JP2014002247A - Development device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a development device and an image forming apparatus, which are capable of preventing occurrence of toner covering a background portion.SOLUTION: A development device includes: a housing 301 for housing a developer; transport screws (a supply screw 211 and an agitation screw 212) for transporting the developer; a bearing part (a bearing 410) for supporting the rotation shaft of a transport screw; a ring-form magnetic seal 412 that is disposed at a position opposite to the rotation shaft, in its axial direction, of the transport screw in the housing 301 and disposed circumferentially the rotation shaft of the transport screw in the axial direction; a space section 430 formed between the magnetic seal 412 and bearing part; a humidity control part (a humidifier 186 and a drive part 188) for adjusting humidity inside the space section 430; and a control part 101 for controlling the humidity adjustment part so as to adjust humidity inside the space section 430 in accordance with the difference in magnitude between the humidity inside the space section 430 and that inside the housing 301.

Description

  The present invention relates to a developing device and an image forming apparatus.

  2. Description of the Related Art Image forming apparatuses such as printers, copiers, facsimile machines, and multi-functional machines are provided with a developing device that develops an electrostatic latent image formed on an image carrier. In the developing device, a developer containing toner and a carrier is held on the outer peripheral surface of the developing roller, and the developer is transported to the photosensitive drum by the developing roller to perform development.

  As a technology related to the developing device, a technology has been proposed in which the temperature rise at the end of the developing device is suppressed in the direction of the rotation axis of the conveying member that conveys the developer (see, for example, Patent Document 1). In the technique described in Patent Document 1, the end portion of the developing device is provided with a vent that communicates the space formed between the bearing portion and the seal member in the rotation axis direction of the conveying member and the outside of the developing device. The generated heat is dissipated outside the developing device.

JP 2003-57927 A

  However, in the technique described in Patent Document 1, the vent is always open to the outside of the developing device, and no opening / closing means is provided. Therefore, the humidity in the space portion depends on the humidity outside the developing device. Therefore, for example, when an image forming apparatus equipped with a developing device is moved to a high humidity environment and the developing device is driven without sufficient humidity control, high humidity air enters the space through the vent and develops. The developer stirred and conveyed in the apparatus passes through the seal member and leaks into the space. Even with a new developer that does not need to be discharged, this leakage phenomenon occurs, resulting in a wasteful cost for the developer. Further, when the developer leaks, there is a problem that the temperature in the developing device rises and the charge amount of the toner contained in the developer decreases, resulting in toner fogging on the background portion.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device and an image forming apparatus that can prevent toner from being fogged on a background portion.

The developing device according to the present invention includes:
A housing for containing the developer;
A conveying screw provided in the housing for conveying the developer;
A bearing portion for supporting a rotation shaft of the conveying screw;
A ring-shaped magnetic seal disposed in the housing at a position opposed to the axial direction of the rotation axis of the conveying screw, and surrounding the rotation axis of the conveying screw in the circumferential direction;
A space formed between the magnetic seal and the bearing,
A humidity adjusting unit for adjusting the humidity in the space;
A control unit that controls the humidity adjustment unit to adjust the humidity in the space unit according to the magnitude relationship between the humidity in the space unit and the humidity in the housing;
Is provided.
An image forming apparatus according to the present invention includes the developing device.

  According to the present invention, it is possible to provide a developing device and an image forming apparatus capable of preventing the toner from being fogged on the background portion.

2 is a control block diagram of the image forming apparatus in the first embodiment of the present invention. FIG. FIG. 3 is a diagram illustrating a configuration of an image forming unit in the first embodiment according to the present invention. 1 is a diagram illustrating a configuration of a developing device according to a first embodiment of the present invention. It is a figure which shows the structure of the axial end part of a supply screw in 1st Embodiment which concerns on this invention. 3 is a flowchart illustrating an operation example of the image forming apparatus according to the first exemplary embodiment of the present invention. It is a figure which shows the structure of the axial end part of a supply screw in 2nd Embodiment which concerns on this invention. 6 is a flowchart illustrating an operation example of the image forming apparatus according to the second embodiment of the present invention. It is a figure which shows the structure of the 2nd comparative example. It is a figure which shows the result of an evaluation experiment about an Example, a 1st comparative example, and a 2nd comparative example. It is a figure which shows the result of an evaluation experiment about an Example, a 1st comparative example, and a 2nd comparative example.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.
[Configuration of Image Forming Apparatus 100]
An image forming apparatus 100 shown in FIG. 1 forms an image on a recording sheet by an electrophotographic process. The image forming apparatus 100 includes a control unit 101, a document reading unit 110, an operation display unit 120, an image processing unit 130, an image forming unit 140, a conveyance unit 150, a fixing unit 160, a first humidity sensor 180, a second humidity sensor 182, A third humidity sensor 184, a humidifier 186, and a drive unit 188 are provided.

  The control unit 101 includes a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, and the like. The CPU 102 reads a program corresponding to the processing content from the ROM 103 and develops it in the RAM 104, and centrally controls the operation of each block of the image forming apparatus 100 in cooperation with the developed program. At this time, various data stored in the storage unit 172 are referred to. The storage unit 172 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 101 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 171. I do. For example, the control unit 101 receives image data transmitted from an external device, and forms an image on a recording sheet based on the image data (input image data). The communication unit 171 includes a communication control card such as a LAN card, for example.

  The document reading unit 110 optically scans the document conveyed on the contact glass, forms an image of reflected light from the document on a light receiving surface of a CCD (Charge Coupled Device) sensor, and reads the document. The document is conveyed onto the contact glass by an automatic document feeder (ADF). However, the document may be manually placed on the contact glass.

  The operation display unit 120 has a touch panel screen. Input operations for various instructions and settings performed by the user can be performed via a touch panel screen. These instruction / setting information is handled by the control unit 101 as job information.

  The image processing unit 130 includes a circuit that performs analog-digital (A / D) conversion processing and a circuit that performs digital image processing. The image processing unit 130 generates digital image data by an A / D conversion process from the analog image signal acquired by the CCD sensor of the document reading unit 110 and outputs the digital image data to the image forming unit 140.

  The image forming unit 140 emits laser light based on the digital image data generated by the image processing unit 130, and irradiates the photosensitive drum with the emitted laser light, whereby an electrostatic latent image is formed on the photosensitive drum. Is formed (exposure process).

  The image forming unit 140 is configured to execute a charging process performed before the exposure process, a development process performed after the exposure process, a transfer process after the development process, and a cleaning process after the transfer process in addition to the exposure process described above. It has.

  In the charging step, the image forming unit 140 uniformly charges the surface of the photosensitive drum by corona discharge from the charging device. In the developing step, the image forming unit 140 forms a toner image on the photosensitive drum by attaching toner contained in the developer in the developing device to the electrostatic latent image on the photosensitive drum.

  In the transfer process, the image forming unit 140 primarily transfers the toner image on the photosensitive drum to the intermediate transfer belt. Further, the image forming unit 140 secondarily transfers the toner image on the intermediate transfer belt onto the recording paper conveyed by the conveyance unit 150. In the cleaning process, the image forming unit 140 removes the toner remaining on the photosensitive drum after the transfer process.

  The fixing unit 160 includes a heating roller, a fixing roller, a fixing belt, and a pressure roller. The heating roller and the fixing roller are arranged apart from each other by a predetermined distance. A fixing belt is stretched between the heating roller and the fixing roller. The pressure roller is disposed in a state of being in pressure contact with the fixing belt in a region where the fixing belt and the fixing roller are in contact with each other. A fixing nip portion is formed at a portion where the fixing belt and the pressure roller are in contact with each other.

  The fixing unit 160 fixes the toner image on the recording sheet by applying heat and pressure to the toner image on the recording sheet introduced into the fixing nip (heating fixing) (fixing step). As a result, a fixed toner image is formed on the recording paper. The recording paper heated and fixed by the fixing unit 160 is discharged to the outside of the image forming apparatus 100.

  The first humidity sensor 180 measures the humidity in the developing device and outputs the measured value to the control unit 101. The second humidity sensor 182 measures the humidity in the developing device and outputs the measured value to the control unit 101. The third humidity sensor 184 measures the humidity in the developing device and outputs the measured value to the control unit 101.

  The humidifier 186 supplies air of a predetermined humidity to the developing device under the control of the control unit 101. The humidifier 186 functions as an air supply unit.

  The drive unit 188 rotates a slide cam 450 described later under the control of the control unit 101. The humidifier 186 and the drive unit 188 function as a humidity adjustment unit.

[Configuration of Image Forming Unit 140]
Next, the configuration of the image forming unit 140 will be described. As shown in FIG. 2, the image forming unit 140 includes a photosensitive drum 201, a charging device 202, an exposure device 203, a developing device 204, and a cleaning device 205. Note that description of the configuration for performing the secondary transfer process is omitted.

  The photosensitive drum 201 is rotationally driven by a driving unit (not shown) and rotates in the arrow B direction. The charging device 202 uniformly charges the outer peripheral surface of the photosensitive drum 201 by corona discharge.

  The exposure apparatus 203 has a semiconductor laser element. The exposure device 203 forms an electrostatic latent image on the outer peripheral surface of the photosensitive drum 201 by irradiating laser light onto the outer peripheral surface of the uniformly charged photosensitive drum 201.

  The developing device 204 receives supply of toner (average particle diameter: 6.5 [μm]) from a toner cartridge (not shown) via a toner hopper 209. The developing device 204 is supplied with a carrier (average particle diameter: 33 [μm]) via a carrier hopper 210. The developing device 204 agitates the supplied toner and carrier with the agitating screw 212 to charge the toner. The developer (toner and carrier) after stirring is supplied to the developing roller 206 by the supply screw 211. The stirring screw 212 rotates in the direction of arrow E. Supply screw 211 rotates in the direction of arrow D. The developing roller 206 rotates in the direction of arrow C.

  In the developing roller 206, the developing sleeve rotates around the magnet roller in a fixed state, and the developer is supplied to the outer peripheral surface of the developing sleeve by the supply screw 211. When the developer supplied to the outer peripheral surface of the developing sleeve moves on the outer peripheral surface of the developing sleeve, the carrier forms a magnetic brush by the magnetic force of the magnetic pole provided on the magnet roller. The toner attached to the magnetic brush adheres to the electrostatic latent image on the photosensitive drum 201. That is, the electrostatic latent image on the photosensitive drum 201 is developed with toner.

  The regulating plate 213 regulates the thickness of the developer that adheres to the outer peripheral surface of the developing sleeve so that a predetermined amount of developer is conveyed by the developing sleeve.

  The cleaning device 205 discharges the outer peripheral surface of the photosensitive drum 201 by exposing the photosensitive drum 201 with the eraser lamp 207. The cleaning blade 208 abuts on the outer peripheral surface of the photosensitive drum 201 to mechanically scrape off and remove the toner remaining on the outer peripheral surface of the photosensitive drum 201 after the primary transfer.

[Configuration of Developing Device 204]
Next, the configuration of the developing device 204 will be described. As illustrated in FIG. 3, the developing device 204 includes a housing 301 that stores a developer. The interior of the housing 301 is partitioned into a stirring tank 303 and a supply tank 304 by a partition wall 302, and contains a developer containing toner and a carrier. The agitating screw 212 is disposed in the agitating tank 303, and agitates the toner and the carrier while conveying them in the direction of arrow F to frictionally charge the toner. The supply screw 211 is disposed in the supply tank 304 and supplies the developer containing the charged toner to the developing roller 206 while conveying the developer in the direction of arrow H.

  The supply screw 211 and the agitation screw 212 are spiral screws provided with spiral blades having a predetermined pitch over almost the entire shaft. The developing roller 206, the supply screw 211, and the stirring screw 212 are disposed so that the rotation axes are parallel to each other.

  The agitation tank 303 communicates with the upstream portion of the supply tank 304 in the developer conveyance direction (arrow H direction) at the downstream portion in the developer conveyance direction (arrow F direction), and the developer is conveyed in the arrow G direction. The supply tank 304 communicates with the upstream portion of the stirring tank 303 in the developer conveyance direction (arrow F direction) at the downstream portion in the developer conveyance direction (arrow H direction), and the developer is conveyed in the arrow I direction. Is done. That is, the developer is conveyed so as to circulate in the housing 301.

  A developer inflow portion 305 is provided on the upstream side of the stirring tank 303 in the developer transport direction. The developer inflow portion 305 includes a carrier supply port 306 and a toner supply port 308. At the carrier supply port 306, the carrier is supplied through the carrier hopper 210. The toner supply port 308 receives toner supply via the toner hopper 209.

  A magnetic permeability sensor 307 for detecting toner concentration is provided at the bottom of the agitation tank 303. The control unit 101 replenishes the developing device 204 with toner by controlling a replenishment screw (not shown) provided in the toner hopper 209 based on the detection signal of the magnetic permeability sensor 307. The control unit 101 replenishes toner according to the image to be formed. The control unit 101 replenishes the developing device 204 with a predetermined amount of carrier via the carrier hopper 210 every time a predetermined number of image forming processes are executed.

[Configuration of shaft end of supply screw 211]
Next, the configuration of the shaft end portion of the supply screw 211 (see the region 310 in FIG. 3) will be described with reference to FIG. In FIG. 4, reference numeral 400 denotes a shaft of the supply screw 211. The shaft 400 is provided with a plurality of spiral blades 406 along the developer conveyance direction. Also, the shaft 400 is provided with two spiral blades 402 and 404 in the vicinity of the shaft end of the supply screw 211, the spiral direction of which is opposite to that of the spiral blade 406.

  Reference numeral 410 denotes a bearing portion (bearing) for rotatably supporting the shaft 400. Reference numeral 412 denotes a ring-shaped magnetic seal (magnet) for preventing the developer in the supply tank 304 from leaking to the shaft end of the supply screw 211.

  The magnetic seal 412 has an outer diameter of 12 to 18 [mm], an inner diameter of 7 [mm], and a thickness of 8 [mm]. The material of the magnetic seal 412 is anisotropic wet ferrite. In the case of contact measurement, the surface magnetic flux density (magnetic force) of the magnetic seal 412 is 130 to 140 [mT]. The lower limit value of the surface magnetic flux density is a magnetic force necessary for sealing the developer. The magnetization direction of the magnetic seal 412 coincides with the thickness direction of the magnetic seal 412. The gap between the magnetic seal 412 and the shaft 400 is 0.5 [mm].

  The thickness of the magnetic seal 412 is preferably 2 [mm] or more, and preferably 6 to 12 [mm]. The material of the magnetic seal 412 may be other than anisotropic wet ferrite. The surface magnetic flux density of the magnetic seal 412 may be 130 to 490 [mT], and preferably 130 to 150 [mT]. The gap between the magnetic seal 412 and the shaft 400 is preferably 0.25 to 1.0 [mm].

  The rubber seal 414 seals the leaked developer in front of the bearing 410 if the developer in the supply tank 304 leaks to the shaft end of the supply screw 211. Spacers 420 and 422 are interposed between the bearing 410 and the magnetic seal 412. An opening 426 is provided between the spacer 420 and the magnetic seal 412. That is, the opening 426 is located below the shaft 400 of the supply screw 211 in the direction of gravity. The size of the opening 426 is 4 [mm] × 5 [mm].

  A first humidity sensor 180 is disposed in the vicinity of the magnetic seal 412. The first humidity sensor 180 measures the humidity in the supply tank 304 and outputs the measured value to the control unit 101.

  A second humidity sensor 182 is disposed in the vicinity of the spacer 420. The second humidity sensor 182 measures the humidity in the space 430 surrounded by the dotted line, and outputs the measured value to the control unit 101.

  Reference numeral 440 denotes an L-shaped shutter, which is adjacent to the bearing 410 and the spacer 420. A slide cam 450 is provided at the left end of the shutter 440. The slide cam 450 can rotate around the fulcrum 452. The drive unit 188 rotates the slide cam 450 when receiving a drive command from the control unit 101. As the slide cam 450 rotates, the shutter 440 moves in the left-right direction in the figure. The shutter 440 is provided to be slidable in a horizontal direction in the drawing in a range including a closed position where the space 430 is closed from below and an open position where the space 430 is not closed from below. The default position of the shutter 440 is the closed position.

  Reference numeral 460 denotes a flow path for allowing air of a predetermined humidity supplied from the humidifier 186 to flow into the space portion 430 through the opening 426 when the shutter 440 is located at the open position. An opening 462 is provided in the flow path 460. When the shutter 440 is located at the open position, the outside of the flow path 460, that is, the outside of the developing device 204 and the space 430 communicate with each other through the opening 462. A third humidity sensor 184 is disposed in the vicinity of the opening 462. The third humidity sensor 184 measures the humidity outside the developing device 204 and outputs the measured value to the control unit 101.

[Operation of Image Forming Apparatus 100]
Next, the operation of the image forming apparatus 100 will be described with reference to the flowchart of FIG. The process in step S100 starts when the image forming apparatus 100 is activated.

  First, the control unit 101 refers to the measurement value of the first humidity sensor 180 and the measurement value of the second humidity sensor 182, and determines whether or not the humidity in the supply tank 304 is less than the humidity in the space part 430. (Step S100). If the control unit 101 determines that the humidity in the supply tank 304 is not less than the humidity in the space 430 (step S100, NO), the process transitions to step S100.

  On the other hand, when it is determined that the humidity in the supply tank 304 is less than the humidity in the space 430 (step S100, YES), the control unit 101 controls the drive unit 188 to bring the shutter 440 into the open position. Move (step S120). Next, the control unit 101 refers to the measurement value of the first humidity sensor 180 and the measurement value of the third humidity sensor 184, and the humidity outside the developing device 204 is set to a predetermined humidity (for example, from the humidity in the supply tank 304). 20 [%]) or less is determined (step S140).

  If the control unit 101 determines that the humidity outside the developing device 204 is lower than the humidity in the supply tank 304 by a predetermined humidity (step S140, YES), the control unit 101 measures the first humidity sensor 180. With reference to the value and the measurement value of the second humidity sensor 182, it is determined whether or not the humidity in the supply tank 304 is equal to or higher than the humidity in the space 430 (step S160).

  If the control unit 101 determines that the humidity in the supply tank 304 is not equal to or higher than the humidity in the space 430 (step S160, NO), the process transitions to step S160. That is, the determination process in step S160 is repeated until air outside the developing device 204 flows into the space 430 and the humidity in the supply tank 304 becomes equal to or higher than the humidity in the space 430.

  On the other hand, when it is determined that the humidity in the supply tank 304 is equal to or higher than the humidity in the space portion 430 (step S160, YES), the control unit 101 controls the driving unit 188 to bring the shutter 440 into the closed position. Move (step S180). Thereafter, the process proceeds to step S100.

  Returning to the determination processing in step S140, when it is determined that the humidity outside the developing device 204 is not lower than the humidity in the supply tank 304 by a predetermined humidity (step S140, NO), the control unit 101 controls the humidifier 186. Then, an operation of supplying air having a predetermined humidity lower than the humidity in the supply tank 304 into the space portion 430 is started (step S200).

  Next, the control unit 101 refers to the measurement value of the first humidity sensor 180 and the measurement value of the second humidity sensor 182 to determine whether or not the humidity in the supply tank 304 is equal to or higher than the humidity in the space part 430. Determination is made (step S220).

  If the control unit 101 determines that the humidity in the supply tank 304 is not equal to or higher than the humidity in the space 430 (step S220, NO), the process transitions to step S220. That is, the determination process of step S220 is repeatedly performed until the air supplied from the humidifier 186 flows into the space 430 and the humidity in the supply tank 304 becomes equal to or higher than the humidity in the space 430.

  On the other hand, when it is determined that the humidity in the supply tank 304 is equal to or higher than the humidity in the space part 430 (step S220, YES), the control unit 101 controls the humidifier 186 to determine a predetermined value based on the humidity in the supply tank 304. The operation of supplying the low-humidity air into the space 430 is terminated (step S240). Thereafter, the process transitions to step S180.

  As described above in detail, in the first embodiment, the housing 301 that stores the developer, the transport screws (the supply screw 211 and the stirring screw 212) that are provided in the housing 301 and transport the developer, and the transport A bearing portion (bearing 410) that supports the rotational axis of the screw, and a ring that is disposed in the housing 301 at a position facing the axial direction of the rotational axis of the conveying screw and that surrounds the rotational axis of the conveying screw in the circumferential direction. -Shaped magnetic seal 412, a space portion 430 formed between the magnetic seal 412 and the bearing portion, a humidity adjusting portion (humidifier 186, drive portion 188) for adjusting the humidity in the space portion 430, a space portion The humidity adjustment unit is controlled so as to adjust the humidity in the space 430 according to the magnitude relationship between the humidity in 430 and the humidity in the housing 301. And a control unit 101 that. When the humidity in the space 430 is higher than the humidity in the housing 301, the control unit 101 controls the humidity adjustment unit so that the humidity in the space 430 is equal to or lower than the humidity in the housing 430.

  According to the first embodiment configured as described above, the humidity in the space 430 is controlled to be equal to or lower than the humidity in the housing 301, so that the developer in the housing 301 does not pass through the magnetic seal 412, and the space It does not leak into part 430. Therefore, a temperature increase in the developing device 204 can be prevented, and a decrease in the charge amount of the toner contained in the developer can be prevented. As a result, it is possible to prevent the toner from being fogged on the background portion.

(Second Embodiment)
Hereinafter, a second embodiment according to the present invention will be described in detail with reference to the drawings. The operation of the image forming apparatus 100 according to the present embodiment is such that the developer is supplied to the shaft end of the supply screw 211 when an image forming process with a low coverage (also referred to as a low printing rate) in which the developer is likely to deteriorate is continuously performed. It differs from the operation in the first embodiment in that it is forcibly discharged from the section. In addition, the same code | symbol is attached | subjected about the thing similar to each part structure in 1st Embodiment, and the description is abbreviate | omitted.
[Configuration of shaft end of supply screw 211]
Next, the configuration of the shaft end portion of the supply screw 211 will be described with reference to FIG. In FIG. 6, when the shutter 440 is in the open position, reference numeral 500 indicates that the developer that has entered the space 430 from the supply tank 304 enters the waste toner box 510 via the opening 426 (hereinafter referred to as the discharge port 426). It is a conveyance path to be conveyed. The conveyance path 500 and the flow path 460 are in communication.

  The waste toner box 510 collects and stores the conveyed developer. A discharge screw 520 for conveying the developer to the waste toner box 510 is provided in the conveyance path 500. Reference numeral 530 denotes a filter for preventing the developer entering the space 430 from the supply tank 304 from entering the flow path 460 when the developer is transported to the waste toner box 510.

[Operation of Image Forming Apparatus 100]
Next, the operation of the image forming apparatus 100 will be described with reference to the flowchart of FIG. The processing in step S300 starts when the control unit 101 detects that the developer has been replaced. Generally, the developer is exchanged while the developing device 204 is mounted on the image forming apparatus 100. The magnetic permeability sensor 307 provided in the developing device 204 is corrected according to the developer history. Therefore, when the developer is replaced, the magnetic permeability sensor 307 is adjusted so that the voltage of the magnetic permeability sensor 307 becomes a value corresponding to the replaced developer (new developer) as an initial adjustment. Therefore, the control unit 101 can detect whether or not the developing device 204, that is, the developer has been replaced, depending on whether or not this adjustment has been performed.

  First, the control unit 101 controls the driving unit 188 to move the shutter 440 to the closed position, thereby closing the discharge port 426 (step S300). Next, the control unit 101 refers to the job information and controls the image forming unit 140 to perform image forming processing for one job (step S320).

  Next, the control unit 101 determines whether or not the developer has been exchanged (step S340). If the control unit 101 determines that the developer has been replaced (step S340, NO), the image forming apparatus 100 ends the processing in FIG. On the other hand, when it is determined that the developer has not been replaced (step S340, YES), the control unit 101 determines whether or not the number of prints after the previous developer replacement is greater than 5000 [sheets]. (Step S360).

  If the control unit 101 determines that the number of printed sheets after the replacement of the developer is not greater than 5000 [sheets] (NO in step S360), the process proceeds to step S320. On the other hand, if it is determined that the number of prints after the developer has been replaced is greater than 5000 [sheets] (YES in step S360), the control unit 101 determines that the most recently formed image of 5000 [sheets] has been printed. It is determined whether or not the average printing rate is smaller than 5 [%] (step S380).

  If the control unit 101 determines that the average printing rate is smaller than 5% (step S380, YES), the control unit 101 controls the driving unit 188 to move the shutter 440 to the open position. Thus, the discharge port 426 is opened (step S400). Next, the control unit 101 refers to the measurement value of the third humidity sensor 184, and during the most recent image formation of 5000 [sheets], the increase in humidity outside the developing device 204 is 20 [ %] Is determined (step S420).

  If the controller 101 determines that the amount of increase in humidity outside the developing device 204 is smaller than 20 [%] (step S420, YES), the controller 101 controls the humidifier 186 to control the humidity 85. The operation of supplying [%] of air into the space 430 is started (step S440). Next, it is determined whether or not the number of printed sheets after the process of step S440 is smaller than 8000 [sheets] (step S460).

  If the control unit 101 determines that the number of prints after the process of step S440 is not smaller than 8000 [sheets] (step S460, NO), the control unit 101 controls the humidifier 186 to control the humidity 85 [ %] Air is supplied to the space 430 (step S520). Thereafter, the process proceeds to step S320.

  On the other hand, when it is determined that the number of prints after the process in step S440 is smaller than 8000 [sheets] (YES in step S460), the control unit 101 performs a power-off operation of the image forming apparatus 100 via the operation display unit 120. It is determined whether or not it is not performed (step S480). If the control unit 101 determines that the power-off operation of the image forming apparatus 100 has been performed (step S480, NO), the process transitions to step S520.

  On the other hand, if it is determined that the power-off operation of the image forming apparatus 100 is not performed (step S480, YES), the control unit 101 refers to the job information and performs image formation so as to perform image forming processing for one job. The unit 140 is controlled (step S500). Thereafter, the process proceeds to step S460.

  Returning to the determination process of step S420, if the control unit 101 determines that the increase in humidity outside the developing device 204 is not smaller than 20 [%] (step S420, NO), the process transitions to step S320. . At this time, high-humidity air outside the developing device 204 flows into the space 430.

  Returning to the determination process in step S380, if it is determined that the average printing rate is not smaller than 5 [%] (NO in step S380), the control unit 101 determines that the image of 5000 [sheets] of the most recently formed image is formed. It is determined whether or not the average printing rate is greater than 50 [%] (step S540). If the control unit 101 determines that the average printing rate is not larger than 50 [%] (step S540, NO), the process proceeds to step S320.

  On the other hand, when it is determined that the average printing rate is higher than 50 [%], that is, when a large amount of toner is used in the image forming process and the developer is hardly deteriorated (YES in step S540), the control is performed. The unit 101 refers to the operation history of the drive unit 188 and determines whether or not the discharge port 426 is open (step S560). If the control unit 101 determines that the discharge port 426 is not open (step S560, NO), the process proceeds to step S320.

  On the other hand, when it is determined that the discharge port 426 is open (step S560, YES), the control unit 101 refers to the measurement value of the third humidity sensor 184, and the image of 5000 [sheets] is formed most recently. In the meantime, it is determined whether or not the increase in humidity outside the developing device 204 is smaller than 20% (step S580). If the controller 101 determines that the amount of increase in humidity outside the developing device 204 is not less than 20 [%] (step S580, NO), the process transitions to step S320. On the other hand, when it is determined that the amount of increase in humidity outside the developing device 204 is smaller than 20% (step S580, YES), the control unit 101 controls the drive unit 188 to move the shutter 440 to the closed position. By doing so, the discharge port 426 is closed (step S600). Thereafter, the process proceeds to step S320.

  As described above in detail, in the second embodiment, when the humidity in the space 430 is equal to or lower than the humidity in the housing 301, the control unit 101 determines that the humidity in the space 430 is the humidity in the housing 301. The humidity adjustment unit (humidifier 186, drive unit 188) is controlled to be larger. Furthermore, a discharge port 426 that is located below the supply screw 211 in the direction of gravity and discharges the developer that has entered the space portion 430 from the housing 301 is provided.

  According to the second embodiment configured as described above, since the humidity in the space 430 is controlled to be higher than the humidity in the housing 301, the developer in the housing 301 passes through the magnetic seal 412. It is pushed out into the space 430. The developer pushed out into the space portion 430 is discharged from the discharge port 426 without collecting in the space portion 430. For this reason, when low coverage image forming processing in which the developer is likely to deteriorate is continuously performed, the developer is forced from the shaft end of the supply screw 211 before the charge amount of the toner contained in the developer decreases. Can be discharged. Therefore, it is possible to prevent the toner from being fogged on the background portion. Further, since the developer is discharged from the discharge port 426 before coming into contact with the rubber seal 414, wear of the rubber seal 414 can be prevented.

  Conventionally, the toner is developed on the photosensitive drum 201 between paper sheets, and the cleaning blade 208 is brought into contact with the photosensitive drum 201 to mechanically discharge the deteriorated toner. Therefore, the cleaning blade 208 was easily worn and deteriorated. In contrast, in the second embodiment, the deteriorated toner can be discharged without imposing a burden on the cleaning blade 208, and the life of the cleaning blade 208 can be extended.

  Further, in the second embodiment, the space 430 is formed in the vicinity of the end located on the downstream side in the developer transport direction in the supply tank 304 among the both ends of the supply screw 211. That is, the position of the space 430 is the farthest from the toner supply port 308 in the developer transport direction. For this reason, the ratio of the deteriorated developer in the developer to be discharged becomes larger than that in the case where the space portion 430 is provided in another place, and the discharge amount of the developer that should not be discharged (soon after being replaced) is reduced. be able to.

  In the second embodiment, the supply screw 211 has a spiral blade 406 provided on the outer peripheral surface of the supply screw 211, and the outer surface of the supply screw 211 located near the magnetic seal 412 has a spiral blade. Spiral blades 402 and 404 having a spiral direction opposite to that of 406 are provided. Therefore, in the supply tank 304, a force opposite to the developer transport direction acts on the carrier, and the ratio of the toner in the discharged developer can be selectively increased. Therefore, it is possible to prevent the carrier that is not caused by the toner fog from being unnecessarily discharged.

  In the second embodiment, the discharge port 426 is closed immediately after the replacement of the developer, so that the developer can be prevented from being unnecessarily discharged from the discharge port 426.

  The first and second embodiments described above are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention is interpreted in a limited manner. It must not be. That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

  Finally, the results of an experiment for confirming the effectiveness in the second embodiment performed by the present inventor will be described.

[Configuration of Shaft End of Supply Screw 211 According to Embodiment]
The configuration of the shaft end portion of the supply screw 211 according to the example is the same as the configuration described in the second embodiment.

[Configuration of the shaft end portion of the supply screw 211 according to the first comparative example]
In the configuration of the shaft end portion of the supply screw 211 according to the first comparative example, none of the magnetic seal 412, the space portion 430, and the discharge port 426 exists. There is a rubber seal for sealing the shaft end of the supply screw 211.

  In the first comparative example, toner is developed on the photosensitive drum 201 between paper sheets, and the cleaning blade 208 is brought into contact with the photosensitive drum 201 to mechanically scrape and clean the deteriorated toner. Specifically, the toner in the developing device 204 is discharged to the photosensitive drum 201 by developing a solid patch corresponding to a printing rate of 2 [%] on A4 paper on the photosensitive drum 201 at all times between sheets, and cleaning means. Then, the toner is discharged to the waste toner box 510.

[Configuration of the shaft end portion of the supply screw 211 according to the second comparative example]
With reference to FIG. 8, the structure of the axial end part of the supply screw 211 which concerns on a 2nd comparative example is demonstrated. In addition, the same code | symbol is attached | subjected about the thing similar to each part structure in an Example, The description is abbreviate | omitted.

  The shaft 400 of the supply screw 211 is provided with a plurality of spiral blades 406, 408, and 409 having the same spiral direction along the developer transport direction. The rubber seal 600 is integrated with the bearing 410. A spacer 610 is interposed between the bearing 410 and the magnetic seal 412. A discharge port 630 is provided between the spacer 610 and the magnetic seal 412. That is, the discharge port 630 is positioned above the shaft 400 of the supply screw 211 in the direction of gravity. The size of the discharge port 630 is 4 [mm] × 5 [mm].

  In the experiment, 50000 [sheets] were printed, and it was confirmed whether or not an image defect due to wear of the cleaning blade 208 occurred. When the cleaning blade 208 is worn by a predetermined amount or more, streaky density unevenness occurs on the image. This density unevenness was visually evaluated, and if it was good, it was determined that the durability of the cleaning blade 208 was sufficient. FIG. 9 shows the result of evaluating the occurrence of density unevenness according to the following evaluation criteria.

(Status of density unevenness)
○: Streaky density unevenness does not occur and is good.
Δ: Streaky density unevenness can be confirmed, but it is an acceptable level depending on the application. For example, when the demand for image quality is strong, such as production print, it is an unacceptable level.
X: Streaky density unevenness occurs, which is a practically problematic level.

  As shown in FIG. 8, in the first comparative example, streak-like density unevenness was confirmed at the time when the print processing of 25000 [sheets] was performed. In the second comparative example, as in the embodiment, the toner is forcibly discharged from the shaft end portion of the supply screw 211 (that is, the cleaning blade 208 is not used for discharging the toner). Unevenness did not occur.

  Further, in the experiment, the fog and the toner charge amount [q / m] during the printing of 50000 [sheets] of an image with low coverage (printing rate 3 [%]) were confirmed. In the middle of the experiment, the NN environment (20 [° C.], relative humidity 50 [%]) and the HH environment (30 [° C.], relative humidity 80 [%]) were switched. Specifically, print processing was performed in a test room set for each operating environment. When switching the operating environment, the printing process was temporarily stopped and the device under test (image forming apparatus 100) was moved to a test room set in the operating environment to be switched. After moving, the machine under test was stopped and the temperature was adjusted for 30 minutes, and then the evaluation was resumed. FIG. 10 shows the results of evaluating the fog according to the following evaluation criteria.

(Cover)
○: The image area ratio of the black toner adhered to the image background is less than 0.04 [%], which is good.
(Triangle | delta): The image area ratio of the black toner adhering to an image background part is 0.05 [%] or more and less than 0.07 [%], and is an acceptable level depending on a use. For example, when the demand for image quality is strong, such as production print, it is an unacceptable level.
X: The image area ratio of the black toner adhering to the image background portion is 0.07 [%] or more, which is a practically problematic level.

  As shown in FIG. 10, in the first comparative example, the phenomenon that the toner slips through the cleaning blade 208 gradually occurs due to wear of the cleaning blade 208 from the time point when the print processing of 25000 [sheets] is performed, and the image Toner adhered to the background. This toner adhesion was detected as fog. The toner charge amount in the first comparative example was equivalent to the toner charge amount in the example.

  In the second comparative example, after the operating environment is switched to the HH environment, the toner in the supply tank 304 passes through the magnetic seal 412 and leaks into the space 430, and the space 430 is filled with toner. The printing process was continued (ie, no toner was discharged). As a result, heat was generated at the rubbing portion between the rubber seal 600 and the shaft 400, and the temperature in the developing device 204 increased and the toner charge amount decreased as compared with the examples and the first comparative example. Due to the decrease in the toner charge amount, the fog deteriorated with an increase in the number of printed sheets. In the example, a good image could be output until a print process of 50000 [sheets] was performed.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Control part 102 CPU
103 ROM
104 RAM
110 Document Reading Unit 120 Operation Display Unit 130 Image Processing Unit 140 Image Forming Unit 150 Conveying Unit 160 Fixing Unit 171 Communication Unit 172 Storage Unit 180 First Humidity Sensor 182 Second Humidity Sensor 184 Third Humidity Sensor 186 Humidifier 188 Drive Unit 201 Photosensitive drum 202 Charging device 203 Exposure device 204 Developing device 205 Cleaning device 206 Developing roller 207 Eraser lamp 208 Cleaning blade 209 Toner hopper 210 Carrier hopper 211 Supply screw 212 Stirring screw 213 Regulatory plate 301 Housing 302 Partition wall 303 Stirring bath 304 Supply bath 305 Developer inlet 306 Carrier supply port 307 Magnetic permeability sensor 308 Toner supply port 310 Area 400 Shaft 402, 404, 406 Spiral blade 410 Bearing 412 Magnetic seal 414 Rubber seal 420, 422 Spacer 426, 462 Opening 430 Space 440 Shutter 450 Slide cam 452 Support point 460 Flow path 500 Conveyance path 510 Waste toner box 520 Discharge screw 530 Filter

Claims (8)

A housing for containing the developer;
A conveying screw provided in the housing for conveying the developer;
A bearing portion for supporting a rotation shaft of the conveying screw;
A ring-shaped magnetic seal disposed in the housing at a position opposed to the axial direction of the rotation axis of the conveying screw, and surrounding the rotation axis of the conveying screw in the circumferential direction;
A space formed between the magnetic seal and the bearing,
A humidity adjusting unit for adjusting the humidity in the space;
A control unit that controls the humidity adjustment unit to adjust the humidity in the space unit according to the magnitude relationship between the humidity in the space unit and the humidity in the housing;
A developing device comprising: The humidity adjusting unit is
The developing device according to claim 1, further comprising: an air supply unit that supplies air having a humidity set by the control unit to the space unit according to a magnitude relationship between the humidity in the space unit and the humidity in the housing.   The said control part controls the said humidity adjustment part so that the humidity in the said space part may be below the humidity in the said housing, when the humidity in the said space part is larger than the humidity in the said housing. Development device.   The said control part controls the said humidity adjustment part so that the humidity in the said space part becomes larger than the humidity in the said housing, when the humidity in the said space part is below the humidity in the said housing. Development device.   5. The developing device according to claim 4, further comprising a discharge port that is positioned below in the gravity direction from the conveying screw and discharges the developer that has entered the space from the housing. The housing is
A supply tank for supplying the developer to the developing roller;
A stirrer tank connected to the supply tank to form a circulation path for the developer and collecting the developer from the developing roller;
Have
The conveying screw is
A supply screw provided in the supply tank;
A stirring screw provided in the stirring tank;
Have
6. The developing device according to claim 4, wherein the space portion is formed in the vicinity of an end portion located on the downstream side in the transport direction of the developer in the supply tank among both end portions of the supply screw. The conveying screw is
A spiral blade provided on the shaft of the conveying screw;
The developing device according to claim 4, wherein a spiral blade having a spiral direction opposite to that of the spiral blade is provided on a shaft of the conveying screw located in the vicinity of the magnetic seal. .   An image forming apparatus comprising the developing device according to claim 1.

Images