WO2019088538A1

WO2019088538A1 - Developing device with magnet

Info

Publication number: WO2019088538A1
Application number: PCT/KR2018/012516
Authority: WO
Inventors: Kazuhiko Takemoto
Original assignee: HP Printing Korea Co Ltd
Current assignee: HP Printing Korea Co Ltd
Priority date: 2017-10-31
Filing date: 2018-10-23
Publication date: 2019-05-09
Anticipated expiration: 2020-04-30
Also published as: JP2019082602A

Abstract

In a developing device, a developer stirring-feeding member adjacent a developer carrier includes a conveyance spiral to rotate in order to stir developer contained in a storage and in order to feed a developer from a storage to the developer carrier. The conveyance spiral has a thickness that is less or equal to 2 mm and a pitch within a range of 5 mm to 8 mm, inclusive. A layer regulating member limits a thickness of a layer of the developer carried on the developer carrier. A magnet of the developer carrier has a layer regulating pole and a drawing-up pole. A peak magnetic force a in a normal direction to the layer regulating pole is greater than a peak magnetic force b in a normal direction to the drawing-up pole, and a sum of the peak magnetic force a and the peak magnetic force b is less or equal to 95 mT.

Description

DEVELOPING DEVICE WITH MAGNET

An image forming apparatus using electrophotography may be mounted on a digital copier, a printer or the like, to develop, with toner, an electrostatic latent image formed by exposing a uniformly-charged outer circumferential surface of a photosensitive drum. The image forming apparatus may form a visualized toner image, and transfer and fix it to a recording medium (for example, paper). The image forming apparatus of this type may use a two-component developer composed of, for example, toner and a carrier, and adhere charged toner, via a developer carrier in a developing device, onto the outer circumferential surface of the photosensitive drum to thereby develop the electrostatic latent image.

FIG. 1 is a front view showing a schematic configuration of an example image forming apparatus including an example developing device.

FIG. 2 is a cross-sectional view in a longitudinal direction of the example developing device.

FIG. 3 is a cross-sectional view of the example developing device taken along line III-III of FIG. 2.

FIG. 4 is a sectional partial and enlarged view showing a developing roller and a photosensitive drum receiving a supply of toner of the example developing roller.

FIG. 5 is a schematic view showing pole magnetic forces of a magnet member located inside the developing roller of the example developing device.

FIG. 6 is a front view of a portion of a stirring-feeding member of the example developing device.

FIG. 7 is a graph showing a relationship between: a magnetic force of a drawing-up pole located inside the developing roller of the example developing device; and a temperature rise reduction effect.

FIG. 8 is a graph showing a relationship between: a magnetic force of a layer regulating pole located inside the developing roller of the example developing device; and a density unevenness.

FIG. 9 is a graph showing a relationship between: a sum of respective peak magnetic forces in a normal direction to the layer regulating pole and the drawing-up pole of the example developing device; and the temperature rise reduction effect.

FIG. 10 is a front view of a portion of a stirring-feeding member of a Comparative Example, in a state where the stirring-feeding member conveys developer.

FIG. 11 is a front view of a portion of a stirring-feeding member of the example developing device, in a state where the stirring-feeding member conveys developer.

FIG. 12 is a graph showing a relationship between a spiral thickness and a spiral-to-spiral distance in the stirring-feeding member of the example developing device; and a density unevenness and a conveyance property of developer.

FIG. 13 is a graph showing a temperature rise reduction effect in a bearing of the stirring-feeding member and the layer regulating member of the example developing device, together with two Comparative Examples.

FIG. 14 is a graph showing a relationship between the developer amount inside a developing unit of the example developing device and a density unevenness, together with two Comparative Examples.

FIG. 15 is a graph showing a relationship between a magnetic force in a normal direction to the layer regulating pole of the example developing device; and the temperature rise reduction effect.

FIG. 16 is a graph showing a relationship between a magnetic force in a normal direction to the drawing-up pole of the example developing device; and a temperature rise reduction effect.

FIG. 17 is a graph showing a relationship between a temperature rise reduction effect; and a peak magnetic force in a tangential direction between peak magnetic forces in a normal direction to the layer regulating pole and the drawing-up pole of the example developing device.

In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted.

In multifunctional machines and printers, speed-enhancement of devices may cause high speed rotation/sliding of motor(s) and other functional member(s), which may increase inner temperatures of devices, thereby increasing stress on a developer, and generating aggregates.

For reducing self-heating in developing devices, it may be effective to decrease an amount of developer carried by a developer carrier (for example, a developing roller) and to decrease an amount of developer regulated by a layer regulating member (for example, a doctor plate). The decrease in the amount of developer may result in a defect in forming a layer composed of the developer and the density unevenness, thereby affecting image quality.

In addition, from the viewpoints of cost and reduction of resources, technologies to prolong the life of devices and consumables have been applied, for example by automatically feeding and discharging a developer such as Auto Developer Refill (ADR) technique, such as for example, a machine with a configuration that changes an amount of developer inside a developing machine.

In an example developing device of an example image forming apparatus, a magnetic force of a magnet held by a developer carrier is reduced and a developer stirring-feeding member for feeding a developer, while stirring, to the developer carrier has a conveyance spiral with a plurality of spirals.

For example, a developing device may include: a storage section for containing a developer; a cylindrical developer carrier disposed in the storage section to rotate to carry and convey the developer to a predetermined developing area; a bar-like developer stirring-feeding member disposed in the storage section in juxtaposition with the developer carrier to supply, while stirring, the developer contained in the storage section to the developer carrier by rotation; and a layer regulating member for regulating, to a predetermined thickness, the thickness of a developer layer formed of the developer adhered to a peripheral surface of the developer carrier.

The developer carrier may be provided therein with a magnet member having a layer regulating pole disposed at a position facing the layer regulating member and a drawing-up (pickup) pole for moving the developer from the developer stirring-feeding member to the developer carrier.

The developer stirring-feeding member may be provided with a conveyance spiral having a plurality of blades on an outer periphery thereof. A peak magnetic force a in the normal direction to the layer regulating pole and a peak magnetic force b in the normal direction to the drawing-up pole may satisfy the formulas (1) and (2), a > b … (1) and a + b ≤ 95 mT … (2). The conveyance spiral may have a thickness t satisfying the formula (3), t ≤ 2 mm … (3). The conveyance spiral may have a pitch w between adjacent blades satisfying the formula (4), 5 mm ≤ w ≤ 8 mm … (4).

Accordingly, the peak magnetic force in the normal direction to the layer regulating pole and the peak magnetic force in the normal direction to the drawing-up pole in the magnet member provided inside the developer carrier may be decreased, in order to reduce an amount of developer carried by the developer carrier and an amount of developer regulated by the layer regulating member.

As a result, a pressure applied to the developer near the layer regulating member is decreased and a torque of the developer carrier is lowered, thus reducing self-heating of the developing device.

In order to reduce density unevenness caused by a defect in forming a layer on the surface of the developer carrier, which is generated by a decrease of magnetic force, a provision of the conveyance spiral with a plurality of blades may feed the developer to the developer carrier at high frequency and in such an amount that reduces roughness and density without dropping a conveyance speed.

In addition, the thickness t of the conveyance spiral may be set to 2 mm or less and the pitch w between adjacent blades may be set to 5 mm ≤ w ≤ 8 mm, in order to optimize the conveyance performance of a conveyance member with an increased number of blades.

Accordingly, the margin for occurrence of density unevenness at the time of change in a developer amount inside the storage section can be increased.

In some examples, the peak magnetic force a in the normal direction to the layer regulating pole may be 60 mT or less.

Accordingly, heat generated by friction between the layer regulating member and a developer near the layer regulating member may be reduced.

In some examples, the peak magnetic force b in the normal direction to the drawing-up pole may be 35 mT or less.

Accordingly, an amount of developer maintained on the developer carrier by the drawing-up pole to reduce the friction between the developer and the surface of the developer carrier may be decreased, thereby reducing heat generation.

In some examples, a peak magnetic force c in the tangential direction formed between the peak magnetic force a in the normal direction to the layer regulating pole and the peak magnetic force b in the normal direction to the drawing-up pole may be 45 mT or less.

Accordingly, friction between the developer and the surface of the developer carrier also decreases, which reduces heat generation.

In some examples, the cylindrical developer carrier may have an outer diameter of 16 mm or more, and 25 mm or less (e.g. between 16 mm and 25 mm, inclusive), for achieving an improved effect of reducing self-heating.

In some examples, the conveyance spiral in the developer stirring-feeding member may have an outer diameter of 10 mm or more, and 21 mm or less (e.g. between 10 mm and 21 mm, inclusive), for achieving an improved effect of reducing self-heating.

In some examples, a distance between an outer peripheral portion of the developer carrier and an outer peripheral portion of the conveyance spiral in the developer stirring-feeding member may be 3.5 mm or more, for achieving an improved effect of reducing self-heating.

In some examples, the example developing device further includes a bar-like developer stirring-conveyance member disposed in the storage section in juxtaposition with the developer stirring-feeding member to convey, while stirring, the developer to the developer stirring-feeding member by rotation, wherein the position of a rotation axis of the developer stirring-feeding member is arranged below the position of a rotation axis of the developer carrier, and wherein the position of the rotation axis of the developer stirring-feeding member is arranged above the position of a rotation axis of the stirring-conveyance member.

Accordingly, even in a configuration wherein the developer carrier, the developer stirring-feeding member and the developer stirring-conveyance member are disposed sequentially from an upper side to cause a remarkable retention of developer, the balance of a retained amount is prevented from being largely deteriorated at the time of circulation conveyance of the developer.

In some examples, the developer is supplied from a developer replenishing device to the storage section while excessive developer may be discharged from the storage section.

Accordingly, in an example developing device having a developer replenishing device, an increase or decrease in the amount of developer occurs in the developing device, depending on various conditions. In this way, even when a fluctuation occurs in the developer amount, images may be provided in a stable manner.

Example image forming apparatuses include a developing device according to examples described herein, to form an image.

According to examples disclosed herein, self-heating caused by a developer in a developing device may be reduced, in order to prevent a defect in forming a layer of developer.

Examples of the disclosure will be described by referring to the drawings.

FIG. 1 shows a schematic configuration (viewed from the side) of an example image forming apparatus (for example, a printer) including an example developing device.

Overall configuration of image forming apparatus

The example image forming apparatus 1 is an apparatus for forming a color image by use of each color of, for example, magenta, yellow, cyan and black. As shown in FIG. 1, the image forming apparatus 1 includes an image forming section 100 and forms an image on paper (recording medium) P. The image forming section 100 is provided with a waste toner collection section (not illustrated), to which excessive developer is discharged. Further, the image forming section 100 receives new developer from a developer replenishing device which is not shown.

The image forming section 100 includes a recording medium feeding unit 10 for conveying paper P, developing devices 20 for developing an electrostatic latent image, a transfer unit 30 for secondary transfer of a toner image on the paper P, photosensitive drums 40 as an electrostatic latent image carrier having an image formed on a circumferential surface thereof, and a fixing unit 50 for fixing the toner image on the paper P.

The recording medium feeding unit 10 conveys the paper P, on which an image is to be formed, on a feeding path R1. The paper P is stacked and accommodated in a cassette K, and picked up one by one and fed by a paper feeding roller.

The developing device 20 is provided for each of the four colors. Each developing device 20 has a developing roller 21 for allowing toner to be carried on a photosensitive drum 40. The developing device 20 adjusts a mixing ratio of a toner and a carrier to a desired ratio, and blends and stirs them, thereby preparing a developer having the toner uniformly dispersed and an optimal charge amount imparted thereto. This developer is carried on the developing roller 21. Then, when the rotation of the developing roller 21 conveys the developer to a region facing the photosensitive drum 40, the toner of the developer carried on the developing roller 21 is moved onto the electrostatic latent image formed on the outer circumferential surface of the photosensitive drum 40, and the electrostatic latent image is developed.

The transfer unit 30 conveys a toner image formed by each developing device 20 to the secondary transfer region R2 where the toner image is to be secondarily transferred to the paper P. The transfer unit 30 has a transfer belt 31, suspending

rollers

31a, 31b, 31c and 31d suspending the transfer belt 31, a primary transfer roller 32 holding the transfer belt 31 together with the photosensitive drum 40, and a secondary transfer roller 33 holding the transfer belt 31 with the suspending roller 31d. The transfer belt 31 is an endless belt, which is circularly moved by suspending

rollers

31a, 31b, 31c and 31d.

Four photosensitive drums 40 are provided for the respective four colors. Each photosensitive drum 40 is provided along a moving direction of the transfer belt 31. The developing device 20, a charging roller 41, an exposure unit 42 and a cleaning unit 43 are located on the photosensitive drum 40.

The charging roller 41 provides charging means that uniformly charges the surface of the photosensitive drum 40 at a predetermined electric potential. The charging roller 41 moves while following the rotation of the photosensitive drum 40. The exposure unit 42 exposes the surface of the photosensitive 40, which is charged by the charging roller 41, in accordance with the image to be formed on the paper P. This changes the electric potential of a portion, which has been exposed by the exposure unit 42, of the surface of the photosensitive drum 40, and thereby, an electrostatic latent image is formed. Four developing devices 20 develop an electrostatic latent image formed on the photosensitive drum 40 by toner supplied from toner tanks N for respective colors provided to face respective developing devices 20, so that a toner image is generated. The cleaning unit 43 collects toner remaining on the photosensitive drum 40 after the toner image formed on the photosensitive toner 40 is primarily transferred to the transfer belt 31.

The fixing unit 50 adheres and fixes the toner image, which is secondarily transferred from the transfer belt 31 to the paper P. The fixing unit 50 has a heating roller 51 for heating the paper P and a pressing roller 52 for pressing the heating roller 51. A fixing nip portion 51a as a contact region is provided between the heating roller 51 and the pressing roller 52. Passing the paper P through the fixing nip portion 51a allows fusing and fixing of the toner image on the paper P. After the secondary transfer of the toner image on the paper P, toner remaining on the transfer belt 31 is collected by a belt cleaning device.

Further, the image forming apparatus 1 is provided with

discharge rollers

53, 54 for discharging the paper P having the toner image fixed by the fixing unit 50 to the outside of the apparatus.

At a developing process of the developing device 20, the electrostatic latent image is developed, so that a toner image is formed. The formed toner image is primarily transferred from the photosensitive drum 40 to the transfer belt 31 in a region where the photosensitive drum 40 and the transfer belt 31 face each other. Toner images formed on four photosensitive drums 40 are sequentially overlaid on the transfer belt 31, so that a single stacked toner image is formed. The overlaid toner image thus formed is secondarily transferred to the paper P fed from the recording medium feeding unit 10 in the secondary transfer region R2 where the suspending roller 31d and the secondary transfer roller 33 face each other.

Developing Device

As shown in FIGS. 2 and 3, the example developing device 20 includes a storage section (housing) 140, a stirring-conveyance part 110 and a feeding-conveyance part 120 each partitioned and contained in the storage section 140, and a developing roller (magnet roller) 21.

The stirring-conveyance part 110 conveys a developer in a left direction in FIG. 2 by a driving force transmitted, for example, via a gear box from the outside of the developing device 20. The developer used herein may be a two-component developer containing a toner and a carrier.

The feeding-conveyance part 120 is arranged above and together with the stirring-conveyance part 110. The developer is delivered from the stirring-conveyance part 110 in an upward direction (the direction indicated by Arrow A) through a first communicating part 142 at a left end portion, and the developer is supplied to the developing roller 21 arranged directly thereabove and therewith while being conveyed in the feeding-conveyance part 120 in a right direction in FIG. 2. When the remaining developer which has been supplied to the developing roller 21 is conveyed to a right end portion of the feeding-conveyance part 120, it is moved in a downward direction (the direction indicated by Arrow B) through a second communicating part 142. Further, it is stirred and conveyed again by the stirring-conveyance part 110 together with toner replenished in accordance with the necessity, and the above circulation is repeated.

The developing roller 21 is composed of, for example, a rotatable sleeve and an axial member, which is fixed therein and has a magnet member with a plurality of magnetic poles. The developer supplied from the feeding-conveyance part 120 is controlled by a layer regulating member 160 (see FIG. 3) to have a predetermined thickness on the developing roller 21, and then, it is conveyed near the photosensitive drum 40 (see FIG. 4), so that an electrostatic latent image formed on a circumferential surface of the photosensitive drum 40 is developed by the toner in the developer.

Stirring-conveyance Part and Feeding-conveyance Part

The stirring-conveyance part 110 is configured so that a bar-like stirring-conveyance member 111 having a rotation axis 111a is provided rotatably via a bearing 112 in the storage section 140. The rotation axis 111a of the stirring-conveyance member 111 has a single spiral blade (conveyance spiral) 111b for conveying a developer while stirring in an area except for an area near an end of conveyance downstream of the developer. The spiral blade 111b may be provided in part with, for example, a paddle for stirring the developer. Further, the rotation axis 111a of the stirring-conveyance member 111 has a reverse spiral blade 111g provided via a gap at conveyance downstream of the developer.

The stirring-conveyance part 110 and the feeding-conveyance part 120 disposed thereabove are partitioned by a partition wall 141, and also they communicate with each other via the above-described first communicating part 142 and second communicating part.

The feeding-conveyance part 120 is configured so that a bar-like stirring-feeding member 121 having a rotation axis 121a is provided rotatably via a bearing 122 between the stirring-conveyance part 110 and the developing roller 21 in the storage section 140. The rotation axis 121a of the stirring-feeding member 121 has multiple spiral blades (conveyance spirals) 121b for supplying the developer to the developing roller 21 while stirring and conveying. As an example, spiral blades 121b with two blades may be employed. The outer diameter of the rotation axis 121a is set to be larger than that of the rotation axis 111a of the stirring-conveyance member 111, and thus, the conveyance speed of the developer by the stirring-feeding member 121 is lower than that of the stirring-conveyance member 111. Note that the outer diameter of the rotation axis 121a may be set to be smaller in the vicinity of the first communicating part 142 than those at other portions of the rotation axis. This facilitates the delivery of the developer that flows into the feeding-conveyance part 120 through the first communicating part 142. Further, there is provided a predetermined space between the outer circumference of the developing roller 21 and the outer circumference of the spiral blade 121b in the stirring-feeding member 121.

Operation of Developing Device

In the example developing device 20, the developer in the stirring-conveyance part 110 is conveyed toward the first communicating part 142 while stirred by the spiral blade 111b. When the developer is conveyed to the first communicating part 142, an action works on the developer in such a way that, at a left end of the gap as described above, the developer is drawn and collected, as if being squeezed, toward the gap by the reverse spiral blade 111g, and lifted upward. At this time, the speed-up of the device results in a further temperature rise of the developer.

The developer conveyed from the stirring-conveyance part 110 to the feeding-conveyance part 120 is conveyed by the spiral blade 121b of the stirring-feeding member 121 in the right direction of FIG. 2, and simultaneously, a portion of the developer is supplied on the peripheral surface of the developing roller 21.

Developing Roller

A configuration of an example developing roller will be described by referring to the drawings.

FIG. 4 shows an enlarged cross-sectional configuration of a portion including the example developing roller 21 and a photosensitive drum 40, which receives a toner supply from the developing roller 21. In addition, FIG. 5 shows detailed examples of polar magnetic force in the example developing roller 21.

As shown in FIGS. 4 and 5, the example developing roller 21 includes a magnet member 21a provided therein, and the magnet member has at least a layer regulating pole N2 disposed at a position facing the layer regulating member 160 and a drawing-up pole S3 for moving the developer from the stirring-feeding member 121 to the developing roller 21. This magnet member 21a may be formed integrally with an axial body of the developing roller 21 or may be formed separately from the axial body. The peak magnetic force a in the normal direction to the layer regulating pole N2 and the peak magnetic force b in the normal direction to the drawing-up pole S3 preferably satisfy a > b and a + b ≤ 95 mT.

Further, as shown in FIGS. 2 and 6, the stirring-feeding member 121 is provided with a spiral blade 121b having several blades on an outer peripheral surface thereof. The spiral blade 121b has a thickness t preferably satisfying t ≤ 2 mm. Hereafter, the thickness t of the spiral blade 121b is also referred to as "spiral thickness t."

Further, the spiral blade 121b has a pitch w between adjacent blades preferably satisfying 5 mm ≤ w ≤ 8 mm. The pitch w between adjacent blades of the spiral blade 121b may also be referred to herein as "spiral-to-spiral distance w."

In examples described above, the magnet member 21a is disposed inside the developing roller 21; the magnetic force a in the normal direction to the layer regulating pole N2 located to face the layer regulating member 160 and the peak magnetic force b in the normal direction to the drawing-up pole S3 for moving the developer from the feeding-conveyance member 121 to the developing roller 21 satisfy a > b and a + b ≤ 95 mT.

Accordingly, as shown in FIG. 5, a smaller peak magnetic force b in the normal direction to the drawing-up pole S3 than a conventional one (Comparative Example) may reduce an amount of developer held by the example developing roller 21. As a result, the friction between the developer and the sleeve as an outer shell of the developing roller 21 is decreased, and also the amount of developer regulated by the layer regulating member 160 is reduced. Therefore, the decreased friction between the developer and the layer regulating member 160 can reduce heat generation of the developer. In this case, when the magnetic force a in the normal direction to the layer regulating pole N2 is set as a fixed value, a pole magnetic force capable of providing a valid effect on a temperature rise is within a region D1 shown in FIG. 7. A region D2 may represent a region wherein a smaller effect is obtained.

In the graph shown in FIG. 7, the horizontal axis shows a peak magnetic force b in the normal direction to the drawing-up pole S3. Further, as described above, the peak magnetic force a in the normal direction to the layer regulating pole N2 is set as a fixed value. The vertical axis shows a temperature difference (reduced value) from that of Comparative Examples. The location for temperature measurement is the layer regulating member 160. A thermocouple is used as a temperature measuring device. A design objective value of the reduced temperature is 3℃ or higher.

Further, in the case that the peak magnetic force b in the normal direction to the drawing-up pole S3 is set as a fixed value and the layer regulating pole magnetic force a is largely varied, a pole magnetic force capable of providing a valid effect on density unevenness is within a region D3 shown in FIG. 8. A region D4 represents a region outside an allowable level.

In the graph shown in FIG. 8, the horizontal axis shows a peak magnetic force a in the normal direction to the layer regulating pole N2. Further, as described above, the peak magnetic force b in the normal direction to the drawing-up pole S3 is set as a fixed value. The vertical axis shows an occurrence grade for density unevenness. The occurrence grade may be referred to as, for example, "G0 (good): no occurrence," "G1: very minor level of occurrence," "G2: minor level of occurrence," "G3: remarkable level of occurrence," "G4: very remarkable level of occurrence" and "G5: significant level of occurrence."

As shown in FIGS. 7 and 8, a pole magnetic force for enabling the reduction of temperature rise and the density unevenness to be compatible has the relationship of a > b. Further, as shown in FIG. 9, satisfying the relationship of a + b ≤ 95 mT provides a reduced temperature difference of 3℃ or higher, yielding a valid effect on the reduction of temperature rise (region D5). In the graph of FIG. 9, the horizontal axis shows a sum of the above peak magnetic forces a and b. The vertical axis shows a temperature difference (reduced value) from Comparative Examples.

However, a decrease of pole magnetic force at the developing roller 21 for reducing a temperature rise of the developer may result in an uneven layer formation on the developing roller 21 due to a defect in drawing up the developer.

Accordingly, the example developing roller 21 is provided with a plurality of blades of the spiral blade 121b on the stirring-feeding member 121, and the spiral blade 121b has a thickness t of 2 mm or less. Further, the spiral blade 121b has a pitch w between adjacent blades, which is set to 5 mm ≤ w ≤ 8 mm. An increased number of blades of the spiral blade 121b can supply the developer at higher frequency, without reducing a conveyance speed, e.g., enabling the developer to be supplied to the developing roller 21 in an amount at an interval not to cause roughness and density.

For example, as shown by a stirring-feeding member 121A according to a Comparative Example of FIG. 10, when the pitch between adjacent blades of the spiral blade 121b is relatively large, the roughness and density occurs on the conveyed developer 60. In the case of the stirring-feeding member 121 according to the example of FIG. 11, the stirring-feeding member 121 having a plurality of blades of the spiral blade 121b conveys the developer 60, thereby preventing the occurrence of the roughness and density, which may occur on the conveyed developer 60.

As the spiral blade 121b having a plurality of blades may include three or more blades, wherein each blade has a thickness t of 2 mm or less and a pitch w between adjacent blades satisfies the range of 5 mm ≤ w ≤ 8 mm.

Even when the number of blades of the spiral blade 121b is increased, the conveyance speed of a developer is reduced and the conveyance amount is decreased.

For example, in the case of a developing device for forming an image by circulation conveyance of a developer, the conveyance balance of a developer would be remarkably deteriorated between a stirring-feeding member 121 for supplying the developer to a developing roller 21; and a stirring-conveyance member 111 for stirring and conveying replenished toner.

The thickness t of the spiral blade 121b is set to 2 mm or less, in order to increase a conveyable volume of developer, thereby increasing an absolute amount of developer to be conveyed by the spiral blade 121b.

In addition, in the case of the example spiral blade 121b having a plurality of blades, setting a pitch w between adjacent blades to 5 mm ≤ w ≤ 8 mm feeds a developer on the developing roller 21 in a state of less roughness and density with a shorter cycle. This can prevent a defect of layer formation from occurring on a developer, thereby enabling an improvement as to density unevenness on images.

Further, a synergistic effect with the thickness of the spiral blade 121b optimizes a conveyance speed and a conveyance amount of developer, thus preventing deterioration of the conveyance balance of developer with the stirring-conveyance member 111.

In addition, even in the case of the configuration wherein the amount of developer in the developing device 20 is largely varied or the state of developer is changed by an environment, time degradation or the like, stable image formation is possible.

FIG. 12 shows a relationship between the spiral thickness and the spiral-to-spiral distance, and the density unevenness and the conveyance property of developer. As shown in FIG. 12, it is understood that a region D6 wherein the spiral thickness is t ≤ 2 mm and the spiral-to-spiral distance is 5 mm ≤ w ≤ 8 mm is a region having less density unevenness and good conveyance property of developer. A region D7 in the figure is a region wherein the spiral-to-spiral distance is small and the spiral thickness is relatively large. In addition, a region D8 is a region wherein the spiral-to-spiral distance is relatively large.

FIG. 13 is a graph showing a comparison in the temperature rise during operation between configurations of Comparative Examples I and II, and of an example configuration III. Bar graphs (I, II and III) at the left side represent temperatures of bearings of respective stirring-feeding members. Bar graphs (I, II and III) at the right side represent temperatures of respective layer regulating members. Comparative Example I is a case in which a high magnetic developing roller is rotated at a low speed (500 rpm). Comparative Example II is a case wherein a high magnetic developing roller is rotated at a high speed (600 rpm). In example configuration III, a low magnetic developing roller 21 is rotated at a high speed (600 rpm). Conditions for measurement are set so that the temperature is 20℃ and the humidity is 55%. A thermocouple is used as a temperature measuring device.

As shown in FIG. 13, in the case of the bar graph of Comparative Example II (high magnetic force and high speed rotation), the bearing of the stirring-feeding member and the layer regulating member exhibit a high temperature. In contrast, in the case of the bar graph of example configuration III (low magnetic force and high speed rotation), the bearing 122 of the stirring-feeding member 121 and the layer regulating member 160 both exhibit the lowest temperature.

Further, FIG. 14 is a graph showing a comparison of the relationship between the developer amount in a developing unit (storage section) and the density unevenness between Comparative Examples IV and V and an example configuration VI during operation. The horizontal axis shows an amount of developer in the developing unit. The vertical axis shows density unevenness, and the occurrence grade (G0 to G5) expressing the degree of the density unevenness as explained for FIG. 8. Comparative Example IV is a case wherein a high magnetic force developing roller and a conventional stirring-feeding member are used. Comparative Example V is a case wherein a low magnetic force developing roller and a conventional stirring-feeding member are used. In example configuration VI, a low magnetic force developing roller 21 and the stirring-feeding member 121 having a plurality of spirals are used. In the above, a target value (design value) of developer amount in a developing unit is 250 ± 25 g.

As shown in FIG. 14, in the case of the graph of Comparative Example V (low magnetic force and conventional stirring-feeding member), the amount of developer required to eliminate density unevenness becomes larger than the design value, thus providing a smaller tolerance relative to the volume of a developer storage chamber. This causes a stirring defect with supplied toner; or when a sensor or the like for density measurement is installed to a developing device, it causes a false detection due to a change in the density of developer. On the other hand, the graph of this example configuration VI (low magnetic force and stirring-feeding member 121 with a plurality of spirals) exhibits a much larger tolerance than the graph of Comparative Example IV (high magnetic force and conventional stirring-feeding member).

The example developing roller 21 may have an outer diameter (sleeve diameter) of 16 mm or more and 25 mm or less, in order to produce an improved effect.

In addition, in the stirring-feeding member 121, the spiral blade 121b may have an outer diameter of 10 mm or more and 21 mm or less (e.g. between 10 mm and 21 mm, inclusive), in order to produce an improved effect.

In addition, a space between an outer periphery of the developing roller 21 and an outer periphery of the spiral blade 121b in the stirring-feeding member 121 may be 3.5 mmm or more, in order to produce an improved effect.

Further, the position of the rotation axis 121a of the stirring-feeding member 121 may be arranged below that of the rotation axis of the developing roller 21, while the position of the rotation axis 121a of the stirring-feeding member 121 may be above that of the rotation axis 111a of the stirring-conveyance member 111. Accordingly, the developing roller 21 is disposed in an upper portion, and the stirring-feeding member 121 and the stirring-feeding member 111 both are disposed sequentially at a lower portion. Accordingly, the developing roller 21, the stirring-feeding member 121 and the stirring-conveyance member 111 are disposed in tandem with each other in the direction of gravitational force. In this case, a developer is lifted up at a downstream end in the conveyance direction of the developer as described above, and thereby, the developer is delivered by circulation conveyance. This enables the developer to be retained at the first communicating part 142 shown in FIG. 2. Even in such a configuration that causes a remarkable retention of developer, the developing device 20 will be prevented from deteriorating the balance of a retained amount at the time of circulation conveyance of the developer.

In addition, a developer may be supplied from a developer replenishing device to the storage section 140, and also, excessive developer may be discharged from the storage section 140. In this way, the example developing device 20 may include a mechanism for receiving an addition of new developer to improve the image quality due to deterioration of developer and discharging excessive developer generated by this addition.

Accordingly, an increase or decrease in the amount of developer occurs in the developing device depending on various conditions. Even when a fluctuation occurs in the developer amount as described above, the example developing device 20 can provide images in a more stable manner.

(First Modified Example/Limitation of Magnetic Force of Layer Regulating Pole)

A first modified example that limits a magnetic force in the layer regulating pole N2 of the magnet member 21a will be described.

In this modified example, the layer regulating pole N2 is disposed at a position facing the layer regulating member 160 of the magnet member 21a, and the peak magnetic force a in the normal direction to the layer regulating pole N2 is set to 60 mT or less. Heat generation caused by friction between a developer and the layer regulating member 160 can thereby be effectively reduced in a region facing the layer regulating member 160 on a periphery of the developing roller 21, as shown in FIG. 15.

The graph shown in FIG. 15 shows the peak magnetic force a in the normal direction to the layer regulating pole N2 as the horizontal axis; and a temperature difference (reduced value) as the vertical axis. From FIG 15, it is understood that when the peak magnetic force a in the normal direction to the layer regulating pole N2 is set to 60 mT or less, more preferably 58 mT or less, a reduced temperature of 3℃ or higher as the design objective value can be achieved (region D9).

(Second Modified Example/Limitation of Magnetic Force of Drawing-up Pole)

A second modified example that limits a magnetic force in the drawing-up pole S3 of the magnet member 21a will be described.

In this modified example, among magnetic forces of the magnet member 21a, the peak magnetic force b in the normal direction to the drawing-up pole S3 for drawing up a developer from the stirring-feeding member 121 to the developing roller 21 is set to 35 mT or less. Accordingly, the drawing-up pole S3 reduces an amount of developer to be carried on a peripheral surface of the developing roller 21 as shown in FIG. 16, which may reduce heat generation caused by friction between a developer and a sleeve constituting the developing roller 21.

The graph shown in FIG. 16 shows the peak magnetic force b in the normal direction to the drawing-up pole S3 as the horizontal axis; and a temperature difference (reduced value) as the vertical axis. From FIG. 16, it is understood that when the peak magnetic force b in the normal direction to the drawing-up pole S3 is set to 35 mT or less, a reduced temperature of 3℃ or higher as the design objective value can be implemented (region D10).

(Third Modified Example/Limitation of Magnetic Force in Tangential Direction Between Layer Regulating Pole and Drawing-up Pole)

A third modified example that limits a peak magnetic force c in the tangential direction between the peak magnetic force in the normal direction to the layer regulating pole N2 and the peak magnetic force in the normal direction to the drawing-up pole S3, will be described.

In this modified example, among magnetic forces of the magnet member 21a, the peak magnetic force c in the tangential direction formed between the peak magnetic force a in the normal direction to the layer regulating pole N2 and the peak magnetic force b in the normal direction to the drawing-up pole S3 is set to 45 mT or less. This peak magnetic force c is indicated in FIGS. 4 and 5.

When this is employed, the drawing-up pole S3 reduces an amount of developer to be carried on a peripheral surface of the developing roller 21 in a similar manner as in the second modified example as shown in FIG. 17, in order to reduce heat generation caused by friction between a developer and a sleeve constituting the developing roller 21.

The graph shown in FIG. 17 shows, as the horizontal axis, the peak magnetic force c in the tangential direction between the peak magnetic force a in the normal direction to the layer regulating pole N2 and the peak magnetic force b in the normal direction to the drawing-up pole S3; and as the vertical axis, a temperature difference (reduce value). From FIG. 17, it is understood that when the peak magnetic force c is set to 45 mT or less, a reduced temperature of 3℃ or higher as a design objective value can be implemented (region D11).

It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail.

Claims

A developing device comprising:

a storage section to store a developer;

a developer carrier located in the storage section to rotate, in order to carry and convey the developer to a predetermined developing area;

a developer stirring-feeding member located in the storage section in juxtaposition with the developer carrier, to feed, while stirring, the developer contained in the storage section to the developer carrier by rotation, the developer stirring-feeding member comprising an outer periphery and a conveyance spiral having a plurality of blades on the outer periphery thereof; and

a layer regulating member to regulate, to a predetermined thickness, the thickness of a developer layer formed of the developer adhered to a peripheral surface of the developer carrier,

wherein the developer carrier comprises a magnet member having a layer regulating pole located at a position facing the layer regulating member and a drawing-up pole to move the developer from the developer stirring-feeding member to the developer carrier,

wherein a peak magnetic force a in a normal direction to the layer regulating pole is greater than a peak magnetic force b in a normal direction to the drawing-up pole,

wherein a sum of the peak magnetic force a and the peak magnetic force b is less or equal to 95 mT,

wherein the conveyance spiral has a thickness t that is less or equal to 2 mm, and

wherein the conveyance spiral has a pitch w between adjacent blades that is within a range of 5 mm and 8 mm, inclusive.
The developing device according to claim 1, wherein the peak magnetic force a in the normal direction to the layer regulating pole is 60 mT or less.
The developing device according to claim 1, wherein the peak magnetic force b in the normal direction to the drawing-up pole is 35 mT or less.
The developing device according to claim 1, wherein a peak magnetic force c in a tangential direction formed between the peak magnetic force a in a normal direction to the layer regulating pole and the peak magnetic force b in the normal direction to the drawing-up pole, is 45 mT or less.
The developing device according to claim 1, wherein the developer carrier is cylindrical and has an outer diameter between 16 mm and 25 mm, inclusive.
The developing device according to claim 1, wherein the conveyance spiral in the developer stirring-feeding member has an outer diameter between 10 mm and 21 mm, inclusive.
The developing device according to claim 1, wherein a distance between an outer peripheral portion of the developer carrier and an outer peripheral portion of the conveyance spiral in the developer stirring-feeding member is 3.5 mm or more.
The developing device according to claim 1, further comprising a bar-like developer stirring-conveyance member disposed in the storage section in juxtaposition with the developer stirring-feeding member to convey, while stirring, the developer to the developer stirring-feeding member by rotation,

wherein the position of a rotation axis of the developer stirring-feeding member is located below the position of a rotation axis of the developer carrier; and

wherein the position of the rotation axis of the developer stirring-feeding member is located above the position of a rotation axis of the developer stirring-conveyance member.
The developing device according to claim 1, the storage section to receive the developer from a developer replenishing device when excessive developer is discharged from the storage section.
An image forming apparatus comprising:

a storage to store a developer;

a developer carrier located in the storage to rotate, in order to carry and convey the developer to a developing area;

a developer stirring-feeding member located adjacent the developer carrier in the storage, the developer stirring-feeding member including a conveyance spiral to rotate in order to stir the developer contained in the storage and in order to feed the developer from the storage to the developer carrier, wherein the conveyance spiral has a thickness t that is less or equal to 2 mm and a pitch w between adjacent blades that is within a range of 5 mm to 8 mm, inclusive; and

a layer regulating member to limit a thickness of a layer of the developer carried on the developer carrier,

wherein the developer carrier comprises a magnet having a layer regulating pole adjacent the layer regulating member and a drawing-up pole to transfer the developer from the developer stirring-feeding member to the developer carrier,

wherein a peak magnetic force a in a normal direction to the layer regulating pole is greater than a peak magnetic force b in a normal direction to the drawing-up pole, and

wherein a sum of the peak magnetic force a and the peak magnetic force b is less or equal to 95 mT.
A developing device comprising:

a storage to store a developer;

a developer carrier located in the storage to rotate, in order to carry and convey the developer to a developing area;

a developer stirring-feeding member located adjacent the developer carrier in the storage, the developer stirring-feeding member including a conveyance spiral to rotate in order to stir the developer contained in the storage and in order to feed the developer from the storage to the developer carrier, wherein the conveyance spiral has a thickness t that is less or equal to 2 mm and a pitch w between adjacent blades that is within a range of 5 mm to 8 mm, inclusive; and

a layer regulating member to limit a thickness of a layer of the developer carried on the developer carrier,

wherein the developer carrier comprises a magnet having a layer regulating pole adjacent the layer regulating member and a drawing-up pole to transfer the developer from the developer stirring-feeding member to the developer carrier,

wherein a peak magnetic force a in a normal direction to the layer regulating pole is greater than a peak magnetic force b in a normal direction to the drawing-up pole, and

wherein a sum of the peak magnetic force a and the peak magnetic force b is less or equal to 95 mT.
The developing device according to claim 11, wherein the peak magnetic force a in the normal direction to the layer regulating pole is 60 mT or less.
The developing device according to claim 11, wherein the peak magnetic force b in the normal direction to the drawing-up pole is 35 mT or less.
The developing device according to claim 11, wherein a peak magnetic force c in a tangential direction formed between the peak magnetic force a in a normal direction to the layer regulating pole and the peak magnetic force b in the normal direction to the drawing-up pole, is 45 mT or less.
The developing device according to claim 11, wherein the developer carrier is cylindrical and has an outer diameter between 16 mm and 25 mm, inclusive.