Patent Grant
10942470
The present invention relates to a developing apparatus, a process cartridge, and an image forming apparatus.
Conventionally, an electrophotographic image forming apparatus using a magnetic single-component developing configuration includes magnetic toner, a developing roller for bearing the magnetic toner, a fixed magnet disposed in the developing roller, and a developing blade for restricting the magnetic toner on the surface of the developing roller to a predetermined toner layer. These components are used to develop toner onto an electrostatic latent image formed on the photosensitive drum. The magnetic toner on the surface of the developing roller is present in the form of chains (hereinafter referred to as “magnetic chains”) by a magnetic field of a fixed magnet, and is frictionally charged when restricted by the developing blade to obtain charge amount necessary for image formation.
However, the charge amount of toner needs to be increased in order to improve development responsiveness of latent images due to the recent increase in speed and image quality of image forming apparatuses. However, there is a problem in that the toner having high charge amount may be increased in electrostatic attachment force and easily stick to the developing roller surface and it is thus more difficult to restrict the toner by the developing blade.
As countermeasures for the problem, before the toner sticking to the developing roller surface is restricted by the developing blade, a stripping member such as a fur brush and a sponge roller has conventionally been brought into contact with the developing roller to strip the toner sticking to the developing roller surface.
It is known that a fur brush is brought into contact with a region where the magnetic field of a fixed magnet is weak (not a magnetic pole position where magnetic field is strong but an interpole region between adjacent magnetic poles) to improve cleaning (stripping) performance (Japanese Patent Application Publication No. H08-54785).
In the configuration in which the fur brush or the sponge roller is brought into contact with the developing roller to strip the toner, the stripping member mechanically rubs the toner, and hence there is a problem in that physical properties of the toner may change due to a peeled or buried external additive. As a result, a problem in that the charge amount of toner decreases to cause fogging or density decrease. This problem is particularly conspicuous when mono-component magnetic toner (developer) is used. The mono-component magnetic toner (developer) is used for, for example, jumping development in non-contact development.
In order to achieve the object described above, a developing apparatus, including:
a developer bearing member that encloses a magnet roller having a plurality of magnetic poles and is rotatable;
a wall that forms a developer storing chamber for storing a magnetic developer therein;
a restricting member configured to restrict a layer thickness of the magnetic developer carried by the developer bearing member; and
a moving member configured to move the magnetic developer carried on the developer bearing member before the magnetic developer is restricted by the restricting member, the moving member being brought into contact with a surface of the developer bearing member, the moved developer being on the developer bearing member after the moving member moved the developer on the developer bearing member,
wherein the moving member is disposed at a position opposed to any of the magnetic pole positions of the plurality of magnetic poles.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention are exemplified below with reference to the accompanying drawings. The dimensions, materials, shapes, and relative arrangement of components described in the embodiments should be appropriately changed depending on the configuration and various conditions of an apparatus to which the invention is applied, and are not intended to limit the scope of the invention to the following embodiments.
In the first embodiment, modes for embodying the invention are described in the following order:
1. Outline of image forming apparatus;
2. Configuration of developing apparatus including moving member;
3. Movement of magnetic chain; and
4. Method of verifying movement.
Description of Image Forming Apparatus
Recording material (paper) 10 is fed by a paper feed roller, and a toner image is transferred onto the surface of the recording material 10 between the photosensitive drum 1 and the transfer roller 11 by transfer bias. In this manner, the transfer roller 11 transfers the toner image developed on the developing roller 7 onto the recording material 10. The transfer roller 11 is an example of a transfer unit. The recording material 10 having the toner image transferred thereon is separated from the surface of the photosensitive drum 1 and conveyed to a fixing unit 12, and is heated and pressurized such that the toner image is fixed. In the photosensitive drum 1 after the toner image is transferred, untransferred toner 3 remaining on the surface without being transferred to the recording material 10 is removed by a cleaning member 2 as cleaning means, and is stored in a cleaning container 5 as waste toner.
After that, the cleaned surface of the photosensitive drum 1 is charged and exposed again, and the developing roller 7 after development is supplied with toner 3 again from the developer container 9. After that, the transfer and fixation are performed on the recording material 10, and a cycle of a series of image formation is performed. In the image forming apparatus according to this embodiment, a process device including the photosensitive drum 1 the charging roller 4, the developer container 9, and the cleaning container 5 is integrally incorporated with a cartridge container. In this manner, a process cartridge 20 removably (removably replaceable) provided to the image forming apparatus main body M is formed.
Outline of Developing Apparatus Including Moving Member
In the developing apparatus in the first embodiment, the brush 23 as a moving member is newly brought into contact with the developing roller 7 in the vicinity of a magnetic pole position of a magnet roller (fixed magnet) 22. In this manner, the toner layer on the developing roller 7 is not stripped by the brush 23 during driving of the developing roller 7, but the brush 23 is caused to reach the lowermost layer toner of magnetic chains to roll or move the lowermost layer toner. The movement of the lowermost layer toner solves the problem of sticking of toner 3 having high charge amount.
Next, the configuration of the developing apparatus including the moving member is described with reference to a cross-sectional view of the developing apparatus according to the first embodiment in
Main parameters in the first embodiment are listed below.
Developing Roller 7
Outer diameter: 18 mm
Material: metallic system (nickel/aluminum/SUS)
Surface roughness: Ra 0.2 to 1.0 μm
Number of rotations: 200 rpm
Spacing between photosensitive member and drum: 0.3 mm
Developing Blade 8
Material: urethan
Thickness: 1.0 mm
Toner 3
Material: styrene acrylic
Specific gravity: 1.6 g/cm3
Weight-average particle diameter: 7 μm
The weight-average particle diameter of the toner 3 is measured by a measuring apparatus. As the measuring apparatus, a precise particle counting and sizing apparatus “Coulter Counter Multisizer 3” (registered trademark, manufactured by Beckman Coulter, Inc.) using a hole electric resistance method provided with an aperture tube of 100 μm is used.
The magnetic pole positions of the magnet roller 22 mainly include the position of a development pole (S1 pole) and the position of a toner moving pole (S2 pole). The position of the development pole (S1 pole) of the magnet roller 22 is near a position at which the magnet roller 22 and the photosensitive drum 1 are opposed to each other. The position of the toner moving pole (S2 pole) of the magnet roller 22 is inside the developer container 9. The brush 23 in the first embodiment is in contact with near the position of the toner moving pole (S2 pole) on the upstream side in the rotation direction of the developing roller 7 restricted by the developing blade 8. In
The brush 23 has a unit obtained by bonding ground fabric 26c transplanted with fibers (raised portions) of the brush 23 to a fixed plate 26d. In this manner, the brush fibers 26a of the brush 23 are fixed to the fixing end formed of the ground fabric 26c and the fixed plate 26d. The material of the brush 23 and the fixed plate 26d is conductive metal, and the brush 23 and the fixed plate 26d are electrically connected to each other at end portions. The brush 23 and the fixed plate 26d are also electrically connected to the developing roller 7, and the brush 23 and the developing roller 7 have the same potential. The fixed plate 26d is mounted to the developer container 9 such that the tip of the brush 23 is in contact with the surface of the developing roller 7 in the vicinity of the magnetic pole position of the magnet roller 22. As illustrated in
In the first embodiment, conductive nylon fibers in which carbon powders are dispersed are used as conductive fibers serving as raised portion. As the fibers, fibers having a single fiber fineness of 2 to 15 dtex [dtex: indicating a mass (unit: grams) per single-fiber 10,000 meters], a diameter of 10 to 40 μm, and a dry strength of 1 to 3 cN/dtex is preferred. The preferable resistivity ρfiber of the fiber is 10 to 108 Ωcm. The resistivity is measured by the following method. For example, 50 fibers are bundled into one, and a metal probe is brought into contact with the surface of the bundle with an interval of about 1 cm. A high resistance meter Advantest R8340A (manufactured by ADVANTEST CORPORATION) is used to actually measure a resistance value Rfiber under an applied voltage of 100 V to calculate the resistivity ρfiber.
The fiber length starting from a ground fabric portion of each fiber is 1 to 5 mm. The brush tip 26 of the brush fiber 26a is a free end, and in this example, the fiber length is set such that the inroad amount of a raised portion (brush fiber) to the outer peripheral surface of the developing roller 7 is 0.5 to 1.0 mm. The fiber material serving as the raised portion is not limited to nylon fiber as long as the material is conductive.
The configuration of the brush 23 and the entry amount in the developing roller 7 should be changed appropriately depending on an image forming apparatus to be used, and are not limited to the above-mentioned configuration and numerical values. In addition, the physical properties of the brush 23 include the fiber height, the fineness, the fiber density, and a weaving method, and any material can be used as long as the brush 23 does not strip the toner 3 on the developing roller by development driving but can move the toner lowermost layer.
Examples of parameters contributing to moving force include, in addition to the charge amount of the toner 3, the force (rotating speed) due to rotational motion of the developing roller, the magnetic force of the magnet roller 22, and physical properties of the brush 23 (pressing pressure of brush 23). Thus, the balance of the forces is important as a moving condition. In the first embodiment, the following Expression (1) is provided in order to clearly specify that the brush 23 as a moving member is disposed for the purpose of moving the lowermost layer toner rather than stripping a toner layer on the developing roller 7.
Fblade/Cblade<Fbrush/Cbrush (1)
Fblade: magnetic attractive force of magnet roller at restricting position
Cblade: restricting force of blade at restricting position
Fbrush: magnetic attractive force of magnet roller at brush contact position
Cbrush: restricting force of brush at brush contact position
The restricting position is a contact position of the developing blade 8 with the developing roller 7. The brush contact position is a contact position of the brush 23 with the developing roller 7. The left side in Expression (1) is “Fblade/Cblade (magnetic attractive force of magnet roller at restricting position/restricting force of blade at restricting position)”. The left side in Expression (1) is obtained by dividing “Fblade”, which attracts the toner layer on the developing roller 7 toward the developing roller 7, by “Cblade”, which strips the toner layer on the developing roller 7 from the developing roller 7. The left side in Expression (1) is an index indicating how much the toner layer tends to remain at a restricting position (between developing roller 7 and developing blade 8) and how much the toner layer is less peeled off (stripped).
The right side in Expression (1) is “Fbrush/Cbrush (magnetic attractive force of magnet roller at brush contact position/restricting force of brush at brush contact position)”. The right side in Expression (1) is an index indicating how much the toner layer tends to remain at the brush contact position (between developing roller 7 and brush 23) and how much the toner layer is less peeled off (stripped). Expression (1) indicates that “how much the toner layer is less stripped at the brush contact position” is larger than “how much the toner layer is less stripped at the restricting position”. Expression (1) indicates that the toner layer is less stripped by the brush 23 at the brush contact position.
As specific values of “Cblade (restricting force of blade)” and “Cbrush (restricting force of brush)”, “Pblade (linear pressure of blade)” and “Pbrush (linear pressure of brush)” can be used. The following Expression (2) may be used instead of Expression (1).
Fblade/Pblade<Fbrush/Pbrush (2)
Pblade: linear pressure of blade at restricting position
Pbrush: linear pressure of brush at brush contact position
In the first embodiment, the blade linear pressure is set to 25 to 30 gf, the brush linear pressure is set to 15 to 20 gf, and the brush linear pressure is set to a value lower than that of the blade linear pressure. The linear pressure as used herein is force itself as understood from the unit “gf”. A method of measuring the linear pressure is described. A contact pressure (blade linear pressure) of the developing blade 8 is a value determined by the following procedure. For example, three SUS sheets (thickness: 50 μm, width: w [cm]) are inserted between the contact nip between the developing roller 7 and the developing blade 8 without toner, and a spring pressure F [gf] obtained when the middle SUS sheet is pulled out is measured. A friction coefficient μ between the SUS sheets is measured. Then, contact pressure (linear pressure) P=μf/w is measured. The contact pressure (brush linear pressure) of the brush 23 is also a value determined by the same procedure. For example, the brush 23 is caused to enter the developing roller 7 by 1 mm without toner, and the above-mentioned three SUS sheets are inserted between contact nips.
The purpose of the brush 23 used in the first embodiment is to move the toner layer on the developing roller 7, not to strip the toner layer on the developing roller 7. Thus, the brush 23 in which the density of hair of the brush 23 (brush fibers) is “sparse” with respect to the density of magnetic chains is used. For example, it is considered that when the density of hair of the brush 23 is “dense” with respect to the density of magnetic chains, the effect of stripping a toner layer on the surface of the developing roller increases. In such a case, the brush restricting force is considered to be substantially the same as the blade restricting force. However, in such a situation, excessive load is applied to the toner 3, which is not preferred in terms of degradation of the toner 3. In other words, the conditional expressions of Expression (1) and Expression (2) are on the assumption that the density of hair (brush fibers) of the brush 23 as a moving member is sparse. The sparse state is achieved by the brush 23 as a moving member which has a plurality of brush fibers and in which one end of each brush fiber is fixed to a fixing end including ground fabric 26c and the other end thereof is a free end, and magnetic chains 25 as a toner layer described later.
In the state in which the brush 23 is brand-new with no attachment on its surface, the influence of stripping may become larger than that of movement. However, the brush 23 immediately becomes a steady state and the influence of movement becomes larger than that of stripping, and hence descriptions of minor stripping in the brand-new state are herein omitted.
Movement of Magnetic Chains
Next, a mechanism for moving magnetic chains in this embodiment is described. Prior to the description, a configuration in a comparative example in which <1> the tip of the brush 23 cannot come into contact with the surface of the developing roller 7 and <2> the movement of magnetic chains does not occur is described.
The configuration in the comparative example in which <1> the tip of the brush 23 cannot come into contact with the surface of the developing roller 7 is described with reference to
Next, the configuration in the comparative example in which <2> the movement of magnetic chains does not occur is described with reference to an enlarged diagram of magnetic chains 25 in FIG. HA and an enlarged diagram of a lowermost layer toner 28 in
Next, the configuration in the first embodiment in which <3> the brush tip 26 can come into contact with the surface of the developing roller 7 and <4> the movement of magnetic chains 25 occurs is described.
First, the configuration in the first embodiment in which <3> the brush tip 26 can come into contact with the surface of the developing roller 7 is described with reference to
Next, the configuration in the first embodiment in which <4> the movement of magnetic chains 25 occurs is described with reference to an enlarged diagram of magnetic chains 25 illustrated in
When the lowermost layer toner 28 of the magnetic chains 25 is moved by the brush 23, charge-transfer occurs in the brush 23. Subsequently, the configuration in the first embodiment in which <5> charge-transfer occurs in the toner 3 and the brush 23 is described with reference to an enlarged diagram of the lowermost layer toner 28 illustrated in
On the other hand, the brush tip 26 comes into contact with positive charge of the developing roller surface 27 separated from the negative charge of the toner surface layer. At the brush tip 26 which is in contact with the positive charge of the developing roller surface 27, the negative charge starts to transfer toward the brush tip 26 so as to correspond to the positive charge. As a result, the negative charge transfers in the brush 23, and a brush current I can be detected. A method of detecting the brush current I and detection results thereof are described later.
When the toner 3 having high charge amount, which is more liable to stick to the developing roller surface 27, sticks directly to the developing roller surface 27, the toner 3 acts so as not to be charged at a predetermined level or more. In the first embodiment, the lowermost layer toner 28 is moved by the brush 23. In this manner, the lowermost layer toner 28 having high charge amount and upper layer toner having low charge amount in the toner layers on the developing roller 7 are mixed together, so that the toner layers on the developing roller 7 can be uniformly charged. In the first embodiment, the brush 23 can be referred to as “charge-transfer promoting means” because the brush 23 promotes the charge-transfer in the lowermost layer toner 28 and promotes the uniform charging of the toner layers on the developing roller 7.
The movement of the toner 3 of the magnetic chains 25 described above includes the case where the toner 3 itself rolls without changing the position of the toner 3 in the magnetic chains 25 and the case where the toner 3 moves from a lower layer to an upper layer in the magnetic chains 25. The movement of the toner 3 of the magnetic chains 25 also includes the case where the toner 3 moves to peripheral magnetic chains 25 and the case where the moved toner 3 forms magnetic chains 25 again.
Method of Verifying Movement
Next, a method of verifying that the lowermost layer toner 28 of the magnetic chains 25 is moved by the brush 23 which is in contact with the lowermost layer toner 28 is described. As described above, when the lowermost layer toner 28 is moved and the brush tip 26 comes into contact with the positively-charged developing roller surface 27, negative charge-transfer occurs in the brush 23. Thus, a detectable brush current I is generated by moving the lowermost layer toner 28. In other words, the detection of the brush current I verifies that the lowermost layer toner 28 of the magnetic chains 25 has been successfully moved.
On the other hand, in the case of the stripping in the conventional technology, the brush current I may flow similarly to the movement in the first embodiment. However, in the case of the stripping in the conventional technology, a fogging image is generated due to insufficient charging of the toner 3, and hence whether the movement has been effectively performed can be easily checked by checking both the brush current I and the fogging image. Here, the brush current I is detected in the state in which no fogging image is generated.
As indicated by the measurement result A of the brush current I in
As indicated by the measurement result B of the brush current I in
In the first embodiment in which the movement state can be detected by such a brush current detection circuit, the movement conditions are determined depending on the purposes such as required image quality and the durable number of sheets. The reason is that the movement conditions relate to the prevention of sticking of highly-charged toner 3 to the developing roller surface 27 and local unevenness of charge amount, and an effect for high image quality can be obtained.
Comparison Results
The following Table 1 indicates a comparison between the first embodiment and a conventional example.
In the conventional example, the brush having high strippability is brought into contact with a portion between poles of the magnet roller 22 so that the toner 3 having charge amount near the developing roller 7 is easily stripped to improve a restriction failure. As a result, the charge amount of the toner 3 before restricted by the blade after a stripping process becomes insufficient to cause fogging. The brush having high strippability mechanically rubs the toner 3, and hence the toner 3 degrades and fogging and density decrease occur.
In the first embodiment, on the other hand, the brush 23 as a moving member is brought into contact with the pole position of the magnet roller 22 such that the toner 3 having high charge amount on the developing roller surface 27 can be moved. In this manner, a restriction failure in which the lowermost layer toner 28 sticks to the developing roller surface 27 with a high reflection force so that it is difficult to restrict the lowermost layer toner 28 by the developing blade 8 can be improved.
Particularly in electrophotographic image formation using mono-component magnetic toner (developer), the problems of fogging and density decrease conspicuously arise due to toner deterioration (charge amount decrease), but the first embodiment can solve or reduce the problems. Specifically, the brush 23 in the first embodiment can suppress the influence of stripping of the toner 3 as compared with the brush described in the conventional example, thereby maintaining and uniformizing the charge amount of the toner 3 after the stripping process and before the blade restriction and improving the fogging. In addition, the brush 23 in the first embodiment does not mechanically rub the toner 3 unlike a brush having high strippability, and hence the degradation of the toner 3 can be suppressed to suppress fogging and density decrease. In other words, the toner 3 of the coat layer can be moved by the brush 23 to prevent the toner 3 having high charge amount from sticking to the developing roller surface, and also the charging of the toner 3 can be maintained and made uniform. Thus, the first embodiment is superior to the conventional example.
The second embodiment is different from the first embodiment in that the moving member is not fixed but has a roller shape and the moving member is in contact with the developing roller 7 in opposite directions (counter contact). The conditions such as the brush fiber (raised portion) and the conditions of Expression (1) and Expression (2) are the same as in the first embodiment, and hence detailed descriptions thereof are omitted. The configuration in the second embodiment can prevent a decrease in the moving effect even in the state in which the toner 3 easily remains in the moving member due to an increase in cohesion degree of the toner 3 caused by degradation of the toner 3 or environmental fluctuations. Thus, the second embodiment is preferred as a configuration for maintaining the moving effect for a long period of time.
A configuration of a moving member in the second embodiment is described. As illustrated in
The material of the brush roller 24 is conductive, and the fiber height, the fineness, the fiber density, and a weaving method as physical properties of the brush may have any value similarly to the first embodiment as long as the brush roller 24 has a roller shape and is capable of moving the toner. The material of the core 24b is SUS, which is conductive. The core 24b is conductive to the brush fibers 24a at end portions thereof. The core 24b is also connected to the developing roller 7 through an electric circuit, and hence the brush fibers 24a and the developing roller 7 have the same potential.
Next, a configuration of a developing apparatus including the brush roller 24 in the second embodiment is described with reference to
The effects obtained when the brush roller 24 rotates are described with reference to the following Table 2.
First, when the brush roller 24 rotates in the reverse direction, a chance of contact between the brush fiber 24a on the brush roller 24 and the developing roller 7 increases. Due to the increased chance of contact, a chance of movement of the magnetic chains 25 on the developing roller 7 increases, and the moving effect improves.
Second, when the brush roller 24 rotates in a direction opposite to the rotation of the developing roller 7, the toner 3 remaining in the brush roller 24 can be effectively removed. In the configuration in the second embodiment in which the brush roller 24 is fixed, when the cohesion degree of the toner 3 becomes higher, the toner 3 more easily adheres to the brush fibers 24a of the brush roller 24. When the toner 3 adheres to the brush fibers 24a of the brush roller 24 and the toner 3 remains between the brush fibers 24a of the brush roller 24, the brush fibers 24a cannot roll the magnetic chains 25 and the moving performance decreases.
In the configuration in the second embodiment, on the other hand, the brush roller 24 rotates in a direction opposite to the rotation direction of the developing roller 7. Thus, as illustrated in
Due to the above-mentioned two effects, the performance of the brush roller 24 for moving the magnetic chains 25 on the developing roller 7 can be improved to improve a restriction failure that occurs when the toner 3 sticks to the developing roller 7. As described above, the configuration in the second embodiment can maintain the moving effect for a long period of time even in the state in which the toner 3 easily remains in the brush roller 24 due to an increase in cohesion degree of the toner 3 caused by degradation of the toner 3 or environmental fluctuations.
The third embodiment is different from the first embodiment in that the brush fibers 24a are spirally wound around the core (metal such as SUS) 24b by double-sided tape 24d to have a roller shape as illustrated in
Next, a configuration and its effects in the third embodiment are described. In the third embodiment, the developing roller 7 and the brush roller 24 rotate in the same direction at a contact position between the developing roller 7 and the brush roller 24. Thus, as the first effect in the third embodiment, the number of times of rubbing between the brush roller 24 and the developing roller 7 can be set smaller than in the first and second embodiments. The number of times of rubbing in the third embodiment is set to a condition that no restriction failure occurs, and as long as the restriction failure does not occur, any number of times of rubbing can be set, and there is an adjustment range on the side where the number of times of rubbing is small. Thus, the configuration in the third embodiment can reduce rubbing damage to the toner 3 while maintaining the movement of the toner layer, and is thus superior to the first and second embodiments in terms of long lifetime of the developing apparatus related to the rubbing damage and the density decrease in the latter half in the durable period.
In the third embodiment, the developing roller 7 and the brush roller 24 rotate in the same direction at the contact position between the developing roller 7 and the brush roller 24. Thus, as the second effect in the third embodiment, the circulation of the toner 3 in a restriction region improves.
On the other hand, the case where the toner 3 remains between the brush fibers 24a of the brush roller 24 and the moving performance decreases when the cohesion degree of the toner 3 increases as in the second embodiment is described. In the configuration in the third embodiment, the number of times of rubbing is small from the beginning. By disposing the brush roller 24 so as to be in contact with a part of the inner wall of the toner storing chamber 40 or providing a scraper so as to enter the inside of the brush roller 24, the toner 3 in the brush roller 24 can be easily removed. The scraper may be a part of the inner wall of the toner storing chamber 40. A part of the inner wall of the toner storing chamber 40 may protrude to the inner side of the toner storing chamber 40.
Superior points of the third embodiment to the conventional example and the first and second embodiments are listed in the following Table 3.
As understood from Table 3, in the third embodiment, the stripping of the toner 3 from the developing roller surface 27 is suppressed while solving the problem (restriction failure) in that the toner 3 sticks to the developing roller surface. Thus, in the third embodiment, the state in which the charge amount of the toner 3 is low as in the conventional example can be avoided, and hence there is an effect on the stripping (fogging) of the toner 3 similarly to the first and second embodiments. The third embodiment has a feature that the brush roller 24 is in contact with the developing roller 7 in the forward direction. The number of times of rubbing between the developing roller 7 and the brush roller 24 can be reduced under the condition that no restriction failure occurs, and hence there is an effect on the load on the toner 3 (density decrease). Thus, the third embodiment has a particular effect that is not obtained by the conventional example and the first and second embodiments.
A configuration in the fourth embodiment is described below. The fourth embodiment is different from the second embodiment in the S2 pole position, the magnitude of magnetic force Fmag of the magnet roller 22, the position of the brush roller 24, and the height of a toner agent surface 41 of the toner 3 in the toner storing chamber 40 by changing the position of the toner storing chamber 40. The toner agent surface 41 is an example of a developer surface. The toner agent surface 41 of the toner 3 in the toner storing chamber 40 is the top surface of the toner 3 in the toner storing chamber 40. The other configurations in the fourth embodiment are the same as the configurations in the second embodiment. According to the configuration in the fourth embodiment, the circulation of the toner 3 around the brush roller 24 is made smooth. In this manner, even when the number of printed sheets has advanced and the toner 3 in the process cartridge 20 has degraded to improve the cohesion degree, the moving effect of the brush roller 24 can be maintained while suppressing the stripping of the toner 3.
The configuration in the fourth embodiment is described in detail below. Regarding the definition of the positional relation of the members in the fourth embodiment, the process cartridge 20 is inserted in the image forming apparatus main body M and located at an image forming operating position.
S2 Pole Position
Description of Magnetic Force Fmag
The magnetic force Fmag of the magnet roller 22 in the fourth embodiment is described with reference to
Fmagup>m×g (3)
The distance between the position P and the rotating center 0 of the developing roller 7 is a distance H. In the fourth embodiment, the distance H is 12 mm. The above-mentioned Fmag is described in detail below. Fmag is expressed by the following Expression (4). “Fr” represents a force in a direction normal to the surface of the developing roller 7, and “Fθ” represents a force in a direction tangent to the surface of the developing roller 7.
[Expression (4)]
{right arrow over (F)}mag=(Fr,F0) (4)
“Fr” and “Fθ” are expressed by the following Expression (5).
Here “μ0” represents the magnetic permeability in vacuum, “μ” represents the magnetic permeability of the toner 3, “b” represents the radius of the toner 3, “B” represents the magnetic flux density, “Br” represents the magnetic flux density in a direction normal to the surface of the developing roller 7, and “Bθ” represents the magnetic flux density in a direction tangent to the surface of the developing roller 7. Thus, when the weight-average particle diameter of the toner 3, the magnetic permeability μ of the toner 3, “Br”, and “Bθ” are known, the magnetic force Fmag can be determined. The magnetic permeability μ of the toner 3 is measured with an external magnetic field of 387.9 kA/m by using a vibrating magnetometer VSM P-1-10 (manufactured by TOEI INDUSTRY CO., LTD.).
Next, a method of measuring “Br” is described. The intensity of a magnetic field from the developing roller 7 over the photosensitive drum 1 is measured by the polar coordinate system, in which the rotating center of the developing roller 7 is the origin, based on which the nearest position between the developing roller 7 and the photosensitive drum 1. As a measurement device, a gaussmeter (manufactured by F.W.Bell Inc.) is used. A jig capable of rotating the magnet roller 22 as magnetic field generating means about an axis overlapping the rotating center of the developing roller 7 is prepared, and a probe of the gaussmeter is fixed placed at a predetermined normal direction distance (in the fourth embodiment, position away from origin by H=12 mm) The magnet roller 22 on the jig is rotated for each predetermined angle, and the value of the gaussmeter is recorded, so that the intensity can be measured.
Next, “Bθ” can be determined from the magnetic flux density Br on the basis of the following Expression (6).
By substituting the measured and calculated “μ”, “Br”, and “Bθ” into the above expression, Fmag can be derived, and the vertically upward component of Fmag is Fmagup. In the fourth embodiment, the magnetic susceptibility of the toner 3 is 1.0, the weight-average particle diameter of the toner 3 is 7 μm, and the specific gravity of the toner 3 is 1.5/cm3.
From the conditions described above, Fmagup=1.0×10−10N and mg=2.1×10−14N in the fourth embodiment, which satisfy Expression (3).
Position of Brush Roller
Next, the position of the brush roller 24 in the second and fourth embodiments is described with reference to
In the fourth embodiment, the distance between the center of the magnet roller 22 and the rotating center of the brush roller 24 and the diameter of the brush roller 24 are the same as in the second embodiment. For example, the diameter of the brush roller 24 is φ11 mm. It is assumed that the upstream direction in the rotation direction of the developing roller 7, which is the horizontal direction from a point N located vertically uppermost on the peripheral surface of the developing roller 7, is an X direction. As illustrated in
The position of the brush 23 in the first embodiment may be the same as the position of the brush roller 24 in the fourth embodiment. In other words, in the configuration in the first embodiment, the brush 23 may be disposed on the vertically lower side of the developing roller 7. In the configuration in the first embodiment, the point S present farthest in the X direction among points present on the peripheral surface of the developing roller 7 may be present toward the X direction side than a point present farthest in the X direction among points present on the outer circumference of the brush 23. In this case, the brush 23 does not protrude from the upstream side in the rotation direction of the developing roller 7 when seen from the vertically upper side. In other words, the brush 23 and an end portion of the developing roller 7 on the upstream side in the rotation direction of the developing roller 7 do not overlap each other in the vertical direction. In addition, the configuration in the fourth embodiment can be applied to the configuration in the third embodiment.
Position of Toner Storing Chamber
The fourth embodiment is different from the second embodiment in the position of the toner storing chamber 40 in which the toner 3 in the developer container 9 is stored. As illustrated in
Tip Position of Developing Blade
As illustrated in
As described above in the second embodiment, when the cohesion degree of the toner 3 increases, the toner 3 remains between the brush fibers 24a of the brush roller 24, and the brush fibers 24a cannot roll the magnetic chains 25 and the moving performance of the brush roller 24 decreases. The configuration in the fourth embodiment enables the circulation of the toner 3 around the brush roller 24 to be smooth to suppress the decrease in moving performance of the brush roller 24. The functions and effects of the fourth embodiment, that is, the motion of the toner 3 around the brush roller 24, is described in detail below with reference to
In the fourth embodiment, the toner agent surface 41 is located at a position lower than the position U on the most downstream side of the contact surface between the developing roller 7 and the brush roller 24 in the rotation direction of the developing roller 7. Thus, the toner 3 is pumped by the toner conveying member 21, and the toner 3 is conveyed in the direction in which the developing roller 7 and the brush roller 24 are disposed (arrow T1). Most of the toner 3 conveyed onto the brush roller 24 rides on the brush roller 24 and is conveyed to near the developing roller 7 (arrow T2), and moves to the developing roller 7 by magnetic force of the magnet roller 22. A part of the toner 3 conveyed onto the brush roller 24 by the toner conveying member 21 enters between the brush fibers 24a (arrow T3). However, when Expression (3) is satisfied as in the configuration in the fourth embodiment, even the toner 3 that has entered the deepest portion (root of brush fiber 24a) of the brush roller 24, that is, the peripheral surface of the rotating shaft of the brush roller 24 can be moved to the developing roller 7 (arrow T4).
When the developing roller 7 rotates, the toner 3 that has moved onto the developing roller 7 is conveyed to near the developing blade 8 (arrow T5). A part of the toner 3 that has been conveyed to near the developing blade 8 passes a contact region between the developing roller 7 and the developing blade 8 and is supplied to a developing zone. Most of the other toner 3 that has been conveyed to near the developing blade 8 is restricted by the developing blade 8 and stripped off from the developing roller 7. A part of the stripped toner 3 returns onto the developing roller 7 (arrow T6), and the other toner 3 drops downward in the direction of gravity due to gravitational force (arrow T7). With the configuration in the fourth embodiment, the dropped toner 3 does not return to the brush roller 24 again but is stored in the toner storing chamber 40.
According to the configuration in the fourth embodiment as described above, as compared with the configuration in the second embodiment, a part of the toner 3 that has been conveyed from the toner storing chamber 40 other than the toner 3 supplied to the developing zone can reliably return to the toner storing chamber 40. The specific effects in the fourth embodiment are described with reference to Table 4.
In Table 4, the moving effect of the brush roller 24 and the suppressing effect of stripping in the configuration in the second embodiment and the configuration in the fourth embodiment are confirmed at the time of the start of use of the process cartridge 20 and after 50,000 sheets of horizontal line images of a printing ratio of about 2% are printed. At the start of use, there is no difference between the second embodiment and the fourth embodiment in the moving effect of the brush roller 24 (effect of suppressing restriction failure due to sticking of toner 3) and the effect of suppressing fogging that degrades when the triboelectricity of the toner 3 decreases after the toner 3 is stripped. After the printing of 50,000 sheets, there is no difference between the second embodiment and the fourth embodiment in the effect of suppressing fogging that degrades after the toner 3 is stripped, but there is a difference in the effect of suppressing a restriction failure due to sticking of the toner 3. Specifically, in an image sample after the printing of 50,000 sheets in the configuration in the second embodiment, extremely minor density unevenness caused by a restriction failure occurred in a halftone image of a printing ratio of about 50%. In the configuration in the fourth embodiment, on the other hand, density unevenness caused by a restriction failure did not occur. This indicates that the configuration in the fourth embodiment can maintain and improve the moving effect while suppressing the stripping of the toner 3 even after the printing of 50,000 sheets.
The reason why extremely minor halftone density unevenness caused by a restriction failure occurred after the printing of 50,000 sheets only in the configuration in the second embodiment is described with reference to
However, in the configuration in the second embodiment, as illustrated in
As described above, according to the configuration in the fourth embodiment, the circulation of the toner 3 around the brush roller 24 is smooth. Thus, even when the number of printed sheets has advanced and the toner 3 in the process cartridge 20 has degraded to improve the cohesion degree, the moving effect of the brush roller 24 can be maintained and improved while suppressing the stripping of the toner 3.
A configuration in the fifth embodiment is described below. The fifth embodiment is different from the fourth embodiment in the tip position of the developing blade 8. For example, there may be a case where the developing blade 8 is required to be brought into contact with the developing roller 7 at a lower position than in the configuration in the fourth embodiment due to an apparatus configurational reason that the size of the image forming apparatus main body M needs to be decreased. Even in such a case, the configuration in the fifth embodiment can maintain and improve the moving effect of the brush roller 24 while suppressing the stripping of the toner 3. The other configurations in the fifth embodiment are the same as the configurations in the fourth embodiment.
The configuration in the fifth embodiment is described in detail below. Regarding the definition of the positional relation of the members in the fifth embodiment, the process cartridge 20 is inserted in the image forming apparatus main body M and located at an image forming operating position.
Tip Position of Developing Blade
As illustrated in
The circulation of toner 3 in the fifth embodiment is described with reference to
In Table 5, the moving effect and the stripping suppressing effect of the brush roller 24 is compared between the configuration in the fourth embodiment and the configuration in the fifth embodiment. Also in the fifth embodiment, the moving effect and the stripping suppressing effect comparable to the fourth embodiment are obtained. Also in the configuration in the fifth embodiment, similarly to the configuration in the fourth embodiment, the toner 3 supplied from the toner storing chamber 40 does not enter between the brush fibers 24a, but the toner 3 is restricted by the developing blade 8 and returns to the toner storing chamber 40 again. In other words, the circulation of the toner 3 in the configuration in the fifth embodiment is similar to the circulation of the toner 3 in the configuration in the fourth embodiment, and hence it is considered that the fifth embodiment has successfully obtained the effects similar to those in the fourth embodiment.
There may be a case where the developing blade 8 is required to be brought into contact with the developing roller 7 at a lower position than in the configuration in the fourth embodiment due to an apparatus configurational reason that the size of the image forming apparatus main body M needs to be decreased. Even in such a case, the configuration in the fifth embodiment can maintain and improve the moving effect of the brush roller 24 while suppressing the stripping of the toner 3. The configuration in the fifth embodiment can be applied to the configurations in the first to third embodiments.
In the second to fifth embodiments, the brush roller 24 as a moving member is used. In the second to fifth embodiments, as illustrated in
An effect mechanism in the sixth embodiment is described with reference to
The brush tip 26 is in contact with the developing roller surface 27 while being inclined in the rotation axis direction of the developing roller 7. Thus, the magnetic chains 25 slightly move on the developing roller surface 27 along a profile locus of the inclined brush tip 26 (toward white arrow direction in
The brush tip 26 comes into contact with the developing roller 7 while being inclined in the rotation axis direction of the developing roller 7, and hence the lowermost layer toner 28 of the magnetic chains 25 is moved by the brush tip 26 with a wider area. Consequently, the toner 3 having high charge amount can be more efficiently prevented from sticking to the developing roller surface 27. In addition, the toner 3 on the developing roller 7 is moved in the longitudinal direction of the developing roller 7, and hence the charged state of the toner 3, the toner coat thickness, and the degradation state of the toner 3 can be made uniform.
In the sixth embodiment, the orientation of the inclination of the brush tip 26 when the brush tip 26 comes into contact with the developing roller surface 27 may be either of right and left. The brush tip 26 only needs to be oriented to the axial direction side of the rotation direction of the developing roller 7 at least when the developing roller 7 and the brush roller 24 are rotationally driven with a peripheral speed difference. The orientation of the inclination of the brush tip 26 in the rotation axis direction of the developing roller 7 may cause longitudinal image density unevenness in an image forming region. Thus, it is desired that the rotating axis of the developing roller 7 and the inclination of the brush tip 26 be orientated in the same direction, but this is not necessary at an end portion of the developing roller 7. On the other hand, when the toner 3 move to the longitudinal inner side of the developing roller 7, the toner coat thickness becomes nonuniform at an end point of the movement of the toner 3 in the longitudinal direction of the developing roller 7. Thus, it is desired to move the toner 3 to the longitudinal outer side of the developing roller 7.
The toner 3 that has moved to an extreme end portion due to the contact of the inclined brush tip 26 with the developing roller 7 is restricted and scraped by the developing blade 8. In addition, if a stripping member made of a sponge roller mentioned in the conventional example comes into contact with a side outer wall of the longitudinal end portion of the developing roller 7, the sponge roller itself is scraped, and hence the moving effect cannot be provided up to the extreme end portion of toner coat on the developing roller 7. On the other hand, in the sixth embodiment using the brush roller 24, the brush roller 24 can be brought into contact with a side outer wall of the longitudinal end portion of the developing roller 7. In other words, according to the sixth embodiment, the moving effect can be provided up to an extreme end portion of toner coat on the developing roller 7. Thus, the toner 3 that has moved to the longitudinal extreme end portion on the developing roller surface 27 can maintain a proper toner coat state due to the scraping by the developing blade 8 and the movement by the brush roller 24. The configuration in the sixth embodiment can provide a more effective moving effect than in the first to fifth embodiments, and can improve the longitudinal uniformity of the toner coat on the developing roller 7. The tip of the brush fiber included in the brush 23 in the first embodiment may come into contact with the developing roller 7 while being inclined in the rotation axis direction of the developing roller 7. Thus, an effective moving effect can be provided also in the configuration in the first embodiment.
According to the disclosure described above, the sticking of a developer to the surface of a developer bearing member can be suppressed while maintaining charge amount of the developer necessary for forming high-quality images.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. This application claims the benefit of Japanese Patent Application No. 2018-098745, filed on May 23, 2018, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-098745 | May 2018 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5095850 | Komuro | Mar 1992 | A |
| 20010038763 | Aoki | Nov 2001 | A1 |
| 20040141772 | Goto | Jul 2004 | A1 |
| 20110274468 | Itagaki | Nov 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| H0854785 | Feb 1996 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20190361370 A1 | Nov 2019 | US |
