JP5954004B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device using a two-component developer and an image forming apparatus using the developing device.

  In recent years, electrophotographic color image forming apparatuses have entered the production market where offset printing machines have been the mainstream, and so-called tandem systems having a plurality of image carriers are the mainstream. In image forming devices for the production market, we must stop to ensure productivity even during non-printing, such as when waiting for post-processing machines such as saddle stitching and ring binders, or when adjusting the temperature of the fixing device. In some cases, the image forming system (photoconductor, developing device, intermediate transfer belt, etc.) is idled.

  This unnecessarily shortens the life of the consumables, and causes damage to the toner in the developer in the developing device (free and embedded toner external additives), thereby causing image blurring. ing. The blur due to the toner damage in the developer can be improved by discharging the toner from the developing device to a non-printing area such as an intermediate transfer belt and supplying a new toner (toner refresh). In this case, the toner is wasted. This leads to an increase in CPP (Cost Per Page).

  For this reason, if the image forming system is unavoidably rotated to ensure productivity, if the developing device is stopped and only the photosensitive member can be idled, then the blur due to toner damage in the developer is reduced. By suppressing the toner refresh amount, an increase in CPP can be suppressed. At this time, when the developing device is stopped and only the photosensitive member is idled, it is necessary to trim the head and bring the developer on the developing sleeve and the photosensitive member into a non-contact state in order to avoid problems such as carrier adhesion. There is.

  Some electrophotographic image forming apparatuses are provided with four developing devices of Black, Cyan, Magenta, and Yellow arranged around a photoconductor as an image carrier. A developer that removes the developer on the developing sleeve and trims the developer is known. As for the method for cutting the panicle, Patent Document 1 discloses a method in which the developing sleeve is rotated in the reverse direction from the time of development, and in Patent Document 2, the fixing position of the magnet roller is changed from the time of development. Disclosed is a technique for stopping and cutting the head.

  However, in the production market, higher speed is demanded, and a developing device having two developing sleeves may be used in order to secure developing capability. However, these are disclosed in Patent Document 1 and Patent Document 2. However, there is a problem in that the developer cannot be reliably trimmed by a simple mechanism having two developing sleeves.

  The present invention is for solving the above-mentioned problems, and an object of the present invention is to provide a developing device capable of reliably cutting off developer with a simple mechanism even if it has two developing sleeves. Is to provide.

  In order to achieve this object, the present invention has the following features.

  A developing device according to the present invention includes two developing rollers each including a developing sleeve that is rotatably supported by including a magnet roller having a plurality of magnetic poles fixedly supported. A developing device that delivers a two-component developer to a developing roller and develops a latent image formed on an image carrier, and includes a mechanism that rotates and stops a magnet roller of the first developing roller by a predetermined angle. When cutting, between two adjacent magnetic poles of the same polarity among the plurality of magnetic poles of the magnet roller of the first developing roller are positioned at the opposing portion of the regulating member that regulates the layer thickness of the developer. The electrode having a different polarity from the agent receiving pole of the second developing roller is located at a portion opposite to the agent receiving electrode of the second developing roller.

  According to the present invention, it is possible to ensure transferability from the first developing roll to the second developing roll during the ear cutting operation, and the developer is placed in the developing chamber or the gap between the first developing roller and the upper cover. It is possible to prevent the occurrence of clogging defects.

1 is a schematic configuration diagram illustrating a main part of a printer according to an embodiment. FIG. 3 is an enlarged configuration diagram illustrating a developing unit of a toner image forming unit and a photoreceptor. It is a cross-sectional view showing one end side of the conveyance three chambers in the development unit. It is a longitudinal cross-sectional view which shows the same conveyance 3 chamber. It is a cross-sectional view which shows the other end side of the same conveyance 3 chamber. It is an enlarged block diagram which shows the state at the time of implementation of the ear cutting in a developing unit.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings.

  Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic color laser printer (hereinafter simply referred to as a printer) will be described. First, a basic configuration of the printer according to the present embodiment will be described.

  FIG. 1 is a schematic configuration diagram illustrating a main part of the printer according to the present embodiment. This printer includes four toner image forming portions 1M, 1C, 1Y, and 1K for forming toner images of respective colors of magenta, cyan, yellow, and black (hereinafter referred to as M, C, Y, and K). Yes.

  Further, a transfer unit 50 is provided on the side of the toner image forming portions 1M, 1C, 1Y, and 1K arranged in the vertical direction. The toner image forming units 1M, 1C, 1Y, and 1K have substantially the same configuration except that the color of the toner used is different.

  The M toner image forming unit 1M for forming an M toner image will be described. The toner image forming unit 1M includes a process unit, an optical writing unit 10M, and a developing unit 20M. The process unit for M has a uniform charging device 4M, a drum cleaning device 5M, a static elimination lamp 6M, etc. around a drum-shaped photoconductor 3M that is driven to rotate counterclockwise in the figure. Is held in a common casing and can be integrally attached to and detached from the printer main body.

  The photoreceptor 3M as a latent image carrier is obtained by coating an organic photosensitive layer on a base tube made of aluminum or the like. The uniform charging device 4M uniformly charges the surface of the photoreceptor 3M, which is driven to rotate counterclockwise in the drawing, to a negative polarity, for example, by corona charging. The optical writing unit 10M includes a light source composed of a laser diode or the like, a regular hexahedral polygon mirror, a polygon motor for rotationally driving the mirror, an fθ lens, a lens, a reflection mirror, and the like.

  A laser beam L emitted from a light source driven on the basis of image information sent from a personal computer (not shown) is reflected on the polygon mirror surface and deflected as the polygon mirror rotates, so that the photosensitive member 3M. To reach. As a result, the surface of the photoreceptor 3M is optically scanned, and an electrostatic latent image for M is formed on the surface of the photoreceptor 3M.

  The developing unit 20M for M as developing means has two developing rolls 21M and 50M that expose a part of the peripheral surface from an opening provided in the casing. The developing rolls 21M and 50M, which are developer carriers, include a developing sleeve made of a non-magnetic pipe that is rotationally driven by a driving means (not shown), and a magnet roller (not shown) that is included so as not to rotate. .

  In the developing unit 20M, an M developer (not shown) including a magnetic carrier and a negatively chargeable M toner is included. The M developer is agitated and conveyed by three conveying screws described later, and the toner roller is charged by friction, and the developing roller 21M rotates and develops by the magnetic force of the magnet roller, which is a magnetic field generating means in the developing roller 21M. It is adsorbed on the sleeve surface and pumped up.

  Then, as the developing sleeve rotates, the layer thickness is regulated when passing through the position facing the developing doctor 25M, which is a regulating member, and then transported to the first developing position 55M facing the photoreceptor 3M. Thereafter, the toner is magnetically transferred to the developing roll 50M, and is again conveyed to the second developing position 56M facing the photoconductor 3M.

  At the developing position, negative M toner is transferred from the sleeve side to the latent image side between the developing sleeve to which a negative developing bias output from a power source (not shown) is applied and the electrostatic latent image on the photoreceptor 3M. The development potential for electrostatic movement acts on the surface. Further, a non-development potential that electrostatically moves negative M toner from the background side to the sleeve side acts between the developing sleeve and the uniformly charged portion (background portion) of the photoreceptor 3M.

  The M toner in the M developer on the developing sleeve is separated from the sleeve by the action of the developing potential and transferred onto the electrostatic latent image on the photoreceptor 3M. By this transfer, the electrostatic latent image on the photoreceptor 3M is developed into an M toner image.

  The M developer that has consumed M toner by development is returned to the casing as the developing sleeve rotates.

  Further, the M toner image on the photoreceptor 3M is intermediately transferred onto an intermediate transfer belt 51 of a transfer unit 50 described later. Further, the developing unit 20M has a toner concentration sensor (not shown) composed of a magnetic permeability sensor. This toner concentration sensor outputs a voltage having a value corresponding to the magnetic permeability of the M developer accommodated in a later-described agent recovery chamber of the developing unit 20M.

  Since the magnetic permeability of the developer shows a good correlation with the toner concentration of the developer, the toner concentration sensor outputs a voltage having a value corresponding to the toner concentration. The value of the output voltage is sent to a toner supply control unit (not shown).

  This toner replenishment control unit is provided with storage means such as a RAM, in which M Vtref, which is a target value of the output voltage from the M toner density sensor, and toner density mounted in other developing units. Vtref data for C, Y, M, which is a target value of the output voltage from the sensor, is stored.

  For the M developing unit 20M, the output voltage value from the M toner density sensor is compared with the M Vtref, and an M toner density replenishing device (not shown) is driven for a time corresponding to the comparison result. As a result, M toner for replenishment is replenished into the agent recovery chamber of the developing unit 20M.

  By controlling the driving of the M toner replenishing device in this way (toner replenishment control), an appropriate amount of M toner is replenished to the M developer whose M toner density has been reduced along with development, and the inside of the developing unit 20M. The M toner concentration of the M developer is maintained within a predetermined range.

  The same toner replenishment control is performed for the developing units 20C, 20Y, and 20K.

  The M toner image developed on the photoreceptor 3M is transferred to the front surface of an intermediate transfer belt 51 described later. The untransferred toner that has not been transferred onto the intermediate transfer belt 51 adheres to the surface of the photoreceptor 3M that has undergone the transfer process.

  This transfer residual toner is removed by the drum cleaning device 5M. The surface of the photoreceptor 3M from which the transfer residual toner has been removed in this manner is discharged by the charge removing lamp 6M and then uniformly charged again by the uniform charging device 4M.

  The toner image forming unit 1M for M has been described in detail. However, in the toner image forming units 1C, 1Y, and 1K for other colors, C, Y, and K toners are formed on the surfaces of the photoreceptors 3C, 3Y, and 3K by the same process. An image is formed.

  A transfer unit 50 is disposed on the right side of the toner image forming units 1M, 1C, 1Y, and 1K that are arranged in the vertical direction. The transfer unit 50 includes a driving roller 52, a tension roller 53, and a driven roller 54 inside a loop of an endless intermediate transfer belt 51.

  Then, while the intermediate transfer belt 51 is stretched by these three rollers, it is moved endlessly in the clockwise direction in the drawing by the rotational drive of the drive roller 52. The intermediate transfer belt 51 moved endlessly in this way has its front surface on the left side of the drawing in contact with the M, C, Y, and K photoconductors 3M, 3C, 3Y, and 3K, respectively. This forms primary transfer nips for M, C, Y, and K.

  In addition to the three rollers described above, four transfer chargers 55M, 55C, 55Y, and 55K are disposed inside the loop of the intermediate transfer belt 51. These transfer chargers 55M, 55C, 55Y, and 55K are arranged on the back side of the primary transfer nip for M, C, Y, and K so as to apply charges to the back surface of the intermediate transfer belt 51.

  By applying this electric charge, the toner is transferred in the primary transfer nip for M, C, Y, and K in such a direction that the toner is electrostatically moved from the photoreceptor 3M, 3C, 3Y, 3K side to the belt front surface side. An electric field is formed.

  A transfer roller to which a transfer bias is applied may be used instead of the corona charge type transfer charger.

  The M, C, Y, and K toner images formed on the photoreceptors 3M, 3C, 3Y, and 3K of the respective colors are put on the belt from the photoreceptor side by the influence of the nip pressure and the transfer electric field in the primary transfer nip of each color. The image is moved to the surface side and transferred onto the intermediate transfer belt 51 in a superimposed manner. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 51.

  A secondary transfer bias roller 56 is in contact with the driving roller 52 on the intermediate transfer belt 51 from the belt front surface side, thereby forming a secondary transfer nip.

  A secondary transfer bias is applied to the secondary transfer bias roller 56 by a voltage applying means including a power source and wiring (not shown). As a result, a secondary transfer electric field is formed between the secondary transfer bias roller 56 and the grounded driving roller 52.

  The four-color toner image formed on the intermediate transfer belt 51 enters the secondary transfer nip as the belt moves endlessly. The printer includes a paper feed cassette (not shown), and accommodates a recording paper bundle in which a plurality of recording papers P are stacked therein. Then, the uppermost recording paper P is sent out to the paper feed path at a predetermined timing.

  The fed recording paper P is sandwiched between the rollers of the registration roller pair 60 disposed at the end of the paper feed path. The registration roller pair 60 rotates both rollers in order to sandwich the recording paper P sent from the paper feed cassette between the rollers. However, as soon as the leading edge of the recording paper P is sandwiched, both rollers rotate. Stop. Then, the recording paper P is sent toward the secondary transfer nip at a timing at which the recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 51.

  In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 51 are collectively transferred onto the recording paper P by the action of the secondary transfer electric field and the nip pressure. A full color image is formed in combination with the white color of the recording paper P. The recording paper P on which the full-color image is formed in this manner is discharged from the secondary transfer nip, and then sent to a fixing device (not shown) to fix the full-color image.

  The secondary transfer residual toner adhering to the surface of the intermediate transfer belt 51 after passing through the secondary transfer nip is removed from the belt surface by a belt cleaning device 57 that sandwiches the intermediate transfer belt 51 with the driven roller 54. Is done.

  FIG. 2 is an enlarged configuration diagram showing the developing unit 20M of the M toner image forming unit 1M and the photoreceptor 3M. In the figure, the drum-shaped photoconductor 3M is arranged in such a posture that its axial direction extends in a direction perpendicular to the drawing sheet. The developing unit 20M has a developing chamber 26M, an agent supply chamber 27M, an agent recovery chamber 28M, and an agent return chamber 29M, and an M developer (not shown) is accommodated in these chambers.

  Further, the developing rolls 21M and 50M described above are rotatably accommodated in the developing chamber 26M. A supply screw 32M is rotatably accommodated in the agent supply chamber 27M. In addition, the receiving screw 35M is rotatably accommodated in the agent recovery chamber 28M. In addition, an inclined screw 38M is rotatably accommodated in the agent return chamber 29M.

  The developing chamber 26M that accommodates the developing roll 21M has an opening in the wall on the side facing the photoreceptor 3M, from which a part of the peripheral surface of the developing sleeve is exposed. The agent supply chamber 27M and the agent recovery chamber 28M communicate with each other on the opposite side of the developing chamber 26M from the side facing the photoreceptor 3M over the entire area in the axial direction of the developing roll 21M.

  The agent supply chamber 27M is disposed directly above the agent recovery chamber 28M in the vertical direction, and both the agent supply chamber 27M and the agent recovery chamber 28M extend across the entire length in the longitudinal direction on the right side (photoconductor side) in the drawing. It communicates with the developing chamber 26M.

  The supply screw 32M accommodated in the agent supply chamber 27M is made of a non-magnetic material such as resin, and has a posture extending in the horizontal direction like the photoconductor 3M and the developing roll 21M. Then, the rod-shaped rotating shaft member and the screw blade spirally provided on the peripheral surface of the rotating shaft member are integrally rotated in the counterclockwise direction in the figure by driving means such as a motor or a drive transmission system (not shown). Driven.

  The receiving screw 35M accommodated in the agent recovery chamber 28M also has a posture extending in the horizontal direction, like the photoconductor 3M, the developing roll 21M, and the supply screw 32M. Then, the rotating shaft member made of a nonmagnetic material such as resin and the screw blade are integrally rotated in the clockwise direction in the drawing by a driving means (not shown).

  An agent return chamber 29M is adjacent to the agent supply chamber 27M and the agent recovery chamber 28M on the side opposite to the side facing the developing chamber 26M. Unlike the other rooms, the agent return chamber 29M is formed to extend in a posture inclined from the horizontal direction.

  An inclined screw 38M in which screw blades made of nonmagnetic material are erected on the peripheral surface of the rotating shaft member made of nonmagnetic material also extends in an inclined posture in the agent return chamber 29M. It is rotationally driven in the counterclockwise direction in the figure by a driving means (not shown).

  Most of the agent return chamber 29M is partitioned from the agent supply chamber 27M and the agent recovery chamber 28M by a partition wall 30M. However, a part is communicated with the agent supply chamber 27M and the agent recovery chamber 28M through an opening (not shown) provided in the partition wall 30M.

  In the agent supply chamber 27M, the M developer (not shown) held in the blades of the supply screw 32M is conveyed from the front side to the back side in the direction perpendicular to the drawing surface as the supply screw 32M rotates. The In this transport process, the M developer is sequentially supplied to the developing sleeve in the developing chamber 26M as indicated by an arrow A in the drawing, and is pumped up to the developing sleeve by the magnetic force of the magnet roller in the developing roll 21M.

  The M developer transported to the vicinity of the downstream end of the supply screw 32M in the agent transport direction (near the rear end in the figure) without being drawn up by the developing sleeve is, as shown by the arrow C in FIG. It falls into the agent recovery chamber 28M from a drop opening provided on the bottom wall of 27M.

  In FIG. 2 described above, the M developer that has been transported to the development position and contributed to the development with the rotation of the developing sleeve is then developed into the developing chamber 26M and the agent recovery chamber 28M with the rotation of the developing sleeve. To the communication position. Then, after separating from the sleeve surface due to the influence of the repulsive magnetic field formed by the magnet roller, it falls into the agent recovery chamber 28M as indicated by an arrow B in the figure.

  In the agent recovery chamber 28M, the M developer (not shown) held in the blades of the receiving screw 35M is transported from the near side to the far side in the direction orthogonal to the drawing sheet as the receiving screw 35M rotates. . In the course of this conveyance, M toner is supplied by the above-described toner supply device. Further, the M developer falling from the drop opening of the agent supply chamber 27M is taken in.

  Thereafter, the M developer transported to the vicinity of the downstream end of the receiving screw 35M in the agent transport direction (near the rear end in the figure) passes through the opening of the partition wall 30M as indicated by the arrow D in FIG. Then, it enters the agent return chamber 29M. The M developer that has entered the agent return chamber 29M is taken into the upstream end of the inclined screw 38M in the agent conveyance direction. Then, along with the rotation of the inclined screw 38M disposed in an obliquely upward posture from the upstream side in the agent transport direction to the downstream side in the agent transport direction, it is transported with an ascending gradient as indicated by an arrow G in FIG.

  When the inclined screw 38M is transported to the vicinity of the downstream end portion in the agent transport direction, it returns to the agent supply chamber 27M through the return opening 42M provided in the partition wall 30M as indicated by an arrow H in FIG. And it is taken in into the agent conveyance direction upstream end part of supply screw 32M.

  In the printer having the above basic configuration, each of the four photoconductors 3M, 3C, 3Y, and 3K functions as a latent image carrier that carries a latent image on a surface that moves endlessly by rotation.

  Further, the optical writing units 10M, 10C, 10Y, and 10K function as a latent image forming unit that forms a latent image on the surface of the photoreceptor after uniform charging. The developing units 20M, 20C, 20Y, and 20K for the respective colors function as developing devices that develop the latent images on the surfaces of the photoreceptors 3M, 3C, 3Y, and 3K, respectively.

  Next, the relationship between the magnetic pole on the developing sleeve and the movement of the developer will be described. In FIG. 2, among a plurality of magnetic poles in the magnet roller of the first developing roll 21M, N1 is a developing magnetic pole facing the photoconductor at the first developing position 55M via the developing sleeve.

  N2 is a regulation magnetic pole for attracting the developer toward the sleeve surface at the layer thickness regulation position by the development doctor 25M while facing the tip of the development doctor 25M via the development sleeve. Further, S1 is a post-regulation for constraining the developer on the sleeve surface after passing through the layer thickness regulation position by the development doctor 25M and entering the first development position as the development sleeve moves. It is a conveyance magnetic pole.

  S3 is a pumping magnetic pole having a function as a regulating upstream magnetic pole adjacent to the regulating magnetic pole N2 on the upstream side in the sleeve surface moving direction and a function of pumping up the developer around the supply screw 32M onto the sleeve surface. . S2 is an agent delivery pole for delivering the developer after passing through the first development position 55M to the N4 pole of the second development roll 50M as the surface of the development sleeve moves.

  Of the plurality of magnetic poles in the magnet roller of the second developing roll 50M, the N4 pole is an agent receiving pole for receiving the developer from the S2 pole of the first developing roll 21M. S4 is a conveying magnetic pole for restraining the developer before entering the second developing position 56M on the sleeve surface as the surface of the developing sleeve moves. N3 is a developing magnetic pole facing the photoconductor at the second developing position 56M via the developing sleeve.

  S5 is a magnetic pole for restraining the developer on the surface of the sleeve before entering the position facing the receiving conveyance screw 35M. Since S5 and the magnetic pole S6 adjacent to the downstream side of the sleeve surface moving direction are the same S pole, a repulsive magnetic field is formed between the two magnetic poles.

  As the surface of the second developing sleeve moves, it is separated from the sleeve surface due to the influence of the repulsive magnetic field and collected in the agent collecting chamber 28M. In addition, the code | symbol corresponding to each magnetic pole is attached | subjected to the location where the magnetic force on the sleeve surface of the magnetic pole becomes the maximum.

  The agent storage chamber 27M that stores the supply screw 32M is partitioned from the agent recovery chamber 28M by a receiving member 43M that is a part of the casing of the developing unit. The receiving member 43M is made of a non-magnetic material such as a resin, and receives the developer existing on the surface of the supply screw 32M on the surface of the supply screw 32M so that the developer can be conveyed by the supply screw 32M. Also bears.

  The supply position at which the developer is supplied from the supply screw 32M to the developing sleeve is such that the downstream end 44M of the receiving member 43M in the sleeve surface moving direction has the maximum pumping magnetic force (reference numeral S3) in the entire surface area of the developing sleeve. It is located beside the part on the downstream side of the part marked with. When the developing sleeve of the developing roll 21M enters the side of the downstream end 44M of the receiving member 43M as indicated by an arrow A in the drawing, the developer starts to be pumped up.

  In such a developing device having two developing rolls, if the fixing position of the magnet roller is changed and stopped from the time of development and the cutting is performed, the agent delivery pole (S2 of the first developing roll) Pole) and the agent receiving pole (N4 pole) of the second developing roll are broken, the transfer from the first developing roll to the second developing roll becomes difficult, and the developer is clogged in the developing chamber 26M. Therefore, the implementation was difficult.

  If the fixed positions of both the first and second magnet rollers are changed from the time of development and stopped, the transfer from the first developing roll to the second developing roll is ensured while ensuring the transferability. Although it may be possible to perform cutting, it is not realistic because two mechanisms for changing the fixing position of the magnet roller are required, resulting in an increase in size and cost of the developing device itself.

  A characteristic configuration of the printer according to the present embodiment will be described with reference to FIG. In the present embodiment, during normal development, the magnet roller of the first developing roll 21M that was in the state shown in FIG. 2 is rotated until it reaches the state shown in FIG. .

  In the state of FIG. 6, when the developing device (developing sleeve and conveying screw) is operated for a certain period of time, the developer around the supply screw 32M is constrained by the S2 pole, but adjacent to the sleeve surface moving direction S2 Since a repulsive magnetic field is formed between the poles S3 and S3, it does not pass the layer thickness regulation position by the developing doctor 25M.

  Further, the developer held on the first developing roll 21M before rotating the magnet roller of the first developing roll 21M is transferred from the S1 pole to the N4 pole and then the same as during normal development. It is transported on the second developing roll 50M and recovered in the agent recovery chamber 28M, and “ear cutting” is completed.

  Here, when the S1 pole of the first developing roll and the N4 pole of the second developing roll are in a positional relationship where the lines of magnetic force are connected to each other, the development from the first developing roll to the second developing roll is performed. Although the agent is delivered and the ear cutting operation can be performed, the developer conveyed on the developing sleeve receives a force in the tangential direction of the developing sleeve at the position of the S1 pole by the rotation of the developing sleeve. The S1 pole is preferably opposed to the upstream side in the rotation direction of the first developing roller rather than the peak position of the N4 pole of the second developing roll because the agent can be transferred more smoothly.

  Further, here, there is an upper cover 70M on the downstream side of the developing doctor 25M above the first developing roll, and in order to prevent toner scattering, the gap between the first developing roll and the upper cover 70M is The gap is set so that the spikes of the developer conveyed on one developing roll come into contact with each other.

  During normal development, the developer is magnetically applied on the developing sleeve from the developing doctor 25M on the first developing roll in the state shown in FIG. 2 to the downstream side in the rotation direction of the developing sleeve (parts S1 to N1 and S2). Is held in. When the magnet roller of the first developing roll 21M is turned in the opposite direction to the arrow F at the time of cutting off in this state, the developer held in the portions S1 to N1 and S2 is normally printed on the developing doctor 25M. On the contrary, it is input and stays downstream of the developing doctor 25M in the developing sleeve rotation direction, causing a problem that the developer is clogged in the gap with the upper cover 70M.

  On the other hand, as in this embodiment, when the magnet roller of the first developing roll 21M is rotated in the direction of arrow F (that is, the same direction as the rotation direction of the developing sleeve) at the time of cutting the ear, Developer from the developing doctor 25M on the downstream side in the rotation direction of the developing sleeve (parts S1 to N1 and S2) is not input to the developing doctor 25M in the reverse direction to that during normal printing. The developer can be smoothly shifted to the ear cutting state without clogging the gap with the developer.

  6 is magnetically held in the S2 pole by the developer supply chamber 27M. In this embodiment, when returning from the ear cutting state, the magnet roller of the first developing roller is rotated in the direction opposite to the direction of rotation of the developing sleeve (the direction opposite to the arrow F), opposite to the time of ear cutting.

  When returning from the ear cutting state, if the magnet roller of the first developing roller is rotated in the same direction as the developing sleeve (in the direction of arrow F) as in the case of the ear cutting, the development held at the S2 pole is performed. Since the agent passes through the development doctor 25M, a relatively large torque is required. However, if the rotation direction is opposite to the arrow F at the time of return, the development is performed on the S3 to N2 to S1 poles at the time of trimming. Since no developer is held, no torque is required to pass the developer through the developing doctor 25M in the reverse direction.

  In this case, the agent magnetically held in the S2 pole at the time of returning from the ear cutting state passes through the gap between the receiving member 43M of the agent supply chamber 27M and the first developing roller, but the receiving member 43M The gap between the first developing rollers is sufficiently wider than the gap of the developing doctor 25M, and the receiving member 43M is a non-magnetic material such as resin, so that there is no magnetic action with the S2 pole. Does not work. (The magnetic member is often used for the regulating member 25M (so-called magnetic blade). In this case, the magnetic field lines of the poles facing the magnetic body are concentrated, so that more torque is required when the agent passes.)

  For this reason, the torque when the agent magnetically held in the S2 pole passes through the gap between the receiving member 43M and the first developing roller can be made relatively small. Therefore, in such a configuration, the mechanism for changing the fixing position of the magnet roller can be made relatively simple.

  Further, in the configuration described above, the developing device (developing sleeve and conveying screw) is operated for a certain period of time in the state of FIG. 6, and the panning is performed. However, the developing sleeve and the conveying screw can be driven separately. In this state, if the conveying screw is stopped and only the developing sleeve is operated for a certain period of time, the amount of developer supplied from the agent supply chamber 27M to the S2 pole is reduced at the time of trimming, and the S2 pole is magnetically applied. Since the amount of the developer to be held is reduced, the return from the ear cutting state can be performed with a lower torque, which is more preferable.

  According to this embodiment, during the cutting operation, transferability from the first developing roll to the second developing roll can be ensured, and the developing chamber 26M and the gap between the first developing roller and the upper cover 70M can be secured. The occurrence of problems such as clogging of the developer can be prevented.

  Moreover, since the return from the cutting state can be performed without requiring a large torque for passing the developer through the developing doctor 25M, the mechanism for changing the fixing position of the magnet roller is relatively simple. can do. Further, since only one mechanism for changing the fixing position of the magnet roller is required, it is possible to minimize the increase in size and cost of the developing device itself.

  So far, the M developing unit has been described in detail, but the developing units for other colors have the same configuration as the M developing unit. Also, a so-called tandem printer that obtains a full-color image by superimposing and transferring toner images of each color formed by a plurality of toner image forming units has been described, but an image forming apparatus that forms a full-color image by a single method The application of the present invention is possible.

  In this single system, a plurality of developing means for each color are arranged around a latent image carrier such as a photoconductor, and visible images of respective colors formed on the latent image carrier while sequentially switching the developing means to be used. Is transferred onto the intermediate transfer member in sequence. The present invention can also be applied to an image forming apparatus that forms only a single color image.

  According to this embodiment, by reducing idling of the developing device, it is possible to provide an image forming apparatus that is compatible with productivity without increasing CPP unnecessarily.

3M, 3C, 3Y, 3K photoconductor 20M, 20C, 20Y, 20K Developing unit 21M First developing roll 25M Developing doctor 32M Supply screw 35M Receiving screw 38M Inclined screw 50M Second developing roll N4 Agent receiving pole

Japanese Patent No. 3390550 Japanese Patent Laid-Open No. 5-232819

Claims (6)

It includes two developing rollers each including a developing sleeve that is rotatably supported by including a magnet roller having a plurality of magnetic poles fixedly supported, and a two-component developer is applied from the first developing roller to the second developing roller. A developing device for transferring and developing the latent image formed on the image carrier,
A mechanism for rotating and stopping the magnet roller of the first developing roller by a predetermined angle;
When performing ear cutting, between two adjacent magnetic poles of the same polarity among the plurality of magnetic poles of the magnet roller of the first developing roller is positioned at the opposing portion of the regulating member that regulates the layer thickness of the developer. In addition, the developing device is characterized in that an electrode having a polarity different from that of the agent receiving electrode of the second developing roller is located at a portion opposite to the agent receiving electrode of the second developing roller.   The pole of the magnet roller of the first developing roller located at the opposite portion of the agent receiving electrode of the second developing roller is more than the peak position of the agent receiving electrode of the second developing roller when cutting the ear. The developing device according to claim 1, wherein the developing device is located upstream of the developing sleeve in the rotation direction of one developing roller.   3. The developing device according to claim 1, wherein the magnet roller of the first developing roller rotates in the same direction as the rotation direction of the developing sleeve when cutting the ear.   4. The developing device according to claim 1, wherein the magnet roller of the first developing roller rotates in a direction opposite to a rotation direction of the developing sleeve when returning from the ear cutting state. 5. . Furthermore, a helical member that conveys the developer is provided,
5. The developing device according to claim 1, wherein the developing sleeve is rotated for a predetermined time while the spiral member is stopped when the ear is cut. 6.   An image forming apparatus comprising the developing device according to claim 1.

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