JP2010237329A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of stably and properly controlling the quantity of a two-component developer discharged through a discharge opening even if the rotating speed of a carrying member is changed. <P>SOLUTION: In a partition wall 47, both longitudinal ends of which have openings, a shielding part 52 is formed on the surface thereof opposite to a conveying screw 46. The shielding part 52 has a wall structure of damming a flow of a two-component developer at a position higher than the central height of a return screw 50, and is positioned at the edge of an opening 47a and formed integral with the partition wall 47. Thus, the two-component developer is guided to the discharge opening 53 through a space interposed between a development container 42 and the return screw 50 which is hardly influenced by rotating speeds of the conveying screws 45, 46. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention increases the rotational speed of a developing device that discharges an old two-component developer little by little from a discharge opening arranged at the end in the longitudinal direction in the developing container, more specifically, a two-component developer conveying member. The present invention relates to a structure that suppresses excessive discharge.

  2. Description of the Related Art Developing devices that circulate while stirring a two-component developer in which a magnetic carrier is mixed with nonmagnetic toner using a pair of conveying screws arranged in the longitudinal direction of a developing container with a partition wall in between are widely used.

  In such a developing device, new non-magnetic toner is supplied as the non-magnetic toner is consumed. On the other hand, since the old magnetic carrier continues to circulate in the developing container, the charging performance of the two-component developer gradually decreases. It is known. For this reason, control is also taken to maintain the charging performance of the magnetic carrier in the developing container constant by discharging the old one little by little and replacing it with a new one.

  In Patent Document 1, a two-component developer for replenishment in which a magnetic carrier is mixed with a non-magnetic toner at a predetermined ratio is supplied to a developing device along with image formation, and an old magnetic carrier in a developing container is gradually added. The developing device to be replaced is shown. Referring to FIG. 2, the two-component developer circulating in the developing container (42) is discharged little by little through the discharge opening (53) arranged at the abutting surface in the conveying direction of the conveying screw (46). Is done.

  The transport screw (46) is transported in the direction (C) in which the two-component developer is circulated, and is downstream of the main spiral portion that feeds into the discharge opening (53). Are connected to each other. The sub-spiral portion (50) pushes back most of the two-component developer conveyed to the main spiral portion and moves toward the discharge opening (53), and the two-component developer discharged through the discharge opening (53) I try not to get too much.

JP 2002-72686 A

  In the case of the conveying screw shown in Patent Document 1, the conveying ability of the main spiral portion and the auxiliary spiral portion are adjusted so that the amount of the two-component developer discharged through the discharging opening becomes a predetermined amount corresponding to the rotation speed of the conveying screw. Carrying capacity is set. Thereby, even if the rotational speed of the conveying screw changes, a fixed ratio of the two-component developer circulating in the developing container is discharged through each circulation.

  However, an experiment was carried out with the rotational speed of the conveying screw being greatly increased, and it was found that the higher the rotational speed of the conveying screw, the more the two-component developer above the design value is discharged through the discharge opening.

  Therefore, the flow of the two-component developer in the developing container (42) was observed with high-speed photography. Then, when the rotational speed of the conveying screw (46) is low, the partition wall (47) and the sub-spiral portion (50) are almost the same as the space between the developing container (42) and the sub-spiral portion (50). ) Was flowing in the space between the two. However, when the rotation speed of the conveying screw (46) increases, the flow of the two-component developer that moves toward the discharge opening (53) through the space sandwiched between the partition wall (47) and the sub-spiral portion (50) is better. It became increasingly prominent.

  For this reason, if the main spiral part and the sub spiral part are designed so that the discharge amount becomes appropriate in accordance with the high-speed rotation, the required discharge amount cannot be secured during the low-speed rotation, and the two-component developer stagnates in the developing device. As a result, the charging performance deteriorates. Conversely, if the main spiral part and the sub-spiral part are designed so that the discharge amount is appropriate in accordance with the low-speed rotation, the discharge amount becomes excessive during the high-speed rotation and the consumption amount of the two-component developer for replenishment increases. .

  An object of the present invention is to provide a developing device in which the discharge amount of the two-component developer through the discharge opening is stably maintained properly even when the rotation speed of the conveying member is changed.

  A developer discharge opening is disposed on one abutting surface in the longitudinal direction, and a developer container is internally partitioned by a longitudinal partition having openings at both ends for delivering the developer, and disposed on one side of the partition A first conveying member connected to a main spiral portion that conveys the developer in the longitudinal direction toward the discharge opening, and a sub spiral portion that urges the developer flow toward the discharge opening in the reverse direction; Second transport that is disposed on the other side of the partition wall and transports the developer transferred from the first transport member through the opening on the side of the sub spiral portion in a direction opposite to the transport direction by the first transport member. And a restricting means for restricting the flow of the developer toward the discharge opening through a space sandwiched between the partition wall and the sub spiral portion.

  In the developing device of the present invention, the developer flow that becomes noticeable due to the high-speed rotation of the first conveying member and the second conveying member is suppressed by the limiting means arranged in the space sandwiched between the partition wall and the sub spiral portion. The space sandwiched between the developer container and the sub-spiral portion where the developer flow does not vary greatly due to the rotational speed, not through the space sandwiched between the partition wall and the sub-spiral portion where the developer flow largely varies depending on the rotational speed. Through to the discharge opening.

  For this reason, the two-component developer discharged through the discharge opening at the time of high speed rotation is reduced only by being hindered by the limiting means. At the time of low-speed rotation, the flow of the two-component developer toward the discharge opening through the same space is not remarkable, so the two-component developer discharged through the discharge opening is not reduced as much as at the time of high-speed rotation.

  Therefore, even if the rotation speed of the conveying member changes, the discharge amount of the two-component developer through the discharge opening is stably and appropriately controlled. Note that the mechanism by which the flow of the two-component developer toward the discharge opening becomes remarkable due to the high-speed rotation of the first transport member and the second transport member will be described later.

It is explanatory drawing of a structure of the image forming apparatus of 1st Embodiment. It is a perspective view explaining the internal structure of a developing device. FIG. 3 is a cross-sectional view of the developing device viewed from the back side of the image forming apparatus. FIG. 4 is an enlarged cross-sectional view of the vicinity of a developer discharge port. It is a perspective view of the conveyance screw which provided the sub spiral part. It is explanatory drawing of the flow of the two-component developer in the developing device of the comparative example without a shielding part. It is explanatory drawing of the flow of the two-component developer in the developing device of Example 1 which provided the shielding part. It is explanatory drawing of the flow of the two-component developer falling to a discharge opening. It is explanatory drawing of the thickness of the shielding part in Example 2. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, as long as the flow of the two-component developer toward the discharge opening through the space sandwiched between the walls and the conveying member is limited, a part or all of the configuration of the embodiment is replaced with the alternative configuration. Other embodiments replaced with can also be implemented.

  Therefore, the present invention can be similarly implemented in various types of image forming apparatuses that share a developing device. It can be carried out without distinction between an intermediate transfer type, a recording material conveyance type, a tandem type, a single drum type, full color, and monochrome. Not only a developing device using a two-component developer but also a developing device using a one-component developer whose charging performance is lowered by stirring for a long time.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

  In addition, about the general matter of the image forming apparatus shown by patent document 1, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of a configuration of the image forming apparatus according to the first embodiment.

  As shown in FIG. 1, the image forming apparatus 100 is a tandem intermediate transfer type full-color printer in which image forming portions Pa, Pb, Pc, and Pd are arranged along the downward surface of the intermediate transfer belt 10.

  In the image forming portion Pa, a yellow toner image is formed on the photosensitive drum 1 a and is primarily transferred to the intermediate transfer belt 10. In the image forming unit Pb, a magenta toner image is formed on the photosensitive drum 1 b and is primarily transferred to the yellow toner image on the intermediate transfer belt 10. In the image forming portions Pc and Pd, a cyan toner image and a black toner image are formed on the photosensitive drums 1c and 1d, respectively, and are sequentially transferred to the intermediate transfer belt 10 so as to be primarily transferred.

  The four-color toner images primarily transferred to the intermediate transfer belt 10 are transported to the secondary transfer portion T2 and collectively transferred to the recording material P. The recording material P on which the four-color toner images are secondarily transferred is heated and pressed by the fixing device 15 to fix the toner images on the surface, and then discharged to the upper tray 17 through the discharge roller 16.

  The separation roller 21 separates the recording materials P drawn from the recording material cassette 20 one by one and sends them to the registration rollers 22. The registration roller 22 receives and waits for the recording material P in a stopped state, and sends the recording material P to the secondary transfer portion T2 in time with the toner image on the intermediate transfer belt 10.

  The fixing device 15 presses the pressure roller 15b against the fixing roller 15a provided with a heater to form a heating nip. The recording material P is heated and pressurized in the process of being nipped and conveyed by the heating nip, melts the toner image, and fixes the full-color image on the surface.

  The image forming portions Pa, Pb, Pc, and Pd are substantially the same except that the color of toner used in the developing devices 4a, 4b, 4c, and 4d is different from yellow, magenta, cyan, and black. Hereinafter, the image forming unit Pa will be described, and the other image forming units Pb, Pc, and Pd will be described by replacing “a” at the end of the reference numerals with “b”, “c”, and “d”.

  The image forming unit Pa surrounds the photosensitive drum 1a and includes a charging roller 2a, an exposure device 3, a developing device 4a, a primary transfer roller 5a, and a cleaning device 6a.

  The photosensitive drum 1a has a negatively charged photosensitive layer formed on the outer peripheral surface of an aluminum cylinder, and rotates at a switchable multi-stage process speed. The charging roller 2a is applied with an oscillating voltage obtained by superimposing an AC voltage on a DC voltage and is driven to rotate by the photosensitive drum 1a, thereby charging the surface of the photosensitive drum 1a to a uniform negative potential.

  The exposure device 3 scans a scanning beam image data obtained by developing a yellow color separation image with a rotating mirror, and writes an electrostatic image of the image on the surface of the charged photosensitive drum 1a. The developing device 4a stirs and charges the two-component developer, carries it on the developing sleeve 43 in a stand-up state, and rubs the photosensitive drum 1a. By applying an oscillating voltage in which an alternating voltage is superimposed on a direct current voltage to the developing sleeve 43, a nonmagnetic toner charged to a negative polarity in an electrostatic image (exposed portion) having a positive polarity relative to the developing sleeve 43 The electrostatic image is reversed and developed.

  The primary transfer roller 5 a presses the inner side surface of the intermediate transfer belt 10 to form a primary transfer portion between the photosensitive drum 1 a and the intermediate transfer belt 10. By applying a positive DC voltage to the primary transfer roller 5a, the negative toner image carried on the photosensitive drum 1a is primarily transferred to the intermediate transfer belt 10 passing through the primary transfer portion.

  The intermediate transfer belt 10 is supported around a tension roller 12, a driving roller 11, and a stretching roller 13, and is driven by the driving roller 11 to rotate in the direction of arrow R2. The secondary transfer roller 14 abuts on the intermediate transfer belt 10 whose inner surface is stretched by the stretch roller 13 connected to the ground potential to form a secondary transfer portion T2. The toner image carried on the intermediate transfer belt 10 is secondarily transferred to the recording material P by applying a positive DC voltage to the secondary transfer roller 14.

<Developing device>
FIG. 2 is a perspective view illustrating the internal structure of the developing device. FIG. 3 is a cross-sectional view of the developing device viewed from the back side of the image forming apparatus. FIG. 4 is an enlarged cross-sectional view of the vicinity of the developer discharge port. FIG. 5 is a perspective view of a conveying screw provided with a sub spiral portion.

  As shown in FIG. 2, the developing container 42 contains a two-component developer composed of a non-magnetic toner and a magnetic carrier, and the mixing ratio of the non-magnetic toner and the magnetic carrier is about 1: 9 by weight. . Here, the mixing ratio of the non-magnetic toner and the magnetic carrier is appropriately adjusted according to the charge amount of the toner, the particle size of the carrier, the configuration of the image forming apparatus (100: FIG. 1), etc. It is not limited to.

  FIG. 3 shows a cross section when the developing device 4a is viewed from the back side of the image forming apparatus (100: FIG. 1), and the back side of the paper surface corresponds to the front side from which the two-component developer is discharged. As shown in FIG. 3, in the developing device 4a, the developing sleeve 43 is rotatably installed so that the developing region of the developing container 42 that faces the photosensitive drum 1a is open, and the developing sleeve 43 is partially exposed from the opening. Has been. Inside the developing sleeve 43, a magnet 44 provided with a plurality of fixed magnetic poles is arranged in a non-rotating manner. The developing sleeve 43 is made of a non-magnetic material, and rotates in the direction of arrow A during the developing operation to hold the two-component developer in the developing container 42 in a layered manner by the magnetic force of the magnet 44 and transport it to the developing region. The developing sleeve 43 supplies only non-magnetic toner to the photosensitive drum 1a in the developing area, and develops the electrostatic image formed on the photosensitive drum 1a. After developing the electrostatic image, the two-component developer on the developing sleeve 43 is collected in the developing container 42 as the developing sleeve 43 rotates.

  The developing device 4a has an automatic developer discharging function that keeps the two-component developer in the developing container 42 at a constant amount even when the rotation speed of the conveying screw 46 that is an example of the first conveying member is switched.

  As shown in FIG. 2, the inside of the developing container 42 is partitioned by a partition wall 47 in the longitudinal direction in which openings 47a and 47b for delivering the two-component developer are formed at both ends. A pair of conveying screws 45 and 46 in which the conveying direction of the two-component developer is set in the opposite direction are arranged with the partition wall 47 interposed therebetween. A conveyance screw 46 that is an example of a first conveyance member conveys the two-component developer in the direction of arrow C while agitating, and a conveyance screw 45 that is an example of the second conveyance member agitates the two-component developer in the direction of arrow B. Transport while. The conveying screw 46 is disposed on one side of the partition wall 47 and the conveying screw 45 is disposed on the other side. Through the openings 47a and 47b formed at both ends in the longitudinal direction of the partition wall 47, the one conveying screw 46 and the other conveying screw 45 smoothly deliver the two-component developer, so that the two-component developer becomes a developing container. Circulate inside 42.

  The two-component developer is transferred from the conveying screw 46 to the conveying screw 45 through the opening 47a on the sub spiral portion side, and the two-component developer is scattered to the developing sleeve 43 in the process of being conveyed to the conveying screw 45. Delivered.

  A return screw 50 that transports the two-component developer so as to push back into the circulation path from outside the circulation path of the two-component developer is connected to the downstream side of the conveyance screw 46 in the conveyance direction of the two-component developer. An opening for delivering the two-component developer from the conveying screw 46 to the conveying screw 45 at a position facing the joint between the main spiral portion (46m: FIG. 5) of the conveying screw 46 and the return screw 50 (sub-spiral portion). There is a portion 47a.

  As shown in FIG. 4, a discharge opening 53 for discharging a part of the circulating two-component developer to the outside of the developing container 42 is provided upstream in the conveying direction of the two-component developer by the return screw 50. . Most of the two-component developer conveyed toward the discharge opening 53 by the main spiral portion of the conveyance screw 46 is pushed back to the return screw 50 and escapes from the discharge opening 53. Then, the two-component developer that has not been pushed back to the return screw 50 is discharged from the circulation path of the developing container 42 through the discharge opening 53.

  The length, diameter, and pitch of the return screw 50 are appropriately changed according to the configuration and discharge conditions of the developing device 4a, the two-component developer amount in the developing container 42, and the target discharge amount. For example, if the length of the return screw 50 is too long, the discharge performance of the two-component developer is suppressed more than necessary, and as a result, the charging performance of the two-component developer in the developing container 42 decreases. On the other hand, if the length of the return screw 50 is too short, the two-component developer is discharged more than necessary, and the amount of the two-component developer in the developing container 42 is insufficient, which hinders development.

  A disc-shaped collar portion 51 is provided in the uppermost stream in the conveying direction of the return screw 50 so as to cover the discharge opening 53. A disc portion (51) facing the discharge opening 53 is connected to the sub spiral portion so as to overlap the discharge opening 53 in the longitudinal direction.

  The collar portion 51 reduces the difference in inertial force of the two-component developer conveyed toward the discharge opening 53 due to the difference in conveyance capability between the main spiral portion of the conveyance screw 46 and the return screw 50. The collar portion 51 eliminates the two-component developer that falls into the discharge opening 53 through the valley at the end of the conveying blade of the return screw 50, and stabilizes the discharge amount of the two-component developer.

  The flange 51 covers the end of the return screw 50 facing the discharge opening 53 and does not expose the screw valley to the discharge opening 53 side. By adopting the return screw provided with the collar portion 51, even if the rotation speed of the conveying screw 46 is switched to the slow side, the necessary discharge amount is secured, and even if the rotating speed of the conveying screw 46 is switched to the fast side. The discharge amount of the two-component developer does not increase rapidly.

  A discharge screw 49 that passes through the center of the discharge opening 53 and is connected to the return screw 50 is disposed. The discharge screw 49 transports the two-component developer that has fallen over the collar portion 51 through the discharge opening 53, conveys it to the developer discharge port 48, and discharges it to the outside of the developing device 4a.

  As shown in FIG. 5 with reference to FIG. 2, the conveying screw 46, which is an example of a first conveying member, has a main spiral portion (50) that urges the developer flow toward the discharge opening 53 in the reverse direction. It is connected to the spiral part 46m. The main spiral portion 46m conveys the developer in the circulation path of the two-component developer toward the discharge opening 53.

<Supply control of replenishment two-component developer>
FIG. 6 is an explanatory diagram of the flow of the two-component developer in the developing device of the comparative example having no shielding part.

  As shown in FIG. 3, the non-magnetic toner consumed by the image formation is supplied upstream of the conveying screw 46 of the developing container 42 by the replenishing mechanism 31 as a replenishing two-component developer containing a new magnetic carrier at a certain ratio. It is replenished to the side (back side of main body). The supply of the two-component developer for replenishment to the developing device 4a is performed by the rotation of the replenishment screw 32 from the hopper of the replenishment mechanism 31 and is received from the replenishment port on the upper side of the developing container 42. The two-component developer for replenishment uses a two-component developer containing a magnetic carrier at a certain ratio (about 10% by weight) in the nonmagnetic toner for replenishment. The ratio is not limited to this.

  The replenishment amount of the replenishment two-component developer is roughly determined by the rotation speed of the replenishment screw 32 of the replenishment mechanism 31. The control unit 30 controls the ON / OFF and rotation speed of the replenishing screw 32 to replenish the replenishing two-component developer so as to keep the toner concentration of the two-component developer inside the developing container 42 constant. .

  At this time, the amount of the two-component developer in the developing container 42 gradually increases with image formation. The non-magnetic toner is consumed by the image formation, but the magnetic carrier is not consumed but remains in the developing container 42 and continues to circulate, so that the amount of the two-component developer in the developing container 42 increases. When the amount of the two-component developer increases, the developer passes over the return screw 50 and the collar 51 shown in FIG. 4, falls into the discharge opening 53, is transferred to the discharge screw 49, and is conveyed to the developer discharge port 48. . The collected developer transported to the developer discharge port 48 is discharged from the developer discharge port 48, joins a developer recovery pipe (not shown), and is collected and stored in a recovery container (not shown) through the developer recovery pipe. The

  In this way, the consumed non-magnetic toner is replenished by the replenishing two-component developer, and in parallel, the two-component developer in the developing container 42 in which the magnetic carrier is excessive is discharged little by little. The The automatic developer discharge function is realized by automatically and gradually replacing the two-component developer so as to keep the two-component developer amount in the developing container 42 constant.

  In the developing device 4a, if the conveying screws 45 and 46 continue to rotate at a constant speed and the circulation speed of the two-component developer in the developing container 42 is always constant, the replacement process of the two-component developer is stable and has no problem. Done.

  However, as shown in FIG. 3 with reference to FIG. 1, in the image forming apparatus 100, the process speed is switched to constant speed = 120 mm / sec, 1/2 speed = 60 mm / sec, and 1/3 speed = 40 mm / sec. It supports thick paper and high resolution. For example, in the thick paper mode, since the heat absorption amount of the recording material when fixing the toner image is large and the fixing device 15 cannot sufficiently heat, the process speed is reduced to 1/2 speed or 1 / speed depending on the thickness stage. Reduce to 3rd speed. In the high resolution mode, the process speed is reduced to 1/2 speed, and the scanning line density in the sub-scanning direction is doubled.

  As the process speed is switched, the rotation speeds of the conveying screws 45 and 46 are switched to constant speed = 300 rpm, 1/2 speed = 150 rpm, and 1/3 speed = 100 rpm. When the transport screws 45 and 46 have a plurality of rotational speeds as described above, the amount of the two-component developer that is transported by the transport screw 46 and reaches the end of the return screw 50 varies. It is necessary to correspond to a plurality of rotational speeds.

  As shown in FIG. 6, the conveying screws 45 and 46 rotate as indicated by the arrow, and the two-component developer is transferred from the conveying screw 46 to the conveying screw 45 through the opening 47a on the sub spiral (50) side as indicated by the arrow F1. It flows and is delivered. When a plurality of process speeds are used in the same developing device 4a, the following phenomenon occurs.

  When the rotational speeds of the conveying screws 45 and 46 are equal to 300 rpm, a part of the two-component developer to be transferred to the conveying screw 45 through the opening 47a is pushed back to the conveying screw 46 through the opening 47a as indicated by an arrow F2. The tendency to be increased. The two-component developer that has flowed back from the conveyance screw 45 to the conveyance screw 46 joins the flow of the two-component developer that is conveyed to the conveyance screw 46 and travels toward the discharge opening 53, and is pushed toward the discharge opening 53. As a result, a phenomenon occurs in which the two-component developer that climbs over the collar portion 51 and falls into the discharge opening 53 rapidly increases. On the other hand, it has been confirmed that this phenomenon does not occur when the rotational speeds of the conveying screws 45 and 46 are 1/2 speed = 150 rpm and 1/3 speed = 100 rpm.

  That is, in the case of the constant speed, the rotational speed and the transport speed of the transport screws 45 and 46 are higher than in the case of the 1/2 speed. Since the screw blades are inclined on the conveying screw 45, a force for conveying the two-component developer also acts in the radial direction of the screw cross section in addition to the two-component developer conveying direction (arrow B). . The two-component developer conveyed in the radial direction of the screw cross section collides with the flow of the two-component developer delivered from the conveyance screw 46 to the conveyance screw 45 through the opening 47a, and the interface height of the two-component developer rises. . The two-component developer thus swelled flows outside the return screw 50 and gets over the collar portion 51, so that it falls into the discharge opening 53 and reaches the discharge screw 49.

  On the other hand, when the number of rotations of the conveying screws 45 and 46 is low, since the force for conveying the developer in the radial direction of the screw cross section is small, the flow of the two-component developer as shown by the arrow F2 does not occur. No back flow from 45 to the conveying screw 46 occurs. Therefore, the flow of the two-component developer returning from the conveying screw 45 to the conveying screw 46 is larger at high speed rotation, and more two-component developer is returned at the constant speed than the 1/2 speed. Reach the end.

  For this reason, there is a problem in that an appropriate developer discharge amount cannot be secured at all process speeds due to the difference in the flow of the two-component developer toward the discharge opening 53 due to the difference between the constant speed, the 1/2 speed, and the 1/3 speed. There was a point.

  Therefore, in the following embodiment, the space sandwiched between the partition wall 47 and the return screw 50 is blocked, and the two-component developer is guided to the discharge opening 53 exclusively through the space sandwiched between the developing container 42 and the return screw 50. Yes. The flow of the two-component developer through the space sandwiched between the developing container 42 and the return screw 50 is such that the flow of the two-component developer that flows through the space sandwiched between the partition wall 47 and the return screw 50 is as high as that of the transport screws 45 and 46. This is because it is not affected by the rotational speed.

<Example 1>
FIG. 7 is an explanatory diagram of the flow of the two-component developer in the developing device of Example 1 provided with a shielding portion.

  As shown in FIG. 3, in Example 1, the shielding part 52 is formed integrally with the partition wall 47 so as to be positioned at the edge of the opening 47a. The shield 52 has a wall structure that blocks the flow of the two-component developer at a position higher than the center height of the return screw 50. The shielding part 52, which is an example of a restricting unit, restricts the flow of the two-component developer toward the discharge opening 53 through a space sandwiched between the partition wall 47 and the return screw 50. The shielding part 52 has a two-component developer heading toward the discharge opening 53 so that more two-component developer flows in the space between the developing container 42 and the return screw 50 than in the space between the partition wall 47 and the return screw 50. Controls developer flow.

  As shown in FIG. 7, a clearance of 1.0 mm is secured on the wall surface of the partition wall 47 with respect to the outer diameter of the return screw 50, and a contour shielding portion 52 is provided along the outer periphery of the return screw 50. The flow (arrow F2) of the two-component developer returned from the transport screw 45 to the transport screw 46 toward the discharge opening 53 collides with the shielding portion 52 and is blocked. Thereafter, the blocked two-component developer is urged by the return screw 50 and rejoins into a flow (arrow F1) toward the conveying screw 45 through the opening 47a as indicated by an arrow F3. Returned to the circulation path of the component developer.

  Since the shielding part 52 only needs to prevent the backflow from reaching the discharge screw 49, the shielding part 52 is effective at any position if it is installed between the opening 47a and the most upstream flow in the conveying direction of the discharge screw 49. To do. The length of the shielding part 52 in the screw thrust direction is not specified. The height of the shield 52 is appropriately changed according to the configuration of the developing device 4a, the discharge conditions, and the target two-component developer amount in the developing container 42. If the height of the shielding portion 52 is too low with respect to the target two-component developer amount of the developing container 42, it becomes difficult to shield the backflow, and a sufficient effect cannot be obtained.

  From the above, the change in the flow of the two-component developer due to the change in the rotation speed of the conveying screws 45 and 46 can be reduced. Therefore, it is possible to suppress fluctuations in the amount of the two-component developer that reaches the discharge screw 49 over the collar portion 51 due to the speed difference from constant speed to 1/3 speed. As a result, fluctuations in the two-component developer discharge amount from the developer discharge port 48 can be suppressed.

  As described above, in the present invention, the developer automatic discharge function is improved by changing only a small part of the partition wall 47 without changing the basic configuration of the developing container 42, the conveying screws 45 and 46, the partition wall 47, and the like. Yes. At a plurality of stirring speeds, the discharge amount of the two-component developer can be stabilized and the two-component developer amount in the developing container 42 can be kept constant. With a simple configuration, the two-component developer can be gradually and automatically replaced to improve maintainability, and a low-cost and long-life developing device that can cope with various development stirring speeds has been realized.

  When the stirring speed is switched, the amount of the two-component developer discharged from the developer discharge port 48 does not change excessively, so that the amount of developer in the developing container 42 is kept constant. An image forming apparatus 100 capable of supporting a plurality of image forming process speeds, corresponding to a plurality of paper transport speeds, and having a developer automatic discharging function is provided.

<Example 2>
FIG. 8 is an explanatory diagram of the flow of the two-component developer falling into the discharge opening. FIG. 9 is an explanatory diagram of the thickness of the shielding portion in the second embodiment.

  As shown in FIG. 8A, also in the second embodiment, the shielding portion 52 is formed integrally with the partition wall 47 so as to be positioned at the edge of the opening portion 47 a. The shield 52 has a wall structure that blocks the flow of the two-component developer at a position higher than the center height of the return screw 50. The shielding part 52, which is an example of a restricting unit, restricts the flow of the two-component developer toward the discharge opening 53 through a space sandwiched between the partition wall 47 and the return screw 50.

  The shielding part 52 blocks the flow of the two-component developer toward the discharge opening 53 through a space sandwiched between the partition wall 47 and the return screw 50. Therefore, the two-component development in which the increase or decrease in the flow of the two-component developer toward the discharge opening 53 through the space between the partition wall 47 and the return screw 50 falls into the discharge opening 53 as shown by the black arrows in the drawing. No effect on the amount of agent. For this reason, the two-component developer that drops into the discharge opening beyond the collar portion 51 is conveyed toward the discharge opening 53 through the space sandwiched between the developing container 42 and the return screw 50 exclusively. The flow in the space between the developing container 42 and the return screw 50 is not affected by the rotation speed of the conveying screws 45 and 46 as much as the flow in the space between the partition wall 47 and the return screw 50. Can also achieve the expected emissions (emission ratio).

  On the other hand, as shown in FIG. 3B, in the comparative example in which the shielding portion is not provided, it is sandwiched between the partition wall 47 and the return screw 50 that are greatly influenced by the rotational speed of the conveying screws 45 and 46. The flow of the space passes over the collar portion 51 and falls into the discharge opening. For this reason, compared to the second embodiment, it becomes impossible to control the discharge amount (discharge ratio) when the rotation speeds of the conveying screws 45 and 46 are switched.

  As shown in FIG. 9, in Example 2, the thickness of the shielding part 52 in the transport direction of the two-component developer is larger than one pitch of the return screw 50 which is an example of the sub spiral part. For this reason, during rotation of the return screw 50 by 360 degrees, the shielding unit 52 does not leak the flow of the two-component developer to the discharge opening 53 side at any rotation angle.

<Example 3>
As shown in FIG. 2, in the first and second embodiments, the auxiliary screw is provided in the conveyance screw 46 on the side far from the developing sleeve 43 to control the discharge amount of the two-component developer. On the other hand, in the third embodiment, a sub spiral is provided on the downstream side of the conveying screw 45 near the developing sleeve 43 to control the discharge amount of the two-component developer. That is, the two-component developer immediately after the non-magnetic toner is consumed by the developing sleeve 43 is discharged from the discharge opening provided at the end of the downstream side of the conveying screw 45.

1a, 1b, 1c, 1d Photosensitive drums 2a, 2b, 2c, 2d Charging roller 3 Exposure devices 4a, 4b, 4c, 4d Developing devices 5a, 5b, 5c, 5d Primary transfer roller 10 Intermediate transfer belt 14 Secondary transfer roller 15 Fixing device 42 Developer container 43 Developer sleeve (developer carrier)
45 Conveying screw (second conveying member)
46 Conveying screw (first conveying member)
47 Separator 47a, 47b Opening 48 Developer discharge port 49 Discharge screw 50 Return screw (sub spiral part)
51 collar 52 shielding part (limitation means)
53 Discharge opening

Claims (5)

A developer container in which a developer discharge opening is disposed on one abutting surface in the longitudinal direction, and the interior is partitioned by a longitudinal partition having openings at both ends for delivering the developer;
Connected to the main spiral part that is arranged on one side of the partition wall and conveys the developer in the longitudinal direction toward the discharge opening, and a sub spiral part that urges the developer flow toward the discharge opening in the reverse direction A first conveying member,
Second transport that is disposed on the other side of the partition wall and transports the developer transferred from the first transport member through the opening on the sub spiral portion side in a direction opposite to the transport direction by the first transport member. A developing device comprising: a member;
A developing device, comprising: a restricting unit that restricts a flow of the developer toward the discharge opening through a space sandwiched between the partition wall and the sub spiral portion.   The developing device according to claim 1, wherein the restricting unit has a wall structure that blocks the flow of the developer at a position higher than a center height of the sub spiral portion.   The developing device according to claim 2, wherein the wall structure is formed integrally with the partition wall at an edge of the opening.   4. The developing device according to claim 2, wherein a thickness of the wall structure in a developer transport direction is larger than one pitch of the sub spiral portion. 5.   5. The developing device according to claim 1, wherein a disc portion facing the discharge opening is connected to the sub spiral portion so as to overlap the discharge opening in a longitudinal direction.

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