JP4645660B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device used in an electrophotographic image forming apparatus and an image forming apparatus using the developing device. The present invention particularly relates to a trickle-type developing device that supplies a new developer little by little and discharges a deteriorated developer little by little, and an image forming apparatus using the developing device.

  As a developing method used in an electrophotographic image forming apparatus, a one-component developing method using toner as a main component of a developer and a two-component developing method using toner and a carrier as main components of a developer are known. Yes.

  In the two-component development method using toner and carrier, both toner and carrier are charged with a predetermined polarity by frictional contact between the toner and carrier, so that the stress received by the toner is higher than that in the one-component development method using one-component developer. It has the feature that there are few. Since the surface area of the carrier is larger than that of the toner, the carrier is less likely to become dirty due to the toner adhering to the surface of the carrier. However, due to long-term use, dirt (spent) adhering to the carrier surface increases, and as a result, the ability to charge the toner gradually decreases. As a result, the problem of fogging and toner scattering occurs. In order to extend the life of the two-component developing device, it is conceivable to increase the amount of carrier accommodated in the developing device, but this is not desirable because it leads to an increase in the size of the developing device.

In order to solve the above-mentioned problems related to the two-component developer, Patent Document 1 discloses that a new developer is gradually supplied into the developing device and a developer whose charging performance is deteriorated is gradually discharged from the developing device. Discloses a so-called trickle-type developing device that suppresses an increase in deteriorated carriers. This developing device is configured to discharge the excess deteriorated developer by using the fluctuation in the developer volume and to keep the developer bulk level in the developing device substantially constant. According to this trickle-type developing device, the deteriorated carrier in the developing device is gradually replaced with a new carrier, and the charging performance of the carrier in the developing device can be kept substantially constant.
JP 59-1000047 A

  However, the volume of the developer in the developing device changes depending on the state of the developer in the developing device, that is, depending on the toner concentration and the deterioration state of the carrier. However, the proportion of the contents constituting the developer is different.

  The toner concentration in the developing device is detected by, for example, a toner concentration detection sensor that detects the magnetic permeability of the developer. For this reason, the measurement accuracy of the toner concentration detection sensor is not so high, and the toner concentration indicated as the measurement value may be different from the true toner concentration. Further, the toner concentration obtained from the toner concentration detection sensor may show an incorrect toner concentration due to the state of the developer being charged around the toner concentration detection sensor and the fluctuation of the surrounding environment of the image forming apparatus.

  Due to various factors as described above, the toner density obtained from the toner density detection sensor may be detected to be higher than the appropriate reference toner density. In a trickle-type developing device, the bulk level of the developer in the developing device is controlled so as to be kept substantially constant, so if it is detected that the toner concentration is high at any moment, Until the toner density of the toner returns to an appropriate reference toner density, normal image formation is continued without supplying the developer for a while. When the toner concentration in the developing device returns to the reference toner concentration, the amount of toner in the developing device, that is, the amount of developer is reduced, so that the bulk level of the developer in the developing device is lowered. A decrease in the bulk level of the developer in the developing device means that the developer is insufficient in the developing device. In order to stir the developer in the developing device, a stirring screw is used. Usually, the stirring screw is disposed along the developing roller in order to transport the developer while stirring the developer in the longitudinal direction of the developing roller. In this state, when the developer is transported by the stirring screw, the thin portion of the developer moves in accordance with the spiral movement of the screw, so that the developing roller is supplied unevenly corresponding to the screw. The Rukoto. The influence of uneven toner supply appears on the formed image. Therefore, the conventional trickle-type developing device has a problem that a high-quality image cannot be maintained because a so-called screw unevenness phenomenon reflecting non-uniform toner supply by a stirring screw occurs.

  Therefore, the technical problem to be solved by the present invention is that a good image can be obtained over a long period of time by minimizing fluctuations in the toner concentration and the bulk level of the developer in the trickle type developing apparatus using a two-component developer. It is an object of the present invention to provide a developing device and an image forming apparatus capable of forming images.

Means and actions / effects for solving the problems

In order to solve the technical problem, according to the present invention,
An agitating member that agitates a developer in a developing tank containing toner and a carrier while being conveyed along a conveying path of the developing tank, and the developer in the developing tank that is disposed adjacent to the agitating member and is agitated is an electrostatic latent image carrier. A developer carrying body to be supplied to the developing device,
A developer supply tank for supplying toner and carrier to the developer tank;
A toner concentration detection sensor for detecting a toner concentration in the developing tank;
A discharge mechanism that is provided in the developing tank and discharges the developer in the developing tank that has exceeded the amount outside the developing tank when the amount of the developer in the developing tank exceeds a predetermined amount;
Developer amount detecting means for detecting the amount of developer in the developing tank in the developing tank;
Stirring member rotation control means for controlling the rotation speed of the stirring member;
Control means for controlling a replenishment operation for replenishing the developer tank with replenishment toner and carrier from the developer replenishment tank when the toner concentration detected by the toner concentration detection sensor is lower than a predetermined reference toner density; Prepared
The stirring member includes a first screw and a second screw disposed to face the first screw,
The transport path includes a first transport path in which the first screw is disposed, a second transport path in which the second screw is disposed, a downstream side of the first transport path, and a second transport path. A first communication path connecting the upstream side; a second communication path connecting the downstream side of the second transport path and the upstream side of the first transport path; and the first transport path, the first communication path, and the first A circulation path through which the developer in the developing tank circulates is formed by the two transport paths and the second communication path,
The agitation member rotation control means further embeds air in the developer tank when the developer amount detection means detects that the amount of developer in the developer tank is below a predetermined level in the developer tank. There is provided a developing device characterized in that the number of rotations of the agitating member is increased so that the apparent volume of the developer in the developing tank increases .

  According to the developing device, when the developer amount detecting means detects that the developer amount in the developing tank is below a predetermined level by the developer amount detecting means, the rotation speed of the stirring member is Is up. Since the developer is vigorously stirred in the developing tank due to the increase in the number of rotations of the stirring member, the developer in the developing tank may entrap more air. The apparent volume of the developer in the developing tank increases due to the inclusion of air in the developer in the developing tank. As a result, the liquid level in the developing tank can be recovered, and image defects such as density unevenness can be suppressed.

  Although the developer amount detecting means can be realized in various forms, the developer amount detecting means has a liquid level detecting sensor for detecting the liquid level of the developer in the developing tank in the developing tank. Configured.

  Although the liquid level detection sensor can be realized in various forms, the liquid level detection sensor is composed of a pair of light emitting elements and light receiving elements arranged in the developing tank, and the light emitting element is made of the developer in the developing tank. Is configured to detect the level of the developer in the developing tank in the developing tank by blocking the light beam from the developing tank.

  When a predetermined purpose is achieved, it is preferable to prevent an excessive load from being applied to the stirring member. Therefore, when the developer amount detecting means determines that the developer amount in the developing tank has returned to a predetermined level in the developing tank, the stirring member rotation control means determines the rotation speed of the stirring member as the original rotation speed. Return to.

In order to solve the technical problem, according to the present invention,
An agitating member that agitates a developer in a developing tank containing toner and a carrier while being conveyed along a conveying path of the developing tank, and the developer in the developing tank that is disposed adjacent to the agitating member and is agitated is an electrostatic latent image carrier. A developer carrying body to be supplied to the developing device,
A developer supply tank for supplying toner and carrier to the developer tank;
A toner concentration detection sensor for detecting a toner concentration in the developing tank;
A discharge mechanism that is provided in the developing tank and discharges the developer in the developing tank that has exceeded the amount outside the developing tank when the amount of the developer in the developing tank exceeds a predetermined amount;
Stirring member rotation control means for controlling the rotation speed of the stirring member;
Control means for controlling a replenishment operation for replenishing the developer tank with replenishment toner and carrier from the developer replenishment tank when the toner concentration detected by the toner concentration detection sensor is lower than a predetermined reference toner density; Prepared
The stirring member includes a first screw and a second screw disposed to face the first screw,
The transport path includes a first transport path in which the first screw is disposed, a second transport path in which the second screw is disposed, a downstream side of the first transport path, and a second transport path. A first communication path connecting the upstream side; a second communication path connecting the downstream side of the second transport path and the upstream side of the first transport path; and the first transport path, the first communication path, and the first A circulation path through which the developer in the developing tank circulates is formed by the two transport paths and the second communication path,
The agitating member rotation control unit further includes the developer in the developing tank in the developing tank when the toner density detecting sensor detects a toner density higher than a reference toner density by a predetermined amount or more . A developing device is provided in which the rotational speed of the stirring member is increased to a rotational speed that increases the bulk .

  In a so-called trickle-type developing device having a discharge mechanism for discharging the developer in the developing tank exceeding the predetermined amount when the developer amount in the developing tank exceeds a predetermined amount, the toner concentration in the developing tank is The fact that it is detected that the toner density is higher than the reference toner concentration means that since the replenishment operation is not performed for a while, the toner is consumed and the amount of developer in the developing tank in the developing tank is near in the future. Expected to decrease. According to the developing device, when it is detected that the current toner density is higher than the reference toner density by a predetermined value or more, the developer amount detection means is used to determine the amount of developer in the developing tank without determining the amount of developer. The stirring member rotation control means controls so as to increase the rotation speed of the member. Since the developer is vigorously stirred in the developing tank due to the increase in the number of rotations of the stirring member, the developer in the developing tank may entrap more air. The apparent volume of the developer in the developing tank increases due to the inclusion of air in the developer in the developing tank. As a result, the liquid level in the developing tank can be recovered, and image defects such as density unevenness can be suppressed.

The developing device described above is agitated while transporting a rotatable electrostatic latent image carrier that carries an electrostatic latent image on its peripheral surface, and the developer in the developing tank containing toner and carrier along the transport path of the developing tank. And an agitating member that is disposed adjacent to the agitating member and that supplies the agitated developer in the developing tank to the electrostatic latent image bearing member.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the following description, terms indicating a specific direction (for example, “up”, “down”, “left”, “right”, and other terms including them, “clockwise direction”, “counterclockwise” ”) Is used to facilitate understanding of the invention with reference to the drawings, and the present invention should not be construed as being limited by the meaning of these terms. Further, in the image forming apparatus 1 and the developing device 34 described below, the same reference numerals are used for the same or similar components.

  The image forming apparatus 1 according to an embodiment of the present disclosure and the developing device 34 used in the apparatus will be described with reference to FIGS.

[Image forming apparatus]
FIG. 1 shows portions related to image formation of an electrophotographic image forming apparatus 1 according to the present invention. The image forming apparatus 1 may be any of a copier, a printer, a facsimile machine, and a multi-function machine having a combination of these functions. The image forming apparatus 1 includes a photoreceptor 12 that is an electrostatic latent image carrier. In the embodiment, the photoconductor 12 is formed of a cylindrical body, but the present invention is not limited to such a form, and an endless belt type photoconductor can be used instead. The photosensitive member 12 is drivingly connected to a motor (not shown), and is rotated in the direction of the arrow based on the driving of the motor. Around the photoconductor 12, a charging device 26, an exposure device 28, a developing device 34, a transfer device 36, and a cleaning device 40 are arranged along the rotation direction of the photoconductor 12.

  The charging device 26 charges the photoreceptor layer that is the outer peripheral surface of the photoreceptor 12 to a predetermined potential. In the embodiment, the charging device 26 is represented as a cylindrical roller. However, instead of this, other types of charging devices (for example, a rotary or fixed brush-type charging device or a wire-discharge-type charging device) may be used. Can be used. The exposure device 28 disposed in the vicinity of the photoreceptor 12 or away from the photoreceptor 12 emits image light 30 toward the outer peripheral surface of the charged photoreceptor 12. On the outer peripheral surface of the photoconductor 12 that has passed through the exposure device 28, an electrostatic latent image is formed that includes a portion where the image light 30 is projected and a portion where the potential is attenuated and a portion where the charged potential is substantially maintained. In the embodiment, the portion where the potential is attenuated is the electrostatic latent image portion, and the portion where the charged potential is substantially maintained is the electrostatic latent image non-image portion. The developing device 34 visualizes the electrostatic latent image using the developer 3 in the developing tank described later. Details of the developing device 34 will be described later. The transfer device 36 transfers the visible image formed on the outer peripheral surface of the photoconductor 12 to a paper 38 such as paper or film. In the embodiment shown in FIG. 1, the transfer device 36 is illustrated as a cylindrical roller, but other types of transfer devices (for example, a wire discharge transfer device) may be used. The cleaning device 40 collects untransferred toner remaining on the outer peripheral surface of the photoconductor 12 without being transferred onto the paper 38 by the transfer device 36 from the outer peripheral surface of the photoconductor 12. In the embodiment, the cleaning device 40 is illustrated as a plate-shaped blade, but other types of cleaning devices (for example, a rotary or fixed brush type cleaning device) may be used instead.

  When the image forming apparatus 1 having such a configuration forms an image, the photoconductor 12 rotates, for example, counterclockwise based on driving of a motor (not shown). At this time, the outer peripheral portion of the photoreceptor 12 that passes through the charging device 26 is charged to a predetermined potential by the charging device 26. The image light 30 is exposed to the outer peripheral portion of the charged photoconductor 12 by the exposure device 28 to form an electrostatic latent image. The electrostatic latent image is conveyed to the developing device 34 along with the rotation of the photosensitive member 12 and is visualized by the developing device 34. The visualized toner image is conveyed to the transfer device 36 along with the rotation of the photoconductor 12 and transferred to the paper 38 by the transfer device 36. The paper 38 to which the toner image has been transferred is conveyed to the fixing device 20 and the toner image is fixed to the paper 38. The outer peripheral portion of the photosensitive member 12 that has passed through the transfer device 36 is conveyed to the cleaning device 40, and the toner remaining on the outer peripheral surface of the photosensitive member 12 without being transferred to the paper 38 is scraped off from the photosensitive member 12.

[Development equipment]
The developing device 34 includes a two-component developer including a non-magnetic toner (hereinafter simply referred to as toner) and a magnetic carrier (hereinafter simply referred to as carrier), and a developing tank 66 that accommodates various members. . The developing tank 66 has an opening that is open toward the photosensitive member 12, and a developing roller 48 is provided in a space formed in the vicinity of the opening. The developing roller 48 as a developer carrying member is a cylindrical member, and is pivotally supported in parallel with the photosensitive member 12 and through a predetermined developing gap with the outer peripheral surface of the photosensitive member 12.

  The developing roller 48 is a so-called magnet roller having a magnet body 48a that is fixed so as not to rotate, and a cylindrical sleeve 48b (first rotating cylinder body) that is rotatably supported around the magnet body 48a. . Above the sleeve 48b of the developing roller 48, a regulating plate 62 that is fixed to the developing tank 66 and extends in parallel with the central axis of the sleeve 48b of the developing roller 48 is disposed to face with a predetermined regulating gap therebetween. . The magnet body 48a inside the developing roller 48 has five magnetic poles N1, S2, N3, N2, and S1 along the rotation direction of the sleeve 48b. Of these magnetic poles, the main magnetic pole N <b> 1 is disposed to face the photoconductor 12. N2 and N3 of the same polarity that generate a repulsive magnetic field for peeling off the developer on the sleeve 48 b are disposed opposite to each other inside the developing tank 66. The sleeve 48b of the developing roller 48 rotates in the direction opposite to the rotation direction of the photosensitive member 1 (in the counter direction).

  FIG. 2 is a schematic cross-sectional view of the developing device 34 as viewed from above. As shown in FIG. 2, a developer stirring and conveying chamber 67 is formed behind the developing roller 48. The developer stirring and conveying chamber 67 partitions the second conveying path 70 formed in the vicinity of the developing roller 48, the first conveying path 68 away from the developing roller 48, the first conveying path 68 and the second conveying path 70. And a partition wall 76. A developer supply tank 80 is disposed above the upstream side of the first conveyance path 68 in the conveyance direction, and the developer supply tank 80 communicates with the first conveyance path 68 via a supply port 82. . The developer supply tank 80 is filled with a supply developer 2 containing toner as a main component and containing a carrier. The carrier ratio of the replenishment developer 2 is preferably 5 to 40% by weight, more preferably 10 to 30% by weight. Further, a developer recovery tank 90 is disposed below the second transport path 70 in the transport direction, and the developer recovery tank 90 communicates with the second transport path 70 via a recovery port 92. ing.

  At the bottom of the developer supply tank 80, a developer supply roller that is driven and controlled by the control unit 100 is disposed. When the developer supply roller is driven to rotate, an amount of new replenishment developer 2 corresponding to the driving time flows down and is supplied to the first transport path 68 of the developing tank 66.

  A first screw 72 that is a stirring member that transports the developer 3 in the developing tank while stirring the developer 3 in the developing tank is rotatably supported in the first transport path 68. A second screw 74 that rotatably conveys the developer 3 in the developing tank from the first conveyance path 68 to the developing roller 48 while being stirred is rotatably supported on the second conveyance path 70. In this case, the communication path is formed by cutting out the upper portions of the partition walls 76 located at both ends of the first transport path 68 and the second transport path 70. The developer 3 in the developing tank that has reached the downstream end of the first transport path 68 in the transport direction is sent to the second transport path 70 through the communication path, and the downstream end of the second transport path 70 in the transport direction. The developer 3 in the developing tank that has reached 1 is fed into the first transport path 68 through the communication path. As a result, the developer 3 in the developing tank circulates in the developer agitating / conveying chamber according to the direction of the arrow in FIG.

  The first screw 72 and the second screw 74 are spiral screws in which spiral blades are fixed to a shaft at a predetermined pitch. 4 is a schematic cross-sectional view of a part of the developing device 34 as viewed from the side, and corresponds to the right end of FIG. As shown in FIG. 4, the second screw 74 extends to the right side in the drawing and extends above the recovery port 92. The second screw 74 has a connecting path from the second transport path 70 to the first transport path 68 and a position corresponding to the downstream side end of the first transport path 68 so that the spiral direction of the spiral screw is different from that of the other part. Has a reverse blade portion 77 configured in the reverse direction. The pitch of the blades of the second screw 74 is smaller at the downstream end (right end in FIG. 2) in the transport direction than at other portions. As a result, when the second screw 74 rotates, the height of the developer 3 in the developing tank at the downstream end (right end) in the transport direction of the second screw 74 becomes higher than the other portions. That is, the rising of the developer 3 in the developing tank is formed at the downstream end (right end) in the transport direction of the second transport path 70.

  Here, since the developing device 34 employs a so-called trickle system, the developing device 34 has an outlet 75 for allowing the excess developer 3 in the developing tank to flow out. That is, the outflow port 75 is formed by providing the notch 75 in which the upper part of the side wall located at the downstream end (right end) in the transport direction of the second transport path 70 is partially cut out. The developer conveyed by the second screw 74 is blocked by the reverse blade portion 77 in a normal state, so that the developer is transferred from the second conveyance path 70 to the first conveyance path 68 as indicated by solid arrows in FIGS. Be transported. When the developer 3 in the developing tank increases in the developing tank and the liquid level in the developing tank rises, the outflow port 75 provided at the upper part of the side wall against the damming action of the reverse blade 77 is provided in the developer in the developing tank. 3 gets over and overflows to the adjacent collection chamber. Excess developer 3 in the developing tank overflowing into the recovery chamber is conveyed to the recovery port 92 according to the dotted arrow in FIG. 4 and recovered (discarded) to the developer recovery tank 90 via the recovery port 92.

  As shown in FIG. 2, the developer agitation transport chamber 67 is provided with a toner concentration detection sensor 78 that detects the toner concentration in the developer agitation transport chamber 67. For example, the toner concentration detection sensor 78 detects the magnetic permeability of the developer 3 in the developing tank conveyed in the developer agitating / conveying chamber 67 from a change in inductance of the coil. From the magnetic permeability detected by the toner concentration detection sensor 78, the ratio of the toner to the developer 3 in the developing tank is obtained. For example, when the amount of carrier contained in the developer 3 in the developing tank is small, it is detected that the toner ratio is high. On the other hand, when the amount of carrier contained in the developer 3 in the developing tank is large, it is detected that the toner ratio is low. The voltage signal output from the toner concentration detection sensor 78 is input to the control unit 100. Based on the detection signal, a necessary supply amount is calculated and the developer supply roller of the developer supply tank 80 is calculated. Is driven, and a predetermined amount of the replenishment developer 2 is replenished into the developing tank 66.

  In the developing device 34, when the toner concentration of the developer 3 in the developing tank circulating is reduced by the printing operation, the replenishment developer 2 containing toner and a small amount of carrier is replenished from the developer replenishment tank 80. . In the replenishment developer 2, the toner and the carrier are supplied in an integrated form, or the toner and the carrier are supplied separately. The supplied new replenishment developer 2 is mixed and agitated with the existing developer tank developer 3 along the first conveyance path 68 and the second conveyance path 70 of the developer agitation conveyance chamber 67. Be transported. Basically, the toner is consumed by the photoconductor 12, whereas the carrier is accumulated in the developing device 34. However, as the number of printed sheets increases, the charging performance of the carrier gradually decreases. Since the replenishment developer 2 contains a small amount of carrier bulkier than the toner, the amount of the developer 3 in the developing tank in the developing device 34 gradually increases as the replenishment developer 2 is replenished. To do. The developer 3 in the developing tank having an increased volume circulates in the developer agitating / conveying chamber 67. The surplus developer 3 in the developing tank that cannot circulate through the developer agitating / conveying chamber 67 gets over the reverse blade portion 77 and is provided at the downstream end (right end) of the second conveying path 70 in the conveying direction. It flows out from the outlet 75 and is collected in the developer collection tank 90 through the collection port 92.

  As shown in FIG. 5, a liquid level detection sensor 112 that constitutes a developer amount detection unit is provided in the developer stirring and conveying chamber 67. The liquid level detection sensor 112 includes, for example, a light emitting element 112a such as an infrared LED and a light receiving element 112b that receives a light beam 112c from the light emitting element 112a. Then, when the light receiving element 112c detects that the light beam 112c from the light emitting element 112a is shielded by the developer 3 in the developing tank, the liquid level (bulk level) of the developer 3 in the developing tank 66 in the developing tank 66 is detected. ) Is at a predetermined level.

  The first conveyance path 68 and the second conveyance path 70 constituting the developer stirring and conveying chamber 67 are arranged at the same height as shown in FIG. 1 or at different heights as shown in FIG. Various configurations can be taken. Such a liquid level detection sensor 112 is disposed at a higher position in the height direction in the developing tank 66.

  The replenishment amount of the replenishment developer 2 includes the toner concentration of the developer 3 in the developing tank detected by the toner concentration detection sensor 78, image information (dot counter) at the time of image formation, and the developer replenishment tank 80. It is determined based on the carrier ratio to the replenishment developer 2. The carrier ratio with respect to the replenishment developer 2 in the developer replenishment tank 80 is adjusted to the extent that the deterioration of the carrier in the developing device 34 is suppressed and the cost is not increased. As the toner is replenished, the carrier is supplied little by little.

  FIG. 3 is a control block diagram relating to the developing device 34 of the image forming apparatus 1.

  The control unit 100 as a control unit includes a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 104, a RAM (Random Access Memory) 106, and the like. The CPU 102 centrally controls various operations in the image forming apparatus 1 according to various processing programs and tables stored in the ROM 104. In the ROM 104, for example, a toner concentration calculation table for converting / calculating the voltage detected by the toner concentration detection sensor 78 to the toner concentration of the developer 3 in the developing tank, or the toner concentration of the actual developer 3 in the developing tank 3 is stored. A developer replenishment table for calculating the amount of developer to be replenished from the difference between the toner density and the reference toner density is stored. The RAM 106 forms a work area for temporarily storing various programs executed by the control unit 100 and data related to these programs.

  Connected to the CPU 102 are a developing device 34, a developer supply tank 80, a counter 108, and a liquid level detection sensor 112 that constitutes a developer amount detecting means. The operations of the agitating members 72 and 74, the toner density detection sensor 78, and the developing roller 48 constituting the developing device 34 are controlled by the CPU 102 of the control unit 100. The CPU 102 of the control unit 100 is used as a stirring member rotation control unit that controls the rotation speed of the stirring members 72 and 74. The toner density of the developer 3 in the developing tank detected by the toner density detection sensor 78, the image information at the time of image formation, the carrier ratio to the replenishment developer 2 in the developer replenishment tank 80, and the like are stored in the RAM 106. Is temporarily stored.

(Developer)
The two-component developer contains toner and a carrier for charging the toner. In the present invention, a known toner that has been generally used in the image forming apparatus 1 can be used. The particle size of the toner is, for example, about 3 to 15 μm. A toner containing a colorant in a binder resin, a toner containing a charge control agent and a release agent, and a toner holding an additive on the surface can also be used.

  The toner is produced by a known method such as a pulverization method, an emulsion polymerization method, or a suspension polymerization method.

  The binder resin used for the toner is not limited. For example, styrene resin (monopolymer or copolymer containing styrene or styrene-substituted product), polyester resin, epoxy resin, vinyl chloride resin, phenol resin. , Polyethylene resin, polypropylene resin, polyurethane resin, silicone resin, or any mixture of these resins. The binder resin preferably has a softening temperature in the range of about 80 to 160 ° C. and a glass transition point in the range of about 50 to 75 ° C.

  For the colorant, a known material such as carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, ultramarine blue, rose bengal, lake red, etc. should be used. Can do. In general, the addition amount of the colorant is preferably 2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

  As the charge control agent, materials conventionally known as charge control agents can be used. Specifically, for the positively charged toner, for example, nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazole compounds, and polyamine resins can be used as charge control agents. For the negatively charged toner, metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkyl salicylic acid metal compounds, and curixarene compounds can be used as charge control agents. The charge control agent is preferably used at a ratio of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  As the release agent, a known release agent conventionally used as a release agent can be used. As the material for the release agent, for example, polyethylene, polypropylene, carnauba wax, sazol wax, or a mixture of them as appropriate is used. The release agent is preferably used at a ratio of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  Furthermore, a fluidizing agent that promotes fluidization of the developer may be added. As the fluidizing agent, for example, inorganic fine particles such as silica, titanium oxide, and aluminum oxide, and resin fine particles such as acrylic resin, styrene resin, silicone resin, and fluorine resin can be used. In particular, it is preferable to use a material hydrophobized with a silane coupling agent, a titanium coupling agent, silicon oil or the like. The fluidizing agent is preferably added at a ratio of 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner. The number average primary particle size of these additives is preferably 9 to 100 nm.

  As the carrier, a known carrier that has been generally used can be used. Either a binder type carrier or a coat type carrier may be used. The carrier particle size is not limited, but is preferably about 15 to 100 μm.

  The binder type carrier is obtained by dispersing magnetic fine particles in a binder resin, and those having fine particles or a coating layer charged positively or negatively on the surface can be used. The charging characteristics such as polarity of the binder type carrier can be controlled by the material of the binder resin, the chargeable fine particles, and the type of the surface coating layer.

  Examples of the binder resin used for the binder-type carrier include thermoplastic resins such as vinyl resins, polyester resins, nylon resins, polyolefin resins, and the like typified by polystyrene resins, and curable resins such as phenol resins. .

  Magnetic fine particles of the binder type carrier include spinel ferrite such as magnetite and gamma iron oxide, and magnets such as spinel ferrite and barium ferrite containing one or more metals other than iron (Mn, Ni, Mg, Cu, etc.). Plumbite type ferrite, iron or alloy particles having an oxide layer on the surface can be used. The shape of the carrier may be granular, spherical, or needle-shaped. In particular, when high magnetization is required, it is preferable to use iron-based ferromagnetic fine particles. In consideration of chemical stability, it is preferable to use ferromagnetic fine particles of magnetoplumbite type ferrite such as spinel ferrite and barium ferrite containing magnetite and gamma iron oxide. A magnetic resin carrier having a desired magnetization can be obtained by appropriately selecting the type and content of the ferromagnetic fine particles. The magnetic fine particles are suitably added in an amount of 50 to 90% by weight in the magnetic resin carrier.

  Silicone resin, acrylic resin, epoxy resin, fluorine resin, etc. are used as the surface coating material for the binder type carrier. The charge imparting ability of the carrier can be improved by coating and curing these resins on the carrier surface to form a coat layer.

  For example, the charging fine particles or the conductive fine particles can be fixed to the surface of the binder type carrier by, for example, mixing the magnetic resin carrier and the fine particles uniformly and adhering the fine particles to the surface of the magnetic resin carrier. This is done by driving fine particles into the magnetic resin carrier by applying a strong impact force. In this case, the fine particles are not completely embedded in the magnetic resin carrier, but are fixed so that a part thereof protrudes from the surface of the magnetic resin carrier. Organic and inorganic insulating materials are used for the chargeable fine particles. Specifically, organic insulating materials include polystyrene, styrene-based copolymers, acrylic resins, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesin, and cross-linked products thereof such as organic insulating fine particles. is there. The charge imparting ability and the charge polarity can be adjusted to the material of the chargeable fine particles, the polymerization catalyst, the surface treatment and the like. As the inorganic insulating material, negatively charged inorganic fine particles such as silica and titanium dioxide, and positively charged inorganic fine particles such as strontium titanate and alumina are used.

  The coat type carrier is a carrier in which carrier core particles made of a magnetic material are coated with a resin, and like the binder type carrier, chargeable fine particles that are charged positively or negatively can be fixed to the surface of the carrier. The charging characteristics such as the polarity of the coated carrier can be adjusted by selecting the type of surface coating layer and the electrifying fine particles. As the coating resin, the same resin as the binder resin of the binder type carrier can be used.

  The mixing ratio of the toner and the carrier in the developer 3 in the developing tank is adjusted so as to obtain a desired toner charge amount. The toner ratio of the developer 3 in the developing tank is preferably 3 to 20% by weight, more preferably 4 to 15% by weight, based on the total amount of toner and carrier. The replenishment developer 2 filled in the developer replenishment tank 80 contains toner and a small amount of carrier, and the carrier ratio of the replenishment developer 2 is preferably 1 to 50% by weight. More preferably, it is 5 to 30% by weight.

  The operation of the developing device 34 configured as described above will be described.

  During image formation, the sleeve 48b of the developing roller 48 rotates in the direction of the arrow (counterclockwise) based on the driving of a motor (not shown). Due to the rotation of the first screw 72 and the rotation of the second screw 74, the developer 3 in the developer tank existing in the developer stirring and transporting chamber 67 is stirred while being circulated and transported through the first transport path 68 and the second transport path 70. Is done. As a result, the toner contained in the developer and the carrier are in frictional contact with each other and are charged with opposite polarities. In the embodiment, it is assumed that the carrier is positively charged and the toner is negatively charged. The chargeability of the toner and carrier used in the present invention is not limited to such a combination. The outer dimension of the carrier is considerably larger than that of the toner. Therefore, the negatively charged toner adheres around the positively charged carrier mainly based on the electrical attraction force of both.

  The charged developer 3 in the developing tank is supplied to the developing roller 48 while being transported to the second transport path 70 by the second screw 74. The developer is held on the surface side of the sleeve 48 b by the magnetic force of the magnet body 48 a inside the developing roller 48, rotates in the counterclockwise direction together with the sleeve 48 b, and is a regulation plate provided facing the developing roller 48. After the passage amount is restricted at 62, the sheet is conveyed to a development area facing the photoconductor 12. In the developing area, a head (magnetic brush) is formed by the magnetic force of the main magnetic pole N1 of the magnet body 48a. In the development region, the toner is caused by the force applied to the toner by the electric field (electric field in which alternating current is superimposed on direct current) formed between the electrostatic latent image on the photoreceptor 12 and the developing roller 48 to which the developing bias is applied. It moves toward the electrostatic latent image on the photoconductor 12, and this electrostatic latent image is developed into a visible image. The developer that has consumed the toner in the developing region is conveyed toward the developing tank 66 and is developed by the repulsive magnetic field of N3 and N2 of the magnet body 48a provided facing the second conveying path 70 of the developing tank 66. It is peeled off from above and collected into the developing tank 66. The collected developer is mixed with the developer 3 in the developing tank being transported through the second transport path 70.

  When the toner is consumed from the developer 3 in the developing tank by such image formation, it is preferable that an amount of toner corresponding to the consumed amount is supplied to the developer 3 in the developer tank. For this purpose, the developing device 34 includes a toner concentration detection sensor 78 that measures the ratio of the toner to the developer 3 in the developing tank existing in the developer agitating / conveying chamber 67. A developer supply tank 80 is provided above the first conveyance path 68.

  Next, the operation of the developing device 34 according to the first embodiment will be described with reference to FIGS.

  FIG. 6 shows a flowchart of the replenishment operation of the developing device 34 according to the first embodiment of the present invention. FIG. 7 shows the measurement results of the volume transition of the developer 3 in the developer tank in the developer tank 66.

  FIG. 6 shows a subroutine related to replenishment control (liquid level control) of the developing device 34 in the overall control (main routine) (not shown).

  In step S <b> 102, the liquid level (bulk level) of the developer 3 in the developing tank in the developing tank 66 is monitored by the liquid level detection sensor 112 as the developer amount detecting means. In step S110, it is determined whether or not the liquid level (bulk level) of the developer 3 in the developing tank 66 in the developing tank 66 is maintained at a predetermined level. When the liquid level (bulk level) of the developer 3 in the developing tank 66 in the developing tank 66 is maintained at a predetermined level, YES is selected, the subroutine is terminated, and the process returns to the main routine.

  In step S110, if the liquid level (bulk level) of the developer 3 in the developing tank in the developing tank 66 is lowered without maintaining a predetermined level, NO is selected, and the stirring in step S120 is performed. Transition to the member rotation speed up mode.

  In the stirring member rotation speed up mode in step S120, for example, the stirring members 72 and 74 that have been rotating at the normal rotation speed of 200 rpm are increased to the rotation speed of 300 rpm. That is, in the stirring member rotation speed increase mode, as an example, the rotation speed of the stirring members 72 and 74 is increased by 50% compared to the normal operation.

  As the number of revolutions of the agitating members 72 and 74 is increased, the developer 3 in the developing tank is vigorously stirred in the developing tank 66, so that the developer 3 in the developing tank entraps more air. Due to entrapment of a large amount of air in the developer tank developer 3, the apparent volume of the developer tank developer 3 in the developer tank 66 gradually increases, and the liquid level gradually increases. The high rotational speed of the stirring members 72 and 74 is maintained until the liquid level in the developing tank 66 returns to a predetermined level. When the liquid level in the developing tank 66 returns to a predetermined level, the rotation speed of the stirring members 72 and 74 is returned to the original rotation speed. As a result, the liquid level in the developing tank 66 is restored to a predetermined level, and the rotational speeds of the stirring members 72 and 74 are also restored to the original rotational speed. When such a stirring member rotation speed up mode subroutine ends, the process returns to the main routine. Further, since the liquid level (bulk level) of the developer 3 in the developing tank in the developing tank 66 is monitored by the liquid level detection sensor 112, if the liquid level (bulk level) is lowered, A subroutine of the stirring member rotation speed up mode is executed. Therefore, the subroutine is repeatedly executed to maintain the high rotational speed of the stirring members 72 and 74 and to maintain the liquid level in the developing tank 66 at a predetermined level.

  FIG. 7 shows the change in the volume of the developer 3 in the developing tank in the developing tank 66. In FIG. 7, the horizontal axis represents the number of printed sheets (sheets), and the vertical axis represents the volume (ml) of the developer 3 in the developing tank 66 in the developing tank 66. In FIG. 7, the rotation speed of 300 rpm is an embodiment of the present invention in which the normal rotation speed of 200 rpm is increased to 300 rpm due to a decrease in the liquid level. The rotation speed of 200 rpm is a comparative example in which the normal rotation speed of 200 rpm is maintained regardless of the fluctuation of the liquid level.

  As shown in FIG. 7, in the case of the comparative example with the rotation speed of 200 rpm, it takes a considerable time until the liquid level of the developer 3 in the developer tank in the developer tank 66 decreases to return to the predetermined level. Although necessary, in the case of the embodiment of the present invention having a rotational speed of 300 rpm, the liquid level of the developer 3 in the developing tank 66 can return to the predetermined level in a short time.

  By shifting to the stirring member rotation speed up mode in the liquid level control subroutine as described above, the liquid level (bulk level) of the developer 3 in the developing tank in the developing tank 66 is restored to a predetermined level, and image formation is performed. As a result of performing image formation with the apparatus 1, it was confirmed that the stirring member rotation speed increase mode is effective for avoiding the occurrence of image defects such as screw unevenness.

  Next, the operation of the developing device 34 according to the second embodiment will be described with reference to FIG.

  FIG. 8 shows a flowchart of a subroutine for replenishment control of the developing device 34 according to the second embodiment of the present invention. In addition, in order to assist the understanding regarding the subroutine of the replenishment control according to the second embodiment, description will be given while presenting the following specific numerical values, but the present embodiment is not limited by the numerical values, and is merely It is only a numerical value presented as an example.

  The reference toner concentration of the developer 3 in the developing tank stored in the trickle developing device 34 is 7% by weight, and the amount is about 250 g. The amount of toner consumed by one patch image formation is about 0.5 g. The carrier ratio of the replenishment developer 2 is 15% by weight. The replenishment amount of the developer 2 for one replenishment is about 0.6 g, which is about 0.5 g in terms of the toner amount.

  FIG. 8 shows a subroutine related to replenishment control of the developing device 34 in the overall control (main routine) (not shown). In step S <b> 202, the toner concentration detection sensor 78 outputs a voltage signal relating to the current toner concentration of the developer 3 in the developing tank existing in the developer stirring and conveying chamber 67. In step S214, the output voltage signal is converted and calculated by the control unit 100 into a current toner density value. In step S220, it is determined whether or not the current toner concentration is lower than the reference toner concentration (7% by weight). If it is determined that the current toner concentration is lower than the reference toner concentration (7% by weight), the current toner concentration detected by the toner concentration detection sensor 78 and the image information (dot counter) at the time of image formation in step S222. The replenishment amount of the replenishment developer 2 is calculated based on the carrier ratio with respect to the replenishment developer 2 in the developer replenishment tank 80. In step S224, after a predetermined amount of replenishment developer 2 is replenished, the process returns to the main routine.

  If it is determined in step S220 that the current toner density is equal to or higher than the reference toner density, in step S230, the current toner density is the reference toner density (7% by weight) + correction value (0.5% by weight) = 7.5. It is determined whether it is lower than wt%. If it is determined that the current toner concentration is lower than 7.5% by weight, the subroutine ends and returns to the main routine. Depending on the measurement accuracy of the toner concentration detection sensor 78, the state in which the developer 3 in the developing tank is filled around the toner concentration detection sensor 78, and the surrounding environment of the image forming apparatus, the current toner concentration may become the reference toner concentration (7 wt%). ) + Correction value (0.5 wt%) = 7.5 wt% or more, for example, when it is determined that the current toner concentration is 9 wt%, the inside of the developing tank in the developing tank 66 It is predicted that the liquid level of developer 3 will decrease. In that case, in step S240, the mode shifts to the stirring member rotation speed up mode.

  In the stirring member rotation speed up mode in step S240, as described later, the stirring members 72 and 74 that have been rotating at the normal rotation speed of 200 rpm are increased to the rotation speed of 300 rpm or the rotation speed of 350 rpm. That is, in the stirring member rotation speed increase mode, as an example, the rotation speed of the stirring members 72 and 74 is increased by 50% or 75% compared to the normal operation.

  As the number of revolutions of the agitating members 72 and 74 is increased, the developer 3 in the developing tank is vigorously stirred in the developing tank 66, so that the developer 3 in the developing tank entraps more air. Due to entrapment of a large amount of air in the developer tank developer 3, the apparent volume of the developer tank developer 3 in the developer tank 66 gradually increases, and the liquid level gradually increases. The high rotational speed of the stirring members 72 and 74 is maintained until the liquid level in the developing tank 66 returns to a predetermined level. When the liquid level in the developing tank 66 returns to a predetermined level, the rotation speed of the stirring members 72 and 74 is returned to the original rotation speed. As a result, the liquid level in the developing tank 66 is restored to a predetermined level, and the rotational speeds of the stirring members 72 and 74 are also restored to the original rotational speed. When such a stirring member rotation speed up mode subroutine ends, the process returns to the main routine. Further, since the liquid level (bulk level) of the developer 3 in the developing tank in the developing tank 66 is monitored by the liquid level detection sensor 112, if the liquid level (bulk level) is lowered, A subroutine of the stirring member rotation speed up mode is executed. Therefore, the subroutine is repeatedly executed to maintain the high rotational speed of the stirring members 72 and 74 and to maintain the liquid level in the developing tank 66 at a predetermined level.

  Table 1 shows the number of printed sheets from the occurrence of the image defect to the elimination after the shift to the stirring member rotation speed increase mode. In the first embodiment, the normal rotation speed of 200 rpm is increased to 300 rpm based on the prediction of the decrease in the liquid level. In Example 2, the normal rotation speed of 200 rpm is increased to 350 rpm based on the prediction of the decrease in the liquid level. In the comparative example, the normal rotation speed of 200 rpm is maintained regardless of the fluctuation of the liquid level.

ここで、〇印は、スクリュームラ等の画像不良が解消していることを意味し、×印は、スクリュームラ等の画像不良が存在することを意味する。

Here, the symbol “◯” means that image defects such as screw unevenness have been eliminated, and the symbol “x” means that image defects such as screw unevenness exist.

  From Table 1, in the case of Examples 1 and 2, image defects such as screw unevenness are resolved at an early stage, whereas in the comparative example, image defects such as screw unevenness are resolved. It can be seen that it took a large number of printed sheets to reach.

  In the replenishment control subroutine as described above, the liquid level (bulk level) of the developer 3 in the developing tank is restored to a predetermined level in the developing tank 66 by shifting to the stirring member rotation speed up mode, and the image forming apparatus. As a result of image formation at 1, it was confirmed that the stirring member rotation speed increase mode is effective for avoiding image defects such as screw unevenness.

  In each of the above embodiments, the description has been made using specific numerical values, but the present invention is not limited by the numerical values, and is within a range not departing from the scope defined by the claims and equivalents. The present invention can be variously modified.

  In the first embodiment described above, it is detected whether there is a predetermined amount of developer in the developing tank by providing some developer amount detecting means called the liquid level detection sensor 112. It goes without saying that other methods such as the use of a torque detection sensor may be used as long as it is possible to detect whether or not the developer is in a predetermined amount.

  In the second embodiment described above, the replenishment amount is calculated based on the current toner density and the image information (dot counter) at the time of image formation, but a constant amount is replenished without calculating the replenishment amount. It can also be configured.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the developing device of the image forming apparatus shown in FIG. 1 as viewed from above. FIG. 3 is a block diagram relating to a developing device of the image forming apparatus shown in FIG. 2. FIG. 2 is a schematic cross-sectional view of a part of the developing device of the image forming apparatus shown in FIG. 1 as viewed from the side. It is a schematic diagram explaining a mode that the liquid level (bulk level) in a developing tank is detected. 3 is a flowchart of a liquid level control subroutine of the developing device according to the first embodiment of the present invention. The measurement result of the volume transition of the developer in the developing tank is shown. It is a flowchart of the replenishment control subroutine of the developing device according to the second embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1: Image forming device 2: Developer for replenishment 3: Developer in developing tank 12: Photoconductor 20: Fixing device 22: Fixing roller 26: Charging device 28: Exposure device 30: Image light 34: Developing device 36: Transfer device 38: Paper 40: Cleaning device 48: Developing roller (developer carrier)
48a: Magnet body 48b: Sleeve 62: Restriction plate 66: Developing tank 67: Developer stirring and conveying chamber 68: First conveying path 70: Second conveying path 72: First screw (stirring member)
74: Second screw (stirring member)
75: Notch (outlet)
76: partition wall 77: reverse blade portion 78: toner concentration detection sensor 80: developer supply tank 82: supply port 90: developer recovery tank 92: recovery port 100: control unit 102: central processing unit (CPU)
104: Read-only memory (ROM)
106: Read / write memory (RAM)
108: Counter 112: Liquid level detection sensor (developer amount detection means)
112a: light emitting element 112b: light receiving element 112c: light beam

Claims (12)

An agitating member that agitates the developer in the developing tank containing the toner and the carrier while being conveyed along a conveying path in the developing tank, and the developer in the developing tank that is disposed adjacent to the agitating member and carries the electrostatic latent image A developer carrying body to be supplied to the body,
A developer supply tank for supplying toner and carrier to the developer tank;
A toner concentration detection sensor for detecting a toner concentration in the developing tank;
A discharge mechanism that is provided in the developing tank and discharges the developer in the developing tank that has exceeded the amount outside the developing tank when the amount of the developer in the developing tank exceeds a predetermined amount;
Developer amount detecting means for detecting the amount of developer in the developing tank in the developing tank;
Stirring member rotation control means for controlling the rotation speed of the stirring member;
Control means for controlling a replenishment operation for replenishing the developer tank with replenishment toner and carrier from the developer replenishment tank when the toner concentration detected by the toner concentration detection sensor is lower than a predetermined reference toner density; Prepared
The stirring member includes a first screw and a second screw disposed to face the first screw,
The transport path includes a first transport path in which the first screw is disposed, a second transport path in which the second screw is disposed, a downstream side of the first transport path, and a second transport path. A first communication path connecting the upstream side; a second communication path connecting the downstream side of the second transport path and the upstream side of the first transport path; and the first transport path, the first communication path, and the first A circulation path through which the developer in the developing tank circulates is formed by the two transport paths and the second communication path,
The agitation member rotation control means further embeds air in the developer tank when the developer amount detection means detects that the amount of developer in the developer tank is below a predetermined level in the developer tank. A developing device characterized in that the number of revolutions of the stirring member is increased to a number of revolutions that increases the apparent bulk of the developer in the developing tank .   The developing device according to claim 1, wherein the developer amount detecting means includes a liquid level detecting sensor that detects a liquid level of the developer in the developing tank in the developing tank.   The liquid level detection sensor is composed of a pair of a light emitting element and a light receiving element disposed in the developing tank, and the light from the light emitting element is shielded by the developer in the developing tank, thereby developing the developing tank in the developing tank. The developing device according to claim 2, wherein the level of the internal developer is detected. The stirring member rotation control means sets the rotation speed of the stirring member to the original rotation speed when the developer amount detection means determines that the amount of developer in the developing tank in the developing tank has returned to a predetermined level. and returning, developing device according to any one of claims 1 to 3. An agitating member that agitates the developer in the developing tank containing the toner and the carrier while being conveyed along a conveying path in the developing tank, and the developer in the developing tank that is disposed adjacent to the agitating member and carries the electrostatic latent image A developer carrying body to be supplied to the body,
A developer supply tank for supplying toner and carrier to the developer tank;
A toner concentration detection sensor for detecting a toner concentration in the developing tank;
A discharge mechanism that is provided in the developing tank and discharges the developer in the developing tank that has exceeded the amount outside the developing tank when the amount of the developer in the developing tank exceeds a predetermined amount;
Stirring member rotation control means for controlling the rotation speed of the stirring member;
Control means for controlling a replenishment operation for replenishing the developer tank with replenishment toner and carrier from the developer replenishment tank when the toner concentration detected by the toner concentration detection sensor is lower than a predetermined reference toner density; Prepared
The stirring member includes a first screw and a second screw disposed to face the first screw,
The transport path includes a first transport path in which the first screw is disposed, a second transport path in which the second screw is disposed, a downstream side of the first transport path, and a second transport path. A first communication path connecting the upstream side; a second communication path connecting the downstream side of the second transport path and the upstream side of the first transport path; and the first transport path, the first communication path, and the first A circulation path through which the developer in the developing tank circulates is formed by the two transport paths and the second communication path,
The agitating member rotation control unit further includes the developer in the developing tank in the developing tank when the toner density detecting sensor detects a toner density higher than a reference toner density by a predetermined amount or more . A developing device characterized in that the rotational speed of the stirring member is increased to a rotational speed that increases the bulk .   The agitation member rotation control means returns the agitation member rotation number to the original rotation number when a toner concentration higher than a reference toner concentration by a predetermined amount or more is not detected by the toner concentration detection sensor. Item 6. The developing device according to Item 5. A rotatable electrostatic latent image carrier that carries an electrostatic latent image on its peripheral surface, and a stirring member that stirs the developer in the developing tank containing toner and carrier while being transported along the transport path in the developing tank; An image forming apparatus comprising: a developer carrying member that is arranged adjacent to the stirring member and supplies the stirred developer in the developing tank to the electrostatic latent image carrier.
A developer supply tank for supplying toner and carrier to the developer tank;
A toner concentration detection sensor for detecting a toner concentration in the developing tank;
A discharge mechanism that is provided in the developing tank and discharges the developer in the developing tank that has exceeded the amount outside the developing tank when the amount of the developer in the developing tank exceeds a predetermined amount;
Developer amount detecting means for detecting the amount of developer in the developing tank in the developing tank;
Stirring member rotation control means for controlling the rotation speed of the stirring member;
Control means for controlling a replenishment operation for replenishing the developer tank with replenishment toner and carrier from the developer replenishment tank when the toner concentration detected by the toner concentration detection sensor is lower than a predetermined reference toner density; Prepared
The stirring member includes a first screw and a second screw disposed to face the first screw,
The transport path includes a first transport path in which the first screw is disposed, a second transport path in which the second screw is disposed, a downstream side of the first transport path, and a second transport path. A first communication path connecting the upstream side; a second communication path connecting the downstream side of the second transport path and the upstream side of the first transport path; and the first transport path, the first communication path, and the first A circulation path through which the developer in the developing tank circulates is formed by the two transport paths and the second communication path,
The agitation member rotation control means further embeds air in the developer tank when the developer amount detection means detects that the amount of developer in the developer tank is below a predetermined level in the developer tank. An image forming apparatus , wherein the number of rotations of the stirring member is increased to a number of rotations that increases an apparent bulk of the developer in the developing tank .   The image forming apparatus according to claim 7, wherein the developer amount detecting unit includes a liquid level detecting sensor that detects a liquid level of the developer in the developing tank in the developing tank.   The liquid level detection sensor is composed of a pair of a light emitting element and a light receiving element disposed in the developing tank, and the light from the light emitting element is shielded by the developer in the developing tank, thereby developing the developing tank in the developing tank. The image forming and developing apparatus according to claim 8, wherein the level of the internal developer is detected. The stirring member rotation control means sets the rotation speed of the stirring member to the original rotation speed when the developer amount detection means determines that the amount of developer in the developing tank in the developing tank has returned to a predetermined level. and returning, the image forming apparatus according to any one of claims 7 to 9. A rotatable electrostatic latent image carrier that carries an electrostatic latent image on its peripheral surface, and a stirring member that stirs the developer in the developing tank containing toner and carrier while being transported along the transport path in the developing tank; An image forming apparatus comprising: a developer carrying member that is arranged adjacent to the stirring member and supplies the stirred developer in the developing tank to the electrostatic latent image carrier.
A developer supply tank for supplying toner and carrier to the developer tank;
A toner concentration detection sensor for detecting a toner concentration in the developing tank;
A discharge mechanism that is provided in the developing tank and discharges the developer in the developing tank that has exceeded the amount outside the developing tank when the amount of the developer in the developing tank exceeds a predetermined amount;
Stirring member rotation control means for controlling the rotation speed of the stirring member;
Control means for controlling a replenishment operation for replenishing the developer tank with replenishment toner and carrier from the developer replenishment tank when the toner concentration detected by the toner concentration detection sensor is lower than a predetermined reference toner density; Prepared
The stirring member includes a first screw and a second screw disposed to face the first screw,
The transport path includes a first transport path in which the first screw is disposed, a second transport path in which the second screw is disposed, a downstream side of the first transport path, and a second transport path. A first communication path connecting the upstream side; a second communication path connecting the downstream side of the second transport path and the upstream side of the first transport path; and the first transport path, the first communication path, and the first A circulation path through which the developer in the developing tank circulates is formed by the two transport paths and the second communication path,
The agitating member rotation control unit further includes the developer in the developing tank in the developing tank when the toner density detecting sensor detects a toner density higher than a reference toner density by a predetermined amount or more . An image forming apparatus characterized in that the number of rotations of the stirring member is increased to a number of rotations that increases the bulk .   The agitation member rotation control means returns the agitation member rotation number to the original rotation number when a toner concentration higher than a reference toner concentration by a predetermined amount or more is not detected by the toner concentration detection sensor. Item 12. The image forming apparatus according to Item 11.

Images