JP5095306B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device for an image recording apparatus such as a printer, a copying machine, a fax machine, and the like, and more particularly to a developing device that applies a developer to a developing roller by a supply screw to perform a developing process.

  In an electrophotographic developing apparatus, for example, a two-component developer having a magnetic carrier and a nonmagnetic toner is used. In such a developing device, a developing roller is configured by including a magnetic field generating means comprising a magnet body having a plurality of magnetic poles inside, and a cylindrical developing sleeve supported rotatably on the outside thereof. The developer is pumped up by a magnetic force from the screw, is made to have a constant layer thickness by a developer regulating member (doctor), is transported to the development area, and develops the latent image on the photoconductor as a latent image carrier. In such magnetic brush system development, in order to obtain a uniform image without unevenness, it is important to stabilize the charge amount of the developer conveyed to the development area.

  In a conventional developing apparatus in which two screws are juxtaposed horizontally and developer is supplied to the developing roller while agitating and conveying the developer, the developer once developed is conveyed along the screw as a supply member. In the meantime, it is pumped up several times by the developing roller (developing sleeve) and used for development. The developer is adjusted to an appropriate toner concentration and charge amount in the upstream portion of the developer roller in the longitudinal direction of the screw, but the toner concentration of the developer pumped down decreases toward the downstream of the developer transfer. As a result, a difference occurs in the toner density of the developer pumped up in the longitudinal direction of the developing roller, and density unevenness appears in the image due to the difference.

  The bulk density of the developer also varies depending on the toner concentration. The lower the toner concentration, the smaller the bulk of the stored developer. In particular, the powder level of the stored developer is lower than the height of the outer diameter portion of the supply screw that supplies the developer to the developing roller (sleeve). When the topmost portion of the supply screw comes out of the stored developer), the amount of developer pumped from the screw to the sleeve varies depending on the location, and density unevenness occurs at intervals of the screw pitch.

As described above, in the downstream portion of the developer sleeve in the longitudinal direction where the agent is transported, density unevenness is likely to occur due to a decrease in toner concentration and bulk of the developer to be pumped up.
The charging of the developer is mainly performed when the developer passes through the gap between the developer regulating member and the developing sleeve. If there is unevenness in the pumping amount in the longitudinal direction of the developing sleeve, unevenness in the charge amount will occur after passing through the regulating member, leading to density unevenness.

  There are already proposals to obtain a stable pumping volume. For example, Patent Document 1 discloses a developer container, a developer agitating / conveying means, a developer carrying body, a magnetic field generating means fixedly arranged inside the developer carrying body, and a developer carrying body. In a two-component developing device having a regulating member for regulating the amount of developer, a developer retaining portion for retaining an excess of developer conveyed by the developer carrying member may be formed in the regulating member. Proposed. In Patent Document 2, in a developing device having a developing roller having a magnet roller disposed inside a non-magnetic sleeve and a screw-like stirring member, a pumping auxiliary member made of a magnetic material is placed between the developing roller and the screw-like stirring member. It has been proposed to do. In Patent Document 3, the second conveying means for supplying the developer to the developer carrying member has an outer diameter of 24 mm to 30 mm, a pitch of 30 mm to 40 mm, and rotates at a rotation speed of 300 times to 500 times per minute, The catch pole is disposed at a position that is 25 ° to 50 ° downstream of the straight line connecting the rotation center of the developer carrier and the rotation center of the second transport unit, and the peeling pole is upstream of the straight line. It is proposed that the ratio A / B between the conveying force A of the first conveying means and the conveying force B of the second conveying means is 1.04 to 1.20. ing.

  However, in the configuration of Patent Document 1, if the volume of the developer is reduced downstream of the supply screw, the amount pumped up to the developing sleeve also decreases. Almost no retention effect can be expected. In Patent Document 2, since the magnetic flux density between the screw and the developing sleeve increases, a stable pumping amount can be obtained. However, in a small developing device, it is possible to secure a space for installing such an auxiliary member. Have difficulty. In the configuration of Patent Document 3, control is complicated and lacks versatility.

JP 2004-184941 A Japanese Patent Laid-Open No. 2005-292301 JP 2006-126545 A

  The present invention reduces unevenness in image density by reducing variations in the amount of developer pumped up to the developing sleeve on the upstream and downstream sides of the developer supply in the longitudinal direction of the supply member that supplies the developer to the developer carrying member. This is the issue.

  It is another object of the present invention to eliminate variations in the charge amount after passing through the developer regulating member by supplying the developer having a rising charge amount to the developing unit.

According to the present invention, there is provided a developer carrier having a magnetic field generating means having a plurality of magnetic poles, a supply member for supplying the developer to the developer carrier, and a thickness of the developer on the developer carrier. A developing unit configured to include a developer regulating member for regulating, an external stirring unit for stirring the toner / developer independent of the developing unit, and a developer circulation means for connecting the developing unit and the external stirring unit In the developing device, the powder level of the developer deposited and conveyed around the supply member arranged horizontally is constant on the downstream side in the longitudinal direction of the supply member regardless of the image information to be formed. As a means for controlling the amount of developer supplied from the external stirring unit to the developing unit, a rotary feeder comprising a rotor having a plurality of rotating blades and a stator covering the rotor is connected to the external stirring unit and the developing unit. Between Referring to the toner density detection result of the toner density detecting means of the developing unit, if the detected toner density is higher than a predetermined value, the rotation of the rotary feeder is slowed, and if it is low, the rotary feeder is rotated faster. This can be solved by controlling the developer supply amount . A developer carrying member having a magnetic field generating means having a plurality of magnetic poles; a supply member for supplying the developer to the developer carrying member; and a developer regulating member for regulating the thickness of the developer on the developer carrying member. A developing device comprising: a developing unit configured to include: an external stirring unit that stirs toner / developer independent of the developing unit; and a developer circulation unit that connects the developing unit and the external stirring unit In this case, the external agitation is performed so that the powder level of the developer deposited and transported around the supply member arranged horizontally is constant on the downstream side in the longitudinal direction of the supply member regardless of the image information to be formed. As a means for controlling the amount of developer supplied from the developing unit to the developing unit, a rotary feeder comprising a rotor having a plurality of rotating blades and a stator covering the rotor is provided between the external stirring unit and the developing unit. Image area of the image There is is lower than a predetermined value to slow down the rotation of the rotary feeder, by controlling the developer supply amount by fast rotation of the rotary feeder is higher, the problem is solved.

It is effective that the supply member is completely buried in the powder surface of the developer during operation of the apparatus on the downstream side in the longitudinal direction of the supply member . As the difference between the charge amount of the developer before and after the current image-regulating member passes is reduced, by raising up in advance to the charge amount necessary for development by controlling the stirring operation with an external stirrer unit it is effective. Conveniently, the developer regulating member has a magnetic member. It is preferable to provide a developer transfer port from the developing section to the developer circulating means at a position higher than the topmost portion of the supply member. It is more effective if the developer supply amount is controlled so that the powder level of the developer on the supply member is higher than the position closest to the developer carrying member of the developer regulating member.

The developer once developed is drawn up to the developing sleeve several times and used for development while being conveyed along the supply member. Therefore, the toner density of the developer pumped down as the developer moves downstream in the developer transfer direction. That is, the developer volume decreases toward the downstream, and image density unevenness may occur. According to the first and second aspects of the present invention, the powder level of the developer deposited and transported around the horizontally arranged supply member is downstream in the longitudinal direction of the supply member, regardless of the image information to be formed. As a means for controlling the amount of developer supplied from the external stirring unit to the developing unit, a rotary feeder comprising a rotor having a plurality of rotating blades and a stator covering the rotor is connected to the external stirring unit. The developer supply amount is controlled by slowing or speeding up the rotation of the rotary feeder according to the toner density detected in the developing unit and the image area ratio of the image to be formed . The pumping amount can be obtained.

Idea launch the charge amount of the advance developer to charge quantity necessary for the developing by an external agitation means, the charge amount variation of the developer before and after passing through the developer regulating member is suppressed, the amount of pumping slightly fluctuates However, it is possible to prevent density unevenness due to variations in charge amount. If the developer regulating member has a magnetic member, the pumping amount after passing the developer regulating member is stabilized by the magnetic flux generated between the developer regulating member and the magnetic pole arranged in the developing sleeve. If the developer transfer port from the downstream part in the developer transfer direction to the developer circulation means in the developing unit is provided at a position higher than the topmost part of the supply member (the highest part of the outer diameter when the supply member is a screw) The developer powder level at the downstream portion in the developer transport direction in the developing unit is always higher than the topmost portion of the supply member, and therefore, the pumping amount unevenness due to the bulk fluctuation is less likely to occur. If the powder surface of the developer on the supply member is higher than the position closest to the developer carrier of the developer restriction member, the developer layer thickness is regulated at a position lower than the powder surface, and the developer on the supply member A stable pumping amount can be obtained without being affected by bulk fluctuations.

  FIG. 1 is a sectional view of a developing portion of a developing device according to the present invention, and FIG. 2 is a perspective view of the entire developing device. The image forming apparatus according to the present invention is an image forming apparatus equipped with a developing device described below. The overall mechanism is the same as the conventional one, and is necessary for forming an image around the photoreceptor. Predetermined devices such as a charging device, an exposure device, and a fixing device are provided. However, since the configuration other than the developing device is sufficiently known even if not described, the entire description is omitted.

  The developing unit 10 mainly includes a developing roller 2 that faces the photosensitive drum 1, a supply screw 11 that serves as a supply member that faces the developing roller 2, and a supply screw 11 that faces the supply screw 11 via a partition member and is newly supplied. A stirring screw 12 that stirs the toner and the developer, and a doctor 3 as a developer regulating member that faces the developing roller 2 and regulates the thickness of the developer. The conveyance downstream side of the supply screw 11 is connected to the stirring screw 12. Reference numeral 13 indicates the powder level (agent level) of the developer deposited and conveyed on the supply screw 11.

  The developing roller 2 includes a magnet 2a that is fixed inside and forms a magnetic pole on the peripheral surface of the roller, and a sleeve 2b that is made of a nonmagnetic material and rotates around the magnet 2a. A plurality of magnetic poles (main pole S1, transport poles N1, N2, pumping pole S3, agent cutting pole S2) are formed on the developing roller 2 (sleeve 2b) by the magnet 2a.

  The developer pumped from the supply screw 11 by the pumping pole S2 is transported to the developing region by the transporting poles N1 and N2. In the development area, a magnetic brush for developing the latent image on the photosensitive drum is formed by the magnetic force of the main pole S1. The developed developer is separated from the developing sleeve by the agent cutting pole S2 and collected by the supply screw 11.

  A developer stirring unit 40 capable of controlling the stirring operation and a rotary feeder 50 for adjusting the supply amount to the developing unit are provided upstream of the supply screw 11 in the developer transport direction (FIG. 2). The rotary feeder 50 includes a rotor having a plurality of rotating blades and a stator that covers the roller, and has excellent quantitativeness and controllability. These units are configured as units separate from the developing unit 10, and the amount of stirring and discharging can be controlled independently of the developing operation by motors 45 and 55 attached to the respective members.

  A developer discharge path 30 from the developing unit 10 is connected to the most downstream side of the stirring screw 12 in the longitudinal direction of developer transfer, and discharges the developer after development toward the external developer stirring unit 40. In the conventional developing device, the agent is directly circulated between the stirring screw 12 and the supply screw 11, but in this example, the developer is not directly circulated from the agitation screw 12 to the supply screw 11, and all the developed developer is developed. It is conveyed to the agent stirring unit 40. The developer agitation unit 40 agitates the developer and toner, and adjusts the charge amount and toner density to an appropriate level. The adjustment is mainly performed by the number of rotations of the member of the stirring unit. Increasing the rotation speed of the stirring blade tends to increase the charge amount. Therefore, the amount of charge can be adjusted to fall within an appropriate range by increasing or decreasing the rotational speed according to environmental fluctuations (detecting humidity). The number of rotations of the stirring blade is changed according to the toner replenishment amount and the image area. Specifically, when the image area ratio is high and the toner replenishment amount is large, the rotation speed is increased and stirred well. When the image area ratio is low and the toner replenishment amount is small, the rotation speed is decreased.

  The adjusted developer passes through a discharge port provided below the stirring unit 40 and enters the rotary feeder 50. A predetermined amount is supplied to the supply screw 11 via the developer circulation path 31 by the rotation operation of the rotor 51 (FIG. 5) in the rotary feeder. In the rotary feeder 50, since the rotational speed of the rotor (blade) 51 and the discharge amount (weight) are in a substantially proportional relationship, the supply amount can be easily controlled. An air pump 60 is used as a means for conveying the developer through the developer discharge path 30 and the developer circulation path 31, and the developer is transferred by air.

  Toner replenishment is performed in the developer stirring unit 40. A toner concentration detecting means 41 is provided below the stirring screw 12, and a toner replenishment amount is determined based on the detection result, and the toner T in the toner bottle 20 is transferred to the developer stirring unit 40 by the toner replenishment motor 28. To be replenished.

  In the developing section, the developer once developed is pumped up to the developing roller (sleeve) several times while being transported along the screw as the supply member, and used for development. The developer adjusted to an appropriate toner concentration and charge amount by the agitating unit 40 is supplied to the upstream portion in the longitudinal direction of the sleeve, but the developer used for development many times as it goes downstream in the longitudinal direction of the screw. The ratio increases and the toner concentration of the developer decreases compared to the upstream side, and the volume of the developer is reduced in the conventional configuration (FIG. 3a). Therefore, in the downstream portion in the longitudinal direction of the sleeve, the amount of developer pumped up by the sleeve is reduced due to the decrease in the volume, and the pumping amount may be reduced as compared with the upstream portion. When the pumping amount fluctuates, the frictional force received by the developer when passing through the doctor gap changes, and the charge amount varies, resulting in density unevenness in the image. Therefore, the developer supply amount is controlled so that the powder surface at the downstream portion of the supply screw is constant. Therefore, as the amount of toner used at the time of image formation increases, the bulk of the developer increases in the upstream portion as shown in FIG.

  The bulk density of the developer varies depending on the toner concentration, the deterioration state, the environment, and the like. However, since the bulk density differs between the toner and the carrier by about 5 times, the bulk variation due to the toner density variation is very large. Therefore, the discharge amount of the rotary feeder is determined based on the number of pixels to be written.

  The flow of controlling the developer supply amount will be described. First, based on the number of pixels written on the image carrier (photosensitive member), the amount of decrease in toner density while the developer is conveyed on the supply screw is estimated. Based on the result, the supply amount from the stirring unit 40 to the developing unit 10 is determined. When the total number of images to be written is large, it is predicted that the toner density is greatly reduced. Therefore, the rotation of the rotary feeder 50 is accelerated and the discharge amount from the stirring unit 40 is increased. When the amount of developer supplied to the developing unit 10 increases (because the amount of toner used at the time of image formation is determined), the amount of decrease in the toner density downstream in the longitudinal direction of the supply screw 11 is controlled by the supply amount control. Compared to the case where it is not performed, it is less. Therefore, a decrease in the bulk of the developer is also suppressed. Furthermore, it is more effective to detect the toner density, the driving time of the developing device (corresponding to deterioration), the toner replenishment amount, the environment in the device, and control the supply amount according to the result.

  Next, a case where the discharge amount of the rotary feeder 50 / stirring unit 40 is controlled based on the toner density detection result will be described. In this example, the toner concentration sensor 41 is below the stirring screw 12. The volume of the supply screw 11 decreases as it goes to the downstream side in the longitudinal direction due to a decrease in toner concentration due to the development process. However, since the toner supply and consumption are not performed in the stirring screw 12, the volume is constant. The volume on the downstream side is equal to the volume of the stirring screw 12, and the toner density sensor 41 detects a change in toner density. When the toner concentration is high, the bulk of the developer increases, and when the toner concentration is low, the bulk decreases. Therefore, referring to the detection result of the toner density detection means in the developing device, when the toner density is high, the rotation of the rotary feeder 50 is slowed down to reduce the supply amount to the developing unit 10, and when the toner density is low, the rotation is fast. By increasing the supply amount to the developing unit 10, the powder level of the developer on the supply screw 11 can be kept constant.

  The lower the toner density, the higher the charge amount of the toner. Therefore, the variation in the charge amount due to fluctuations in the pumping amount increases. Therefore, pitch unevenness is relatively likely to occur when the toner density is low. Therefore, when a developer having a low toner concentration is circulating, such as in the case of high temperature and high humidity, it is effective to control the height of the powder surface to be high.

  By repeating image formation, the developer deteriorates. In particular, when an image with a small number of pixels is printed over a long period of time, the amount of toner consumption is reduced, so the toner in the developing device is less replaced, and the bulk of the developer is reduced due to toner deterioration. Therefore, it is desirable to record the driving time of the developing device and the toner replenishment amount, and to control the rotation of the rotary feeder 50 to increase the supply amount when the toner replenishment amount is small with respect to the driving time.

  By controlling the supply amount as described above, the powder surface on the supply screw 11 can be kept constant, and fluctuations in the pumping amount can be prevented. It is only during image formation that the toner concentration and the bulk of the developer fluctuate between the upstream side and the downstream side of the supply screw 11 in the longitudinal direction. Therefore, it is sufficient to control the conveyance amount from the stirring unit to the developing unit as described above only during image formation.

  Further, the developer discharge port from the developing unit 10 to the developer circulation means is connected to the connecting portion between the stirring screw 12 and the developer discharge path 30 so that only the developer exceeding the height of the outer diameter of the supply member is discharged. Is provided with a partition member 18 (FIG. 2b). By installing this member, the volume can always be kept constant in the downstream portion, which is effective.

  The position of the developer regulating member (doctor) will be described. In FIG. 1, the doctor 3 brings its tip 3a close to the surface of the developing roller (sleeve 2b) (gap Gd), and the developer on the developing roller rotating in the direction of the arrow passes through this gap. The thickness of the developer layer is constant, and the amount of developer conveyed to the development area can be constant. On the other hand, on the supply screw 11, the volume of the developer varies along the pitch of the screw. In particular, when the height of the powder surface on the supply screw is lower than the height of the supply screw outer diameter, the amount of developer pumped from the screw 11 to the developing roller varies depending on the location, and density unevenness occurs at intervals of the screw pitch. appear.

  4a and 4c are views of the supply screw 11 and the doctor 3 as seen from the right side of FIG. 4B and 4D are views of the developing roller 2 as viewed from the upper side of FIG. When the tip 3a of the doctor 3 is higher than the powder surface 13 as shown in FIG. 4a, the water is pumped up to the developing roller 2 in a state where the pumping amount varies depending on the location as shown in FIG. 4b. When the developer thus pumped up is conveyed to the development area, unevenness along the pitch of the screw appears in the image. Therefore, as shown in FIG. 4c, if the doctor tip 3a is arranged at a position lower than the powder level of the developer on the supply screw, the doctor tip is always buried in the developer. Thus, it is not affected by the dispersion of the powder surface, and a stable pumping amount can be obtained as shown in FIG. 4d.

  Next, regarding the material of the doctor, the doctor has a doctor blade made of a nonmagnetic material such as SUS or aluminum, and a magnetic plate is attached to the doctor blade. By doing in this way, the direction of the magnetic spikes is easily aligned by the magnetic flux generated between the doctor 3 and the magnet in the developing roller (the magnetic pole line emanating from the magnet extends toward the magnetic member of the doctor), and the developer layer It becomes easy to regulate the thickness, and the layer thickness after passing through the doctor gap is stabilized. Further, if the material is made of a material that is not easily bent, it is possible to reduce the difference in the strength of the magnetic field generated between the central portion and the end portion, and to easily make the developer passing through the doctor gap uniform in the axial direction.

  FIG. 5 is a cross-sectional view of the stirring unit 40. The stirrer housing has a shape such as an inverted cone that decreases in diameter toward the discharge port. A developer supply port 33 is provided on the upper surface, and a discharge port 34 is provided on the lower surface. A screw 43 that conveys the developer from the bottom to the top is provided at the center, and two rotatable rod-like members 44 are provided on the outside thereof, and the developer is mixed by the rotating operation of these stirring members. Gravity is used for conveyance from the supply port to the discharge port in the storage unit. Since there is always a developer as a buffer in the lower part of the storage unit, there is no risk that unmixed developer is discharged as it is. Also, the presence of the buffer can increase or decrease the discharge amount of the rotary feeder 50. In the agitating unit 40, the newly replenished toner and developer are agitated by rotating a plurality of agitating members, and are completely mixed. Compared with a stirring structure in which two screws in a conventional developing device are arranged in parallel, the developer stirring and mixing effects are higher.

  In general, in the conventional developing device, when the charge amount of the developer on the screw is compared with the charge amount of the developer after passing through the doctor gap, the charge amount of the developer on the screw is about 10 μC / g. That is, the developer on the screw is not completely charged, and is charged by a doctor. The amount of charge imparted by the doctor depends on the width of the gap and the amount of pumping. If there is a slight difference in the pumping amount before passing through the doctor gap, the force received when passing through the doctor gap is different, and the amount of charge varies. In this example, in order to reduce the unevenness of the charge amount, the charge to the developer is applied in advance to the charge amount necessary for development by the stirring unit 40 without depending on the doctor. As a result, the difference in developer charge amount before and after passing through the doctor gap was reduced, and the unevenness in image density due to the uneven charge amount was greatly reduced.

  FIG. 6 shows the result of examining the relationship between the height of the powder surface 13 of the developer on the supply screw 11 and the image density on the paper as the recording medium. In the graph, the solid line represents an experimental result when an image having an image area ratio of 5% on A3 paper is printed, and the dotted line represents an experimental result when 100 images having an image area ratio of 100% are printed. ○ means a sufficient density without density unevenness. Δ indicates that unevenness (thin portion) is present if observed well. X is a state where the density is low and density unevenness occurs.

  FIG. 6A is an embodiment in which the discharge amount is controlled so that the powder level of the developer is constant based on the number of pixels of the image to be formed at the downstream in the longitudinal direction on the supply screw 11 based on the toner concentration. When the image area ratio of the image to be formed was high, the supply amount was increased, and vice versa. As a result, regardless of the image area ratio, the height of the powder surface at the downstream portion of the supply screw was constant, and no density unevenness occurred on the image. FIG. 6b is a comparative example when the supply amount is not controlled. The amount (weight) of developer supplied from the rotary feeder to the developing unit is always constant. When an image with a low image area ratio of about 5% is formed, density unevenness does not occur in the downstream portion. However, as the image area increases, the powder surface decreases in the downstream direction of the developing sleeve. Due to the powder level reduction, the density of the image is reduced in the downstream portion, and a sufficient image density cannot be obtained, resulting in unevenness.

FIG. 3 is a cross-sectional view of a developing unit of the developing device according to the present invention. FIG. 2A is a perspective view of the entire developing device, and FIG. 2B is a view for explaining a state in which an internal partition member is provided at a connection portion between the supply screw and the developer discharge path. It is a figure which shows a mode that the volume of a developer falls as it advances to the developer transfer direction downstream of a supply screw. 4A and 4C are views of the supply screw and the doctor as viewed from the right side of FIG. 1, and FIGS. 4B and 4D are views of the developing roller as viewed from the upper side of FIG. It is sectional drawing of an external stirring part. FIG. 6A shows the result of investigating the relationship between the height of the developer powder surface on the supply screw and the image density on the recording medium, and FIG. 6A shows the downstream of the longitudinal direction of the supply screw 11 based on the toner concentration. FIG. 6B is an example in which the discharge amount is controlled so that the powder level of the developer is constant based on the number of pixels of the image to be formed, and FIG. 6B is a comparative example when the supply amount is not controlled.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 Developing roller 10 Developing part 11 Supply screw 12 Agitation screw 20 Toner bottle 28 Toner replenishing motor 30 Developer discharge path 31 Developer circulation path 40 External stirring part 45 Motor 50 Rotary feeder 51 Rotor 55 Motor 60 Air pump

Claims (8)

A developer carrier having a magnetic field generating means having a plurality of magnetic poles; a supply member for supplying the developer to the developer carrier; and a developer regulating member for regulating the thickness of the developer on the developer carrier. A developing unit comprising: a developing unit configured as described above; an external stirring unit that stirs toner / developer independent of the developing unit; and a developer circulation unit that connects the developing unit and the external stirring unit.
From the external stirrer, the powder level of the developer deposited and transported around the supply member arranged horizontally is constant on the downstream side in the longitudinal direction of the supply member regardless of the image information to be formed. As a means for controlling the amount of developer supplied to the developing unit, a rotary feeder comprising a rotor having a plurality of rotating blades and a stator covering the rotor is provided between the external stirring unit and the developing unit, and the toner in the developing unit Referring to the toner density detection result of the density detecting means, if the detected toner density is higher than a predetermined value, the rotation of the rotary feeder is slowed, and if it is low, the rotation of the rotary feeder is speeded up to supply the developer. developing device and controls the. A developer carrier having a magnetic field generating means having a plurality of magnetic poles; a supply member for supplying the developer to the developer carrier; and a developer regulating member for regulating the thickness of the developer on the developer carrier. A developing unit comprising: a developing unit configured as described above; an external stirring unit that stirs toner / developer independent of the developing unit; and a developer circulation unit that connects the developing unit and the external stirring unit.
From the external stirrer, the powder level of the developer deposited and transported around the supply member arranged horizontally is constant on the downstream side in the longitudinal direction of the supply member regardless of the image information to be formed. As a means for controlling the amount of developer supplied to the developing unit, a rotary feeder comprising a rotor having a plurality of rotating blades and a stator covering the rotor is provided between the external agitating unit and the developing unit. A developing device, wherein the developer supply amount is controlled by slowing the rotation of the rotary feeder when the image area ratio is lower than a predetermined value, and by increasing the rotation of the rotary feeder when the image area ratio is high. 3. The developing device according to claim 1, wherein the supply member is completely buried in the powder surface of the developer during operation of the apparatus on the downstream side in the longitudinal direction of the supply member. As the difference between the charge amount of the developer regulating member passes through the developer before and after is reduced, according to claim 1 to 3, characterized in that launching advance until the charge amount necessary for development by controlling the stirring operation with an external stirrer unit The developing device according to any one of the above. An apparatus according to any one of claims 1 to 4, the developer regulating member and having a magnetic member. An apparatus according to any one of claims 1 to 5, characterized in that providing the developer transfer port from the developing unit to the developer circulating means at a position higher than the topmost portion of the feed member. Any one of claims 1 to 6, the powder surface of the developer in the supply member and controls the developer supply amount to be higher than the position closest to the developer carrying member of the developer regulating member The developing device according to 1. Image forming apparatus including a developing device according to any one of claims 1-7.

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