JP3716899B2 - Development device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device applied to an image forming apparatus such as a copying machine or a printer such as an electrophotographic system or an electrostatic recording system, and in particular, a developing bias in which an AC bias is superimposed on a DC bias is applied to a developing roll. The present invention relates to an improvement of a two-component developing system developing device in which a two-component developer comprising a toner and a carrier is used.
[0002]
[Prior art]
Conventionally, as a developing device of this type of two-component development system, for example, a developing roll is disposed facing a photosensitive drum as a latent image carrier, and a two-component developer composed of a toner and a carrier is provided on the developing roll. Furthermore, a predetermined developing electric field is formed between the developing roll and the photosensitive drum by applying a predetermined developing bias to the developing roll, and the electrostatic potential on the photosensitive drum is generated by the action of the developing electric field. The image is visualized with toner on the developing roll.
Here, as the developing bias, only a DC bias may be used. However, from the viewpoint of further improving the developability, by using a DC bias in which an AC bias is superimposed, it is possible to use the developing bias on the developing roll. It is preferable to increase the developability by applying an oscillating electric field to the developer to increase the number of times the toner flies between the photosensitive drum and the developing roll.
[0003]
[Problems to be solved by the invention]
By the way, in such a two-component developing system developing device, for example, as shown in FIG. 12, when the photosensitive drum rotates, the charger is turned on substantially simultaneously, and the photosensitive drum area charged by the charger is turned on. When the toner reaches the developing position, the developing device is driven (developing roll and others are driven and rotated), and a DC bias (DC bias) of the developing bias is applied. A control method is employed in which an AC bias (AC bias) of the developing bias is applied when the portion where () is written) reaches the developing position.
However, when such a control method is employed, a carry-over phenomenon (so-called BCO: Bead Carry Over) occurs in which carriers are transferred to the photosensitive drum side when AC bias rises (ON timing). In image formation, it was easy to lead to image quality defects such as white spots, and the photosensitive drum was easily damaged along with carrier adhesion.
[0004]
The present inventors have sought the cause of such a technical problem, and have found that the waveform shape at the time of AC bias rising has an influence.
That is, as an AC bias power source in this type of developing device, one that generates an AC bias by turning ON / OFF the DC power source at a predetermined frequency may be used from the viewpoint of cost reduction, for example. .
The AC bias VAC generated by this type of AC bias power source is caused by the power source configuration, for example, as shown in FIG. 13, the positive waveform VST (+) and the negative side at the time of rising (A region in the figure). The waveform VST (-) becomes asymmetric. In FIG. 13, VP-P represents the peak-to-peak voltage of the AC bias VAC.
[0005]
At this time, for example, when a reversal development method (a method in which an exposure part is developed as an image part) is adopted for a negative photosensitive drum, as shown in FIG. When +) is a mode that rises more rapidly than the negative waveform VST (-), as shown by the hatched portion M in FIG. 13, the positive waveform VST (+) and the negative waveform VST (-) During this time, the potential difference ΔVST is generated, and the DC bias VDC level of the developing bias apparently changes by the potential difference ΔVST.
As a result, the potential difference between the background portion potential VH and the DC bias VDC of the developing bias (hereinafter referred to as a cleaning potential if necessary) temporarily increases. It is presumed that the over phenomenon occurs.
This type of carry-over phenomenon occurs when a normal development operation is performed with a DC bias applied, and does not occur when a DC bias is not applied.
[0006]
To avoid this type of carry-over phenomenon, it is sufficient to use a method that uses an AC power supply without using a method that vibrates the DC bias. In addition, when adopting a method of vibrating the AC bias, it may be possible to oscillate the DC bias at a low level and amplify it with a transformer or the like. There are aspects that do not meet the demand for lower prices, and none of them are desirable.
[0007]
The present invention has been made in order to solve the above technical problem, and is capable of reducing the carry-over phenomenon (carrier adhesion) to the latent image carrier at the time of AC bias rising while satisfying the demand for cost reduction of the apparatus. It is an object of the present invention to provide a developing device that reliably avoids various problems associated with carrier adhesion.
[0008]
[Means for Solving the Problems]
That is, as shown in FIG. 1, the present invention has a developing roller 2 facing the latent image carrier 1, and carries and conveys a two-component developer G composed of toner and carrier on the developing roller 2. 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, and an electrostatic latent image formed on the latent image carrier 1 is visualized with a developer G. In the developing device, the developing bias applying means 3 includes a DC bias applying means 4 for applying a DC bias VDC, and at least a positive waveform VST (+) and a negative waveform VST (-) at the time of rising. AC bias applying means 5 for applying an AC bias VAC having an asymmetrical bias, while the waveform component on the side of the rising waveform of the AC bias VAC that suddenly changes the carrier on the developing roll 2 as the latent image carrier 1. It is characterized in that a carrier transition inhibition means 6 for inhibiting the acting as a field of shifting provided to.
[0009]
In such a technical means, the developing device according to the present application uses the two-component developer G and develops the developing bias VB in which the AC bias VAC is superimposed on the DC bias VDC. The mode may be such that the developer G contacts the latent image carrier 1 in the region, or may be a mode in which the developer G is disposed in a non-contact manner. Further, 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 used as a background portion and a non-exposed portion is developed as an image portion. Good.
[0010]
The developing bias applying means 3 includes a DC bias applying means 4 and an AC bias applying means 5, and the AC bias applying means 5 is at least a positive waveform VST (+) and a negative waveform at the time of rising. Any AC bias VAC that is asymmetric with VST (-) may be used.
Here, a typical example of the AC bias applying means 5 is a mode in which a DC power source is turned on / off at a predetermined frequency. In this mode, if a positive DC power source is used, an AC bias is used. Of the rising waveform of VAC, the positive waveform VST (+) rises more rapidly than the negative waveform VST (-). On the other hand, if a negative polarity DC power supply is used, the negative waveform of the rising waveform of AC bias VAC The waveform VST (-) rises more rapidly than the positive waveform VST (+).
[0011]
Further, the carrier transition inhibiting means 6 may be appropriately selected as long as it suppresses carrier transition due to the waveform component on the rapidly changing side of the rising waveform of the AC bias VAC. After the time t0 when the rising waveform of the bias VAC stabilizes, at least the actual area where latent images can be formed on the latent image carrier 1 with respect to the development area between the latent image carrier 1 and the developing roll 2 is actually measured. A device that controls the developing bias applying means 3 so as to pass through the latent image forming region is mentioned.
At this time, the application timing of the DC bias VDC needs to be turned ON when the leading end of the latent image formable area (for example, the initial charging area by the charging unit) reaches the developing area. It is necessary to always keep the bias VDC synchronized with the development area so that no toner band or BCO is generated in the background area.
Here, from the viewpoint of surely avoiding the carry-over phenomenon, the AC bias VAC is applied at a timing that is at least a time t0 before the rising waveform of the AC bias VAC stabilizes from the timing at which the DC bias VDC is applied. In addition, it is preferable to control the developing bias applying means 3.
Further, in the first mode of the carrier transfer inhibiting means 6, the AC bias applying means 5 is controlled from the viewpoint of simplifying the configuration and stabilizing the operation, or the driving start timing of the latent image carrier 1 or It is preferable to control the application timing of the AC bias VAC by the AC bias applying means 5 in synchronization with the charging start timing.
[0012]
Further, as a second mode of the carrier transfer inhibiting means 6, the waveform component on the abruptly changing side of the rising waveform of the AC bias VAC acts as an electric field in the direction of pressing the carrier on the developing roll 2 toward the developing roll 2. As described above, one constituting the AC bias applying means 5 can be mentioned.
In this aspect, the waveform component on the side that rapidly changes in the rising waveform of the AC bias VAC acts in the opposite direction to the electric field that transfers the carrier on the developing roll 2 to the latent image carrier 1 side. It does not lead to the so-called carryover phenomenon.
[0013]
Further, as a third mode of the carrier transfer inhibiting means 6, the rising time t0 of the AC bias VAC is extended and adjusted, and the positive rising waveform VST (+) and the negative rising waveform VST (-) of the AC bias VAC are obtained. One that corrects substantially symmetrically is mentioned.
According to this aspect, since the potential difference between the positive rising waveform VST (+) and the negative rising waveform VST (−) of the AC bias VAC is suppressed, the carrier on the developing roll 2 is generated when the AC bias VAC rises. The electric field itself that moves toward the latent image carrier 1 does not increase rapidly, and the so-called carry-over phenomenon is effectively suppressed.
[0014]
Next, the operation of the technical means described above will be described.
In FIG. 1, the developing bias applying means 3 includes a DC bias applying means 4 and an AC bias applying means 5.
At this time, the AC bias VAC applied by the AC bias applying means 5 has at least a positive waveform VST (+) and a negative waveform VST (-) at the time of rising, that is, both. The balance is broken.
Now, as indicated by the hatched portion M in FIG. 1, the potential difference between the positive rising waveform VST (+) and the negative rising waveform VST (-) causes the carrier on the developing roll 2 to move to the latent image carrier 1 side. Even if it acts in the direction of shifting, in this application, the carrier transfer inhibiting means 6 works, and the potential difference M acts as an electric field for shifting the carrier on the developing roll 2 to the latent image carrier 1 side. Deter.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 2 shows an example of an image forming apparatus incorporating Embodiment 1 of the developing device according to the present invention.
In the figure, reference numeral 10 denotes a negative photosensitive drum as a latent image carrier, 11 denotes a charger such as a corotron for charging the photosensitive drum 10, and 12 denotes an electrostatic latent image on the charged photosensitive drum 10. An exposure device such as a laser scanning device for writing the image, 13 is a two-component developing type developing device that visualizes the electrostatic latent image formed on the photosensitive drum 10 with a developer, and 14 is on the photosensitive drum 10 A transfer device such as a corotron for transferring the toner image on a recording sheet (not shown) such as paper, 15 a sheet peeling static eliminator such as a corotron for peeling the recording sheet from the photosensitive drum 10, and 16 a photosensitive drum. A cleaner 17 for cleaning the residual toner on 10, and a charge eliminator 17 such as a lamp for removing residual charges on the photosensitive drum 10.
[0016]
In this embodiment, as shown in FIGS. 2 and 3, the developing device 13 has a developing housing 21 that opens to face the photosensitive drum 10, and the developing housing 21 includes a two-component composed of toner and a carrier. The developer G is accommodated, and a developing roll 22 is disposed in the opening of the developing housing 21.
The developing roll 22 has a magnet roll 221 having predetermined magnetic poles arranged in a fixed manner, and a non-magnetic developing sleeve 222 rotatably disposed around the developing roll 222. The developer G is carried and conveyed, and the developer G is supplied to the developing area between the photosensitive drum 10 and the developing roll 22.
In the developing housing 21, the agitating / conveying member (not shown) such as an auger that agitates and conveys the two-component developer G and supplies it to the developing roll 22, and the layer thickness of the developer G on the developing roll 22 are set. A layer thickness regulating member (not shown) for regulating is disposed.
[0017]
A developing bias applying device 23 is connected to the developing sleeve 222 of the developing roll 22.
The developing bias applying device 23 includes a DC bias power source 24 that generates a DC bias, a DC switch 25 that turns the DC bias power source 24 ON / OFF at a predetermined timing, an AC bias power source 26 that generates an AC bias, An AC switch 27 for turning ON / OFF the AC bias power supply 26 at a predetermined timing is provided.
In particular, in the present embodiment, the AC bias power supply 26 desires a DC power supply 261 that generates, for example, a positive DC voltage (in this example, +1.5 kV is used) and a DC voltage from the DC power supply 261. A high-voltage switching element 262 that is turned ON / OFF at a frequency (4 kHz in this example) and a capacitor 263 that stably holds an oscillating voltage switched by the high-voltage switching element 262 for a predetermined time.
[0018]
Next, the developing method of the developing device according to the present embodiment will be described.
In the present embodiment, the developing device 13 employs a reversal developing method, and as shown in FIG. 4A, a photosensitive drum that is initially charged to VH (−700 V in this example) by the charger 11. A developing bias VB (DC bias VDC is -550 V in this example) is applied under the condition that an image part (image part potential VL: -200 V in this example) Z is formed on 10 by beam irradiation by the exposure device 12. The image portion Z is visualized with the toner T when applied.
At this time, the contrast potential Vcont leading to developability for making the image portion Z visible is | VB−VL |, which is set to 350 V in this example, and the toner is developed from the photosensitive drum 10. The cleaning potential Vcln that leads to the electric field in the direction of transfer to the roll 22 side is | VH−VB |, which is set to 150 V in this example.
[0019]
Next, driving of the developing device and bias application timing according to the present embodiment will be described.
In the present embodiment, as shown in FIG. 5, after applying the AC bias (AC bias) VAC of the developing bias VB in synchronization with the ON timing of the rotational drive of the photosensitive drum 10, the rotation of the photosensitive drum 10 is performed. Immediately after the driving 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 the like are driven and rotated). And a control method of applying a direct current bias (DC bias) VDC of the developing bias VB is employed.
In particular, in the present embodiment, of the developing bias VB, the difference B between the rising timing of the AC bias VAC and the rising timing of the DC bias VDC (in FIG. 5).Diagonal lineAs shown in FIG. 6, the portion corresponding to the portion is set to a time A or longer (longer than A in this example) until the rising waveform VST of the AC bias VAC is stabilized.
[0020]
When the developing device 13 is driven and 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 (+) is certainly the negative rising waveform VST (-). As shown by M in FIG. 6, a potential difference ΔVST between the positive rising waveform VST (+) and the negative rising waveform VST (−) is generated. In FIG. 6, the dotted waveform that divides M shows a symmetrical waveform of the negative 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 is not yet applied to the developing roll 22, and the photosensitive drum 10 region charged by the charger 11 is not yet applied. Has not reached the development position.
For this reason, even if the above-described potential difference ΔVST is generated, the potential difference ΔVST does not affect the cleaning potential Vcln, and an electric field for transferring the carrier to the photosensitive drum 10 side is not generated.
Therefore, in the present embodiment, the carrier transfer to the photosensitive drum 10 side is effectively suppressed when the AC bias VAC rises in the developing bias VB.
For this reason, various problems (such as white spots at the time of image formation and damage to the photosensitive drum 10) that are caused in the previous embodiment can be effectively avoided.
[0021]
In the present embodiment, the application timing of the AC bias VAC of the developing bias VB is synchronized with the rotation driving timing of the photosensitive drum 10, but the present invention is not limited to this.
For example, from the viewpoint of suppressing carrier adhesion to the entire image formable area of the photosensitive drum 10, the AC bias of the developing bias VB is reached when the photosensitive drum 10 area charged by the charger 11 reaches the developing position. Any timing may be selected as long as the VAC rising waveform VST is stable.
Further, from the viewpoint of suppressing carrier adhesion to an actual image portion (latent image formation region) in the image formable region of the photosensitive drum 10, as indicated by a virtual line (two-dot chain line) in FIG. At least the AC bias VAC is applied at a timing earlier than the time when the image portion on the photosensitive drum 10 reaches the developing position by a time B that exceeds the rising waveform VST of the AC bias VAC of the developing bias VB. That's fine.
[0022]
Further, the developing device according to the first embodiment adopts the reversal development method, but is not limited to this, and a regular development method can also be adopted.
In this case, as shown in FIG. 4B, for example, the developing device 13 is irradiated with a beam by the exposure device 12 on the photosensitive drum 10 initially charged to VH (in this example, −800 V) by the charger 11. A developing bias VB (DC bias VDC is −250 V in this example) is applied under a condition for exposing a background part (background part potential VL: −150 V in this example) other than the image part Z, and the image part Z Is visualized with toner T.
At this time, the contrast potential Vcont leading to developability for making the image portion Z visible is | VH−VB |, which is set to 550 V in this example, and the toner is developed from the photosensitive drum 10. The cleaning potential Vcln that leads to the electric field in the direction of transfer to the roll 22 side is | VB−VL |, and is set to 100 V in this example.
[0023]
In such a development device of the normal development system, for example, even if a device in which the positive DC voltage of the DC power supply 261 of the AC bias power supply 26 shown in FIG. By adopting the same development drive control method (drive and bias application timing), various problems due to carrier adhesion can be effectively eliminated.
When the AC bias power supply 26 similar to that shown in FIG. 3 is used in the regular development type developing device, various adverse effects due to carrier adhesion are effectively eliminated by the same action as in the second embodiment described later.
[0024]
Embodiment 2
FIG. 7 shows a second embodiment of a developing device to which the present invention is applied.
In the present embodiment, the basic configuration of the developing device is substantially the same as that of the first embodiment, but includes an AC bias power supply 26 different from that of the first embodiment. Components similar to those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof is omitted here.
In the present embodiment, unlike the first embodiment, the AC bias power supply 26 uses a DC power supply 264 that generates a negative DC voltage (−1.5 kV in this example), and a DC voltage from the DC power supply 264 is used. Are switched by the high voltage switching element 262 and the voltage is held by the capacitor 263.
Further, regarding the drive and bias application timing of the developing device 13 according to the present embodiment, for example, the timing shown in FIG. 12, that is, the charging device 11 is turned on (ON) substantially at the same time as the photosensitive drum 10 rotates. When the area of the photosensitive drum 10 charged by the device 11 reaches the developing position, the developing device 13 is driven (developing roll and others are driven and rotated), and a DC bias (DC bias) VDC of the developing bias VB is applied. Thereafter, when the image portion (the portion where the electrostatic latent image is written by the exposure apparatus) reaches the development position, the control is performed at the timing of applying the AC bias (AC bias) VAC of the development bias VB. ing.
[0025]
Therefore, according to the present embodiment, as shown in FIG. 8, when the developing bias VB rises in the AC bias VAC, the negative rising waveformV ST(-) Rises more rapidly than the positive rising waveform VST (+), and as shown by the hatched portion M in FIG. 8, between the positive rising waveform VST (+) and the negative rising waveform VST (-). A potential difference ΔVST is generated. In FIG. 8, a dotted waveform that divides M indicates a symmetrical waveform of the positive rising waveform VST (+).
At this time, the DC bias VDC level of the developing bias VB apparently changes by the potential difference ΔVST.
[0026]
However, in this embodiment, since the reversal development method is adopted for the negative photosensitive drum 10, even if the potential difference ΔVST is generated, the potential difference ΔVST is a negative potential. The cleaning potential Vcln (see FIG. 4A), which is a potential difference between the background portion potential VH and the DC bias VDC of the developing bias VB, temporarily decreases.
For this reason, since the cleaning potential Vcln does not increase temporarily, a carry-over phenomenon does not occur, and the situation of white spots on image formation and damage to the photosensitive drum 10 due to carrier adhesion is effectively avoided. The
[0027]
Therefore, in the present embodiment, it is possible to follow the conventional development drive control method (drive and bias application) as it is, with a simple method of changing a part of the AC bias power supply 26.
In the case of adopting the same configuration as that of the second embodiment in the development device of the regular development system, the negative DC voltage of the DC power supply 264 of the AC bias power supply 26 shown in FIG. 7 is changed to the positive DC voltage. What is necessary is just to use the thing of the changed aspect.
[0028]
Embodiment 3
FIG. 9 is an explanatory view showing Embodiment 3 of the developing device to which the present invention is applied.
In this embodiment, the basic configuration of the developing device is substantially the same as that of the first embodiment, but includes an AC bias power supply 26 different from that of the first embodiment. Components similar to those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof is omitted here.
In the present embodiment, the AC bias power supply 26 includes a DC power supply 261, a high-voltage switching element 262, and a capacitor 263, as in the first embodiment. However, unlike the first embodiment, the output of the capacitor 263 is further increased. A delay circuit 265 including a resistor 266 and a capacitor 267 is connected in series at the end.
On the other hand, the drive and bias application timing of the developing device 13 according to this embodiment.InAs in the second embodiment, the control is performed at the timing shown in FIG.
[0029]
Therefore, according to the present embodiment, as shown in FIG. 10, when the AC bias VAC rises in the developing bias VB, the delay time 265 causes the rise time of the AC bias VAC to be the reference rise time A (using the delay circuit 265). Rise time when not: (in this example, 100 ms.) Is set to A + α, which is longer by α.
For this reason, the rising of the AC bias VAC becomes gentle, and the potential difference ΔVST between the positive rising waveform VST (+) and the negative rising waveform VST (−) is suppressed to that extent.
Therefore, even if the cleaning potential Vcln (see FIG. 4A), which is a potential difference between the background portion potential VH and the developing bias VB, increases due to the potential difference ΔVST, the increase is very small, so that the cleaning is performed. As the potential Vcln increases, the amount of carriers transferred to the photosensitive drum 10 side can be suppressed to an extremely small amount.
[0030]
Here, in this embodiment, the rising 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 rising (the entire axial direction, 16 cm).²The relationship shown in FIG. 11 was obtained.
However, as an experimental condition in FIG. 11, a developer having a toner concentration of 4.82% and a toner charge amount of 22.5 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 number of carriers on the photosensitive drum 10 is 16 cm.²The delay time α by the delay circuit 265 is set to 90 ms. 150 ms. 240 ms. When the number of carriers on the photosensitive drum 10 at the time of rising was checked twice, the number of carriers on the photosensitive drum 10 was 16 cm.²It is understood that the number is significantly reduced to about 1.4 to 2.4 per hit.
Therefore, according to this experiment, the delay time is +90 ms. If set to the above, it is confirmed that the carrier adhesion phenomenon is effectively suppressed.
[0031]
Of course, it is possible to adopt the same configuration as that of the third embodiment for the development device of the regular development system.
[0032]
【The invention's effect】
As described above, according to the present invention, in a two-component developing type developing device using a developing bias in which an AC bias is superimposed on a DC bias, a positive rising waveform and a negative rising waveform generated when the AC bias rises. Is prevented from acting as a carrier transition electric field, so that it is possible to prevent the carry-over phenomenon (carrier adhesion) to the latent image carrier that occurs when the AC bias rises. It is possible to reliably prevent image quality deterioration due to white spots on image formation due to adhesion and damage to the latent image carrier.
Further, according to the present invention, as the AC bias applying means, it is possible to use an aspect in which at least the positive waveform and the negative waveform at the time of rising of the AC bias are asymmetric as they are, so that the AC bias applying means There is no concern that the cost itself increases unnecessarily, and it is possible to satisfy the demand for lowering the device cost.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an outline of a developing device according to the present invention.
FIG. 2 is an explanatory diagram showing an example of an image forming apparatus incorporating the first embodiment of a developing device to which the present invention is applied;
FIG. 3 is an explanatory diagram illustrating details of the developing device according to the first embodiment.
4A is an explanatory diagram illustrating an example of the developing potential of the developing device according to the first embodiment, and FIG. 4B is an explanatory diagram illustrating another example of the developing potential of the developing device according to the first embodiment. is there.
FIG. 5 is a timing chart showing drive and bias application timings of the developing device according to the first embodiment.
FIG. 6 is a graph showing a change in developing bias of the developing device according to the first embodiment.
FIG. 7 is an explanatory diagram illustrating details of the developing device according to the second embodiment.
FIG. 8 is a graph showing a change in developing bias of the developing device according to the second embodiment.
FIG. 9 is an explanatory diagram illustrating details of the developing device according to the third embodiment.
FIG. 10 is a graph showing a change in the developing bias of the developing device according to the third embodiment.
FIG. 11 is an explanatory diagram showing a relationship between a rising time and the number of carriers on the photosensitive drum at the time of rising in the third embodiment.
FIG. 12 is a timing chart showing driving and bias application timings of a conventional developing device.
FIG. 13 is a graph showing changes in the developing bias of a conventional developing device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Latent image carrier, 2 ... Developing roll, 3 ... Development bias application means, 4 ... DC bias application means, 5 ... AC bias application means, 6 ... Carrier transfer suppression means, VB ... Development bias, VAC ... AC bias, VDC ... DC bias, VST (+) ... Positive rising waveform, VST (-) ... Negative rising waveform, t0 ... Time when AC bias VAC rising waveform is stable, M ... Positive rising waveform VST (+) and negative Potential difference with side rising waveform VST (-)

Claims (6)

A developing roll is provided opposite the latent image carrier, and a two-component developer composed of toner and carrier is carried on the developing roll, and an AC bias is superimposed on a DC bias on the surface of the developing roll. In a developing device in which a developing bias is applied and the electrostatic latent image formed on the latent image carrier is visualized with a developer,
The development bias applying means includes a DC bias applying means for applying a DC bias, and an AC bias applying means for applying an AC bias having at least a positive waveform and a negative waveform at the time of rising.
Development characterized in that a carrier transfer inhibiting means is provided for inhibiting the waveform component on the rapidly changing side of the rising waveform of the AC bias from acting as an electric field for transferring the carrier on the developing roll to the latent image carrier side. apparatus. The developing device according to claim 1,
The carrier transfer suppression means has at least one of the latent image formable regions on the latent image carrier with respect to the development region between the latent image carrier and the developing roll after the time when the rising waveform of the AC bias stabilizes. A developing device that controls a developing bias applying unit so as to pass through an actual latent image forming region. The developing device according to claim 2, wherein
The carrier transfer inhibiting means controls the developing bias applying means so that the AC bias is applied at a timing before the timing at which the rising waveform of the AC bias is stabilized at least before the timing at which the DC bias is applied. A developing device. The developing device according to claim 2, wherein
The developing device characterized in that the carrier transfer suppression means controls the application timing of the AC bias by the AC bias application means in synchronization with the drive start timing or charging start timing of the latent image carrier. The developing device according to claim 1,
The carrier transfer suppression means is configured as an AC bias application means so that the waveform component on the side of the AC bias rising rapidly acting on the developing roll acts as an electric field in the direction of pressing the carrier on the developing roll toward the developing roll side. A developing device. The developing device according to claim 1,
The developing device characterized in that the carrier transfer suppression means extends and adjusts the rising time of the AC bias, and corrects the positive rising waveform and the negative rising waveform of the AC bias substantially symmetrically.

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