JP5495548B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a developing device or an image forming apparatus that develops an electrostatic latent image with a developer. More specifically, the developer is provided between a first chamber and a second chamber that are partitioned in the vertical and vertical directions. The present invention relates to a circulating developing device or an image forming apparatus.

  2. Description of the Related Art Conventionally, as a configuration of a developing device used in an electrophotographic image forming apparatus, there is a horizontal stirring and developing device in which a developing chamber and a stirring chamber are arranged in a horizontal direction. This circulates the developer in a circulation path formed by the developing chamber and the agitating chamber, and imparts a charge amount necessary for image formation.

On the other hand, in order to reduce the size in the horizontal direction, there has been considered a vertical agitation developer in which the developing chamber and the agitation chamber are divided into two in the vertical direction of gravity as in Patent Document 1. The configuration of this vertical agitation developer is shown in FIG. 1 and FIG. In the vertical agitation developer, the developer subjected to development on the developer carrying member is collected in the agitation chamber 4 after the toner concentration is lowered. The toner collected in the agitating chamber 4 is sufficiently mixed with the replenishing toner replenished in the agitating chamber 4 and then pumped up to the developing chamber 3 and used again for development. For this reason, the developer on the developing chamber side always contains only the developer that has been sufficiently agitated. Therefore, compared to the conventional lateral agitating and developing device, image defects due to uneven toner density are reduced, and the image density is in-plane uniform. The improvement of sex can be expected. In addition, since the vertical agitation developer can vertically arrange the chambers in the container, the developer can be elongated in the vertical direction. As a result, the width of the main body can be reduced, and the main body can be downsized.
JP 2003-029522 A

  However, as in Patent Document 1, the vertical agitation developer has the advantages as described above, but has the following problems. That is, the developer in the developing container tends to be biased to the stirring chamber 4 below the gravity direction. When the image forming operation is performed in such a situation, the developer on the developing sleeve 8 may not be taken into the stirring chamber 4 because the stirring chamber 4 is filled with the developer. If the developing sleeve is driven in such a case, there is a problem that the developer is not taken into the agitating chamber 4 and the developer overflows outside the developing container and the inside of the apparatus is contaminated with the developer.

  In particular, the pumping section for pumping the developer from the stirring chamber 4 to the developing chamber 3 has a high developer surface and a large amount of developer as shown in FIG. In addition, since the developer is pumped up against the gravity in the pumping unit, the developer cannot be pumped up immediately even if the screws 5 and 6 rotate. Therefore, the overflow of the developer as described above is likely to occur. In addition, the above problems may occur when the developing device is installed in the main body, when the developing device is tilted during conveyance of the developing device, and the developer surface in the developing device is biased to the stirring chamber, or when the main body is moved. This is likely to occur when the developer is biased to the stirring chamber due to vibration.

  In view of the above, a countermeasure such as providing a seal member between the agitating chamber 4 and the developing chamber 3 at the time of shipment of the developing container to prevent the bias may be considered. In this case, once the seal member is removed, the above problem occurs, which is not a fundamental countermeasure.

  Accordingly, an object of the present invention is to provide a developing device that circulates a developer between a first chamber and a second chamber that are respectively partitioned in the vertical and vertical directions, even if the developer is biased in one chamber. An object of the present invention is to provide a developing device capable of suppressing the overflow of the developer outside the apparatus.

In order to achieve the above object, the configuration of the present invention includes a first chamber that can store a developer, and a second chamber that can communicate with the first chamber in a vertically downward direction to form a circulation path and store the developer. An image carrier that carries the developer supplied from the first chamber, a conveying unit that conveys and circulates the developer in the circulation path formed by the chamber, the first chamber, and the second chamber. The electrostatic latent image formed in the first chamber is transported to a developing position for developing, and a developer carrying member for transporting the developed developer to the second chamber, the first chamber, powder level height of the inner of the developer, and a discharge port capable of discharging the developer in the case of more than a predetermined height, a developing device provided detachably on the main body, when the power activation of the image forming apparatus Alternatively, when the developing device is removed from the apparatus main body, the developer carrier is rotated before image formation. A mode in which the developer biased to the second chamber can be transferred to the first chamber side by driving the conveying means at a lower speed than that at the time of image formation in a state where the speed is lower than that at the time of image formation. And a controller.

Or the structure of this invention for achieving the said objective can be connected to the 1st chamber which can store a developer, and the said 1st chamber below in the perpendicular direction, can form a circulation path, and can store a developer. A second chamber; a conveying unit configured to convey and circulate the developer in a circulation path formed by the first chamber and the second chamber; and a developer supplied from the first chamber. A developer carrier that transports the electrostatic latent image formed on the carrier to a development position for developing, and transports the developed developer to the second chamber, and is provided in the first chamber . A developing device detachably provided on the main body, and a power source for the image forming apparatus, and a discharge port for discharging the developer when the powder surface height of the developer in the chamber is a predetermined height or more Before starting image formation when starting up or when the developing device is removed from the main assembly, A controller capable of executing a mode in which the developer biased to the second chamber can be transferred to the first chamber side by driving the conveying unit at a lower speed than that during image formation in a state where rotation of the toner is stopped. It is characterized by having.

  According to the present invention, in the developing device that circulates the developer between the first chamber and the second chamber that are partitioned in the vertical and vertical directions, even if the developer is biased in one chamber, It is possible to provide a developing device capable of suppressing the overflow of the developer.

Example 1
In this embodiment, the developing device is used in an image forming apparatus as described below, for example. However, the developing device is not necessarily limited to this form, and can be applied to an electrostatic recording type.

  FIG. 1 shows Y, M, C, and K stations in the full-color image forming apparatus as shown in FIG. The Y, M, C, and K stations have substantially the same configuration, and form yellow (Y), magenta (M), cyan (C), and black (K) images in a full-color image, respectively.

  In the following description, for example, if the developing device 1 is used, the developing device 1Y, the developing device 1M, the developing device 1C, and the developing device 1K in each of the Y, M, C, and K stations are commonly referred to. Other members provided for C, Y, and K are also shown.

[Image forming apparatus]
First, the operation of the entire image forming apparatus will be described with reference to FIG.

  The photosensitive drum 10 as an image carrier is rotatably provided. The photosensitive drum 10 is uniformly charged by a primary charging unit 21 and modulated in accordance with an information signal by a light emitting element 22 such as a laser. An electrostatic latent image (latent image) is formed by exposure with the emitted light. The latent image is visualized as a toner image by the developing device 1 in the following process. The developing device 1 is detachably provided to the main body of the image forming apparatus, and can be removed as appropriate.

  Next, the visible image is transferred by the transfer charger 23 to the transfer paper 27 conveyed by the transfer paper conveyance sheet 24 and further fixed by the fixing device 25 to obtain a permanent image. Further, the transfer residual developer on the photosensitive drum 10 is removed by the cleaning device 26. Further, the developer (toner) consumed in the image formation is supplied from the toner supply tank 20.

  The developing device of this example used a two-component developer containing nonmagnetic toner and a low magnetization high resistance carrier as described below.

  The non-magnetic toner is configured by using an appropriate amount of a binder resin such as a styrene resin or a polyester resin, a colorant such as carbon black, a dye or a pigment, a release agent such as wax, a charge control agent, or the like. Such a non-magnetic toner can be produced by a conventional method such as a pulverization method or a polymerization method.

The non-magnetic toner (negative charging characteristics) preferably has a triboelectric charge amount of about −1 × 10 ⁻² to −5.0 × 10 ⁻² C / kg. When the triboelectric charge amount of the non-magnetic toner is out of the above range, the developing efficiency is lowered, the counter charge amount generated in the magnetic carrier is increased, the white spot level is deteriorated, and an image defect may occur. The triboelectric charge amount of the non-magnetic toner may be adjusted according to the type of material used, or may be adjusted by adding an external additive described later.

  The triboelectric charge amount of the non-magnetic toner is the charge induced in the measuring container by using a general blow-off method, with the developer amount being about 0.5 to 1.5 g, and sucking the toner from the developer by air suction. It can be measured by measuring the amount.

  A conventionally known magnetic carrier can be used as the magnetic carrier. For example, a resin carrier formed by dispersing magnetite as a magnetic material in a resin, and carbon black dispersed for conductivity and resistance adjustment, or the resistance of the magnetite simple substance surface such as ferrite is oxidized and reduced. You may have done. Moreover, what coated with the magnetite single-piece | unit surface resin, such as a ferrite, and adjusted resistance, etc. can be used. The method for producing these magnetic carriers is not particularly limited.

The magnetic carrier preferably has a magnetization of 3.0 × 10 ⁴ A / m to 2.0 × 10 ⁵ A / m in a magnetic field of 0.1 Tesla. Reducing the amount of magnetization of the magnetic carrier has the effect of suppressing the scavenging by the magnetic brush, but it becomes difficult for the magnetic field generating means to adhere to the non-magnetic cylinder, leading to image defects such as adhesion of the magnetic carrier to the photosensitive drum, This may cause a close-up image. If the magnetization of the magnetic carrier is larger than the above range, an image defect may occur due to the pressure of the magnetic brush as described above.

Further, the volume resistivity of the magnetic carrier is preferably 10 ⁷ to 10 ¹⁴ Ωcm in consideration of leakage and developability.

  The magnetization of the carrier was measured using an oscillating magnetic field type magnetic property automatic recording apparatus BHV-30 manufactured by Riken Denshi Co., Ltd. As the magnetic characteristic value of the carrier powder, an external magnetic field of 0.1 T is created, and the strength of magnetization at that time is obtained. The carrier is packed in a cylindrical plastic container so as to be sufficiently dense. In this state, the magnetization moment is measured, the actual weight when the sample is put is measured, and the strength of magnetization is obtained (Am2 / kg). Next, the true specific gravity of the carrier particles is determined by a dry automatic density Accupic 1330 (manufactured by Shimadzu Corporation), and the true specific gravity is multiplied by the magnetization strength (Am2 / kg), thereby being used in this example. The intensity of magnetization per volume (A / m) can be determined.

[Developer]
Next, the operation of the developing device 1 will be described with particular reference to FIG. In the developer container 2 in which the developer is accommodated, a developing sleeve 8 as a developer carrying member and a spike cutting member 9 for regulating the ears of the developer carried on the developing sleeve 8 are provided.

  Further, there is an opening at a position corresponding to the developing portion of the developing container 2 facing the photosensitive drum 10, and the developing sleeve 8 is rotatably disposed in this opening so as to be partially exposed in the direction of the photosensitive drum 10. Yes. The developing sleeve 8 is made of a non-magnetic material, and a magnet roller 8 'serving as a magnetic field means is installed in a non-rotating state in the developing sleeve 8. The magnet roller 8' is a developing pole located in the developing portion. S1 and magnetic poles S2, N1, N2, and N3 for conveying the developer.

  Here, the nonmagnetic cylindrical body of the developing sleeve 8 is preferably formed of a conductive material. As such a material, various conventionally known materials such as metals such as stainless steel and aluminum and resin bodies imparted with conductivity by dispersion of conductive particles can be used. Further, the developing sleeve 8 may be subjected to processing such as roughening the surface by blasting or the like in order to improve the developer transportability.

  Further, as the magnet roll 8 ′ which is a magnetic field generating means, a plurality of magnetic poles are fixed inside the developing sleeve 8 so as to be relatively immovable with respect to the developing sleeve 8 a. The magnet roll 8 'may be a magnet or the like that constantly generates a magnetic field, or may be an electromagnet or the like that can arbitrarily generate a constant magnetic field or a magnetic field having a different polarity.

  Thus, as shown in FIG. 1, the developing sleeve 8 is rotated in the direction indicated by the arrow by the developer carrier driving device 31 as a driving means during development. A panning member 9 as a regulating member is disposed at a position facing the developing sleeve 8. The developer on the developing sleeve 8 is regulated to a predetermined layer thickness by the ear cutting member 9. A magnetic pole S <b> 2 is provided inside the developing sleeve 8 facing the ear cutting member 9, a magnetic brush is formed on the developing sleeve 8, and the layer thickness is regulated by the ear cutting of the ear cutting member 9. Then, the two-component developer whose layer thickness is regulated is conveyed to a developing unit facing the photosensitive drum 10, and the developer is supplied to the latent image formed on the photosensitive drum 10 to develop the latent image. At this time, in order to improve the developing efficiency (that is, the toner application rate to the latent image), a developing bias voltage in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 8 from a power source.

  The ear cutting member 9 is made of a non-magnetic member such as aluminum, and is disposed upstream of the photosensitive drum 10 in the rotation direction of the developing sleeve 8. Then, both the non-magnetic toner of the developer and the magnetic carrier are sent to the developing portion through the space between the tip of the ear cutting member 9 and the developing sleeve 8. Incidentally, by adjusting the gap between the surface of the developing sleeve 8 of the ear cutting member 9, the amount of the developer magnetic brush carried on the developing sleeve 8 is regulated and the amount of the developer conveyed to the developing unit is reduced. Adjusted.

  As shown in FIG. 1, the developing container 1 can store a developer by forming a circulation path by communicating with the developing chamber 3, which is a first chamber that can store the developer, in the vertical direction with the developing chamber 3. A stirring chamber 4 is provided as a second chamber. That is, a substantially central portion in the developing container 1 is divided vertically into an upper developing chamber 3 and a lower stirring chamber 4 by a partition wall 7 extending in a direction perpendicular to the paper surface. 3 and the stirring chamber 4.

  Here, the developing device 1 will be described in more detail with reference to FIG. FIG. 2 is a schematic cross-sectional view of the developing container 2 portion of the developing device 1 shown in FIG. 1 according to the present invention cut along the first and second conveying screws 5 and 6 in the axial direction and in the vertical direction. The developing chamber 3 is provided with a first conveying member (conveying screw) 5 as conveying means for stirring and conveying the developer. Inside the agitation chamber 4, a second conveying member (conveying screw) 6 is provided as conveying means for agitating and conveying the developer. As shown in FIG. 1, the first and second conveying screws 5 and 6 are configured to be driven by a stirring member driving device 32 as a driving means during a developing operation.

  In the present embodiment, the first conveying screw 5 has a screw structure in which blade members made of a nonmagnetic material are provided in a spiral shape around a rotating shaft made of a ferromagnetic material. The first conveying screw 5 is disposed substantially parallel to the bottom of the upper developing chamber 3 along the axial direction of the developing sleeve 8 and rotates to allow the developer T in the developing chamber 3 to move along the axial direction. Transport in one direction.

  Similarly to the first conveying screw 5, the second conveying screw 6 has a screw structure in which a blade member is provided in a spiral shape around the rotation axis in a direction opposite to the first conveying screw 5. The second conveying screw 6 is disposed at the bottom of the lower stirring chamber 4 substantially in parallel with the first conveying screw 5 and rotates in the same direction as the first conveying screw 5. Developer T is conveyed in the opposite direction to the first conveying screw 5.

  In this way, the developer is circulated in the circulation path formed by the developing chamber 3 and the stirring chamber 4 by the conveyance by the rotation of the first and second conveyance screws 5 and 6. A partition wall 7 shown in FIG. 1 is provided between the developing chamber 3 and the stirring chamber 4, and through openings (communication portions) 11 and 12 provided at both ends of the partition wall 7 in the developer conveying direction. Developer circulates.

  In the upper developing chamber 3, the first conveying screw 5 supplies the developer being conveyed to the developing sleeve 8 while conveying the developer conveyed from the lower stirring chamber 4 in the circulation direction. Then, the developer that has not been supplied to the developing sleeve 8 is transported in the circulation direction, and is transported again from the communication portion 12 to the stirring chamber 4.

  The developer supplied from the developing chamber 3 to the developing sleeve 8 under the restriction of the ear cutting member 9 is transported to the developing portion which is a portion facing the photosensitive drum 10 by the operation described above. Then, after passing through the developing section, the developer is returned to the stirring chamber 4 by the rotation of the developing sleeve 8.

  In the lower stirring chamber 4, the second conveying screw 6 equalizes the toner density of the developer and conveys it to the developing chamber 3. In the agitation chamber 4, replenishment toner is replenished from the toner replenishment tank 20 shown in FIG. 3 to the upstream side of the second conveying screw 6 in the agitation chamber 4 through a replenishment port (not shown). Further, the developer that passes through the communication portion 12 and is transported from the developing chamber 3 and the developed developer that is transported from the developing sleeve 8 are transported to the stirring chamber 4. The second conveying screw 6 conveys these developers toward the developing chamber while stirring them.

  That is, the developer is supplied to the developing sleeve 8 in the developing chamber 3, and the developer is collected from the developing sleeve 8 in the stirring chamber 4. For this reason, after being carried on the developing sleeve 8, transported to the developing unit and used for development, the developer remaining without being developed in the developing unit is moved to the developing chamber 3 side with the rotation of the developing sleeve 8. Instead, it is collected on the stirring chamber 4 side. For this reason, only the developer sufficiently stirred in the stirring chamber 4 is always present in the developing chamber 3.

  Therefore, a developer having a uniform density is always supplied to the developing sleeve 8, and a uniform image without image unevenness or density difference in the thrust direction can be obtained.

  As described above, in the developing device 1, the developing chamber 3 and the stirring chamber 4 are arranged vertically above and below. The developer from the developing chamber 3 to the stirring chamber 4 is developed from the top to the bottom, and from the stirring chamber 4 to the developing chamber 3 is pushed up from the bottom by the pressure of the developer accumulated at the end. The developing device to which the agent is delivered.

  Accordingly, after the developer is transferred from the agitating chamber 4 to the developing chamber 3, the developer is conveyed in the axial direction of the conveying screw 5 in the developing chamber 3, and is supplied to the developing sleeve 8 on the way, There are components recovered in the stirring chamber 4 after passing through. The developer is transferred to the developing sleeve 8 over almost the entire image area in the rotation axis direction of the developing sleeve 8. For this reason, the amount of developer conveyed by the first conveying screw 5 in the developing chamber 3 decreases from the upstream end toward the downstream end. On the other hand, since the amount of developer conveyed by the second conveying screw 6 in the stirring chamber 4 tends to gradually increase from the upstream end to the downstream end, the distribution of the developer T in the developing device 1 There is a tendency to be offset.

  When this deviation occurs greatly in the stirring chamber 4, the amount of developer in the vicinity of the pumping portion downstream of the developing chamber is extremely increased, so that the pumping portion is filled with the developer and used for developing the sleeve 8. The developer is not collected in the developing chamber 4. As a result, the developer that could not be collected overflows outside the developing container, and the inside of the apparatus is contaminated with the developer. That is, the developer conveyed by the sleeve 8 during driving is not taken into the developing device and overflows outside the container.

[Developer leveling mode]
In the developing apparatus of this embodiment, during normal image formation, the sleeve 8 is set to 500 rpm, the screw 5 and 6 are set to 700 rpm, and the downstream agent surface height T ′ of the stirring chamber 4 is optimized as shown in FIG. .

  However, if the developing device is excessively tilted when the developing device is installed, or if vibration is applied when the main body is moved, the developer surface in the developing container is placed in the stirring chamber and the pumping portion as shown in FIG. Is likely to be biased. In this case, if the main body is operated at the same speed of the sleeve 8 and the speed of the screws 5 and 6 as in normal image formation, the developer overflow as described above occurs.

  Therefore, in this embodiment, it is proposed to solve the developer overflow problem by executing the developer leveling mode at the timing as described above.

  In the present embodiment, the developer leveling mode is a mode in which the screws 5 and 6 are rotated without rotating the developing sleeve 8. The drive speed of the screws 5 and 6 in the developer leveling mode is driven at 700 rpm, which is the same rotational speed as that during normal image formation (development). Here, normal image formation or development refers to the following. That is, it means that an area on which an image is formed corresponding to the conveyed recording material on the photosensitive drum as an image carrier passes through a developing position facing the developing sleeve.

By doing so, the developer biased to the stirring chamber 4 can be forcibly fed to the developing chamber 3 side. At the same time, since the driving of the developing sleeve is stopped, the conveyance of the developer from the developing chamber 3 to the stirring chamber 4 can be stopped. As a result, the developer on the developing sleeve is not fed into the agitating chamber 4, so that overflow from the agitating chamber 4 can be suppressed.
Next, the timing for executing the developer leveling mode will be described.

(I) At the time of inserting / removing the developing device First, the developer may be biased to the stirring chamber 4 when the developing device is handled outside the main body. For this reason, when the opening / closing sensor of the door of the main body is detected, the following developer leveling mode can be executed. In this embodiment, as shown in FIG. 1, the detection of insertion / removal of the developing device is performed based on the detection result of the opening / closing detection circuit 1002 as a door opening / closing detection means for detecting whether the developing device replacement door is opened or closed. Yes. A signal from the open / close detection circuit 1002 is stored in a ROM (not shown) as storage means. The CPU can detect whether the door opening / closing operation has been performed based on information stored in the ROM. A configuration may be provided in which a sensor for directly detecting whether the developing device is mounted is provided.

(Ii) When the apparatus main body is installed The developer may be biased to the stirring chamber 4 when the main body is moved (installed). In this embodiment, it is determined that the main body of the apparatus has been moved (installed) by detecting that the plug for supplying commercial power to the main body has been removed from the outlet, and the developer leveling mode can be executed. ing. In this embodiment, when the plug of the apparatus main body is removed from the outlet and the power supply from the commercial power supply is cut off, another power supply (not shown) provided on the image forming apparatus main body side is provided. Using this power source, the fact that the power supply from the commercial power source has been cut off is stored in a ROM (not shown). The CPU can detect whether the power supply from the commercial power supply is cut off based on the information stored in the ROM.

(Iii) When the apparatus power is turned on In this embodiment, when the main switch of the power supply of the image forming apparatus main body is turned off, the main switch is turned on because the developing device cannot be inserted or removed (opening / closing of the door). The developer leveling mode is executed each time (at startup). The image forming apparatus according to the present embodiment is configured such that power is supplied to a substrate (not shown) provided in the apparatus main body even when the main switch of the power supply of the image forming apparatus main body is turned off. It is possible to detect whether the switch is turned on or off.

  Next, in order to define the time required for the operation of the developer leveling mode, a method for determining the time from when the developer has accumulated in the stirring chamber 3 to the steady state will be described.

  In this embodiment, 350 g of developer is used, and when the developer is sufficiently filled in the stirring chamber 4, about 300 g of developer is accommodated in the stirring chamber. FIG. 5 shows the relationship between the time during which the screws 5 and 6 are rotated at 700 rpm without rotating the sleeve 8 from this state and the developer amount in the stirring chamber 4.

  Until the stirring time is up to 4 seconds, the developer amount in the stirring chamber 4 does not decrease so much, but after 5 seconds it decreases rapidly, and after 8 seconds it stabilizes at a steady state at 200 g.

  Therefore, the overflow of the developer can be prevented by stopping the sleeve 8 for 8 seconds at the longest and rotating the screws 5 and 6 at 700 rpm.

  The developer leveling mode in this embodiment will be described with reference to the operation flowchart of FIG. 6 and the control block diagram of FIG. First, the CPU 100 as the controller in FIG. 1 determines whether the power supply from the commercial power supply has been cut off, whether the main body power supply has been turned off, or whether the developing device has been inserted or removed (opening / closing the main body door). (S1) When the power source of the image forming apparatus main body is activated (ON), or when the door is opened and closed, the developer may be biased, so the developer leveling mode is executed. (S2). The developer leveling mode in this embodiment is a mode in which only the screws 5 and 6 are rotated for 8 seconds by the stirring member driving device 32 of FIG. 1 in a state where the driving of the developing sleeve 8 is stopped (S11). After executing the developer leveling mode, normal printing operation, density control, and various controls are performed (S3).

  In this embodiment, the rotational speeds of the screws 5 and 6 in the developer leveling mode are rotated at the same speed as in normal image formation. However, the present invention is not limited to this. For example, if the developer is rotated at a speed higher than that during normal image formation, the developer biased to the stirring chamber 4 can be stabilized to a steady state in a shorter time. Further, the rotation speeds of the screws 5 and 6 in the developer leveling mode may be rotated at a slower speed than that in normal image formation.

  Further, in this embodiment, the example in which the above-described mode is executed when the opening / closing sensor of the door of the main body is detected or when the outlet of the main body is inserted / removed has been described, but this is performed every time before the image forming operation is performed. It is good also as a structure.

(Example 2)
In Example 1, it was possible to prevent the developer conveyed by the sleeve 8 during driving from being taken into the developing device and overflowing outside the container. However, in a vertical agitation developer having a discharge port 9 on the developing chamber 3 side for discharging the developer in the developer as shown in FIG. 7, the developer may be excessively discharged. . For example, when the means of Example 1 is executed when the developer in the developing device is hardly biased to the stirring chamber, the developer surface in the developing chamber 3 becomes higher than that during normal image formation. The agent is discharged excessively.

  Then, at the time of normal image formation, the developer is insufficient in the downstream portion of the developing chamber 3, and the developer is not coated on the sleeve 8, resulting in an image defect.

  Therefore, in this embodiment, in the vertical agitation developing device having the developer discharge port 9 in the developing chamber, the overflow of the developer due to the deviation of the developer that occurs when the developing device is installed or removed, or when the main body is moved is prevented. Suggest means.

  In the developing device of this embodiment, during normal image formation, the sleeve 8 is rotated at 500 rpm and the screws 5 and 6 are rotated at 700 rpm so that the downstream agent surface height T ′ of the stirring chamber 4 is optimized as shown in FIG. ing.

  However, if the developing device is excessively tilted when the developing device is installed, or if vibration is applied when the main body is moved, the developer surface in the developing container is placed in the stirring chamber and the pumping portion as shown in FIG. Is likely to be biased. In this case, if the main body is operated at the same speed of the sleeve 8 and the speed of the screws 5 and 6 as in normal image formation, the developer overflow as described above occurs.

  Therefore, in this embodiment, by stopping the sleeve 8 and rotating only the screws 5 and 6 slower than usual at the timing as described above, two problems of the developer overflow and the excessive discharge from the developer discharge port 9 are solved. Suggest to solve.

  FIG. 8 shows the powder surface when the speeds of the screws 5 and 6 are swung while the sleeve 8 is stopped. When only the screw is rotated at 700 rpm, which is the same as that during normal image formation, the powder level in the developing chamber increases as the developer no longer moves from the sleeve to the stirring chamber. Therefore, when the screw is rotated at 600 and 500 rpm, which is slower than that at the time of image formation, the same powder surface as at the time of normal image formation is obtained at just 500 rpm.

  If the developer surface of the developing chamber 3 is higher than the developer discharge port, naturally the developer is discharged excessively, which leads to image defects such as coating defects. For this reason, this embodiment proposes an operation for stabilizing the developer biased to the stirring chamber in a steady state by rotating only the screw at 500 rpm or less at which the powder level is lower than the developer discharge port.

  Here, in order to define the time required for the above operation, the time from the state where the developer has accumulated in the stirring chamber 3 to the steady state is calculated.

  In this embodiment, 350 g of developer is used, and when the developer is sufficiently filled in the stirring chamber 4, about 300 g of developer is accommodated in the stirring chamber. FIG. 9 shows the relationship between the time when the screws 5 and 6 are rotated at 500 rpm without rotating the sleeve 8 from this state and the amount of developer in the stirring chamber 4.

  The developer amount in the stirring chamber 4 rapidly decreases from about 4 seconds after the start of stirring, and the developer amount stabilizes at 230 g in about 8 seconds.

  Therefore, the overflow of the developer and the excessive discharge of the developer from the developer discharge port can be prevented by stopping the sleeve 8 for 8 seconds at the longest and rotating the screws 5 and 6 at 500 rpm.

  Since the operation flow of this embodiment is the same as that of the first embodiment, a description thereof will be omitted. As described above, the developer in the vertical agitation developer may be biased toward the agitation chamber when the developer is installed or the main body is moved. In this case, only the screw is driven without turning the sleeve after the main body is activated. Then, rotate the sleeve at a lower speed than in normal image formation so that the powder surface near the developer discharge port provided in the developing chamber is the same as in image formation, and then adjust the developer surface before rotating the sleeve. . By doing so, it is possible to prevent the developer from overflowing from the developing device while keeping the developer in the developing device constant.

  The developer leveling mode of the present invention has been described by taking as an example a configuration in which the rotation of the developing sleeve is stopped and only the screws 5 and 6 are rotated. However, the developing sleeve may be slightly driven as long as the developer does not leak from the developing container. That is, as long as the developer does not leak from the developing container, the screws 5 and 6 may be rotated with the developing sleeve driving speed lower than that during image formation.

Schematic sectional view and control block diagram showing an embodiment of the developing device of the present invention Diagram for explaining developer circulation during normal image formation 1 is a schematic cross-sectional view showing a schematic configuration of an embodiment of an image forming apparatus of the present invention. The figure explaining the agent level when the developer is biased in the stirring chamber Relationship between stirring time and amount of developer in the stirring chamber in Example 1 Flow chart of the first embodiment The figure explaining the circulation of the developer at the time of normal image formation of the developing device having the developer discharge port Relationship diagram between stirring speed and developer surface Relationship diagram between stirring time and stirring chamber developer amount in Example 2

Explanation of symbols

3 Developing chamber 4 Stirring chamber 8 Developing sleeve 10 Photosensitive drum

Claims (3)

A first chamber that can store a developer; a second chamber that communicates with the first chamber vertically below to form a circulation path and that can store the developer; the first chamber and the second chamber; A transporting means for transporting and circulating the developer in the circulation path formed by the developer, and a development position for carrying the developer supplied from the first chamber and developing the electrostatic latent image formed on the image carrier. And a developer carrier for transporting the developed developer to the second chamber, and the powder level of the developer in the first chamber is set to a predetermined height. the developer and a discharge port capable of discharging when the above is a developing device provided detachably on the main body, when at power-up of the image forming apparatus, or said developing device is inserted and removed from the apparatus main body In addition, before carrying out image formation, the developer carrying member is rotated at a lower speed than that during image formation. And a controller capable of executing a mode in which the developer biased to the second chamber can be transferred to the first chamber side by driving the means at a lower speed than during image formation. apparatus. A first chamber that can store a developer; a second chamber that communicates with the first chamber vertically below to form a circulation path and that can store the developer; the first chamber and the second chamber; A transporting means for transporting and circulating the developer in the circulation path formed by the developer, and a development position for carrying the developer supplied from the first chamber and developing the electrostatic latent image formed on the image carrier. And a developer carrier for transporting the developed developer to the second chamber, and the powder level of the developer in the first chamber is set to a predetermined height. the developer and a discharge port capable of discharging when the above is a developing device provided detachably on the main body, when at power-up of the image forming apparatus, or said developing device is inserted and removed from the apparatus main body In addition, before the image formation, the transporting unit is set to the image forming state with the rotation of the developer carrier stopped. Also by driving at a low speed, the image forming apparatus characterized by having a controller capable of executing a migratable mode to the first chamber side developer biased to the second chamber.   The developing device is detachably provided in the image forming apparatus, and has an open / close detecting means for detecting an opening / closing operation of a replacement door for replacing the developing device, and the controller opens / closes the door The image forming apparatus according to claim 1, wherein the mode is executed when an operation is performed.

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