JP6544210B2 - Image forming device - Google Patents

Description

  The present disclosure relates to an image forming apparatus, and more particularly, to control after completion of a developing operation of an image forming apparatus according to an electrophotographic method.

  As an electrophotographic development system, a two-component development system using a developer containing toner and magnetic carrier is widely used. In the image forming process of the image forming apparatus according to the two-component developing method, first, the surface of the photosensitive member is negatively charged, and an electrostatic latent image is formed on the photosensitive member by the exposure device. Subsequently, a developing bias voltage of negative polarity is applied to the developing roller of the developing device to prevent the carrier from adhering to the photosensitive member and to make the toner adhere to the electrostatic latent image.

  The developing bias voltage is similarly applied for a predetermined time also after the charging of the photosensitive body is finished in order to prevent the carrier from being attached to the photosensitive drum. Therefore, when the non-charged area of the photosensitive member passes through the developing unit, toner adheres to the surface of the photosensitive member.

  The toner not used for image formation is collected in a waste toner tank disposed in the vicinity of the photosensitive drum.

  Japanese Patent Application Laid-Open No. 7-129035 (Patent Document 1) relates to a technology for reducing the amount of waste toner, in which the discharge lamp is turned on before the photosensitive drum is rotated, and charging by the charging device to the photosensitive drum starts. At the same time, a configuration for irradiating a developing bias to the developing device and irradiating the erasing beam from the exposure device is disclosed.

  In addition, a technology has also been devised to reduce the amount of toner adhesion to the photosensitive member by lowering the charging bias voltage and the developing bias voltage in multiple steps at the end of the printing operation. The control is performed to gradually lower the photosensitive member surface potential so that the potential difference between the photosensitive member surface potential and the developing roller in the development region is maintained such that the toner deposition does not occur as much as possible and the carrier deposition does not occur. It is a thing.

JP 7-129035 A

  However, in the technique disclosed in Patent Document 1, when charging of the layer on the photosensitive drum by the charging device is finished, when the area of the photosensitive drum which has been brought close to the charging device passes through the developing device. The application of the development bias is stopped. That is, in the same technology, in order to avoid the carrier adhesion, the configuration is adopted in which the application of the developing bias is stopped after the toner is attached to the photosensitive drum, so waste toner which is not used for image formation is generated.

  Further, even in the case of using a technique for lowering the charging bias voltage and the developing bias voltage in multiple steps, although it is possible to reduce the amount of toner adhesion to the photosensitive member, it can not be completely eliminated. In addition, there has been a problem that the traveling distance of the photosensitive member is extended in some cases in order to lower the bias voltage in multiple stages.

  The present disclosure has been made to solve the problems as described above, and an object in one aspect is to provide an image forming apparatus according to a two-component development system that reduces the amount of toner consumption that occurs after the end of the development operation. It is.

  An electrophotographic image forming apparatus performing a developing operation using a developer containing toner and a carrier is disposed in contact with or in proximity to an image carrier rotating forwardly in the developing operation and the surface of the image carrier A charging device for applying a charging bias voltage to an image carrier through a charging member, and a developing bias voltage having the same polarity as the charging bias voltage are applied to a developer carrier to charge the image carrier in the forward direction The developing device for developing a latent image on the image carrier by bringing the developer close to the image carrier in a development region located downstream of the device, and disposed between the charging device and the developer, An exposure device for forming a latent image on a carrier, and after completion of a developing operation, the application of the charging bias voltage by the charging device is stopped, or the image carrier is uniformly exposed in the rotational axis direction by the exposure device. Of the image carrier Potential relaxation means for relieving the surface potential to the ground potential, and a first rotational position corresponding to the end closer to the developing device in the area where the surface potential has been mitigated by the potential relaxation means reaches the development area Means for stopping the application of the developing bias voltage by the developing device and the non-relaxed area from the first rotational position to the second rotational position in the forward rotation direction after the application of the developing bias voltage is stopped passing the developing area. And rotation control means for rotating the image carrier at a lower rotation speed than at the time of developing operation. The second rotational position is the rotational position of the image carrier corresponding to the development region when the application of the development bias voltage is stopped.

  Preferably, the potential reducing means reduces the surface potential of the image carrier toward the ground potential by stopping the application of the charging bias voltage by the charging device. The non-relaxed area is a first rotational position in the forward rotation direction from the third rotational position of the image bearing member that contacts or is closest to the charging member when the charging bias voltage becomes the ground potential by the potential relaxation means Including the area of

  Preferably, the rotation control means rotates the image carrier forward so that at least a part of the non-relaxed area passes the development area, and reverses the image carrier so that the area passing the development area passes the development area again. Let

  An electrophotographic image forming apparatus performing a developing operation using a developer containing toner and a carrier is disposed in contact with or in proximity to an image carrier rotating forwardly in the developing operation and the surface of the image carrier A charging device for applying a charging bias voltage to an image carrier through a charging member, and a developing bias voltage having the same polarity as the charging bias voltage are applied to a developer carrier to charge the image carrier in the forward direction The developing device for developing a latent image on the image carrier by bringing the developer close to the image carrier in a development region located downstream of the device, and disposed between the charging device and the developer, An exposure device for forming a latent image on a carrier, and after completion of a developing operation, stop the application of the charging bias voltage by the charging device, or uniformly expose the image carrier by the exposure device in the rotational axis direction. By the front of the image carrier A potential relaxation means for relaxing the potential toward the ground potential and a first rotational position corresponding to an end closer to the developing device in the area where the surface potential is relaxed by the potential relaxation means reaches the development area. And means for stopping the application of the developing bias voltage by the developing device, and at least a part of the non-relaxed area from the first rotational position to the second rotational position in the forward rotation direction after stopping the application of the developing bias voltage. The image carrier is rotated forward so as to pass through the area, and rotation control means is provided to reverse the image carrier so as to pass through the development area again in the area having passed through the development area. The second rotational position is the rotational position of the image carrier corresponding to the development region when the application of the development bias voltage is stopped.

  Preferably, the rotation control means reverses the image carrier at a rotational speed lower than the rotational speed of the image carrier during the developing operation.

  Preferably, a transfer member for transferring the toner attached to the image carrier to a medium, and a cleaning device for contacting the image carrier and recovering the toner remaining on the image carrier after passing through the transfer member in a recovery area And further comprising The rotation control means reverses the image carrier before the non-relaxed area reaches the recovery area.

  Preferably, the apparatus further comprises a power supply that generates the charging bias voltage and the developing bias voltage via a common transformer. The potential reducing means reduces the surface potential of the image carrier toward the ground potential by uniformly exposing the image carrier in the rotational axis direction by the exposure device.

  Preferably, the rotation control unit is configured to use the image carrier based on at least one of the information indicating the developing bias voltage, the information indicating the humidity around the image carrier, and the information indicating the density of the toner relative to the carrier. It includes determination means for determining whether to perform reverse.

  Preferably, the image bearing member further includes a light reflection type sensor disposed downstream of the developing area and measuring the density of the developer on the image bearing member when the image bearing member rotates in the forward direction. The rotation control means includes determination means for determining whether or not to reverse the image bearing member based on the density of the developer in the non-relaxed area which has passed through the developing area in the normal direction.

  Preferably, the potential reducing means reduces the surface potential of the image carrier toward the ground potential by uniformly exposing the image carrier at the exposure position in the rotational axis direction by the exposure device. The rotation control means causes the exposure position to pass through the non-relaxation region, which passes through the development region, and reverses the image carrier to ease the surface potential toward the ground potential, and then development is performed again in the passage region. The image carrier is rotated forward to pass through the area.

  Preferably, the carrier comprises a magnetic substance. The developer carrier includes a magnetic field generator for adsorbing the carrier by a magnetic field formed by the plurality of magnetic poles. The magnetic field generator forms a low magnetic force area that separates the developer from the developer carrier. The rotation control means rotates the developer carrier by a predetermined distance in the direction opposite to the rotation direction of the developer carrier during the developing operation before reversing the image carrier. The predetermined distance is equal to or greater than the distance from the developing region to the low magnetic force region in the rotational direction of the developing agent carrier during the developing operation.

  More preferably, the developer carrier and the image carrier are configured to rotate by a common drive source. The rotation control means rotates the image carrier forward by a predetermined distance before stopping the application of the developing bias voltage and then reversing the image carrier.

  Preferably, the rotation control means is at least one of information indicating a developing bias voltage, information indicating a humidity around the image carrier, information on a film thickness of the image carrier, and information indicating a density of toner with respect to a carrier. It further includes distance control means for controlling the distance from the first rotational position to the second rotational position in the forward rotation direction based on the one information.

  Preferably, when the non-relaxed area passes through the development area, the rotation control means rotates the developer carrier at a lower rotational speed than in the developing operation, or stops the rotation of the developer carrier.

  Preferably, the means for stopping the application of the developing bias voltage stops the application of the developing bias voltage when the rotation of the image carrier is stopped.

  The image forming apparatus according to the two-component developing method according to one embodiment can reduce the amount of toner consumption that occurs after the end of the developing operation.

It is a figure explaining related technology about control after completion of development operation. FIG. 2 is a diagram for explaining an exemplary configuration of an image forming apparatus according to an embodiment. It is a figure explaining the imaging unit according to embodiment. It is a figure explaining the control part according to embodiment. 5 is a flowchart illustrating a series of control after the developing operation. It is a timing chart of control shown in FIG. It is a figure explaining the development field according to an embodiment. It is a figure explaining the imaging unit according to other embodiment. It is a flowchart explaining a series of control after development operation according to other embodiments. It is a timing chart of control shown in FIG. It is a flow chart explaining a series of control after development operation according to a modification. It is a flow chart explaining a series of control after development operation according to a modification. FIG. 21 is a diagram for describing an imaging unit according to still another embodiment. It is a flowchart explaining a series of control after development operation according to another embodiment. It is a timing chart of control shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference characters, and the description thereof will not be repeated.

<A. Introduction>
FIG. 1 is a diagram for explaining related art related to control after completion of the developing operation. In FIG. 1 (a), the drum type photosensitive member is normally rotated clockwise. The charging roller is disposed in contact with the photosensitive member, and the surface of the photosensitive member is negatively charged by applying a charging bias voltage from a power supply device (not shown). Further, the developing roller is disposed in contact with or in proximity to the photosensitive member, and becomes a negative potential when a developing bias voltage is applied from a power supply (not shown). At this time, the absolute value of the surface potential of the developing roller is set to be lower than the absolute value of the surface potential of the photosensitive member.

  The developing roller performs a developing operation for attaching toner to a latent image (image pattern) formed on the photosensitive member by an exposure device (not shown) in a developing area where the developing roller and the photosensitive member are close to each other.

  When this developing operation is completed, the output of the charging bias voltage applied to the charging roller is stopped. The rotational position on the photosensitive member when the output of the charging bias voltage is stopped is taken as a point X (which is a line because there is actually a depth).

  Next, the output of the developing bias voltage applied to the developing roller is stopped. In the example shown in FIG. 1 (b1), the output of the developing bias voltage is stopped when the point X reaches the developing area. FIG. 1 (b2) shows an enlarged view of the broken line in FIG. 1 (b1).

  When the photosensitive member normally rotates, the surface of the photosensitive member is charged downstream of the point X, whereas the surface upstream of the point X is substantially at the ground potential. Therefore, the positively charged carrier on the developing roller adheres to the charging area on the downstream side of the point X of the photosensitive member.

  If the carrier adheres to the photosensitive member, the cleaning blade and the photosensitive member may be damaged when the carrier is collected by a cleaning blade (not shown), which may cause a fatal failure in the subsequent printing process.

  Therefore, as shown in FIG. 1 (c1), it is conceivable to stop the output of the developing bias voltage after the point X passes through the developing area. FIG. 1 (c2) shows an enlarged view of the broken line in FIG. 1 (c1).

  In this case, the carrier is prevented from adhering to the photosensitive member, but the toner on the developing roller is adhered to the non-charged region on the upstream side of the point X of the photosensitive member. The toner attached to the photosensitive member after the completion of the developing operation is collected as waste toner in the tank, which is a waste.

  Therefore, a configuration and control will be described below, in which unnecessary toner generated after the end of the developing operation is suppressed as much as possible, and carrier adhesion to the photosensitive member is also prevented.

<B. Embodiment 1-Normal rotation>
(B1. Image forming apparatus 100)
FIG. 2 is a diagram for explaining an exemplary configuration of the image forming apparatus 100 according to the embodiment. The image forming apparatus 100 is an electrophotographic image forming apparatus such as a laser printer or an LED printer. As shown in FIG. 2, the image forming apparatus 100 is provided with an intermediate transfer belt 1 as a belt member at a substantially central portion inside. Below the lower horizontal portion of the intermediate transfer belt 1, four image forming units 2Y, 2M, 2C, and 2K corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K). Are arranged side by side along the intermediate transfer belt 1.

  The secondary transfer roller 4 is in pressure contact with the portion of the intermediate transfer belt 1 supported by the intermediate transfer belt drive roller 3, and secondary transfer is performed in the area. A fixing heating unit 7 having a fixing roller 5 and a pressure roller 6 is disposed at a downstream position of the transport path R1 behind the secondary transfer area.

  At the lower part of the image forming apparatus 100, a sheet feeding cassette 8 is detachably disposed. The sheets P stacked and stored in the sheet feeding cassette 8 are fed one by one from the uppermost sheet to the conveyance path R1 by the rotation of the sheet feeding roller 9.

  In the present embodiment, the image forming apparatus 100 employs, as an example, an intermediate transfer method having a plurality of imaging units (2Y, 2M, 2C, 2K), but is not limited to this. The image forming apparatus may be an electrophotographic system. Specifically, the image forming apparatus may have a single imaging unit or may be of a rotary type.

(B2. Outline operation of the image forming apparatus 100)
Next, an outline operation of the image forming apparatus 100 configured as described above will be described. When an image signal is input from an external device (for example, a personal computer or the like) to the control unit 70 of the image forming apparatus 100, the control unit 70 creates a digital image signal obtained by color converting this image signal into yellow, cyan, magenta, and black. Then, based on the input digital signal, a toner image is formed by each of the image forming units 2Y, 2M, 2C and 2K.

  The toner images of the respective colors are sequentially superimposed and primarily transferred onto the intermediate transfer belt 1 moving in the direction of the arrow Tr in FIG. The toner images formed on the intermediate transfer belt 1 are collectively secondarily transferred onto the sheet P by the action of the secondary transfer roller 4.

  The toner image secondarily transferred to the sheet P reaches the fixing and heating unit 7. The toner image is fixed to the sheet P by the action of the heated fixing roller 5 and the pressure roller 6. The sheet P on which the toner image is fixed is discharged onto the sheet discharge tray 60 via the sheet discharge roller 50.

(B3. Imaging unit)
Next, the operation of the image forming unit will be described. Here, the image forming units 2Y, 2M, 2C, 2K are different in toner (yellow, magenta, cyan, black) to be used, but the device configuration is the same. I will explain.

  FIG. 3 is a diagram for explaining an imaging unit 2 according to the embodiment. The image forming unit 2 includes a drum type photosensitive body 10 as an image carrier. As an example, the diameter of the photosensitive member 10 is 30 mm. At the time of developing operation, the photosensitive member 10 is normally rotated clockwise by the drive motor 11 via the drive transmission unit 12. Around the photosensitive member 10, in the order of its rotation direction, the charging roller 13, the print head unit 15 as an exposure device composed of the laser 15A and the polygon mirror 15B, the developing device 20, and the charge removing LED An array 17 and a cleaning blade 18 are arranged.

  The charging roller 13 is in contact with the photosensitive member 10 and is driven to rotate as the photosensitive member 10 rotates. As an example, the diameter of the charging roller 13 is 15 mm. The charging roller 13 is made of conductive rubber, and a charging bias voltage is applied from the power supply transformer 14. The charging bias voltage is, for example, -1000V. As a result, the surface of the photosensitive member 10 is negatively charged by the charging roller 13 as a charging member. The surface potential of the photosensitive member 10 exposed by the print head unit 15 is relaxed to substantially the ground potential.

  The developing device 20 performs a developing operation of causing toner to adhere to the latent image on the photosensitive member 10 corresponding to the image pattern in the developing region DE.

  The toner image formed on the photosensitive member 10 is transferred to the intermediate transfer belt 1 by the action of the transfer roller 16. Subsequently, the surface potential of the charged photosensitive member 10 is relaxed to the ground potential by the charge removal LED array 17. The LED array 17 for static elimination is configured by arranging a plurality of LED arrays in the axial direction of the photosensitive member. The cleaning blade 18 recovers the toner which is not transferred to the intermediate transfer belt 1 and remains on the surface of the photoreceptor 10 in a recovery area RE in contact with the photoreceptor 10.

  In another aspect, a noncontact corona discharge type charging device may be disposed in proximity to the photosensitive member, instead of the charging roller, as charging means for the photosensitive member.

(B4. Developing device 20)
Next, the configuration and schematic operation of the developing device 20 will be described. Inside the developing device 20, a two-component developer including a toner and a carrier is accommodated. The carrier is a magnetic substance, and as an example, the carrier is made of ferrite.

  The transport screw 27 has an axis extending in the depth direction of the drawing, and stirs the developer while circulating and transporting it. As a result, the developer toner and the carrier come into frictional contact with each other, and are charged in opposite polarities to each other. Here, it is assumed that the carrier is positively charged and the toner is negatively charged. The negatively charged toner adheres to the periphery of the positively charged carrier mainly by the electric attraction between the both. Then, the developer is supplied to the developing roller 24 in the process of being transported by the transport screw 27.

  A magnetic toner concentration sensor 31 mounted on the bottom of the developing device 20 measures the weight ratio of toner in the developer. The toner supply device (not shown) performs toner supply control in the developing device 20 so as to maintain the toner weight ratio of 7%.

  The developing roller 24 receives a developing bias voltage from the power supply transformer 26 and is negatively charged. The developing bias voltage is, for example, -300V. As an example, the diameter of the developing roller 24 is 20 mm.

  In addition, the developing roller 24 includes a rotating shaft 21, a magnet 22, and a transport sleeve 23. The rotating shaft 21 is configured to rotate clockwise by the drive motor 28 via the drive transmission unit 29. The magnet 22 has a plurality of magnetic poles (not shown) and is fixed so as not to rotate. A magnetic field 25 for transporting the developer by the transport sleeve 23 is formed by the plurality of magnetic poles. The transport sleeve 23 is made of aluminum and rotates with the rotation shaft 21.

  The developer supplied to the transport sleeve 23 spikes along the lines of magnetic force formed by the magnet 22 to form a so-called magnetic brush. Then, the developer is conveyed clockwise as the conveyance sleeve 23 rotates, and is regulated to a constant thickness by passing through the gap with the developer regulating member 30.

  In the development area DE, the negatively charged toner is brought close to the photosensitive member 10 through the spiked carrier, and is attached to the latent image (generally the ground potential) formed on the photosensitive member 10. At this time, the potential difference between the potential of the surface of the photosensitive member 10 charged by the charging roller 13 (hereinafter referred to as the photosensitive member potential) and the potential of the surface of the transport sleeve 23 to which the developing bias voltage is applied (hereinafter referred to as the developing potential) is 100V. Set to a degree. Therefore, the carrier charged to the positive polarity is attracted to the transport sleeve 23 by the magnetic field formed by the magnet 22 and does not adhere to the photosensitive member 10 charged to the negative polarity.

  When the developer that has passed through the development area DE reaches the low magnetic force area LM formed by the magnet body 22, the developer idles on the conveyance sleeve 23 and is not conveyed by the conveyance sleeve 23. When the developer idled in the low magnetic force area LM exceeds a predetermined number, the developer separates from the transport sleeve 23 by pressure and is accommodated again in the housing of the developing device 20.

(B5. Control unit 70)
FIG. 4 is a diagram for explaining the control unit 70 according to the embodiment. The control unit 70 includes a central processing unit (CPU) 72, a random access memory (RAM) 74, a read only memory (ROM) 76, and an interface (I / F) 78 as its main control elements.

  The CPU 72 implements overall processing of the image forming apparatus 100 by reading and executing a program stored in the ROM 76 described later. The CPU 72 may be any of a microprocessor (Microprocessor), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a digital signal processor (DSP), and a circuit having other arithmetic functions.

  The RAM 74 is typically a DRAM (Dynamic Random Access Memory) or the like, and temporarily stores data and image data necessary for the CPU 72 to operate a program. Therefore, the RAM 74 functions as a so-called working memory.

  The ROM 76 is typically a flash memory or the like, and stores programs executed by the CPU 72 and various setting information related to the operation of the image forming apparatus 100.

  The interface 78 is connected to the drive motors 11 and 28, the power supply transformers 14 and 26, the print head unit 15, and the charge removal LED array 17. The CPU 72 outputs the charging bias control signal to the power source transformer 14 and the developing bias control signal to the power source transformer 26 through the interface 78 to control the application of the charging bias voltage and the developing bias voltage.

  The CPU 72 also transmits control signals for controlling the rotational speeds of the photosensitive member 10 and the developing roller 24 to the drive motors 11 and 28 via the interface 78. In the present embodiment, as an example, the rotational speed of the photosensitive member 10 during the developing operation is 100 mm / sec, and the rotational speed of the developing roller 24 is 200 mm / sec.

(B6. Control after developing operation)
Next, a series of control performed by the control unit 70 after the developing operation (image formation) will be described with reference to FIGS. 5 and 6. FIG. 5 is a flow chart for explaining a series of control after the developing operation. FIG. 6 is a timing chart of the control shown in FIG. The process shown in FIG. 5 is realized by control unit 70 executing a control program stored in ROM 76. In other aspects, some or all of the processing may be performed by circuit elements or other hardware. These assumptions also apply to the flowchart shown below.

  The control unit 70 ends the developing operation for causing the toner to adhere to a predetermined latent image (image pattern) on the photosensitive member 10 (step S2).

  The control unit 70 controls the power supply transformer 14 to stop applying the charging bias voltage to the charging roller 13 at time T4 shown in FIG. 6 which is a predetermined time after the end of the developing operation. A control signal is transmitted (step S4). The predetermined time is, for example, a time from the end of the developing operation to the time when the toner image formed on the photosensitive member 10 is transferred to the intermediate transfer belt 1.

  The rotational position of the photosensitive member 10 in contact with the charging roller 13 when the application of the charging bias voltage is stopped is taken as a point A (which is a line because there is an actual depth).

  Next, at time T6 when the point A reaches 4 mm upstream from the developing area DE in the forward rotation direction, the control signal to the drive motor 11 and the drive motor 28 is stopped. It outputs (step S6). As a result, the photosensitive member 10 and the developing roller 24 stop rotating.

  Next, at time T8 when a predetermined time has elapsed from time T6, control unit 70 transmits a developing bias control signal to the power supply transformer 26 to stop applying the developing bias voltage to developing roller 24 (step S8). ). A position corresponding to the development region of the photosensitive member 10 when the application of the development bias voltage is stopped is defined as a point B.

  Next, at time T10, the control unit 70 transmits a control signal to the driving motor 11 so as to forwardly rotate the photosensitive member 10 at 50 mm / sec, which is half the speed during the developing operation. In addition, the control unit 70 causes the static elimination LED array 17 to light at time T10 (step S10).

  Here, development is performed in a region (hereinafter also referred to as a “non-relaxed region”) AB where the negative polarity from the point A to the point B where the surface potential is not relaxed by stopping the output of the charging bias voltage The toner charged to the negative polarity on the roller 24 does not adhere to the photosensitive member 10. This is because they have the same polarity and the absolute value of the photosensitive member potential is larger.

  In addition, as shown in step S8, before the rotational position A corresponding to the end close to the developing device in the area where the surface potential is relaxed by stopping the output of the charging bias voltage reaches the developing area DE, Application of the development bias voltage is stopped. In response to this, the potential of the toner on the developing roller 24 is rapidly relaxed toward the ground potential from time T8. Therefore, the toner on the developing roller 24 does not adhere to the photosensitive member 10 even when the region on the upstream side of the point A of the photosensitive member 10 where the surface potential is relaxed passes the developing region.

  Therefore, the image forming apparatus 100 according to the present embodiment can suppress the generation of waste toner attached to the photosensitive member 10 after the completion of the developing operation.

  Furthermore, when the non-relaxed area AB charged to the negative polarity passes through the development area DE, the positively charged carrier on the developing roller 24 is likely not to be attached to the surface of the photosensitive member 10. The reason will be described with reference to FIG.

  FIG. 7 is a view for explaining the developing area DE in which the photosensitive member 10 and the developing roller 24 are close to each other. Referring to FIG. 7, the developer including the carrier, which is a magnetic substance, is magnetized by the magnetic field 25 formed by the magnet body 22 to form a magnetic brush on the transport sleeve 23.

  However, when the photosensitive member 10 and / or the developing roller 24 rotates at high speed, the behavior of the developer is not stable, and the magnetic brush formed on the conveying sleeve 23 is broken. If the application of the development bias voltage is stopped while the behavior of the developer is not stable, the magnetic force at which the carriers attract each other does not work sufficiently, and some of the carriers are negatively charged. It adheres to

  On the other hand, in the present embodiment, the rotational speed of the photosensitive member 10 when the non-relaxed region AB where the carrier adhesion to the photosensitive member 10 may occur passes through the developing region DE is set slower than that during the developing operation. Therefore, the behavior of the developer on the transport sleeve 23 is stable, and the magnetic brush does not largely collapse. As a result, since the carrier is attracted by the magnetic force of the carriers, the possibility of the carrier adhering to the photosensitive member 10 is reduced. The rotational speed of the photosensitive member 10 when the non-relaxed area AB passes through the development area DE is, for example, half of that during the development operation, but may be slower than during the development operation.

  Further, in the present embodiment, the rotation of the developing roller 24 is stopped when the application of the developing bias voltage is stopped. As a result, the region where carrier adhesion to the photosensitive member 10 can occur can be suppressed to the vicinity of the point B.

  Further, in this example, when the non-relaxed area AB passes through the developing area DE, the rotation of the developing roller 24 is stopped. As a result, since the rubbing between the carrier on the developing roller 24 and the photosensitive member 10 is reduced, the behavior of the developer in the developing area DE is more stable.

  Also, during time T4 to time T10, the surface potential of the non-relaxed region AB is gradually relaxed toward the ground potential by natural discharge. Therefore, by setting the time from time T4 to time T10 long, it is possible to prevent the carrier adhesion to the photosensitive member 10 more reliably.

  Again referring to FIG. 5, at time T12 when point A reaches the lighted area of the charge removal LED array 17, the control unit 70 controls the drive motor 11 to stop the driving of the photosensitive member 10. A signal is output (step S12). Furthermore, at time T12, the control unit 70 extinguishes the static elimination LED 17. Thereby, the surface potential of the photosensitive member 10 is relaxed to the ground potential uniformly.

  The timings at which each control shown in FIG. 5 is performed are all design values, and the intervals between the respective times in FIG. 6 (for example, the times T8 to T10) are stored in the ROM 76 of the control unit 70. It is assumed that

  According to the above, the image forming apparatus according to the present embodiment can suppress unnecessary consumption of toner that is not used for image formation after the end of the developing operation, and reduce the possibility of carrier adhesion to the photosensitive member. it can.

  In the above example, the non-relaxed area AB is defined as the area from the rotational position A to the point B of the photosensitive member 10, but is not limited thereto. There is a delay time from when the application of the charging bias voltage is actually stopped until the charging bias voltage becomes the ground potential. Therefore, the charging roller 13 charges the photosensitive member 10 during the delay time after the application of the charging bias voltage is stopped. Since the area of the photosensitive member 10 charged during the delay time is negatively charged, carrier adhesion may occur.

  Therefore, in another aspect, the non-relaxation area AB rotates in the forward direction from the rotational position of the photosensitive member 10 in contact with the charging roller 13 when the charging bias voltage becomes the ground potential after the application of the charging bias voltage is stopped. It may be defined as a region up to the rotational position B point in the direction. When a non-contact corona discharge device or the like is used as the charging means, the non-relaxed area AB is in the normal direction from the rotational position of the photosensitive member 10 closest to the charging device when the charging bias voltage becomes the ground potential. It is defined as the area up to the rotational position B point in.

  Thereby, the carrier that may be attached in the non-relaxed area AB can be reliably recovered to the developing roller 24 side.

(B7. Modification-Control of the position at which application of development bias voltage is stopped)
In the above example, the control unit 70 stops the application of the developing bias voltage when the point A reaches 4 mm upstream from the developing area DE in step S6. In the present modification, the control unit 70 controls the stop distance S between the point A and the development area DE when the application of the development bias voltage is stopped.

  The stop distance S is a distance in the sub scanning direction (rotational direction) of the non-relaxed area AB. The longer the stopping distance S, the wider the area where carrier adhesion to the photosensitive member 10 may occur. Therefore, it is preferable that the stopping distance S be short. On the other hand, when the stop distance S is too short, the toner of the developing roller 24 adheres to the photosensitive member 10 as shown in FIG. 1 (c2).

  At this time, the larger the absolute value of the developing bias voltage is, the wider the toner adhesion range to the photosensitive member 10 is. Therefore, the control unit 70 according to the present modification sets the stop distance S based on the value of the developing bias voltage. More specifically, the control unit 70 defines S = −0.005 × Vb (mm). Vb is a value of the developing bias voltage. In this example, since Vb is -300 (V), the control unit 70 sets the stopping distance S to 1.5 mm.

  However, when the absolute value of the developing bias voltage is less than 200 V, the control unit 70 sets the stopping distance to 1 mm.

  According to the above, the image forming apparatus according to the present modification can minimize the area where carrier adhesion to the photosensitive member 10 may occur.

  In another aspect, the control unit 70 takes into consideration the toner concentration Ct in the developer, the absolute humidity Ha in the image forming unit 2 and the film thickness Th of the photosensitive member 10 as parameters relating to toner adhesion to the photosensitive member. Good.

  When the toner concentration Ct is high, the developability is increased as the absolute humidity Ha is increased and the film thickness Th is increased, so that the toner easily adheres to the photosensitive member 10 from the developing roller 24.

As an example, when the toner concentration Ct exceeds 8%, the absolute humidity Ha exceeds 11 g / m ³ , and the thickness Th of the photosensitive member exceeds 30 μm, the control unit 70 performs at least one of the conditions. Setting lower limit value of the stop distance S is 2 mm. Therefore, even if the developing bias voltage Vb is -300 V and the stop distance S is calculated to be 1.5 mm from the above equation, the control unit 70 sets the stop distance S to 2 mm when the above conditions are satisfied. Do.

  According to the above, the image forming apparatus can suppress the toner adhesion to the photosensitive member 10 while minimizing the area where the carrier adhesion to the photosensitive member 10 may occur.

  The toner concentration Ct is measured by the magnetic toner concentration sensor 31. The absolute humidity Ha is measured by a humidity sensor (not shown) in the imaging unit 2. The humidity sensor is configured of, for example, an electric resistance type humidity sensor or a capacitance type humidity sensor.

  In addition, the film thickness Th of the photosensitive member 10 may be predicted from the traveling distance of the photosensitive member 10, and a contact-type film thickness measuring method such as a step difference meter or an eddy current film thickness meter, a color difference method, an interference method It may be measured using a non-contact film thickness measurement method using a light absorption method or the like.

<C. Embodiment 2-Inversion>
(C1. Overview)
In the first embodiment, the control for suppressing the unnecessary toner consumption and the carrier adhesion to the photosensitive member by rotating the photosensitive member 10 only in the same rotation direction (forward rotation direction) as the developing operation has been described. However, depending on the behavior of the developer when the non-relaxed area AB where carrier adhesion may occur passes the development area DE, carrier adhesion to the photoreceptor 10 may occur with a low probability.

  Therefore, in the present embodiment, after the non-relaxed area AB where carrier adhesion may occur passes through the development area DE, the photoconductor 10 is reversed again (reverse rotation as in the developing operation) to reliably prevent carrier adhesion. Control will be described. The basic configuration of the image forming apparatus 100A in the present embodiment is the same as that of the image forming apparatus 100, so only the differences will be described.

(C2. Imaging unit 2A)
FIG. 8 is a diagram for explaining an imaging unit 2A according to another embodiment. The power supply transformer 14A is electrically connected to the charging roller 13 and the power supply transformer 26A. The power supply transformer 14A applies a charging bias voltage to the charging roller 13, and the power supply transformer 26A applies a developing bias voltage to the developing roller 24. That is, the charging bias voltage and the developing bias voltage are generated directly or indirectly by the common power supply transformer 14A.

  By sharing the power supply transformer for generating the developing bias voltage and the charging bias voltage, the production cost of the image forming apparatus 100A can be significantly reduced.

  However, the power supply transformer 26A is restricted in that the developing bias voltage can not be output when the power supply transformer 14A does not output the charging bias voltage.

(C3. Control after developing operation)
Next, a series of controls performed by the control unit 70 after the developing operation will be described with reference to FIGS. 9 and 10. FIG. 9 is a flow chart for explaining a series of control after the developing operation according to another embodiment. FIG. 10 is a timing chart of the control shown in FIG. It is to be noted that, in FIG. 9, the portions given the same reference numerals as in FIG. 5 have the same control, and therefore the description thereof will not be repeated.

  Referring to FIG. 9, control unit 70 reduces the surface potential of photoreceptor 10 in exposure region EX at time T20 shown in FIG. 10, which is a predetermined time after the end of the developing operation (step S20). ). More specifically, the control unit 70 uniformly exposes the photosensitive member 10 in the rotational axis direction by the print head unit 15 (hereinafter, also referred to as “full-width exposure”), and thereby the surface potential of the photosensitive member 10 is obtained. ease. A rotational position corresponding to the exposure area EX of the photosensitive member 10 when the full-width exposure by the print head unit 15 is started is set as a point C.

  In the present embodiment, when the power supply transformer 14A stops the application of the charging bias voltage, the application of the developing bias voltage is also stopped. Therefore, if the application of the charging bias voltage (and the application of the developing bias voltage) is stopped immediately after the completion of the developing operation, the carrier is spread over a wide range from the rotational position of the photosensitive member 10 in contact with the charging roller 13 to the developing region DE. An area where adhesion occurs may occur. Therefore, in the present embodiment, the full-width exposure by the print head unit 15 is used as a means for reducing the surface potential of the photosensitive member 10 in order to minimize the area (non-relaxed area) where carrier adhesion may occur. It is used.

  Next, at time T22 when point C reaches the upstream side of 4 mm with respect to the normal rotation direction from the development area DE, application of the developing bias voltage and the charging bias voltage is stopped to the power supply transformer 14A. A control signal to the effect is transmitted (step S22). When the application of the developing bias voltage and the charging bias voltage is stopped, the rotational position corresponding to the development region DE on the photosensitive member 10 is D point, and the rotational position in contact with the charging roller 13 is E point.

  Next, the control unit 70 causes the photosensitive member 10 to rotate forward by 4 mm from time T22 to time T24 when the application of the developing bias voltage and the charging bias voltage is stopped. At time T24, the control unit 70 outputs a control signal indicating that the driving is stopped to the drive motor 11 and the drive motor 28 (step S24). As a result, the photosensitive member 10 and the developing roller 24 stop rotating.

  In this step, when the non-relaxed area CD charged to the negative polarity from the point C to the point D passes the developing area DE, there is a possibility that the carrier on the developing roller 24 adheres to the photosensitive member 10 is there. This is because the rotational speeds of the photosensitive member 10 and the developing roller 24 when the non-relaxed area CD passes through the developing area DE are high (the same as in the developing operation).

  Next, at time T26, the control unit 70 transmits a control signal to the drive motor 11 so as to reverse the photosensitive member 10 at 50 mm / sec, which is half the speed during development operation (step S26).

  At this time, by reversing the rotational speed of the photosensitive member 10 later than in the developing operation, the behavior of the developer is stabilized in the developing area DE, and a magnetic brush is formed. Therefore, even if carrier adhesion occurs in the non-relaxed area CD of the photosensitive member 10, the adhered carrier will form the magnetic brush by the magnetic force of the carrier forming the magnetic brush when passing through the development area DE again. To be collected.

  Next, the control unit 70 reverses the photosensitive member 10 until time T28, and controls the point D to pass through the exposure region EX. As a result, the surface potential of the non-relaxed area CD where carrier adhesion may be generated is relaxed to near the ground potential by the full-width exposure of the print head unit 15. Further, at time T28, the control unit 70 transmits a control signal to the drive motor 11 so as to cause the photosensitive member 10 to rotate forward at a half speed during the developing operation, and turn on the static elimination LED array 17 ( Step S28).

  Since the non-relaxed region CD is generally at the ground potential, there is almost no force for holding the carrier. Therefore, even if the carrier is adhered to the non-relaxed area CD, the carrier is reliably recovered to the developing roller 24 side by the magnetic force of the carrier forming the magnetic brush when it passes through the developing area DE again. .

  Next, at time T30 when point E reaches the lighted area of the charge removal LED array 17, the control unit 70 outputs a control signal to the drive motor 11 to stop the driving of the photosensitive member 10 (see FIG. Step S30). Furthermore, at time T12, the control unit 70 extinguishes the static elimination LED 17. Thereby, the surface potential of the photosensitive member 10 is relaxed to the ground potential uniformly.

  According to the above, in the image forming apparatus 100A according to the present embodiment, even if carrier adhesion occurs in the non-relaxed area CD of the photosensitive member, the non-relaxed area CD is positively relaxed to the ground potential by the exposure device. Can. Therefore, the image forming apparatus can reliably collect the carrier to the developing device by passing the non-relaxed area CD again to the developing area.

  Further, in the present image forming apparatus, as in the first embodiment, before the point C, which corresponds to the end closer to the developing device, of the area in which the surface potential has been alleviated by full width exposure of the print head portion reaches the developing area. The application of the developing bias voltage is stopped (step S22). Therefore, the present image forming apparatus can suppress generation of waste toner which is attached to the photosensitive member 10 after the completion of the developing operation.

  Further, since the present image forming apparatus uses the common power supply transformer 14A for generating the developing bias voltage and the charging bias voltage, the production cost can be suppressed as compared with the image forming apparatus 100 of the first embodiment.

  Furthermore, when a common power supply transformer is used to generate the developing bias voltage and the charging bias voltage, the traveling distance of the photosensitive member is significantly increased by using the conventional technology for dropping the charging bias voltage and the developing bias voltage in multiple steps. There was a problem that it would grow. The reason is that in order to avoid the occurrence of carrier adhesion, it is necessary to perform the fall control in multiple stages while suppressing the potential difference between the photosensitive member potential and the developing potential to a fixed value (for example, 100 V) or less.

  On the other hand, the present image forming apparatus is capable of performing control after the end of the developing operation with a short traveling distance of the photosensitive member, even if a configuration using a common power transformer is used to generate the developing bias voltage and the charging bias voltage. Become. As a result, the image forming apparatus can improve the durability of the photosensitive member.

  In the above example, although a configuration using a common power supply transformer is employed to generate the developing bias voltage and the charging bias voltage, the present invention is not limited to this. In the reverse control, as in the first embodiment, the charging bias voltage and the developing bias voltage may be generated from independent power supply transformers.

  Further, in the above-described example, the control unit 70 performs control of causing the photosensitive member 10 to rotate in the forward direction by 4 mm after stopping application of the developing bias voltage, but is not limited thereto. The control unit 70 reverses the photosensitive member 10 before the point D at the tip of the non-relaxed region CD in the normal rotation direction where carrier adhesion may occur reaches the recovery region which is the contact point between the photosensitive member 10 and the cleaning blade 18. Just do it.

  In the above example, the control unit 70 causes the photosensitive member 10 to rotate in the normal direction at the same speed as in the developing operation after stopping application of the developing bias voltage in steps S22 to S24. The rotational speed may be set to be slower than that during the developing operation.

  As a result, the behavior of the developer in the development area DE is stabilized, so that carrier adhesion to the photosensitive member 10 is less likely to occur when the non-relaxed area CD passes through the development area DE.

  Further, in the above-described example, the control unit 70 reverses the photosensitive member 10 after rotating the photosensitive member 10 in the forward direction so that the entire non-relaxation region CD passes through the development region DE. I can not. The control unit 70 may reverse the photosensitive member 10 after rotating the photosensitive member 10 in the forward direction so that at least a part of the non-relaxed region CD passes through the developing region DE.

(C4. Modification-determination of whether or not to perform reverse rotation)
In another aspect, the control unit 70 may determine whether to perform the reverse operation of the photosensitive member 10. In other words, the control unit 70 determines whether or not carrier adhesion to the photosensitive member 10 occurs, and does not perform the reverse operation of the photosensitive member 10 when determining that carrier adhesion does not occur. As a result, the image forming apparatus according to this modification can perform control after the end of the developing operation with a shorter traveling distance of the photosensitive member. The control flow will be described below with reference to FIG. The same reference numerals as in FIG. 9 denote the same control, and the description thereof will not be repeated.

  After starting full width exposure by the print head unit 15 in step S20, the control unit 70 predicts whether carrier adhesion to the photosensitive member 10 occurs in step S21.

  The prediction of whether or not carrier adhesion to the photosensitive member 10 occurs will be described below. Parameters related to carrier adhesion include the charging bias voltage Vc, the toner concentration Ct, and the absolute humidity Ha.

  As the absolute value of the developing bias voltage Vb is higher, the absolute value of the charging bias voltage Vc is set higher. When the charging bias voltage Vc is high, the electric field strength in the direction of causing the carrier to adhere to the photosensitive member 10 becomes high, so that the carrier adhesion tends to occur.

  As the toner concentration Ct is lower, the carrier is more easily exposed to the photosensitive member 10 because the coverage with the toner is lower. Further, the lower the toner concentration Ct, the lower the electrical resistance of the developer, and the more likely carrier adhesion occurs.

  As the absolute humidity Ha is lower, the charge amount of the developer is increased, and as a result, the charge amount of the carrier is also increased, so that carrier adhesion tends to occur.

Therefore, in the present modification, when the absolute value of the developing bias voltage Vb is 400 V or more, and the film thickness Th of the photosensitive member exceeds 30 μm, and the toner concentration Ct is 8% or less. And, when the absolute humidity Ha is 8 g / m ³ or less, it is judged that the carrier adhesion to the photosensitive member 10 occurs.

  In another aspect, the control unit 70 may determine that carrier adhesion to the photosensitive member 10 occurs when at least one of the above conditions is satisfied. Further, the numerical values used for the above conditions are merely examples, and the present invention is not limited to these.

  If the control unit 70 predicts that the carrier adhesion to the photosensitive member 10 will occur (YES in step S21), the control proceeds to step S22, and then the reverse operation of the photosensitive member 10 is performed in step S26.

  On the other hand, when control unit 70 predicts that carrier adhesion to photoreceptor 10 will not occur (NO in step S21), point C (the rotational position of photoreceptor 10 at which full-width exposure has been started) is development in step S25. The output of the developing bias voltage (and the charging bias voltage) is stopped when reaching 3 mm upstream of the area. Subsequently, at step S30, when the point E (the rotational position of the photosensitive member 10 in contact with the charging roller 13 at the time of the development bias voltage application stop) reaches the lighting region of the charge removal LED array 17, the control unit 70 Stop driving 10

  According to the above, the image forming apparatus according to the present modification can perform control after the end of the developing operation with a shorter traveling distance of the photosensitive member when it is predicted that carrier adhesion to the photosensitive member will not occur.

  In another aspect, the image forming apparatus may determine whether or not carrier adhesion has occurred after all or part of the non-relaxed area CD capable of causing carrier adhesion has passed through the development area DE. More specifically, the control unit 70 measures the developer concentration on the non-relaxed area CD which has passed through the development area DE by a reflective optical sensor (not shown), and the density is equal to or more than a predetermined threshold Alternatively, it may be determined that carrier adhesion to the photosensitive member 10 is occurring.

  The reflection type light sensor is composed of a light emitting unit such as an LED and a light receiving unit such as a photodiode. The reflection type light sensor is disposed to be close to the surface of the photosensitive member 10 on the downstream side in the normal rotation direction from the development region DE. When the transfer roller 16 is disposed downstream of the transfer roller 16, the transfer roller 16 and the photosensitive member 10 (intermediate transfer belt 1) are separated from each other as compared with the developing operation in order to prevent the carrier from adhering to the intermediate transfer belt 1. It is preferable to keep the

  A control flow in the case of using a reflection type optical sensor will be described with reference to FIG. The same reference numerals as in FIG. 9 denote the same control, and the description thereof will not be repeated.

  Referring to FIG. 12, in step S <b> 21 </ b> A, control unit 70 determines whether carrier adhesion to photoreceptor 10 has occurred. More specifically, when the developer concentration on the non-relaxed area CD which has passed through the development area DE is equal to or higher than a predetermined threshold value, it is determined that the carrier adhesion to the photosensitive member 10 occurs.

  When it is determined that the carrier adhesion to the photosensitive member 10 is occurring (YES in step S21A), the control unit 70 advances the control to step S26, and performs the reverse operation of the photosensitive member 10.

  On the other hand, when it is determined that the carrier adhesion to the photosensitive member 10 has not occurred (NO in step S21A), the control unit 70 rotates the photosensitive member 10 forward at half speed during the developing operation in step S27.

  According to the above, the image forming apparatus according to the present modification can more accurately detect the presence or absence of the carrier adhesion to the photosensitive member, and further performs control after the end of the developing operation with a short traveling distance of the photosensitive member. be able to.

<D. Embodiment 3 Developer Concentration in Developing Region at Reverse Direction>
(D1. Overview)
As described with reference to FIG. 7, the higher the density of the carrier (developer) in the development area DE, the more magnetic brushes are formed, and hence, the force of the magnetic force that attracts the carriers causes the photosensitive member to receive Carrier adhesion is less likely to occur.

  Therefore, in the present embodiment, control is performed to increase the developer density in the developing area when the area (non-relaxed area) where carrier adhesion to the photosensitive member occurs passes the developing area. The basic configuration of the image forming apparatus 100B in the present embodiment is the same as that of the image forming apparatus 100A, so only the differences will be described.

(D2. Imaging unit 2B)
FIG. 13 is a diagram for explaining an imaging unit 2B according to still another embodiment. The drive transmission unit 12 for rotating the photosensitive member 10 and the drive transmission unit 29 for rotating the developing roller 24 are connected to a common drive motor 11A.

  By sharing the drive motor of the photosensitive member 10 and the developing roller 24, the production cost of the image forming apparatus 100B can be reduced.

  However, in such a configuration, the photosensitive member 10 and the developing roller 24 are controlled to start / stop rotation at the same timing.

(D3. Control after developing operation)
Next, a series of control performed by the control unit 70 after the developing operation will be described with reference to FIGS. 14 and 15. FIG. 14 is a flow chart for explaining a series of control after the developing operation according to another embodiment. FIG. 15 is a timing chart of the control shown in FIG. It is to be noted that, in FIG. 14, the portions given the same reference numerals as in FIG. 9 have the same control, and therefore the description thereof will not be repeated.

  Referring to FIG. 14, control unit 70 stops the application of the developing bias voltage (and the charging bias voltage), and then rotates photosensitive body 10 forward by 5 mm at time T40 to detect photosensitive body 10 and developing roller 24. Is stopped (step S40).

  Next, at time T42, the control unit 70 outputs, to the drive motor 11A, a control signal indicating that the photosensitive member 10 and the developing roller 24 are reversely rotated at a half speed during the developing operation (step S42).

  Next, at time T44 when the point D (rotational position corresponding to the developing area on the photosensitive member 10 when application of the developing bias voltage is stopped) reaches the developing area DE, the control unit 70 The developing roller 24 is rotated forward at a speed of 1⁄3 during the developing operation, and the static elimination LED array 17 is turned on (step S44).

  Here, the distance “5 mm” in step S40 is the rotational position F point corresponding to the low magnetic force area LM in the forward rotation direction (rotation direction during development operation) from the rotational position corresponding to the development area DE of the developing roller 24. It corresponds to the distance to

  Since the developer idles on the transport sleeve 23 in the low magnetic force area LM, the density of the developer is higher than the area on the other transport sleeves. The developer present in the low magnetic force area LM moves at the rotational position of point F with the reverse rotation of the developing roller 24 in step S42. Then, when the point D reaches the development area in step S44, the point F where the density of the developer is high also reaches the development area.

  Among the non-relaxed areas CD in which carrier adhesion to the photosensitive member 10 may occur, the point D existing in the development area when the application of the development bias voltage is stopped is most likely to cause carrier adhesion. The image forming apparatus 100B according to the present embodiment can increase the density of the developer in the development area DE when the point D passes the development area DE in step S44. Therefore, the image forming apparatus can reliably collect the carrier attached to the photosensitive member 10 in steps S42 to S44 by the magnetic brush in the development area DE.

  Further, the image forming apparatus can pass the development area DE again through the non-relaxation area CD in a state where the developer density in the development area DE is high. Therefore, the carrier attached to the photosensitive member 10 is reliably collected by the magnetic brush in the development area DE.

  Referring to FIG. 14, control unit 70 controls E point (a rotational position of photosensitive member 10 in contact with charging roller 13 when application of development bias voltage is stopped) is a region where LED array 17 for discharging is turned on. At time T46 when the temperature of the photosensitive drum 10 and the developing roller 24 is stopped, the static elimination LED array 17 is turned off.

  According to the above, in the present image forming apparatus, as in the second embodiment, the point C corresponding to the end closer to the developing device in the area in which the surface potential is alleviated by the full width exposure of the print head portion is the developing area. Before reaching, the application of the developing bias voltage is stopped (step S22). Therefore, the present image forming apparatus can suppress generation of waste toner which is attached to the photosensitive member after the completion of the developing operation.

  Further, in the image forming apparatus according to the present embodiment, by increasing the developer density in the development area when the non-relaxed area through which the carrier adhesion to the photoconductor may occur passes, the carrier adhered to the photoconductor can be reliably developed. It can be collected to the side. In addition, the present image forming apparatus can perform a series of control after the end of the developing operation with a shorter traveling distance of the photosensitive member than the image forming apparatus 100A of the second embodiment.

  Furthermore, in the present image forming apparatus, the photosensitive member and the developing roller are driven by the common drive motor, so that the production cost can be reduced.

  In another aspect, the control unit 70 may determine whether to perform the reverse operation (step S42) as in the modification of the second embodiment.

  In addition, when the photosensitive member and the developing roller are controlled by the independent drive motor, the control unit 70 reverses the developing roller 24 before starting the reverse rotation operation of the photosensitive member 10, and the developer in the developing area DE Control to increase the density may be performed.

  In the above example, the control unit 70 reverses the photosensitive member 10 after rotating the photosensitive member 10 forward 5 mm (the distance from the development area DE to the low magnetic force area LM) from the stop of application of the development bias voltage. It may be a longer distance.

  It is also possible to provide a program that causes a computer to function to execute the control as described in the above-described flow. Such a program is recorded on a non-temporary computer readable recording medium such as a flexible disk attached to a computer, a CD-ROM (Compact Disk-Read Only Memory), a RAM, a ROM and a memory card, and the program product It can also be provided as Alternatively, the program can be provided by being recorded in a recording medium such as a hard disk built in the computer. Also, the program can be provided by downloading via a network.

  The program may execute a process by calling a required module among program modules provided as part of an operating system (OS) of a computer in a predetermined arrangement at a predetermined timing. In that case, the program itself does not include the above module, and the processing is executed in cooperation with the OS. A program not including such a module may also be included in the program according to the present invention.

  Also, the program according to the present invention may be provided incorporated in part of another program. Also in this case, the program itself does not include a module included in the other program, and the process is executed in cooperation with the other program. Programs incorporated into such other programs may also be included in the program according to the present invention.

  The provided program product is installed and executed in a program storage unit such as a hard disk. The program product includes the program itself and a recording medium in which the program is recorded.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is indicated not by the above description but by the claims, and is intended to include all the modifications within the meaning and scope equivalent to the claims.

  DESCRIPTION OF SYMBOLS 10 photosensitive body, 11, 11A, 28 drive motor, 12, 29 drive transmission part, 13 charging roller, 14, 14A, 26, 26A power transformer, 15 print head part, 15A laser, 15B polygon mirror, 16 transfer roller, 17 LED array for static elimination, 18 cleaning blade, 20 developing device, 24 developing roller, 70 control unit, 100, 100A, 100B image forming device, AB, CD non-relaxed area, Ct toner density, DE developed area, EX exposed area, Ha Absolute humidity, LM low magnetic force area, RE recovery area, S stop distance, Th film thickness, Vb developing bias voltage, Vc charging bias voltage.

Claims (15)

An electrophotographic image forming apparatus that executes a developing operation using a developer including toner and a carrier.
An image carrier that rotates in the normal direction during developing operation;
A charging device that applies a charging bias voltage to the image carrier via a charging member disposed in contact with or in proximity to the surface of the image carrier;
When the developing bias voltage having the same polarity as the charging bias voltage is applied to the developer carrier and the image carrier rotates in the forward direction, the developer is used as the image in the developing area located downstream of the charging device. A developing device for developing a latent image on the image carrier by bringing the carrier close to the carrier;
An exposure device disposed between the charging device and the developing device to form the latent image on the image carrier;
After the completion of the developing operation, the application of the charging bias voltage by the charging device is stopped, or the image carrier is uniformly exposed in the rotational axis direction by the exposure device. Potential relaxation means for mitigating the surface potential toward the ground potential;
The application of the developing bias voltage by the developing device before the first rotational position corresponding to the end closer to the developing device in the region where the surface potential is relaxed by the potential relaxation means reaches the developing region. Means to stop the
When the non-relaxed area from the first rotational position to the second rotational position in the forward rotation direction passes the development area after the application of the development bias voltage is stopped during the developing operation And rotation control means for rotating at a lower rotation speed,
The image forming apparatus, wherein the second rotational position is a rotational position of the image carrier corresponding to the developing area at the time of stopping application of the developing bias voltage. The potential reducing means reduces the surface potential of the image carrier toward the ground potential by stopping the application of the charging bias voltage by the charging device.
The non-relaxed area is in contact with the charging member when the charging bias voltage is brought to the ground potential by the potential alleviating means, or from the third rotational position of the image carrier closest to the charging member to the normal rotation direction The image forming apparatus according to claim 1, further comprising an area up to the first rotational position in the image forming apparatus.   The rotation control means rotates the image carrier so that at least a part of the non-relaxed area passes the development area, and the image carrying area passes the development area again to the area passing the development area. The image forming apparatus according to claim 1, wherein the body is reversed. An electrophotographic image forming apparatus that executes a developing operation using a developer including toner and a carrier.
An image carrier that rotates in the normal direction during developing operation;
A charging device that applies a charging bias voltage to the image carrier via a charging member disposed in contact with or in proximity to the surface of the image carrier;
When the developing bias voltage having the same polarity as the charging bias voltage is applied to the developer carrier and the image carrier rotates in the forward direction, the developer is used as the image in the developing area located downstream of the charging device. A developing device for developing a latent image on the image carrier by bringing the carrier close to the carrier;
An exposure device disposed between the charging device and the developing device to form the latent image on the image carrier;
After the development operation is completed, the application of the charging bias voltage by the charging device is stopped, or the image carrier by the exposure device is uniformly exposed in the rotational axis direction. Potential relaxation means for mitigating the surface potential toward the ground potential;
The application of the developing bias voltage by the developing device before the first rotational position corresponding to the end closer to the developing device in the region where the surface potential is relaxed by the potential relaxation means reaches the developing region. Means to stop the
After the application of the developing bias voltage is stopped, the image carrier is positively moved so that at least a part of the non-relaxed area from the first rotational position to the second rotational position in the forward rotation direction passes the developing area. Rotation control means for rotating the image bearing member so as to pass the developing area again in the area having passed through the developing area;
The image forming apparatus, wherein the second rotational position is a rotational position of the image carrier corresponding to the developing area at the time of stopping application of the developing bias voltage.   The image forming apparatus according to claim 3, wherein the rotation control unit reverses the image carrier at a rotation speed lower than a rotation speed of the image carrier at the time of developing operation. A transfer body for transferring the toner attached to the image bearing member to a medium;
The cleaning apparatus further includes a cleaning device in contact with the image carrier and recovering the toner remaining on the image carrier after passing through the transfer body in a recovery area.
The image forming apparatus according to any one of claims 3 to 5, wherein the rotation control unit reverses the image carrier before the non-relaxed area reaches the recovery area. The power supply device further includes a power supply that generates the charging bias voltage and the developing bias voltage via a common transformer.
7. The image forming apparatus according to any one of claims 3 to 6, wherein the potential reducing means reduces the surface potential of the image carrier toward the ground potential by uniformly exposing the image carrier in the rotational axis direction by the exposure device. The image forming apparatus according to claim 1.   The rotation control means may perform the image based on at least one of information indicating the developing bias voltage, information indicating the humidity around the image carrier, and information indicating the concentration of the toner relative to the carrier. The image forming apparatus according to any one of claims 3 to 7, further comprising determination means for determining whether or not to reverse the support. The image carrier further includes a light reflection type sensor disposed downstream of the developing area and measuring the density of the developer on the image carrier when the image carrier rotates in the forward direction.
The rotation control means includes a determination means for determining whether or not to reverse the image bearing member based on the density of the developer in the non-relaxed area which has passed through the developing area in the forward rotation direction. The image forming apparatus according to any one of claims 3 to 7. The potential reducing means uniformly exposes the image carrier at the exposure position in the direction of the rotation axis by the exposure device, thereby relaxing the surface potential of the image carrier toward the ground potential.
The rotation control means reverses the image bearing member to pass the exposure position to a passing area which has passed through the developing area among the non-relaxation area so as to relax the surface potential toward the ground potential. The image forming apparatus according to any one of claims 3 to 9, wherein the image carrier is rotated forward so as to pass through the development area again in the passage area. The carrier contains a magnetic substance,
The developer carrier includes a magnetic field generator for adsorbing the carrier by a magnetic field formed by a plurality of magnetic poles,
The magnetic field generator forms a low magnetic force area for separating the developer from the developer carrier.
The rotation control means rotates the developer carrier by a predetermined distance in a direction opposite to the rotation direction of the developer carrier during the developing operation before reversing the image carrier.
The image forming apparatus according to any one of claims 3 to 10, wherein the predetermined distance is equal to or more than a distance from the developing region to the low magnetic force region in a rotational direction of the developing agent carrier during a developing operation. The developer carrier and the image carrier are configured to rotate by a common drive source,
The image forming apparatus according to claim 11, wherein the rotation control unit rotates the image carrier forward by the predetermined distance before stopping the application of the developing bias voltage and then reversing the image carrier.   The rotation control means includes at least one of information indicating the developing bias voltage, information indicating the humidity around the image carrier, information on the film thickness of the image carrier, and information indicating the concentration of the toner relative to the carrier. The distance control means which controls the distance from the said 1st rotation position to the said 2nd rotation position in the said normal rotation direction based on any one information is further included in any one of Claims 1-12. The image forming apparatus according to claim 1.   The rotation control means rotates the developer carrier at a rotational speed lower than that during the development operation, or stops the rotation of the developer carrier when the non-relaxed area passes through the development area. Item 14. An image forming apparatus according to any one of items 1 to 13.   The image forming apparatus according to any one of claims 1 to 14, wherein the means for stopping the application of the developing bias voltage stops the application of the developing bias voltage when the rotation of the image bearing member is stopped.

Images