JP5633263B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention is a developing device that is provided in an image forming apparatus such as a copying machine, a facsimile machine, or a printer, and that develops an image carrier with a developer, and supplies a developing unit facing the image carrier and the developing unit. The present invention relates to a developing device having a stirring unit for stirring a developer, and such an image forming apparatus having the developing device.

  2. Description of the Related Art Image forming apparatuses such as copying machines, facsimile machines, and printers that form an image using an image carrier such as a photoconductor include a developing device that develops the image carrier with a developer (for example, , [Patent Document 1] to [Patent Document 6]).

  A conventional general developing apparatus is an integrated type in which functions such as stirring of the developer and supply of the developer to the image carrier are realized by components housed in a single container (for example, [ Patent Document 1] to [Patent Document 3]).

  On the other hand, in recent years, the agitation unit for agitating the developer of the developing device is separated from the developing unit for supplying the developer to the image carrier, and the developer is sufficiently agitated and then sent to the developing unit. The system is known (for example, see [Patent Document 4] to [Patent Document 6]). As a configuration of such a developing unit, a configuration having a developer carrying member such as a developing roller and a developer carrying member that supplies the developer to the developer carrying member while carrying the developer is known (for example, [See Patent Document 4] and [Patent Document 5]).

  In the separation method, since the stirring unit is provided at a position away from the developing unit, there is an advantage that the volume of the developer container occupying the periphery of the image carrier can be reduced as much as possible with the developing unit as a minimum volume. In addition, as for the conveyance of the developer from the agitation unit to the development unit, an air conveyance method (for example, refer to [Patent Document 4]) that conveys the developer together with the air flow is a free path and a large amount of development with a simple configuration. This is effective in that the agent can be stably conveyed.

  By the way, in the separation type developing device, the developer conveyance amount from the stirring unit to the developing unit and the developer conveyance from the developing unit to the stirring unit are affected by the bulk density, fluidity, and toner concentration of the developer. The amount changes. In the air conveyance system, the developer conveyance amount varies depending on the air pressure variation due to the environment. When the transport amount of the developer changes, the balance of the developer amount changes between the developing unit and the stirring unit.

  When the amount of developer in the developing unit decreases due to such a change, in the configuration having the developer transport member described above, the bulk of the developer around the developer transport member decreases, and a sufficient amount of development is performed on the developer carrier. When the developer is not supplied, the amount of developer carried on the developer carrying member decreases, and image density unevenness may occur. On the other hand, when the developer amount in the developing unit increases due to such changes, the developer in the stirring unit decreases, the time for sufficiently stirring the developer is not maintained, and a developer with insufficient stirring is developed in the developing unit. Therefore, a phenomenon called so-called background fogging may occur in which unnecessary toner adheres to the background portion of the image.

  In order to avoid such a problem, in order to stabilize the balance of the developer amount between the stirring unit and the developing unit and to optimize the amount of developer carried on the developer carrying member, the developer circulation amount is constant. Need to control.

  In this regard, as a technique for stabilizing the balance, the developer agent stored in the stirring unit is used to control the height of the developer surface stored in the stirring unit within a certain range. A level sensor that detects the height of the surface, based on a light transmission type or magnetic permeability detection, and a rotary feeder that is a part that controls the amount of developer transported from the stirring unit to the developing unit based on the detection result of the level sensor. A technique for changing the rotational speed has been proposed (see, for example, [Patent Document 4]). In an integrated developing device, it is known to use a piezoelectric element, a permeability sensor, an optical sensor, an ultrasonic sensor, etc. as a sensor for detecting the height of the developer surface (for example, [See Patent Document 1] to [Patent Document 3]).

  However, although this technique is certainly effective in securing the developer amount in the stirring unit and maintaining the stirring time, the developer in the developer carrying member by securing the developer amount in the developing unit. It is not necessarily sufficient to ensure the amount of the supported amount.

  This is because the balance of the developer amount in the agitating unit and the developing unit is determined not only by the developer amount in the developing unit and the developer amount in the agitating unit, but also by the developer amount in the transport path connecting them. It is. That is, even when the amount of developer in the agitating portion does not change, if the amount of developer in the transport path increases, the amount of developer in the developing portion decreases, and in the worst case, the developer amount is depleted.

  As described above, the balance of the developer amount in the agitating unit and the developing unit is determined and maintained in consideration of the amount of developer in the transport path, so that the developer in the agitating unit as described above. In some cases, the amount of developer in the developing unit may not be ensured only by detecting the amount. Therefore, in this technique, as described above, a sufficient amount of developer is not supplied to the developer carrier, and image density unevenness can occur.

  Therefore, in order to maintain the balance of the developer amount in the agitating unit and the developing unit and to optimize the developer amount in the developing unit, it is also necessary to consider the developer amount in the conveyance path from the agitating unit to the developing unit. There is.

  By the way, the above-described optical sensor, magnetic permeability sensor, piezoelectric element, and ultrasonic sensor as sensors capable of detecting the developer amount have the following characteristics. That is, the optical sensor and the ultrasonic sensor have a problem that the detection accuracy decreases due to the adhesion of the developer. Since the output of the magnetic permeability sensor varies depending on both the height of the agent surface and the toner concentration, there is a problem that the detection accuracy is low unless the accurate toner concentration is known. The piezoelectric element is an element for determining whether the developer surface of the developer is greater than or less than a predetermined height, and is thus effective as a limiter for a predetermined value. However, the piezoelectric element is unsuitable for determining how far the agent surface is from a predetermined height.

  The present invention is provided in an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, and develops an image carrier with a developer. The developing unit facing the image carrier and the developer supplied to the developing unit are agitated. And a developing device that optimizes the amount of developer in the developing unit in consideration of the amount of developer in the transport path from the stirring unit to the developing unit, and an image forming apparatus including the developing device. Objective.

In order to achieve the above-mentioned object, the invention according to claim 1 stirs a developing section provided with a developer carrying body disposed opposite to an image carrying body and carrying a developer, and a developer supplied to the developing section. And a developer conveying means for conveying the developer from the agitating unit toward the developing unit. The developing unit conveys the developer by its rotation, and the developer being conveyed is A developer carrying member carried by the developer carrying member, and a developer surface position detecting unit for detecting whether or not the developer surface position in the developer carrying region by the developer carrying member is at a predetermined position; And is detected by the agent surface position detecting means and is based on first information on whether or not the agent surface position is at a predetermined position and second information on the rotation speed of the developer conveying member. The developer transport amount by the developer transport means The developer conveying quantity control means possess that, the developer transport amount control means, first information, at the time when the developer surface position showed that switched whether in place, the The number of rotations for controlling the number of rotations so that the conveyance amount is controlled based on the information of 2 and the first information indicates whether or not the agent surface position is switched to a predetermined position. It exists in the developing device which has a control means .

  According to a second aspect of the present invention, in the developing device according to the first aspect, the developer transport amount control means includes the first information, the second information, and the third information relating to the bulk density of the developer. Based on this, the transport amount is controlled.

  According to a third aspect of the present invention, in the developing device according to the second aspect, the image forming apparatus further includes a toner concentration detecting unit that detects a toner concentration in the developer, and third information is detected by the toner concentration detecting unit. It is obtained based on the toner density.

  According to a fourth aspect of the present invention, in the developing device according to the third aspect, the toner density detecting means detects the toner density of the developer in the developing unit.

According to a fifth aspect of the present invention, in the developing device according to any one of the first to fourth aspects, on the condition that the first information indicates that the agent surface position is at a predetermined position. A developing device comprising: a rotation speed control means for increasing the rotation speed .

A sixth aspect of the present invention is an image forming apparatus comprising the developing device according to any one of the first to fifth aspects .

  The present invention relates to a developing unit provided with a developer carrying member disposed opposite to an image carrier and carrying a developer, an agitation unit for agitating a developer supplied to the developing unit, and the development unit from the agitation unit to the development unit. A developer conveying means that conveys the developer toward the portion, the developing portion conveys the developer by its rotation, and the developer being conveyed is carried on the developer carrier A conveying member; and a developer surface position detecting unit that detects whether or not the developer surface position of the developer in the developer transport region by the developer conveying member is at a predetermined position. Based on the detected first information relating to whether or not the agent surface position is at a predetermined position and second information relating to the number of rotations of the developer carrying member, the developer carried by the developer carrying means Development having developer transport amount control means for controlling transport amount Therefore, it is possible to control the amount of developer conveyed from the stirring unit to the developing unit so that the amount of developer in the developing unit is stable at an appropriate amount, and it is possible to perform good development and good It is possible to provide a developing device that can contribute to stable image formation.

  If the developer transport amount control means controls the transport amount based on the first information, the second information, and the third information regarding the bulk density of the developer, the developer transport amount control means The amount of developer conveyed to the developing unit can be controlled with higher accuracy so that the amount of developer in the developing unit is stabilized at an appropriate level, and good development can be performed with good development. A developing device that can contribute to the above can be provided.

  If there is a toner density detecting means for detecting the toner density in the developer, and the third information is obtained based on the toner density detected by the toner density detecting means, the stirring section and the developing section The third amount of information is obtained by using a toner concentration detecting means that may be used for toner concentration control in two-component development so that the amount of developer conveyed to the developing portion is stabilized at an appropriate amount. Therefore, it is possible to provide a developing device that can be controlled with higher accuracy, can perform good development, and can contribute to good image formation.

  If the toner concentration detecting means detects the toner concentration of the developer in the developing unit, the amount of developer conveyed from the stirring unit to the developing unit is stabilized with an appropriate amount of developer in the developing unit. As described above, it is possible to control with higher accuracy by obtaining the third information by the developer in the developing unit using the toner density detecting means that may be used for toner density control in the two-component development, It is possible to provide a developing device that can perform good development and contribute to good image formation.

  The developer conveyance amount control means determines the conveyance amount based on the second information at a timing when the first information indicates whether or not the agent surface position is at a predetermined position. If controlled, it is possible to accurately control the amount of developer conveyed from the agitating unit to the developing unit so that the amount of developer in the developing unit is stabilized at an appropriate amount, and good development is performed. Therefore, it is possible to provide a developing device that can contribute to good image formation.

  If the first information includes rotation speed control means for controlling the rotation speed so as to indicate whether or not the liquid surface position is at a predetermined position, the liquid surface position is determined in advance. While maintaining the position, it is possible to control the amount of developer conveyed from the agitating unit to the developing unit so that the amount of developer in the developing unit is stabilized at an appropriate amount, and good development can be performed. A developing device that can contribute to good image formation can be provided.

  On the condition that the first information indicates that the agent surface position is at a predetermined position, the first information is conveyed from the agitating unit to the developing unit if it has a rotation speed control means for increasing the rotation speed. The developing device can control the amount of developer to be developed relatively easily so that the amount of developer in the developing unit is stable and stable, can perform good development, and can contribute to good image formation Can be provided.

  Since the present invention is in an image forming apparatus having such a developing device, it is possible to control the amount of developer conveyed from the stirring unit to the developing unit so that the amount of developer in the developing unit is stabilized at an appropriate amount. Therefore, it is possible to provide an image forming apparatus capable of performing good development and capable of performing good image formation.

1 is a schematic front view of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic perspective view of a developing device provided in the image forming apparatus shown in FIG. 1. FIG. 3 is a front sectional view of a developing unit provided in the developing device shown in FIG. 2. FIG. 3 is a cross-sectional view showing an internal structure of a stirring unit provided in the developing device shown in FIG. 2. FIG. 3 is a side sectional view of a developing unit provided in the developing device illustrated in FIG. 2. FIG. 6 is a schematic view for explaining the characteristics of the agent surface position detecting means provided in the developing unit shown in FIG. 5. FIG. 4 is a correlation diagram illustrating a relationship between the number of rotations of a developer conveying member provided in the developing unit illustrated in FIG. 3 and a developer feeding speed. FIG. 3 is a schematic view showing a geometrical relationship between the developer surface position in the developing unit shown in FIG. 3 and the cross-sectional area of the developer conveying member provided in the developing unit that substantially functions to feed the developer. It is. FIG. 4 is a correlation diagram showing the relationship between the number of rotations of the developer conveying member provided in the developing unit shown in FIG. 3 and the amount of developer conveyed by the developer conveying member when the agent surface position is at a predetermined position. is there. FIG. 5 is a correlation diagram showing the relationship between toner density, developer bulk density, and output of a toner density sensor.

  FIG. 1 schematically shows an image forming apparatus to which the present invention is applied, which is a multicolor image forming apparatus capable of forming a color image. The image forming apparatus 100 is a combination machine of a color laser printer and a facsimile, but may be another type of image forming apparatus such as another type of printer, facsimile, copying machine, copying machine and printer combination machine, or the like. . The image forming apparatus 100 performs an image forming process based on an image signal corresponding to image information received from the outside. This is the same when the image forming apparatus 100 is used as a facsimile. The image forming apparatus 100 can form an image on a sheet-like recording medium using not only plain paper generally used for copying, but also OHP sheets, cardboard, cardboard, cardboard, and envelopes. It is.

  The image forming apparatus 100 is a cylindrical photosensitive member that is a latent image carrier as a plurality of image carriers that can form images as images corresponding to colors separated into yellow, magenta, cyan, and black. This is a tandem structure that adopts a tandem structure in which body drums 20Y, 20M, 20C, and 20BK are arranged side by side, in other words, a tandem type, that is, a tandem type image forming apparatus.

  The photoconductive drums 20Y, 20M, 20C, and 20BK have the same diameter, and the outer peripheral surface of the transfer belt 11 as an intermediate transfer belt that is an endless belt disposed almost in the center of the main body 99 of the image forming apparatus 100. They are arranged at equal intervals on the side, that is, on the image forming surface side.

  The photosensitive drums 20Y, 20M, 20C, and 20BK are arranged in this order from the upstream side in the A1 direction that is the moving direction of the transfer belt 11. The photoconductive drums 20Y, 20M, 20C, and 20BK are image stations 60Y, 60M, 60C, and 60BK that are image forming units as image forming units for forming yellow, magenta, cyan, and black images, respectively. Is provided.

  Visible images, that is, toner images formed on the respective photosensitive drums 20Y, 20M, 20C, and 20BK are respectively superimposed and transferred onto the transfer belt 11 that moves in the direction of the arrow A1, and then transferred as a recording material as a recording medium. It is designed to be transferred all at once to transfer paper as a medium.

  In the superimposing transfer to the transfer belt 11, the toner images formed on the photosensitive drums 20Y, 20M, 20C, and 20BK are transferred to the same position on the transfer belt 11 while the transfer belt 11 moves in the A1 direction. As described above, primary transfer rollers 12Y, 12M, 12C, and 12BK as transfer chargers that are transfer means disposed at positions facing the respective photosensitive drums 20Y, 20M, 20C, and 20BK with the transfer belt 11 interposed therebetween. Is applied at a transfer position that is opposite to each of the photosensitive drums 20Y, 20M, 20C, and 20BK and the transfer belt 11 by shifting the timing from the upstream side toward the downstream side in the A1 direction.

  The transfer belt 11 is an elastic belt whose entire layer is formed using an elastic member such as a rubber agent. The transfer belt 11 may be a single-layer elastic belt, may be an elastic belt using a part of the elastic belt, or a conventionally used fluorine-based resin, polycarbonate resin, or polyimide resin. Or an inelastic belt may be used.

  The image forming apparatus 100 is an intermediate transfer apparatus that includes four image stations 60Y, 60M, 60C, and 60BK, and is disposed to face the photosensitive drums 20Y, 20M, 20C, and 20BK, and includes a transfer belt 11. A transfer belt unit 10 as a certain belt unit, and a transfer member that is disposed opposite to the transfer belt 11 and contacts the transfer belt 11 and rotates in the same direction as the transfer belt 11 at the contact position with the transfer belt 11. And a secondary transfer roller 5 as a transfer device.

  The image forming apparatus 100 also includes a cleaning device 18 as an intermediate transfer belt cleaning device provided with an intermediate transfer cleaning brush disposed opposite to the transfer belt 11 and cleaning the transfer belt 11, and image stations 60Y, 60M, and 60C. , And an optical scanning device 8 as a writing device as an optical writing device which is an optical writing means disposed oppositely below 60BK.

  The image forming apparatus 100 is also transported from the sheet feeding device 61, a sheet feeding device 61 on which transfer paper transported between the photosensitive drums 20 </ b> Y, 20 </ b> M, 20 </ b> C, 20 </ b> BK and the transfer belt 11 is stacked. A pair of registration rollers that feeds the recording paper to the transfer portion between the transfer belt 11 and the secondary transfer roller 5 at a predetermined timing in accordance with the timing of toner image formation by the image stations 60Y, 60M, 60C, and 60BK. 13 and a sensor (not shown) for detecting that the leading edge of the transfer paper has reached the registration roller pair 13.

The image forming apparatus 100 also includes a fixing device 6 as a fixing unit of a belt fixing system for fixing the toner image to the transfer paper on which the toner image is transferred, and a transfer paper that has passed through the fixing device 6 as a main body. A paper discharge roller 7 that discharges to the outside of the main body 99; a paper discharge tray 17 that is disposed above the main body 99 and stacks transfer paper discharged to the outside of the main body 99 by the paper discharge roller 7; , Toner bottles 9Y, 9M, 9C, and 9BK as toner hoppers filled with magenta, cyan, and black toners.
Although not shown, the image forming apparatus 100 also includes a control means 65 that includes a CPU and storage means such as a ROM and a RAM and controls the overall operation of the image forming apparatus 100.

  In addition to the transfer belt 11, the transfer belt unit 10 includes primary transfer rollers 12Y, 12M, 12C, and 12BK, and a driving roller that is a driving member as a plurality of winding members around which the transfer belt 11 is wound. The transfer entrance roller 73 also serves as a driven roller 72. The transfer entrance roller 73 is driven to rotate by driving a motor as a drive source (not shown), whereby the transfer belt 11 is driven to rotate in the A1 direction.

  The fixing device 6 includes a fixing unit 63 having a heat source (not shown), and a pressure roller 62 pressed against the fixing unit 63, and transfers a transfer sheet carrying a toner image between the fixing unit 63 and the pressure roller 62. By passing the toner image through a fixing portion that is a pressure contact portion, the carried toner image is fixed on the surface of the transfer paper by the action of heat and pressure.

The optical scanning device 8 scans and exposes the surfaces to be scanned formed by the surfaces of the photosensitive drums 20Y, 20M, 20C, and 20BK, and forms a laser beam based on an image signal for forming an electrostatic latent image. The beams LY, LM, LC, and LBK, which are laser beams of the above, are emitted.
The sheet feeding device 61 includes a paper feed tray 15 on which transfer paper is stacked and a paper feed roller 16 that feeds transfer paper stacked on the paper feed tray 15.

  Regarding the image stations 60Y, 60M, 60C, and 60BK, the configuration will be described as a representative of the configuration of the image station 60Y including the photosensitive drum 20Y. Since the configuration of the other image station is substantially the same, in the following description, for the sake of convenience, a reference numeral corresponding to the reference symbol assigned to the configuration of the image station 60Y is attached to the configuration of the other image station. Further, detailed description will be omitted as appropriate, and those with Y, M, C, and K at the end of the reference numerals are configurations for forming yellow, magenta, cyan, and black images, respectively. Will be shown.

  The image station 60Y provided with the photoconductive drum 20Y is for cleaning the primary transfer roller 12Y and the photoconductive drum 20Y around the photoconductive drum 20Y along its rotation direction B1, which is counterclockwise in the drawing. A cleaning device 70Y as a cleaning means, a charging device 30Y as a charging means for charging the photosensitive drum 20Y to a high voltage, and a development that is a dry two-component developer including toner and a carrier. And a developing device 50Y as developing means for developing with an agent.

  The photosensitive drum 20Y, the cleaning device 70Y, the charging device 30Y, and the developing device 50Y are integrated to form a process cartridge. The process cartridge is detachable from the main body 99. Making a process cartridge in this way is very preferable because it can be handled as a replacement part, so that the maintainability is remarkably improved.

  With the configuration described above, the surface of the photosensitive drum 20Y is uniformly charged by the charging device 30Y as it rotates in the B1 direction, and corresponds to the yellow color by the exposure scanning of the beam LY from the optical scanning device 8. An electrostatic latent image is formed. The electrostatic latent image is formed by scanning the beam LY in the main scanning direction, which is a direction perpendicular to the paper surface, and performing sub scanning in the circumferential direction of the photosensitive drum 20Y by rotating the photosensitive drum 20Y in the B1 direction. This is done by scanning in the direction as well.

  The electrostatic latent image formed in this way is charged with yellow toner charged by the developing device 50Y, developed to yellow and visualized, in other words, visualized and obtained by development. The yellow toner image, which is a visible image of yellow, is primarily transferred to the transfer belt 11 moving in the A1 direction by the primary transfer roller 12Y, and foreign matters such as toner remaining after the transfer are scraped off and stored by the cleaning device 70Y. The photosensitive drum 20Y is subjected to the next charging by the charging device 30Y.

  Similarly, toner images of the respective colors are formed on the other photosensitive drums 20C, 20M, and 20BK, and the formed toner images of the respective colors are transferred to the A1 direction by the primary transfer rollers 12C, 12M, and 12BK. 11 is sequentially transferred to the same position on the head.

  The toner image superimposed on the transfer belt 11 moves to the transfer portion that is the secondary transfer portion that is the position facing the secondary transfer roller 5 as the transfer belt 11 rotates in the A1 direction. Secondary transferred onto transfer paper.

  The transfer paper conveyed between the transfer belt 11 and the secondary transfer roller 5 is fed out from the sheet feeding device 61, and the toner on the transfer belt 11 is detected by the registration roller pair 13 based on the detection signal from the sensor. The image is sent out at the timing when the leading edge of the image faces the secondary transfer roller 5.

  When the toner images of all colors are collectively transferred and carried on the transfer paper, the transfer paper enters the fixing device 6 and acts by heat and pressure when passing through the fixing portion between the fixing unit 63 and the pressure roller 62. Thus, the carried toner image is fixed, and by this fixing process, a color image which is a composite color image is formed on the transfer paper. The fixed transfer paper that has passed through the fixing device 6 passes through the paper discharge roller 7 and is stacked on the paper discharge tray 17. On the other hand, the transfer belt 11 that has finished the secondary transfer is cleaned by the cleaning device 18 to prepare for the next primary transfer.

  In the image forming apparatus 100, the developing devices 50Y, 50M, 50C, and 50BK have substantially the same configuration. Hereinafter, the developing devices 50Y, 50M, 50C, and 50BK will be described as the developing device 50. The photosensitive drums 20Y, 20M, 20C, and 20BK will be described as the photosensitive drum 20, and the toner bottles 9Y, 9M, 9C, and 9BK will be described as the toner bottle 9.

As shown in FIG. 2, the developing device 50 is disposed in the vicinity of the photosensitive drum 20 so as to face the photosensitive drum 20, and is separate from the developing unit 81 that has a function of developing the photosensitive drum 20. And a stirring unit 82 that functions as a developer stirring unit that stirs the developer supplied to the developing unit 81, and the developer is refluxed and circulated between the developing unit 81 and the stirring unit 82. And a toner replenishing portion 79 as a toner replenishing means for detachably attaching the toner bottle 9 and supplying new toner in the toner bottle 9 to the agitating portion 82.
Thus, the developing device 50 is a developing stirring separation type developing device.

  The reflux unit 83 includes a circulation return path 84 as a developer transport path that forms a first flow path forming unit that forms a developer flow path from the stirring unit 82 to the developing unit 81, and the stirring unit 82 from the developing unit 81. And a circulation forward path 85 as a developer discharge flow path that constitutes a second flow path forming portion that forms a flow path for the developer.

  As illustrated in FIG. 3, the developing unit 81 includes a developing roller 51 serving as a developer carrying member that supplies the developer disposed and opposed to the photoconductive drum 20 to the photoconductive drum 20, and a photoconductive drum 20. A developing case 55 as a casing having an opening at the opposite portion and exposing a part of the developing roller 51 from the opening to the photosensitive drum 20 as desired, and on the developing roller 51 supported by the developing case 55 And a developing blade 52 as a doctor as a restricting member for restricting the developer to a certain height.

  The developing unit 81 also serves as a mechanism for circulating and transporting the developer in the developing case 55 by a first transport screw 53 and a second transport screw 54 that transport the developer in the developing case 55 and a part of the developing case 55. A first storage chamber 58 configured to partition the space between the first conveyance screw 53 and the second conveyance screw 54 and divide the space in the developing case 55 into two to accommodate the first conveyance screw 53 and the second conveyance screw 54 are accommodated. A partition wall 57 as a partition plate formed with the second storage chamber 59, and a motor 64 shown in FIG. 2 as development driving means for rotationally driving the developing roller 51, the first transport screw 53, and the second transport screw 54; And a transmission mechanism (not shown) that transmits the driving force of the motor 64 to the developing roller 51, the first conveyance screw 53, and the second conveyance screw 54.

  As shown in FIG. 3, the developing unit 81 is also a powder level position detecting unit as a powder level position detecting unit for detecting the powder level position, that is, the level position of the developer in the developing unit 81. An agent surface position detection sensor 66 composed of a piezoelectric element, a toner concentration detection sensor 56 as a toner concentration sensor as a toner concentration detection means for measuring the toner concentration in the developer, and a DC component developing bias are applied. Bias applying means (not shown).

  The agent surface position detection sensor 66 is disposed so as to face the first storage chamber 58 so as to detect the agent surface position of the developer in the developing unit 81 in the first storage chamber 58. The agent surface position detection sensor 66 determines whether or not the agent surface position of the developer in the first storage chamber 58 is at a predetermined position, that is, at the disposition position, specifically, whether or not the disposition position is reached. Is detected.

  The toner concentration detection sensor 56 is disposed so as to face the second storage chamber 59 so as to detect the toner concentration of the developer in the second storage chamber 59 where the toner is consumed by the development. The toner concentration detection sensor 56 applies the change in magnetic permeability depending on the amount of developer present in the measurement space. That is, in a developer containing toner and a magnetic carrier, the magnetic permeability increases because the carrier ratio increases when the toner concentration is low, and the magnetic permeability decreases because the carrier ratio decreases when the toner concentration is high. It is something that uses that.

  Both the signal relating to the agent surface position detected by the agent surface position detection sensor 66 and the signal relating to the toner concentration detected by the toner concentration detection sensor 56 are input to the control means 65. Both the bias applying unit and the motor 64 are controlled by the control unit 65. In controlling the driving of the motor 64, the control unit 65 monitors the rotational speed of the motor 64 and controls the rotational speed of the first transport screw 53. In this respect, the control means 65 functions as a rotation speed control means for controlling the rotation speed of the first conveying screw.

  Based on the signal relating to the agent surface position detected by the agent surface position detection sensor 66, the control means 65 changes the agent surface position of the developer in the first storage chamber 58 to the position where the agent surface position detection sensor 66 is disposed. First information regarding whether or not there is present is acquired. The control means 65 acquires second information related to the rotation speed of the first conveying screw 53 under the control of the motor 64.

  The developing roller 51 extends in a direction perpendicular to the paper surface in FIG. This direction is the width direction of the developing roller 51, in other words, the axial direction, and the extending direction of the photosensitive drum 20, that is, the width direction of the photosensitive drum 20, in other words, the direction parallel to the axial direction. Although not shown in detail, the developing roller 51 includes a magnet roller as a magnetic field generating unit, a non-magnetic developing sleeve that includes the magnet roller and is driven in the C1 direction, which is counterclockwise in the figure, by the developing driving unit. have.

  Although not shown, the magnet roller has a plastic roller fixed to the developing case 55 and a magnet block that is a plurality of magnets forming a plurality of magnetic poles embedded in the plastic roller.

  The developing sleeve is rotatably supported by the developing case 55 and the magnet roller. A developing bias having an appropriate size is applied between the developing sleeve and the photosensitive drum 20 by bias applying means. A gap between the developing sleeve and the photosensitive drum 20 in the developing region, that is, a developing gap is set to be 0.3 mm.

  The developing blade 52 is made of a SUS material. The gap between the developing blade 52 and the developing sleeve, that is, the doctor gap, is set to be 0.5 mm, so that the developer on the developing sleeve is equalized to a certain amount.

  The first transport screw 53 and the second transport screw 54 are disposed so as to extend in the width direction of the developing roller 51, in other words, the longitudinal direction of the developing roller 51, the direction perpendicular to the paper surface in FIG. 3. . The first conveying screw 53 and the second conveying screw 54 are shaft parts 53a and 54a as rotating shafts that are rotated by receiving a rotational driving action by the developing driving means, and surfaces of the shaft parts 53a and 54a, specifically shafts. The blades 53b and 54b are formed as a single unit in a manner projecting on the peripheral surfaces of the portions 53a and 54a, and serve as a conveyance unit that conveys the developer while stirring the developer by rotation of the shaft portions 53a and 54a. Yes. The blade portions 53b and 54b have a spiral shape, in other words, a spiral shape and are formed as a spiral portion. However, the blade portions 53b and 54b may have a swash plate shape inclined with respect to the shaft portions 53a and 54a.

  The first conveying screw 53 is disposed opposite to the developing roller 51 so as to be adjacent to the developing roller 51, and is driven to rotate in the direction D <b> 1 by the motor 64, so that the first conveying screw 53 in the developer conveying region. This is a supply screw that supplies the developer in a certain first storage chamber 58 to the developing roller 51 while transporting the developer from the front side to the back side in FIG. 3 along the width direction of the developing roller 51.

  As for the partition wall 57, the edge part of the back | inner side in FIG. 3 interrupts as shown in FIG. 5, and has the opening part 57a. The developer transported to the vicinity of the end portion in the first storage chamber 58 by the first transport screw 53 enters the second storage chamber 59 by dropping through the opening 57a, and enters the second storage chamber 59 from the second transport screw 53. It moves toward the transport screw and is delivered to the second transport screw 54.

  The second transport screw 54 is disposed below the first transport screw 53 and is driven to rotate by a motor 64 in a second storage chamber 59 that is a developer transport area by the second transport screw 54. Thus, the developer sent from the first storage chamber 58 is transported along the width direction of the developing roller 51 in the direction E1 shown in FIG. The recovery screw recovers the developer that is carried on the photosensitive drum 20 but is not used for the development of the photosensitive drum 20.

As described above, the first conveying screw 53 and the second conveying screw 54 convey the developer by the rotation thereof, and the developing device 50 has a developer flow in one direction in the developing unit 81. The direction circulation system is adopted. The first transport screw 53 is a developer transport member on which the developer transported in this way is carried on the developing roller 51.
Note that the front end of the partition wall 57 in FIG. 3 is integral with the developing case 55, and no opening or the like is formed.

  As shown in FIG. 2, the developer case 55 includes, on the downstream side in the E1 direction, a developer carry-in portion 86 as a developer supply portion that constitutes a developer carry-in port that receives the developer stirred by the stirring portion 82, and a second It has a developer discharge portion 87 as a developer discharge portion which constitutes a developer discharge port for sending the developer conveyed in the E1 direction in the storage chamber 58 by the conveyance screw 54 toward the stirring portion 82. The developer carry-in part 86 and the developer carry-out part 87 are respectively located on the near side of the first transport screw 53 and the second transport screw in FIG.

  As shown in FIG. 2, the circulation return path 84 has a developer charging section 67 connected to the developer loading section 86 at the end on the developing section 81 side, and a stirring section 82 and a developer loading section 86. And connected. The circulation outward path 85 connects the stirring unit 82 and the developer carrying-out unit 87.

  The circulation outward path 85 has a hanging portion 88 that is suspended from the developer carrying-out portion 87 and directly connected to the stirring portion 82. The hanging portion 88 is configured by a tube formed of a flexible material such as a rubber tube. The inside of the hanging part 88 is hollow, and the developer carried out from the developer carrying-out part 87 enters the stirring part 82 due to free fall and is put into the stirring part 82.

  As will be described later, the circulation return path 84 is connected to a rotary feeder 90 as a developer storage unit for temporarily storing the stirred developer carried out from the stirring unit 82, and a lower end of the rotary feeder 90, and a developer loading unit 86. And a transport unit 92 for transporting the stirred developer.

  The rotary feeder 90 rotates the rotor 90d so as to cover the rotor 90d and the rotor 90d, which is an impeller having a plurality of blades 90c extending radially as shown in FIG. And a stator 90b that is freely supported.

  When the rotor 90d rotates at a constant speed, the rotary feeder 90 discharges a fixed amount of developer from the lower end portion of the stator 90b. The driving of the motor 90a is controlled by the control means 65 so as to control the rotational speed of the rotor 90d. Therefore, the control means 65 functions as a developer discharge amount control means for controlling the developer discharge amount from the rotary feeder 90.

  The conveying portion 92 is connected to the lower end of the stator 90b and is connected to a joint conduit 92c as a merging portion for receiving the agitated developer discharged from the rotary feeder 90, and is connected to the developer charging portion 67 at one end and is the other end. A tube 92a formed of a flexible material, such as a rubber tube, having a joint pipe line 92c connected to the inlet 92g, and a tube connected to the opposite side of the joint pipe line 92c to which the tube 92a is connected. 92d, an air pump 92b serving as an air supply means connected to the tube 92d on the opposite side to that connected to the joint conduit 92c, and a flow path adjusting valve 92e disposed in the middle of the tube 92d. doing.

  The air pump 92b has a supply port 92f, which is an output port, connected to the tube 92d, and blows air into the tube 92d. The tube 92d is an air passage through which the air blown by the air pump 92b passes toward the joint pipe line 92c. In this manner, the air pump 92b pumps the air blown into the tube 92d into the developing case 55 via the joint conduit 92c, the tube 92a, and the developer charging unit 67. At this time, the developer that has entered the joint pipe line 92c from the rotary feeder 90 is supplied to the inside of the developing case 55 by being put on this air flow. As described above, the transport unit 92 supplies the developer stirred by the stirring unit 82 to the developing unit 81 by air transport.

  Therefore, the circulation return path 84 functions as a developer transport unit that transports the developer from the stirring unit 82 toward the developing unit 81.

  The flow path adjustment valve 92e is provided to adjust the flow rate of the air that enters the joint pipe line 92c through the tube 92d, puts the developer, and flows into the developing portion 81. The opening state of the flow path adjustment valve 92e is controlled by the control means 65 so as to adjust the flow rate of the air. This air flow rate affects the amount of developer conveyed from the agitating unit 82 toward the developing unit 81 by the conveying unit 92. The control means 65 functions as a developer transport air volume control means.

  The control unit 65 functions as at least one of the developer discharge amount control unit and the developer transport air amount control unit, so that the developer transport amount from the stirring unit 82 to the development unit 81 through the circulation return path 84, in other words, development. It functions as a developer conveyance amount control means for controlling the amount of supplied agent.

  The air pump 92b uses a diaphragm type air pump in this embodiment. However, if the air pump 92b has a function of conveying the developer to the developing unit 81 through the tube 92a by the air flow generated thereby, a butterfly type air pump, a rotary Other means such as a mold air pump may be used.

  The stirrer 82 includes a stirrer 93 and a stirrer driving means 95 that rotationally drives the stirrer 93, and stirs and mixes new toner with the existing developer to uniformize the toner concentration in the developer. The toner in the developer is brought into a predetermined charged state.

The stirrer 93 is provided with a developer supply port 93b on the upper surface and a discharge port 93c on the lower surface. The stirrer 93 has a casing 93a having an inverted conical shape whose diameter decreases toward the discharge port 93c.
The developer supply port 93b is connected to the hanging portion 88. The discharge port 93 c communicates with the rotary feeder 90.

  The stirrer 93 is also disposed in the center of the casing 93a, and a screw 96 that conveys the developer from the bottom to the top, and two rotatable stirring members 97 that are disposed outside the screw 96, Each stirring member 97 has a support portion 98 to which the upper end is fixed. The stirrer 93 has a screw 96 and a support portion 98 that are rotatable, and stirs and mixes the developer by rotating the screw 96 and each stirring member 97.

  The agitation drive means 95 is a reduction gear having a plurality of gears 95c, 95d, 95e, and 95f that are driven to rotate by the motor 95a and a motor 95a that is a drive means whose drive is controlled by the control means 65. And a reduction gear train 95b as a train.

  The screw 96 and the stirring member 97 are rotationally driven by a motor 95a. Specifically, the screw 96 is directly connected to the motor 95a, and the stirring member 97 is decelerated and rotated via the reduction gear train 95b. The support portion 98 is directly connected to the reduction gear train 95b. As shown in FIG. 4A, the stirring member 97 is fixed obliquely with respect to the support portion 98. The conveyance from the supply port 93b to the discharge port 93c uses gravity. The stirrer 193 functions as a buffer and a developer is always present therein, so that the unstirred developer is not discharged as it is.

  In such a stirrer 93, the developer is lifted up from below by the rotation of the screw 96, and moves downward along with the rotation of the stirring member 97 that rotates on the outside of the screw 96, and around the screw 96. They are gathered together and lifted again from below by the screw 71.

  Thus, the developer is constantly convected in the stirrer 93. By this convection, the entire internal developer is uniformly mixed. Since the toner is charged by the friction between the toner and the carrier, it is important to increase the contact probability between the toner and the carrier in order to quickly obtain the charge amount. It has been found that the contact probability of the developer is increased and the damage to the developer is small.

  As shown in FIG. 2, the toner replenishing unit 79 is provided in the pipe 79a as a toner supply path to which the toner bottle 9 can be freely attached and removed, and the new toner that has fallen from the toner bottle 9 into the pipe 79a. A helical coil which is a small screw (not shown) as a conveying member that conveys toward the stirrer 93 by rotating in a predetermined direction, and a coil whose driving is controlled by a control means provided at one end of the pipe 79a And a motor 79b as a drive motor for rotating the motor in a predetermined direction.

  The other end of the pipe 79a is connected to the casing 93a. The coil is driven to rotate at a constant speed by a motor 79b so that the amount of new toner conveyed is constant per drive time, and a constant amount of new toner is supplied into the casing 93a.

  In the developing device 50 configured as described above, an appropriate amount of developer that is uniformly dispersed in the agitating unit 82 and is in a charged state suitable for development is conveyed by the circulation return path 84, and is supplied to the developer carrying unit. 86 to the developing unit 81.

  In the developing unit 81, the developer is transported in the direction opposite to the E1 direction along the developing roller 51 from the developer carrying-in unit 86 by the rotation of the first transporting screw 53. In this process, the first transporting screw 53 and the developing roller In the region facing 51, it is pumped up by the magnet roller and carried on the surface of the developing roller 51.

  The developing roller 51 in which the developer carrying amount is regulated by the developing blade 52 and the layer thickness is regulated, in the developing region between the developing roller 51 and the photosensitive drum 20 due to the rotation and the developing bias by the bias applying means. The developer whose amount is made appropriate by the developing blade 52 is conveyed.

  In the developing area, the developer is sprinkled on the developing sleeve by a magnet roller to form a magnetic brush, and the developing potential acts on the toner in the developer, particularly at the tip of the magnetic brush, by the bias applied by the bias applying means. Then, the toner is electrostatically transferred from the surface of the magnetic carrier to the electrostatic latent image formed on the surface of the photosensitive drum 20, and the electrostatic latent image is visualized as a toner image of a predetermined color. The toner blade charging is also promoted by the regulation by the developing blade 52, and even if the charge amount is reduced during the conveyance process from the stirring unit 82 to the developing unit 81, the decrease is compensated.

  The developer that has consumed toner by the development is returned to the storage chamber 58 of the developing case 55 as the developing roller 51 rotates. The developer conveyed to the downstream end of the second storage chamber 59 in the E1 direction by the rotation of the second conveying screw 54 is sent out of the developing unit 81 from the developer carrying-out part 87, and again through the circulation forward path 85. It enters the stirring unit 82.

  As described above, in the developing unit 81, the developer stirred and conveyed by the conveying screw 53 is pumped up by the magnetic force of the magnet roller and carried on the developing sleeve, and is sucked and conveyed to the developing region facing the photosensitive drum 20, Toner is supplied to the latent image on the photosensitive drum 20 for development. The developer that has consumed the developed toner is released from the surface of the developing sleeve into the storage chamber 58, stirred with the developer in the storage chamber 58 by the transport screw 53, and pumped up again to the surface of the developing sleeve. The magnet block is arranged to repeat such a cycle.

  In such a cycle, since the toner in the developer is consumed, the toner density is lowered. The decrease in the toner density is detected by the toner density detection sensor 56 when the developer passes through the second storage chamber 59. When the output value indicating the toner density detected by the toner density detection sensor 56 and input to the control means 65 is lower than the control value of the toner density which is the control information stored in the control means 65, the control is performed. The means 65 drives the toner replenishing unit 79 to supply new toner from the toner hopper 9 to the stirring unit 82.

  At this time, the agitator 93 causes the supplied new toner to be convected while being agitated and mixed in the developer. As a result, the replenished new toner diffuses into the existing developer of the developing device 50. In the process, the supplied new toner is charged by friction with the carrier and other toner in the developer. In this way, the new toner is uniformly dispersed in the existing developer by the agitating unit 82 and is in a charged state suitable for development.

  In this way, the control means 65 collates and compares the output value and the control value so that the toner density of the developer becomes a predetermined value suitable for development, and the toner replenishment operation by feedback control is performed. Done. As a result, the mixing ratio of the toner to the carrier is always kept at an appropriate value, and a high-quality image can be obtained.

  As described above, in the developing device 50, the developer is agitated by the agitating unit 82 and is brought into a state suitable for development. Therefore, in the developing unit 81, the developer is transported by the developing roller 51. It is only necessary to perform the main purpose, and the stirring action of the developer is not required or it is only necessary to ensure the stirring action to the minimum, and the configuration of the developing unit 81 is thereby simplified. Therefore, the developing unit 81 can be downsized, and particularly, various members can be closely packed, and the configuration around the photosensitive drum 20 for forming a color image can be downsized, and there is a margin in the arrangement of the various members.

  In addition, the ambient temperature tends to be higher around the photosensitive drum 20, the temperature of the developer located around the photosensitive drum 20 is likely to be high, and the developer that has become high has a development quality such as aggregation. Although this may cause a decrease, the size of the developing unit 81 is reduced, so that the amount of the developer stored in the developing unit 81 is reduced, and the majority of the developer is stored and stored in the stirring unit 82. Therefore, by disposing the stirring unit 82 at a position that is favorable for storage of the developer, the frequency of exposure of the developer to the high temperature is reduced, and the quality and developing performance of the developer are maintained.

  In addition, the stirring unit 82 for stirring the developer can be disposed in a relatively vacant space inside the image forming apparatus 100. Since a part of the reflux portion 83, that is, the hanging portion 88 and the tube 92a are made of a flexible tube, the handling is easy, the transportability of the developer is ensured, and the attachment and detachment is easy.

  Here, as described above, in order to perform good development and image formation, the balance of the developer amount in the developing unit 81 and the agitating unit 82 is important. The amount of the developer is determined not only by the amount of the developer in the stirring unit 82 but also by the amount of the developer in the circulation return path 84 that connects them and conveys the developer from the stirring unit 82 to the developing unit 81. In order to optimize the amount of developer in the portion 81, it is necessary to consider the amount of developer in the circulation return path 84 as well.

  Therefore, in the developing device 50 and the image forming apparatus 100, the developer in the first storage chamber 58 acquired by the detection signal of the agent surface position detection sensor 66 when the control unit 65 functions as the developer transport amount control unit. The first information regarding whether or not the liquid surface position is at the position where the liquid surface position detection sensor 66 is disposed, and the second information regarding the rotational speed of the first conveying screw 53 acquired by the control of the motor 64. Based on this, the developer conveyance amount by the circulation return path 84 is controlled.

This control will be described below.
As shown in FIG. 5, the agent surface position detection sensor 66 is disposed in the vicinity of the upstream end portion of the first storage chamber 58 in the developer transport direction by the first transport screw 53.

  Here, the relationship between the drug surface position and the output of the drug surface position detection sensor 66 will be described with reference to FIG. As shown in FIG. 6A, the agent surface position detection sensor 66 has a disc-shaped detection surface 66a, and the developer is covered up to a detection height which is a detection position at a substantially central position thereof. Then, as shown in FIG. 5B, the output changes from the output off state to the output on state. In FIG. 7B, the transition region indicates the output from when the agent surface position is applied to the detection surface 66a until reaching the detection height. The transition region is small, the response level of the drug surface position detection sensor 66 is high, and the output is switched between on and off.

  Accordingly, the agent surface position detection sensor 66 is effective as a limiter for a predetermined value for determining whether the agent surface position is above or below the detection height. However, except in a few cases in the transition region near the detection height, it can only determine whether the powder level is above or below the detection height, and how much the actual drug surface position is from the detection height Although it does not have a function of determining whether or not there is a deviation, it is difficult to perform fine control of the developer conveyance amount by itself.

  Therefore, in the developing device 50, the surface level of the sensor 70 having such characteristics is increased or decreased by changing the rotation speed of the first conveying screw 53, and the surface level of the surface is intentionally detected. The output of 66 is changed to a detected height so as to optimize the amount of developer in the developing section 81, and the actual transport amount is determined from the number of rotations of the first transport screw 53.

Here, the developer amount (M [g / s]) transported by the first transport screw 53 is a passing cross-sectional area (S [cm ^) that is a cross-sectional area of the first transport screw 53 at a site where the developer is transported. 2]), an axial feed speed (V [cm / s]) that is the speed at which the first transport screw 53 feeds the developer in the axial direction, and the bulk density of the developer that affects the transport efficiency at that time ( ρ [g / cm ^ 3]) and is estimated by the following formula (Formula 1).
(Formula 1) M = ρVS

Further, the relationship between the axial feed speed (V [cm / s]) and the rotational speed of the first conveying screw 53, in other words, the rotational speed (R [rpm]) is as shown in FIG. ).
(Formula 2) V = kR (where k is a proportional coefficient)

Next, the passing cross-sectional area (S [cm ^ 2]) is as follows.
As shown in FIG. 8A, in the cross section perpendicular to the axial direction of the first transport screw 53, the developer transported by the first transport screw 53 is in a region where the blade portion 53b exists in the same cross section. It is only the developer which exists in the overlapping and shaded area. For example, the developer present in the region surrounded by the broken-line circle in FIG. 5A between the first conveying screw 53 and the developing roller 51 is restrained by the magnetic force of the magnet roller. 53 is not conveyed.

Thus, since the developer is transported in such a region, the height (h) of the powder surface equal to the agent surface position as shown in FIG. S [cm ^ 2]), the diameter of the portion including the blade portion 53b of the first conveying screw 53 is D, and the diameter of only the shaft portion 53a is d. There is a relationship represented by (Expression 3) and the following expression (Expression 4). Since the diameter D and the diameter d are constants, the powder surface height (h) is proportional to the passage cross-sectional area (S).
(Expression 3) S = (π−φ) D ^ 2/4 + [(h−1 / 2) D] ^ 2 * tan (φ) −π (d / 2) ^ 2
(Formula 4) 2d / D-1 = cos (φ)

  In this embodiment, since the shape of the first conveying screw 53 is relatively simple, the relationship between the passage cross-sectional area (S) and the height (h) of the powder surface is calculated by the simple equation (Equation 3). Although it was possible to formulate as shown in (Equation 4), even in the case of a more complicated geometrical arrangement, the cross-sectional area (S) is proportional to the height (h) of the powder surface What you do does not change, and if you actually measure it, the relationship becomes clear.

The following formula (Formula 5) is a simplified version of the above formulas (Formula 1) to (Formula 4). From this equation, when the developer amount (M) transported by the first transport screw 53 and the bulk density (ρ) of the developer are constant, the rotational speed (R) of the first transport screw 53 and the powder surface There is a uniform inverse proportion relationship with the height (h) of the powder. When the rotational speed is increased, the powder surface height is decreased, and when the rotational speed is decreased, the powder surface height is decreased. You can see that it rises.
(Formula 5) h∝M / (ρ * R) or M∝h * ρ * R

  According to the above formula (formula 5), for example, if the amount of developer (M) transported by the first transport screw 53 simply increases, the height (h) of the powder level increases, and the surface level detection sensor The output of 66 will exceed the changing detection height. However, when the rotational speed (R) of the first conveying screw 53 is controlled so that the height (h) of the powder surface is always at the detection height at which the output of the agent surface position detection sensor 66 changes, the development is performed. If the bulk density (ρ) of the agent and the rotation speed (R) of the first conveying screw 53 are known, the height (h) of the powder surface is the detection height at which the output of the agent surface position detection sensor 66 changes. The developer amount (M) transported by the first transport screw 53 is determined under the above conditions.

  The control means 65 functioning as the developer transport amount control means is a developer transport amount in which the same amount of developer as the developer amount (M) is transported from the agitating portion 82 toward the developing portion 81, in other words, development. It is detected as the agent supply amount. At this time, the control means 65 functioning as the developer conveyance amount control means determines whether or not the developer surface position of the developer in the first storage chamber 58 is at the position where the agent surface position detection sensor 66 is disposed, that is, the detection height. At the timing when the first information related to this indicates that whether or not the dosage surface position is at such a detection height, the second information related to the rotational speed of the first conveying screw 53 is acquired, and this Based on the second information, the amount of developer transported from the stirring unit 82 toward the developing unit 81, that is, the transport amount is detected. Based on the detected transport amount, the control unit 65 that functions as a developer transport amount control unit controls the amount of developer transported from the stirring unit 82 toward the developing unit 81 to be appropriate.

  FIG. 9 shows the screw rotation speed, that is, the rotation speed (R) of the first conveying screw 53 and the height (h) of the powder surface at the detection height at which the output of the agent surface position detection sensor 66 changes. The result of actual measurement of the transport amount, that is, the developer amount (M) transported by the first transport screw 53 with respect to the case where the bulk density (ρ) of the developer used is standard time, maximum time, and minimum time is shown. .

  From the figure, it can be seen that the screw conveyance amount is determined from the screw rotation speed in any state where the bulk density (ρ) of the developer to be used is in the maximum to minimum state. Further, in any state where the bulk density (ρ) of the developer to be used is from the maximum to the minimum, the determined screw conveyance amount is a deviation of about 5 [g / s] from the standard bulk density. It can be seen that the screw conveyance amount can be determined with high accuracy.

  However, in order to determine the screw conveyance amount with higher accuracy, the output of the toner density detection sensor 56 is used. As described above, the toner density detection sensor 56 applies the change in the magnetic permeability depending on the amount of developer existing in the measurement space, but the amount of developer present in the measurement space is the amount of developer. Since this is equivalent to the bulk density, the state of the bulk density of the developer is determined by the output value. As shown in FIG. 10, the decrease in toner density (TC) and bulk density (ρ) and the increase in voltage Vout, which is the output of the toner density detection sensor 56, are in a substantially direct relationship.

  As described above, the signal related to the toner density detected by the toner density detection sensor 56 is input to the control means 65. Therefore, the control means 65 uses the fact that the output of the toner density sensor changes uniformly with respect to the bulk density (ρ) of the developer, as shown in FIG. The third information related to the bulk density is obtained by obtaining the bulk density of the developer transported by one transport screw 53, and more accurate developer amount (M) is determined from the relationship shown in FIG. To do. The developer amount (M) is set as the transport amount by the control means 65 that functions as the developer transport amount control means.

A specific example of the control described above will be shown as an example.
Example 1
In the present embodiment, the first conveying screw is controlled by the control means 65 functioning as the rotation speed control means so that the height of the drug surface, that is, the height (h) of the powder surface is always the detection height of the drug surface position sensor 66. The number of rotations of 53 is controlled so that the first information indicates whether or not the height (h) of the powder surface is at the detected height.

  Specifically, when the output of the agent surface position detection sensor 66 is in the on state, the control means 65 that functions as the rotation speed control means increases the rotation speed of the first conveying screw 53, and the agent surface position detection sensor. The powder level is pulled down to the transition region where the output of 66 starts to decrease. When the conveyance amount determined from the rotation speed at this time exceeds a predetermined upper limit range of the conveyance amount, that is, a threshold value, the control unit 65 functioning as the developer conveyance amount control unit The rotational speed of the rotor 90d is decreased, or the flow rate adjustment valve 92e is throttled to suppress the air flow rate sent from the air pump 92b and sent to the joint pipe line 92c, and the transport amount supplied to the developing unit 81 is lowered.

  Conversely, when the output of the surface detection sensor 66 is in the off state, the control means 65 that functions as the rotation speed control means decreases the rotation speed of the first conveying screw 53 and outputs the output of the surface detection sensor 66. Pull the powder surface into the transition region where it begins to increase. When the conveyance amount determined from the number of rotations at this time falls below a predetermined lower limit of the conveyance amount, that is, a threshold value, the control unit 65 that functions as the developer conveyance amount control unit is configured so that the rotor 90d of the rotary feeder 90 Or the flow rate adjustment valve 92e is opened to increase the flow rate of air sent from the air pump 92b and sent to the joint pipe line 92c, and the transport amount supplied to the developing unit 81 is increased.

Example 2
In the present embodiment, the first information indicates that the powder level height (h) is at the detection level of the drug surface position detection sensor 66, that is, the detection level is greater than or exceeds the detection level. As a condition, the number of revolutions of the first conveying screw 53 is increased by the control means 65 functioning as the number of revolutions control means.

  Specifically, even during normal operation, that is, when the output of the drug surface position detection sensor 66 is off or the output of the drug surface position detection sensor 66 is on, a predetermined timing elapses after it is turned on. Before the operation, the rotation speed of the first conveying screw 53 is fixed at a standard speed, and when the powder surface height is lower than the detection height of the agent surface position detection sensor 66, the developer conveying amount control means is used. The functioning control means 65 increases the rotational speed of the rotational speed of the rotor 90d of the rotary feeder 90, or opens the flow path adjusting valve 92e to increase the flow rate of air sent from the air pump 92b and sent to the joint pipe line 92c. The conveyance amount supplied to the section 81 is increased so that the height of the powder surface becomes the detection height of the agent surface position detection sensor 66.

  On the other hand, when the output of the agent surface position detection sensor 66 is in the on state, the control means 65 that functions as the rotation speed control means has the first conveying screw 53 at a predetermined timing after being turned on. The rotational speed is increased, and the powder level is lowered to the transition region where the output of the drug surface position detection sensor 66 starts to decrease. When the conveyance amount determined from the rotation number at this time exceeds a predetermined upper limit range of the conveyance amount, that is, a threshold value, the control unit 65 that functions as the rotation number control unit The control unit 65 that sets the rotation number to be an average value of the standard rotation number and the increased rotation number when the powder level has fallen to the transition region, and functions as a developer conveyance amount control unit, The rotational speed of the rotor 90d of the rotary feeder 90 is reduced until the powder level falls to the transition region where the output of the drug surface position detection sensor 66 starts to decrease, or the flow path adjustment valve 92e is throttled and sent from the air pump 92b to the joint pipe. The flow rate of air supplied to 92c is suppressed, and the transport amount supplied to the developing unit 81 is reduced. Then, the rotation speed of the 1st conveyance screw 53 is returned to a standard speed.

  The timing at which the screw rotation speed is increased can be controlled with higher accuracy if the interval is shortened. In this embodiment, however, a printing start instruction, that is, an image formation instruction in the image forming apparatus 100 is issued, and the developing device It is implemented only at the timing when 50 starts operation.

  A comparison between the case where the control operation of the transport amount is performed and the case where the transport amount is not performed is as follows. When the control operation is not performed, the developer amount in the developing section varies in the range of about 150 g to 250 g with respect to the developer amount of 1000 g in the entire area of the used developing device, and 10% when viewed in terms of the total developer amount. When viewed in the developing section, a fluctuation of about 50% occurred. However, when this control operation is performed, even when this is performed using only the first and second information without using the third information, the amount of variation in the developing unit is reduced to about 10%. This value is sufficient to prevent image density unevenness due to the developer phenomenon in the developing portion and background fogging due to the developer phenomenon in the stirring portion. Further, when the third information is also used, the fluctuation amount in the developing unit is reduced to 5% or less, and more accurate conveyance amount control is possible.

  In this way, by using the method for determining the transport amount, and controlling the developer supply amount to the developing unit based on the determination result, the transport amount is stabilized within a predetermined range, and the developer amount in the developing unit is reduced. The predetermined amount is maintained to prevent image density unevenness and background fogging.

  However, in such a control operation, an operation for determining the conveyance amount from the rotation speed is performed, but the determination of the conveyance amount is not performed, and the upper and lower limits are given to the rotation speed itself, and the developing unit is directly determined from the rotation value. You may make it control the conveyance amount supplied to 81. FIG. Values relating to the transport amount and the rotation speed used as the threshold value are stored in the control means 65 functioning as the developer transport amount control means and the control means 65 functioning as the rotation speed control means, respectively.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  For example, the rotation speed control means, the developer discharge amount control means, the developer transport air volume control means, and the developer transport amount control means are each realized as a function of the control means 65 and are provided in the developing device. May be provided independently.

In the above-described embodiment, the piezoelectric element is used as the agent surface position detecting means, but other types of sensors may be used as long as they detect whether the agent surface position is at a predetermined position.
The toner density detecting means has an advantage that the detection accuracy can be improved by detecting the toner density of the developer in the developing unit, but the toner density may be detected at other parts.

  The developer is not limited to the two-component developer but may be a one-component developer.

  Similarly to a so-called tandem type image forming apparatus, a so-called one-drum type image forming apparatus that sequentially forms toner images of respective colors on a single photosensitive drum and sequentially superimposes the color toner images to obtain a color image. Applicable. Further, the present invention can be applied not only to a color image forming apparatus but also to a monochrome image forming apparatus. In any type of image forming apparatus, a toner image of each color may be directly transferred onto a transfer sheet or the like without using an intermediate transfer member.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

20, 20Y, 20M, 20C, 20BK Image carrier 50, 50Y, 50M, 50C, 50BK Developer 51, 51Y, 51M, 51C, 51BK Developer carrier 53 Developer transport member 56 Toner density detection means 65 Developer transport Volume control means, rotation speed control means 66 Agent surface position detection means 81 Developing section 82 Stirring section 84 Developer conveying means 100 Image forming apparatus

JP 2009-198967 A JP-A-8-36294 JP 2009-58939 A JP 2009-204630 A Japanese Patent No. 3349286 Japanese Patent No. 3391926

Claims (6)

A developing unit including a developer carrier disposed opposite to the image carrier and carrying a developer;
An agitation unit for agitating the developer supplied to the development unit;
Developer transport means for transporting the developer from the stirring unit toward the developing unit;
The developing unit conveys the developer by its rotation, a developer conveying member on which the developer being conveyed is carried on the developer carrying member, and a developer in a developer conveying region by the developer conveying member And a drug surface position detecting means for detecting whether or not the liquid surface position is at a predetermined position,
Based on the first information on whether or not the agent surface position is at a predetermined position and the second information on the number of rotations of the developer conveying member detected by the agent surface position detecting means. have a developer conveying quantity control means for controlling the amount of the developer conveyed by the powder transport means,
The developer conveyance amount control means determines the conveyance amount based on the second information at a timing when the first information indicates whether or not the agent surface position is at a predetermined position. control and,
A developing device comprising: a rotation speed control means for controlling the rotation speed so that the first information indicates whether or not the agent surface position is at a predetermined position . The developing device according to claim 1,
The developer conveying amount control unit controls the conveying amount based on first information, second information, and third information related to a bulk density of the developer. The developing device according to claim 2, wherein
A toner concentration detecting means for detecting the toner concentration in the developer;
3. The developing device according to claim 3, wherein the third information is obtained based on the toner density detected by the toner density detecting means. The developing device according to claim 3.
The developing device according to claim 1, wherein the toner concentration detecting means detects the toner concentration of the developer in the developing section. In the developing device according to any one of claims 1 to 4,
A developing device comprising: a rotation speed control means for increasing the rotation speed on condition that the first information indicates that the agent surface position is at a predetermined position . An image forming apparatus comprising the developing device according to claim 1 .

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