Developing device, image forming apparatus, and image forming structure

A developing device includes: a developing device main body in which a developer chamber containing a developer is formed; a pressure application area forming unit that is provided in the developer chamber so as to form a pressure application area where pressure is applied to the developer in the developer chamber because of movement of the developer contained in the developer chamber; and a pressure regulating unit that regulates the pressure applied to the developer in the pressure application area in response to temperature of the developer in the pressure application area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-239983 filed Oct. 19, 2009.

BACKGROUND

1. Technical Field

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

SUMMARY

According to an aspect of the invention, there is provided a developing device comprising: a developing device main body that a developer chamber containing a developer is formed; a pressure application area forming unit that is provided in the developer chamber so as to form a pressure application area where pressure is applied to the developer in the developer chamber because of movement of the developer contained in the developer chamber; and a pressure regulating unit that regulates the pressure applied to the developer in the pressure application area in response to temperature of the developer in the pressure application area.

DETAILED DESCRIPTION

FIG. 1shows an image forming apparatus10according to a first exemplary embodiment of the present invention. The image forming apparatus10has an image forming apparatus main body12, whose the upper part serves as an output section16at which a sheet is output. Further, the image forming apparatus main body12has an image forming section100and e.g. two sheet supply devices300.

The image forming section100has a photoreceptor110being in e.g. a drum-shape, employed an electrophotographic printing and serving as an image carrier holding a latent image, a charging device112uniformly charging the photoreceptor110, a latent image forming device114forming a latent image by writing a latent image with a light on the photoreceptor110subjected to the charge of the charging device112, a developing device200developing the latent image formed on the surface of the photoreceptor110by the latent image forming device114, a transfer device118consisting of e.g. a transfer roller and transferring the developer image formed on the surface of the photoreceptor110by developing device200to a sheet, a cleaning device120with e.g. a cleaning blade scraping away developer particle remaining on the photoreceptor110, and a fixing device122fixing the transferred developer image on the sheet with the transfer device118on the sheet. The latent image forming device114consists of e.g. a scanning laser exposure device, and forms a latent image on the photoreceptor110. As other exemplary embodiment of the latent image forming device, a light emitting diode, a surface emitting device, or the like may be employed.

The sheet supply devices300have respectively a sheet container304consisting of e.g. a sheet feed cassette, a pick up roller306to pick up a topmost sheet contained in the sheet container304, and a feed roller308to feed the sheet picked up by the pick up roller306toward downstream side of the sheet transporting direction. Therefore, the sheet supply devices300feed a sheet stacked in the sheet container304to the image forming section100respectively.

Downstream the feed roller308along a sheet feed direction, a registration roller360is disposed, and downstream the registration roller360the transfer device118and the photoreceptor110are disposed. Also the fixing device362is disposed downstream the transfer device118and the photoreceptor110. An exit roller362outputs the sheet having a developer image fixed by the fixing device122thereon toward the output section16.

The developing device200works with a two-component developer including a toner and a carrier for developing. That is, the two-component developer consisting of a nonmagnetic toner and a magnetic carrier is used in the developer device200. The toner is a fine particle generated by attaching a color particle such as carbon to e.g. an electric charged plastic particle. The toner, charged due to e.g. friction, provides latent image development by electrostatically attaching a latent image. The carrier is a fine particle generated by coating a magnetic material with e.g. an epoxy resin or the like. When the carrier and the toner are mixed and stirred together, the carrier charges the toner, and accordingly the toner has electrical charge.

The developing device200is configured so as to be detachable in the image forming apparatus main body12, and serves as an image forming structure attaching or removing to or from the image forming apparatus main body12. As an alternative to the singly attachment or removal of the developing device200to or from the image forming apparatus main body12, the image forming structure that, for instance, the developing device200and the entire or a part of the image forming section100except the developing device200are integrated may be detachable in the image forming apparatus main body12.

As shown inFIG. 2andFIG. 3, the developing device200has a developing device main body210, which has a developing opening212opposite to the photoreceptor110. The developing device main body210has a receiving opening214for receiving a toner particle supplied from a toner particle container omitted from the illustration. The developing device main body210further has a wall part216for separating in the developing device main body210. The inner space of the developing device main body210serves as a developer chamber220for containing a developer, which the developer chamber220partially has an area in which pressure is applied to the developer contained in the developer chamber220because of movement of the developer, i.e. a pressure application area S. The developing device main body210further serves as the image forming structure attached or removed to or from the image forming apparatus main body12.

Inside the developing device main body210, a development roller240, transport members260and270, a layer thickness regulating member230, and a pressure application area forming member280are disposed.

The development roller240is arranged in one side of the developing chamber220(the left side face ofFIG. 2), and serves as a developer carrier for sending a developer by holding. The development roller240has a development sleeve242and a magnet roller246which is positioned inside the development sleeve242and fastened in the developing device main body210.

The development sleeve242is cylindrically-shaped and made of e.g. aluminum. The development sleeve242is connected to a drive source130such as a motor with a power transmission mechanism (not shown) such as a gear. Thus, when the drive from the drive source130is transmitted, the development sleeve242turns around in the direction of the arrow mark a illustrated in FIG.2. The magnet roller246has a plurality of South Pole and North Pole consisting of permanent magnets, in the appropriate position. Therefore, a carrier is attached on the surface of the development sleeve242, and a magnetic brush is kept on the surface of the development sleeve242.

The transport members260and270serve as transport sections for transporting the developer contained in the development roller240side of the separated space inside the developer chamber220(the front side of the developing device, left side face inFIG. 2) and the other side (the back side of the developing device, the right side face inFIG. 2) toward the development roller240.

The transport member260has a shaft262mounted in the developing device main body210for rotating and plural blades264mounted on the shaft262. Therefore, the transport member260turns around after receipt of the power transmitted from the drive source omitted from the illustration to transport the toner particles received at a receiving opening214and the developer contained in the developing device main body210from the right side (downside inFIG. 3) toward the left side (upside inFIG. 3) of the developing device main body210while stirring. The arrow mark b shown inFIG. 3represents the transporting direction of the developer with the transport member260.

The transport member270has a shaft272mounted in the developing device main body210for rotating and plural blades274mounted on the shaft272. Therefore, the transport member270turns around after receipt of the power transmitted from the drive source omitted from the illustration to transport the developer transported by the transport member260and be in the left side of the developing device main body210toward the right side of the developing device main body210(downside inFIG. 3) while stirring. The arrow mark c shown inFIG. 3represents the transporting direction of the developer with the transport member260.

The layer thickness regulating member230is mounted on the developing device main body210so that a clearance is formed between the layer thickness regulating member230and the development sleeve242at a predetermined value. Therefore, when the development sleeve242turns around in the arrow mark a direction inFIG. 2, the layer thickness regulating member230regulates the layer thickness of the developer held on the development sleeve242by scraping an excess developer on the development sleeve242but remaining the developer in the predetermined thickness. After the scraping, the scraped developer by the layer thickness regulating member230stays in the developer chamber220.

The pressure application area forming member280serves as a pressure application area forming unit and a pressure regulating unit. The pressure application area forming member280further serves as a discharge amount regulating unit for regulating an amount of the developer discharged from the pressure application area S in response to the temperature of the developer in the pressure application area S. The pressure application area forming member280furthermore serves as a discharge port forming unit for forming a discharge port290through which the developer is discharged from the pressure application area S (refer toFIG. 5).

One end of the pressure application area forming member280abuts or is close to the layer thickness regulating member230, and the other end thereof is fastened to the wall part216. Therefore, the arrangement of the pressure application area forming member280provides the pressure application area S surrounded with the pressure application area forming member280, the layer thickness regulating member230, and the development roller240. As the described above, the pressure application area forming member280serves as the pressure application area forming unit which forms the pressure application area S in which pressure is applied to the developer contained in the developer chamber220because of movement of the developer.

In the pressure application area S, the developer transported by the transport member270and the developer scraped from the surface of the development sleeve242by the layer thickness regulating member230move in a circle with pressure, thereby the toner of the developer sufficiently charges. During the circulating, the developer heats in the pressure application area S due to e.g. heat from the drive source130, the drive transmitting mechanism connecting the drive source130to the development sleeve242, or the like. When the temperature of the developer rises in the pressure application area S, the fluidity and the circulation of the developer are reduced and thereby the density of the developer and the applied pressure against the developer increases in the pressure application area S. Thus, in the pressure application area S, the cohesion of the developer may occur, or the toner may not be sufficiently charged.

The pressure application area forming member280may be entirely constituted by e.g. a bimetallic strip. Note that, the bimetallic strip is a structure made of two or more metallic plates having different bending degree with temperature each other. The two or more kinds of metallic plates having a different thermal expansion coefficient each other are created by adding a material such as manganese, chrome, and copper to e.g. a Fe—Ni alloy. Further bonded the two or more kinds of metallic plates in e.g. cold-rolling, the bimetallic strip is produced. The bimetallic strip for the pressure application area forming member280may have a permissible temperature from −20 C.° to 150 C.° and the radius of the curvature more than 13×10−6K.

The radius of the curvature of the bimetallic strip k is a constant number defined by formula (I):
D=(k×t)/(L×L×T)
wherein D represents an amount of change, i.e. a warp amount in millimeters; t represents a thickness of the bimetallic strip in millimeters; L represents a length of the bimetallic strip in millimeters; T represents a varying temperature; and k represents a radius of the curvature.

If the temperature of the developer is equal to or less than a predetermined value in the pressure application area S, as shown inFIG. 2, one end of the pressure application area forming member280abuts or is close to the layer thickness regulating member230. The state prevents the developer in the pressure application area S from leaking from the position between the layer thickness regulating member230and the pressure application area forming member280, and allows the developer in the pressure application area S to be subjected to pressure and charging compared to a state in which the developer easily leaks from the pressure application area S.

The upward facing surface, inclined and opposite from the surface contacting the pressure application area5, of the pressure application area forming member280and the upward facing surface inclined of the wall part216serve as guides which guide the developer leaked from the pressure application area S toward the other end of the developer chamber220(the front side of the developing device200, i.e. the left side face inFIG. 2) opposite from the one end in which the development roller240is arranged (the back side of the developing device200, i.e. the right side face inFIG. 2).

FIG. 5illustrates the pressure application area forming member280.

As described above, when the temperature of the developer is equal to or less than the predetermined value in the pressure application area S, one end of the pressure application area forming member280abuts or is close to the layer thickness regulating member230. However, when the temperature of the developer in the pressure application area S rises because of e.g. a heat transfer from the drive source130, the pressure application area forming member280constituted by a bimetallic strip deforms in the direction of the arrow mark f inFIG. 5so as to increase the amount of the developer discharged from the pressure application area S. That is, as shown in a solid line inFIG. 5, the pressure application area forming member280deforms so that the discharge port290defined a clearance between one end of the pressure application area forming member280and the layer thickness regulating member230at a width D is formed or so that the width D of the discharge port290widens.

When the developer is increasingly discharged from the pressure application area S in the direction of an arrow mark h shown inFIG. 5because of the deformation of the pressure application area forming member280with temperature rising, the rise of the density of the developer and the rise of the pressure in the pressure application area S, caused by the temperature rising, are suppressed, and then the disadvantages that the developer is agglutinated and the toner particles of the developer is insufficiently charged is less likely to be caused.

As the temperature of the developer drops in the pressure application area S, the deformed pressure application area forming member280for discharging the developer deforms to reduce the discharge amount of the developer. That is, the deformation, toward the direction of two-dot chain line inFIG. 5, of the pressure application area forming member280with temperature falling provides the loss of the discharge port290defining a clearance between one end of the pressure application area forming member280and the layer thickness regulating member230at a width D or the reducing of the width D.

When the discharge amount of the developer in the pressure application area S decreases because of the deformation of the pressure application area forming member280with temperature falling, the pressure in the pressure application area S is likely to increase, and the toner particles is likely to be charged in the pressure application area S.

As described above, the pressure application area forming member280serves as the pressure application area forming unit and the pressure regulating unit. The pressure application area forming member280further serves as the discharge amount regulating unit that regulates the discharge amount of the developer discharged through the discharging port290from the pressure application area S with temperature of the developer in the pressure application area S. The pressure application area forming member280furthermore serves as the discharge port forming unit that forms the discharge port290through which the developer in the pressure application area S is discharged, and regulates a size of the discharge port290with the temperature of the developer in the pressure application area S.

FIG. 6illustrates the modified example of the pressure application area forming member280.

The pressure application area forming member280according to the first exemplary embodiment of the present invention is entirely constituted by a bimetallic strip (refer toFIG. 4). However one end of the pressure application forming member680according to the modified example of the present invention, which abuts or is close to the layer thickness regulating member230, has a bimetallic section682constituted by a bimetallic strip and partially arranged in one end thereof. Thus, the bimetallic section682deforms in response to the temperature of the developer in the pressure application area S in one end of the pressure application forming member680.

FIG. 7andFIG. 8illustrate a key part of the developing device700according to a second exemplary embodiment of the present invention. The developing device200according to the first exemplary embodiment described above has the pressure application area forming member280, which serves as the pressure application area forming unit, the pressure regulating unit, the discharge amount regulating unit regulating the discharge amount of the developer discharged from the pressure application area S in response to the temperature of the developer in the pressure application area S, and the discharge port forming unit forming the discharge port290through which the developer in the pressure application area S is discharged. However, the developing device700according to the second exemplary embodiment of the present invention has a pressure application area forming member780and a support786supporting the pressure application area forming member780, serving together as a pressure application area forming unit, a pressure regulating unit, a discharge amount regulating unit, and a discharge port forming unit.

The pressure application area forming member780is constituted by e.g. a plate made of aluminum. The support786constituted by a bimetallic strip has one end in which a pressure application area forming member780is mounted and the other end in which the wall part216is mounted.

When the temperature of the developer is equal to or less than the predetermined value in the pressure application area S, the pressure application area forming member780and the support786are in the position illustrated by two-dot chain line inFIG. 7, that one end of the pressure application area forming member780abuts or is close to a layer thickness regulating member730. In the two-dot chain line position, when the temperature of the developer rises in the pressure application area S, since the support786constituted by a bimetallic strip deforms, the pressure application area forming member780is displaced as shown by a solid line inFIG. 7so that the discharge amount of the developer from the pressure application area S increases.

When the temperature of the developer falls in the pressure application area8, the pressure application area forming member780, staying in the position to increase the discharge amount of the developer with temperature rising, is further displaced in the direction for reducing the discharge amount of the developer from the pressure application area S corresponding to the deformation of the support786. That is, the pressure application area forming member780is displaced toward the position shown by a two-dot chain lines inFIG. 7so as to lose the discharge port790or reduce the width of the discharge port790.

Note that, the developing device700according to the second exemplary embodiment of the present invention has same components as the above image forming apparatus10according to the first exemplary embodiment except the described-above parts. Then, the description of the same components will be omitted, and the same components will be denoted the same reference numerals in the description of the second exemplary embodiment of the present invention.

FIG. 9illustrates a modification example of the developing device700according to the second exemplary embodiment of the present invention.

While the developing device700of the second exemplary embodiment of the present invention described-above has the support786extending along a longitudinal direction of the development roller240(refer toFIG. 2) which supports the pressure application area forming member780singly (refer toFIG. 8), the modified developing device700has two supports786supporting together the pressure application area forming member780.

FIG. 10illustrates a key part of a developing device1000according to a third exemplary embodiment of the present invention. As described above, the pressure application area forming member780of the developing device700according to the second exemplary embodiment is supported by the support786having an approximately flat shape (refer toFIG. 7andFIG. 8). However, in the developing device1000according to the third exemplary embodiment of the present invention, a support1086supporting a pressure application area forming member1080has a coil shape.

The pressure application area forming member1080is constituted by e.g. a plate made of aluminum as well as the pressure application area forming member780of the second exemplary embodiment. The support1086, constituted by e.g. a bimetallic strip, is connected to the pressure application area forming member1080at the top. A left end and a right end of the pressure application area forming member1080are mounted inside the developing device main body10.

FIG. 10Aexplains the positions of the pressure application area forming member1080and the support1086in the case that the temperature of the developer is equal to or less than the predetermined value in the pressure application area S, and one end of the pressure application area forming member1080abuts or is close to the layer thickness regulating member230. When the temperature of the developer rises in the pressure application area S, the pressure application area forming member1080staying in the position shown inFIG. 10Ais displaced, as shown inFIG. 10B, in the direction for increasing the discharge amount of the developer from the pressure application area S corresponding to the deformation of the support1086constituted by a bimetallic strip.

As the temperature of the developer drops in the pressure application area S, the pressure application area forming member1080displaced for discharging the developer is displaced corresponding to the deformation of the support1086so as to reduce the discharge amount of the developer from the pressure application area S. That is, the pressure application area forming member1080is displaced to the position shown inFIG. 10Aso as to lose the discharge port290between one end of the pressure application area forming member1080and the layer thickness regulating member230or reduce the width D of the discharge port290.

Note that, the developing device1000according to the third exemplary embodiment of the present invention has same components as the above image forming apparatus10according to the first exemplary embodiment except the described-above parts. Then, the description of the same components will be omitted and the same components will be denoted the same reference numerals in the description of the third exemplary embodiment of the present invention.

In every exemplary embodiments described above, it is described herein that for instance the pressure application area forming member280constituted by a bimetallic strip allows regulation of the pressure applied to the developer, the discharge amount of the developer, and the size of the discharge port290with the temperature of the developer in the pressure application area S. Alternatively, the regulation of the pressure applied to the developer, the regulation of the discharge amount of the developer, and the regulation of the size of the discharge port290may be achieved by e.g. controlling mechanically the pressure application area forming member280in response to the temperature of the developer in the pressure application area S.

As described-above, the present invention is capable of being applied to an image forming apparatus such as a coping machine, a fax, and a printer and a developing device of these image forming apparatuses.