JP4813043B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus such as a printer or a copying machine. More specifically, the present invention relates to an image forming apparatus called cleanerless that does not have a cleaning device for discarding residual toner on an image carrier.

  Conventionally, there are electrophotographic image forming apparatuses such as printers and copying machines. In such an image forming apparatus, generally, a toner image is formed on an image carrier such as a photosensitive drum. Then, the toner image is transferred to a transfer medium to obtain an image. Conventional image forming apparatuses have a blade or the like for scraping off toner remaining from the image carrier after transfer. In addition, the scraped toner is generally discarded. On the other hand, various image forming apparatuses called cleanerless have been proposed (see, for example, Patent Document 1).

  A cleanerless image forming apparatus does not include a cleaning device such as a blade. That is, the residual toner remaining on the image carrier after transfer is not scraped off. The charging device and the exposure device are passed through while being placed on the image carrier. Then, it is collected and reused by the developing device. This was devised to reduce waste toner and reduce the size of the device.

  Further, in the image forming apparatus described in Patent Document 1, a residual toner uniformizing unit and a toner charge amount control unit are provided on the downstream side of the transfer device. For example, a brush is used for these means. Then, the dispersion state of the residual toner and the charge amount are adjusted. Further, a bias for making the residual toner the same polarity as the developing toner is applied to the toner charge amount control means.

In some cases, a portion where the residual toner is agglomerated may be formed. Alternatively, there may be a case where toner of reverse polarity is included. On the other hand, an image forming apparatus for reliably collecting even in such a case has been proposed (see, for example, Patent Document 2). The image forming apparatus described in this document includes a brush roll that contacts the image carrier. Residual toner on the image carrier is smoothed by the rotation of the brush roll. Further, a bias voltage is applied to the brush roll and the case covering it. As a result, the toner charged to the opposite polarity is collected by the brush roll.
JP 2003-167476 A JP 2002-372878 A

  However, the image forming apparatus disclosed in Patent Document 1 has a problem that it is difficult to control the voltage of the toner charge amount control means. For example, in order to adjust the toner to a predetermined charge state, it is necessary to apply a strong bias to the toner charge amount control means. However, if this is done, there is a risk of causing uneven charging by also affecting the potential of the photoreceptor. On the other hand, in order not to cause uneven charging of the photosensitive member, only a moderate bias can be applied in the toner charge amount control means. In this case, there is a problem that the toner may not be adjusted to a desired charge state.

  Further, a bias in a direction for collecting the residual toner is applied to the toner charge amount control means. For this reason, it is difficult to discharge toner. If discharge failure occurs, toner may accumulate in the toner charge amount control means. If toner is accumulated, there is a problem that the charge control function of the toner charge amount control means is lowered.

  In the image forming apparatus disclosed in Patent Document 2, the toner having the opposite polarity is captured separately from the toner having the normal polarity. After that, it is discarded. This is to prevent the toner having the opposite polarity from being conveyed by the image carrier as it is and reaching the position facing the charging device. This is because toner of reverse polarity may adhere to the charging member. However, even if the toner has a reverse polarity, it should be reusable if the charge can be readjusted. Therefore, there has been a demand to reduce the amount of waste toner as much as possible.

  Further, the charged state of the residual toner tends to vary depending on the operating environment (temperature, humidity, etc.). Further, the variation is larger than the general toner charge amount in the developing device. If such residual toner is directly faced to the developing device as it is, there is a risk of causing poor collection. For example, if the charge amount of the residual toner is too high, the adhesive force with the image carrier is too strong. Therefore, there is a possibility that it cannot be collected by the developing device.

  In addition, toner having a reverse polarity or having a too low charge amount may contaminate the charging member while being conveyed. In particular, toner adhesion tends to occur in a contact-type charging member such as a charging roller. On the other hand, the contact-type charging member has a smaller amount of ozone emission than a non-contact charging member such as a corona discharge type. Therefore, there is an advantage that an ozone filter or the like can be omitted. In other words, it is suitable for miniaturization of equipment, and there was a demand to adopt it if possible.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, an object of the present invention is to provide an image forming apparatus that is a cleanerless image forming apparatus that uses a contact-type charging device and that can be reliably collected by the developing device without contaminating the charging device. It is in.

The image forming apparatus of the present invention, which has been made for the purpose of solving this problem, includes a photoconductor, a charger for charging the surface of the photoconductor, an exposure device for forming an electrostatic latent image on the surface of the photoconductor, and a photoconductor. An image forming apparatus having a developing unit that develops an electrostatic latent image of toner with a toner and a transfer unit that transfers a toner image on a photosensitive member to a transfer target, at a position downstream from the transfer unit and upstream from the charging unit A conductive contact rotating member that contacts the photosensitive member and temporarily collects at least a part of the transfer residual toner on the photosensitive member, and discharges the collected toner onto the photosensitive member; A first electrode and a second electrode facing the contact rotating member at a position other than the contact position, and a voltage applying unit for separately applying a voltage to the contact rotating member, the first electrode, and the second electrode. For the average voltage V0 after the transfer of the body surface, Tactile average voltage applied to the rotary member V1, and the average polarity of the applied voltage V2 to the first electrode are both the same as the charging polarity of the time of the toner developing, and,
| V0 | <| V1 | <| V2 |
(Both are absolute values with respect to ground voltage , the same applies hereinafter )
It satisfies the relationship.

  According to the image forming apparatus of the present invention, the untransferred toner comes into contact with the contact rotating member before facing the charger. A part of the transfer residual toner is collected by the contact rotating member. Further, the collected toner faces the first electrode and the second electrode. At this time, since the voltage is applied to these electrodes by the voltage application unit, the charged state of the collected toner is adjusted. Here, since the average voltage applied to the contact rotating member and the first electrode is the same polarity as the charging polarity at the time of developing the toner with respect to the average voltage after the transfer on the surface of the photoreceptor, the charged state of the residual toner Is brought close to the charged state at the time of developing the toner. Further, since V2 is set so as to satisfy the above equation, the toner is strongly charged by the first electrode. Therefore, the image forming apparatus is a cleanerless image forming apparatus using a contact type charging device, and can be reliably collected by the developing device without contaminating the charging device.

Further , in the first invention of the present invention , the average applied voltage V2 to the first electrode is higher than the voltage V1q having a larger absolute value among the peak voltages of the applied voltage to the contact rotating member.
| V1q | <| V2 |
The voltage V3 applied to the second electrode with respect to the average voltage V0 after the transfer of the surface of the photoreceptor is the same as the charging polarity during toner development, and the difference between the voltage V3 and the voltage V1 is satisfied. Is smaller than the absolute value of the difference between the voltage V2 and the voltage V1, the second electrode is disposed downstream of the first electrode in the rotation direction of the contact rotating member, and the first electrode and the second electrode Is for adjusting the charge of the toner facing each other.
In this way, the toner collected on the contact rotating member first faces the first electrode and then faces the second electrode. Here, since the absolute value of the difference between the average voltage V2 of the first electrode and the average voltage V1 of the contact rotating member is larger than the average voltage V3 of the second electrode, first, the toner is strongly charged by the first electrode. Adjusted. Then, it can be narrowed down to a more appropriate range by the second electrode.

An image forming apparatus according to a second aspect of the present invention includes a photosensitive member, a charger, an exposure device, a developing device, and a transfer device, and further includes a contact rotating member, a first electrode and a second electrode, A voltage application section, and the polarity of the average applied voltage V1 to the contact rotating member and the average applied voltage V3 to the second electrode with respect to the average voltage V0 after the transfer of the surface of the photosensitive member is at the time of developing the toner. And the same charging polarity as
| V0 | <| V1 | <| V3 |
(Both absolute values with respect to ground voltage)
Are those that satisfy the relationship, with respect to the average voltage V0 after transfer on the surface of the photoreceptor, the applied voltage V 2 to the first electrode is a charge polarity opposite to when the toner development, the second electrode, the first from first electrode is disposed in the rotational direction lower stream side of the contact rotating member, the first electrode and the second electrode, Ru der those charged adjusting the toner facing.
In this way, the toner collected on the contact rotating member first faces the second electrode and then faces the first electrode. Here, since the average voltage V3 of the second electrode is opposite to the charging polarity at the time of developing the toner, the toner facing the second electrode is once brought close to the reversely charged state. On the other hand, the average voltage V2 of the first electrode has the same polarity as the charging polarity when the toner is developed. Therefore, a more appropriate charged state can be obtained by facing the first electrode.

Furthermore , in the third aspect of the present invention , in addition to the configuration of [0012]
The average applied voltage V2 to the first electrode is higher than the voltage V1q having a larger absolute value among the peak voltages of the applied voltage to the contact rotating member.
| V1q | <| V2 |
The voltage V3 applied to the second electrode with respect to the average voltage V0 after the transfer of the surface of the photoreceptor is opposite to the charging polarity during toner development, and the second electrode is the first electrode. more is disposed downstream in the rotation direction of the contact rotating member, the first electrode and the second electrode, Ru der those charged adjusting the toner facing.
In this way, the toner collected on the contact rotating member first faces the first electrode and then faces the second electrode. Here, the average voltage V2 of the first electrode is the same polarity as the charging polarity at the time of developing the toner, and a strong voltage is applied so as to satisfy the above formula. The charge is adjusted. Next, since the average voltage V3 of the second electrode to which the toner faces is opposite to the charging polarity at the time of developing the toner, the strongly charged toner is slightly returned. Therefore, an appropriate charge state can be obtained.

Furthermore, the present invention has an environmental sensor that acquires the temperature value and / or humidity value in the apparatus, and the voltage application unit reduces the absolute value of the difference between the voltage V2 and the voltage V0 at low temperature or low humidity. , It should be increased at high temperature or high humidity.
In high temperature or high humidity environment, the charging performance of toner decreases. That is, even when the same voltage as in a low temperature or low humidity environment is applied, the charge amount of the toner becomes small. Thus, if this is done, almost the same charged state can be achieved regardless of the environmental state.

  According to the image forming apparatus of the present invention, the image forming apparatus is a cleanerless image forming apparatus using a contact-type charging device, and can be reliably collected by the developing device without contaminating the charging device. ing.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a cleanerless color printer.

  The color printer 1 of the present invention has image forming units 10Y, 10M, 10C, and 10Bk for each color, as schematically shown in FIG. The color printer 1 further includes an intermediate transfer belt 11, a secondary transfer device 12, and a belt cleaner 13. The image forming units 10Y, 10M, 10C, and 10Bk for each color are arranged along the intermediate transfer belt 11. Then, toner images of the respective colors are formed on the intermediate transfer belt 11 so as to overlap each other. The superimposed toner images are transferred to the recording paper 14 by the secondary transfer device 12. The toner remaining on the intermediate transfer belt 11 is scraped off by the belt cleaner 13. In the following description, the subscript YMCBk for each color is omitted when there is no need for distinction.

  Each color image forming unit 10 has the same configuration. As shown in FIGS. 1 and 2, each image forming unit 10 has a charging device 30, an exposure device 40, a developing device 50, and a transfer device 60 around the photosensitive drum 20. Here, a contact-type charging roller is used as the charging device 30. The developing device 50 is a type using negatively charged toner. Other devices are general ones. In the color printer 1 of this embodiment, a charge control unit 70 is further provided between the transfer device 60 and the charging device 30.

  Further, the color printer 1 of the present embodiment includes a controller 80 and an environment measuring unit 81. The controller 80 controls the charge controller 70 for each color. The environment measuring unit 81 measures, for example, the temperature and humidity in the color printer 1 during operation. The measurement result of the environment measuring unit 81 is input to the controller 80.

  As shown in FIG. 2, the charge control unit 70 includes a brush roller 71, a case 72, and charge electrodes 73 and 74. All of these are provided so that the longitudinal direction thereof is parallel to the axial direction of the photosensitive drum 20. Further, at least the entire image forming width of the photosensitive drum 20 is covered. Power sources 75, 76, and 77 are connected to the brush roller 71 and the two charged electrodes 73 and 74, respectively. Thereby, different voltages can be applied. The controller 80 controls the power supplies 75, 76 and 77. Thereby, the voltage applied to the brush roller 71 and the charging electrodes 73 and 74 is appropriately controlled.

  The brush roller 71 has a conductive and flexible linear member planted around a rotating shaft. Alternatively, a sponge roller may be used instead of the brush roller 71. The brush roller 71 is rotatable around a rotation axis. The tip of the linear member of the brush roller 71 is in contact with the surface of the photosensitive drum 20. The case 72 is formed in a box shape so as to cover the brush roller 71 except for the side facing the photosensitive drum 20. The case 72 is disposed in a non-contact manner on the photosensitive drum 20.

  The charging electrodes 73 and 74 are conductive members formed in a strip shape in the axial direction of the photosensitive drum 20. The charging electrodes 73 and 74 are fixed inside the case 72. That is, the charging electrodes 73 and 74 face the brush roller 71. With respect to the rotation direction of the brush roller 71, the charging electrode 73 is disposed upstream of the charging electrode 74. Further, the charging electrodes 73 and 74 are arranged in a non-contact manner with respect to the photosensitive drum 20. The charging electrodes 73 and 74 and the brush roller 71 may be arranged in contact or non-contact. When the brush roller 71 is in contact with the charging electrodes 73 and 74, the amount of biting is preferably smaller than that for the photosensitive drum 20.

  Next, the voltage applied to the brush roller 71 and the charging electrodes 73 and 74 will be described. A superimposed voltage of direct current and alternating current is applied to the brush roller 71 by the power source 75 as described above. The applied voltage value of the brush roller 71 is set to be within a predetermined range with respect to the surface potential of the photosensitive drum 20. On the other hand, only DC voltage is applied to the charging electrodes 73 and 74 by the power sources 76 and 77. This applied voltage value is controlled by the controller 80 in accordance with conditions such as the operating environment.

  First, the average surface potential after the transfer of the photosensitive drum 20 is V0, the average voltage applied to the brush roller 71 is V1, the voltage applied to the charging electrode 73 is V2, and the voltage applied to the charging electrode 74 is V3. And These four voltages V0, V1, V2, and V3 have the same polarity with respect to the ground. Here, since negatively charged toner is used for the developing device 50, these voltages are all negative values.

The voltage V2 applied to the charging electrode 73 is set so as to satisfy the relationship of the following formula 1.
| V0 | <| V1 | <| V2 | (Formula 1)
Here, this V0 corresponds to “average voltage V0 after transfer of the surface of the photosensitive member”. Further, V1 corresponds to “average applied voltage V1 to the contact rotating member”. V2 corresponds to “average applied voltage V2 to the first electrode”.

The peak voltages of the voltage applied to the brush roller 71 are V1p and V1q. The voltage applied to the brush roller 71 changes between V1p and V1q. The range is set so as to satisfy the relationship of the following expression 2.
| V1p | <| V0 | <| V1 | <| V1q | <| V2 | (Formula 2)
Further, V1p and V1q are set to such an extent that the charged state of the photosensitive drum 20 is not changed. V1p may have a polarity different from V0 with respect to ground.

Further, the voltage V3 applied to the charging electrode 74 is set as follows.
| V0 | <| V1 | ≦ | V3 | <| V2 | (Formula 3)
That is, V3 is smaller than V2 and close to V1.

  Next, the operation of the image forming unit 10 in the color printer 1 of this embodiment will be described. The surface of the photosensitive drum 20 is uniformly charged by the charging device 30. Next, an electrostatic latent image based on the image data is formed by the exposure device 40. The formed electrostatic latent image is developed by the developing device 50 to become a toner image. Further, the image is transferred to the intermediate transfer belt 11 by the transfer device 60. At this time, toner remaining on the photosensitive drum 20 without being transferred to the intermediate transfer belt 11 is residual toner.

  When the photosensitive drum 20 is further rotated, the residual toner faces the charge control unit 70. At this time, the brush roller 71 of the charge controller 70 is rotated in the counter direction with respect to the photosensitive drum 20, as shown in FIG. Further, the tip of the hair of the brush roller 71 is in contact with the surface of the photosensitive drum 20. Therefore, the residual toner on the surface of the photosensitive drum 20 is loosened and leveled by the brush roller 71.

  Further, since the bias is applied as described above, the residual toner is once taken into the brush roller 71 from the surface of the photosensitive drum 20. Next, the toner taken into the brush roller 71 faces the charging electrodes 73 and 74 in this order by the rotation of the brush roller 71. The charge is adjusted first by the charge electrode 73 and then by the charge electrode 74. Further, the charge-adjusted toner is discharged again to the non-image area or the like of the photosensitive drum 20. That is, the residual toner is only temporarily taken into the brush roller 71. It is not collected in the brush roller 71.

  At this time, since each applied voltage is set as described above, the toner can be smoothly transferred between the brush roller 71 and the photosensitive drum 20. Furthermore, as shown in Expression 2, the absolute value | V2 | of the voltage applied to the charging electrode 73 is set sufficiently large. Accordingly, the charge amount of the toner is strongly adjusted by the charging electrode 73. Even if the reverse polarity toner is mixed, the polarity is adjusted by the charged electrode 73.

  However, there is a possibility that toner in a negatively charged state that is too strong may be mixed. If the negative polarity is too strong, there is a possibility of causing a recovery failure in the developing device, which is not preferable. In this embodiment, since the charging electrode 74 is further provided and the applied voltage V3 is set as described above, the charged state of the toner is finely adjusted. Accordingly, the appropriately charged toner is returned to the brush roller 71.

  These applied voltages V1, V2, and V3 may be set as follows, for example. First, the voltage applied to the brush roller 71 by the power source 75 is a superimposed voltage of direct current and alternating current. Therefore, the AC component is Vpp = 300V, and the DC component is Vdc = −100V with respect to the photoreceptor potential V0. Further, the AC component is a rectangular wave having a frequency f = 100 Hz and Duty = 50%. The voltage V2 applied to the charging electrode 73 by the power source 76 is a DC voltage, and V2 = −500V may be set. Further, the voltage V3 applied to the charging electrode 74 by the power source 77 is a DC voltage, and V3 = −100V may be set.

  In this way, the toner is charged in order by the charging electrodes 73 and 74, as shown in FIG. FIG. 3 a) is an example of the distribution of the charge state of the toner when facing the brush roller 71. The variation is large, and some toners with reverse polarity are included. When this toner is taken into the brush roller 71 and faces the charging electrode 73, it is shifted to the negative side as shown in FIG. The toner then faces the charging electrode 74, so that the strong-toner is shifted to the weak-toner as shown in FIG. Therefore, according to such setting, the toner whose charge is appropriately adjusted is returned to the brush roller 71.

  Further, the setting of the applied voltages V2, V3 of the charging electrodes 73, 74 can be different from the above. For example, V2 may be a positive voltage and V3 may be a negative voltage. Then, the charged state of the entire toner is first shifted to the + side by the charging electrode 73. Next, the charge electrode 74 is shifted to the negative side. In this way, as shown in FIG. 4, it is possible to change the charge distribution state of toner having a large variation to a sharp distribution state. For example, V2 = + 100V and V3 = −400V may be set.

  In this setting, the toner charge distribution changes as follows. FIG. 4a) is similar to FIG. 3a). When this toner is taken in by the brush roller 71 and faces the charging electrode 73, the toner is shifted to the positive side as shown in FIG. At this stage, the toner of reverse polarity also increases. Next, the toner faces the charging electrode 74, so that the toner is shifted to the negative side as shown in FIG. Almost no toner of reverse polarity remains. Therefore, the toner whose charge is appropriately adjusted is returned to the brush roller 71 by such setting.

  Alternatively, V2 can be a strong minus voltage and V3 can be a weak plus voltage. Then, first, the charged state of the entire toner is largely shifted to the negative side by the charging electrode 73. At this stage, almost no reverse polarity toner remains. Next, the charge electrode 74 is slightly shifted to the + side for fine adjustment. For example, V2 = −600V and V3 = + 100V may be set. Even with such a setting, the toner whose charge is appropriately adjusted is returned to the brush roller 71. Even in this case, the change is almost the same as in FIG.

  In general, the charge amount of the toner supplied from the developing device 50 onto the photosensitive drum 20 changes as shown in FIG. First, the amount of charge is greatly reduced by passing through the transfer device 60. In some cases, a reverse polarity toner whose polarity is reversed appears. Furthermore, as shown in FIG. 5, the charging performance of the toner particles varies considerably depending on the environment. In the figure, “LL” indicates low temperature and low humidity, “RT” indicates standard environment, and “HH” indicates high temperature and high humidity. Especially at high temperature and high humidity, charging performance deteriorates.

  Therefore, in the color printer 1 of this embodiment, the voltage applied to the charging electrodes 73 and 74 is adjusted according to the operating environment. That is, the controller 80 receives the measurement result of the environment measurement unit 81 and controls the applied voltage of the power supplies 76 and 77. For example, in the standard environment, the applied voltage is moderate. For high temperature and high humidity, the applied voltage is high. For low temperature and low humidity, the applied voltage is low. In this way, charge adjustment is particularly powerful in a high temperature and high humidity environment. Therefore, as shown in FIG. 5, it is possible to approach the desired charge amount in any environment.

Here, the desirable charge amount of the toner is a range that satisfies both the fact that the toner does not adhere to the charging device 30 and that the recovery by the developing device 50 is good. This range Q is indicated by an arrow at the right end in FIG. It is desirable that the charge amount Q1 of the toner discharged from the charge control unit 70 and attached to the photosensitive drum 20 again falls within this range. Therefore, the controller 80 controls the voltage values of the power supplies 76 and 77 so that Q1 falls within the range Q. Here, it is assumed that an average value of the toner charge amount in the developing device 50 is Q0. According to this embodiment, the charge amount Q1 of the discharged toner is at least within a range satisfying the following expression 3.
0.5 × Q0 ≦ Q1 ≦ 3 × Q0 (Formula 3)
In addition, the direction of the inequality sign in the expression 3 represents the charge amounts Q0 and Q1 as their absolute values.

  Therefore, in the color printer 1 of this embodiment, the residual toner is processed as follows. First, the residual toner adheres to the surface of the photosensitive drum 20 and faces the charge control unit 70. At this time, it is leveled by the brush roller 71 in contact with the photosensitive drum 20. Further, the brush roller 71 is applied with an AC bias having an average voltage V1. Therefore, the residual toner is taken into the brush roller 71. The taken-in toner is carried by the rotation of the brush roller 71.

  The toner taken into the brush roller 71 faces the charging electrodes 73 and 74 in order. A DC bias stronger than that of the brush roller 71 is applied to the charging electrode 73 or the charging electrode 74. Therefore, the charge amount of the toner attached to the brush roller 71 is adjusted. The brush roller 71 and the charging electrodes 73 and 74 are not in contact with each other, or even if they are in contact with each other, the amount of biting into the charging electrodes 73 and 74 of the brush roller 71 is small, so that the toner does not adhere to the charging electrodes 73 and 74. .

  Furthermore, in this embodiment, the environment measurement unit 81 measures the operating environment. In response to the result, the controller 80 controls the bias intensity of the charging electrodes 73 and 74. Therefore, the residual toner charge amount is adjusted within an appropriate range regardless of the original charge amount of the residual toner and changes in the operating environment. Further, even if the residual toner includes toner having a reverse polarity, the polarity is corrected. Further, the charge-adjusted toner is discharged to a non-image area or the like of the photosensitive drum 20.

  The toner adhering to the photosensitive drum 20 passes through the charging device 30. At this time, the charge amount of the residual toner is adjusted to a value that is not attracted to the charging device 30 as described above. Therefore, the charging device 30 is not soiled. Further, the residual toner faces the developing device 50. At this time, the charge amount of the residual toner is a value suitable for collection by the developing device 50. Therefore, it is recovered satisfactorily by the developing device 50. Further, the residual toner can be mixed with the toner in the developing device 50 and used again for development.

  The shape of the charging electrodes 73 and 74 is not limited to that shown in FIG. For example, arc-shaped charged electrodes 91 and 92 as shown in FIG. In this way, the toner taken in by the brush roller 71 can be reliably faced. Further, roller-type charging electrodes 93 and 94 as shown in FIG. 7 and brush-type charging electrodes 95 and 96 as shown in FIG. 8 may be used. A combination of these may also be used.

  As described above in detail, according to the color printer 1 of the present embodiment, since the charge adjustment unit 70 is provided, the charge amount of the residual toner is adjusted. The charge adjusting unit 70 includes a brush roller 71 and a charging electrode 73. A moderate AC bias is applied to the brush roller 71. Therefore, toner can be taken in and discharged smoothly. In addition, a direct current bias is applied to the charging electrodes 73 and 74. The size is controlled according to the result of the environment measurement unit 81. Therefore, the bias strength corresponding to the charging performance of the toner is selected. Accordingly, the toner discharged from the charge adjusting unit 70 is adjusted to an appropriate charge amount. That is, it can pass through without being attached to the charging device 30. Then, it can be recovered well by the developing device 50. As a result, this is a cleanerless image forming apparatus using a contact type charging device, and can be reliably collected by the developing device without contaminating the charging device.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, in the above embodiment, the brush roller 71 is rotated in the counter direction with respect to the photosensitive drum 20. However, this rotation direction is not necessarily the counter direction.
Further, for example, the arrangement and number of the charging electrodes 73 and 74 are not limited to this, and a plurality of charging electrodes 73 and 74 may be provided in the vicinity of the brush roller 71.
Further, for example, the conditions for controlling the voltage applied to the charging electrodes 73 and 74 are not limited to the operating environment. It is preferably controlled according to various conditions related to the toner charge amount and charging performance.
Further, for example, in addition to the above-described embodiment, a cleaning sequence may be executed.
Further, for example, in the present embodiment, the present invention is applied to the color printer 1, but the present invention is not limited to this, and can also be applied to a copying machine, a FAX machine, and the like. Further, not only a color machine but also a monochrome machine may be used, and it may be directly transferred onto a recording sheet without using an intermediate transfer belt.

1 is a schematic configuration diagram of a main part of a color printer according to an embodiment. It is a schematic block diagram of the image formation part of each color. FIG. 6 is an explanatory diagram showing a change in toner charge amount distribution. FIG. 6 is an explanatory diagram showing a change in toner charge amount distribution. FIG. 6 is an explanatory diagram illustrating a transition state of a charge amount of toner. It is explanatory drawing which shows another example of a charged electrode. It is explanatory drawing which shows another example of a charged electrode. It is explanatory drawing which shows another example of a charged electrode.

Explanation of symbols

1 Color printer (image forming device)
20 Photosensitive drum (photosensitive member)
30 Charging device (charger)
40 Exposure equipment (exposure device)
50 Developer (Developer)
60 Transfer device (transfer device)
71 Brush roller (contact rotating member)
73, 74 Charged electrodes (first electrode, second electrode)
75, 76, 77 Power supply (voltage application unit)
81 Environmental measurement unit (environmental sensor)

Claims (4)

A photoconductor, a charger for charging the surface of the photoconductor, an exposure device for forming an electrostatic latent image on the surface of the photoconductor, a developer for developing the electrostatic latent image on the photoconductor with toner, In an image forming apparatus having a transfer device for transferring a toner image on the photoreceptor to a transfer target,
The photosensitive member is brought into contact with the photosensitive member at a position downstream from the transfer unit and upstream from the charging unit, and at least a part of the transfer residual toner on the photosensitive member is temporarily recovered, and the recovered toner is transferred onto the photosensitive member. A conductive contact rotating member to be discharged;
A first electrode and a second electrode facing the contact rotating member at a position other than a contact position between the photoconductor and the contact rotating member;
A voltage applying unit that applies a voltage separately to the contact rotating member, the first electrode, and the second electrode;
The polarity of the average applied voltage V1 to the contact rotating member and the average applied voltage V2 to the first electrode with respect to the average voltage V0 after the transfer of the surface of the photoreceptor is the same as the charging polarity at the time of developing the toner. And
| V0 | <| V1 | <| V2 |
(Both are absolute values with respect to ground voltage , the same applies hereinafter )
Satisfying the relationship
The average applied voltage V2 to the first electrode is higher than the voltage V1q having a larger absolute value among the peak voltages of the applied voltage to the contact rotating member.
| V1q | <| V2 |
Satisfying the relationship
The applied voltage V3 to the second electrode with respect to the average voltage V0 after the transfer of the surface of the photoreceptor is the same as the charging polarity at the time of developing the toner,
The absolute value of the difference between the voltage V3 and the voltage V1 is smaller than the absolute value of the difference between the voltage V2 and the voltage V1,
The second electrode is disposed downstream of the first electrode in the rotation direction of the contact rotating member ;
The first electrode and the second electrode, the image forming apparatus according to claim der Rukoto those charged adjusting the toner facing. A photoconductor, a charger for charging the surface of the photoconductor, an exposure device for forming an electrostatic latent image on the surface of the photoconductor, a developer for developing the electrostatic latent image on the photoconductor with toner, In an image forming apparatus having a transfer device for transferring a toner image on the photoreceptor to a transfer target,
The photosensitive member is brought into contact with the photosensitive member at a position downstream from the transfer unit and upstream from the charging unit, and at least a part of the transfer residual toner on the photosensitive member is temporarily recovered, and the recovered toner is transferred onto the photosensitive member. A conductive contact rotating member to be discharged;
A first electrode and a second electrode facing the contact rotating member at a position other than a contact position between the photoconductor and the contact rotating member;
A voltage applying unit that applies a voltage separately to the contact rotating member, the first electrode, and the second electrode;
To the average voltage V0 after the transfer of the surface of said photosensitive member, said contact average voltage applied to the rotary member V1, and the polarity of the average voltage applied to V 3 to the second electrode are both, the charge polarity at the time of the toner developing The same, and
| V0 | <| V1 | <| V 3 |
(Both absolute values with respect to ground voltage)
Satisfying the relationship
Wherein with respect to the average voltage V0 after the transfer of the surface of the photosensitive member, wherein the applied voltage V 2 to the first electrode, a charge polarity opposite to when the toner development,
The second electrode, from the first electrode, are disposed in the rotational direction lower stream side of the contact rotating member,
The image forming apparatus according to claim 1, wherein the first electrode and the second electrode are for adjusting the charge of toner facing each other. A photoconductor, a charger for charging the surface of the photoconductor, an exposure device for forming an electrostatic latent image on the surface of the photoconductor, a developer for developing the electrostatic latent image on the photoconductor with toner, In an image forming apparatus having a transfer device for transferring a toner image on the photoreceptor to a transfer target,
The photosensitive member is brought into contact with the photosensitive member at a position downstream from the transfer unit and upstream from the charging unit, and at least a part of the transfer residual toner on the photosensitive member is temporarily recovered, and the recovered toner is transferred onto the photosensitive member. A conductive contact rotating member to be discharged;
A first electrode and a second electrode facing the contact rotating member at a position other than a contact position between the photoconductor and the contact rotating member;
A voltage applying unit that applies a voltage separately to the contact rotating member, the first electrode, and the second electrode;
The polarity of the average applied voltage V1 to the contact rotating member and the average applied voltage V2 to the first electrode with respect to the average voltage V0 after the transfer of the surface of the photoreceptor is the same as the charging polarity at the time of developing the toner. And
| V0 | <| V1 | <| V2 |
(Both are absolute values with respect to the ground voltage.
Satisfying the relationship
The average applied voltage V2 to the first electrode is higher than the voltage V1q having a larger absolute value among the peak voltages of the applied voltage to the contact rotating member.
| V1q | <| V2 |
Satisfying the relationship
The applied voltage V3 to the second electrode with respect to the average voltage V0 after the transfer of the surface of the photoreceptor is opposite to the charging polarity at the time of developing the toner,
The second electrode is disposed downstream of the first electrode in the rotation direction of the contact rotating member;
The image forming apparatus according to claim 1, wherein the first electrode and the second electrode are for adjusting the charge of toner facing each other. In the image forming apparatus according to any one of claims 1 to 3,
It has an environmental sensor that acquires the temperature value and / or humidity value in the device,
The image forming apparatus, wherein the voltage application unit decreases an absolute value of a difference between the voltage V2 and the voltage V0 at a low temperature or low humidity and increases an absolute value at a high temperature or high humidity.

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