the alternating-current bias VAC that changes abruptly is such that the carrier on the developing roll 2 is pressed against the developing roll 2 side. One that constitutes the AC bias applying means 5 so as to act as an electric field may be mentioned. In this embodiment, the waveform component of the rising waveform of the AC bias VAC on the side that changes rapidly is
Since the carrier on the developing roll 2 acts in the opposite direction to the electric field moving to the latent image carrier 1 side, it does not lead to the so-called carryover phenomenon.

Further, as a third mode of the carrier transition suppressing means 6, the rising time t0 of the AC bias VAC is extended and adjusted, and the positive side rising waveform V of the AC bias VAC is adjusted.
One that corrects the ST (+) and the negative-side rising waveform VST (-) substantially symmetrically. According to this aspect, since the potential difference between the positive-side rising waveform VST (+) and the negative-side rising waveform VST (-) of the AC bias VAC is suppressed to a small value, the carrier on the developing roll 2 is discharged when the AC bias VAC rises. The electric field itself that moves to the latent image carrier 1 does not suddenly increase, and the so-called carry-over phenomenon is effectively suppressed.

Next, the operation of the above technical means will be described. In FIG. 1, the developing bias applying means 3
A DC bias applying unit 4 and an AC bias applying unit 5 are provided. At this time, the AC bias VAC applied by the AC bias applying means 5 is such that at least the positive waveform VST (+) and the negative waveform VST (-) at the time of rising are asymmetric, in other words, Imbalance. Now, as shown by the hatched portion M in FIG. 1, the potential difference between the positive-side rising waveform VST (+) and the negative-side rising waveform VST (-) causes the carrier on the developing roll 2 to move to the latent image carrier 1 side. Even if the potential difference acts in the present application, in the present application, the carrier transition suppressing means 6 operates to make the potential difference M
From acting on the developing roller 2 as an electric field for moving the carrier to the latent image carrier 1 side.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows an example of an image forming apparatus incorporating a first embodiment of a developing device according to the present invention. In FIG. 1, reference numeral 10 denotes, for example, a photosensitive drum having a negative polarity as a latent image carrier;
Is a charger such as a corotron for charging the photosensitive drum 10,
Reference numeral 12 denotes an exposure device such as a laser scanning device that writes an electrostatic latent image on the charged photosensitive drum 10. Reference numeral 13 denotes a developing device that visualizes the electrostatic latent image formed on the photosensitive drum 10 with a developer. A developing device of a component developing system;
A transfer unit 15 such as a corotron for transferring the upper toner image onto a recording sheet (not shown) such as paper;
A sheet removing static eliminator such as a corotron for removing a recording sheet from the printer, 16 a cleaner for cleaning residual toner on the photosensitive drum 10, and 17 a static eliminator such as a lamp for removing residual charges on the photosensitive drum 10. is there.

In this embodiment, the developing device 13
As shown in FIGS. 2 and 3, the developing device has a developing housing 21 that is open to face the photosensitive drum 10, and a two-component developer G including a toner and a carrier is provided in the developing housing 21.
And a developing roll 22 is disposed at the opening of the developing housing 21. The developing roll 22 is a magnet roll 22 on which predetermined magnetic poles are arranged.
1 and a non-magnetic developing sleeve 22
2 is rotatably disposed, and the developing sleeve 22
2, the two-component developer G is carried and transported on the surface of the developing roller 2, and the developer G is transferred to a developing area between the photosensitive drum 10 and the developing roll 22.
Is to supply. In the developing housing 21, a stirring and conveying member (not shown) such as an auger that stirs and conveys the two-component developer G to the developing roll 22 and a layer thickness of the developing agent G on the developing roll 22 A regulating member (not shown) for regulating the layer thickness is provided.

The developing sleeve 22 of the developing roll 22
2, a developing bias applying device 23 is connected. The developing bias applying device 23 includes a DC bias power supply 24 for generating a DC bias, and a DC bias power supply 24
Switch 25 for turning ON / OFF at a predetermined timing, and an AC bias power supply 26 for generating an AC bias
And the AC bias power supply 26 is turned on at a predetermined timing.
And an AC switch 27 for N / OFF. In particular, in the present embodiment, the AC bias power supply 26 is, for example, a DC power supply 261 for generating a positive DC voltage (in this example, +1.5 kV is used) and a DC voltage from the DC power supply 261 is desired. O at frequency (4 kHz in this example)
The high-voltage switching element 262 for N / OFF and the capacitor 263 for stably holding the oscillation voltage switched by the high-voltage switching element 262 for a predetermined time.

Next, a developing method of the developing device according to the present embodiment will be described. In the present embodiment, the developing device 13 adopts a reversal developing method,
As shown in (a), an image portion (image portion potential VL: in this example) is irradiated on the photosensitive drum 10 initially charged to VH (−700 V in this example) by the charger 11 by beam irradiation by the exposure device 12. Under the condition that Z is formed, the developing bias VB (in this example, the DC bias VDC
Is applied to the image portion Z and the toner T
Is to make a visible image. At this time, the image part Z
The contrast potential Vcont leading to the developability for visualizing the image is | VB-VL |, which is set to 350 V in this example, and transfers the toner from the photosensitive drum 10 to the developing roll 22 side. The cleaning potential Vcln leading to the electric field in the direction is | VH-VB |
It is set to 50V.

Next, the driving of the developing device according to the present embodiment and the timing of bias application will be described. In the present embodiment, as shown in FIG. 5, after applying an AC bias (AC bias) VAC of the developing bias VB in synchronization with the ON timing of the rotation drive of the photosensitive drum 10, the rotation of the photosensitive drum 10 is started. Immediately after the drive ON timing, the charger 11 is turned on (ON), and when the area of the photosensitive drum 10 charged by the charger 11 reaches the developing position, the developing device 13 is driven (the developing roll and others are driven and rotated). ), And a control method of applying a DC bias (DC bias) VDC of the developing bias VB. In particular, in the present embodiment, the developing bias V
Among B, the difference B (corresponding to the lane portion in FIG. 5) between the rising timing of the AC bias VAC and the rising timing of the DC bias VDC is determined by the fact that the rising waveform VST of the AC bias VAC becomes stable as shown in FIG. Time to reach A
This is set as above (in this example, longer than A).

When the driving of the developing device 13 is controlled at such timing, as shown in FIG. 6, when the AC bias VAC of the developing bias VB rises, the positive rising waveform VST (+) certainly becomes the negative rising waveform VST. The potential rises more rapidly than (−), and as shown by M in FIG. 6, a potential difference ΔVST between the positive rise waveform VST (+) and the negative rise waveform VST (−) is generated. In FIG. 6, the dotted waveform defining M indicates a symmetric waveform of the negative-side rising waveform VST (-). However, while the rising waveform VST of the AC bias VAC is unstable, the DC bias VDC of the developing bias VB has not yet been applied to the developing roll 22, and the photosensitive drum 10 charged by the charger 11 has not yet been applied.
The area has not reached the development position. Therefore, even if the above-described potential difference ΔVST is generated, the potential difference ΔVST
Does not affect the cleaning potential Vcln,
No electric field for transferring the carrier to the photosensitive drum 10 is generated. Therefore, in the present embodiment, the developing bias V
When the AC bias VAC of B rises, the transfer of the carrier to the photosensitive drum 10 side is effectively suppressed. For this reason, various inconveniences (white spots during image formation, damage to the photosensitive drum 10, etc.) due to the carry-over phenomenon occurring in the previous embodiment can be effectively avoided.

In this embodiment, the developing bias VB
Timing of the AC bias VAC of the photosensitive drum 1
Although it is synchronized with the rotation drive timing of 0, it is not limited to this. For example, from the viewpoint of suppressing carrier adhesion to the entire image forming area of the photosensitive drum 10, when the photosensitive drum 10 area charged by the charger 11 reaches the developing position, the AC bias of the developing bias VB is applied. Any suitable timing may be used as long as the rising waveform VST of the VAC is stable.
Further, from the viewpoint of suppressing carrier adhesion to an actual image portion (latent image forming region) of the image-forming region of the photosensitive drum 10, as shown by a virtual line (two-dot chain line) in FIG. The AC bias V is at a timing earlier than the time at which the rising waveform VST of the AC bias VAC of the developing bias VB stabilizes at least the time B at which the image portion on the photosensitive drum 10 reaches the developing position.
AC may be applied.

Although the developing device according to the first embodiment employs the reversal developing system, the developing device is not limited to this, and it is also possible to employ the regular developing system.
In this case, as shown in FIG. 4B, for example, as shown in FIG.
V) The exposure device 1 is placed on the photoreceptor drum 10
The developing bias VB (in this example, the DC bias VDC in this example) is exposed under the condition that the background portion (background portion potential VL: -150 V in this example) other than the image portion Z is exposed by the beam irradiation by the light source 2.
Is applied to the image portion Z and the toner T
Is to make a visible image. At this time, the image part Z
The contrast potential Vcont leading to the developability for visualizing the image is | VH-VB |, which is set to 550 V in this example, and transfers the toner from the photosensitive drum 10 to the developing roll 22 side. The cleaning potential Vcln leading to the electric field in the direction is | VB-VL |
It is set to 00V.

In such a developing device of the regular developing system, even if, for example, an embodiment in which the positive DC voltage of the DC power supply 261 of the AC bias power supply 26 shown in FIG. Development drive control method (drive and bias application timing) similar to the first embodiment.
By adopting the above, various adverse effects due to carrier adhesion can be effectively eliminated. Incidentally, in the developing device of the regular developing system, FIG.
When the same AC bias power supply 26 is used, various problems caused by carrier adhesion can be effectively eliminated by the same operation as in the second embodiment described later.

Second Embodiment FIG. 7 shows a developing device according to a second embodiment of the present invention. In the present embodiment, the basic configuration of the developing device is as follows.
The second embodiment is substantially the same as the first embodiment, but includes an AC bias power supply 26 different from the first embodiment. Embodiment 1
The same components as in the first embodiment are denoted by the same reference numerals as in the first embodiment, and the detailed description thereof is omitted here. In the present embodiment, the AC bias power supply 26
Unlike DC voltage of negative polarity (-1.5 kV in this example)
DC power supply 264 that generates
Is switched by the high-voltage switching element 262, and the voltage is held by the capacitor 263. The drive and bias application timings of the developing device 13 according to the present embodiment are, for example, the timings shown in FIG. 12, that is, the charger 11 is turned on (O
N) and the photosensitive drum 1 charged by the charger 11
When the area 0 reaches the developing position, the developing device 13 is driven (the developing roll and others are driven and rotated), and a DC bias (DC bias) VDC of the developing bias VB is applied. When the electrostatic latent image is written to the developing position, the timing is controlled by applying an AC bias (AC bias) VAC of the developing bias VB.

Therefore, according to the present embodiment, as shown in FIG. 8, when the AC bias VAC of the developing bias VB rises, the negative rising waveform VS (-) is more abrupt than the positive rising waveform VST (+). 8, a potential difference ΔVST between the positive-side rising waveform VST (+) and the negative-side rising waveform VST (−) is generated as shown by a hatched portion M in FIG. In FIG. 8, a dotted waveform defining M indicates a symmetrical waveform of the positive-side rising waveform VST (+). At this time, the DC bias VDC level of the developing bias VB is equal to the potential difference ΔVS
A situation occurs in which apparently the amount changes by T minutes.

However, in the present embodiment, since the reversal development method is adopted for the photosensitive drum 10 of the negative polarity, even if the potential difference ΔVST is generated, the potential difference ΔVST has the negative potential. Therefore, the background portion potential VH
The cleaning potential Vcln (see FIG. 4A), which is the potential difference between the developing bias VB and the DC bias VDC, temporarily decreases. As a result, the cleaning potential Vcln does not temporarily increase, so that a carry-over phenomenon does not occur, and a situation such as white spots on image formation and damage to the photosensitive drum 10 due to carrier adhesion is effectively avoided. You.

Therefore, in the present embodiment, the conventional developing drive control method (driving and bias application) is performed by a simple method of changing a part of the AC bias power supply 26.
Can be followed as it is. When the same configuration as that of the second embodiment is adopted in the developing device of the regular developing system, the negative DC voltage of the DC power supply 264 of the AC bias power supply 26 shown in FIG. What is necessary is just to use the thing of the changed aspect.

Third Embodiment FIG. 9 is an explanatory view showing a developing device according to a third embodiment of the present invention. In this embodiment, the basic configuration of the developing device is substantially the same as that of the first embodiment, but is provided with an AC bias power supply 26 different from that of the first embodiment. still,
The same components as those in the first embodiment are described in the first embodiment.
The same reference numerals are given, and the detailed description is omitted here. In the present embodiment, the AC bias power supply 26
As in the first embodiment, a DC power supply 261, a high-voltage switching element 262, and a capacitor 263 are provided. However, unlike the first embodiment, a delay circuit 2 including a resistor 266 and a capacitor 267 is provided at the output terminal of the capacitor 263.
65 are connected in series. On the other hand, the drive and bias application timing of the developing device 13 according to the present embodiment are controlled, for example, at the timing shown in FIG. 12 similarly to the second embodiment.

Therefore, according to the present embodiment, as shown in FIG. 10, when the AC bias VAC of the developing bias VB rises, the rise time of the AC bias VAC is set to the reference rise time A (delay circuit) by the operation of the delay circuit 265. (The rising time when the H.265 is not used: 100 ms in this example) is set to A + α which is longer by α than α. For this reason, the rising of the AC bias VAC becomes gentle, and the positive-side rising waveform VST
Potential difference ΔVST between (+) and the negative side rising waveform VST (−)
Is reduced. Therefore, if the potential difference ΔVST
Even if the cleaning potential Vcln (see FIG. 4A), which is a potential difference between the background potential VH and the developing bias VB, increases, the increase is extremely small. Therefore, the cleaning potential Vcln increases with the cleaning potential Vcln. , Photosensitive drum 1
The amount of carriers that transfer to the 0 side can be kept extremely small.

Here, in the present embodiment, the relationship between the rise time of the AC bias VAC of the developing bias VB and the number of carriers on the photosensitive drum 10 at the time of rise (entire area in the axial direction, per 16 cm ² ) was examined. , FIG.
The result shown in FIG. 1 was obtained. However, as the experimental conditions in FIG. 11, the toner concentration is 4.82% and the toner charge amount is 2%.
A developer of 2.5 μC / g was used. According to the figure, when the rising time of the AC bias VAC is the reference rising time (100 ms.), The photosensitive drum 10
While the number of upper carriers is 17.7 per 16 cm ^{2, the} delay time α by the delay circuit 265 for the rise time of the AC bias VAC is 90 ms. , 150m
s. , 240 ms. And the number of carriers on the photosensitive drum 10 at the time of startup was checked twice, and the number of carriers on the photosensitive drum 10 was 1.4 to 16 cm ^2.
It is understood that the number is greatly reduced to about 2.4. Therefore, according to this experiment, the delay time was set to +90 ms. With the above settings, it is confirmed that the carrier adhesion phenomenon is effectively suppressed.

It is needless to say that the same configuration as that of the third embodiment can be adopted for the developing device of the regular developing system.

[0032]

As described above, according to the present invention,
In a two-component developing system using a developing bias in which an AC bias is superimposed on a DC bias, an electric field due to a potential difference between a positive rising waveform and a negative rising waveform generated at the time of the AC bias rising is regarded as a carrier transfer electric field. This prevents the carry-over phenomenon (carrier adhesion) on the latent image carrier, which occurs when the AC bias rises, and prevents white spots on the image formation due to carrier adhesion and latent image holding. Image quality degradation due to damage to the body can be reliably prevented. Further, according to the present invention, as the AC bias applying means, it is possible to use, as it is, an aspect in which at least the positive side waveform and the negative side waveform at the time of rising of the AC bias are asymmetrical. There is no concern that the cost of the apparatus itself is unnecessarily increased, and it is possible to satisfy the demand for reducing the apparatus cost.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an outline of a developing device according to the present invention.

FIG. 2 is a first embodiment of a developing device to which the present invention is applied.
FIG. 1 is an explanatory diagram illustrating an example of an image forming apparatus in which is incorporated.

FIG. 3 is an explanatory diagram illustrating details of a developing device according to the first embodiment;

4A is an explanatory diagram showing an example of a developing potential of the developing device according to the first embodiment, and FIG. 4B is an explanatory diagram showing another example of a developing potential of the developing device according to the first embodiment; is there.

FIG. 5 is a timing chart showing driving and bias application timings of the developing device according to the first embodiment.

FIG. 6 is a graph illustrating a change in a developing bias of the developing device according to the first exemplary embodiment;

FIG. 7 is an explanatory diagram showing details of a developing device according to a second embodiment.

FIG. 8 is a graph showing a change in a developing bias of the developing device according to the second embodiment.

FIG. 9 is an explanatory diagram showing details of a developing device according to a third embodiment.

FIG. 10 is a graph showing a change in a developing bias of a developing device according to a third embodiment.

FIG. 11 is an explanatory diagram showing a relationship between a rise time and the number of carriers on a photosensitive drum at the time of rise in a third embodiment;

FIG. 12 is a timing chart showing a conventional driving and bias application timing of a developing device.

FIG. 13 is a graph showing a change in a developing bias of a conventional developing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Latent image carrier, 2 ... Development roll, 3 ... Development bias application means, 4 ... DC bias application means, 5 ... AC bias application means, 6 ... Carrier transition suppression means, VB ... Development bias, VAC ... AC bias, VDC: DC bias, VST
(+): Positive rising waveform, VST (-): Negative rising waveform, t0: Time during which the rising waveform of AC bias VAC stabilizes, M: Positive rising waveform VST (+) and negative rising waveform VST (- ) And potential difference

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA22 DA32 DA38 EA05 EC11 ED02 ED03 ED09 EE02 EF06 EG06 ZA07 2H073 AA01 AA05 AA07 BA04 BA09 BA13 BA23 BA41 BA45 CA03

Claims (6)

[Claims] A developing roller facing the latent image carrier, carrying and transporting a two-component developer including a toner and a carrier on the developing roller, and applying a direct current bias to an alternating current bias on the surface of the developing roll. Is applied with a developing bias superimposed thereon, and the electrostatic latent image formed on the latent image carrier is visualized with a developer. DC bias applying means for applying AC bias, and AC bias applying means for applying an AC bias in which at least the positive side waveform and the negative side waveform at the time of rising are asymmetrical. A carrier transfer suppressing means for preventing a waveform component on a side of the developing roll from acting as an electric field for moving a carrier on a developing roll toward a latent image carrier. Developing apparatus is characterized. 2. The developing device according to claim 1, wherein the carrier transfer suppressing means is configured to control a developing area between the latent image carrier and the developing roll after a lapse of time during which a rising waveform of the AC bias is stabilized. A developing device for controlling a developing bias applying unit so as to pass at least an actual latent image forming area of a latent image forming area on a latent image carrier. 3. The developing device according to claim 2, wherein the carrier transfer suppressing means applies the AC bias at a timing at least a time before the rising timing of the AC bias is stabilized from the timing of applying the DC bias. And a developing bias control unit. 4. The developing device according to claim 2, wherein the carrier transfer suppressing unit controls the application timing of the AC bias by the AC bias applying unit in synchronization with the driving start timing or the charging start timing of the latent image carrier. A developing device. 5. The developing device according to claim 1, wherein the carrier transition suppressing means includes an electric field in which a waveform component on a rapidly changing side of the rising waveform of the AC bias presses the carrier on the developing roll toward the developing roll. An AC bias applying means configured to function as a developing device. 6. The developing device according to claim 1, wherein the carrier transfer suppressing means extends and adjusts a rising time of the AC bias, and corrects a positive rising waveform and a negative rising waveform of the AC bias substantially symmetrically. A developing device, characterized in that: