JP6213495B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus.

  In an electrophotographic image forming apparatus, a two-component development system is known. In the two-component development method, an electrostatic latent image on the outer peripheral surface of the photoconductor is obtained when a developing roller carrying a magnetic brush containing toner and a carrier contacts the outer peripheral surface of the rotating photoconductor. Is developed into a toner image.

  On the other hand, in the image forming apparatus, it is known that static elimination before transfer is performed in order to improve transferability of the toner image from the photoreceptor to a transfer medium such as a sheet or a belt member (for example, Patent Document 1). The charge removal before transfer is to irradiate the region between the development position and the transfer position of the toner image on the outer peripheral surface of the photoreceptor.

Japanese Unexamined Patent Publication No. 64-13578

  By the way, in the two-component development method, a problem of carrier transfer may occur. The carrier shift is a phenomenon in which the carrier of the magnetic brush moves to the outer peripheral surface of the photoconductor. The carrier transfer may be referred to as carrier development. When the charging potential of the photosensitive member or the bias voltage of the developing roller is adjusted, the carrier transfer and the development failure are in a trade-off relationship.

  The development failure may be caused by, for example, developing fog in which toner adheres to a region that should not be developed on the outer peripheral surface of the photoconductor, or the toner adhering to the photoconductor being pulled by the electric force of the carrier. For example, the rear end pool that accumulates on the side.

  Therefore, it is difficult to improve the carrier transfer problem while avoiding the development failure by adjusting the charge amount of the photoconductor or the chargeability of the carrier.

  In addition, when the power supply to the image forming apparatus is stopped due to a power failure or other unforeseen event, the photoconductor and the developing roller are slightly affected by inertia even after the power supply to the motor that is a driving source thereof is stopped. It continues to rotate in time. In this case, in the state where the application of the bias voltage to the developing roller is stopped, the already charged portion on the outer peripheral surface of the photoconductor passes through the developing position. For this reason, the problem of carrier shift becomes more prominent.

  In addition, it is difficult to increase the holding force of the carrier in the developer by increasing the magnetic force of the magnet in the developer due to space restrictions in the developer.

  An object of the present invention is to provide an image forming apparatus capable of improving the problem of carrier transfer while avoiding the occurrence of defective development when development is performed by a two-component development method.

  An image forming apparatus according to an aspect of the present invention includes a photoconductor, a developer, a pre-discharge light-emitting unit, a first pre-discharge power supply unit, and a second pre-discharge power supply unit. The photosensitive member is a rotating member that is rotationally driven by a first motor and forms an electrostatic latent image on the outer peripheral surface at the exposure position. The exposure position is a position on the downstream side in the rotation direction of the photoconductor with respect to the charging position facing the charging unit. The developing body is a rotating body that is driven to rotate by a second motor while being applied with a bias voltage. The developer carries a magnetic brush containing toner and a carrier, and the electrostatic brush is brought into contact with an effective outer peripheral surface on the outer peripheral surface of the photoconductor at which the electrostatic latent image can be formed at a development position. The latent image is developed into a toner image. The development position is a position downstream of the exposure position in the rotation direction of the photoconductor. The pre-discharge light emitting unit is a light emitting unit that irradiates a charge removal target region on the effective outer peripheral surface of the photoconductor. The area to be neutralized includes an area from a part of the magnetic brush contact area that contacts the magnetic brush on the effective outer peripheral surface of the photoconductor to an area between the magnetic brush contact area and the toner image transfer position. It is. The first pre-charger power supply unit feeds power to the pre-charger light emitting unit when power is supplied to the first motor and the second motor and the bias voltage is applied to the developer. The pre-discharge light emitting unit is caused to emit light. The second pre-neutralization power feeding unit is configured to perform the pre-neutralization in a temporary period after at least one of power feeding to the first motor or the second motor and application of the bias voltage to the developer is stopped. The pre-discharge light emitting unit is caused to emit light by continuing to supply power to the light emitting unit.

  According to the present invention, it is possible to provide an image forming apparatus capable of improving the problem of carrier transfer while avoiding the occurrence of development failure when development is performed by the two-component development method.

FIG. 1 is a configuration diagram of an image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a configuration diagram of the pre-discharge light emitting unit and its peripheral part when viewed along the first direction in the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is a configuration diagram of the pre-discharge light emitting unit and its peripheral portion when viewed along the second direction in the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a block diagram of control-related equipment in the image forming apparatus according to the first embodiment of the present invention. FIG. 5 is a schematic configuration diagram of a pre-neutralization power feeding unit in the image forming apparatus according to the first embodiment of the present invention. FIG. 6 is a flowchart illustrating an example of the procedure of pre-discharge light control in the image forming apparatus according to the first embodiment of the present invention. FIG. 7 is a graph showing the relationship between the printing rate of the first charge removal target area and the amount of charge removal light in the image forming apparatus according to the first embodiment of the present invention. FIG. 8 is a time chart of various voltages and the photosensitive member rotation speed when a power feeding failure state occurs in the image forming apparatus according to the first embodiment of the present invention. FIG. 9 is a configuration diagram of the pre-discharge light emitting unit and its peripheral portion when viewed along the first direction in the image forming apparatus according to the second embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the following embodiment is an example which actualized this invention, Comprising: It does not have the character which limits the technical scope of this invention.

First Embodiment: Schematic Configuration of Image Forming Apparatus
First, a schematic configuration of the image forming apparatus 10 according to the first embodiment of the present invention will be described with reference to FIGS. The image forming apparatus 10 is an electrophotographic image forming apparatus. As shown in FIG. 1, the image forming apparatus 10 includes a sheet supply unit 2, a sheet conveyance unit 3, a toner supply unit 40, an image forming unit 4, an optical scanning unit 5, a fixing unit 6, and a control unit 8 in a casing 100. And an operation display unit 80 and the like.

  The image forming apparatus 10 is, for example, a printer, a copier, a facsimile machine, or a multifunction machine. The multifunction machine has both the printer function and the copier function.

  An image forming apparatus 10 shown in FIG. 1 is a tandem type image forming apparatus and is a color printer. Therefore, the image forming unit 4 further includes an intermediate transfer belt 48, a secondary cleaning unit 480, and a secondary transfer unit 49.

  The image forming unit 4 includes a plurality of single-color image forming units 4x corresponding to each color of cyan, magenta, yellow, and black. Further, the image forming apparatus 10 includes a plurality of toner replenishing units 40 that supply toners 91 of cyan, magenta, yellow, and black to the developing units 43 described later.

  The sheet supply unit 2 includes a sheet receiving unit 21 and a sheet sending unit 22. The sheet receiving unit 21 is configured to be able to stack a plurality of recording sheets 9. The recording sheet 9 is a sheet-like image forming medium such as paper, coated paper, postcard, envelope, and OHP sheet.

  The sheet delivery unit 22 rotates in contact with the recording sheet 9 to send the recording sheet 9 from the sheet receiving unit 21 toward the conveyance path 30.

  The sheet conveyance unit 3 includes a registration roller 31, a conveyance roller 32, a discharge roller 33, and the like. The registration roller 31 and the conveyance roller 32 convey the recording sheet 9 supplied from the sheet supply unit 2 toward the secondary transfer unit 49 of the image forming unit 4. Further, the discharge roller 33 discharges the recording sheet 9 after image formation from the discharge port of the conveyance path 30 onto the discharge tray 101.

[Image forming unit]
Each single color image forming unit 4x includes a drum-shaped photoconductor 41, a charging unit 42, a developing unit 43, a pre-discharge light emitting unit 44, a primary transfer unit 45, a primary cleaning unit 46, a post-discharge light emitting unit 47, and the like. The photoreceptor 41 is a member on which an electrostatic latent image is written by laser light, and is an example of a toner image carrier that carries a toner image while rotating. For example, each of the photoconductors 41 may be an organic photoconductor or an amorphous silicon photoconductor.

  Hereinafter, a region where the electrostatic latent image can be formed on the outer peripheral surface of the photoconductor 41, that is, a region of the maximum width on the outer peripheral surface of the photoconductor 41 where an image can be formed is referred to as an effective outer peripheral surface 410. The first direction D1 shown in FIGS. 1 to 3 is the width direction of the photoconductor 41, that is, the horizontal direction along the rotation center of the photoconductor 41. The second direction D2 is a direction orthogonal to the first direction D1 in the horizontal plane.

  The photoconductor 41 rotates and the charging unit 42 uniformly charges the effective outer peripheral surface 410 of the photoconductor 41. The photosensitive body 41 has a rotation shaft connected to the first motor 419 through the first connection mechanism 4190 and is driven to rotate by the first motor 419. Hereinafter, the position facing the charging portion 42 on the outer periphery of the photoconductor 41 is referred to as a charging position P1. Note that the first motor 419 may also serve as the second motor 439.

  Further, the optical scanning unit 5 including the laser light source 51 irradiates the charged effective outer peripheral surface 410 of the photoreceptor 41 with the laser light by scanning the laser light. The laser beam is applied to the effective outer peripheral surface 410 at the exposure position P2 on the downstream side in the rotation direction of the photoconductor 41 with respect to the charging position P1. As a result, an electrostatic latent image is formed on the effective outer peripheral surface 410 of the photoconductor 41 at the exposure position P2.

  Further, the developing roller 430 of the developing unit 43 supplies the toner 91 to the photoconductor 41 at the developing position P3, thereby developing the electrostatic latent image into the toner image. The development position P3 is a position downstream of the exposure position P2 in the rotation direction of the photoconductor 41.

  The developing roller 430 is a rotating body to which a developing bias voltage is applied. The developing bias voltage is applied to the developing roller 430 by a bias applying circuit (not shown). The rotation shaft of the developing roller 430 is coupled to the second motor 439 through the second coupling mechanism 4390, and is rotated by the second motor 439. The developing roller 430 is an example of a developer.

  Further, the primary transfer unit 45 transfers the toner image on the effective outer peripheral surface 410 of the photoreceptor 41 to the intermediate transfer belt 48 at the transfer position P4. The transfer position P4 is a position downstream of the developing position P3 in the rotation direction of the photoconductor 41.

  Further, the primary cleaning unit 46 removes the toner 91 remaining on the outer peripheral surface of the photoreceptor 41. In the present embodiment, the intermediate transfer belt 48 is an example of a transfer medium onto which the toner image is transferred from the photoreceptor 41.

  The intermediate transfer belt 48 is an endless belt-like member formed in an annular shape. The intermediate transfer belt 48 rotates while being stretched between two rollers. In the image forming unit 4, each single color image forming unit 4 x transfers the toner image of each color onto the surface of the rotating intermediate transfer belt 48. As a result, a color image in which the toner images of the respective colors are superimposed is formed on the intermediate transfer belt 48.

  The secondary transfer unit 49 transfers the toner image formed on the intermediate transfer belt 48 to the recording sheet 9. The secondary cleaning unit 480 removes the toner 91 remaining on the intermediate transfer belt 48 after passing through the secondary transfer unit 49.

  The fixing unit 6 sends the recording sheet 9 on which an image is formed between the heating roller 61 and the pressure roller 62 that encloses the heater 611 to the subsequent process. As a result, the fixing unit 6 heats the image on the recording sheet 9 and fixes the image on the recording sheet 9.

  The developing unit 43 in the present embodiment performs development using a two-component development method. That is, the developing unit 43 charges the toner 91 by stirring the two-component developer 90 including the toner 91 and the carrier 92, and supplies the charged toner 91 to the photoreceptor 41.

  The carrier 92 is a granular material having magnetism. For example, the carrier 92 may be a granular body including a granular magnetic body and a synthetic resin film such as an epoxy resin coated on the surface of the magnetic body.

  As shown in FIG. 2, the developing unit 43 includes a developing tank 4300, a developing roller 430, a stirring member 437, and a blade 438. Further, the developing unit 43 includes a developing magnet 431. The magnet 431 is included in the developing roller 430. The developing roller 430 and the magnet 431 constitute a magnet roller for carrying a two-component developer.

  The developing tank 4300 is a container for storing the two-component developer 90. The developing roller 430 and the stirring member 437 rotate in the developing tank 4300. The developing roller 430 is rotatably supported so as to face the photoreceptor 41 in a non-contact state.

  During the developing operation, the developing roller 430 rotates in the direction opposite to the rotation direction of the photoconductor 41. As a result, the mutually opposing portions of the developing roller 430 and the outer peripheral surface of the photoreceptor 41 move in the same direction.

  The agitating member 437 agitates the two-component developer 90 in the developing tank 4300. As a result, the toner 91 is charged with a predetermined polarity. Further, the carrier 92 is charged with a polarity opposite to the charging polarity of the toner 91.

  The developing roller 430 is an example of a two-component developer carrying member that rotates while carrying the stirred two-component developer 90. The developing roller 430 supplies the charged toner 91 of the carried two-component developer 90 to the photoreceptor 41.

  More specifically, the developing roller 430 carries the two-component developer 90 as the magnetic brush 900 by the action of the magnetic force of the magnet 431 included therein, and conveys the magnetic brush 900 to a position facing the photoconductor 41. .

  Further, the developing roller 430 develops the electrostatic latent image into the toner image by bringing the magnetic brush 900 into contact with the effective outer peripheral surface 410 of the rotating photoreceptor 41. Hereinafter, a region on the effective outer peripheral surface 410 of the photoconductor 41 that is in contact with the magnetic brush 900 is referred to as a magnetic brush contact region 411.

  The toner 91 in the magnetic brush 900 moves from the surface of the developing roller 430 to the portion of the electrostatic latent image on the effective outer peripheral surface 410 of the photoreceptor 41 by the action of the developing bias voltage applied to the developing roller 430. As a result, the electrostatic latent image is developed as a toner image.

  The blade 438 limits the thickness of the magnetic brush 900 at a position where the magnetic brush 900 carried on the outer peripheral surface of the developing roller 430 reaches the magnetic brush contact region 411.

  The potential difference between the outer peripheral surface of the developing roller 430 and the electrostatic latent image portion on the effective outer peripheral surface 410 of the photoreceptor 41 is the same as the charging polarity of the toner 91. Further, the potential difference between the outer peripheral surface of the developing roller 430 and the portion other than the electrostatic latent image on the effective outer peripheral surface 410 of the photoconductor 41 is opposite to the charging polarity of the toner 91. Therefore, the charged toner 91 in the magnetic brush 900 selectively adheres to the portion of the electrostatic latent image on the photoconductor 41 in the magnetic brush contact area 411.

  On the other hand, the carrier 92 in the magnetic brush 900 is held on the developing roller 430 by the attractive force of the magnet 431 even after passing through the magnetic brush contact region 411.

[Static elimination light emitting part]
The pre-discharge light emitting unit 44 is a light emitting unit that irradiates the first charge removal target region 413 upstream of the transfer position P4 on the effective outer peripheral surface 410 of the photoconductor 41 with respect to the rotation direction of the photoconductor 41. The transfer position is a position facing the primary transfer unit 45 and is a position downstream of the position facing the developing unit 43 in the rotation direction of the photoconductor 41.

  The post-discharge light emitting unit 47 is a light emitting unit that irradiates the second charge removal target region 414 on the downstream side in the rotation direction of the photoconductor 41 with respect to the transfer position P4 on the effective outer peripheral surface 410 of the photoconductor 41. The second static elimination target area 414 is an area between the transfer position P4 and the charging position. The charging position is a position facing the charging unit 42 and is a position on the downstream side in the rotation direction of the photoconductor 41 with respect to the transfer position P4.

  Each of the pre-discharge light emitting unit 44 and the post-discharge light emitting unit 47 is, for example, an LED array formed extending along the first direction D1. Each of the pre-discharge light emitting unit 44 and the post-charge light emitting unit 47 outputs the discharge light having a predetermined wavelength according to the photosensitive characteristics of the photoconductor 41.

  In the example shown in FIG. 1, the post-discharge light emitting unit 47 irradiates the charge removing light on a region between the cleaning position facing the primary cleaning unit 46 on the effective outer peripheral surface 410 of the photoreceptor 41 and the charging position. It is also conceivable that the post-discharge light emitting unit 47 irradiates the area on the effective outer peripheral surface 410 of the photoconductor 41 between the transfer position and the cleaning position with the discharge light.

  The neutralization light is irradiated from the preliminary neutralization light emitting unit 44 to the first neutralization target region 413 on the effective outer peripheral surface 410 of the photoconductor 41, whereby the toner image of the toner image from the photoconductor 41 to the intermediate transfer belt 48 at the charging position. Transferability is improved.

  Further, the discharge light is irradiated from the post-discharge light emitting unit 47 to the second charge removal target region 414 on the effective outer peripheral surface 410 of the photoconductor 41, thereby eliminating the variation in potential on the effective outer peripheral surface 410 of the photoconductor 41. . As a result, the effective outer peripheral surface 410 of the photoconductor 41 is more uniformly charged through the charging process by the charging unit 42.

  The control unit 8 controls various electric devices included in the image forming apparatus 10 based on input information input through the operation display unit 80 and detection results of various sensors. In addition, the control unit 8 displays an operation menu or the like on the operation display unit 80. Further, the control unit 8 receives an image forming job from the host device, and executes image processing on the image of the image forming job.

  For example, as illustrated in FIG. 4, the control unit 8 includes an MPU (Micro Processor Unit) 81, a storage unit 82, an image processing unit 83, a charge removal light control unit 84, a laser light control unit 85, and a communication unit 86.

  The MPU 81 is a processor that executes various arithmetic processes. The storage unit 82 is a nonvolatile information storage medium in which programs for causing the MPU 81 to execute various processes and other information are stored in advance. Furthermore, the storage unit 82 is also an information storage medium in which various information can be read and written by the MPU 81.

  The control unit 8 comprehensively controls the image forming apparatus 10 by the MPU 81 executing various programs stored in the storage unit 82 in advance.

  The image processing unit 83 inputs an image forming job from a host device (not shown) through the communication unit 86 and executes image processing. For example, the image processing unit 83 generates image data from an image forming job obtained from the host device.

  The laser light control unit 85 controls the output light amount of the laser light source 51 according to the density of each pixel indicated by the image data obtained from the image processing unit 83. As a result, the electrostatic latent image corresponding to the image data is formed on the effective outer peripheral surface 410 of the photoreceptor 41.

  The communication unit 86 executes wired or wireless communication with the host device such as a personal computer or a portable terminal. For example, the communication unit 86 receives the image forming job from the host device.

  The static elimination light control unit 84 controls the light emission state of each of the front static elimination light emission unit 44 and the post static elimination light emission unit 47. More specifically, the static elimination light control unit 84 controls the pre-neutralization power feeding unit 87 that supplies power to the pre-neutralization light emitting unit 44 and the post-neutralization power feeding unit 88 that supplies power to the post-neutralization light emitting unit 47.

  The pre-neutralization power feeding unit 87 includes a first pre-neutralization power feeding unit 871 and a second pre-neutralization power feeding unit 872. The first pre-neutralization power supply unit 871 supplies power to the pre-neutralization light emitting unit 44 when power is supplied to the first motor 419 and the second motor 439 and the development bias voltage is applied to the developing roller 430. The pre-discharge light emitting unit 44 is caused to emit light.

  On the other hand, the second pre-removing power supply unit 872 causes the pre-removing light emitting unit 44 to emit light by supplying power to the pre-removing light emitting unit 44 in a state where power supply to the image forming apparatus 10 is stopped or insufficient.

  FIG. 5 shows an example of the configuration of the pre-static discharge power supply unit 87. In the example shown in FIG. 5, the pre-neutralization power feeding unit 87 includes a first pre-neutralization power feeding unit 871, a second pre-neutralization power feeding unit 872, and an output changeover switch 873. Further, the first pre-neutralization power feeding unit 871 includes a constant voltage power source 8711 and a PWM circuit 8712. The second pre-static charge feeding unit 872 includes a booster circuit 8721 and a capacitor 8722.

  The constant voltage power supply 8711 is a power supply that outputs a reference voltage VL0 having a predetermined level. The PWM circuit 8712 outputs the first supply voltage Vo1 after the pulse width modulation in which the duty ratio is adjusted according to the control signal from the static elimination light control unit 84. The static elimination light control unit 84 controls the light amount of the pre-static elimination light emitting unit 44 by controlling the PWM circuit 8712.

  The booster circuit 8721 is a circuit that boosts the reference voltage VL0 output from the constant voltage power supply 8711. The output voltage of the booster circuit 8721 is applied to the capacitor 8722. The capacitor 8722 is a secondary battery that stores electricity when the output voltage of the booster circuit 8721 is applied. The capacitor 8722 outputs the second supply voltage Vo2 when discharging.

  The output changeover switch 873 selectively selects one of the first supply voltage Vo1 of the PWM circuit 8712 and the second supply voltage Vo2 of the capacitor 8722 depending on whether or not the constant voltage power supply 8711 outputs a normal signal. This is a change-over switch applied to the pre-discharge light emitting unit 44.

  The constant voltage power supply 8711 outputs the normal signal only when power supply is possible. Accordingly, the constant voltage power supply 8711 outputs the normal signal when the power supply to the image forming apparatus 10 is sufficient, but does not output the normal signal when the image forming apparatus 10 is in the power supply incomplete state.

  The output changeover switch 873 applies the first supply voltage Vo1 to the pre-discharge light emitting unit 44 when the normal signal is output, and supplies the second supply to the pre-discharge light emitting unit 44 when the normal signal is not output. A voltage Vo2 is applied.

  The capacitor 8722 of the second pre-neutralization power feeding unit 872 stores power during power feeding from the first pre-neutralization power feeding unit 871 to the pre-neutralization light emitting unit 44. Further, the capacitor 8722 is switched to the state in which the output changeover switch 873 selects the second supply voltage Vo2 as the output voltage, that is, the power supply from the first pre-discharge power supply unit 871 to the pre-discharge light emitting unit 44 is stopped. To discharge from.

  The operation and effect of the pre-neutralization feeding unit 87 including the first pre-neutralization feeding unit 871 and the second pre-neutralization feeding unit 872 will be described later.

  In addition, it is possible that the post static elimination power supply part 88 is equipped with the same structure as the 1st front static elimination power supply part 871. Further, the post-removing power supply unit 88 may include a constant voltage power source and a switch for switching whether to apply the output of the constant voltage power source to the post-removing light emitting unit 47 in accordance with a control signal from the neutralization light control unit 84. Conceivable. It is also conceivable that the constant voltage power supply 8711 of the pre-neutralization power supply unit 87 may also serve as the constant voltage power source of the post static electricity supply unit 88.

  The neutralization light control unit 84 maintains the post neutralization light emitting unit 47 in a lighting state while the charging unit 42 and the developing unit 43 are in operation. The details of the control of the pre-discharge light emitting unit 44 by the discharge light control unit 84 will be described later.

  By the way, in the two-component development method, a problem of carrier transfer may occur. The carrier shift is a phenomenon in which the carrier 92 of the magnetic brush 900 moves to the outer peripheral surface of the photoreceptor 41. When the charging potential of the photoconductor 41 or the charging property of the carrier 92 is adjusted, the carrier transfer and the development failure are in a trade-off relationship.

  The development failure is, for example, development fog or rear end accumulation. The development fog is development in which the toner 91 adheres to an area on the effective outer peripheral surface 410 of the photoconductor 41 that should not be developed. The rear end accumulation is a phenomenon in which the toner 91 adhering to the photoconductor 41 is attracted by the electric force of the carrier 92 on the developing roller 430 and accumulated on the downstream side in the rotation direction of the photoconductor 41.

  Therefore, it is difficult to improve the carrier transfer problem while avoiding the development failure by adjusting the charge amount of the photoconductor 41 or the chargeability of the carrier 92.

  Further, when power supply to the image forming apparatus 10 is stopped due to a power failure or other unexpected event, the photoconductor 41 and the developing roller 430 stop supplying power to the first motor 419 and the second motor 439 that are driving sources thereof. After that, it rotates continuously for a short time due to inertia. In this case, in the state where the application of the bias voltage to the developing roller 430 is stopped, the already charged portion on the outer peripheral surface of the photoconductor 41 passes through the developing position P3. For this reason, the problem of carrier shift becomes more prominent.

  Further, it is difficult to increase the holding force of the carrier 92 in the developing roller 430 by increasing the magnetic force of the magnet 431 in the developing unit 43 due to space restrictions in the developing roller 430 and the like.

  On the other hand, when the image forming apparatus 10 having the configuration shown below is employed, when the development is performed by the two-component development method, the problem of the carrier shift is improved while avoiding the occurrence of the development failure. Can do.

[Pre-transfer static neutralizer]
In the present embodiment, the static elimination light control unit 84 that controls the lighting state of the preliminary static elimination light emitting unit 44 and the preliminary static elimination light emitting unit 44 irradiates the first static elimination target region 413 on the effective outer peripheral surface 410 of the photoreceptor 41 with the static elimination light. FIG.

  The first static elimination target region 413 in the present embodiment includes a part from the magnetic brush contact region 411 to a region between the magnetic brush contact region 411 and the transfer position P4. Further, the front charge removal light emitting unit 44 emits the charge removal light toward the magnetic brush contact region 411 from a position downstream of the developing unit 43 in the rotation direction of the photoconductor 41.

  In the present embodiment, a part of the charge removal light from the previous charge removal light emitting unit 44 is applied to the magnetic brush contact region 411. In this case, the static elimination light is mainly applied to a portion of the magnetic brush contact region 411 on the downstream side in the rotation direction of the photoconductor 41, and the progress of the static elimination light to the upstream side is blocked by the magnetic brush 900.

  In general, the carrier transfer is likely to occur in the downstream portion of the magnetic brush contact region 411. In the downstream portion of such a magnetic brush contact region 411, when the charge amount of the photoconductor 41 becomes small due to the irradiation of the charge eliminating light, the occurrence of carrier transfer is suppressed.

  In particular, the region where the carrier transfer is likely to occur is the magnetic brush contact region from the position where the magnetic force component in the magnetic force peak direction D0 in the magnetic field generated by the magnet 431 of the developing unit 43 toward the photoconductor 41 becomes 80% of the peak magnetic force. This is a region up to the end on the transfer position P4 side in 411. The magnetic force peak direction D0 is a direction in which the magnetic force in the magnetic field generated by the magnet 431 toward the photoconductor 41 becomes a peak.

  In the example illustrated in FIG. 2, the main pole 4311 closest to the photoconductor 41 in the magnet 431 of the developing unit 43 generates a magnetic field toward the photoconductor 41. A magnetic brush 900 that the magnetic pole generated by the main pole 4311 rises toward the photosensitive member 41 is formed.

  Accordingly, the position where the magnetic component in the magnetic force peak direction D0 in the magnetic field generated by the main pole 4311 of the magnet 431 toward the photoconductor 41 is 80% of the peak magnetic force is the first static elimination target area where the static elimination light is irradiated. 413 is preferably included.

  Further, due to the light shielding action of the magnetic brush 900, the influence of the static elimination light is small in the upstream portion of the magnetic brush contact area 411, that is, in the development area where the toner 91 mainly moves to the photoconductor 41. For this reason, the development failure due to the reduction of the charge amount of the development region by the static elimination light is unlikely to occur.

  The development failure caused by the charge removal light of the front charge removal light emitting unit 44 is a phenomenon in which a part of the toner image is lost due to a decrease in the holding force of the toner 91 on the effective outer peripheral surface 410 of the photoreceptor 41. The effective outer peripheral surface 410 of the photoconductor 41 holds the toner 91 by electrical attraction.

  By the way, it is desired that the development failure caused by the charge removal light can be avoided more reliably. For example, the development failure due to the charge removal light may be caused even when the pre-discharge light emitting unit 44 having a relatively high output is selected, or when the change in the light shielding effect occurs due to the change in the formation state of the magnetic brush 900. It is desirable that it can be avoided.

  Therefore, the pre-discharge light emitting unit 44 and the discharge light control unit 84 in the present embodiment change the light amount of the pre-discharge light emitting unit 44 according to the density of the toner image in the first charge removal target region 413 of the photoconductor 41. As will be described later, the static elimination light control unit 84 reduces the light amount of the previous static elimination light emitting unit 44 when the density of the toner image in the first static elimination target region 413 is larger than when the density of the toner image is small. .

  As shown in FIG. 3, the pre-discharge light emitting unit 44 in the present embodiment is formed over the entire range in the first direction D <b> 1 in the first charge removal target region 413. As a result, the pre-discharge light emitting unit 44 can irradiate the entire range in the first direction D1 in the first charge removal target region 413 with the charge removal light.

[Pre-charge control]
Next, an example of pre-discharge light control will be described with reference to FIGS. The pre-discharge light control is control of the light emission state of the pre-discharge light emitting unit 44 by the charge eliminating light control unit 84. FIG. 6 is a flowchart showing an example of the procedure of the pre-discharge light control. FIG. 7 is a graph showing the relationship between the printing rate of the first charge removal target area 413 and the light quantity of the charge removal light.

  In the following description, S1, S2,... Represent identification codes of respective steps executed by the static elimination light control unit 84. The pre-discharge light control is executed as part of an image forming process that is started when the communication unit 86 receives the image forming job from the host device.

<Process S1>
In the previous charge removal light control, first, the charge removal light control unit 84 calculates the printing rate of the first charge removal target region 413. The charge removal light control unit 84 calculates the printing rate by counting pixels having a predetermined density or more in the image data obtained from the image processing unit 83. The printing rate of the first charge removal target area 413 corresponds to the density of the toner image in the first charge removal target area 413.

  In this embodiment, the static elimination light control part 84 calculates the said printing rate about the whole range of the 1st direction D1 in the 1st static elimination object area | region 413. FIG. As described above, the first direction D1 corresponds to the width direction of the photoconductor 41.

<Process S2>
Subsequently, the charge removal light control unit 84 adjusts the light amount of the previous charge removal light emitting unit 44 to a light amount corresponding to the printing rate of the first charge removal target region 413. The static elimination light control unit 84 reduces the amount of light of the previous static elimination light emitting unit 44 when the printing rate of the first static elimination target area 413 is larger than when the printing rate is small. When the adjusted light quantity is not zero, the static elimination light from the previous static elimination light emitting unit 44 is irradiated to the entire range of the first static elimination target area 413 with the adjusted light quantity.

  In the example shown in FIG. 7, the static elimination light control unit 84 gradually reduces the light quantity of the previous static elimination light emitting unit 44 from the maximum light quantity as the printing rate of the first static elimination target area 413 increases. Note that, as in the two-dot chain line graph shown in FIG. 7, the static elimination light control unit 84 continuously changes the light amount of the preliminary static elimination light emitting unit 44 in accordance with the printing rate of the first static elimination target area 413. Is also possible.

  In the example illustrated in FIG. 7, the static elimination light control unit 84 turns off the previous static elimination light emitting unit 44 when the printing rate of the first static elimination target area 413 exceeds a predetermined upper limit value. The static elimination light control unit 84 controls the PWM circuit 8712 to adjust the light quantity of the pre-static elimination light emitting unit 44.

<Process S3>
Further, after step S <b> 2 is executed, the static elimination light control unit 84 determines whether or not the development processing corresponding to the image forming job has been completed. And the static elimination light control part 84 repeats the process of process S1, S2 until the said development process is complete | finished.

  As described above, the static elimination light control unit 84 in the present embodiment performs the preliminary static elimination light emission according to the density (printing rate) of the toner image in the entire range in the first direction D1 in the first static elimination target area 413. The amount of light that the unit 44 irradiates the first static elimination target area 413 is changed.

  In general, the carrier transfer tends to occur in an area where the non-image area where the toner image is not formed on the effective outer peripheral surface 410 of the photoconductor 41 is large. On the other hand, the development failure such as a part of the toner image being lost tends to occur in a region where the toner image occupies a large proportion.

  In the present embodiment, the static elimination light of the previous static elimination light emitting unit 44 is applied to the first static elimination target region 413 with a larger amount of light when the first static elimination target region 413 becomes the non-image region or a state close thereto. Irradiated.

  In other words, the static elimination light of the preliminary static elimination light emitting unit 44 is applied to the first static elimination target area 413 with a larger amount of light when the effect of suppressing the carrier transfer is high and the development failure is unlikely to occur.

  Further, when the density of the toner image in the first static elimination target area 413 is large, the static elimination light of the pre-eliminating light emitting unit 44 is applied to the first static elimination target area 413 with a smaller amount of light, or the first static elimination target. The target area 413 is not irradiated.

  In other words, is the charge removal light of the pre-charge light emitting unit 44 irradiated to the first charge removal target region 413 with a smaller amount of light when the effect of suppressing the carrier transfer is low and the development failure is likely to occur? Alternatively, the first static elimination target area 413 is not irradiated. As a result, it is possible to more reliably avoid the development failure due to the charge removal light.

[Operation when the power supply incomplete state occurs]
Next, with reference to the time chart shown in FIG. 8, changes in various voltages and the rotation speed of the photoconductor 41 in the image forming apparatus 10 when the insufficient power supply state occurs will be described. The power supply incomplete state is, for example, a state in which a power failure has occurred, or a state in which a power cable plug is unplugged from a commercial power outlet.

  FIG. 8 shows changes in various voltages and the rotation speed of the photoconductor 41 when the power supply state to the image forming apparatus 10 changes from the normal state to the power supply incomplete state during the image forming process by the image forming unit 4. Show. In FIG. 8, the time when the power supply state to the image forming apparatus 10 changes from the normal state to the power supply incomplete state is a power supply incomplete occurrence time t0.

  When the power supply incomplete state occurs during the image forming process, the voltage supply to each of the first motor 419 and the second motor 439 is quickly stopped. Furthermore, the voltage supply to the charging unit 42 is also stopped quickly.

  However, even if the power supply to the first motor 419 is stopped, the first motor 419 continues to rotate due to inertia until a relatively short first period t1 elapses. The same applies to the developing roller 430.

  In the present embodiment, the output of the normal signal by the constant voltage power supply 8711 stops at the time t0 when the power feeding failure occurs. Therefore, the voltage applied to the pre-discharge light emitting unit 44 is switched from the first supply voltage Vo1 to the second supply voltage Vo2 (see FIG. 5).

  That is, the second pre-discharge light-feeding unit 872 has a pre-discharge light-emitting unit in a temporary period after the power supply to the first motor 419 and the second motor 439 and the application of the developing bias voltage to the developing roller 430 are stopped. 44 is caused to emit light. In FIG. 8, the second period t2 is a period in which the pre-charge light emitting unit 44 emits light by applying the second supply voltage Vo2.

  Therefore, after the time t0 when the power feeding failure occurs, the problem of carrier transfer is solved while the already charged portion of the outer peripheral surface of the photoconductor 41 passes the developing position P3 in a state where the application of the developing bias voltage is stopped. The

  In addition, the peak level VL2 of the second supply voltage Vo2 is higher than the peak level VL1 of the first supply voltage Vo1 due to the action of the booster circuit 8721 of the second pre-neutralization power feeding unit 872. For this reason, the power supplied to the pre-discharge light emitting unit 44 is larger than before the power supply deficiency occurrence time t0 at least in a certain period from the power supply deficiency occurrence time t0.

  Further, the second supply voltage Vo2 that is the discharge voltage of the capacitor 8722 is not pulse-modulated. Therefore, until the level of the second supply voltage Vo2 is slightly lower than the peak level VL1 of the first supply voltage Vo1, the supply power to the pre-discharge light emitting unit 44 is larger than the supply power before the power supply failure occurrence time t0. continue.

  In other words, the second pre-neutralization power feeding unit 872 causes the pre-neutralization light emitting unit 44 to emit light with a larger amount of light than the first pre-neutralization power feeding unit 871 at least for a certain period from the time t0 when the power feeding failure occurs. As a result, the carrier transfer problem can be solved more reliably.

  In addition, in the first period t1 in which the photoconductor 41 and the developing roller 430 rotate due to inertia after the power supply failure occurrence time t0, it is necessary to consider the problem of the development failure caused by the light amount of the pre-discharge light emitting unit 44 being too large. There is no. The development failure is a phenomenon such as a part of the toner image being lost.

  In the example shown in FIG. 8, the second pre-neutralization power feeding unit 872 waits until at least the first period t <b> 1 in which at least one of the photoconductor 41 and the developing roller 430 continuously rotates due to inertia after the power feeding failure time t <b> 0 ends. The pre-discharge light emitting unit 44 is continuously caused to emit light.

  If the rotation of the photoconductor 41 and the developing roller 430 is stopped, the carrier transfer problem does not occur. Therefore, if the second period t2 is equal to or longer than the first period t1, the carrier shift problem is more reliably solved.

  Here, the portion of the outer peripheral surface of the photoconductor 41 that is present at the charging position P1 at the time t0 when the power feeding failure occurs is referred to as a charging terminal portion. After the charging deficiency occurrence time t0, after the charging terminal portion passes the magnetic brush contact region 411, the problem of carrier transfer does not occur.

  Accordingly, it is conceivable that the second pre-charger power supply unit 872 causes the pre-charger light emitting unit 44 to emit light during a period until the charging terminal portion passes the magnetic brush contact region 411 after the power supply failure occurrence time t0. As a result, the carrier transfer problem can be solved more reliably. The power supply deficiency occurrence time t0 is an example of the time when the application of the developing bias voltage is stopped.

[Results of evaluation experiment]
Hereinafter, the result of the evaluation experiment comparing the case where the pre-charger light emitting unit 44 is lit up and the case where the pre-charged light emitting unit 44 is not lit in the power supply incomplete state will be described. The conditions of the evaluation experiment are as follows. In the evaluation experiment, images were formed on 30 recording sheets 9 continuously for 1 minute. In the evaluation experiment, the peripheral speed of the photoconductor 41 is 157 mm / sec. The peripheral speed of the developing roller 430 is 1.6 times the peripheral speed of the photoconductor 41. In the evaluation experiment, the distance between the outer peripheral surface of the developing roller 430 and the effective outer peripheral surface 410 of the photoconductor 41 is 0.3 nm. In the evaluation experiment, the potential of the non-image area on the effective outer peripheral surface 410 of the photoconductor 41 is + 450V, and the potential of the electrostatic latent image is + 100V. Further, in the evaluation experiment, the photoconductor 41 is an organic photoconductor. In the evaluation experiment, the bias frequency, the duty ratio, the peak-to-peak potential difference, and the midpoint potential of the developing roller 430 are 4.7 kHz, 50%, 1250 V, and 350 V, respectively. The toner 91 is positively charged.

  In the first example of the evaluation experiment, the pre-discharge light emitting unit 44 is 0.7 μJ until the first period t1 from the occurrence of the insufficient power supply state until the rotation of the photoconductor 41 and the developing roller 430 stops. This is an example of light emission with a light quantity of / cm2.

  Further, in the second example of the evaluation experiment, the pre-discharge light emitting unit 44 is set to 1 until the first period t1 from the occurrence of the insufficient power supply state until the rotation of the photosensitive member 41 and the developing roller 430 stops. This is an example of light emission with a light quantity of 5 μJ / cm 2.

  In addition, the comparative example of the evaluation experiment is a case where the pre-discharge light emitting unit 44 is turned off when the power supply incomplete state occurs.

  In the comparative example, the amount of the carrier 92 transferred to the photoreceptor 41 was the largest.

  In the first embodiment, the amount of the carrier 92 transferred to the photoconductor 41 is reduced to about 17.0% in the case of the comparative example.

  In the second embodiment, the amount of the carrier 92 transferred to the photoconductor 41 is reduced to about 3.8% in the case of the comparative example.

  From the evaluation experiment, it can be seen that the carrier transfer problem can be improved if the image forming apparatus 10 is employed.

[Second Embodiment]
Next, an image forming apparatus 10A according to the second embodiment will be described with reference to FIG. The image forming apparatus 10A has a configuration in which the developing unit 43 in the image forming apparatus 10 is replaced with a developing unit 43A.

  FIG. 9 is a configuration diagram of the pre-discharge light emitting unit 44 and its peripheral portion when viewed along the second direction D2 in the image forming apparatus 10A. 9, the same components as those shown in FIGS. 1 to 8 are given the same reference numerals. Hereinafter, differences between the image forming apparatus 10A and the image forming apparatus 10 will be described.

  The developing unit 43A of the image forming apparatus 10A has a configuration in which a collecting roller 432 and a carrier collecting magnet 433 are added to the developing unit 43 of the image forming apparatus 10. The magnet 433 is included in the collection roller 432. The collection roller 432 and the magnet 433 constitute a magnet roller for collecting the carrier 92 transferred to the photoreceptor 41 into the developing tank 4300.

  The collection roller 432 rotates in a non-contact state with respect to the photosensitive member 41 at a position downstream of the developing roller 430 in the rotation direction of the photosensitive member 41.

  A bias is applied to the collection roller 432 so that the potential difference with respect to the photoconductor 41 is the same as the charging polarity of the toner 91. Due to the bias applied to the collection roller 432, a force that draws them to the collection roller 432 acts on the carrier 92 and the poorly charged toner 91 that have moved to the photoreceptor 41. Further, the magnet 433 in the collection roller 432 generates a magnetic field that attracts the carrier 92 on the photosensitive member 41 side.

  Accordingly, the collection roller 432 draws and collects the carrier 92 and the poorly charged toner 91 that have moved to the photoreceptor 41.

  In the image forming apparatus 10 </ b> A, the pre-discharge light emitting unit 44 is disposed at a position downstream in the rotation direction of the photoconductor 41 with respect to the position of the collection roller 432. In this case, the static elimination light from the preliminary static elimination light emitting unit 44 reaches the magnetic brush contact region 411 through a gap between the recovery roller 432 and the photoreceptor 41.

  If the image forming apparatus 10 </ b> A is employed, the carrier transfer is suppressed by irradiating the magnetic brush contact area 411 with the charge removal light, as in the case where the image forming apparatus 10 is employed. In addition, a small amount of the carrier 92 that has been transferred to the photosensitive member 41 is also collected into the developing tank 4300 by the collection roller 432.

[Application example]
In the image forming apparatuses 10 and 10A described above, a method other than the calculation of the printing rate is adopted as a method for determining whether or not the density of the toner image in the first charge removal target region 413 is low. It is also conceivable.

  For example, when image formation is continuously performed on a plurality of recording sheets 9, it is determined whether or not the first charge removal target area 413 corresponds to an area between two continuous recording sheets 9. The light control unit 84 determines. In this case, when the first charge removal target area 413 is in a state corresponding to the area between two continuous recording sheets 9, the charge removal light control unit 84 determines the density of the toner image in the first charge removal target area 413. Is determined to be low.

  Further, it is conceivable that the pre-transfer charge eliminating section including the pre-discharge light emitting section 44 and the charge eliminating light control section 84 is applied to a monochrome image forming apparatus.

  The image forming apparatus according to the present invention can be freely combined with the above-described embodiments and application examples, or can be appropriately modified within the scope of the invention described in each claim. Alternatively, it may be configured by omitting a part.

2: Sheet feeding unit 3: Sheet conveying unit 4: Image forming unit 4 x: Monochromatic image forming unit 5: Optical scanning unit 6: Fixing unit 8: Control unit 9: Recording sheet 10, 10 A: Image forming apparatus 21: Sheet receiving unit 22: Sheet sending unit 30: Conveying path 31: Registration roller 32: Conveying roller 33: Discharging roller 40: Toner replenishing unit 41: Photoconductor 42: Charging unit 43, 43A: Developing unit 44: Pre-charge elimination light emitting unit 45: Primary transfer Unit 46: primary cleaning unit 47: post-discharge light emitting unit 48: intermediate transfer belt 49: secondary transfer unit 51: laser light source 61: heating roller 62: pressure roller 80: operation display unit 81: MPU
82: storage unit 83: image processing unit 84: neutralization light control unit 85: laser light control unit 86: communication unit 87: front neutralization power supply unit 88: rear neutralization power supply unit 90: two-component developer 91: toner 92: carrier 100 : Casing 101: discharge tray 410: effective outer peripheral surface 411 of the photoconductor: magnetic brush contact area 413: first static elimination target area 414: second static elimination target area 419: first motor 430: developing roller 431: developing magnet 432: Recovery roller 433: Carrier recovery magnet 437: Stirring member 438: Blade 439: Second motor 480: Secondary cleaning unit 611: Heater 871: First pre-static charge feeding unit 872: Second pre-neutralization power supply unit 873: Output changeover switch 900: magnetic brush 4190: first coupling mechanism 4300: developing tank 4311: development magnet Electrode 4390: second coupling mechanism 8711: constant-voltage power supply 8712: PWM circuit 8721: step-up circuit 8722: Condenser D0: force peak Direction P1: a charging position P2: exposure position P3: developing position P4: the transfer position

Claims (6)

A photosensitive member that is rotationally driven by a first motor and has an electrostatic latent image formed on the outer peripheral surface at an exposure position downstream of the charging position facing the charging unit in the rotation direction;
A bias voltage is applied and the second motor rotates to carry a magnetic brush including toner and a carrier. A developing position downstream of the exposure position in the rotation direction of the photosensitive member on the outer peripheral surface of the photosensitive member. A developer that develops the electrostatic latent image into a toner image by bringing the magnetic brush into contact with an effective outer peripheral surface on which the electrostatic latent image can be formed;
The neutralizing light is applied to a static elimination target area including a part of the magnetic brush contact area on the effective outer peripheral surface of the photoconductor, which is in contact with the magnetic brush, and an area between the magnetic brush contact area and the transfer position of the toner image. A pre-emission light emitting unit for irradiation;
The first discharge light emitting section emits light by supplying power to the previous discharge light emitting section when power is supplied to the first motor and the second motor and the bias voltage is applied to the developer. A pre-static charge feeding unit;
In a temporary period after the supply of power to the first motor and the second motor and the application of the bias voltage to the developer are stopped, the supply of power to the pre-discharge light emitting unit is continued, thereby An image forming apparatus comprising: a second pre-neutralization power feeding unit that emits light from the static elimination light emitting unit.   The second pre-neutralization power supply unit is configured to perform the operation until at least one of the photoconductor and the developer continuously rotates due to inertia after power supply to the first motor and the second motor is stopped. The image forming apparatus according to claim 1, wherein the static elimination light emitting section emits light.   The second pre-charging power supply unit includes a charging terminal portion on the outer peripheral surface of the photoconductor that was present at the charging position when the application of the bias voltage was stopped after the application of the bias voltage was stopped. The image forming apparatus according to claim 1, wherein the pre-discharge light emitting unit emits light during a period until it passes through the magnetic brush contact area.   The second pre-discharge power supply unit stores power during power supply from the first pre-discharge power supply unit to the pre-discharge light-emitting unit, and power supply from the first pre-discharge power supply unit to the pre-discharge light-emission unit is stopped. The image forming apparatus according to any one of claims 1 to 3, further comprising a secondary battery that is discharged from the battery.   5. The image forming apparatus according to claim 1, wherein the second pre-neutralization power feeding unit causes the pre-neutralization light emitting unit to emit light with a larger amount of light than the first pre-neutralization power feeding unit.   The area to be neutralized on the effective outer peripheral surface of the photoconductor includes a position where a magnetic component in a direction in which the magnetic force generated by the developer toward the photoconductor reaches a peak is 80% of the peak magnetic force. The image forming apparatus according to claim 1.

Images