JP5232805B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to development of an electrostatic latent image executed in an image forming apparatus.

  The electrophotographic technology develops an electrostatic latent image formed on a photosensitive drum by supplying toner to a photosensitive drum from a roller called a developing roller. Touchdown development is one of the development methods used in electrophotographic technology. In touchdown development, an electrostatic latent image is developed by the following process. From a magnetic brush composed of a two-component developer and formed on a magnetic roller, toner is supplied to the developing roller by a two-component developing method to form a toner thin film on the developing roller. A bias in which a DC voltage and an AC voltage are superimposed is applied to the developing roller, and the toner is ejected from the developing roller at a position facing the developing roller and the photosensitive drum to supply the toner to the photosensitive drum. As a result, the electrostatic latent image formed on the photosensitive drum is developed.

  In order to speed up development in electrophotographic technology, there is a technology for supplying toner to an electrostatic latent image formed on a photoreceptor belt with two developing rollers (see Patent Document 1).

JP 2007-33587 A

  In the touch-down development, toner is supplied to the electrostatic latent image while jumping the toner at a position where the developing roller and the photosensitive drum face each other. Some toner returns to the developing roller without being supplied to the electrostatic latent image. If the balance between the toner supplied to the electrostatic latent image and the toner returning to the developing roller is lost, the image quality of the image is lowered.

  A solid image and a half image are used when evaluating the image quality of an image formed by the image forming apparatus. A solid image is a high-density image recorded on the entire surface of a sheet. A half image is a dot image, for example, an image formed by supplying toner once to four dots. It is desirable that both the solid image and the half image are uniform images.

  In an electrostatic latent image of a solid image, an electric field is large at the trailing edge of the electrostatic latent image due to the edge effect. Therefore, the balance is lost and toner accumulates at the trailing edge of the solid toner image. As a result, the image quality of the solid image is lowered.

  The distance between the photosensitive drum and the developing roller opposite to each other, that is, the gap varies depending on the rotation of the photosensitive drum and the developing roller. This causes unevenness in the pitch between dots of the toner image in the half image. Since the half image is a dot image, the electrostatic latent image of the half image has a weak electric field. For this reason, the electrostatic latent image of a half image is difficult to develop, and if the development speed increases, the developability decreases and the unevenness becomes severe. Although unevenness can be suppressed by increasing the bias applied to the developing roller, there is a problem that the toner accumulates in a solid image.

  An object of the present invention is to provide an image forming apparatus capable of forming a uniform solid image and a half image even when the development speed is increased.

  An image forming apparatus according to an aspect of the present invention that achieves the above object is provided with an image carrier, and the electrostatic latent image formed on the image carrier is arranged to face the image carrier. A first roller that is sometimes used to supply toner to the electrostatic latent image, and is disposed opposite the image carrier downstream of the first roller in the rotational direction of the image carrier. A developing device including a second roller used for rearranging the toner supplied to the electrostatic latent image during the development, and an AC voltage continuously applied during the development. A first roller power supply unit that generates a bias in which a DC voltage is superimposed and is applied to the first roller, and a blank pulse bias in which the DC voltage is superimposed on an AC voltage that is intermittently applied during the development. By generating and applying to the second roller A second roller power source unit to rearrange the toner to the second roller, characterized by comprising a.

  According to this configuration, developability is improved by applying a bias in which a DC voltage is superimposed on a continuously applied AC voltage to the first roller. As a result, even when the development speed is increased, the unevenness of the pitch between the dots of the toner image can be suppressed in the half image, so that a uniform half image can be obtained. In addition, a second roller is disposed downstream of the first roller in the rotation direction of the image carrier. A blank pulse bias obtained by superimposing the DC voltage on the AC voltage applied intermittently is applied to the second roller on the downstream side. Thus, the toner is peeled off from the electrostatic latent image, and the toner is rearranged by supplying the toner to the electrostatic latent image again while moving the toner. Accordingly, it is possible to suppress the toner from accumulating at the trailing edge of the toner image in the solid image, so that a uniform solid image can be obtained.

  In the above configuration, a bias pulse generated by the first roller power source and applied to the first roller and a blank pulse generated by the second roller power source and applied to the second roller The bias can be such that the duty ratio and frequency of the AC voltage are the same.

  According to this configuration, it is possible to prevent the bias and the blank bias from interfering with each other and disturbing the waveforms of these biases.

  In the above configuration, the developing device conveys the two-component developer by rotating while carrying the two-component developer, and the toner in the two-component developer is opposed to the first and second rollers. A third roller used to supply the first and second rollers to the first roller by applying a bias generated by the first roller power supply, The toner may be supplied from the first roller to the electrostatic latent image formed on the image carrier by flying the toner.

  In this configuration, the present invention is applied to an image forming apparatus of a touch-down development system.

  According to the present invention, uniform solid images and half images can be formed even if the development speed is increased.

1 is a diagram illustrating an outline of an internal structure of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus. FIG. 2 is a view showing a cross section of a pair of photosensitive drums and a developing device provided in the image forming apparatus. It is a block diagram which shows the structure of the power supply part for 2nd rollers. It is a figure which shows an example of the bias applied to the 1st roller, Comprising: The bias which superimposed the DC voltage on the AC voltage applied continuously. It is a figure which shows an example of the blank pulse bias which is a bias applied to a 2nd roller, Comprising: A DC voltage is superimposed on the AC voltage applied intermittently. It is a table | surface which shows the experimental result of a comparative example. It is a table | surface which shows the experimental result of an Example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an outline of the internal structure of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 is a tandem color printer. The image forming apparatus 1 includes a sheet storage unit 110, an image forming unit 130, and a fixing unit 160.

  The sheet storage unit 110 is disposed at the lowermost part of the image forming apparatus 1 and includes a sheet tray 111 that can store a bundle of sheets P. The paper tray 111 is inserted into the image forming apparatus 1 and attached. When replenishing the paper P, the paper tray 111 is pulled out from the image forming apparatus 1. In the bundle of sheets P stored in the sheet tray 111, the uppermost sheet P is fed out toward the sheet conveyance path 115 by driving the pickup roller 113. The paper P is transported to the image forming unit 130 through the paper transport path 115.

  The image forming unit 130 forms a toner image on the conveyed paper P. The image forming unit 130 includes a magenta unit 133M, a cyan unit 133C, a yellow unit 133Y, and a black unit 133Bk, which are arranged in tandem according to the order in which the toner images are transferred to the transfer belt 131. These units have the same configuration, and a magenta unit 133M will be described as an example.

  The magenta unit 133M includes a photosensitive drum 135. Around the photosensitive drum 135, a charger 137, an exposure device 139, a developing device 141, and a cleaner 143 are arranged. The charger 137 uniformly charges the peripheral surface of the photosensitive drum 135. The exposure device 139 generates light corresponding to magenta data in the image data transmitted from a personal computer or the like, and irradiates the circumferential surface of the uniformly charged photosensitive drum 135. As a result, an electrostatic latent image corresponding to the magenta data is formed on the peripheral surface of the photosensitive drum 135. In this state, by supplying magenta toner from the developing device 141 to the peripheral surface of the photosensitive drum 135, a toner image corresponding to magenta data is formed on the peripheral surface.

  The transfer belt 131 can move in the D direction (clockwise) while being sandwiched between the photosensitive drum 135 and the primary transfer roller 145. The toner image corresponding to the magenta data is transferred from the photosensitive drum 135 to the transfer belt 131. The magenta toner remaining on the peripheral surface of the photosensitive drum 135 is removed by the cleaner 143. The above is the description of the magenta unit 133M.

  A toner image corresponding to magenta data is transferred to the transfer belt 131, and a toner image corresponding to cyan data is transferred onto the toner image. Similarly, a toner image corresponding to yellow data and a toner corresponding to black data are transferred. The image is transferred in layers. As a result, a color toner image is formed on the transfer belt 131. This color toner image is transferred by the secondary transfer roller 149 onto the paper P conveyed from the paper storage unit 110 described above.

  The sheet P on which the color toner image is transferred is sent to the fixing unit 160. The fixing unit 160 includes a heating roller 161 and a pressure roller 163. The paper P on which the color toner image is transferred is sandwiched between these rollers. As a result, heat and pressure are applied to the color toner image, and the color toner image is fixed to the paper P. The paper P is discharged to the paper discharge unit 169.

  FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus 1 shown in FIG. The image forming apparatus 1 includes a sheet storage unit 110, an image forming unit 130, a fixing unit 160, a control unit 200, an operation display unit 300, a first roller power unit 61, a second roller power unit 63, and a third roller. The power supply units 65 for use are connected to each other by a bus. The sheet storage unit 110, the image forming unit 130, and the fixing unit 160 have been described with reference to FIG.

  The control unit 200 includes a micro processing unit (MPU), a read only memory (ROM), a random access memory (RAM), and an image memory. The MPU performs control necessary for operating the image forming apparatus 1 on the hardware constituting the image forming apparatus 1. The ROM stores software necessary for controlling the operation of the image forming apparatus 1. The RAM is used for temporary storage of data generated during execution of software, storage of application software, and the like. The image memory temporarily stores image data (such as image data transmitted from a personal computer).

  The operation display unit 300 is provided with operation keys and a display screen. The display screen displays various operations and details of operations.

  The first roller power supply unit 61, the second roller power supply unit 63, and the third roller power supply unit 65 supply a bias obtained by superimposing a DC voltage and an AC voltage to the developing device 141, and the bias is supplied to the developing device 141. Apply to the roller in the developing device 141. These power supply units will be described in detail later.

  Next, the configuration and operation of the developing device 141 will be described. FIG. 3 is a view showing a cross section of a pair of the photosensitive drum 135 and the developing device 141. The photosensitive drum 135 is an example of an image carrier. The developer used in the developing device 141 is a two-component developer. The toner and carrier constituting the two-component developer are not shown. Since the elements constituting the developing device 141 and the like are expressed by omitting the thickness, they are not hatched.

  The developing device 141 includes a first roller 9, a second roller 11, a third roller 13, stirring screws 15 and 17, and a casing 19 that accommodates these.

  The stirring screws 15 and 17 are disposed in the stirring chamber 21 in the housing 19. The stirring chamber 21 is divided into two stirring spaces 25 and 27 by a partition plate 23. The stirring screw 17 is disposed in the stirring space 25, and the stirring screw 15 is disposed in the stirring space 27. Two-component developers are accommodated in the stirring spaces 25 and 27.

  The two-component developer is stirred by rotating the stirring screws 15 and 17. As a result, the toner and the carrier are frictionally charged, and the toner and the carrier are electrostatically coupled. Of the two-component developer in this state, the two-component developer accommodated in the stirring space 27 is pumped up by the third roller 13 by magnetic force.

  The third roller 13 is called a magnetic roller, and is disposed in the housing 19 so as to face the stirring screw 15, the first roller 9, and the second roller 11. A portion where the third roller 13 faces the first roller 9 is a facing portion 37-1, and a portion facing the second roller 11 is a facing portion 37-2. The third roller 13 is disposed below the first roller 9 and the second roller 11.

  The third roller 13 covers the non-rotating portion 29 in a state having a gap with the peripheral surface 31 provided in the non-rotating portion 29. The non-rotating portion 29 has a thick cylindrical shape, and the shaft 33 is rotatably disposed in the cylinder. The third roller 13 is fixed to the shaft 33. The third roller 13 rotates in the rotation direction R3 along the peripheral surface 31 as the shaft 33 rotates.

  On the peripheral surface 31 of the non-rotating portion 29, N-pole magnetic poles and S-pole magnetic poles are alternately arranged along the rotation direction R3. A magnetic field for attracting (supporting) the two-component developer to the third roller 13 in the state of a magnetic brush is formed by the magnetic force of these magnetic poles. The third roller 13 rotates in the rotation direction R3 while carrying the two-component developer in a magnetic brush state, so that the two-component developer is conveyed to the opposite location 37-1 and the opposite location 37-2. In the middle of this, the thickness of the two-component developer carried on the third roller 13 is regulated by the blade 35.

  The toner in the two-component developer is supplied to the first roller 9 that rotates in the rotation direction R1 at the facing portion 37-1, and is supplied to the second roller 11 that rotates in the rotation direction R2 at the facing portion 37-2. The Specifically, a bias in which the DC voltage generated by the third roller power supply unit 65 and the AC voltage are superimposed is applied to the third roller 13. In a state where the carrier is attracted to the third roller 13, only the toner flies by the bias and is attracted to the first roller 9 and the second roller 11, and the first roller 9 and the second roller 11. Stick to.

  The two-component developer containing toner that has not been supplied to the first roller 9 and the second roller 11 is carried by the third roller 13 and conveyed onto a magnetic pole called a peeling pole. Next to this magnetic pole is a magnetic pole called a pumping pole. The pumping electrode has a function of pumping up the two-component developer accommodated in the stirring space 27 described above. The polarity of the peeling electrode and the pumping electrode are the same. For this reason, since a magnetic field is not formed between these magnetic poles, the two-component developer is peeled off from the third roller 13 and guided to the stirring chamber 21 for reuse.

  The first roller 9 will be described. The first roller 9 is used to supply toner to the electrostatic latent image when developing the electrostatic latent image formed on the photosensitive drum 135. The first roller 9 is disposed to face the photosensitive drum 135 at a facing portion 47-1. The first roller 9 covers the non-rotating portion 39 in a state having a gap with the peripheral surface 41 provided in the non-rotating portion 39. The non-rotating portion 39 has a thick cylindrical shape, and the shaft 43 is rotatably disposed in the cylinder. A first roller 9 is fixed to the shaft 43. The first roller 9 rotates in the rotation direction R1 along the peripheral surface 41 as the shaft 43 rotates. The rotation direction R1 is the same direction as the rotation direction R3 of the third roller 13, and is clockwise in this embodiment.

  The first roller 9 sucks the toner in the facing region 37-1 facing the third roller 13, and conveys the toner by rotating in the rotation direction R1 while carrying the toner. Then, the toner is supplied to the photosensitive drum 135 in the facing region 47-1. Specifically, the photosensitive drum 135 rotates in a rotation direction R4 opposite to the rotation direction R1. The first roller 9 is applied with a bias in which the DC voltage generated by the first roller power supply 61 and the AC voltage are superimposed. The conveyed toner flies from the first roller 9 due to the bias, is attracted by the electrostatic latent image formed on the peripheral surface of the photosensitive drum 135, and moves to the photosensitive drum 135. As a result, the electrostatic latent image on the peripheral surface of the photosensitive drum 135 is developed, and a toner image is formed on the peripheral surface.

  The second roller 11 is used to rearrange the toner supplied to the electrostatic latent image during development. The second roller 11 is disposed to face the photosensitive drum 135 at a facing portion 47-2. The second roller 11 is disposed above the first roller 9 and downstream of the first roller 9 in the rotation direction R4 of the photosensitive drum 135. The rotation direction R2 of the second roller 11 is the same as the rotation direction R1 of the first roller 9. The dimensions (roller diameter, etc.) of the second roller 11 are the same as the dimensions of the first roller 9. Similar to the first roller 9, the second roller 11 includes a non-rotating portion and a shaft. Since these structures are the same as those of the non-rotating portion 39 and the shaft 43 provided in the first roller 9, description thereof will be omitted.

  A transfer belt 131 in contact with the photosensitive drum 135 is disposed on the photosensitive drum 135. The transfer belt 131 moves in the D direction. After the toner is rearranged by the second roller 11, the toner image (developed electrostatic latent image) is transferred to the transfer belt 131.

  As described above, the third roller 13 is used to supply the toner in the two-component developer to the first roller 9 and the second roller 11. The first roller 9 is used to supply toner to the electrostatic latent image formed on the photosensitive drum 135. The second roller 11 is used to reposition the toner supplied to the electrostatic latent image. In order to fulfill this role, a bias in which a DC voltage and an AC voltage are superimposed is applied to the first roller 9, the second roller 11, and the third roller 13, respectively.

  The bias applied to the first roller 9 is supplied from the first roller power supply 61. A bias (blank pulse bias) applied to the second roller 11 is supplied from the second roller power supply unit 63. The bias applied to the third roller 13 is supplied from the third roller power supply unit 65. Since these power supply units have the same configuration, the second roller power supply unit 63 will be described as an example. FIG. 4 is a block diagram showing the configuration of the second roller power supply unit 63.

  One end of the second roller power supply unit 63 is grounded via a capacitor 67. The other end of the second roller power source 63 serves as an output end and is connected to the second roller 11. The second roller power supply unit 63 includes a voltage generation unit 71 and a voltage control unit 73. The voltage generator 71 includes a DC power supply 75 and an AC power supply 77. These power supplies 75 and 77 are connected in series. In the DC power source 75, the AC generated by the transformer 79 is rectified by the diode 81 to generate DC. In the AC power source 77, AC is generated by the transformer 83. A voltage obtained by superimposing the DC voltage output from the DC power supply 75 and the AC voltage output from the AC power supply 77 is applied to the second roller 11.

  The voltage control unit 73 controls the DC voltage output from the DC power supply 75 and the AC voltage output from the AC power supply 77.

  The developing device 141 according to the present embodiment includes two developing rollers, that is, a first roller 9 and a second roller 11, and one of the features is that these rollers share a role. The first roller 9 has a role to sufficiently develop toner by sufficiently supplying toner to the electrostatic latent image. As a result, even if the development speed is increased, it is possible to suppress uneven pitch between the dots of the toner image in the half image.

  The second roller 11 is disposed downstream of the first roller 9 in the rotation direction R4 of the photosensitive drum 135. The second roller 11 has a role of peeling waste toner out of the toner supplied to the electrostatic latent image and rearranging the toner. As a result, toner can be prevented from accumulating at the rear end of the toner image in the solid image, the toner image can be made uniform in the half image, and the toner can be collected when fogging occurs.

  In order to fulfill these roles, the bias applied to the first roller 9 and the bias applied to the second roller 11 during development are different. A bias obtained by superimposing a DC voltage on an AC voltage applied continuously is applied to the first roller 9. A blank pulse bias obtained by superimposing a DC voltage on an AC voltage that is intermittently applied is applied to the second roller 11.

  FIG. 5 is a diagram illustrating an example of a bias applied to the first roller 9. The bias waveform is a continuous rectangular wave. By increasing the bias, developability can be improved.

  FIG. 6 shows an example of a blank pulse bias applied to the second roller 11. The blank pulse bias is composed of a vibration part made up of a rectangular wave and a rest part made up of only a DC component. The blank pulse bias can be generated by the voltage control diagram 73 shown in FIG.

  In the blank pulse bias of FIG. 6, three pulses are on and one pulse is off. Three pulses are vibration parts, and one pulse is a rest part. The blank pulse shown in FIG. 6 is used when the toner is a plus toner. In one pulse off, the toner is peeled off from the electrostatic latent image in the process of changing the voltage from minus to plus, and the toner is supplied to the electrostatic latent image while moving the toner at a low speed in the process of constant voltage (resting portion). As a result, the toner is rearranged.

  Next, the main effects of this embodiment will be described using examples and comparative examples.

[Common conditions for Examples and Comparative Examples]
<Photosensitive drum 135>
・ Material: Amorphous silicon ・ Surface potential: 250V
・ Line speed: 380mm / sec
<First roller 9 (first developing roller)>
・ Diameter: 10mm
・ Gap with the photosensitive drum 135 (distance between the opposed portions 47-1): 100 μm
·bias
DC voltage: 100V
AC voltage: Differs between Example and Comparative Example
<Second roller 11 (second developing roller)>
・ Diameter: 10mm
・ Gap with the photosensitive drum 135 (distance between the facing portions 47-2): 100 μm
·bias
DC voltage: 100V
AC voltage: 1.8Kvp-p, duty ratio 50%, frequency 4.5kHz
Waveform: Blank pulse
<Third roller 13 (magnetic roller)>
・ Diameter: 20mm
-Gap between the first roller 9 and the second roller 11 (distance between the facing portions 37-1 and 37-2): 320 μm
·bias
DC voltage: variable
AC voltage: 1.8 Kvp-p, duty ratio 70%, frequency 4.5 kHz
<Two-component developer>
-Toner number average particle diameter: 6 μm
-Carrier number average particle diameter: 35 μm
-Toner charge amount: 15 μC / g
[Specific conditions of comparative example]
<Bias applied to the first roller 9>
・ AC voltage: 0kV
・ Waveform: DC waveform [Specific conditions of the embodiment]
<Bias applied to the first roller 9>
AC voltage: 1.8Kvp-p, duty ratio 50%, frequency 4.5kHz
・ Waveform: Continuous rectangular wave (waveform shown in Fig. 5)
For the example and the comparative example, an experiment was performed in which a solid toner image and a half toner image were formed while changing the blank pulse waveform conditions. The linear speed of the photosensitive drum 135 was 380 mm / sec, and high-speed development was performed. The experimental result of the comparative example is shown in FIG. 7, and the experimental result of the example is shown in FIG. “Waveform” indicates the waveform of a blank pulse. For example, 3on_1off is a waveform in which 3 pulses shown in FIG. 6 are on and 1 pulse is off. Further, 1on_1off is a waveform in which one pulse is on and one pulse is off.

  The “solid image” column is an evaluation of the level of toner accumulated in the trailing edge of the toner image in the solid image. Visual evaluation of “◯”, “Δ”, and “×” was made according to the level of accumulated toner. This indicates that toner accumulation can be suppressed as “x”, “Δ”, and “◯” are obtained.

  The “half image” column is an evaluation of the level at which unevenness occurs in the pitch between dots of the toner image in the half image. Visual evaluation of “◯”, “Δ”, and “×” was made according to the level of unevenness. It shows that unevenness can be suppressed as “x”, “Δ”, and “◯”.

  For the “solid image”, the example and the comparative example had the same result. A blank pulse bias is applied to the second roller 11. Therefore, the toner is peeled off from the electrostatic latent image in the process of changing the voltage from negative to positive, and the toner is supplied to the electrostatic latent image while moving the toner at a low speed in the process of constant voltage (resting part), so that the toner is regenerated. It is arranged. As a result, it has been found that toner can be prevented from accumulating at the trailing edge of the toner image.

  When the waveform of the blank pulse bias was a waveform in which 10 pulses were on and 1 pulse was off, the result was “Δ”. This waveform is similar to the continuous rectangular wave shown in FIG. 5, and it was found that the effect of toner rearrangement was weakened. An experiment was also conducted in the case where a continuous rectangular wave bias shown in FIG. 5 was applied to the second roller 11 instead of a blank pulse bias. The results were even worse, and both the examples and comparative examples were “x”.

  On the other hand, for the “half image”, the example was better than the comparative example. In the comparative example, since no AC voltage was applied to the first roller 9, the developability deteriorated, and therefore unevenness in the pitch between dots of the toner image could not be suppressed. In the example, by applying an AC voltage to the first roller 9, the developability was improved and unevenness in the pitch between dots of the toner image could be suppressed.

  In the example, the half image was “Δ” only in the case of a waveform in which one pulse is on and one pulse is off. From this, it was found that the blank pulse bias is also related to the developability, and if the on ratio is made larger than the off ratio, the developability is improved. Although not shown in FIGS. 7 and 8, the experiment was performed even when the second roller 11 was applied with the continuous rectangular wave bias shown in FIG. 5 instead of the blank pulse bias. As a result, the half image was “◯” in both the example and the comparative example. Since the half image of the comparative example was “◯”, it was found that the blank pulse bias had a weaker effect of improving developability than the continuous rectangular wave bias.

  As described above, in the present embodiment, the roles of the first roller 9 and the second roller 11 are shared, and the developability is improved by the first roller 9, and the toner is recycled by the second roller 11. It is arranged. Therefore, even if the development speed is increased, it is possible to satisfy both the suppression of toner accumulation at the trailing edge of the toner image in a solid image and the suppression of uneven pitch between dots of the toner image in a half image. Therefore, uniform solid images and half images can be formed.

  In the embodiment, the bias generated by the first roller power supply 61 and applied to the first roller 9 and the bias generated by the second roller power supply 63 and applied to the second roller 11 are applied. The blank pulse bias has the same duty cycle and frequency of the AC voltage. Therefore, it is possible to prevent the bias and the blank bias from interfering with each other and disturbing the waveforms of these biases.

  In the present embodiment, the case where it is applied to touchdown development has been described. The present invention is not limited to this, and the present invention can be applied to two-component development and one-component development other than touch-down development as long as development is performed using two developing rollers.

  In the present embodiment, a printer has been described as an example of the image forming apparatus 1. However, the present embodiment can also be applied to a copier, a facsimile machine, and a multifunction machine having these functions.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 9 1st roller 11 2nd roller 13 3rd roller 61 1st roller power supply part 63 2nd roller power supply part 135 Photosensitive drum (image carrier)
141 Developer

Claims (3)

An image carrier;
A first roller disposed opposite to the image carrier and used to supply toner to the electrostatic latent image when developing the electrostatic latent image formed on the image carrier; It is disposed opposite to the image carrier on the downstream side in the rotation direction of the image carrier with respect to one roller, and is used for rearranging the toner supplied to the electrostatic latent image during the development. A developing device comprising: a second roller;
A first roller power supply unit that generates a bias in which a DC voltage is superimposed on an AC voltage that is continuously applied during the development and applies the bias to the first roller;
During the development, a second pulse pulse bias is generated by superimposing a DC voltage on an AC voltage that is intermittently applied, and applied to the second roller to re-arrange the toner on the second roller. An image forming apparatus comprising: a power supply unit for a roller.   The bias generated by the first roller power supply unit and applied to the first roller and the blank pulse bias generated by the second roller power supply unit and applied to the second roller are alternating currents. 2. The image forming apparatus according to claim 1, wherein the voltage duty ratio and frequency are the same. The developing device includes:
The two-component developer is transported by rotating while carrying the two-component developer, and the toner in the two-component developer is transferred to the first and second rollers at opposite positions facing the first and second rollers. A third roller used to supply the
By applying a bias generated by the first roller power supply unit to the first roller, the toner is ejected from the first roller to form an electrostatic latent image formed on the image carrier. The image forming apparatus according to claim 1, wherein an image forming apparatus is supplied.

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