JP4835051B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, a facsimile machine, and a multifunction machine in which two or more of these are combined.

  In general, an electrophotographic image forming apparatus charges a surface of an image carrier (for example, a drum-type photosensitive member that is driven to rotate) by a charging device so that the surface moves. The area is exposed from an exposure device according to the image to be formed to form an electrostatic latent image, and the electrostatic latent image is developed by the developing device while applying a developing bias voltage to the developing device. Thus, a visible toner image is formed, and an image forming process for transferring the visible toner image to a transfer target can be performed.

Such image forming apparatuses can be roughly classified into a monochrome image forming apparatus and a color image forming apparatus (typically, a full color image forming apparatus) capable of forming an image using two or more colors of toner.
In a monochrome image forming apparatus, generally, a visible toner image formed on an image carrier is directly transferred and fixed on a recording medium.
In a color image forming apparatus, taking a tandem type color image forming apparatus as an example, an image carrier, a charging device for charging the surface thereof, an image exposure device, a developing device for developing an electrostatic latent image on the image carrier, etc. A plurality of image forming units including the toner image are sequentially arranged along the intermediate transfer member according to the color of the toner, and the toner images formed on the image carrier in each image forming unit are superimposed on the intermediate transfer member. Then, the multiple toner image on the intermediate transfer member is transferred to a recording medium and fixed.

  In addition, whether it is a monochrome image forming apparatus or a color image forming apparatus, a developing apparatus used for developing an electrostatic latent image is roughly divided into one that employs a so-called one-component developer mainly composed of toner, toner and carrier. The main component is a so-called two-component developer.

  By the way, in a monochrome image forming apparatus or a color image forming apparatus, after the visible toner image formed on the image carrier is transferred to the transfer object, the electric charge remains on the image carrier. In addition, unnecessary charges may exist for some reason. When the next image forming process is carried out while leaving such charges as they are, image defects such as a target image not being clearly formed or a ghost image being formed over the target image occur.

Therefore, the image forming apparatus uses a tungsten lamp, an LED array, or the like on the surface of the image carrier after the toner image formed on the image carrier is transferred to the transfer target (recording medium or intermediate transfer member). An exposure is performed by the eraser, and unnecessary charges such as residual charges are erased to prepare for the next image formation.
An image forming apparatus provided with such an eraser is disclosed in, for example, Japanese Patent Laid-Open No. 59-201066.

JP 59-201066 A

  However, if such an eraser is used, the cost is high, and the cost of the eraser is not only high, but the structure of the image forming apparatus becomes complicated and the miniaturization becomes difficult to provide the eraser. To do.

  In view of this, the present invention charges the surface of an image carrier that is driven so that the surface moves with a charging device, and performs exposure according to an image to be formed from the image exposure device to the charged area. A latent image is formed, and the electrostatic latent image is developed by a developing device using a two-component developer containing toner and a carrier while applying a developing bias voltage to the developing device to form a visible toner image. An image forming apparatus capable of carrying out an image forming process for transferring the visible toner image to a transfer object, and performing an erasing process of charges on the image carrier prior to the execution of the image forming process. Compared to a conventional image forming apparatus that uses an eraser as a means for erasing the charge on the body, it is less expensive, and the structure of the image forming apparatus can be simplified and the charge can be erased on the image carrier. Providing an image forming device capable of processing The first object to.

  The present invention also provides an image forming apparatus that suppresses the occurrence of a situation in which the developer unnecessarily shifts from the developing device to the image carrier along with the charge erasing process on the image carrier. A second object is to provide an image forming apparatus capable of performing charge erasing processing on a carrier.

In order to solve the above problems, the present invention
The surface of the image carrier that is driven so that the surface moves is charged by a charging device, and an exposure according to the image to be formed is applied to the charged area from the image exposure device to form an electrostatic latent image. The electrostatic latent image is developed by a developing device using a two-component developer containing toner and carrier under application of a developing bias voltage to the developing device to form a visible toner image. An image forming apparatus capable of carrying out an image forming process for transferring the image onto a transfer medium, and erasing the charge on the image carrier prior to the execution of the image forming process. It is carried out by performing continuous exposure from the image exposure device to the charge erasure target area on the image carrier while driving the body ,
In the charge erasing process prior to the execution of the image forming process after the image forming process is interrupted at an improper timing, after the driving of the image carrier, the development bias voltage is started to be applied to the developing device, and the image carrier After the start of driving, application of a charging voltage for charging the surface of the image carrier to the charging device is started after the time required for the surface of the image carrier to rotate from the charging position by the charging device to the developing position by the developing device,
In the charge erasing process prior to the execution of the image forming process that is not the image forming process after the image forming process is interrupted at the improper timing, the surface of the image carrier is charged to the charging device after the image carrier driving is started. The charging voltage to be applied is started,
In any of the charge erasing processes, after the charging voltage is started to be applied to the charging device, the time required for the surface of the image carrier to rotate from the charging position by the charging position to the exposure position by the image exposure apparatus. When the time passes, the image carrier surface starts full exposure by continuous exposure in the image exposure apparatus, and then the development takes place when the time required for the exposure region by the full exposure on the image carrier surface to rotate to the development position elapses. Application of a bias voltage at the time of all exposure that generates an electric field that suppresses the movement of the developer from the developing device to the entire exposure area of the image carrier is started in the apparatus, and after the application of the bias voltage at the time of full exposure is started to the developing apparatus, Provided is an “image forming apparatus” in which all exposure by the image exposure apparatus is stopped when the time required for the surface potential of the image carrier to be uniform has elapsed .

Here, the “development bias voltage” is a bias voltage for developing the electrostatic latent image on the image carrier, in other words, a development bias voltage during image formation (printing).
“Before the image forming process is performed” may be at a stage after the end of the image forming process, or may be performed either when an image is to be formed from now on, or both.

  According to this image forming apparatus, since the charge erasing process on the image carrier can be performed using an image exposure apparatus, the image forming apparatus is less expensive than the conventional image forming apparatus that employs an eraser. The structure can be made simple and the size can be reduced, and the charge erasing process on the image carrier can be performed.

  The image forming apparatus according to the present invention may be a monochrome image forming apparatus or a color image forming apparatus (typically a full color image forming apparatus) capable of forming an image using two or more colors of toner. . In addition, a transfer target to which a visible toner image is transferred is usually a recording medium in a monochrome image forming apparatus, and is usually an intermediate transfer body or further a recording medium in a color image forming apparatus.

  In the case of a color image forming apparatus, taking a tandem type color image forming apparatus as an example, a plurality of image forming units are provided along an intermediate transfer body (usually an endless intermediate transfer belt that is rotationally driven). The image forming unit includes an image carrier, a charging device that charges the surface of the image carrier, an image exposure device, and a developing device that develops an electrostatic latent image on the image carrier. This charge erasing process may be performed by the image exposure apparatus in the image forming unit.

Further, in the image forming apparatus according to the present invention, when performing the full exposure, the bias during full exposure that generates an electric field that suppresses the movement of the developer from the developing device to the full exposure area of the image carrier in the developing device. voltage is Ru is applied.

  If the voltage applied to the developing device remains the same as the developing bias voltage (developing bias voltage at the time of printing) for developing the electrostatic latent image with respect to the area on the image carrier that has been fully exposed, for example, negative charging When a developing device that reversely develops an electrostatic latent image using a conductive toner (therefore, the carrier is positively charged) is used, the image carrying the potential attenuated by the entire exposure from the developing device due to the developing bias voltage The toner moves to the entire exposed area of the body, and the toner is wasted. However, when a bias voltage having a polarity opposite to the developing bias voltage is applied to the developing device, the positively charged carrier instead of the toner moves to the entire exposure region of the image carrier.

  In this regard, according to the image forming apparatus, when performing full exposure, a bias voltage during full exposure is applied to the developing device to generate an electric field that suppresses the movement of the developer from the developing device to the entire exposed area of the image carrier. The charge erasing process on the image carrier can be performed while suppressing the occurrence of a situation where the developer unnecessarily moves from the developing device to the image carrier along with the charge erasing process on the image carrier.

  In this image forming apparatus, 0 V can be exemplified as the bias voltage at the time of all exposure. By adopting 0 V as the bias voltage at the time of full exposure, at least the movement of the toner to the full exposure area of the image carrier is suppressed.

  By the way, an image carrier (typically a photoconductor) is provided with a cleaning blade for removing a developer remaining on the image carrier after the toner image is transferred to the transfer body. If the image carrier drive integration time increases, film scraping of the image carrier surface may occur. Compared with the case of, the amount of attenuation of the surface charge decreases.

  Then, for example, when a developing device that reversely develops an electrostatic latent image using a negatively chargeable toner (and thus the carrier is positively charged) is used, for example, 0 V is used as the bias voltage at the time of all exposure. Even in such a case, the carrier may adhere to a region where the attenuation is not sufficient.

Therefore, in consideration of the accumulated driving time of the image carrier, the bias voltage during all exposure may be set according to the accumulated driving time of the image carrier.
For example, if the drive integration time of the image carrier is less than a predetermined drive integration time, it is set to 0 V, and if it is longer than the predetermined drive integration time, it is changed to a value other than 0 V according to the drive integration time. It may be. By doing so, even when the use of the image forming apparatus is repeated, the movement of the carrier to the entire image carrier exposure area can be suppressed.

  As another problem, if the image forming process is interrupted at an improper timing due to a jam (recording medium clogging) or the like, there may be a charge remaining on the image carrier during the image forming process. . In carrying out the image forming process after the image forming process is interrupted by such improper tamming, when performing the charge erasing process on the image carrier prior to the execution of the image forming process, the image carrier in which such residual charges are present. If the bias voltage (for example, 0 V) is applied to the developing device also for the body region, the electrostatic latent image is reversely developed using, for example, negatively charged toner (and thus the carrier is positively charged). In the case where the developing device is employed, a situation occurs in which carriers adhere to the residual charge existing region.

Therefore, in the present invention, when the charge erasing process is performed prior to the execution of the image forming process in performing the image forming process after the image forming process is interrupted at an improper timing, The developing bias voltage (development bias voltage during printing) is applied to the developing device until the image carrier area not charged by the charging device reaches the developing position by the developing device and finishes passing .

For example, when the bias voltage for all exposure is set to 0 V, the charge erasing process is performed prior to the execution of the image forming process when the image forming process is performed after the image forming process is interrupted at an improper timing. In carrying out the charge erasing process, after the start of driving the image carrier, the development is performed until the image carrier region not charged by the charging device arrives at the development position by the developing device and finishes passing. The developing bias voltage is applied to the apparatus.

  As described above, according to the present invention, the surface of the image carrier that is driven so that the surface moves is charged by the charging device, and exposure corresponding to the image to be formed from the image exposure device to the charged area is performed. To form an electrostatic latent image, and the electrostatic latent image is developed by a developing device using a two-component developer containing toner and a carrier while applying a developing bias voltage to the developing device and is visible. An image forming apparatus that can perform an image forming process of forming a toner image and transferring the visible toner image to a transfer target, and performing an erasing process of charges on the image carrier prior to the execution of the image forming process. Compared to conventional image forming apparatuses that employ an eraser as means for erasing the charge on the image carrier, the image bearing apparatus can be reduced in size and the structure can be simplified and the size can be reduced. You can erase the charge on your body It is possible to provide an image forming apparatus.

  In addition, according to the present invention, in such an image forming apparatus, it is possible to suppress the occurrence of a situation in which the developer is unnecessarily transferred from the developing device to the image carrier along with the charge erasing process on the image carrier. An image forming apparatus capable of performing charge erasing processing on an image carrier can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an example of an image forming apparatus according to the present invention.
The image forming apparatus in FIG. 1 is a printer P1 that forms a monochrome image (prints a monochrome image). The printer P1 includes an image carrier 10 and a charging device 20, an image exposure device 30, a developing device 40, and a transfer roller 50 arranged sequentially around the image carrier 10.

Here, the image carrier 10 is a drum-type negatively chargeable photoconductor. The charging device 20 is a scorotron charger in this example.
In this example, the image exposure apparatus 30 performs exposure using a laser beam, and can perform image exposure on the photoconductor 10 according to image information provided from a personal computer (not shown) or the like.
The developing device 40 is a two-component developing device that reversely develops the electrostatic latent image on the photoreceptor 10 using a developer Dp containing a negatively chargeable toner and a positively chargeable carrier.

  The developing device 40 includes a sleeve-shaped developing roller 41, a magnet member MgR that is built in the roller and has N and S poles disposed on the peripheral surface, a head height regulating member 42 that faces the roller 41, and the like. The developer Dp supplied to the developing roller 41 in the developing device is held in the form of a developer spike on the surface of the roller surface by the action of the magnet member MgR, and developed by the spike height regulating member 41 along the way by the rotation of the roller 41. The amount of the agent is regulated, and the photosensitive member 10 and the roller 41 are conveyed to a developing position where they face each other, where they are used for developing the electrostatic latent image.

  A recording medium S accommodating cassette 80 such as recording paper is provided below the image exposure device 30. The recording medium S accommodated in the cassette is pulled out one by one by a medium supply roller 801 and conveyed. It can be conveyed by a roller R or the like and supplied to a timing roller pair TR.

A fixing device 60, a medium discharge roller pair 7E, and a medium discharge tray T are provided on the downstream side of the transfer roller 50 in the recording medium conveyance direction.
Further, as a sensor for detecting a recording medium, a medium supply sensor SE2 is provided for the medium supply roller 801, a pre-timing roller sensor SE1 for the timing roller pair TR, a medium discharge sensor SE3 for the medium discharge roller pair 7E, and the like. Yes.

  FIG. 2 is a block diagram showing an outline of the control circuit of the printer P1. As shown in FIG. 2, the photosensitive member 10 is driven by the photosensitive member driving motor M1, the developing roller 41 is driven by the developing roller driving motor M2, the medium supply roller 801 is driven by the motor M3, and the medium conveying roller R and the timing roller pair TR are driven. The motor M4 is rotationally driven in a predetermined direction at a predetermined timing under the instruction of the control unit Cont1 that controls the operation of the image forming apparatus.

  Further, the charging device 20 has a photosensitive member charging voltage from the power source PW1, the developing roller 10 has a developing bias voltage from the power source PW2, and the transfer roller 50 has a transfer bias voltage from the power source PW3. It is applied at a predetermined timing under the instruction. The image exposure device 30, the fixing device 60, and the like also operate at a predetermined timing under the instruction of the control unit Cont1.

  In addition to the above, the control unit Cont1 includes a print key for inputting a signal (print command) for instructing the start of image formation (print start) to the control unit Cont1, a numeric keypad for designating the number of image formations, etc. An operation panel PA on which a display unit for displaying information from Cont1 is mounted is connected, and recording medium detection information by the sensors SE1 to SE3 is also input to the control unit Cont1.

  According to the printer P1, the image forming process is executed as follows under the instruction of the control unit Cont1. That is, the photosensitive member 10 is rotated in the clockwise direction in the drawing, and the surface thereof is charged to a predetermined potential by the charging device 20 to which a charging voltage (charging grid voltage) is applied from the power source PW1, and image exposure is performed in the charging region. Image exposure according to the image to be formed is performed from the apparatus 30, and an electrostatic latent image is thereby formed. This electrostatic latent image is developed by the developing roller 41 to which a developing bias voltage (developing bias voltage at the time of printing) is applied from the power source PW2 in the developing device 40 to be a visible toner image.

The charging voltage applied from the power source PW1 to the charging device 20 is about −500 V in this example, but can be appropriately adjusted in the range of −300 V to −900 V depending on the ambient temperature and humidity of the image forming apparatus. .
The developing bias voltage applied to the developing roller 10 from the power source PW2 is about −400 V in this example, but can be appropriately adjusted in the range of −200 V to −800 V depending on the ambient temperature and humidity of the image forming apparatus. is there.

  On the other hand, the recording medium S is pulled out from the cassette 80 by the supply roller 801 and supplied to the timing roller pair TR. The rotation of the timing roller pair TR is turned on and off by a clutch (not shown), and the recording medium S is supplied to the transfer area as the toner image on the photoreceptor 10 arrives at the transfer roller 50. Then, the toner image on the photoconductor 10 is transferred to the recording medium S by the transfer roller 50 to which the transfer bias voltage is applied from the power source PW3, and then the recording medium S is passed through the fixing device 60 so that the toner image is transferred. It is fixed under heat and pressure and discharged to the tray T. In this way, the image forming process is executed.

  The transfer bias voltage applied from the power source PW3 to the transfer roller 50 is about +1000 V in this example, but is appropriately adjusted in the range of +500 V to +5000 V depending on the type of recording medium, ambient temperature of the image forming apparatus, humidity, and the like. Is possible.

  After the toner image is transferred, the developer remaining on the photoconductor 10 is removed and cleaned by a cleaner 70. Further, after transfer of the toner image, charges such as charges remaining on the photosensitive member 10 are erased by charge erasure processing prior to the image forming process (in this example, in the process startup control). That is, the control unit Cont1 includes a control unit for charge erasing processing, and the control unit is prior to the visible toner image forming process on the image carrier (in this example, in the process startup control). While driving the image carrier (photoreceptor), the charge erasing target area on the image carrier is continuously exposed from the image exposure device 30 to be fully exposed to erase the charge on the image carrier. As described above, drive control of the image carrier (photosensitive member) and control of the image exposure apparatus are performed.

  In addition, the controller for the charge erasing process transfers the developer from the developing device to the image bearing member (photosensitive member) full exposure region when the full exposure is performed. The bias voltage applied to the developing device (developing roller) is controlled under the control of the bias voltage power supply PW2 for the developing device so that a bias voltage for all exposures that generates an electric field that suppresses the above is applied.

Next, process start-up control by the control unit for charge erasing processing included in the control unit Cont1 will be described with reference to the flowcharts of FIGS.
When a print command is received from the operation panel PA, the photoconductor drive motor M1 is turned on to start rotating the photoconductor 10 (steps S1 and S2).

Next, it is checked whether or not a jam has occurred in the previous image forming process (S3). When there is no jam history, a charging voltage (charging grid voltage) is applied from the power source PW1 to the charging device 20 to charge the surface of the photoconductor when the time T1 when the rotation of the photoconductor 10 is stabilized passes. Is turned on (S4, S7).
Note that the control unit has a built-in measurement unit that measures the drive time (photoreceptor rotation time in this example) of the image carrier (photoreceptor 10 in this example), such as time T1 and time T2 to be described later. Furthermore, the drive integration time (rotation integration time) of the photoconductor 10 can also be measured by the measurement unit.

  The presence or absence of a jam is detected by the control unit, for example, that the elapsed time after the medium supply sensor SE2 is turned on is longer than the normal time required from the sensor SE2 on to the sensor SE1 on before the timing roller. The jam history is stored in the control unit.

  If there is a jam history in step S3, a developing bias voltage at the time of printing is applied to the developing device 40 (developing roller 41), and after the time T6 required for the photosensitive member surface to rotate from the charging position to the developing position, further photosensitive is performed. After the time that the rotation of the body 10 stabilizes, the charging device 20 is turned on (S5, S6, S4, S7). By such control when there is a jam history, it is possible to prevent the positively charged carrier from adhering to the photoreceptor 10.

After the charging device 20 is turned on in step S7, when the time T2 required for the surface of the photoconductor to rotate from the charging position by the charging device 20 to the exposure position by the image exposure device 30 has elapsed, the image exposure device 20 continues the surface of the photoconductor. The exposure of the surface of the photoreceptor starts with exposure (S8, S9).
Further, when the time T3 required for the photosensitive member surface to rotate from the exposure position to the development position by the developing device 40 has elapsed, selection control processing for the bias voltage during all exposure is executed (S10, S11).

  In the selection control of the bias voltage at the time of all exposure in step S11, as will be described later with reference to FIG. 4, an electric field that suppresses the movement of the developer to the photoconductor 10 according to the driving integration time of the photoconductor 10 is applied. A bias voltage for all exposures to be generated is selected and applied to the developing roller 10 in step S12.

  Thereafter, when a time T4 required until the surface potential of the photoconductor becomes uniform has elapsed, continuous exposure (all exposures) by the exposure device 30 is stopped, and further, the time required for the surface of the photoconductor to rotate from the exposure position to the development position. When T5 elapses, application of a developing bias voltage during printing to the developing roller 10 is started, the developing roller driving motor M2 is turned on, and the developing roller 10 is started to rotate (steps S13 to S17).

  Thus, the residual charge erasing process on the photoconductor 10 is executed in a state where the movement of the developer from the developing roller 41 to the photoconductor 10 is suppressed, the process start-up process is completed, and the normal image forming process is started. A state that can be transferred is obtained.

  In the above-described bias voltage selection control (S11), as shown in FIG. 4, the accumulated driving time (rotational accumulated time) of the photosensitive member 10 is the photoconductor surface film shaving corresponding to the accumulated rotational time of the photosensitive member. In consideration of the decrease in the attenuation of the potential during exposure due to the above, if it is less than the drive integration time RT1 previously obtained by experiments or the like, the bias voltage for all exposure (0 V) is selected (S111, S112).

  When the accumulated driving time is RT1 or more, less than RT2 (> RT1), and the charging voltage is lower than the predetermined voltage V1, the bias voltage for full exposure (−150 V) is selected, and the charging voltage is equal to or higher than the voltage V1. In this case, the bias voltage for all exposure (−300 V) is selected (S113, S114, S115, S116). If the drive integration time is equal to or greater than RT2 in step S113, a full exposure bias voltage (-300 V) is selected.

Here, the charging voltage is taken into consideration because the fogging margin (difference between the charging voltage and the bias voltage applied to the developing device) is kept at an appropriate value, and the photosensitive member is deteriorated by the photosensitive member, ambient temperature, humidity, etc. This is because the charging voltage is checked so that the toner can be prevented from adhering to the non-exposed area (fogging) even when the surface potential varies.
Thus, even when the photoconductor 10 is used for a long time, the toner and the carrier are prevented from moving to the photoconductor in the charge erasing process of the photoconductor.

An example of the relationship between the charging voltage V1, the photosensitive member rotation integration time, and the total exposure bias voltage Vb is shown below.
Photoconductor rotation integration time
Less than 2000 minutes 2000 to 8000 minutes 8000 minutes or more Charge voltage lower than V1 −750V Vb: 0V −150V −300V
−750V or more Vb: 0V −300V −300V

Next, another example of the image forming apparatus according to the present invention will be described with reference to FIGS.
The image forming apparatus shown in FIG. 5 is a tandem type full-color printer.
The printer P2 has an endless intermediate transfer belt 4 wound around a driving roller 31 and a roller 32 facing the driving roller 31.

The counter roller 32 faces a cleaner CL for cleaning secondary transfer residual toner and the like on the transfer belt 4, and the drive roller 31 faces the secondary transfer roller 5.
The surface layer portion of the secondary transfer roller 5 is formed of an elastic material, and is pressed against the intermediate transfer belt 4 by pressing means (not shown) to form a nip portion N between the intermediate transfer belt 4 and the intermediate transfer belt. 4 or according to the movement of the recording medium S fed into the nip portion N as will be described later.

A fixing device 6 is disposed above the secondary transfer roller 5, a timing roller pair TR is disposed below, and a cassette 8 containing a recording medium such as recording paper is disposed below the fixing device 6. ing.
The recording medium S accommodated in the recording medium accommodating cassette 8 can be pulled out one by one by the medium supply roller 81 at a predetermined timing and supplied to the timing roller pair TR.

A pre-timing roller sensor SE1 that detects the recording medium S is disposed on the entrance side of the timing roller pair TR.
When the recording medium S starts to be supplied by the roller 81, the medium supply sensor SE2 detects this.

Above the intermediate transfer belt 4, a medium discharge tray T ′ for discharging the recording medium S on which an image has been formed is disposed. The image-formed recording medium S coming out of the fixing device 6 is transported by the transport roller pair R1 and can be discharged onto the discharge tray T ′ by the discharge roller pair 7E. A discharge sensor SE3 for detecting the discharge of the recording medium is provided on the exit side of the discharge roller pair 7E.
Sensors SE1, SE2, and SE3 are used for jam detection and the like.

  Between the rollers 31 and 32 around which the intermediate transfer belt 4 is wound, the yellow image forming unit Y, the magenta image forming unit M, the cyan image forming unit C, and the rollers 32 to 31 are arranged along the transfer belt 4. Black image forming portions K are arranged in this order.

  Each of the image forming units Y, M, C, and K includes a drum-type photoconductor 11 as an image carrier, and a charging device 12, an image exposure device 13, a developing device 14, and a primary are arranged around the photoconductor. A cleaner 15 for removing the transfer roller 2 and the primary transfer residual toner and the like on the photosensitive member is arranged in this order. The primary transfer roller 2 faces the photoreceptor 1 with the transfer belt 4 in between. The exposure device 13 can expose the photoconductor 11 using a laser beam. The primary transfer roller 2 rotates following the rotation of the belt 4.

In this example, the developing device 14 in each image forming unit uses a developer containing a negatively chargeable toner and a positively charged positive carrier, and a developing bias voltage is applied to the electrostatic latent image formed on the photoreceptor 11. The developing roller 141 can be reversed and developed.
Although not shown in the figure, each image forming unit is accompanied by a photosensitive member driving motor, a developing roller driving motor, a charging device power source, a developing device bias power source, and the like.
A transfer voltage is applied to the primary transfer roller 2 from the primary transfer bias voltage power supply PW3 ′ to the secondary transfer roller 5 from the secondary transfer bias voltage power supply PW4 at predetermined timings (see FIG. 6).

FIG. 6 is a block diagram showing an outline of the control circuit of the printer P2. As shown in FIG. 6, the photosensitive member drive motor, the developing roller drive motor, the charging device power supply, the bias power supply for the developing device, the image exposure device, and the like of each image forming unit include Operates under instructions.
The medium supply roller 81 is controlled by a medium supply roller drive motor M3 ′, the transport roller R1, the timing roller pair TR and the like are driven by a medium transport roller drive motor M4 ′, and the drive roller 31 of the intermediate transfer belt is controlled by a motor M5. Is driven to rotate in a predetermined direction at a predetermined timing.
The primary transfer bias voltage power supply PW3 ′ and the secondary transfer bias voltage power supply P4 also apply a transfer voltage to the corresponding transfer roller at a predetermined timing under the instruction of the control unit Cont2.

  In addition to the above, the control unit Cont2 includes a print key for the user to input a signal (print command) instructing start of image formation (print start) to the control unit Cont2, a numeric keypad for designating the number of image formations, etc. An operation panel PA ′ on which a display unit for displaying information from Cont2 is mounted is connected, and recording medium detection information from the sensors SE1 to SE3 is also input to the control unit Cont1.

  According to the printer P2, the image forming process is executed as follows under the instruction of the control unit Cont2. Image formation is performed using one or more of Y, M, C, and K image forming units.

  Taking a case where a full color image is formed using all of the image forming portions Y, M, C and K as an example, first, a yellow toner image is formed in the yellow image forming portion Y, and this is primarily transferred onto the transfer belt 4. Is done.

  That is, in the yellow image forming unit Y, the photoconductor 11 is rotationally driven in the clockwise direction in the drawing. Then, image exposure for the yellow image is performed from the image exposure device 13 to the charged area of the photoconductor 11 whose surface is uniformly charged to a predetermined potential by the charging device 12 to which a charging voltage is applied from the charging device power source. As a result, a yellow electrostatic latent image is formed on the photoreceptor 11. This electrostatic latent image is developed by a developing roller 141 to which a developing bias voltage is applied in a developing device 14 having yellow toner to become a visible yellow toner image, and the toner image is applied with a primary transfer voltage 1 The image is transferred onto the transfer belt 4 by the next transfer roller 2.

  Similarly, a magenta toner image is formed in the magenta image forming unit M and transferred to the transfer belt 4, a cyan toner image is formed in the cyan image forming unit C and transferred to the transfer belt 4, and in the black image forming unit K. A black toner image is formed and transferred to the transfer belt 4.

Yellow, magenta, cyan, and black toner images are formed at the timing when these toner images are transferred onto the intermediate transfer belt 4 in an overlapping manner.
Thus, the multiple toner image formed on the transfer belt 4 moves toward the secondary transfer roller 5 by the rotation of the transfer belt 4.

On the other hand, the recording medium S is pulled out from the recording medium accommodating cassette 8 by the medium supply roller 81 and supplied to the timing roller pair TR.
Thus, the recording medium S supplied to the timing roller pair TR is placed in a nip portion N between the transfer belt 4 and the secondary transfer roller 5 in accordance with the multiple toner image sent by the intermediate transfer belt 4. The multiple toner image is secondarily transferred onto the recording medium S by the secondary transfer roller 5 supplied and applied with the secondary transfer bias voltage. Thereafter, the recording medium S is passed through the fixing device 6, where the multiple toner images are fixed to the recording medium S under heat and pressure, and are subsequently discharged to the discharge tray T ′ by the conveying roller pair R1 and the discharge roller pair 7E. .

  As described above, an image is formed. Also in this printer P2, the charge on the photoconductor 11 is set in each of the Y, M, C, and K image forming units under the instruction of the control unit Cont2. An erasure process is performed. The charge erasing process is performed by the same procedure as that shown in the flowcharts of FIGS. 3 and 4 in the process startup control in each image forming unit. Such process startup control is sequentially performed for each image forming unit.

  The present invention provides an image forming apparatus that can perform charge erasing processing on an image carrier by reducing the size of the image forming apparatus and reducing the size of the image forming apparatus in comparison with a conventional image forming apparatus that employs an eraser. Can be used to do.

1 is a diagram illustrating a schematic configuration of an example (printer) of an image forming apparatus according to the present invention. FIG. 2 is a block diagram illustrating an outline of an operation control circuit of the printer in FIG. 1. 2 is a flowchart showing process start-up control including charge erasing processing in the printer of FIG. 1. 4 is a flowchart showing details of selection control of a bias voltage for all exposures in the flowchart of FIG. 3. It is a figure which shows schematic structure of the other example (color printer) of the image forming apparatus which concerns on this invention. FIG. 3 is a block diagram illustrating an outline of an operation control circuit of the printer of FIG. 2.

Explanation of symbols

P1 Printer 10 Photoconductor 20 Charging device 30 Image exposure device 40 Developing device 41 Developing roller 42 Head height regulating member MgR Magnet member Dp Developer 50 Transfer roller 60 Fixing device S Recording medium 80 Recording medium storage cassette 801 Medium supply roller R Medium transport roller Pair TR Timing roller pair T Medium discharge tray 7E Medium discharge roller pair SE1 Timing roller front sensor SE2 Medium supply sensor SE3 Medium discharge sensor Cont1 Control unit M1 Photoconductor drive motor M2 Development roller drive motor M3 Medium supply roller drive motor M4 Medium transport roller Drive motor PW1 Charging device power supply PW2 Bias voltage power supply PW3 for developing device Transfer bias voltage power supply PA Operation panel

P2 Color printer Y Yellow image forming unit M Magenta image forming unit C Cyan image forming unit K Black image forming unit 11 Photoconductor 12 Charging device 13 Image exposing device 14 Developing device 141 Developing roller 2 Primary transfer roller 31 Driving roller 32 Opposite roller 4 Intermediate transfer belt CL Cleaner 5 Secondary transfer roller 6 Fixing device TR Timing roller pair R1 Medium transport roller pair 7E Medium discharge roller pair T 'Paper discharge tray 8 Recording medium storage cassette 81 Medium supply roller Cont2 Control unit M3' Medium supply roller Drive motor M4 ′ Medium transport roller drive motor M5 Intermediate transfer belt drive motor PW3 ′ Primary transfer bias voltage power supply PW4 Secondary transfer bias voltage power supply PA ′ Operation panel

Claims (4)

The surface of the image carrier that is driven so that the surface moves is charged by a charging device, and an exposure according to the image to be formed is applied to the charged area from the image exposure device to form an electrostatic latent image. The electrostatic latent image is developed by a developing device using a two-component developer containing toner and carrier under application of a developing bias voltage to the developing device to form a visible toner image. An image forming apparatus capable of carrying out an image forming process for transferring the image onto a transfer medium, and erasing the charge on the image carrier prior to the execution of the image forming process. It is carried out by performing continuous exposure from the image exposure device to the charge erasure target area on the image carrier while driving the body,
In the charge erasing process prior to the execution of the image forming process after the image forming process is interrupted at an improper timing, after the driving of the image carrier, the development bias voltage is started to be applied to the developing device, and the image carrier After the start of driving, application of a charging voltage for charging the surface of the image carrier to the charging device is started after the time required for the surface of the image carrier to rotate from the charging position by the charging device to the developing position by the developing device,
In the charge erasing process prior to the execution of the image forming process that is not the image forming process after the image forming process is interrupted at the improper timing, the surface of the image carrier is charged to the charging device after the image carrier driving is started. The charging voltage to be applied is started,
In any of the charge erasing processes, after the charging voltage is started to be applied to the charging device, the time required for the surface of the image carrier to rotate from the charging position by the charging position to the exposure position by the image exposure apparatus. When the time passes, the image carrier surface starts full exposure by continuous exposure in the image exposure apparatus, and then the development takes place when the time required for the exposure region by the full exposure on the image carrier surface to rotate to the development position elapses. Application of a bias voltage at the time of all exposure that generates an electric field that suppresses the movement of the developer from the developing device to the entire exposure area of the image carrier is started in the apparatus, and after the application of the bias voltage at the time of full exposure is started to the developing apparatus, An image forming apparatus , wherein all exposure by the image exposure apparatus is stopped when a time required until the surface potential of the image carrier becomes uniform has elapsed .   The image forming apparatus according to claim 1, wherein the bias voltage during full exposure is set to 0V.   The image forming apparatus according to claim 1, wherein the all-exposure bias voltage is set in accordance with a driving integration time of the image carrier.   The bias voltage during full exposure is set to 0V when the drive integration time of the image carrier is less than a predetermined drive integration time, and other than 0V depending on the drive integration time after the predetermined drive integration time. The image forming apparatus according to claim 3, wherein the image forming apparatus is changed and set to a value of.